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ETA-12 - NCEP's Limited Area Step Mountain Coordinate Model

New! Eta MOS Guidance from the Meteorological Development Laboratory | Technical Procedures Bulletin New!

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The NCEP are testing a new method of computing convective available potential energy (CAPE) in the Eta post production process.

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Change to Eta Model to improve surface temperature guidance.

NCEP Operations has scheduled the following crisis change to be made to the Meso Eta Model runs starting with 12z 26 February 2002.

The change addresses complaints this winter about nighttime surface temperatures over snow being too cold in the Meso Eta. The problem has been linked to two factors. The first is that our new gridscale cloud scheme has less cloud than the one it replaced. This results in more radiational cooling situations. While the old scheme had a definite bias (too much cloud), we feel the new scheme may have too little cloud. This is being looked into and will be addressed in the future. The second factor relates to thermal conductivity of the land-surface layer when snow cover is present. The formulation of this was refined in July 2001 to incorporate a treatment of patchy snow. There was nothing wrong with that treatment, however, we have found that more heat needs to get through to the atmosphere to keep the skin, shelter and 1st layer temperatures from cooling too much at night. Consequently, this change will increase the treatment of thermal conductivity for both patchy snow and full snow cover. A brief presentation can be found at ftp://ftp.ncep.noaa.gov/pub/emc/wd20er/caftiinfo.feb02/v3_document.htm

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Experimental CAPE Formulations

The NCEP are testing a new method of computing convective available potential energy (CAPE) in the Eta post production process. They have been producing a surface-based CAPE (actually the parcel with the highest theta-e in the lowest 70 mb) and a most unstable CAPE (lift the 30 mb layer with the highest theta-e among the six "boundary layers"). Research conducted by the Storm Prediction Center has indicated that the best representation of the afternoon planetary boundary lebel (PBL) may be a 100 mb deep mean parcel. The SPC has asked the Mesoscale Modeling Branch (MMB) to compute CAPE using such a mean layer. To simplify the coding, the MMB is computing a CAPE by averaging the three lowest 30 mb layers, resulting in a 90 mb deep mean parcel.

This code is now running in the 32-km parallel control run of the Eta model parallel, with a primitive comparison of all three methods presented at: www.emc.ncep.noaa.gov/mmb/research/return02/comparecape.html

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