STRUCTURE OF A COLD FRONT NEAR THE CENTER OF AN EXTRATROPICAL DEPRESSION

Abstract

Hourly aerological soundings released at Bedford, Mass. in April 1960, together with all available conventional synoptic observations, are used for a detailed analysis of a cold front south of the center of a northeastward-moving depression. It is shown that in this case the dynamically important change from one air mass to another throughout the entire troposphere occurred several hours after the passage of a weak surface cold front. The major cooling over Bedford presented itself in a nearly vertical column from about 500 m. above the ground to heights of around 8 km., with the main decrease of temperature at the surface occurring during the following two hours. It is suggested that this case is not an exceptional one, but that it rather may reflect the typical structure of a strong cold air invasion near the center of a depression in which the horizontal wind component normal to the front increases with height. Under such conditions an analysis according to the classical Norwegian scheme, with the wedge-shaped cold air mass, would be unrealistic.