Date: Wed Feb 29 2012 - 13:00:49 MST
Hello
I'm trying to calculate the advection term (u*(dT/dx)+v*(dT/dy)). I wanted
to do this in 2 steps: 1st step is to calculate the gradient, the 2nd is to
multiply it by u and v
So I calculated gradient as shown in the example:
http://www.ncl.ucar.edu/Document/Functions/Built-in/igradsF.shtml
T_grad_lon = theta ; create arrays to hold output, same
size and type as input
T_grad_lat = theta
; this procedure will overwrite
; values in T_grad_lon and T_grad_lat
*gradsf* <http://www.ncl.ucar.edu/Document/Functions/Built-in/gradsf.shtml>
(theta, T_grad_lon, T_grad_lat)
T_grad_lon@long_name = "longitudinal gradient (derivative)"
T_grad_lat@long_name = "latitudinal gradient (derivative)"
theta = *igradsF* (T_grad_lon, T_grad_lat)
Then I had to multiply gradient by u and v to get (u*(dT/dx)+v*(dT/dy).
I did 2 different ways:
1st way.
u*T_grad_lat+v*T_grad_lon. You may see on the picture ("1way.png")
that the plot looks pretty much the same all over the domain. I don't
see the maximum advection where it is supposed to be by the west coast
of Greenland.
2 way
u*theta+v*theta. I got the right pattern, but values are off. There
can't be advection 700 K/s.
I think that this way is not correct because theta has 2 dimensions:
theta(T_grad_lon,T_grad_lat), so when I do the multiplication (
u*theta+v*theta) I end up having:
u*T_grad_lon+u*T_grad_lat+v*T_grad_lon+v*T_grad_lat, whereas I need
only 2 highlighted terms
Could you help me find out what is wrong and how can I get it fixed?
-- regards ******************************************************* *Alexander Semenov* * * PhD Student - Research Assistant International Arctic Research Center Department of atmospheric sciences University of Alaska Fairbanks 930 Koyukuk dr, 408c3 Fairbanks, AK, USA, 99775 work phone +19074742672
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