Measurements of the foreign-broadened continuum of water vapor in the 6.3 (mu)m band at -30 °C

The foreign-broadened continuum of water vapor in the v2 band (5-7.7 (mu)m, 1300-2000 cm^-1) is important for satellite-based retrievals of water vapor in the upper troposphere, where temperatures are below -25 °C. Continuum coefficients have previously been measured mostly at or above +23 °C. We present continuum coefficients in the v2 band retrieved from measurements made in Antarctica at temperatures near -30 °C: atmospheric transmission at South Pole Station and atmospheric emission at Dome C. The continuum coefficients derived from these measurements are generally in agreement with the widely used Mlawer, TobinClough, Kneizys, Davies continuum. Differences are at most 30%, corresponding to a 6% relative error in retrieved upper-tropospheric humidity.