The role of subsynoptic processes in synoptic -scale extratropical cyclone development
Abstract
The explosive development phase of an extratropical cyclone (ETC) is examined using output generated by the fifth generation PSU/NCAR Mesoscale Model (MM5). MM5 was used to simulate the Intensive Observation Period (IOP) 4 storm of 4–5 January 1989 from the Experiment on Rapidly Intensifying Cyclones over the Atlantic (ERICA). MM5 output was generated by a full-physics model run using a 79 x 139 grid with a 60km grid spacing and using a moveable 115 x 193 nested grid with a 20km grid spacing. A diagnosis of the simulated ETC is performed using the Zwack-Okossi (Z-O) equation to examine the forcing mechanisms influencing development. A second-order Shapiro filter is used to partition the terms in the Z-O equation into synoptic-scale and subsynoptic-scale contributions to the near-surface synoptic-scale geostrophic vorticity tendency. The results at the two grid spacings were compared and reveal additional subsynoptic-scale terms at 20km grid spacing that were determined to be important contributions to development. These results lead to the conclusion that results are dependent on model grid spacing. Compared to results from a prior study analyzing the same cyclone, these results also show some differences regarding processes that were important to development of the IOP4 cyclone. This observation leads to the conclusion that results are dependent on the model used. Finally, these results demonstrate that subsynoptic-scale diabatic heating consistently yielded significant positive contributions to development. Furthermore, subsynoptic vertical motions, which are directly responsive to the subsynoptic heating, were the dominant factor in non-diabatic subsynoptic influences at both grid spacings.
Degree
Ph.D.
Advisors
Smith, Purdue University.
Subject Area
Geophysics|Environmental science
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