Anticyclones

Question 1

Define Anticyclone (high)

Answer 1

A region of relatively high pressure, with winds circulating around the point with the highest pressure anticlockwise in the Southern Hemisphere.

Question 2

Features of an Anticyclone (5)

Answer 2

1. Divergence at the SFC
2. Air subsides from above (creating high pressure at SFC)
3. Anticlockwise winds in SH
4. Surrounded by at least one more or less circular isobar.
5. associated with light winds and warm temps

Question 3

What are the two types of anticyclone?

Answer 3

1. Warm

2. Cold

Question 4

Give an example of a warm anticyclone

Discuss how this works

Answer 4

• Sub tropical highs
  1. General circulation causes air to rise at equator
  2. This moves South in the high troposphere, cooling and converging - this causes the air to sink to the SFC (convergence occurs faster than outfow @ SFC)
  3. As dry air from aloft sinks, it warms at DALR = warm
  4. This results in high pressure system created at SFC (generally around 30deg South.

Question 5

General path for warm anticyclones

Answer 5

Migrate N in winter, and S in summer

Question 6

How are warm anticyclones intensified

Answer 6

• Increased absolute vorticity above developing high (creates more convergence within jetstream over the high, downward motion is enhanced = intensified high).

Question 7

WX conditions associated with warm anticyclones (4)

Answer 7

1. East of AC: Southerly wind creates slightly unstable conditions = partial cloud/Tcu, light showers (heavier the further east, weaker the further west in zone)
2. Clear skies in centre/North of AC
3. West of AC: ‘dirty’ side, Northerly being cooled from the SFC upward, and aersols create ‘gloom’, lots of Stratocumulus.
4. NW of AC: poor WX.

Question 8

Type/height of inversion found in warm anticyclones

Answer 8

Usually a Subsidence (temp) inversion b/t 3000 - 8000ft

Question 9

Discuss the formation of a cold anticyclone

Give an example overseas and in NZ

Answer 9

1. Air in contact with SFC cools via conduction and becomes more dense.
2. SFC pressure increases as a result, the anticyclone is formed.
   E.g. (usually develop in winter)
   - Siberian High
   - Central Otago in NZ

Question 10

What is the max depth of a cold anticyclone

Where is the temp inversion located?

Answer 10

• 3000 to 5000ft max

- 3000ft

Question 11

What are the (7) hazards associated with Anticyclones

Answer 11

1. Convective Showers (on exposed coast to E of high)
2. Extensive low cloud (100 - 500ft)
3. Poor Vis due to Drizzle on W of High
4. High winds and turb on fringes of High
5. Haze due to trapped aerosols beneath inversions
6. Fog due to radiation cooling under clear skies in centre of High.
7. Summertime TS due increasing divergence aloft and not enough SFC heating to overcome subsidence inversion. Sea breezes can assist.