Recently I wrote the Webmaster for the 20th Century Reanalysis V2 data plotting pages, regarding grid incompatibility between the following two data files:<div><br></div><div><span style="border-collapse:collapse;color:rgb(80, 0, 80);font-family:arial, sans-serif;font-size:14px">Monthly means:<br>
<a href="ftp://ftp.cdc.noaa.gov/Datasets/20thC_ReanV2/Monthlies/monolevel/air.sig995.mon.mean.nc" style="color:rgb(42, 93, 176)" target="_blank">ftp://ftp.cdc.noaa.gov/Datasets/20thC_ReanV2/Monthlies/monolevel/air.sig995.mon.mean.nc</a><br>
Monthly longterm means:<br> <a href="ftp://ftp.cdc.noaa.gov/Datasets/20thC_ReanV2/Derived/Monthlies/monolevel/air.sig995.mon.ltm.nc" style="color:rgb(42, 93, 176)" target="_blank">ftp://ftp.cdc.noaa.gov/Datasets/20thC_ReanV2/Derived/Monthlies/monolevel/air.sig995.mon.ltm.nc</a></span><br>
<div><br></div><div>I can plot the "air" variable from each without a problem, but when I subtract the longterm mean from the mean to create an anomaly, I get a grid incompatibility error. The means file was sdfopened first, the longterm means file second. For example, doing Aug1969:</div>
<div><br></div><div><span class="Apple-style-span" style="border-collapse: collapse; font-family: arial, sans-serif; font-size: 13px; "><div>ga-> d air(time=aug1969)-air.2(t=8)</div><div>Operation error: Incompatable grids</div>
<div> Dimension ranges aren't equivalent</div><div> Dimension = 0</div><div> 1st grid range = 1 181 2nd = 1 181</div><div> Error ocurred at column 29</div><div>DISPLAY error: Invalid expression</div><div> Expression = air(time=aug1969)-air.2(t=8)</div>
<div><br></div><div>My workaround is to first regrid the longterm mean to a 2-deg linear grid, but it would be preferable to do a simple difference as in example above. The Webmaster suggests it's a GrADS bug. His response:</div>
<div><br></div></span></div><div><span style="border-collapse:collapse;font-family:arial, sans-serif;font-size:13px">"The grids are identical. This appears to be a GrADS bug. No such<br>
problem obtains in NCL. GrADS appears to insist that the longitudes<br>in the LTM file don't wrap, even when they are manually set to do so.<br>We have run every test we can think of, including dumping the longitudes<br>
from both files and comparing them. They are the same."</span></div><div><span style="border-collapse:collapse;font-family:arial, sans-serif;font-size:13px"><br></span></div><div><span style="border-collapse:collapse;font-family:arial, sans-serif;font-size:13px">I have tried this with OpenGrADS versions 2.0.a7.oga.3 and 2.0.a9.oga.3 with equal results, but have not tried with the COLA version of either. Can one of the developers or other user shed some light on this?</span></div>
<div><font class="Apple-style-span" face="arial, sans-serif"><span class="Apple-style-span" style="border-collapse: collapse;"><br></span></font></div><div><font class="Apple-style-span" face="arial, sans-serif"><span class="Apple-style-span" style="border-collapse: collapse;">I am using GrADS on a Windows XP.</span></font></div>
<div><span style="border-collapse:collapse;font-family:arial, sans-serif;font-size:13px"><div style="color:rgb(80, 0, 80)"><br></div><div style="color:rgb(80, 0, 80)">Stephen McMillan</div>
</span></div></div>
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