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