Rossby Waves. Tropopause variation with latitude.
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Transcript of Rossby Waves. Tropopause variation with latitude.
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