Understanding the Variabiility of Winter Mortality Using Composite Back Trajectory Analysis

A composite back trajectory analysis for 95 high and low mortality events for the Northern England county of Yorkshire is presented. The purpose of the analysis is to establish whether basic differences exist between the BT patterns and the physical properties of their associated air masses for high and low winter mortality events. Analysis results reveal basic differences in the nature of the back trajectory patterns between high and low mortality events as well as the speed of air mass movement, its heat content as described by potential temperature, pressure tendency and the rate of change of pressure and temperature along the air mass trajectory. The general synoptic meteorological situation associated with the back trajectories linked with high and low mortality is described. An explanation is also offered for why the nature of the air masses and their trajectories may be important for differentiating between high and low mortality events.