Radiometersonde Observations of Infrared Flux Emissivity of Water Vapor

Abstract

Employing 211 nocturnal radiometersonde observations of upward upward infrared flux, air temperature, and relative humidity in the atmosphere, the water vapor flux emissivity as a function of optical depth has been determined. The principal results of this study are: (a) A new curve of water vapor flux emissivity, obtained from “in situ” atmospheric measurements, is compared with previous work. The emissivities are most reliable for optical depths typical of the troposphere as most of the data were obtained in those levels. One low stratospheric ascent made possible the measurement of a few values at low pressure and very shallow optical depth. (b) When calculating infrared radiative flux in the atmosphere from temperature, humidity and pressure data, the accuracy will be improved if a pressure-reduced optical depth of (p/p₀)^.85 is used. (c) There is evidence will be improved if a presure-reduced optical depth ratio will not serve over a wide range of optical depths, including both the stratosphere and troposphere But no further work would be profitable until more statospheric ascents at very shallow optical depths are available.