The Linear Dynamics of Squall Line Mesohighs and Wake Lows

Two surface pressure features that commonly accompany squall lines, the mesohigh and the wake low, may be explained at least in part as a linear response to the low-level cooling associated with stratiform precipitation. This response is numerically simulated for two- and three-dimensional, moving and stationary low-level coolings characteristic of squall line stratiform regions. When the cooling is defined to move and to have three-dimensional structure both a mesohigh and a mesolow develop, and their structures and evolutions resemble those of squall line mesohighs and wake lows. When an upper boundary is introduced directly above the cooling the response approaches a steady state in which a mesohigh–mesolow couplet is centered on the cooling. The simulations and the steady-state analysis presented here help to explain observed characteristics of squall line mesohighs and wake lows, including their life cycles and positioning relative to precipitation structures.