A pyrheliometer of the bimetallic type used to measure the intensity of direct solar radiation.

Companion to the wet-bulb thermometer in a psychrometer. Used to measure ambient air temperature.

Solar and terrestrial radiation directed downwards (towards the earth's surface); incoming radiation.

An instrument for measuring differences in electric potential.

The standard deviation (positive square-root of the variation) of the errors associated with physical measurements of an unknown quantity, or statistical estimates of an unknown parameter or of a random variable.

A rain gauge which automatically records the amount of precipitation collected, as a function of time.

A record obtained from a meteorograph. A chart in which meteorological variables are plotted against time.

A unit of pressure which directly expresses the force exerted by the atmosphere. Equal to 1000 dynes/cm2 or 100 pascals.

A white disk 12" or more in diameter which is lowered into the sea to estimate transparency of the water. The depths are noted at which it first disappears when lowered and reappears when raised.

An instrument consisting of a series of graduated cylinders possessing selective collection efficiencies. It is used for the measurement of quantities relating to the size distribution of cloud droplets.

The total of direct solar radiation and diffuse sky radiation received by a unit horizontal surface. Global radiation is measured by pyranometers.

The ratios, to the mean wind speed, of the average magnitudes of the component fluctuations of the wind along three mutually perpendicular axes.

An aneroid barograph designed to record atmospheric pressure variations of very small magnitude.

A hygrometer in which the rotation of the hygrometric element is a function of humidity.

The level at which ice crystals and snowflakes melt as they descend through the atmosphere.

The algebraic difference between the upper and lower limits of the measuring range of an instrument, i.e. a thermometer with a range of -35 to 50

Name given to the unit of pressure in the International System of Units (SI). Equal to 1 newton/meter2 or 0.01 millibar.

Liquid water at temperatures colder than freezing.

Rain gauge which registers precipitation that is too light to be registered by ordinary recording of the depth of water from precipitation. Same as ombrometer.

Frozen or partly frozen rain.