With cycle 45r1 the following new variables have been introduced:
These two variables represent maximum values in the past 6 hours derived from a combination of (A) standard hourly model output, and (B) values of CAPE and CAPE-shear computed every time step (450 s for HRES and 720 s for ENS) at gridpoints where the convection scheme is active. The method of computation for (A) is the standard ECMWF method used for some time. However the way in which CAPE is computed in (B) is physically different (and is done within the convection scheme, with zeros applied outside convectively active areas). These new parameters may help users to better assess the potential for convection than using instantaneous values. As the plots below illustrate, the new fields tend to be smoother and more continuous. This is because model CAPE at a given location on a given day can increase and decrease quite sharply, over timescales much less than 6 hours.
ECMWF is considering adapting the method of computation of these new fields in the next cycle, to achieve greater consistency.
Maximum CAPE versus instantaneous CAPE (left) and Maximum CAPE-shear versus instantaneous CAPE-shear (right).