Python Xarray module provides a built-in function to group together months of a specific season and calculate seasonal means. This is straightforward for most seasons, but calculating the DJF mean (December-January-February) requires additional effort, as it spans months from two consecutive years (e.g., December of 1989 and January-February of 1990). Simply taking the annual mean of the DJF months would yield erroneous results, as it would calculate seasonal means for each individual year. Correctly calculating DJF seasonal means can be achieved using various methods. Below, I will demonstrate three different approaches. DJF seasonal mean: Here, I am briefly explaining the Method 1 only. Method 2 and 3 should be self-explanatory. Method 1 Step 1: Select only the DJF months first. Rest will be masked out with nan values. Step 2: Apply 3-months rolling mean to calculate DJF mean values. Only the January values will be available. Why?? (Think carefully!!) Step3: Group by years. Annual mean doesn't impact at all since there is only January value in each year. Note that, the first year will have nan value. MAM/JJA/SON:
Rest of the seasons can be calculated in a single line. Here is the example of SON. Vx_FC_SON = Vx_FC.sel(time=Vx_FC['time.season']=='SON').groupby('time.year').mean('time')
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AuthorMahdi Hasan Archives
September 2023
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