Rob Wilson - lecture 3

Question 1

ENSO

Answer 1

El Nino Southern Oscillation

Question 2

who made primary observations of ENSO, when?

Answer 2

1877 - failure of indian monsoon- Gilber Walker- noted:

1. a pressure oscillation between northern Australia and the Central Pacific
2. He termed this the “Southern Oscillation”
3. This pressure gradient varies over time – pseudo-cyclic

Question 3

what is ENSO?

Answer 3

ENSO is a “coupled” phenomenon: atmosphere drives the ocean and the ocean drives the atmosphere

An irregularly periodical variation in winds and sea surface temperatures over the tropical eastern Pacific Ocean, affecting much of the tropics and subtropics

Question 4

what are the two phases of ENSO?

Answer 4

(WARM) El Niño – last 12-18 months

(COLD) La Niña – last from 1-3 years

Question 5

La nina

Answer 5

Cool Phase – “norm” state

• Strong easterly winds induce upwelling of cold water in the equatorial eastern Pacific
  Shallow oceanic thermocline in the east Pacific (due to upwelling)
  Warm SSTs confined to western Pacific with a deep thermocline
  Low pressure and convection in west Pacific
  High pressure and subsidence (clear air) in east Pacific

Question 6

El Nino

Answer 6

warm phase

Weaker easterly winds result in less upwelling of cold water
Warm SSTs “spread” to east Pacific (also solar heating not offset by upwelling)
Increase in the east Pacific thermocline
Low pressure and convection shifts to the east Pacific
High pressure and subsidence shifts to the west Pacific