Precipitation from a cumuliform cloud. Characterized by the suddenness of beginning and ending, by the rapid change in intensity, and usually by a rapid change in the condition of the sky. The solid or liquid water particles are usually bigger than the co ...

A type of recording siphon barometer. The mechanically magnified motion of a float resting on the lower mercury surface is used to record atmospheric pressure on a rotating drum.

The change in barometric pressure within a specified period of time (typically 3 hours for meteorological observations).

One of several constant-pressure levels in the atmosphere for which a complete evaluation of data derived from upper air observations is required.

meter-An instrument for measuring the transmissivity of the atmosphere; a type of transmissometer. It consists of a constant- intensity collimated light source located at a suitable distance from a photoelectric cell. Variation in the turbidity of the atm ...

Downward scattered and reflected solar radiation, coming from the whole hemisphere with the exception of the solid angle of the sun's disc on a surface perpendicular to the axis of this cone.

Same as precipitation- effectiveness index.

An instrument used to measure changes in the level of the water in an evaporation pan. The gauge is normally placed in a Stillwell and adjusted so that the point of the hook just breaks the water surface. The change in water level is read on the attached ...

Same as ombrometer.

A photometer which measures the intensity of radiation as a function of the frequency (or wavelength) of the radiation.

A cylinder installed in a body of water or an evaporation pan to hold a sensor, such as a float to measure water level or a hook gage. The stillwell is constructed so that there is free movement of water in and out of it, and it therefore provides a repre ...

An atmometer which uses a filter paper disc as the evaporating element. The amount of water evaporated through the paper is read at the graduated tube reservoir.

A type of modulation in which the frequency of a continuous radio carrier wave is varied in accordance with the properties of a second (modulating) wave.

See photometer.

The upward force produced by the gas in a balloon. It is equal to the free lift plus the weight of the balloon and the attached equipment.

A measure of long-term precipitation effectiveness. The ratio of the normal annual rainfall to the normal annual evaporation.

The closeness of agreement among measurements of the same value of the same quantity where the individual measurements are made under different defined conditions, i.e. by different methods or with different measuring instruments.

Board that holds graph paper on which is plotted information obtained from a pilot-balloon observation.

A device, similar to a phytometer, for measuring transpiration. It consists of a small vessel containing water and sealed so that the only escape of moisture is by transpiration from a leaf, twig, or small plant with its cut end inserted in the water.

A type of electrical thermometer in which the thermal element is a substance whose electrical resistance varies with the temperature. Such thermometers can be made with very short time constants and are capable of highly accurate measurements.