updrafts and downdrafts

ascents and subsidence. The term wind is applied only to horizontal movement.

Direction of movement

(1) Pressure

(2) Coriolis’s effect

(3) Frictional effect

Low-pressure centers are called cyclones, and the associated wind movement is said to be cyclonic.

Low pressure is associated with air rising. With air rising, condensation may occur and result in precipitation.

A high pressure is known as an anticyclone, and the associated wind movement is said to be anticyclonic.

A high pressure is associated with air descending, so normally with clear sky.

Hedley cell.

Farrel cell

polar cell.

ITCZ

Hurricanes are tropical cyclones with winds that exceed 64 knots (74 mi/hr) and circulate counter-clockwise about their centers in the Northern Hemisphere (clockwise in the Southern Hemisphere).

Before a hurricane develops, several requirements should be met:

(a)warm oceans in the tropics with temperatures in excess of 26.5 C (or 81 F).

(b)Warm water at the sea must be quite thick;

(c)Related to having warm ocean water, high relative humidities in the lower and middle

troposphere are also required for hurricane development.

(d)At least a few degrees north or south of the equator.

(e)weak wind shear

(f)preexisting disturbance

Tropical Depression

Tropical Storms

Hurricane

Category Central Pressure (millibars) Winds (mph) storm surge (m) Damage

1 >979 74-95 1.2-2.5 minimal

2 965-979 96-110 1.6-2.4 Moderate

3 945-964 111-130 2.5-3.6 Extensive

4 920-944 131-155 3.7-5.4 Extreme

5 < 920 >250 > 5.4 Catastropic

(1) storm surge

(2). Wind

(3). Rainfall