A Quasi-Global Analysis of Tropospheric Water Vapor Content from TIROS IV Radiation Data

Abstract

Coordinated measurements of the earth's radiation to space within the 6.3-μ band of water vapor and the 8–13 μ atmospheric window were made over a five month period from February to June 1962 from the TIROS IV meteorological satellite. These measurements were analyzed to infer the spatial and temporal variations, on a nearly global (hereinafter called “quasi-global”) scale, of the following three quantities: 1) the mean relative humidity of the upper troposphere, 2) the mean effective temperature of the cloud top, land, or ocean surfaces, and 3) in conjunction with radiosonde temperature data, the water vapor mass above the 500-mb level. The results show major regions of high moisture content over South America, Central Africa, and the western Pacific Ocean near the intertropical convergence zone, plus several less prominent moist regions near the polar frontal zones in both hemispheres. The subtropical highs of both hemispheres are regions of low moisture content, as would be expected from the general circulation pattern in the troposphere. At equatorial latitudes the average surface temperatures exhibit a persistent minimum along a narrow band identified with clouds in the intertropical convergence zone. Elsewhere the magnitudes and patterns of the mean surface temperatures are associated with semi-permanent climatic regions, as well as with synoptic-scale weather features along storm tracks in middle latitudes, especially during winter in each hemisphere. The distribution pattern of water vapor mass above 500 mb strongly follows the 500-mb temperature field. Near the equator 0.3–0.4 gm cm−2 of precipitable water vapor are found, while in middle latitudes on the average only 0.02–0.04 gm cm−2 are present in the upper troposphere. An as yet unresolved question of fundamental importance remains concerning the interpretation of the data acquired over high, cold clouds. The validation of the method at these upper levels by means of conventional radiosonde measurements has not been possible because the radiosonde moisture errors are particularly prevalent in the upper troposphere. A resolution of this question should be advanced when data of high spectral resolution over the 6.3-μ and 8–13 μ regions of the spectrum become available from spectrometers scheduled to fly in the near future in the Nimbus meteorological satellite series.