Further study on internal variability and the Monsoon Flashcards Preview

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What is the walker circulation?

A latitudinal convective cell in the equatorial Pacific, where there is low pressure and rising air in the west Pacific and descending air and high pressure in the east Pacific.
This is associated with an easterly equatorial surface current, upwelling off the coast of S America, and
reliable Trade winds.


What happens in a normal year of the walker circulation?

sees pressure in Tahiti (mid Pacific) relatively high compared with Darwin, Australia, and the western Pacific experiencing convergence and convective rain.


What happens in an el nino of the walker circulation?

Pressure low in Tahiti; the low
pressure centre has shifted east and causes more rain over the central Pacific.
West Pacific dry and high pressure.
Warm sea-surface temperature
anomalies in the eastern Pacific correlate with the pressure shifts.
Upwelling is suppressed, warm water lies at the surface, the Trades weaken, and there is instability.
Storms and unusually high rainfall result, affecting the Pacific coasts of the Americas.


What happens in a la nina of the walker circulation?

Very cold water and dry conditions in the eastern
Pacific and particularly wet conditions in the west Pacific – an exaggerated ‘normal’ mode.


What is the North Atlantic Oscillation?

Describes the winter conditions of two pressure centres: the Iceland Low and the Azores High.


What is the NAO index?

Measures the difference between low pressure in the North over Iceland and high pressure in the South over Azores.


(NAO index) A positive index allows...

Mild westerly winds to reach NW Europe producing mild wet winters in the UK.


(NAO index) Negative index blocks...

Westerly winds producing cold snowy winters in the UK.


The NAO accounts for much of the warming, where?

North Hemisphere


Where are the main jet streams?

Middle and subtropical latitudes.


What is the temperate jet stream?

flows from west to east. It also travels in a wavy manner, going north and south.


What is the polar jet stream?

In winter, two branches of the polar jet stream are anchored by the Himalayas - one going
to the north and the other to the south of the mountains.


What does the southern part of the polar jet stream cause?

Subsidence in the atmosphere in the northwestern part of India and as a result, a centre of high pressure develops there with
out-flowing winds going southerly.
From NW India the High sends winds that form the northeast monsoon.