ust = rhoa*exf_BulkCdn(usm)*us*uw
vst = rhoa*exf_BulkCdn(usm)*us*vw
_RL exf_BulkCdn
exf_BulkCdn = cdrag_1/umps + cdrag_2 + cdrag_3*umps
_RL function exf_BulkCdn(
tmpbulk= exf_BulkCdn(sh)
tmpbulk= exf_BulkCdn(uzn)
exf_BulkCdn = 0.0