Many methods in meteorology consider a threshold of grid points that satisfy a certain criterion. I want to select, from daily Era-Interim gridded data, those days in with areas of potential vorticity greater than 20 grid points.
you can use if / else / endif statement in Grads scripting. For example
One way to control the flow of script execution is via the if/else/endif construct. The format is as follows:
if expression script record script record . . else script record . . endif
for more documentation please check: http://cola.gmu.edu/grads/gadoc/script.html
Here is some Matlab coding that should be able to be modified for Grads pretty easily; that takes advantage of the power of matrices and indexing which are common to both Matlab and Grads
So if you take an array (e.g., velocity) and test for a variable (speed) criteria; e.g., speed greater than 33 knots; so then you just find an index (sel2) and then apply that index to the original dataset to subset the data you want. So, essentially only two lines vice a lot of ifs/endifs/elseifs, etc.
sel2 = find (speed > 33); %sel2 becomes your index variable
NEWvelocity = velocity (:,sel2);
So now you have a new matrix (NEWvelocity) with just wind speeds > 33 kts
Thank you. But, how can I count the number of grid points that fulfill that condition? (Wind speed > 33 kts).
%Create a new matrix;
NANvelocity =velocity;
%Select Storm Intensities and set to NaN to count later
sel2 = find (wind_speed > 33);
NANvelocity (sel2)=isnan(sel2);
NANvelocity(sel2) = NaN;
yy=isnan(NANvelocity);
%Count Up NaNs
zz = sum(yy); %sums each column for number of NaNs
hh = sum(zz); %Total number of NaNs
So, here you are using NaNs as a proxy for velocity > 33; and hh is the number you want. Give it a try.
We find the solution for the question.
This is the code. We create a counter that sweep the study area from southwest to northeast. It counts values greater than -80 but lower than -2.
Then with the option prnopts and write we include these values in a .txt file
(Thanks to Kelita Quispe).
k=0
contar=0
while (k
Okay; whatever works for you; I like to avoid a lot of if/endif/else statements and use the power of the vector matrices, but again, if that works for you, great!
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