The Orographic Modulation of Pre-Warm-Front Precipitation in Southern New England

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  • 1 Massachusetts Institute of Technology, Department of Meteorology and Physical Oceanography, Cambridge, MA 02139
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Abstract

Topographic forcing over the hills and small mountains of southern New England plays an important role in determining the distribution of pre-warm-front precipitation from winter cyclones. Upslope regions receive 20–60% more precipitation than do nearby downslope or coastal regions. Both the intensity and duration of precipitation contribute to the positive upslope anomalies. The magnitude of the upslope anomalies, the details of the precipitation intensity distributions at proximal upslope and downslope gauges, and the results of simple models indicate that precipitation scavenging in orographic clouds can explain the orographic enhancement. Also, the existence of a positive precipitation anomaly over the coastal plain suggests that frictional convergence may be generating weak, but persistent vertical motions.

Abstract

Topographic forcing over the hills and small mountains of southern New England plays an important role in determining the distribution of pre-warm-front precipitation from winter cyclones. Upslope regions receive 20–60% more precipitation than do nearby downslope or coastal regions. Both the intensity and duration of precipitation contribute to the positive upslope anomalies. The magnitude of the upslope anomalies, the details of the precipitation intensity distributions at proximal upslope and downslope gauges, and the results of simple models indicate that precipitation scavenging in orographic clouds can explain the orographic enhancement. Also, the existence of a positive precipitation anomaly over the coastal plain suggests that frictional convergence may be generating weak, but persistent vertical motions.

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