Using Currents To Sail Around The World? The 13 New Answer

Ocean Motion Teacher Guide Lesson 1

navigating the ocean

Table of Contents

Teacher’s Guide Lesson Matrix

Click on the titles to skip through the lesson

How did you do that?

What do you know?

drifter model

rubber ducks

dead reckoning

Astronomical fix

Find your place in the sun

Columbus voyages

trip of the bounty

Credit: Daniel Forester, Volvo Ocean Race

Lesson Objectives Summary Performance Tasks Explain how currents at the sea surface affect the trajectories of floating objects. Create and run a computer model experiment that studies the path of drifting objects around the world. To describe how early seafarers navigated the ocean based on speed and direction. Describe how early navigators measured speed and direction. To trace Columbus’ first voyage to America. Manipulate and collect data from a visualizer using velocities and directions observed by Columbus and accounting for magnetic declination and surface currents. Description of the role of oceanographers in gathering scientific information. Search Captain William Bligh’s journal for his measurements of magnetic variation and compare them to a computer model.

Materials:

Study Guide (PDF file)

Computer with web browser

Internet access

Number of pages: 16

Grade level: high school, level 1

Supported Courses: Earth Sciences, History, Mathematics and Physics

Glossary: ​​controls, data, dead reckoning, hypothesis, independent variable, laminar flow, latitude, longitude, magnetic declination, model

Introduction: how did they do it?

“Historians believe that Pacific Islanders explored the entire South Pacific well before the era of recorded history. Historians suggest that around 2500 B.C. began migrating through the Pacific.1” Their 100-foot (30.5-meter) canoes, pictured left, were navigated by men who were taught from childhood to decipher nautical information such as star positions, ocean currents, wave echoes, and prevailing winds and the habits of migratory birds. “More than 1,300 years ago, Polynesian explorers set out from Havai’i (now Raiatea, in the Society Islands) in large, double-hulled canoes to traverse the vast, uncharted expanses of the North Pacific. By accident they discovered and colonized the Hawaiian Islands. A long canoe voyage across the uncharted ocean must have required an extraordinary level of navigational skill. By observing the stars, winds and currents, ancient navigators were able to approximate their geographic position.2”

Sea surface currents have played an important role in navigation from ancient times through the exploration of the world by sail to today’s shipping. Most ships today are propeller driven and less dependent on the wind, but all ships benefit greatly from being carried by ocean currents.

In Lesson 1, students experiment with the effects of sea surface currents on floating objects. Students use a simple computer model to study the motion of objects floating on the sea surface. Students will also learn how Columbus sailed to the New World using tools such as a compass, astrolabe, hourglass, maps and charts, dead reckoning, wind and currents. Students will read Captain William Bligh’s journal and find out how he survived the mutiny on his ship Bounty when he set sail in a small boat near Tahiti without instruments.

1 Adapted with permission from the Mariners Museum

2 The Blue Planet, An Introduction to Earth System Science”, B. Skinner, S. Porter, D. Botkin

Get Involved: Poll on Prejudice, “What Do You Know?”

Students are asked to answer an online question consisting of eight questions. When they submit their answers online, a pop-up window will appear showing the correct answer to each question and providing additional clarifying information. All eight questions, the correct answers, and additional information are below.

Engagement activities like these are typically not graded.

True or

False Statement 1 False A west wind blows west. Winds are named for the direction from which they blow. A westerly wind blows from the west in an easterly direction. 2 True A compass is a magnet that is free to rotate. A compass is a magnet balanced on a fulcrum, the ends of which are marked N and S. The N end is the north-seeking pole of the magnet and points to the magnetic north pole of the earth. The pole is near but not at the true North Pole. The geographic pole is along the Earth’s axis of rotation. 3 False A compass points to the true North Pole. A compass points to the Earth’s magnetic poles, which generally do not coincide with the Earth’s geographic poles, which lie along the Earth’s axis of rotation. 4 False Chicago, Illinois, and New Orleans, Louisiana are at similar latitudes but very different longitudes. Latitude measures how far north or south a place is relative to the equator. Longitude measures how far east or west a place is relative to Greenwich, England. Philadelphia, Pa, and Lima, Peru are approximately equidistant west of Greenwich. 5 The real Tokyo, Japan, and San Francisco, California are at similar latitudes but very different longitudes. Latitude measures how far north or south a place is relative to the equator. Longitude measures how far east or west a place is relative to Greenwich England. San Francisco and Tokyo are roughly equidistant north of the equator. 6 False Philadelphia, Pennsylvania, and Lima, Peru are at similar latitudes but very different longitudes. Latitude measures how far north or south a place is relative to the equator. Longitude measures how far east or west a place is relative to Greenwich England. Philadelphia, Pa., and Lima, Peru are approximately equidistant west of Greenwich. 7 False solar noon is when the local time is 12:00 noon (between 11:00 and 13:00). Solar noon is the time when the sun is highest above the horizon. A local time of 12:00 p.m. is not determined by the sun but by time zone borders. 8 True Sailing vessels always sailed in the same direction as sea surface currents. Sailing ships use the wind in their sails to move upwind or downwind. They don’t always follow ocean currents. Currents can speed up a ship’s voyage, so a crew tries to find favorable currents for long voyages. 100 Total Score (%)

Explore: A drifter model

How do sea surface currents affect the movement of floating objects?

Driven by winds and controlled by the earth’s rotation and gravity, the waters of the world’s oceans are constantly in motion. Water moves horizontally (east, west, north, and south) and vertically (falling and rising). The following investigation focuses on the horizontal circulation of water at the sea surface. Ocean water is gravity stratified, so water at greater depths is typically denser (colder, saltier) than surface water. This stratification prevents the layers from mixing and decouples surface movement from the deeper waters. A simplified model for surface currents would envision them as a thin layer of circulating ocean water over more static, deeper layers.

What is a drifter model?

To experiment with floating objects carried by sea surface currents, use a computer model. The model uses historical monthly ship drift data collected through sea surface current circulation and simple physical equations of motion to predict drifter motion. The OSCAR visualizer, located on this page, contains more recent and accurate sources of sea surface current data. OSCAR data is used in other lessons.

The drifter database consists of the following values ​​for sea surface locations:

• Mean east-west (zonal) velocity component, u, and estimate of its variability.

• Mean north-south velocity component (meridional) v and estimate of its variability.

For example, a value for u in a given month and location might be 0.3 meters/second with a variability of 0.1 meters/second. Simply put, on any given day, the mean or average zonal flow was moving east 0.3 meters (about 1 foot) in one second. Actual current can vary 0.1 meter per second above and below this value. Frequently observed zonal flows could fall in the 0.2 to 0.4 meter/second range.

Click Ship Drift Model to link to the model on your computer. This model accounts for the circulation of currents and does not include the effects of wind/waves or the dynamics of the floating object. The drifter is thought of as a small object floating on the surface, with a density close to that of seawater. The model does not apply to sailing or motor ships.

The Ship Drift Model page, shown at right, shows a world map with arrows representing the mean or average direction of sea surface currents. The current patterns are quite complex and show the effects of continental landmasses. The arrows indicate the flow direction and the arrow colors indicate the flow speed. Below the map is a color scale that provides the key to converting each yellow, green, red, or blue arrow into a speed in meters per second.

1. Look closely at the image below (or on your computer screen) to find the speeds that correspond to the colored arrows. Ask students to fill in the blank boxes with actual speeds.

Arrow Color Dark Blue Light Blue Green Yellow Orange Red Dark Red Current Speed ​​(m/s) 0 0.4 0.5 0.6 0.7 0.85 1.0

Using the ship drift model on your computer

Look at the bottom part of the data visualization. There are three options: 1. Latitude/Longitude,

2. The month picker and 3. The pop-up card.

• To find the latitude and longitude of a point on the map, hover over the map. The latitude and longitude for that point is shown in the box at the bottom of the current chart.

• To view currents in more detail, select a month from the drop-down menu on the left, then click the pop-up map button on the right and a large, zoomable map will appear in a separate window displayed. The pop-up map is helpful in tracking surface current circulation.

• To begin your Drifter journey, move the computer’s cursor over the ocean and click on the map. A second window with a map showing the tracks of five drifters will appear.

In the example shown below, the start click was made near the southeast coast of the United States. A square, black, outlined box marks the beginning of the Drifter’s journey (marked with the word “Start” in the image). The colored tracks (purple, blue, red, orange, blue) follow five drifters under the influence of different currents over five years. A color-coded diamond-shaped frame marks the end of each track. The five different tracks show the approximate effects of sea surface current variability.

The coordinates on the map below use longitude (horizontal scale) and latitude (vertical scale). The starting point has a longitude near -80o and a latitude near 31o.

2. Estimate the final positions of the five drifters and enter the number in the table below.

Drifter Color Blue Green Orange Red Purple Finished Length -69 8 -64 -77 -64 Finished Width 28 61 34 31 34

Experiment with your own drifter

Try to create your own Voyager drifter. Use the ship drift model main map as well as the higher resolution map to choose a starting location and make a prediction of where your drifters will travel to.

3. Initial length ______________ Initial width ______________

4. Sketch your prediction for the Prowler’s Trail on the map on the next page. If in doubt, trace out several possible routes.

5. Click on your chosen start location on the map. Estimate the ending positions of each of the five drifters:

Drifter Color Blue Green Orange Red Purple Finished Length Finished Width

6. How well does your estimate of the drifter route match the computer model? Where is there agreement? Where do predictions disagree the most?

Elaborate: Rubber Duckies venture around the world

What do you know about the global flow of electricity?

Many tools are used to study the flow

of the ocean. Curt Ebbesmeyer, pictured

left with tub toy, says he uses every tool available to study the trajectories of sea surface currents. He studies satellite images and data from buoys. He throws objects into the water to see where they go.

In January 1992, his tool kit just got bigger. A storm washed several containers off a ship bound for Tacoma, Washington from Hong Kong. A container contained 29,000 bath toys. Ten months later, plastic ducks, turtles, frogs and beavers began washing up near Sitka, Alaska. A new experiment had begun, and Curt’s career as a pioneer in the study of flotsam was in full swing.

Today, Curt leads a network of thousands of beachcombers. These volunteers and hobbyists walk the beaches of the world and grab shoes, hockey gear, survey stakes, bowling balls, Legos, tobacco cans, utility poles, fishing gear, survival suits (with and without body parts), and the occasional message from a bottle and report their findings to Curt. Curt studies the information, ponders what it all means, and compiles those stories into a newsletter, Beachcombers Alert, which he sends out to his subscribers four times a year. When a new cargo is spilled, Curt notifies his network what to look for.

Read more about Curt by clicking on his name in the first paragraph.

Discover: Dead Reckoning

How to navigate the open ocean – determine the location?

When not using the stars, sun, or moon to determine their location, navigators and explorers navigated by derivative (or dead) calculations. This was the method used by Columbus and most other sailors of his time. In dead reckoning, the navigator finds his position by measuring the course and distance he has sailed from a known point. Starting from a known point, the navigator measures his course and distance from that point on a map and jabs a pin into the map to mark the new position. The end position of each day would be the starting point for the next day’s course and distance measurement. For this method to work, the navigator needed a way to measure his course and measure the distance sailed. The course was measured with a magnetic compass, known in Europe since at least 1183. The distance was determined by a time and speed calculation: the navigator multiplied the ship’s speed by the time traveled to get the distance.

7. To determine the speed on old sailing boats, sailors often used a log line. Describe how a log line was used and draw what a log line looked like. A flat board was weighted along one edge to make the edge sink in the water, and it was tied at its corners so that one of its flat sides always faced the ship when the rope was under tension. Knots were tied in the rope at regular intervals of about 12-15 meters to facilitate speed measurement. The flat board was necessary to maximize water resistance, or friction, to keep the board stationary in the water after being thrown overboard. Sailors measured the ship’s speed by the number of knots in the rope that was unwound from the spool in 30 seconds. Knowing the speed, one can easily calculate the distance traveled using the equation:

distance = speed x time

The fundamental flaw in using this log line method of determining distance is that it does not take into account the effects of surface currents. The log line method measures the ship’s speed relative to the surface water. It provides no way of estimating how fast the water itself is flowing. If a boat is being carried west by a strong current, the log line method will not indicate the existence of the current. This fact is related to Newton’s first law of motion, which states that steady motion in a straight line is “natural” and unknowable without reference to an external reference object.

8. How do you think a speedometer on a car measures speed? Are there any circumstances that could cause this measurement to be incorrect and not reveal the “true” speed of the car?

The car speedometer can count how many times the wheels are turning per second and can use this count to estimate the speed. If the wheels have a larger or smaller radius than recommended by the manufacturer, the speed will be misjudged. Speed ​​during a spin would not be measured.

To determine their direction of travel, sailors used the compass. The compass is a magnet whose ends are marked N and S. The N end points to the Earth’s magnetic north pole. This pole is located in northern Canada and does not coincide with the geographic North Pole (the “North Pole”). True north is along the Earth’s axis of rotation and points in the direction of Polaris, the North Star.

9. Click on the Magnetic Declination link and write a definition of it. Include a drawing showing the difference between True North and Magnetic North.

Magnetic declination, sometimes called magnetic variation, is the angle between magnetic north and true north. Declination is considered positive when east of true north and negative when west.

In order to plot their trail on a chart, sailors observed the course or direction their ship was traveling. Then they compared their heading to magnetic north, as indicated by a compass. Sailors were aware that magnetic declination did not represent true north, so to compensate for this they attempted to map magnetic declinations around the globe. North, as measured by the compass, is usually off by several degrees; this fluctuation is location-dependent and changes over decades.

Both the log line and the compass provided seafarers with deduced calculation (often abbreviated to ded or dead reckoning) so that they could at least approximately reconstruct their voyages. On the ocean, this task is vital and critical to success, as there are few stable landmarks in a liquid environment.

10. You may be used to using derived calculations when traveling from one place to another. Let’s say you’re in a car or train and estimate that you’re “30 minutes from downtown.” What simple assumptions does this make about your journey? You assume that your journey will proceed at a normal pace and that no unusual or unforeseen events will delay or hasten your arrival.

Closed-Loop Survey To practice and test your measurement and derived calculation skills, try conducting a closed-loop survey. This activity can be done both on a small desktop and outside. Measuring your voyages in a closed loop, where you end up where you started, provides an easy review of navigation methods. Returning to the same point, your measurements should determine a path that draws a closed loop.

Sailors knew that surface currents affected the accuracy of their navigational predictions. They called the difference between their derived and astronomically determined positions ship drift. Astronomical positioning on Earth from the sun and stars is possible because the stars appear fixed and the sun follows a cyclical, predictable motion. The measured differences between positions, determined by dead reckoning and astronomical methods, provided the earliest estimates of sea surface currents.

Elaborate: The astronomical fix

How can you determine where you are on planet earth?

The stars, moon, and sun provide reference points needed to accurately determine one’s position. As the earth rotates, astronomical objects follow a path in the sky. The time at which they reach certain positions can be used to determine your longitude and latitude.

Our earth is a sphere and angles are used to indicate the position of places on the earth’s surface. In the east-west direction, longitude is measured at 0o in Greenwich, England. Moving west (towards America), the longitude angles are negative: between -180o and 0o. Towards the east (towards Europe, Middle East and Russia) the longitude angles are positive: between 0o and +180o.

In the north-south direction, latitude is measured at 0o at the earth’s equator. To the north (towards the North Pole), positive latitude angles lie between 0o and 90o. To the south (towards the South Pole) lie negative latitude angles between -90o and 0o.

Over the course of 24 hours, the earth rotates 360 degrees and the stars appear to rotate in the opposite direction. The positions of the stars, moon, and sun in the sky at any given time depend on your location. By carefully measuring both the positions of astronomical objects and the times, you can find your latitude and longitude. This is called an “astronomical fix”.

Find your place in the sun by measuring your longitude and latitude.

The easiest time to determine your position is when the celestial bodies are passing overhead or reaching their highest elevation above the horizon. Solar noon is when the sun is highest in the sky. On a clear day, it is easy to determine the time of solar noon. As an investigation, measurements of the sun around solar noon can be used to determine longitude and latitude.

Discover: The Columbus Voyages

How can we trace a voyage of Columbus?

In celestial navigation, the navigator observes celestial bodies (sun, moon, and stars) to measure latitude. (In Columbus’ time, it was usually impossible to measure longitude.) Even in ancient times, finding latitude was fairly easy by looking at the sun and the stars, as long as you weren’t too concerned about accuracy . Every star has a celestial latitude or declination. If you know the declination of a star directly overhead, you can know your latitude on Earth. Even if a star is not directly overhead, you can still determine your latitude by measuring the angle between the star and the point above you (called the zenith)—provided you measure the star at the nighttime when the star is highest the sky.

Use Table 1 (below) to recreate Columbus’ voyages with the Voyager model. To make the replica as accurate as possible, this model provides three tools: ocean current data, a historical model of the Earth’s magnetic field, and kinematic equations to track the ship’s movements. Because ocean currents are unknown at the time of Columbus, this model uses monthly surface current data based on ship drift observations made primarily in the 20th century. Observed current fluctuations (i.e. the “variable current” in the model) are simulated with random numbers. This model does not simulate the action of winds. Rather, it uses speeds measured by Columbus and his crew. These log line speeds reflect both the wind conditions and the way the ship was sailed.

To determine his direction (or course), Columbus relied on a compass, and his readings were not corrected for the difference between magnetic north and true north. The Voyager model includes a magnetic model that maps the Earth’s magnetic field at the surface between 5000 B.C. and 1950 AD predicted.

Historical records provide navigational details of Columbus’ voyages. Table 1 is based on Columbus’ records of his first voyage to the Americas. The values ​​have been adapted and simplified from Keith A. Pickering’s website.

11. Begin a simulation of Columbus’ voyage by manipulating the Voyager model and entering the latitude and longitude values ​​for 34 days in the year 1492 in Table 1. On the left side of the model enter:

• Year: 1492

• Month September

• Initial longitude: -17.0

• Initial latitude: -28.0

• Compass heading

• Log line speed (meters/second) as reported in Table I for each of the days.

• After entering the data for the first day, click the Start button.

• For each subsequent day, enter the compass heading and logline speed from the table and click Next.

The columns on the right side of the model panel show amperage, longitude and latitude at the end of the day, and magnetic field information. The magnetic variation is called “magnetic field declination”. Record the final longitude and latitude in Table 1.

Table 1 – Recreation of Columbus’ first voyage to America starting at latitude and longitude -17.0, 28.0 1st column data Compass heading speed (m/s) Last Lang, Lat 2nd column data continued Compass heading speed (m /s) Last Long, Lat 8 Sep 270 0.52 -17.5, 27.9 Sep 25 234.4 1.23 -47.7, 27.9 Sep 977.7 3.09 -20.3, 28.2 Sep 26 261 ,3 1.77 -49.4, 27.5 Sep 10 270 3.43 -23.5, 28.1 Sep 270 1.37. -25.9, 28.1 Sep 28 270 0.80 -51.6, 27.4 Sep 12 270 1.89 -27.7, 28.1 Sep 29 270 1.37 -52.9, 27.4 Sep 13 270 1.89 -29.5, 28.0 Sep 30 270 0.80 -53.6, 27.4 Sep 14 270 1.14 -70.70 0.80 -53.6, 27.4 Sep 14 270 1.14 -30.70,70.80 -53.6, 27.4 Sep 14 270 1.14 -30.70, 70 0.80-53.6, 27.4 Sep 14 270 1.14 -7.70.70 0.80-53.6, 27.4 Sep 14, 270 1.14 -30.70,70.80 -53.6, 27.4 Sep 14, 270 1.14, , 27.9 Oct 1, 270 1.43 -54.9, 27.4 Sep 15, 270 1.83 -32.4, 27.8 Oct 2, 270 2.23 -56.9, 27.3 16 Sep 270 2.23 -34.4, 27.6 Oct 3 270 2.69 -59.3, 27.20 Oct 4 270 3.61 – 62.5, 26.8 Sep 18 270 3.15 – 39.9, 27.5 Oct 5 270 3.26 – 65.3, 26.6 Sep 19 266 1.60 -68.7, 26.4 Sep 21 270 0, 92 -42.9, 27.2 Oct 8 247.5 0.6 6 -69.3, 26.3 Sep 22 292.5 2.06 -44.7, 27.6 Oct 9 248.2 1.80 -70.8 , 25.8 Sep 235 1.83 -46.0, 28.6 Oct 75.9, 23.9 2.67 nautical miles = 1 league; 1 nautical mile = 1852 meters Final longitude and latitude: -73.7, 22.2

team project

12. Once you have recorded all longitude and latitude, use these values ​​and trace the simulated journey on the map below.

Note: If you are repeating the trip or have multiple student teams, use the model; You will notice that the final predicted location (longitude and latitude) of the ship varies on October 11th. This variation is due to the measured uncertainty in the current data. The model intentionally simulates flow fluctuations unless you turn this feature off by setting Variable Flow to No. You can use the same model to simulate a journey starting somewhere else in the world On another site you can set the “log line” speed to the mean speed of Columbus.

Work out: cruising speeds

What can we learn from Columbus’ recorded speeds?

The mean cruising speed of Columbus was 1.91 m/s. This speed was measured using a Logline device and does not include sea surface currents. Unlike today’s self-propelled boats that burn coal, gas, or oil, Columbus’ boats relied on wind power. Windkraft hat den Nachteil, dass sie variabel ist, hat aber den Vorteil, dass sie frei verfügbar ist. Die Abbildung rechts zeigt ein Histogramm der Reisegeschwindigkeiten: Die horizontale Achse zeigt die Geschwindigkeit und die vertikale Achse die Anzahl der Tage bei jeder Geschwindigkeit. Beachten Sie, dass die Geschwindigkeit von Columbus stark variierte, was vielleicht größtenteils die unterschiedlichen Wind- und Segelbedingungen widerspiegelt.

13. Messen Sie Ihre Gehgeschwindigkeit. Wie verhält sich Ihre Gehgeschwindigkeit im Vergleich zur Durchschnittsgeschwindigkeit von Columbus? Die meisten Menschen haben eine Gehgeschwindigkeit von fast 1 Meter pro Sekunde, was fast der Hälfte der Geschwindigkeit von Kolumbus auf seiner Reise nach Amerika entspricht.

Elaborate: The Voyage Of The Bounty – Auf den Spuren von Captain Bligh

Welche Art von Informationen haben Entdecker während ihrer Reisen gesammelt?

Die berühmte Reise von Kapitän William Bligh (links) auf der HMS Bounty nach Tahiti ist ein Beispiel, bei dem astronomische Fixpunkte und Koppelnavigation eine wichtige Rolle bei der Navigation spielten. Nachdem sie um die halbe Welt gesegelt waren, meuterten einige von Blighs Besatzung und ließen den Kapitän und seine treuen Besatzungsmitglieder in einem kleinen Boot in der Nähe von Tahiti in See stechen.

Auf der Bounty hatte Kapitän Bligh Zugang zu einer genauen Uhr, die die Zeit von Greenwich, England, anzeigte, sodass er während der Fahrt seinen Längengrad basierend auf der Zeitdifferenz zwischen Sonnenmittag und Greenwich-Zeit berechnen konnte. Da sich die Erde einmal (360o) in 24 Stunden dreht, entspricht jeder Längengrad einer Zeitverschiebung des Sonnenmittags relativ zu Greenwich von 24 h/360o oder 4 Minuten Zeit pro Längengrad. Bligh musste auf seiner Reise eine Uhr mitbringen, um mit Greenwich im Takt zu bleiben. Heute wurde die Greenwich-Zeit durch die Weltzeit ersetzt und wir können die aktuelle Weltzeit über das Internet finden (http://aa.usno.navy.mil/faq/docs/UT.html).

Nach der Meuterei verwendeten Bligh und die treuen Mitglieder seiner Crew, die keinen Zugang zu einer Uhr hatten, Schätzungen der Geschwindigkeit und Richtung seines kleinen Segelboots, um Längen- und Breitengrade zu schätzen, die sich auf nahe gelegene Inseln und Sehenswürdigkeiten bezogen.

Verwenden Sie Kapitän Blighs Tagebuch von seiner Reise, um einen Teil seiner Reisen zu reproduzieren. Der Text seines Tagebuchs ist in einem interaktiven Bounty Log-Formular verfügbar, das unten abgebildet ist. Mit Blighs Worten verfolgen wir einen Teil seiner Reise und lernen etwas über seine Messungen der magnetischen Variation.

Wählen Sie einen der folgenden Datumslinks aus. Die Links erzeugen eine Karte, auf der Sie Blighs Reise planen können.

Dezember 1787, Januar 1788, Februar 1788, März 1788, Mai 1788, Juli 1788,

August 1788, September 1788, Oktober 1788, Mai 1789

Greifen Sie auf Blighs Tagebuch für den Monat zu, indem Sie auf dem Formular „Datum auswählen“ verwenden und die Schaltfläche „GO“ drücken. Der Tagebuchtext für den Monat erscheint im Textauswahlbereich. Durchsuchen Sie den Tagebuchtext nach Kapitän Blighs Werten für Längengrad, Breitengrad und magnetische Abweichung (magnetische Abweichung ist dasselbe wie magnetische Deklination). Jeder sollte mit Grad, Minuten, Sekunden und Umrechner in Dezimalgrad umgewandelt werden.

Vergleichen Sie für die Orte, an denen die magnetische Variation verfügbar ist, deren Wert mit den Vorhersagen des magnetischen Modells im Voyager-Modell.

14. Füllen Sie Tabelle 2 mit Ihren Daten aus.

Tabelle 2 – Verfolgung von Kapitän Bligh Datum Länge Breite Magnetische Variation Grad (o) Minuten (‘) Dezimalgrad (o) Minuten (‘) Dezimalgrad (o) Minuten (‘) Dezimal 7. April 1788 75 o, 54′ W -75,9 60 o, 24′ S -60,4 27 o, 9′ O +27,15 9 76 o, 58′ W -76,97 59 o, 31′ S -59,52 13 76 o, 1′ W -76,02 58 o, 9′ S -58,15 21 70°, 7′ W -70,12 58°, 31′ S -58,52 25 57°, 4′ W -57,07 54°, 16’ S -54,27

15. Verfolgen Sie während Ihres ausgewählten Monats die Reise von Captain Bligh auf der Karte. Zeichne Pfeile, um seine Fahrtrichtung anzuzeigen.

16. Wie gut stimmen die Vorhersagen der magnetischen Variation mit den Beobachtungen von Captain Bligh überein?

April hatte nur eine Beobachtung der magnetischen Variation. Das Modell und Bligh sind sich bezüglich des Datums vom 7. April 1788 nicht einig. Das Modell passt magnetische Daten über die ganze Erde und für 7 Jahrtausende an. Um das Modell für 1788 zu beurteilen, benötigen Sie mehr Daten sowohl von Bligh als auch von anderen Quellen.

Ausarbeitung: Pfade des Weltozeans

Die Schüler können mit dem Schiffsdriftmodell ihre eigenen Untersuchungen erstellen.

Stellen Sie sich schwimmende Objekte auf der Meeresoberfläche vor, wie z. B. eine ins Wasser geworfene Flasche. Testen Sie, wohin es aufgrund der Bewegung von Strömungen reisen könnte.

Erfahren Sie mehr über Schiffsladung, die auf See verloren gegangen ist. Lesen Sie Beispiele für Newsletter von Curt Ebbesmeyer für die neuesten Strandgut-Geschichten. Überprüfen Sie die mögliche Treibgutroute mit dem Schiffsdriftmodell.

Auswertung: Matrix zur Benotung von Lektion 1

Proficiency Level Description 4 Expert Responses show an in-depth understanding of the models and explorations used to explain the scientific concepts and processes used in the lesson. Data collection and analyses are complete and accurate. Predictions and follow through with accuracy of predictions are explained and fully supported with relevant data and examples. 3 Proficient Responses show a solid understanding of the models and explorations used to explain scientific concepts and processes in the lesson. Data collection and analyses are mostly complete and accurate. Predictions and follow through with accuracy of predictions are explained and mostly supported with relevant data and examples. 2 Emergent Responses show a partial understanding of the models and explorations used to explain the scientific concepts and processes in the lesson. Data collection and analyses are partially complete and sometimes accurate. Predictions and follow through with accuracy of predictions are sometimes explained and supported with relevant data and examples. 1 Novice Responses show a very limited understanding of the models and analogies used to explain scientific concepts and processes in the lesson Data collection and analyses are partially complete and sometimes accurate. Predictions and follow through with accuracy of predictions are not well explained and are not supported with relevant data and examples.

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The ASL fingering provided here is most commonly used for proper names of people and places; it is also used in some languages ​​for concepts for which no character is currently available.

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What does it take to beat the stream?

Back to the topic

After sailing the rivers around Pittsburgh’s Point in the summer of 2009, the answer to that question is clear: wind. Almost any wind is enough. This is true in all but the strongest currents. The only time I couldn’t get past the current was when the wind died down and died down so I calmed down and the current slowly and inexorably washed me back.

Once you know this is the situation to avoid, 99% of success on the rivers just requires you picking a windy enough day. Currents on the rivers are less than 1mph and mostly much less than that. The winds are usually much stronger than that and almost any sailboat can use these winds to move well in excess of 1mph. It’s an unequal battle that the sailboat will win.

Some useful facts

Of course, there is more to say beyond this final summary. Here are some useful things you should know:

Winds can blow from all directions in the open waters of the Point. But once you are in the small valley formed by a river valley, the winds almost always tend to be diverted towards the river. This can be seen in the GPS tracks linked on the main page. Once my boat is in a river valley, tacking into the wind is a symmetrical zigzag showing the wind as blowing along the river.

Therefore, on the river there are only two cases that usually occur: you have the wind directly behind you; or you are sailing directly against the wind. The first of these is easy. The second is more difficult. Both are discussed in more detail below.

Wind forecasts from weather.com are fairly accurate. You generally get the right wind direction. However, the wind speeds on the water are more variable. Typically they are less than predicted, presumably due to obstructions at the river edges. A 12 mph forecast can produce wind speeds of 6-12 mph. A 5 mph forecast will likely produce wind speeds of 0-5 mph. The 0-mile end is serious. It means no wind; you are reassured. For wind certainty I prefer days with forecasts of 8-10mph or more.

There are two ways I lost wind on the river. One is that it’s a relatively calm day with forecasts of say 5mph. Then the variability of the wind brings calm moments. The other is due to obstacles on the river bank. At Newport Marina on the Ohio, where I launched, a large hill on the south shore can block even strong southerly winds to create an uncomfortable calm. I’ve also found that the section of the Allegheny River in front of the convention center has similar issues due to the mass of the convention center.

Now consider the two cases:

The simple case:

Current and wind in opposite directions

To go upstream, the bows are simply pointed directly upstream and the sail left out to “walk downwind”. At this point of sail the boat can go quite fast. With a wind of 5 mph the boat can approach the maximum of 5 mph. Because typical currents are less than 1 mph, the boat can easily beat the current.

When returning, the boat must tack against the wind. But now the current supports progress instead of hindering it.

Since this is the simple case, I have chosen days with this configuration of wind and current for practically all my sailing days. The only days I had issues were on the harder configuration.

The hard case:

Current and wind in the same direction

In order to move against the current, the boat must now turn against the wind.

This means that the boat must zigzag across the wind, sailing “close-hauled” – that is, as close as the boat can be brought into the wind direction. Looking at the GPS tracks it is clear that my little Hobie Bravo is quite capable of sailing at an angle of about 45 degrees to the wind. Using the data below, the boat is also generally capable of speeds of half wind speed when run close-hauled. (This half is just a rough average. Higher speeds were often achieved.)

Unfortunately, only part of that speed puts the boat directly into the wind. A rough estimate is that 50% of the speed will eventually be put into the wind. The calculation is that a vector component of boat speed of magnitude cos(45 degrees) = 0.71 points points into the wind. However, there are also further losses if the sailboat stops while tacking and if the boat is not exactly close-hauled.

The result is that I can expect my sailboat to only make about 1/4 the wind speed against the current. This factor can take a toll. Imagine a worst case scenario, if I’m in a section of river where the winds are stalled and moderated to 4mph and there’s a very strong 1mph current to work against, then I become effective stalled. But if there is more wind I will still arrive against the current. (I would not sail in these conditions!)

A lot depends on the currents and the special characteristics of your sailing boat. Each combination leads to different results. I list some dates.

Currents in the Allegheny and Ohio Rivers

Allegheny River

Flow at the dam at Natrona on Allegheny (upstream from Point)

Very rough conversion: 10,000 cu. foot/sec = 0.36 km/h

Monongahela

Flow at the dam at Elizabeth on the Monongahela PLUS flow at the dam at Youghiogheny in Sutersville (both upstream from Point)

These are added because the Mon at Point is the combined flow of the Mon at Elizabeth and the Young at Suterville.

Very rough conversion: 10,000 cu. foot/sec = 0.47 km/h

Ohio River

River at the dam in Sewickley on the Ohio (downstream from Point)

Very rough conversion: 10,000 cu. foot/sec = 0.22km/h

For a more detailed discussion of flow velocities see this.

Performance of Hobie Bravo

After examining the speed encoded GPS tracks for my river sails this summer of 2009, it is possible to summarize the sailboat’s performance as follows.

Date Wind Speed ​​Running Speed ​​On 8 Jul 2009 GPS 0-5 mph WNW 1-5 mph 0-4 mph 9 Aug 2009 GPS 5-10 mph SW 0-5 mph 1-7 mph 29 Aug 2009 GPS 10-12 mph WSW 2-5 mph 3-6 mph 6 Sep 2009 GPS 4-8 mph ESE 4-6 mph 1-5 mph 13 Sep 2009 GPS 4-8 mph NW 2-5 mph 3-6 mph

Note that speeds running downwind seem to have maxima of 5-6 mph. Part of the limit comes from the boomless sail’s poor performance when running. It tends to flap and fold. This limits performance, as does my reefing the sail to avoid too much annoying flapping.

The speeds achieved by the Bravo’s catamaran hull are greater than what a normal monohull of the same length (12 feet) could achieve. Displacement hulls are limited by the “hull speed” I describe in the June 27, 2009 post. For a 12 foot displacement monohull hull speed is 4.3 miles per hour. I logged the Bravo at a sustained speed of 9.5 mph (on September 6, 2009).

The Antarctic Circumpolar Current is the strongest and arguably the most important current on the planet. It is the only current that flows clearly around the globe without being diverted by any landmass.

It connects all of the oceans and is believed to have played a key role in regulating Earth’s natural climate variability for millions of years. But much is still unknown about how the electricity works, including how it might now respond to climate change.

Starting this month, around 30 scientists from 13 countries plan to study the past dynamics of the currents by drilling holes in the seafloor in some of the most remote marine regions on earth.

They will set sail May 20 from Puntas Arenas, Chile aboard the scientific drillship JOIDES Resolution to embark on Expedition 383 of the International Ocean Discovery Program. IODP is an NSF-supported collaboration of scientists from around the world studying the history of the Earth as recorded in sediments and rocks beneath the seafloor.

“A better understanding of the sea-air exchange in the Antarctic Circumpolar Current will enable a more accurate prediction of the rate and magnitude of future climate changes associated with rising atmospheric carbon dioxide levels,” says Jamie Allan, program director in the NSF Division of Ocean Sciences.

The cruise’s co-chief scientist Gisela Winckler, a geochemist and paleoclimatologist at Columbia University’s Lamont-Doherty Earth Observatory, adds: “This is a key element of the world’s climate system because that’s where so much heat and carbon is exchanged between the ocean and the earth.” The atmosphere. We should learn how the winds, the ocean, and the Antarctic ice sheet have responded to warming in the past. That will help us know what they might do in the future.”

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Earth’s ocean currents are known as the “global conveyor belt” — a planetwide system that moves warm water north and cool water south. Now the strongest current of all is accelerating – and man is to blame. WP Get the full experience. Choose Your Plan ArrowRight That’s according to a study in the journal Nature Climate Change, which finds a “robust acceleration” in the Antarctic Circumpolar Current (ACC).

The current circulating around Antarctica is the strongest on the planet and the only one not blocked by landmasses. The giant circular current carries water clockwise around the globe, pushing more water than any other current and keeping the Antarctica it orbits cold.

The scientists used decades of data for the study, including satellite data on sea surface height and information collected by Argo, an international fleet of robotic instruments that float across the world’s oceans.

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Although the current is mainly driven by wind, the researchers found that the acceleration is mainly due to changes in ocean heat. As the temperature difference between hot and cold water increases, the adjacent currents accelerate.

That’s exactly what’s happening with the ACC, and the researchers say man-made global warming is to blame. The region absorbs much of the heat pumped into the atmosphere by human activities. As the planet continues to warm, researchers expect the trend to continue.

While scientists are still working to understand the consequences of accelerating currents, they believe faster circulation will change the way heat is distributed in the world’s oceans and affect marine life in areas with warmer waters.

Earlier this year, researchers found that the flow has also accelerated in the past – between 115,000 and 130,000 years ago during the last interglacial period. This acceleration could have caused everything from weather changes to a decrease in the ocean’s ability to absorb carbon dioxide. Their work was published in the journal Nature Communications.

– Erin Blakemore

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List of world ocean currents: Oceans are the lifelines of the earth and mankind because they play an important role in the earth’s climate and global warming. Over half of the world’s oxygen is produced by the oceans and absorbs 50 times more carbon dioxide than our atmosphere.

Check the list of world ocean currents along with their type in this article.

List of ocean currents in the world

Name of current Type of current North Equatorial Current Hot or warm Kuroshio Current Warm North Pacific Current Warm Alaskan Current Warm Counter-Equatorial Current Warm El Nino Current Warm Tsushima Current Warm South Equatorial Current Warm East Australian Current Warm Humboldt or Peruvian Current Cold Kuril or Oya shio Cold California Current Cold Antarctic Current Cold Okhotsk Current Cold Florida Current Warm Gulf Stream Warm Norwegian Current Warm Irminger Current Warm Rannell Current Warm Antilles Current Warm Brazil Current Warm Labrador Current Cold Canary Current Cold East Greenland Current Cold Benguela Current Current Cold Antarctic Current Cold Falkland Current Cold Mozambique Current Warm and stable Agulhas Current Warm and stable Southwest Monsoon Current Warm and unstable Northeast Monsoon Current Cold and unstable Somali Current Cold and unstable Western Australia Current Cold and stable South Indian Ocean Current Cold

What are ocean currents?

Ocean currents are made up of horizontal and vertical components of the ocean water circulation system created by gravity, wind friction and variations in water density in different parts of the ocean. They are classified into three parts based on flow direction, speed and shape i.e. H. Drift, Current and Stream. They can be cold, warm and hot.

Warm ocean currents originate near the equator and move towards the poles or higher latitudes, while cold currents originate near the poles or higher latitudes and move towards the tropics or lower latitudes. The direction and speed of the current depend on the shoreline and the seabed. They can flow thousands of miles and are found in all of the world’s major oceans.

Ocean currents in the northern hemisphere deflect to the right, while in the southern hemisphere they are deflected to the left due to the Coriolis force. The only exception to this rule of seawater flow is found in the Indian Ocean, where the direction of current flow changes with the change in direction of monsoon wind flow. It is noteworthy that the number of cold streams is less compared to the warm or hot streams.

List of famous local winds in the world

Mass flows of water, or currents, are essential to understanding how thermal energy moves between the Earth’s water bodies, landmasses, and atmosphere. The ocean covers 71 percent of the planet and contains 97 percent of its water, making the ocean a key factor in storing and transferring thermal energy around the world. The movement of this heat by local and global ocean currents affects the regulation of local weather conditions and temperature extremes, the stabilization of global climate patterns, gas cycling, and the supply of nutrients and larvae to marine ecosystems.

Ocean currents are found on the sea surface and in deep water below 300 meters (984 feet). They can move water horizontally and vertically and occur on both local and global scales. The ocean has an interconnected flow or circulation system driven by wind, tides, the Earth’s rotation (the Coriolis effect), the sun (solar energy), and differences in water density. The topography and shape of ocean basins and nearby landmasses also affect ocean currents. These forces and physical properties affect the size, shape, speed, and direction of ocean currents.

Surface ocean currents can occur on local and global scales and are typically driven by wind, resulting in both horizontal and vertical water movement. Horizontal surface currents, which are local and typically short-term, include rip currents, longshore currents, and tidal currents. In ascending currents, vertical water movement and mixing brings cold, nutrient-rich water to the surface while warmer, less dense water is pushed down, where it condenses and sinks. This creates a cycle of lift and downforce. Prevailing winds, sea surface currents and the associated mixing affect the physical, chemical and biological properties of the ocean and the global climate.

Deep-sea currents are density-driven and differ from surface currents in volume, speed, and energy. The density of water is affected by the temperature, salinity (salinity) and depth of the water. The colder and saltier the seawater is, the denser it is. The greater the density differences between different layers in the water column, the greater the mixing and circulation. Density differences in seawater contribute to a global circulation system, also known as the global conveyor belt.

The global conveyor belt includes both surface and deep-sea currents that circulate around the globe on a 1,000-year cycle. The circulation of the global conveyor belt is the result of two simultaneous processes: warm surface currents, which transport less dense water away from the equator towards the poles, and cold deep-sea currents, which transport denser water away from the poles towards the equator. The global ocean circulation system plays a key role in distributing thermal energy, regulating weather and climate, and cycling vital nutrients and gases.

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This article provides an introduction to the major circulation patterns in the ocean.

introduction

By redistributing heat across the globe, ocean currents have a major impact on global climate. They cause, for example, the relative mildness of the western European climate. Ocean and atmospheric currents form a coupled dynamic system. Instabilities in this system, particularly the El Nino Southern Oscillation (ENSO), produce important climate variability. Ocean currents not only distribute heat, but also play a crucial role in the global ecosystem by storing [math]CO_2[/math] and recycling nutrients.

streams

There are two main types of ocean currents: currents that are primarily driven by wind and currents that are primarily driven by density differences. The density depends on the temperature and salinity of the water. Cold and salty water is dense and sinks. Warm and less salty water floats. Although tides are generally a dominant motor of water movement in shallow coastal waters, their relative importance in the oceans is less. However, it should be noted that tides are mainly generated in the oceans (by the gravitational forces of the moon and sun) and amplified as they propagate to the continental shelf (see article Ocean and Shelf Tides).

Wind driven ocean currents

Global wind field

The large-scale global wind field consists of dominant westerly winds at latitudes between 30 and 60 degrees in the northern and southern hemispheres (the westerly winds) and dominant easterly winds in the tropical/subtropical zone (the trade winds). This wind field pattern results from the low atmospheric pressure in the tropics (warm air rising) and the high atmospheric pressure in the subtropics (cooled air descending). The air flow near the ground – towards the equator at low latitudes and towards the poles at high latitudes (known as Hadley cells) – is deflected by the Earth’s rotation, giving rise to the west winds and the trade winds.

surface currents

Wind stress creates strong currents (up to several m/s) in the sea surface layer. The thickness of the wind-borne surface layer is of the order of 500 meters (about the thickness of the thermocline at low and mid-latitudes) to a maximum of 2000 meters. Due to the Earth’s rotation, the main current system of the oceans consists of large anticyclonic gyres (clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere) [1]. There are five major gyres: the North Atlantic, the South Atlantic, the North Pacific, the South Pacific, and the Indian Ocean Gyre, see Figure 1. The Antarctic Circumpolar Current is located in the Southern Ocean and is constantly circling Antarctica because there are no land masses to accommodate the currents interrupt. It is an easterly flowing current, driven by the westerly winds prevalent at that latitude.

The most famous ocean current, the Gulf Stream, is a huge, moving body of water that transports a tremendous amount of heat from the Caribbean across the ocean to Europe. Due to the northward increasing Coriolis effect [3], it passes the US east coast as a narrow jet and then spreads across the ocean as a meandering current while creating a series of mesoscale eddies and eddies. The North Atlantic Gyre is completed by the Canary Current in the eastern Atlantic, which carries relatively cold water south and west. The Kuroshio is a warm boundary current in the Northwest Pacific, similar to the Gulf Stream. It is part of the great gyre formed by the California Current and the North Equatorial Current. The North Equatorial Current and South Equatorial Current are driven by the easterly trade winds over the Pacific. The South Pacific Gyre is completed by the warm Western Australia Current and the cold Peru Current.

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In regions where the Ekman transport diverts the boundary current away from the coast, water from the deep sea rises to the sea surface, see Figure 2. This phenomenon is called “upwelling” and is very important for the enrichment of surface waters with organic matter and nutrients . Upwelling zones are characterized by very rich marine life with ample resources for fishing. Upwelling zones exist on the south-flowing boundary currents in the northern hemisphere (California Current along the US west coast, Canary Current along the West African coast) and on the north-flowing boundary currents in the southern hemisphere (Peru Current along the South American west coast). and Benguela Current along South Africa’s west coast).

Buoyancy also occurs at the equator on the Pacific Ocean (equatorial buoyancy). As a result of the Coriolis effect, the North Equatorial Current is deflected north and the South Equatorial Current is deflected south. This results in upwelling of nutrient-rich waters and cooling of surface waters near the Pacific equator, see Figure 3. Downwelling zones exist north and south of the equator.

Southern El Nino Oscillation

The instability of the coupled ocean-atmosphere dynamics produces large variations in the Pacific region’s climate that are felt on a global scale. The weakening of the easterly trade winds allows warm water from the western Pacific to flow back with the equatorial countercurrent to the eastern South American border, where rising currents are blocked by cold deep-sea water. This results in a relative warming of the eastern Pacific (decreasing sea surface atmospheric pressure) and a relative cooling of the western Pacific (increasing sea surface atmospheric pressure), thus inducing a further weakening of the easterly trade winds. This feedback amplifies the so-called El Nino phase of the oscillation [5][6]. The shutdown of the food-rich upwelling currents has serious consequences for marine life and fisheries. [7]. After a number of years (three on average, but variable), the system reverts to the opposite phase called La Nina. The beginning and end of the oscillation are not yet fully understood.

deep-sea circulation

Deep-sea circulation is mainly driven by density differences. It is called the thermohaline circulation because density differences are due to temperature and salinity. The density differences are small and the flow velocity is low, of the order of a few cm/s. However, the masses of water moving through thermohaline circulation are huge. Water fluxes are on the order of 20 million [math]m3/s[/math]. Density gradients alone are not sufficient to sustain deep-sea circulation. Buoyancy and mixing processes are also required to bring deep sea water back to the surface [8].

deep water formation

Surface water density increases when cold air blows across the ocean at high latitudes in winter. The density of the water continues to increase due to evaporation and the release of salt from the formation of sea ice. Deep-sea water masses are formed in the Arctic and Antarctic regions when dense water with a temperature of less than 4 °C sinks from the surface to great depths. From these regions, a cold deep water layer spreads across the entire ocean basin.

conveyor belt

Fig. 4. Schematic representation of the Atlantic meridional overturning current.

The thermohaline circulation moves water masses between the different ocean basins [9][10]. “Ocean Conveyor Belt” is the popular name of this circulation between the basins. The conveyor belt is fed in the northern North Atlantic with saline water (by evaporation) from the Gulf Stream, which after cooling in the Arctic sinks to great depths and forms the North Atlantic Deep Water (NADW). The replacement of this dense sink water creates a continuous surface current that feeds the conveyor belt. The NADW flows south from the Arctic region as a deep boundary current along the American shelf [11]. This current compensates for the net northward surface current in the Atlantic Ocean. This circulation along the north-south axis is called the Atlantic Meridional Overturning Circulation (AMOC), see Figure 4.

The NADW eventually empties into the Antarctic Circumpolar Current and penetrates the Indian and Pacific Oceans. The cold dense waters from the Antarctic Zone fill the deep water layer in these oceans and then gradually rise and mix with the surface waters of the Indian and Pacific Oceans. The mixing of deep sea water is promoted by strong surface winds, tides, upwelling and abyssal circulation[12][8]. The circulation is finally completed by a warm surface return to the Atlantic Ocean, passing south of Africa and the Americas, see Figure 5. The entire journey takes more than 1,000 years.

[13]. Fig. 5. Simplified scheme of the global thermohaline circulation, adapted from Broecker (1991)

Energy to sustain the large-scale thermohaline circulation

It has been estimated that about 2.1 TW ([math]10^{12}[/math] Watts) of mixing energy is required to sustain the large-scale ocean thermohaline circulation (Munk and Wunsch, 1998) [14] . It has long been known that wind and tides are two important sources of mechanical energy for driving the mixing of the ocean interior. Although most of the lunar and solar tidal energy on the global ocean is dissipated in the shallow seas, perhaps 1.0 TW or more of the tidal energy dissipation in the deep sea occurs through the scattering of surface tides by seafloor topography into internal tidal waves ( Egbert and Ray, 2000) [15]. Internal wave breaking is believed to be a major contributor to pelagic turbulence.

The winds can also generate internal gravity waves in the surface layer of Earth’s oceans, known as near-inertial oscillations because of the peak wave energy near the inertial frequency. They are thought to play an important role in diapycnal mixing to maintain the global system of thermohaline circulation. But the exact contribution of wind power to these near-sluggish motions, and the relative importance of wind compared to tidal forces, remain subjects of heated debate. Near-sluggish wind power feed-in estimates varied widely from 0.3 to 1.5 TW using numerical models. However, recent calculations based on observations suggest that wind power is only 0.3–0.6 TW and the strongest energy flux occurs between 30° and 60° latitudes during the winter season, when storms are most common (Liu et al. , 2019) [16].

In recent decades, biogenic mixing is believed to be another important factor in ocean mixing (Katija and Dabiri, 2009) [17]. From small zooplankton to large mammals, swimming animals can carry bottom water with them as they migrate upwards, and this movement actually creates an inversion that leads to ocean mixing. The global power input from this process is estimated to be of the order of 1 TW energy, comparable to the values ​​caused by wind and tides. After all, every day billions of tiny krill and some jellyfish migrate hundreds of meters from the deep sea to the surface where they feed.

Importance of deep-sea circulation

The deep sea is a huge storehouse of heat, carbon, oxygen and nutrients. Deep-sea circulation regulates the uptake, distribution, and release of these elements. The low rate of tipping stabilizes our global climate. By transporting oxygen to the deeper layers, it supports the largest habitat on earth.

Deep-sea circulation and climate change

Current theories explaining deep-sea circulation predict that global warming will have negative effects on deep-sea circulation. Most studies have focused on the North Atlantic [18]. The formation of dense sinking surface water in the Arctic is counteracted by higher atmospheric temperature and by the release of freshwater from ice melt. This reduces the feeding of the Atlantic Meridional Overturning Circulation, which drives warm Gulf Stream water north. In addition, the density of the North Atlantic deep water will be lower; hence the cold return current will flow closer to the sea surface. It is expected that these factors will lead to a significant cooling of the western European climate.

The melting of ice and the resulting release of freshwater in the Antarctic region will impede the formation of Antarctic Groundwater (AABW). Model simulations indicate that this may result in significant warming of deep waters throughout the Pacific; It can also affect the Atlantic by enhancing the Atlantic meridional overturning circulation. The impacts of freshwater releases in the Antarctic region on global climate and sea level rise may be even greater than the impacts of refreshing Arctic waters, as discussed in the article Thermohaline Circulation of the Oceans.

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references

↑ Munk, W. H. 1950. About the wind-driven ocean circulation. J. Met. 7, 79-93. ↑ http://www.gkplanet.in/2017/05/oceanic-currents-of-world-pdf.html ↑ Stommel, H. 1948. The western intensification of wind-driven ocean currents. Transactions, American Geophysical Union, 29:202-206. ↑ http://www-das.uwyo.edu/~geerts/cwx/notes/chap11/equat_upwel.html ↑ Bjerknes, J. 1969. Atmospheric teleconnections from the equatorial Pacific. Mon Weather Rev. 97:163-172. ↑ Wyrtki, K. 1973. Teleconnections in the Equatorial Pacific Ocean. Science 180: 66-68. ↑ Rice T. 2000. Deep Sea. The Natural History Museum, London. 8.0 8.1 Rahmstorf, p. 2006. Thermohaline Ocean Circulation. In: Encyclopedia of Quaternary Sciences, edited by S.A. Elias. Elsevier. ↑ Wüst, G. 1968. History of investigation of the longitudinal deep-sea circulation (1800-1922). Bulletin de l’Institut Oceanographique, Monaco, Numero Special 2, 109-120. ↑ Stommel H. and Arons, A.B. 1960. On the abyssal circulation of the world ocean – II. An idealized model of the circulation pattern and amplitude in oceanic basins. Deep Sea Research 6: 217–233. ↑ Stommel H., Arons, A.B. and Faller, A.J. 1958. Some examples of steady-state flow patterns in confined basins. Tellus 10(2): 179-187. ↑ Stommel H. 1958. The abysmal circulation. Deep Sea Research 5(1): 80–82. ↑ Broecker, W.S. 1991. The Promoter of the Great Ocean. Oceanography 4: 79-89 ↑ Munk, W.H. and Wunsch C. 1998. Abyssal Recipes II: Energetics of tide and wind mixer. Deep-Sea Research 45: 1977-2010 ↑ Egbert, G.D., and Ray RD. 2000. Significant dissipation of tidal energy in the deep sea derived from satellite altimeter data. Nature 405: 775-778 ↑ Liu, Y., Z. Jing, and Wu L. 2019. Wind force on oceanic near-inertial oscillations in global ocean estimated by surface drifters. Geophysical Research Letters 46: 2647-2653 ↑ Katija, K. and Dabiri J.O. 2009. A viscosity-enhanced mechanism for biogenic ocean mixtures. Nature. 460: 624-626 ↑ Broecker, W. S. 2003. Is the trigger for abrupt climate changes in the ocean or in the atmosphere? Science 300: 1519–1522.

See also

S. Rahmstorf: Thermohaline Ocean Circulation. In: Encyclopedia of Quaternary Sciences, edited by S.A. Elias. Elsevier, Amsterdam 2006.

Stommel, H.M. 1957. A survey of the theory of ocean currents. Deep Sea Research 4, 149–184.

Great ocean currents

https://www.britannica.com/science/ocean-current

The two main components of currents are velocity and direction. To measure currents, buoys are equipped with Global Positioning System technology or satellite communications that relay data and information.

What are tides and currents?

Tide. If you live near the coast or have visited the beach before, you are probably familiar with the tides. But did you know that tides are really big waves moving through the ocean in response to the forces of the moon and sun? Tides start in the ocean and move toward the shore, where they appear as regular rising and falling of the sea surface. How much the water level changes throughout the day depends on where you are and what day it is.

streams. Currents bring movement to the sea! With tides, water moves up and down; Currents involve the movement of water back and forth. Currents are driven by several factors. Tides are one of them. Wind, the shape of the land and even the water temperature are other factors that drive currents.

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Why study tides and currents?

We need accurate tide and current data to aid navigation, but these measurements also play an important role in keeping people and the environment safe. A change in water level (due to tides) can leave someone stranded (or flooded). And knowing how fast water moves—and in which direction—is important for anyone involved in water-related activities. Forecasting and measuring tides and currents is essential for getting cargo ships in and out of ports safely, determining the extent of an oil spill, building bridges and piers, determining the best fishing spots, emergency preparedness, tsunami tracking, swamp cleanup, and more much more.

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How we measure tides

NOS has been measuring and forecasting tides since the early 1800s. We’ve come a long way since putting a stick in water to determine the water level. Today we use engineered air acoustics and pressure systems to automatically detect and record changes in water levels. All data is recorded electronically, transmitted by satellite every six minutes and made available online. The backbone of this system is a network of long-term, continuously operated water level stations known as the National Water Level Observation Network

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How we measure currents

The two main components of currents are velocity and direction. To measure a current, throw an object into the water and measure how long it takes to reach a certain point at a known distance. Admittedly, technology allows us to be a bit more accurate and sophisticated in our measurements. For example, the object in the water could be a buoy equipped with Global Positioning System technology or satellite communications that relay data and information.

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high tide and low tide

Do you want to know the high and low tides for places in the United States? Visit the Center for Operational Oceanographic Products and Services website. You can find tide forecasts for more than 3,000 water stations across the United States. Some of the stations (referred to as “reference stations”) contain full daily forecasts, while others (referred to as “substations”) require a little math to apply differences between tide times and heights at substations and at specific reference stations.

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tide data

If the water level is constantly changing, how do we know how much the water level has risen or fallen from “normal”? To define “normal,” scientists use a reference or datum as the starting point from which all measurements are made. The numbers that appear on a nautical chart represent water depths measured relative to such datum. The mean lower low tide, or the average of all observed lower low tides (the lower of the two low tides on each tide day) is known as the chart datum in most areas. Mean high tide, or the average of all observed high tide levels, is the datum used to represent the coastline on maps. Tide data also provides base definitions for the exclusive economic zone and boundaries between private, state and federal property and jurisdiction.

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clearing a bridge

When a ship is going under a bridge, it’s best if the ship doesn’t touch the bridge… right? It might sound like a no-brainer, but ships are getting bigger and space under bridges stays the same, creating a potentially tight bottleneck. In order to know how much space is available under a bridge, you need to know how high the water is at any given time. NOAA uses microwave “air gap” sensors mounted on bridges over navigation channels. The sensor sends microwave signals down to measure the position of the water surface. This information provides ship captains with a direct measurement of clearance under bridges, helping them determine if passage is safe. cool what?

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Navigating a busy port

What goes on in a busy port is similar to what goes on in a busy airport. Just as airplanes flying in and around an airport need up-to-date weather and ground conditions, ships entering a port need to know exactly what’s going on in the water and in the air in real time. Enter the Physical Oceanographic Real-Time System or PORTS®. PORTS provides seafarers with real-time information such as water level, current speed and direction, wind, air temperature, water temperature and salinity. This data stream is freely available online and ship captains can also access the data over the phone.

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Sea level monitoring

Climate change has certainly attracted a lot of attention. Climate change doesn’t just mean changes in air temperature or weather patterns…it could also affect the ocean. A warmer climate could mean higher sea levels, both from melting sea ice and expanding seawater. The Center for Operational Oceanographic Products and Services maintains records of long-term water levels that can be used to determine the rate at which local sea levels are changing. With more than half of us living in coastal states, this is news many of us want to know.

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search and rescue efforts

When someone is lost at sea, time is of the essence. Knowing the speed and direction of currents can help the US Coast Guard conduct search and rescue operations with greater accuracy. The Integrated Ocean Observation System uses high frequency radar systems to develop maps of surface currents for use by the Coast Guard in their operations. These cards can also be used to support other scientific work, e.g. For example, responding to oil spills, monitoring harmful algal blooms, and assessing water quality.

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In the previous article – Mastering Ship Navigation – Part 1, we explained how a deck officer can use the power of the wind to maneuver the ship safely and efficiently.

In this article, we look at a completely different aspect that is equally important when maneuvering a ship at sea. Let’s figure out how to steer a ship under various effects of sea currents.

The effects of ocean currents

Sea currents play a very important role in ensuring the stability of the ship.

When dealing with ships in water, the influence of currents must therefore also be taken into account.

The effects of current are particularly important when the vessel is under the influence of onshore winds, near offshore platforms, when maneuvering in narrow channels and on the open sea, or in inland waterways or harbors. When the ship is in harbors or inland waters and the current has a constant strength and direction, the handling of the ship becomes much easier.

Such conditions exist only in comparatively narrow river channels.

However, navigating officers should take into account different currents that may be present in a small area in which the ship must manoeuvre.

The key difference between currents and winds is that currents affect the ship in specific and predictable ways, unlike wind.

Even in open water, when the vessel approaches an oil rig or mooring buoy, due consideration should be given to the effect of the current for safer manoeuvres.

The current from the front will reduce the ship’s speed over the ground, improve the ship’s response to the rudder and also give more time to assess and correct developing situations.

Shallow water effects on ships – Ship Squat

When a ship moves through water, it pushes the water forward. This volume of water flows back down the sides and under the bottom of the ship. The streamlines of the reflux are accelerated under the ship, causing a drop in pressure and causing the ship to fall vertically into the water.

When the ship falls vertically into the water, it trims both forward and backward. This general reduction in static ground clearance under the keel, both fore and aft, is known as ship’s squat.

When the ship moves forward at greater speed in shallow water where the keel spacing is 1.0 to 1.5 meters, there is a high probability of running aground due to excessive bow or stern squats.

What Factors Determine Ship’s Squat?

The main factor on which the squat of the ship depends is the speed of the ship. The squat varies roughly with the square of the speed.

The blocking factor “S” is another factor to consider when understanding ship squat. The clogging factor is defined as the submerged cross-section of the ship’s midships section divided by the water cross-section within the canal or river.

The blocking factor ranges from around 8.25 b for supertankers to around 9.50 b for general cargo ships and up to around 11.25 ship widths for container ships.

The presence of another ship in a narrow river also affects squats, so squats can double in value when the ship passes or crosses the other ship.

How do I find out if a ship has entered shallow water?

1. Wave generation from the bottom of the ship increases, especially at the front end of the ship.

2. Ship becomes sluggish when manoeuvring.

3. Draft gauges or echo sounders show changes in final drafts

4. The propeller RPM indicator shows a decrease. When the ship is in “open water”, i. H. without width limitation, this reduction can be as much as 15% of the operating speed in deep water. If the ship is in a narrow fairway, this speed reduction can be up to 20% of the operating speed.

5. The ship’s speed decreases. When the ship is in open water, this reduction can be as high as 35%. If the ship is in a narrow waterway such as a river or canal, this reduction can be as high as 75%.

6. The ship may suddenly begin to vibrate. This is due to the effects of the water causing the natural hull frequency to become resonant with another frequency associated with the vessel.

7. Any roll, pitch and heave will be reduced as the vessel moves from deep water to shallow water conditions. The reason for this is the dampening effect of the narrow layer of water under the bottom shell of the ship.

8. The appearance of mud clouds is visible in the water around the ship’s hull when the ship moves over a raised shelf or a submerged wreck.

9. Turning Circle Diameter (TCD) increases. TCD in shallow water could increase by 100%.

10. Stopping distances and stopping times are longer compared to ships in deep waters.

11. The effectiveness of the rowing oar is decreasing.

You may also want to read – Top 10 Celestial Navigation Books

Mass flows of water, or currents, are essential to understanding how thermal energy moves between the Earth’s water bodies, landmasses, and atmosphere. The ocean covers 71 percent of the planet and contains 97 percent of its water, making the ocean a key factor in storing and transferring thermal energy around the world. The movement of this heat by local and global ocean currents affects the regulation of local weather conditions and temperature extremes, the stabilization of global climate patterns, gas cycling, and the supply of nutrients and larvae to marine ecosystems.

Ocean currents are found on the sea surface and in deep water below 300 meters (984 feet). They can move water horizontally and vertically and occur on both local and global scales. The ocean has an interconnected flow or circulation system driven by wind, tides, the Earth’s rotation (the Coriolis effect), the sun (solar energy), and differences in water density. The topography and shape of ocean basins and nearby landmasses also affect ocean currents. These forces and physical properties affect the size, shape, speed, and direction of ocean currents.

Surface ocean currents can occur on local and global scales and are typically driven by wind, resulting in both horizontal and vertical water movement. Horizontal surface currents, which are local and typically short-term, include rip currents, longshore currents, and tidal currents. In ascending currents, vertical water movement and mixing brings cold, nutrient-rich water to the surface while warmer, less dense water is pushed down, where it condenses and sinks. This creates a cycle of lift and downforce. Prevailing winds, sea surface currents and the associated mixing affect the physical, chemical and biological properties of the ocean and the global climate.

Deep-sea currents are density-driven and differ from surface currents in volume, speed, and energy. The density of water is affected by the temperature, salinity (salinity) and depth of the water. The colder and saltier the seawater is, the denser it is. The greater the density differences between different layers in the water column, the greater the mixing and circulation. Density differences in seawater contribute to a global circulation system, also known as the global conveyor belt.

The global conveyor belt includes both surface and deep-sea currents that circulate around the globe on a 1,000-year cycle. The circulation of the global conveyor belt is the result of two simultaneous processes: warm surface currents, which transport less dense water away from the equator towards the poles, and cold deep-sea currents, which transport denser water away from the poles towards the equator. The global ocean circulation system plays a key role in distributing thermal energy, regulating weather and climate, and cycling vital nutrients and gases.