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The Linear Dynamics of Squall Line Mesohighs and Wake Lows

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  • 1 Department of Atmospheric Science, Colorado State University, Fort Collins, Colorado
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Abstract

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.

Corresponding author address: Dr. Patrick Haertel, Department of Atmospheric Science, Colorado State University, Fort Collins, CO 80523-1371.

Email: haertel@thunder.atmos.colostate.edu

Abstract

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.

Corresponding author address: Dr. Patrick Haertel, Department of Atmospheric Science, Colorado State University, Fort Collins, CO 80523-1371.

Email: haertel@thunder.atmos.colostate.edu

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