Influence of Cold Advection in Mid–and–upper Troposphere on Squall Line Occurrence

The occurrence of squall lines is frequently associated with instability energy and vertical wind shear. In this paper, a method for diagnosing temperature advection in mid-and-upper troposphere is proposed, with which the advection magnitudes between 700 and 300 hPa in several cases are analysed. Results show that the cold advection would cause an increase in the instability energy E between 700 hPa and 300 hPa and the magnitudes of E and could present a certain indication for the formation of strong squall lines. It is pointed out that vertical wind shear and its change are closely correlated with the temperature advection. It is also emphasized that analysis of horizontal distribution of instability energy and cold advection is useful for forecasting the area in which squall lines occur.