ANALYSIS OF FRONTOGENESIS AND FRONTOLYSIS BY MEANS OF Q-VECTOR DIAGNOSTICS COMBINED WITH SATELLITE IMAGES

The correlation between the normal component of the Q-vector(Q(n)) and the pixel values in IR satellite images has been investigated on a si x-months data set. The average linear correlation coefficients are neg ative in all three selected isobaric levels, but not of significant ma gnitude (the correlation is best for the 850 hPa level, with a correla tion coefficient of about 0.3), indicating an only slight tendency for negative values of Q(n) to be associated with high IR grey shade valu es or, in other words, with cold cloud tops. It is explained why a bet ter correlation should be expected for frontal cases, followed by an e valuation of 14 IR images containing cloudiness of cold fronts that oc curred in February 1995. The correspondence between Q(n) at the 850 hP a level and IR pixel values in those cases is compared to the statisti cs for the whole month of February 1995, including also nonfrontal cas es. The more pronounced connection is found for frontal cases, as expe cted. Finally, examples of frontogenesis and frontolysis demonstrate t he possibility of using the prognostic quantity Q(n) in combination wi th IR satellite imagery as a tool for operational nowcasting and/or fo recasting of the development or decay of frontal cloudiness.