Atmospheric layer throughout which there is no change of temperature with height, i.e. a zero lapse rate.

Apparatus designed to measure the amount of precipitation falling in the form of snow. The device determines the weight of the snow or the volume of water after the snow melts.

Same as evaporative power.

Psychrometer to which a small chain or rotary handle is attached so that the observer can rotate the instrument rapidly to properly ventilate the thermometer bulbs.

Moisture contained in the soil above the water table, including water vapor which is present in the soil pores. In some cases this term refers strictly to the humidity contained in the root zone of plants.

Amount of water, expressed as a depth or as a mass, which would be obtained if all the water vapor in a specified column of the atmosphere were condensed and precipitated.

A sudden, significant increase in station pressure.

Instrument used to measure the amount of water evaporated from the soil surface during a given time interval.

Snow gauge composed of a metal cylinder, closed at one end, used to obtain a sample of snow from which the water is measured after melting.

Operation mode of a communication circuit in which one end can only transmit and the other end can only receive.

The processing of the form or mode of a signal so as to make it intelligible to, or compatible with, a given device.

Contraction for pilot balloon observation.

Radiation with wavelengths less than 4 microns.

An aneroid barometer with a scale graduated in altitude instead of pressure units.

An instrument for measuring differences in electric potential.

A large plastic constant-level balloon for duration flying at very high altitudes.

Meteorological information issued by a watch office concerning the occurrence or forecast of weather phenomena which may affect the safety of aircraft operations.

An element that can control current without moving parts, heated filaments, or vacuum gaps.

The amount of precipitation falling in one day, or other specified period, that is likely to be equalled or exceeded in any given place only once in a century. That is, a precipitation amount that has a return period of 100 years.

The amount of moisture which, if available, would be removed from a given land area by evapotranspiration. Expressed in units of water depth.