Weather Data for SE Asia


We first looked at rainfall data from the Global Daily Summary CDROM from the National Climate Data Center.


This shows our study basins, the 2° buffer used for selecting weather stations, and the 5° used for selecting radiosonde stations. The rectangle indicates the size of the data grids being passed on the the VIC model.

For January ,1997 through September, 2000, we downloaded the daily records from the National Climatic Data Center 1254 stations fall within 2 degrees of our study area. The number of stations with data on any given day is:

The initial phase of our processing is done in geographic coordinates. This gives a bias to the weights of stations to the east or west of a point, but the effect is small at these latitudes. Subsequent calculations involving areas all use corrected values. Max temperature, min temperature, wind, and precip, were extracted from the NCDC ASCII files and placed in 1056 daily files. These files were converted to ARC/INFO "coverage" format.

Quarter-degree grids of wind speed were created for each day by using an inverse-distance-weighted algorithm built into ARC/INFO. The algorithm averages all stations within 0.4 degrees of the grid center, but extending the search until at least 3 stations are found.

Precipitation grids were made in a similar manner, but with less confidence. We judged the NCDC GPCP (Gloabal Precipitation Climatology Project) one-degree rainfall to be superior to any product we could devise, so we created our grids only for comparison. ...

digression year 2000 data

We needed a different data source for rain in 2000, so Sarah downloaded TRMM data from [?]. Data file names are: 3B42.990101.5.HDF etc. The data is column-major, south-north, west-east. We uncompress, skip to the data, clip out our (86,-12) to (140,36) rectangle, and rotate in one opeeration, e.g.
zcat 3B42.990101.5.HDF.Z | cutout 320 54 48 112 85414 4 90 > 990101
OR
foreach month (01 02 03 04 05 06 07 08 09 10 11 12)
  foreach fil (3B42.??${month}*)
    zcat $fil | cutout 320 54 48 112 85414 4 90 > `echo $fil | cut -d '.' -f2`
  end
end
Comparing 990101 to the NCDC 1dd data (after multiplying by 25.4), the mean difference is 0.22 mm, with a with abs(diff) of 3.33 mm, while all rainfall patterns are maintained.

Questions: Harvey Greenberg