Parameterization of clear sky effective emissivity under surface-based temperature inversion at Dome C and South Pole, Antarctica.

For most parts of the year the Antarctic Plateau has a surface temperature inversion with strength c. 20 K. Under such conditions the warmer air at the top of the inversion layer contributes more to the clear sky atmospheric longwave radiation at surface level than does the colder air near the ground. Hence, it is more appropriate to relate longwave irradiance (LWI) to the top of the inversion layer temperature (T_m) than to the ground level temperature (T_g ). Analysis of radio soundings carried out at Dome C and South Pole during 2006-08 shows that the temperature at 400 m above the surface (T_400 ) is a good proxy for T_m and is linearly related to T_g with correlation coefficients greater than 0.8. During summer, radiosonde measurements show almost isothermal conditions, hence T 400 still remains a good proxy for the lower troposphere maximum temperature. A methodology is presented to parameterize the clear sky effective emissivity in terms of the troposphere maximum temperature, using ground temperature measurements. The predicted LWI values for both sites are comparable with those obtained using radiative transfer models, while for Dome C the bias of 0.8 W m^-2 and the root mean square (RMS) of 6.2 W m^-2 are lower than those calculated with previously published parametric equations.