search

ORAC-CC / orac

Optimal Retrieval of Aerosol and Cloud
GNU General Public License v3.0
30 stars 20 forks source link

ECMWF level zero is set to incorrect parameters #13

Closed simonrp84 closed 5 years ago

simonrp84 commented 5 years ago

For the ECMWF processing (including ERA5) the top layer is set to an incorrect value, rendering the results inaccurate.

adamcpovey commented 5 years ago

Could you be a tad more precise? I remember being careful about the top and bottom levels so I'm curious what I misunderstood (or changed between versions, as I didn't check the changelog exhaustively).

simonrp84 commented 5 years ago

Sorry, wrote it in a rush. The top level of the atmosphere is set to zero pressure, which is not realistic. This seems to come from the avec and bvec having values of 0 in the first index of their arrays (each array is len=138, it should be 137 with the first value gone). I tried to change this but that screwed up RTTOV, so not as simple as deleting the first values and going with that. I do plan to look at this, but it probably won't be any time soon.

w-k-jones commented 5 years ago

Hi Simon,

The avec and bvec values should give the half level pressures, so the top level pressure should in fact be the average of the pressures given by the 1st and 2nd avec, bvec values. Not sure if this would work with the code, but is ho it should be according to the ERA definitions (https://www.ecmwf.int/en/forecasts/documentation-and-support/60-model-levels)

Cheers, Will

From: Simon Proud notifications@github.com Sent: 03 December 2018 09:00:04 To: ORAC-CC/orac Cc: Subscribed Subject: Re: [ORAC-CC/orac] ECMWF level zero is set to incorrect parameters (#13)

Sorry, wrote it in a rush. The top level of the atmosphere is set to zero pressure, which is not realistic. This seems to come from the avec and bvec having values of 0 in the first index of their arrays (each array is len=138, it should be 137 with the first value gone). I tried to change this but that screwed up RTTOV, so not as simple as deleting the first values and going with that. I do plan to look at this, but it probably won't be any time soon.

— You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHubhttps://github.com/ORAC-CC/orac/issues/13#issuecomment-443635927, or mute the threadhttps://github.com/notifications/unsubscribe-auth/AVxqXTYTk7ip5PvtwKw1KFcAoF7IrvEnks5u1OgUgaJpZM4Y87FU.

simonrp84 commented 5 years ago

I'm not convinced that what we're doing in ORAC is right, but I'm closing this issue as it makes no difference to the output (unless we get a cloud at 1Hpa).