Lab #7 Winds and Currents S21 Key
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Feb 20, 2024
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Lab #7 Global Winds, Ocean Currents and Regional Climate Patterns - Answer Key Part I - General Atmosphere and Surface Ocean Circulation Patterns
1.
Winds are generated due to pressure differences, which are themselves generally the result of unequal heating of Earth’s surface. Atmospheric pressure can be idealized in order to understand basic atmospheric circulation. Use Figure 2 in the lab introduction as a reference to assist in completing the following chart using t
he terms “
high pressure
” or “
low pressure
.
”
Latitude Location
Average Relative Atmospheric Pressure
0° (Equator) ________
Low Pressure
_______ 30° North & South ______ High Pressure ______ 60° North & South _______ Low Pressure _____ 90° North & South _______ High Pressure _______ 2. Winds across Earth’s surface are produced due to pressure differences (gradients).
Winds flow from areas of (circle one): high pressure
/ low pressure
to areas of (circle one): high pressure
/ low pressure
The (circle one): smaller
/ greater the pressure difference, the stronger the winds. 3. Vertical movement of air within each pressure zone is part of a much larger circulation pattern within the atmosphere related to large-scale convection. Vertical air movement may be air rises
or air sinks
. As a result of the vertical movement of air within each pressure zone, a distinct general climate is established for that region. This general climate may be considered as clear, dry & sunny skies or cloudy conditions with rain likely
dependent upon the atmospheric pressure. Based upon information from the lab introduction, use the above terminology to complete the following chart: Low Pressure
High Pressure
Vertical Air Movement
Air rises Air sinks General Climate Cloudy conditions with rain likely Clear, dry & sunny skies
4. In response to the atmospheric pressure differences, surface winds are produced. In all, the four pressure zones identified in Question #1, generate three global wind belts in each hemisphere. Match the labeled arrows on the diagram with the proper name of the wind belt. Pay close attention to not only the name of the wind belt but its direction of flow as well. Hint: Winds are named for the directions from which they come. A
- 90°-60° North = NE Polar Easterlies
B
- 60°-30° North = SW Westerlies
C
- 30°-0° North = NE Trade Winds
D
- 30°-0° South = SE Trade Winds E
- 60°-30° South = NW Westerlies
F
- 90°-60° South = SE Polar Easterlies
Due to Earth’s rotation, prevailing winds do not blow directly north or south. Wind direction choices are terms such as northeast, southeast, northwest and southwest
. The wind belts are the Trade Winds, the Westerlies, and
Polar Easterlies
. Thus an example of a wind belt might be NE Trade Winds. Place the full correct wind name (including direction) in the spaces provided above for each latitude belt. 5. In this satellite image of Earth's surface, a distinct band of clouds is seen along the equatorial Pacific. Referred to as the ITCZ or Intertropical Convergence Zone, it represents the convergence of the __
Trade
____winds
, producing clouds as a result of a dominant _____
Low
_____ pressure.
(Fill in the blanks with the correct response)
6. Largely a function of the spherical shape of the planet, Trade Winds and Westerlies play a much larger role in generating the ocean's surface circulation than Polar Easterlies. As Trade Winds and Westerlies blow across the ocean surface, energy is transferred from the atmosphere to the ocean surface, setting the water in motion. The currents that are produced are called "geostrophic" currents as they are affected by not only the winds, but also Earth's rotation (hence "geostrophic" means "earth turned.") In this image, ocean currents driven by the Trade Winds move from ___
_
east to west __
and those ocean currents driven by the Westerlies move from _
___
west to east ___. Choices are: from east to west, from west to east, from north to south, from south to north As the currents encounter land, they are deflected. This is where Earth's rotation comes in to play. Currents in the Northern Hemisphere will be directed to the __
right
__
of the intended direction while currents in the Southern Hemisphere will be directed to the __
left
__
of the intended direction. Word choices are: left, right, north, south, east, west This produces the main surface ocean circulation patterns referred to as subtropical gyres. Subtropical gyres flow __
clockwise
__
in the Northern Hemisphere and _
counterclockwise
__
in the Southern Hemisphere. Word choices are: clockwise, counterclockwise The end result is that winds and currents move in the ___
same
____
direction. Word choices are: same, opposite This is the result of the __
Coriolis
___ Effect. Word choices are: Feynman, Coriolis, Wegener, Hawking In both hemispheres, the name "subtropical" derives from the location of the gyre, which is centered at ____
30°
_____
latitude. Choices are: 0°, 30°, 60°, 90° Thus the currents circulate around an atmospheric
__
high
___ pressure. Word choices are: low, high
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7. Worldwide, there are ___
5
____ subtropical gyres representing the major ocean basins. Within each gyre there are ___
4
____ major currents. Choices are: 3, 4, 5 For each of the locations labeled A through E give the correct subtropical gyre name. Location Gyre Name A __
North Atlantic Subtropical Gyre
__
B __
South Atlantic Subtropical Gyre
__
C __
South Pacific Subtropical Gyre
__
D __
North Pacific Subtropical Gyre
__
E __
South Indian Subtropical Gyre
__
Word choices are: North Pacific Subtropical Gyre, North Atlantic Subtropical Gyre, North Indian Subtropical gyre, South Pacific Subtropical Gyre, South Atlantic Subtropical Gyre, South Indian Subtropical Gyre, Artic Subtropical Gyre, Antarctic Subtropical Gyre
8. Due to the physics of water movement, the flow of surface water forms a "hill' of water referred to as "dynamic topography" extending across the entire ocean basin. In cross-
section, one can see that this hill is ___
asymmetric
______ Word choices are: flat, symmetric, asymmetric
This results in uneven water flow from one side of the ocean basin to the other. In map view, one can see that currents flowing on the western side of the ocean basin are __
narow and strong
__
and currents flowing on the eastern side of the basin are __
_wide and weak
___
. Choices are: wide and weak narrow and strong
9. Review Figure 5 in the lab introduction. Dynamic topography can be mapped as a function of variations in sea level height. Although a change of a few centimeters may seem trivial, remember that this is over tens of millions of square miles so the oceanographic and climate impact is significant. Using Figures 3 and 5 and Table 1 in the lab introduction, determine the correct set of characteristics for the boundary currents in the following figure. You will be determining boundary location, relative speed, relative volume and relative temperature for locations A through D. A _
western, fast, large warm
__
B _ eastern, slow, small, cold
__
C __ eastern, slow, small, cold
__
D __ western, fast, large warm
__
For each of the letters A through D, characterize the following for each part of the gyre:
eastern vs
western
fast vs
slow
small vs
large (volume)
warm vs
cold (temperature)
10. Summarizing your findings from the previous question, you have discovered that __
western
___ boundary currents are intensified (fast moving, with large volumes) thus moving (
western, eastern, northern, southern) choose one
___
warmer
__________ temperature water (warmer, colder) choose one ___
poleward
____ resulting in a profound impact on regional climate patterns. (poleward, equatorward) choose one
Part II - Case Studies of Ocean Currents
Subtropical Boundary Currents and Climate - Southern Africa 11. Although tropical and subtropical regions (extending from the Equator to about 35° latitude) are generally warm, the climate of coastal regions in these latitudes is heavily influenced by the temperature of the boundary currents and by the prevailing winds. These climate patterns are repeated along the coasts of all continents, but we will focus on southern Africa here, specifically a comparison between Walvis Bay, Namibia and Inhambane, Mozambique. Review the Global Sea Surface Temperature resource map so that you understand the location of these two coastal areas as you will need to identify the boundary currents and the prevailing winds. Refer to the South African Climate Data reference page to complete the following data table: Please note that you are given the units so you only need to provide the number as it is given in the reference material. When putting this information into the Canvas quiz, please do not include extra spaces as Canvas will mark it as incorrect. And yes, spelling does matter. Walvis Bay, Namibia Inhambane, Mozambique Annual Mean Temperature, given in degrees Celsius 15.4 °C 24 °C Average Precipitation, given in millimeters 11 mm 950
mm Using what you have learned in Part I of this lab activity about ocean currents and wind flow, and knowing the location of these two coastal areas, complete the following chart: Walvis Bay, Namibia Inhambane, Mozambique Name of ocean current Benguela Agulhas Is this an eastern or western boundary current? Eastern Western Is the general temperature of the current warm or cold? cold warm Is the source of the water from the tropics or subpolar? subpolar tropics The prevailing winds affecting this region are the: SE Trade Winds SE Trade Winds
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12. Based upon the data that you have collected for the previous question, write a paragraph (using complete sentences and proper grammar) to summarize and explain the general climate for Walvis Bay and Inhambane. You should include the effects of the ocean currents and the prevailing winds on the general climate for these two areas. Be sure to include the names of the ocean currents and the winds in your explanation for each area. Namibia has a cooler and drier climate than Mozambique due to the effects of the coastal currents. Namibia is affected by the cool waters of the Benguela Current (eastern boundary current), moderating the temperature and leading to less evaporation and therefore precipitation. Mozambique is affected by the warm waters of the Agulhas Current (western boundary current) leading to warmer temperatures and more evaporation and thus significantly more precipitation. In addition to the currents, wind flow does play a role. Based on their latitudes (23°-24° South), both regions are impacted by the SE Trade Winds. In the case of Mozambique, these winds are onshore, flowing over the warm Agulhas Current. For Namibia, on the opposite side of the continent, those same winds are offshore, thus moving any potential moisture from the cold Benguela Current away from the coastal region. Case Study: The Search for Malaysian Flight MH370 13. In the rare, and unfortunate, occurrence of a plane crashing into the ocean, scientists make use of an ocean circulation model known as a drifter model
to aid in search and recovery of evidence from the crash. Unfortunately, on March 8, 2014 Malaysian Flight MH370 went "missing" while flying over a portion of the Indian Ocean thus dictating a need to utilize this ocean circulation model. In the background information provided, you will read about this incident and use the information as a resource for completing the next several questions that follow. An important aspect of the ocean circulation model described in the information is that it uses data from "drifters." Based upon the details provided in the reading, what is a drifter? A drifter is a buoyant object influenced by ocean currents rather than direct winds.
14. The search for evidence for MH370 constituted the largest search operation in history as the search area covered 4.5 million square kilometers (1.7 million square miles) of ocean surface, an area equivalent to about ____
half or 50%
___ of the area of the continental United States. The primary search area was determined based upon an "arc" or the potential flight path the plane was on when it disappeared. This potential flight path is determined by what is called a ____
handshake
____, which is the automatic communication between a plane and a satellite.
15. The following image shows an example of a drifter model produced for the MH370 search efforts. The various symbols and colors are explained in the caption provided below. Based upon this model, which areas on the map show predicted flow paths where debris might be found. Mark only those answers that apply. Indian Ocean, Pacific Ocean, Arabian Sea, Red Sea, Persian Gulf, Bay of Bengal 16. Beginning in July 2015, and for several years after, debris confirmed to be from Flight MH370 has been discovered in several locations including Reunion Island, Mauritius Island, Tanzania, and Mozambique (if you do not know where these places are located, look them up). Based upon this information, which color flow path from the drifter model shown above best matches the locations of the confirmed debris? Blue
17. Based upon your understanding of surface ocean circulation from Part I of this lab activity, which surface current is most likely responsible for carrying the debris? South Equatorial Current