1. David Tedesco Physical Oceanography
La Niña
David Tedesco
Physical Oceanography

2. What is La Nina?
La Niña is characterized by unusually cold ocean temperatures in the Equatorial Pacific, compared to El Niño, which is characterized by unusually warm ocean temperatures in the Equatorial Pacific. (NOAA)
Counterpart of ENSO
“The Girl”

3. What is La Nina? Occurs on average every 3-5 years
Conditions last for about 9-12 months
Sea surface temps can drop to 7ͦ F below normal
Typically peaks during Northern Hemisphere winter

4. Intensification of Trade Winds

6. Walker Circulation
Normally brings east-west surface winds and west-east upper air winds
In La Nina years, this circulation intensifies
This pushes more warm water to West while upwelling cools East

7. Thermocline and Sea Slope:
In very strong La Niña episodes, the thermocline can actually come very close to the ocean surface for extended periods. This cooling represents a decreased depth of the oceanic mixed layer, and accompanies the appearance of nutrient- rich waters very close to the ocean surface. Thus, its existence is quite beneficial to marine life throughout the region. Accompanying these conditions, the sea level height is lower than normal over the eastern Pacific, resulting in an increased slope of the ocean surface across the basin (~60cm)

8. Effects Around the Globe:
U.S: Cold, Wet in Northwest, Warm and Dry in Southeast. Increased chance of Hurricanes in Atlantic
Asia: subtropical ridge shifts west -> more threat to cyclones
Africa: Wetter than average months for Southern Africa
South America: Extremely dry on west coast, Massive rainfall of Andes, which leads to catastrophic flooding of Bolivia

9. La Nina and Hurricanes Largely due to vertical shear wind profile
Less vertical shear → increased number of Atlantic storms
More intense storms

10. References http://www.pmel.noaa.gov/tao/elnino/la-nina-story.html