What's the difference between U_gll and U, and between V_gll and V

[jihwang@colorado_edu]

Dear All:

I just realized that there is output U_gll and V_gll. They are the wind field on GLL grid. However, I don't really understand what U or V on GLL grid means.

Can anybody tell me more specifically what's the difference between U_gll and U, and between V_gll and V?

Thanks a lot.

Aaron