Meteorology

Part A ---- Theory

Lapse rate: the rate of decrease of an atmospheric variable* with height

*(variable being temperature, unless otherwise specified)

Environmental Lapse RateELR: the rate of decrease of temperature with altitude in the stationary atmosphere at a given time and location.

international standard atmosphere (ISA) with a temperature lapse rate of6.49 K(C)/1,000 mfrom sea level to 11km

Dry Adiabatic Lapse RateDALR: the rate of temperature decrease with height for aparcelof dry or unsaturated air rising under adiabatic* conditions.The rate of temperature decrease is9.8 C/km.

*(adiabatic: no heat transfer occurs into or out of the parcel) ~Air has lowthermal conductivity, and the bodies of air involved are very large, so transfer of heat by conductionis negligibly small.

Saturated Adiabatic Lapse RateSALR: the rate of temperature decrease with height for aparcelof moist or saturated air rising under adiabatic conditions.moist adiabatic lapse rate(MALR)A typical value is around5 C/km.The reason for the difference between the dry and moist adiabatic lapse rate values is thatlatent heatis released when water condenses, thus decreasing the rate of temperature drop as altitude increases.

Formation of Cloudshttp://www.atmosphere.mpg.de/enid/25p.html

Cumulonimbus Cloudis a towering verticalcloudthat is very tall, dense, and involved inthunderstormsand other inclementweather.

Dangers of CB Cloudcan produce heavyrain, flash flooding, as well asstraight-line windscontain severe convection currents, with very high, unpredictable winds, therefore extremely dangerous toaircraftsnow and ice conditions can develop in the colder upper portions of the cloudsforms mesocyclones, which can causehailand tornadoes

Mesocyclone: - first stage of tornado formation - strong changes of wind speed and/or direction with height (wind shear)

Wind shear (red) sets air spinning (green). The updraft (blue) 'tips' the spinning air upright. The updraft then starts rotating.

Hail: consists of balls or irregular lumps of ice, each of which is referred to as a hail stone.

Straight-line winds:are very strong winds that can produce damage, demonstrating a lack of a rotational damage pattern.

Wind Sheara difference inwindspeedanddirectionover a relatively short distance in theatmospherecommonly observed nearmicroburstsand downburstscaused bythunderstorms

Downbursta very localized column of sinking air, producing damaging divergent andstraight-line windsat the surface distinguishable fromtornadoes which generally have convergent damagetwo types: dry downbursts and wet downbursts three stages in their life cycle: the downburst, outburst, and cushion stages

Dry Downburst: When rain falls below cloud base or is mixed with dry air, it begins to evaporate and this evaporation process cools the air. The cool air descends and accelerates as it approaches the ground.Wet Downburst: Wet microbursts are downbursts accompanied by significant precipitation at the surface which are warmer than their environment. These downbursts rely more on the drag of precipitation for downward acceleration of parcels. Melting of ice, particularly hail, appears to play an important role in downburst formation especially in the lowest one kilometer above ground level.

THE END~Hao Fang