4 SUBROUTINE ustarhb(knon, u, v, cd_m, ustar)
 
   31   REAL zxt, zxq, zxu, zxv, zxmod, taux, tauy
 
   41     zx_alf2 = 1.0 - zx_alf1
 
   42     zxu = u(i, 1)*zx_alf1 + u(i, 2)*zx_alf2
 
   43     zxv = v(i, 1)*zx_alf1 + v(i, 2)*zx_alf2
 
   44     zxmod = 1.0 + sqrt(zxu**2+zxv**2)
 
   45     taux = zxu*zxmod*cd_m(i)
 
   46     tauy = zxv*zxmod*cd_m(i)
 
   47     ustar(i) = sqrt(taux**2+tauy**2)
 
subroutine ustarhb(knon, u, v, cd_m, ustar)