Lecture 12: Tropical Cyclones (Conditions (CF (rising air rotates…
Lecture 12: Tropical Cyclones
usually lasts 1-4 weeks & diminish in intensity when
reach a location where large scale flow aloft is unfavourable
move onto land
move over ocean H2Os that X supply warm, moist tropical (30N, S) air, temperate areas
CF (rising air rotates anticlockwise in NH, clockwise in SH). rotation of earth causes rising columns to twist. weak @ equator.
surrounding air from HerP areas rushes inwards in spiralling manner to replace rising warm air. easterly trade winds that blow during that period converge towards LP cells.
@ low latitudes, sufficient heating to cause intense instability & high lvls of evap, esp. in summer. low pressure cells develop as unstable air rises. discharges H2O(g) thru condensation, releasing latent heat, which causes air to remain even warmer, fuelling greater instability. force air up even higher. condenses to form clouds.
Coriolis effect to spin the system
unstable, warm, humid air
seawater at least 26-27C in upper 60m of ocean.
Saffir-Simpson Scale ranks the relative intensities of tropical cyclones (Cat 1-5) based on central pressure of storm, mean wind speed & height of accompanying storm surge.
: 20km/h. wind & rain intensity increases, calm (around an hour or more), storm continues.
: bands of clouds w/ heavy rain (caused by intense condensation) & strong winds.
: rapidly rising hot air & violent winds. strong pressure grad. so winds spiral inwards towards eye wall quickly. as warm, moist surface air approaches core, rises in a ring of cumulonimbus towers (16km). greatest wind speeds, thickest clouds, heaviest rainfall (2500mm/hr).
: centre, ranges from 30-50km. precip ceases, wind subsides. low pressure (<950mb), cloudless, v. warm as air gradually descends & heats by compression.
temporal distribution based on movement of ITCZ/summer (in NH, June-Nov, SH, Nov-Apr)