The Mechanics of Instability-Line Formation

It is proposed that under certain conditions of wind flow that temperature changes due to horizontal advection and vertical motion produce a trend towards the formation within a few hours of a line or narrow band of vertical thermal instability associated with a marked increase in low-level convergence along the same line or narrow band. An assumed distribution of winds, chosen to represent typical conditions observed preceding by a few hours the formation of an instability line, is studied and a model presented. The model agrees well with synoptic observation and studies. The atmospheric mechanism derived is of the mesoscale and is directly applicable to instability line formation in the “High Plains” and most pre-cold frontal instability lines in other areas can be explained by it.