The Presidents' Day Cyclone of 18–19 February 1979: Influence of Upstream Trough Amplification and Associated Tropopause Folding on Rapid Cyclogenesis

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Abstract
A diagnostic analysis of an amplifying polar jet-trough system and associated tropopause fold which preceded the 19 February 1979 Presidents' Day cyclone is presented. The analysis is based on conventional radiosonde data, infrared and visible satellite imagery, 6.7 μm water vapor measurements from the Temperature-Humidity Infrared Radiometer (THIR), and ozone measurements from the Total Ozone Mapping Spectrometer (TOMS). The case study indicates that dynamically forced meso-α scale vertical circulations played an important role in the extrusion of stratospheric air along the axis of a polar jet and the subsequent development of the storm system. Specific findings include: 1) Tropopause folding accompanying an amplifying polar jet–trough system occurred along the axis of the intensifying polar jet in response to subsidence forced by geostrophic deformation patterns associated with the jet streak. 2) The folding process extruded dry stratosphere air marked by high values of potential vorticity dow... Abstract A diagnostic analysis of an amplifying polar jet-trough system and associated tropopause fold which preceded the 19 February 1979 Presidents' Day cyclone is presented. The analysis is based on conventional radiosonde data, infrared and visible satellite imagery, 6.7 μm water vapor measurements from the Temperature-Humidity Infrared Radiometer (THIR), and ozone measurements from the Total Ozone Mapping Spectrometer (TOMS). The case study indicates that dynamically forced meso-α scale vertical circulations played an important role in the extrusion of stratospheric air along the axis of a polar jet and the subsequent development of the storm system. Specific findings include: 1) Tropopause folding accompanying an amplifying polar jet–trough system occurred along the axis of the intensifying polar jet in response to subsidence forced by geostrophic deformation patterns associated with the jet streak. 2) The folding process extruded dry stratosphere air marked by high values of potential vorticity dow...

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