Weather balloons measure atmospheric gradient, including ambient and adiabatic rates, important for meteorology. International standard lapse rates vary due to inversion layers. Dry adiabatic lapse rate (DAR) cools air packets as they rise, while saturated adiabatic gradient (SAR) varies with moisture. Stable atmospheres occur when ambient gradient is greater than DAR. Super-adiabatic gradient in southwestern US and lake-effect snow winds can cause storms.
Most people know that weather balloons take measurements of some kind. In those little boxes suspended from balloons, one of the measurements taken is the atmospheric gradient: the rate of decrease in temperature with increasing height. These small monitoring stations, each smaller than a shoebox, measure temperatures twice a day for two types of rates: ambient and adiabatic, the lapse rate. These rates are important in meteorology, which is the atmospheric science responsible for predicting weather changes, studying vertical stabilities, and monitoring cloud formation and behavior.
The rate of environmental decay is never fixed, but varies from time to time and from place to place. When measurements are taken at a specific place and time, the International Civil Aviation Organization (ICAO) can define an international standard lapse rate, giving readings that vary with identical heights, as inversion layers can cause an inverse increase in temperature with increasing heights. These ambient readings compared to dry or wet adiabatic rates can signal stability or instability that is important to be aware of, as dry air packets lack the lift of wet air packets.
A dry adiabatic lapse rate (DAR) is found in a packet of air that is sealed and has a fixed mass. Isolated from its surroundings, the pressures of a dry adiabatic air packet, both indoors and out, are usually matched, and the only way to change the temperature of the packet is to cause changes in these pressures. As a packet of air rises, it will encounter less external pressure from the increase in altitude and its temperature will cool. The cooling expansion rate of an air packet is known as the DAR. The cooling surge eventually reaches the dew point, when condensation can begin to form clouds. As a parcel of air descends, pressures build and the heat causes internal energies that form strong winds like the dry Santa Ana winds that occasionally come down to scorch Los Angeles, California for days on end.
The saturated adiabatic gradient (SAR) varies with the amount of moisture in the air. Increases in altitude cause the air packets in pockets of moist air to cool and expand more slowly as the condensation within them heats them internally. The release of heat during the formation of condensation is a factor in the development of thunderstorms. Air is stable when the ambient gradient is less than the SAR.
The thermodynamics of the atmosphere is expressed in dry and wet adiabatic forces within air particles and forms the basis for weather forecasting. Stable atmospheres occur when the ambient gradient is greater than the dry adiabatic rate. During periods of intense solar warming of the Earth’s surface, a super-adiabatic gradient in a thin layer across the surface can occur in the southwestern United States and is an unstable condition. Similarly, lake-effect snow winds moving across the surface of a lake create super-adiabatic surface layers that cause storms, when there is enough moisture in the air.
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