ANTICYCLONES

Question 1

Define an anticyclone
How does air move within a high?

Answer 1

A region of high pressure, winds circulate anti-clockwise (SH).
Divergence at the surface and air converges & subsides from above

Question 2

Draw the three main anticyclones in the general global circulation

Answer 2

met book pg 190

Question 3

How is the belt of sub-tropical anticyclones formed (30deg S)

Answer 3

Gen circulation is a poleward flow from the tropics in the high troposphere.
Air cools & converges, starts to descend as it goes south, sinks to SFC at 25-30deg south = high pressure at the surface.
mean position of the belt shifts a little with the seasons.

Question 4

What else can contribute to the development of a surface high?
What can form as a result of this?

Answer 4

Increase in absolute vorticity which increases convergence aloft and within the jetstream = enhances downward motion & therefore high pressure at the surface.

Subsidence inversion (high level air is usually dry, descends & warm at DALR. vs. cooler surface air temps over oceans = layer of cumulus 3000-8000ft)

Question 5

WX associated with far eastern fringe of a high?

Answer 5

Southerly wind component = unstable condxs.
Partly cloudy, light SHRA & TCU (heavier in east, lighter in west)

Question 6

WX associated with Eastern 1/2 of a high?

Answer 6

Fine weather, light winds

Question 7

WX associated with Western1/2 of a high?

Answer 7

“dirty” section of a high, inversions tend to be stronger & northerly wind tends to bring more moisture to the flow.
Area includes trapped aerosols (esp sea salt) which results in anticyclonic gloom. (StratoCu)

Question 8

WX associated with far NW fringe of a high?

Answer 8

Poor wx, especially when this NE flow brings very moist air onto exposed coasts.

Question 9

How do cold anticyclones form?
Where would you find a temp inversion?

Answer 9

Ground cools considerably > air above cools & becomes denser > SFC pressure rises = Anticyclone
e.g. Antarctica where the ice reflects majority of incoming solar radiation.

Shallow systems, inversion at ~3000ft

Question 10

WX associated with cold anticyclone?

Answer 10

Over land: fine wx, potential for fog overnight. Haze trapped below inversion = reduced vis.

Near coast/at sea: May be Sc or haze under inversion due moisture & aerosols supplied from the sea

Question 11

List the 6 hazards associated with Anticyclones

Answer 11

1. low cloud
2. fog (especially overnight)
3. drizzle
4. high winds
5. haze reducing horizon def (<10km)
6. summer TS

Question 12

Explain the high winds sometimes associated with a High?

Answer 12

Around fringes of a high the isobars can be spaced closer together in comparison to the centre.
Localised troughs of low pressure can increase strength also
Results in low level turb

Question 13

What must be overcome if summer TS are to occur?
How do sea breezes help?

Answer 13

The subsidence inversion.
Upper level divergence & surface warming need to be sufficient to “punch through” the inversion.
Development of sea breezes may enhance possibility of TS by carrying moisture inland