Figure 4. 



Number of cydolysis events per 3x10^ km^ during GALE, traveling 

 cyclones only (from Neilsen and Dole (1992)) 



vicinity, the system will tend to interact and coalesce, following the geopoten- 

 tial height falls. In this case, the pressure deficit will be less than the deepen- 

 ing because the far-field pressure will tend to fall as well. Nielsen and Dole 

 concluded that "...while strong deej)ening does not necessarily imply a large 

 pressure deficit, a large pressure deficit is a good indicator of rapid prior deep- 

 ening." This statement implies that when a large pressure deficit appears on a 

 chart but does not appear on earher charts, it is likely that a system was form- 

 ing but went undepicted on the earlier charts. Figure 7 shows the maximum 

 12-hr deepening of traveling cyclones by continental and Atlantic classes. 

 Note that Atlantic cyclones tend to exhibit much greater deepening than do 

 continental cyclones. That the rapid deepening cyclones are almost exclusive 

 to an oceanic regime is consistent with the findings of Sanders and Gyakum 

 (1980). 



The preceding section of this chapter discusses issues that concern the 

 identification and selection of significant extratropical cyclone events based 

 upon available meteorological information. The magnitudes of the factors that 

 are considered in the selection such as size, intensity, duration, and position 

 are shown to depend upon the analyzed depiction of the event. Events that 

 cause substantial coastal damage or have significant effects on maritime ship- 

 ping are likely to be analyzed in greater detail, resulting in more accurate 



Chapter 2 Operational Analysis Depictions 



