URLs from the phone conversation with NwsMeterologists:
Bryan Bulter's VLA Memo on PWV: VLA Memo 176
http://www.aoc.nrao.edu/vla/html/Memos/scimemolist.shtml
Wes Young thinks that historical site opacity data would be very useful for the development of a good weather model.
It turns out that we don't keep this value ('Tau') around; rather, AIPS models this value at FILLEM time with a value derived from weather parameters. Further, the weather parameters used are a weighted average of site-measured actual weather and a seasonal weather model; this was determined empirically to have nice properties in the resulting data file. And we cannot measure the actual weather parameters for the entire atmosphere column, anyway; we only measure the 50 ft above ground weather...
indxr.for
File named OPACTY.FOR in APLSUB of the AIPS source base.
Thanks to Eric Greisen for this info.
Information is available from http://www-frd.fsl.noaa.gov/mab/soundings/java/raob_format.html as an ASCII format.
The service maintainer, Bill Moninger, and I have been trying to debug a simple Perl script that he sent as an example of how to pull data from this service. So far, little progress on that front, despite his prompt and helpful comments.
However, from this exchange I was able to determine a working service URL that can be used with wget or other tools to automatically pull the data via a CRON job.
I implemented a simple GRIB parser in Java, using the examples from http://jgrib.sourceforge.net
The Eclipse Java IDE makes this very easy.
The next step in using GRIB data is to determine the particular data cells that correspond to the VLA site.
Mon Apr 14 21:33:41 GMT 2003 ... Start of JgribDemo
Using gribtab table from class path (jar)
Processing precipitable water record of 157 records!
IS section:
Grib Edition 1
length: 106646 bytes
GDS section:
Lambert Conformal Grid (332x371)
1st point: Lat: 25.97 Lon: -127.973
Grid length: X-Direction 8000.0m; Y-Direction: 8000.0m
Orientation - East longitude parallel to y-axis: 0.0
Resolution and Component Flags:
Direction increments not given
Earth assumed spherical with radius = 6367.47 km
u and v components are relative to the grid
Scanning mode:
Points scan in the +i direction
Points scan in the +j direction
Adjacent points in i direction are consecutive
The first latitude from pole at which the secant cone cuts the spherical earth: 40.0
The second latitude from pole at which the secant cone cuts the spherical earth: 40.0
Latitude of the southern pole: 0.0
Longitude of the southern pole: 0.0
PDS header:
center: 7
subcenter: 0
table: 2
grid_id: 246
time: 14.4.2003 0:0 (dd.mm.yyyy hh:mm)
center: 7
subcenter: 0
process id: 84
table: 2
table version: 2
Parameter:
parameter id: 200
name: entire atmosphere layer
description: entire atmosphere layer
units:
short descr: entire atmosphere layer
increasing up?: true
single layer?: true
value1: 0.0
value2: 0.0
dec.scale: 0
GDS exists
BMS exists
Scan order is 64
BDS section:
min/max value: 1.1907988 27.8158
ref. value: 1.1907988
is a constant: false
bin. scale: -3
num bits: 8
123172
Mon Apr 14 21:33:43 GMT 2003 ... End of JgribDemo!