Figure 10. 0000-hr UTC, 29 October 1991, 500-mb height/temperature 

 analysis 



treated by Bleck (1990). The basis of Bleck's treatment stems from a hypoth- 

 esis advanced by Hoskins, Mchityre, and Robertson (1985), and involves the 

 mutual amplification of quasi-geostrophic positive vorticity perturbations 

 (PVs) in the presence of baroclinic instability. Determination of the value of 

 PV over a specified volume is given by 



Chapter 3 Halloween Storm 



15 



