Development of air mass climatology analysis for the determination of characteristic marine atmospheres. Part I: North Atlantic

A method of determining characteristic marine atmospheres was developed based on analysis of air mass types and occurrences. A 10-year set of radiosonde and surface observations collected over the North Atlantic Ocean from a combination of land-based stations, oceanographic buoys, and weather ships, was obtained from the archives of meteorological agencies from 6 different countries. Through a mixture of man-machine objective analysis of upper air measurements of air temperature at the 85, 70, and 50 kPa levels, a total of 16 typical air mass categories could be identified. They are cA, cA/cmA, cA/cmA/mA, cA:cmA, cmA, cmA/mA, cmA/mA/mP, cmA:mA, mA, mA/mP, mA/mP/mT, mP, mP/mT, mT(f), mT, and mT(d). Analysis of the data showed that regions of near air mass homogeneity can be identified. The frequency of occurrence of single air mass categories coincided with their source regions, and the categories with combinations of air masses coincided with well known storm tracks. Vertical profiles of characteristic categories were then developed and applied to the modelling of evaporative duct heights and calculations of precipitable water. These test results showed strong dependence of derived parameters on the defining air mass category and compared well with data from other independent studies. The value of this type of analysis has been demonstrated and results have been produced which can be used in downscaling studies whereby changes in the occurrence of regional weather elements may be found that are associated with variations in large-scale air mass features.