SNAP documentation

MRI

The MRI files can be found in /group_workspaces/jasmin/snap/mri/phase1. The files can be found in directories of the form YYYYMMDD, where the date is the start date. Inside these directories, the files are the form <VAR>_MRI_phase1_YYYYMMDD_<NN>.nc, where <VAR> is OGWD (Orographic gravity wave tendencies), PV, Precip, T2m, T, U10, U, V10, V and Z (geopotential height), and <NN> runs from 01 to 51 (I DON'T KNOW WHAT THIS IS).

Each of the <VAR>_MRI_phase1_YYYYMMDD_<NN>.nc files contain

  • OGWD: double lat (lat), double lon (lon), double plev(plev), double time(time) and float OGWD(time, plev, lat, lon), but plev is only upper levels
  • PV: float x(x), float y(y), double theta(theta), float t(t) and float PV(t, theta, y, x)
  • Precip: double lat (lat), double lon (lon), double time(time) and float Precip(time, lat, lon).
  • T2m: double lat (lat), double lon (lon), double time(time) and float T2m(time, lat, lon).
  • T: double lat (lat), double lon (lon), double plev(plev), double time(time) and float T(time, plev, lat, lon).
  • U10: double lat (lat), double lon (lon), double time(time) and float U10(time, lat, lon).
  • U: double lat (lat), double lon (lon), double plev(plev), double time(time) and float U(time, plev, lat, lon).
  • V10: double lat (lat), double lon (lon), double time(time) and float V10(time, lat, lon).
  • V: double lat (lat), double lon (lon), double plev(plev), double time(time) and float V(time, plev, lat, lon).
  • Z: double lat (lat), double lon (lon), double plev(plev), double time(time) and float Z(time, plev, lat, lon).

where

  • PV is the only variable to use x, y and t - instead of lon, lat and time. And this dimensions are floats rather than doubles
  • lon/x = 240
  • lat/y = 121
  • time/t = 64 (6 hour intervals, so 16 days)
  • plev = 37 (is 15 for OGWD)
  • theta = 5 (in PV file only)

Putting all the variables into one file

All these variables are put into file with the script /home/users/stringer/snap/bin/conformMri.scr, which requires two arguments: the directory containing the data and the value of <NN>. The script then carries out the following

  • Loop across all the input files
    • Copies files to work directory, /home/users/stringer/snap/data, so will only modify copies.
    • Converts the double variable to floats.
    • Flip the latitude
    • Ensure that dimensions all have the same name
    • Rename plev in OGWD to pres_upp, so it does get confused with the plev in the other files - which has a number of extra pressure levels
  • Put the data all into one file
  • Rename dimensions and variables according to the table below and add and delete attributes
VariableLong name New variable nameNew long name
timetime ttime
lon/xlongitude longitudelongitude
lat/ylatitude latitudelatitude
thetanone thetapotential temperature
plevpressure level p/p_2pressure
OGWDOrographic gravity wave tendencies GWOD*Orographic gravity wave tendencies
PrecipPrecipitation TPRainfall rate
PVnone PVPotential vorticity
T2mNear-Surface Air Temperature T22 metre temperature
TAir Temperature TTemperature
U10Eastward Near-Surface Wind U1010 metre U wind component
UEastward Wind UU velocity
V10Northward Near-Surface Wind V1010 metre V wind component
VNorthward Wind VV velocity
ZGeopotential Height ZH*Geopotential height (geopotential is in ERA-Interim files but not geopotential height)
* variable cannot be found in ERA-interim files

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