DETERMINATION OF HUMIDITY AND TEMPERATURE-FLUCTUATIONS BASED ON MOZAIC DATA AND PARAMETRIZATION OF PERSISTENT CONTRAIL COVERAGE FOR GENERAL-CIRCULATION MODELS

Humidity and temperature fluctuations at pressure levels between 166 a nd 290 hPa on the grid scale of general circulation models for a regio n covered by the routes of airliners, mainly over the Atlantic, have b een determined by evaluation of the data obtained with almost 2000 fli ghts within the MOZAIC programme. It is found that the distributions o f the fluctuations cannot be modelled by Gaussian distributions, becau se large fluctuations appear with a relatively high frequency. Lorentz distributions were used for the analytical representation of the fluc tuation distributions. From these a joint probability distribution has been derived for simultaneous temperature and humidity fluctuations. This function together with the criteria for the formation and persist ence of contrails are used to derive the maximum possible fractional c overage of persistent contrails in a grid cell of a GCM. This can be e mployed in a statistical formulation of contrail appearance in a clima te model.