please help me calculate the frequency

[na na]

Thank you very much for your ideas.
  What I was trying to do is to make a bar plot for NYC and to show how many days during these 20 years have higher than normal temperatures or precipitation.
  I think I can figure out a way to do it based on your sum and mask idea.
  Thank you,


  Mary Jo Nath <Mary-Jo.Nath at NOAA.GOV> wrote:
  Diana,

I'm not exactly sure what you are trying to do. But maybe this example will help you figure a solution.
Ex:
Say you have a lat-lon grid, temp, which has 20*365 (=7300) days of data, and you just want to sum up the number of days over that period at each grid point when the temperature was > 300. You could do something like:

'define ndays = sum( maskout(temp/temp,temp-300.), t=1,t=7300)'

"sum" is a grads function which sums over the dimensions specified. In this case, we sum over time. (Please see the grads documentation for full explanation.)
ndays is a new lat-lon field created by adding the value of one (="temp/temp") for each grid point and day over the period from t =1 to t = 7300 whenever "temp-300" > 0.. (At whichever grid point and time  temp < 300,  maskout will set "temp/temp" = missing for that grid point and time and not included it in the sum).

Does this help?
MJ

na na wrote:     Dear all,
  I am trying to find the frequency of extreme events ( higher than normal temperatures and precipitation) from 20 years of daily .nc data. I don't know how to calculate the frequency so I thouhgt that if I construct a loop through time it would work. So, I tried to construct a loop to pull from these 20 years only values of temperature higher than a certain value (for example tmax > 300K) but it didn't work and I don't know what else to do. Can anyone please please help me with an advice?
  Thank you,

  Diana Pop


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Diana Pop
research assistant
Hunter College, CUNY

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