Glossary of Meteorological Terms (E)

E

EBCDIC

Extended Binary Coded Decimal Interchange Code. A standard code used to represent data using 8 bits per character.

Ebert ion-counter

An ion counter of the aspiration condenser type, used for the measurement of the concentration and mobility of small ions in the atmosphere.

Eddy velocity

Difference between the instantaneous wind velocity at a point and the mean wind velocity taken over a given time interval. Also called fluctuation velocity.

Effective snow melt

That part of snow melt that reaches stream channels as runoff.

Effective terrestrial radiation

The difference between the outgoing infrared terrestrial radiation of the earth’s surface and the downcoming infrared counterradiation from the atmosphere.

Electrical hygrometer

A hygrometer which uses a transducing element whose electrical properties are a function of atmospheric water vapor content. The humidity strip and carbon-film hygrometer element are examples of such a transducer.

Electrical thermometer

A thermometer which uses a transducing element whose element properties are a function of its thermal state. Common meteorological examples of such thermometers are the resistance thermometer and the thermoelectric thermometer.

Electrolytic strip

Same as humidity strip.

Electrometer

An instrument for measuring differences of electric potential.

Electronic theodolite

See radar theodolite, radio direction-finder.

Electroscope

A general name for instruments which detect the presence of (but do not necessarily measure) small electrical charges by electrostatic means. Compare to electrometer.

Emanometer

An instrument for the measurement of the radon content of the atmosphere.

Eolian

Same as Aeolian.

Eppley pyrheliometer

A pyrheliometer of the thermoelectric type. Radiation is allowed to fall on two concentric silver rings, the outer covered with magnesium oxide and the inner covered with lamp black. A system of thermocouples (thermopile) is used to measure the temperature difference between the rings. Attachments are provided so that measurements of direct and diffuse solar radiation may be obtained.

EPROM

Erasable Programmable Read Only Memory. Programmable read-only memory which can be erased, usually by ultraviolet light, and re-programmed.

Error

The difference between the measured value and the true value. See instrument error, observational error, random error, standard error, systematic error. See also accuracy, accuracy rating, measured accuracy.

Error distribution

The probability distribution of random errors, typically a normal distribution with a zero mean.

Evaporation

The process by which a liquid is transformed to a vapor. The opposite of condensation.

Evaporation gauge

General name for an instrument which measures the evaporation rate of water into the atmosphere. Same as atmometer.

Evaporation hook gauge

See hook gauge.

Evaporation opportunity

The ratio of the actual amount of water evaporated into the atmosphere to the evaporative power. Also called relative evaporation.

Evaporation pan

A type of atmometer. It is a pan used in the measurement of the evaporation of water into the atmosphere. The NWS Class A pan is a cylindrical container 48 inches in diameter and 10 inches deep.

Evaporation pan coefficient

The ratio of the amount of evaporation from a large body of water to that measured in an evaporation pan. The coefficient varies seasonally, as well as from region to region.

Evaporation rate

The volume of liquid water evaporated per unit area in unit time, usually measured as the depth of liquid water lost per unit time from the whole area.

Evaporative power (or capacity)

A measure of the degree to which the weather or climate of a region is favorable to the process of evaporation. Usually considered to be the rate of evaporation, under existing atmospheric conditions, from a surface of water which is chemically pure and has the temperature of the lowest layer of the atmosphere.

Evaporimeter

Same as atmometer.

Evaporograph

Instrument which measures and records the amount of evaporation over time.

Evapotranspiration (ET)

The combined processes by which water is transferred from the earth’s surface to the atmosphere: evaporation of liquid or solid water plus transpiration from plants.

Evapotranspirometer

A type of lysimeter that measures the rate of evapotranspiration. It consists of a vegetation soil tank so designed that all water added to the tank and all water left after evapotranspiration can be measured.

Extinction

The attenuation of light.