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 See instrument error, observational error, random error, standard error, systematic error.      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 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 An instrument which 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.