WRF U/V wind basic; wind_d->math_d
为什么要提这么basic的东西？因为u/v->Vt/Vr需要使用math angle, 而我的polar transform使用的是wind angle，差点踩坑了……
for example, ncl script doing Vt/Vr calculation by this:
Vt(it,len,ang) = va_po(it,len,ang)*cos(1.*ang*pp)-ua_po(it,len,ang)*sin(1.*ang*pp)
Vr(it,len,ang) = va_po(it,len,ang)*sin(1.*ang*pp)+ua_po(it,len,ang)*cos(1.*ang*pp)
The \(1.*ang*pp\) here is theta, and is math angle, not wind angle!