Problems with the gradient function

Dear all,

  I am running into a problem with the gradient function. The gradient
function is outputting missing values at pressure levels that are very
close to the surface (1000mb, 925mb, and 850mb), which is negatively
impacting a moisture budget I am trying to perform at one specific
location. I know this is an artifact of the function because the
specific humidity data I am using has data at each level except the
surface for the specific lat/lon location. The problem is the missing
values that are arising at levels above 1000mb. Is there a way to
mitigate this somehow?

I have tried to shrink the spatial domain of my data to remove high
elevation areas. This has helped slightly. However, I am still running
into missing values above 1000mb. The main goal is to obtain the
gradient of specific humidity at one point only, so the size of the
domain isn't a problem, assuming that there are enough data points to
perform the differencing scheme. Is there a way to perform the
gradient around missing values so as to not eliminate an entire level?
Has anyone had this problem before or worked with the gradient function?

     Thank you,
          Katie Holman
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Received on Tue Dec 1 13:26:01 2009