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New type of Level: departure level of most unstable parcel of air #16
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@wmo-im/tdcf : any feedback would be much appreciated! |
Do we also need a parameter for the departure level? With the definition of the level I can have a field providing the value of the highest value of CAPE, but it might be important to know at which level it is. I see two fields one with the value of CAPE at the "Departure level of the most unstable parcel of air (MUDL)" and one with the level (model level number) for that value of CAPE |
Yes we are already producing a CAPE parameter (and a CIN parameter) at each model level, this is how the most unstable CAPE is computed: CAPE is computed for all model level and at each grid point the highest value a CAPE is retained. We will produce a CAPE50 (and CAPE100) which is calculated this way: A mean CAPE is computed between surface and a level differing by 50hPa (and 100hPa) from the surface. I am planning to ecode these this way: Discipline=0 although I don't know how to specify that the layer represented by surface to P0-P=50 is an average, not an integration, a max, a min, or anything else. All the statistical transformations are specific to Time, I am not aware of a way to specify this for an horizontal grid and a vertical column. |
As discussed with our subject matter experts here at MSC/CCMEP, we are fine with supporting this field as part of our model output for future implementation. |
Note we are also looking into CAPE and CIN and happy to bring in our subject matter experts to discus further. |
I got comments from our research colleagues. They support the proposal and they provide following comments with an extension of the proposal: Comment I: Comment II: New entry 18 in Code table 4.5
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Dear @SibylleK , thank you for your coontribution. Do I understand correctly that if I associate a value of 50 to this new type of level 18, it means that my mixed air parcel is computed as the mean value of CAPE/CIN from surface to a difference from surface of 50hPa? More generally for GRIB3, it would be better to have a way to specify if a layer is an average, an accumulation, etc. within that layer. |
@sebvi Hi, Sebastien, I created a new branch for this issue. And I added entries 17 and 18 to the Code Table 4.5. Could you please check it? Thanks. |
Dear colleagues, Please find below a GRIB file (zipped for uploading) which might serve as one example for the newly proposed fixed-surface types. We used ecCodes (version 2.14.1) to interpret the GRIB file. test_new_levelType_17_and_18.grb.zip |
@chenxiaoxia2019 the branch looks ok to me as well. I could also decode the samples provided by DWD. |
SUMMARY: Add entries, 17 & 18, to code table 4.5. |
Approved by FT-2020-2. |
Branch
https://github.com/wmo-im/GRIB2/tree/issue-16
Summary and purpose
ECMWF is requesting a new type of level to properly encode 2 new parameters: Most Unstable Convective Available Potential Energy (MUCAPE) and Most Unstable Convective INhibition (MUCIN)
Action proposed
ECMWF kindly asks the team to review the proposal and accept it during the next session.
Discussions
In a coming release of its IFS model, ECMWF will make available 2 new parameters, the most unstable CAPE and the most unstable CIN.
These 2 new parameters require to locate in the vertical air column the most unstable parcel of air (as shown in the attached pdf). The location of this parcel of air is grid dependent, which means it can't be encoded at a fixed height, an isobaric or isothermal level.
Following a recent proposal to introduce the entries 14-16 in the Code Table 4.5, we propose to define a new type of level called "Departure Level of the most unstable parcel" and assign it the code 17 (since this new type of level complements the newly created entries 14-16).
mucape.pdf
Detailed proposal
add a new entry 17 in Code Table 4.5:
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