Rossby Waves

Tropopause variation with latitude

Jet stream – wind field and temperatures

Isotachs and isotherms

Mid-latitude Cyclones

Formation revisited

Polar front

Upper atmosphere pressure and winds

Current circulation model

Tropical Climate

Monsoon

Asian monsoon - 1Winter (northern hemisphere)

Cold air over Asia creates high pressure.

Dry air drawn southwards from Himalaya

Asian monsoon - 2Summer (northern hemisphere)Land heats to give low pressure over Asia.Moist air drawn northwards from equatorial oceans

Hurricane Mitch

Distribution of Hurricanes

Hurricane DamageScale

NumberCategory

Central Pressure

mbinches

Wind Speedsmi/hrknots

Storm Surgefeet

meters

ObservedDamage

1 >=980 >=28.94

74-95 64-82

4-5 ~1.5

some damage to trees, shrubbery, and unanchored mobile homes

2 965-979 28.50-28.91

96-110 83-95

6-8 ~2.0-2.5

major damage to mobile homes; damage buildings' roofs, and blow trees down

3 945-964 27.91-28.47

111-130 96-113

9-12 ~2.5-4.0

destroy mobile homes; blow down large trees; damage small buildings

4 920-944 27.17-27.88

131-155 114-135

13-18 ~4.0-5.5

completely destroy mobile homes; lower floors of structures near shore are susceptible to flooding

5 <"920" <"27.17"

>"155" >"135"

>"18" >"5.5"

extensive damage to homes and industrial buildings; blow away small buildings; lower floors of structures within 500 meters of shore and less than 4.5 m (15 ft) above sea level are damaged

Hurricane Eye Wall

Cross-section of hurricane

Spin up process• Air converges from radius of

order 1000 km• Air that is stationary w.r.t. the

earth is travelling eastwards w.r.t. a frame of reference fixed in space at a speed

• Hence air drawn from N travels more slowly and that from S faster than the centre of the hurricane, leading to rotation.

convergence

rising air,condensation

release oflatent heat

surface low pressure

cosv R

Rθ

cosv R

Ω

cosR

relative to space

Conserving angular momentum about eye mvr is constant so: 0 0

2102

20

sin

2

eye eye

eye eye

eyeeye

mv r m r r

v r fr

rv f

r

relative to earth

0d d sin sinv R r

dv

0 dr R