WATER-VAPOR CONTINUUM ABSORPTION IN MIDLATITUDES - AIRCRAFT MEASUREMENTS AND MODEL COMPARISONS

Recently reported measurements by the Meteorological Research Flight C -130 aircraft over the tropical Atlantic have shown that existing mode ls of infrared water vapour continuum absorption underestimate its mag nitude by up to 30%. This paper presents additional results from more recent measurements made close to the south-west approaches of the Bri tish Isles and over the eastern Mediterranean Sea. These measurements are compared with two models: GENLN2, a line-by-line model, and the wi dely used band model LOWTRAN7. The measured radiances suggest a consis tent underestimate in both models of the water vapour continuum absorp tion. The modified parametrization for the water vapour continuum abso rption, inferred from the tropical results, was also used here to chec k its validity for lower water vapour amounts and lower temperatures. As with the tropical results, increasing the self-broadening coefficie nt by a constant factor, or increasing the temperature dependence, imp roves the agreement between the measurements and the model predictions .