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Message: CAPE change in RUC2

Posted by Stan Benjamin on 15 Apr 98, 13:14 MT

A small change was made in the CAPE diagnostic for RUC2 this morning. Previously, the search for positive area was made from the level of free convection (LFC) upward, and sometimes, there was a very small stable layer just above a very small unstable layer that the algorithm interpreted as the cloud top. This resulted in negligible CAPE, even though the sounding showed large instability. In previous RUC2 CAPE fields, due to this problem, there would sometimes be areas of near-zero CAPE "bitten" out of the side of an area of very large CAPE, or sometimes even out of the middle of a large CAPE area.

Now, the algorithm searches from the top of the column downward, integrating positive area. This avoids the CAPE hole problem.

The convective inhibition (CIN) values still are the same as before in areas where CAPE > 0, BUT now large values are being produced in CAPE=0 regions. They are meaningless and should be ignored. I apologize for the fact that the CIN is not masked in this new version that is improved as far as CAPE is concerned.

Thanks to Phillip Bothwell and others at SPC for bringing these problems up. Phillip has also noted a couple of occasions where the diagnosed CIN was larger than it should have been, so we will be looking more at that. Most of the time, the CIN seems to be right on the money. Comments?



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