A PV Perspective on the Vertical Structure of Mature Midlatitude Cyclones in the Northern Hemisphere

Jana Čampa, Heini Wernli
2012 Journal of the Atmospheric Sciences  
Development of extratropical cyclones can be seen as an interplay of three positive potential vorticity anomalies: an upper-level stratospheric intrusion, low-tropospheric diabatically produced potential vorticity (PV), and a warm anomaly at the surface acting as a surrogate PV anomaly. This study, based on the interim ECMWF Re-Analysis (ERA-Interim) dataset, quantifies the amplitude of the PV anomalies of mature extratropical cyclones in different regions in the Northern Hemisphere on a
more » ... logical basis. A tracking algorithm is applied to sea level pressure (SLP) fields to identify cyclone tracks. Surface potential temperature anomalies Du and vertical profiles of PV anomalies DPV are calculated at the time of the cyclones' minimum SLP in a vertical cylinder around the surface cyclone center. To compare the cyclones' characteristics they are grouped according to their location and intensity. Composite DPV profiles are calculated for each region and intensity class at the time of minimum SLP and during the cyclone intensification phase. In the mature stage all three anomalies are on average larger for intense than for weak winter cyclones [e.g., 0.6 versus 0.2 potential vorticity units (PVU; 1 PVU 5 10 26 K kg 21 m 2 s 21 ) at lower levels, and 1.5 versus 0.5 PVU at upper levels]. The regional variability of the cyclones' vertical structure and the profile evolution is prominent (cyclones in some regions are more sensitive to the amplitude of a particular anomaly than in other regions). Values of Du and low-level DPV are on average larger in the western parts of the oceans than in the eastern parts. Results for summer are qualitatively similar, except for distinctively weaker surface Du values.
doi:10.1175/jas-d-11-050.1 fatcat:s4pl6pjvvnaihfahxjbjlkq2ie