A Numerical Investigation of Coastal Frontogenesis and Mesoscale Cyclogenesis during GALE IOP 2

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  • 1 Department of Meteorology, The Pennsylvania State University, University Park, Pennsylvania
  • | 2 Department of Meteorology and Earth System Science Center, The Pennsylvania State University, University Park, Pennsylvania
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Abstract

The Pennsylvania State University-NCAR Mesoscale Model is used to examine the structure and dynamics of coastal frontogenesis and mesoscale cyclogenesis observed during intensive observation period 2 (IOP 2) of the Genesis of Atlantic lows Experiment (GALE). The model accurately simulates many of the observed mesoscale Features including cold-air damming to the cast of the Appalachian Mountains, a coastal trough, coastal frontogenesis, and mesoscale cyclogenesis.

The coastal front becomes apparent approximately 6 h after the formation of a coastal trough in the vicinity of the Gulf Stream. An analysis of the model results indicates that both latent beating from banded precipitation over the Gulf Stream and surface sensible heating contribute to trough development. The deformation resulting from the isallobaric accelerations, associated with the pressure changes that occur as the coastal trough forms, initiates the coastal frontogenesis. Numerical sensitivity tests reveal that the diabatic processes dominate the coastal trough and front development. Initially, the frontogenetic effects of the deformation over the Gulf Stream are opposed by the frontolytic differential diabatic effects. The frontogenctic effects of differential diabatic heating at the coastline promote the westward movement of the northern portion of the front. With this westward movement of the coastal front, the deformation and diabatic effects act in concert to significantly strengthen the baroclinic zone.

A small-scale weak cyclone develops along the coastal front as a result of the strong low-level diabatic forcing associated with intense marine atmospheric boundary layer sensible heating and latent heating from copious precipitation. The mesoscale cyclone is characterized by a warm-core structure, with areas of ascent, cyclonic vorticity, and convergence confined to the lowest 3 km of the atmosphere. As the coastal cyclone moves northward along the coastal front, the baroclinic zone weakens substantially to its rear due to diabatic heating of the postfrontal air mass and strengthening westerlies to the rear of the cyclone.

Abstract

The Pennsylvania State University-NCAR Mesoscale Model is used to examine the structure and dynamics of coastal frontogenesis and mesoscale cyclogenesis observed during intensive observation period 2 (IOP 2) of the Genesis of Atlantic lows Experiment (GALE). The model accurately simulates many of the observed mesoscale Features including cold-air damming to the cast of the Appalachian Mountains, a coastal trough, coastal frontogenesis, and mesoscale cyclogenesis.

The coastal front becomes apparent approximately 6 h after the formation of a coastal trough in the vicinity of the Gulf Stream. An analysis of the model results indicates that both latent beating from banded precipitation over the Gulf Stream and surface sensible heating contribute to trough development. The deformation resulting from the isallobaric accelerations, associated with the pressure changes that occur as the coastal trough forms, initiates the coastal frontogenesis. Numerical sensitivity tests reveal that the diabatic processes dominate the coastal trough and front development. Initially, the frontogenetic effects of the deformation over the Gulf Stream are opposed by the frontolytic differential diabatic effects. The frontogenctic effects of differential diabatic heating at the coastline promote the westward movement of the northern portion of the front. With this westward movement of the coastal front, the deformation and diabatic effects act in concert to significantly strengthen the baroclinic zone.

A small-scale weak cyclone develops along the coastal front as a result of the strong low-level diabatic forcing associated with intense marine atmospheric boundary layer sensible heating and latent heating from copious precipitation. The mesoscale cyclone is characterized by a warm-core structure, with areas of ascent, cyclonic vorticity, and convergence confined to the lowest 3 km of the atmosphere. As the coastal cyclone moves northward along the coastal front, the baroclinic zone weakens substantially to its rear due to diabatic heating of the postfrontal air mass and strengthening westerlies to the rear of the cyclone.

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