Clouds, Cloud Formation, and Stability(PPT-42)文档.pptVIP

Unstable Atmosphere Buoyant parcels are accelerated upward As they rise and cool, they are still warmer than the environment since the environment is cooling faster than the adiabatic lapse rate Larger instabilities lead to larger updrafts Large updrafts lead to the formation of cumulonimbus clouds and thunderstorms * Examples Unstable Unstable * Lifting a Parcel * Sources of Lift 4 ways to lift a parcel to the LCL Frontal Boundary Orographic Convergence Convection * CAPE CAPE = Convective Available Potential Energy CAPE is the energy available to a rising parcel to accelerate it On a Skew-T, CAPE is proportional to the area between the parcel’s temperature and the environment’s when the parcel is warmer CAPE gives an upper limit on how high updraft speeds can get in a severe storm High values of CAPE are associated with the possibility of strong convection * CAPE * CIN CIN = Convective INhibition This is the energy that must be overcome in order to lift a parcel to its LFC On a Skew-T, CIN is proportional to the area between the parcel’s temperature and the environment’s when the parcel is colder Large values of CIN will prevent the formation of storms, but often the presence of some CIN can add strength to a storm if this energy is overcome * CAPE and CIN * More Uses for Skew-T’s Finding cloud levels Forecasting precipitation type * More Uses for Skew-T’s Finding cloud levels – useful for aviation Clouds are likely present at three layers on this diagram. Can you find them? * More Uses for Skew-T’s Forecasting precipitation type The 00C isotherm in this skew-T shows that the precipitation will fall through a layer which is above freezing, thus implying that freezing rain is possible * Clouds, Cloud Formation, and Stability Lab 6 October 12, 2009 * Condensation Water vapor does not readily condense on its own Water has high surface tension Needs unreasonably high relative humidities or very cold temperatures (~-40oC) Cloud condensation nuclei are needed