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A Diagnostic Study of an Explosively Developing Extratropical Cyclone and an Associated 500-hPa Trough Merger

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  • 1 Department of Earth and Atmospheric Sciences, Purdue University, West Lafayette, Indiana
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Abstract

This paper presents a diagnosis of an explosively developing cyclone (1.3 Ber) that occurred in conjunction with a 500-hPa synoptic-scale trough merger over the eastern United States in November 1999. The explosive development occurred in response to cyclonic vorticity and warm air advections that maximized in the 250–200-hPa layer and latent heat release. Explosive development commenced 12 h before trough merger began and then accelerated through the 12-h merger period. During merger, development was enhanced by increased warm air advection above 300 hPa and reduced adiabatic cooling. Finally, comparison of this case with other explosive cyclogenesis–trough merger cases suggests that at the synoptic scale trough merger is an evolutionary process that requires as little as 12 h to complete and that, although trough merger is not required to initiate explosive cyclogenesis, the occurrence of merger can be expected to increase the development rate.

* Current affiliation: SAIC, Monterey, California.

Corresponding author address: Prof. Phillip J. Smith, Department of Earth and Atmospheric Sciences, Purdue University, 1397 Civil Engineering Building, West Lafayette, IN 47907-1397.Email: pjsmith@purdue.edu

Abstract

This paper presents a diagnosis of an explosively developing cyclone (1.3 Ber) that occurred in conjunction with a 500-hPa synoptic-scale trough merger over the eastern United States in November 1999. The explosive development occurred in response to cyclonic vorticity and warm air advections that maximized in the 250–200-hPa layer and latent heat release. Explosive development commenced 12 h before trough merger began and then accelerated through the 12-h merger period. During merger, development was enhanced by increased warm air advection above 300 hPa and reduced adiabatic cooling. Finally, comparison of this case with other explosive cyclogenesis–trough merger cases suggests that at the synoptic scale trough merger is an evolutionary process that requires as little as 12 h to complete and that, although trough merger is not required to initiate explosive cyclogenesis, the occurrence of merger can be expected to increase the development rate.

* Current affiliation: SAIC, Monterey, California.

Corresponding author address: Prof. Phillip J. Smith, Department of Earth and Atmospheric Sciences, Purdue University, 1397 Civil Engineering Building, West Lafayette, IN 47907-1397.Email: pjsmith@purdue.edu

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