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 - 1
Winter (northern
hemisphere)
Cold air over Asia
creates high
pressure.
Dry air drawn
southwards from
Himalaya
Asian monsoon - 2
Summer (northern
hemisphere)
Land heats to give
low pressure over
Asia.
Moist air drawn
northwards from
equatorial oceans
Hurricane Mitch
Distribution of Hurricanes
Hurricane Damage
Scale
Number
Category
Central
Pressure
mb
inches
>=980
>=28.94
Wind
Speeds
mi/hr
knots
74-95
64-82
Storm
Surge
feet
meters
4-5
~1.5
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
1
Observed
Damage
some damage to trees, shrubbery, and unanchored mobile
homes
Hurricane
Eye Wall
Cross-section of hurricane
Spin up process
•
convergence
•
surface low
pressure
rising air,
condensation
•
release of
latent heat
Ω
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 v  R cos
Hence air drawn from N travels
more slowly and that from S faster
than the centre of the hurricane,
leading to rotation.
dv  Rd sin    r0  sin 
R cos
v  R cos  
θ
R
relative to space
r0  Rd
Conserving angular momentum
about eye mvr is constant so:
mveye reye  m r0  sin  r0
veye reye 
dv
relative to earth
veye
1
2
fr02
r02
 f
2reye