A Contrast Diagnostic Study of Two Cases of Explosive Northeastern Lows in Spring

The diagnostic study of two spring explosive northeast lows (Case A: 25~26 April, 1983; Case B: 28~29 April, 1983) is made. The IPV (Isentropic potential vorticity), frontogenesis and stability distributions have been calculated. The results show that: (1) The diabatic heating and local baroclinic instability are the crucial factors for case A; the rapid increases of the horizontal advection of potential vorticity and its vertical coupling with the high IPV in the low-level play an important role for the development of case B. (2) The greatest difference between the two storms is that the impacts of diabatic heating in degrees on cyclone intensity are different. And, another difference may be that cyclonic vorticity generated in the midtroposphere in connection with upper-level frontogenesis may contribute to the upward increase in cyclonic vorticity advection over the deepening storm center in case B.