K index

Calculate k index from FNL data.

#Add file
f = addfile('D:/Temp/grib/fnl_20110416_00_00')
#Calculate K index
#850hPa
T850 = f['Temperature_isobaric'][0,'85000.0','10:35','90:125'] - 273.16
rh = f['Relative_humidity_isobaric'][0,'85000.0','10:35','90:125']
Td850 = T850-((14.55+0.114*T850)*(1-0.01*rh) + pow((2.5+0.007*T850)*(1-0.01*rh),3) + (15.9+0.117*T850)*pow((1-0.01*rh),14))
#700hPa
T700 = f['Temperature_isobaric'][0,'70000.0','10:35','90:125'] - 273.16
rh = f['Relative_humidity_isobaric'][0,'70000.0','10:35','90:125']
Td700 = T700-((14.55+0.114*T700)*(1-0.01*rh) + pow((2.5+0.007*T700)*(1-0.01*rh),3) + (15.9+0.117*T700)*pow((1-0.01*rh),14))
#500hPa
T500 = f['Temperature_isobaric'][0,[50000.0],[10,35],[90,125]] - 273.16
K = T850-T500+Td850-(T700-Td700)
#Plot
axesm()
geoshow('country', edgecolor='k')
levs = arange(-40,36,2.5)
layer = contour(K, levs)
clabel(layer)
colorbar(layer)
t = f.gettime(0)
title('K index (' + t.strftime('%Y-%m-%d %H:00') + ')')