FG departures of for 2D-OI (2m temperature, relative humidity and snow depth analysis) are calculated at in fg2obs.F90. At first, observations are sorted by OBS_RAWTABLE(jpraw_refcoord, jtotal) based on latitude and longitude (prepared at in scan_cma_odb.F90).
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izlat = int( zlat * 100.0_JPRB)
izlon = int( zlon * 100.0_JPRB)
i_refcoord = sign(1,izlat) * (abs(izlat) * 100000 + izlon)
OBS_RAWTABLE(jpraw_refcoord, jtotal) =&
&sign(1,i_refcoord) * (abs(i_refcoord) +&
&1 * 0.01_JPRB) |
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The observations should be sorted in ascending order by latitude because FG departures are calculated in turn from the south pole to the north pole by the following code.
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However, latitude is rounded down to the second decimal place when OBS_RAWTABLE(jpraw_refcoord, jtotal) is calculated. As a resultsresult, the indexes indices are sometimes not in ascending order precisely and the FG departures are not calculated from surrounded 4 model grids. The following table shows the an example. ZOBSLAT should be at the latitude between ALAT(jlatN) and ALAT(jlatS) but it is not there (at the south side of ALAT(jlatS)).
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