Name:__________________                                                 

LAB 3

 

Ocean Circulation and El Niño

 

OUTLINE:

 

1) Identify key surface currents (e.g., Gulf Stream, etc.)
2) Understand Ekman spiral and ocean upwelling
3) Understand normal and abnormal sea surface temperatures and El Nino/La Nina
4) Know climatic consequences of El Nino/La Nina.

 

NOTE:  We will illustrate several concepts using visuals in class.

 

You may also wish to see the following movies:

 

Ocean Upwelling Movie:
http://svs.gsfc.nasa.gov/vis/a010000/a010000/a010019/
 
El Nino Movie:
http://www.atmos.umd.edu/~owen/CHPI/MOV-MPEG/enso82aE.html

 

From the information given during the lab period, you will be able to answer most of these questions. Additional help can be found at www.elnino.noaa.gov and in Chapter 16 of your textbook (see p. 364-368, 379-381).

 

Please write answers on your own sheet of paper.

 

1.      Where does the cold water in Ecuador come from?

It upwells from the deep ocean

2.      Which way are the surface winds blowing off the West coast of South America?

They are blowing from the Northeast and Southeast towards the equator

3.      How does sea surface water temperature affect the distribution of high pressure and low pressure?

Warm water creates rising air and low pressure.  Stormy skies

Cold water creates sinking air and high pressure.  Clear skies

4.      If freshwater comprises only about 3% of Earths Water, how can it have such a profound effect on sea surface temperatures?

Fresh water floats on salt water and does not mix instantaneously.

5.      What is El Nino? What is La Nina?

El Nino is a Disruption in the coupled circulation of the Oceans and the atmosphere characterized by the following:

  1. Decrease in the strength of the trade winds around South America.
  2. A reduction or even cecession of upwelling on the west coast of the Americas
  3. Increase in sea surface temperatures over the Equtorial east pacific.
  4. Increased precipitation over Western South America
  5. Droughts in S.E. Asia and Australia.

La Nina is an enhancement in East Pacific Upwelling and trade wind circulation often following an El Nino event leading to abnormally cold sea surface temperatures across the eastern equatorial pacific.  The effects toen

 

6.      Describe how the Pacific Ocean surface temperatures vary for El Nino versus normal conditions.

Warmer in the East Pacific by as much a 9 Degrees C.  Slightly cooler

7.      How does the weakening of the Trade Winds affect coastal upwelling?

Water is no longer being pushed away from the continent’s edge

8.      When were the two strongest El Nino events? (for past 20 years)

1997-1998, and 1982-1984

9.      Describe how Pacific wind patterns change from normal to El Nino years. (Draw diagram showing normal wind pattern and another diagram showing El Nino wind patter)

I will be looking for some evidence of weakening of trade winds in the central equatorial pacific.   Also it would be good to show a shifting of the low pressure and rising air further east, and a reorganization of the Walker circulation.

 

 

10.  How has El Nino affected weather patterns in

a)      Australia?  Drier

b)      Indonesia? Drier

c)      North America?  Wetter in South,  Warmer in NE and NW

11.  Give three examples of socio-economic impacts of El Nino.

Floods and property damage (Americas)

Droughts and crop damage (Indonesia)

Fires in Australia (Australia)

Warmer beach water (Americas)

 

12.  How are El Nino events detected? What is ENSO?

El nino Events are detected with an array of buoys in the Pacific ocean capable of sensing the temperature down to a depth of 600 m.  The onset of an El nino event is indicated by a rise in sea surface temperatures in the Central and Eastern Equatorial Pacific.

El Nino Southern Oscillation:  This term describes the full range and cyclicity of climate events in the tropical pacific.

13.  Why does sea surface temperature distribution affect weather so profoundly?

Hint:  Where does air rise?  Where does it descend?

The air is more likely to rise convectively over warm water.  Rising Air is associated with precipitation.  Conversely Air is more likely to descend over cold water.  Descending air tends to bring about clear dry weather.

 

Bonus Question:

Does El Nino affect storm development? If so, where and what are the effects?

What effect does a warm pool of water off the West Coast of Mexico have on Texas weather?  Is this a result of the trade winds or the Westerlies?  (Hint:  winter)  (Coriolis force?)

Texas is located at the boundary between the temperate westerlies and the tropical Trade winds.  During an El Nino event there is often in increase in the presence of warm water south of Baja.  When the westelies are stronger, this region is often upwind from us.  Much of our El Nino precipitation is associated with this weather system.  (Of course Texas is in a unique position to experience a wide range of weather.)