A Three-Dimensional Numerical Investigation Of a Carolina Coastal Low-Level Jet 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 Stage 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 three low-level jets (LLJs) observed during the second intensive observation period of the Genesis of Atlantic Lows Experiment: 1) a Piedmont LLJ along the east slope of the Appalachians, 2) a coastal LLJ (the focus of this study) along the Carolina coastline, and 3) an LLJ to the rein of a cold-frontal system positioned over the Gulf Stream. Geostrophic forcing was important for the formation of the LLJs. Shallow local baroclinity near the top of the cold dome associated with the cold air dammed to the east of the Appalachian Mountains forced the Piedmont LLJ. An analysis of the model momentum tendencies reveals that the coastal LLJ developed and was maintained by strong geostrophic forcing associated with the coastal baroclinic zone, and its strength was modulated by strong, inertial accelerations. Significant horizontal structure in the coastal LLJ developed during the daytime as a result of the different vertical mixing properties associated with continental and maritime parcel source regions.

Model sensitivity experiments indicate that diabatic processes substantially influence the evolution of the coastal and cold-frontal LLJs, Latent heating associated with banded precipitation over the Gulf Strum to the rear of the front was the primary Forcing mechanism for the frontal LLJ. Sensible heating within the marine atmospheric boundary layer acted to enhance the coastal baroclinic zone and low-level geostrophic forcing, and to subsequently strengthen the coastal LLJ. Cold-air damming and strong lower-tropospheric sensible and latent heating in the vicinity of the Gulf Stream, which frequently occur during autumn and winter months along the East Coast, combine to produce a favorable mesoscale environment for LLJ formation with a wind direction parallel to the coastline.

Abstract

The Pennsylvania State University-NCAR Mesoscale Model is used to examine the structure and dynamics of three low-level jets (LLJs) observed during the second intensive observation period of the Genesis of Atlantic Lows Experiment: 1) a Piedmont LLJ along the east slope of the Appalachians, 2) a coastal LLJ (the focus of this study) along the Carolina coastline, and 3) an LLJ to the rein of a cold-frontal system positioned over the Gulf Stream. Geostrophic forcing was important for the formation of the LLJs. Shallow local baroclinity near the top of the cold dome associated with the cold air dammed to the east of the Appalachian Mountains forced the Piedmont LLJ. An analysis of the model momentum tendencies reveals that the coastal LLJ developed and was maintained by strong geostrophic forcing associated with the coastal baroclinic zone, and its strength was modulated by strong, inertial accelerations. Significant horizontal structure in the coastal LLJ developed during the daytime as a result of the different vertical mixing properties associated with continental and maritime parcel source regions.

Model sensitivity experiments indicate that diabatic processes substantially influence the evolution of the coastal and cold-frontal LLJs, Latent heating associated with banded precipitation over the Gulf Strum to the rear of the front was the primary Forcing mechanism for the frontal LLJ. Sensible heating within the marine atmospheric boundary layer acted to enhance the coastal baroclinic zone and low-level geostrophic forcing, and to subsequently strengthen the coastal LLJ. Cold-air damming and strong lower-tropospheric sensible and latent heating in the vicinity of the Gulf Stream, which frequently occur during autumn and winter months along the East Coast, combine to produce a favorable mesoscale environment for LLJ formation with a wind direction parallel to the coastline.

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