Organization and structure of clouds and precipitation on the mid-Atlantic coast of the United States. Part VII: Diagnosis of a nonconvective rainband associated with a cold front aloft

• Published in: Monthly weather review 2002-02, Vol.130 (2), p.278-297
• Main Authors: LOCATELLI, John D, STOELINGA, Mark T, HOBBS, Peter V
• Format: Article
• Language: English
• Subjects: Earth, ocean, space; Exact sciences and technology; External geophysics; Meteorology; USA, mid-Atlantic; Water in the atmosphere (humidity, clouds, evaporation, precipitation)
• ISSN: 0027-0644; 1520-0493
• DOI: 10.1175/1520-0493(2002)130<0278:OASOCA>2.0.CO;2

A numerical simulation using the Pennsylvania State University-National Center for Atmospheric Research fifth-generation Mesoscale Model (MM5) was run on a rainband associated with a cold front aloft (CFA) in a warm occluded structure on the U.S. east coast. The storm originally developed in the lee of the Rocky Mountains as a Pacific cold front overtook a Rocky Mountain lee trough. This formed a warm-type, occluded structure that was essentially maintained as the storm proceeded to the East Coast. The CFA was a thermal front and therefore dynamically active. The prominence of the CFA in the equivalent potential temperature field was due primarily to the strong upward transport of water vapor from lower levels in the updraft associated with the CFA. The baroclinic zone was characterized by a tipped-forward lower region, where the CFA coincided with a maximum in potential temperature, and a tipped-backward upper region, where the CFA coincided with the leading (warm-side) edge of a zone of enhanced thermal gradient. The tipped-backward upper region displayed many of the characteristics of a vertically propagating gravity wave. In both of these regions, the potential temperature pattern produced a corresponding change in pressure gradient within the baroclinic zone; the imbalance of forces acting on air parcels as they moved through this pressure gradient produced the convergence in the lower baroclinic zone that was responsible for the CFA rainband. Neither the dry quasigeostrophic nor dry Sawyer-Eliassen diagnosis resolved the details of the simulated mesoscale lifting associated with the CFA rainband. This is because the baroclinic zone of the CFA was mesoscale and structurally complex.