Lecture 12: Tropical Cyclones (Characteristics (temporal distribution…
Lecture 12: Tropical Cyclones
temporal distribution based on movement of ITCZ/summer (in NH, June-Nov, SH, Nov-Apr)
: centre, ranges from 30-50km. precip ceases, wind subsides. low pressure (<950mb), cloudless, v. warm as air gradually descends & heats by compression.
: 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).
: bands of clouds w/ heavy rain (caused by intense condensation) & strong winds.
: 20km/h. wind & rain intensity increases, calm (around an hour or more), storm continues.
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.
seawater at least 26-27C in upper 60m of ocean.
unstable, warm, humid air
Coriolis effect to spin the system
@ 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.
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.
CF (rising air rotates anticlockwise in NH, clockwise in SH). rotation of earth causes rising columns to twist. weak @ equator.
move over ocean H2Os that X supply warm, moist tropical (30N, S) air, temperate areas
move onto land
reach a location where large scale flow aloft is unfavourable
usually lasts 1-4 weeks & diminish in intensity when