cdn=(0.5+0.091*u10n)*0.001#Smith et al. 1991 #(0.27 + 0.116*u10n)*0.001 Smith et al. 1992
# Smith et al. 1991 #(0.27 + 0.116*u10n)*0.001 Smith et al. 1992
cdn=(0.5+0.091*u10n)*0.001
elif(method=="HEXOSwave"):
cdn=cdn_from_roughness(u10n,Ta,Tp,method)
elif(method=="YT96"):
cdn=np.where((u10n<6)&(u10n>=3),(0.29+3.1/u10n+7.7/u10n**2)*0.001,np.where((u10n<=26)&(u10n>=6),(0.60+0.070*u10n)*0.001,(0.61+0.567/u10n)*0.001))# for u<3 same as Smith80