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I need 6-hour MERRA-2 reanalysis data to do some research. I downloaded the data from this website: https://disc.gsfc.nasa.gov/datasets/M2I6NPANA_5.12.4/summary?keywords=merra

When I used ncview to check this data, I found that V and U wind are missing values over land at 1000 hPa pressure level. enter image description here Have you ever seem this problem before? Thank you so much.

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    $\begingroup$ The land surface can be higher than 1000 hPa $\endgroup$
    – Christoph
    Nov 14 '19 at 5:10
  • $\begingroup$ @Christoph Yes, it is. But the JRA and ERA-Interim are different from MERRA-2, the U and V field in these two reanalysis products are no missing values. All of them are checked at 1000 hPa isobaric level. $\endgroup$
    – Love_qq_xq
    Nov 14 '19 at 16:10
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TL;DR: It is not a problem, it is a feature.

As it was pointed in the comments, 1000 hPa over land (and sometimes over ocean) is below the surface. MERRA is just fair enough not to put any values where they do not exist. Other reanalyses use some procedure to fill the gaps and make fields without holes. The procedure is reanalysis specific, and, can ususlly be found in corresponding technical manual. The gap-filled fields have little physical meaning anyway.

If the gaps do not make sense for you, 1000-hPa wind is, probably, not the field you need. E.g. if you are after near-surface wind, 10-m wind is more appropriate quantity.

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  • $\begingroup$ Thanks for your comments, helps me a lot. I just got an email from the MERRA2 official, it said that "MERRA-2 data does not extrapolate data to pressure levels greater than the surface pressure." $\endgroup$
    – Love_qq_xq
    Nov 19 '19 at 23:44
  • $\begingroup$ @Love_qq_xq Related - earthscience.stackexchange.com/questions/8779/… $\endgroup$
    – gansub
    Nov 20 '19 at 6:43

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