SUBROUTINE EXTRAP1D_SURFACEWIND_X(numInterpSets, srcNumLevels, 
destNumLevels, src_ijDim, dst_ijDim, vLevelSource, stateSource, stateDerivSource, 
posnDestInSrc, vLevelDestn, stateDestn, stateDerivDestn, extrapEnableDown, 
extrapEnableUp, extrapGuideDown, extrapGuideUp, m_slStateValue, numExtArraysIn,
numExtArraysOut, ExtArraysIn, ExtArraysOut)

integer, intent(in) :: numInterpSets
integer, intent(in) :: srcNumLevels
integer, intent(in) :: destNumLevels

integer, intent(in) :: src_ijDim
integer, intent(in) :: dst_ijDim

real, dimension(src_ijDim, srcNumLevels), intent(in) :: vLevelSource
real, dimension(src_ijDim, srcNumLevels), intent(in) :: stateSource
real, dimension(src_ijDim, srcNumLevels), intent(in) :: stateDerivSource

integer, dimension(dst_ijDim, destNumLevels), intent(in) :: posnDestInSrc
real, dimension(dst_ijDim, destNumLevels), intent(in) :: vLevelDestn
real, dimension(dst_ijDim, destNumLevels), intent(out) :: stateDestn
real, dimension(dst_ijDim, destNumLevels), intent(out) :: stateDerivDestn

logical, intent(in) :: extrapEnableDown, extrapEnableUp
real, intent(in) :: extrapGuideDown, extrapGuideUp

external m_slStateValue

integer, intent(in) :: numExtArraysIn
integer, intent(in) :: numExtArraysOut
real, dimension(src_ijDim, numExtArraysIn), intent(in)  :: ExtArraysIn
real, dimension(dst_ijDim, numExtArraysOut), intent(out) :: ExtArraysOut
DESCRIPTION 
This routine has the same effect for vectors (i.e. the wind) as Extrap1D_Surface_X
has for scalars.

For each destination level that is between the two lowest source levels, a state
value (but not a derivative) is extrapolated.  It is presumed that the lowest level
supplied represents the Earth's surface; however, the value at that level is ignored
and the value of zero is used by the passed routine.  Technically, that makes this
an interpolation, or perhaps a guided extrapolation of the results from the forecast
model.  Other values that would be interpolated, or extrapolated upward, are
untouched by the routine.

Through the routine that is passed as an argument, this extrapolation takes into
account the physics that governs diffusion near the Earth's surface.  Thus, it is
not applied to extrapolation above the highest vertical level.  Moreover, it should
not be used for a general mathematical extrapolation; the algorithm makes sense
only when considering the surface of the Earth.

N.B.:  It must be noted that the routine passed as an argument probably (This cannot
       be stated absolutely, because the user is free to supply whatever routine he
       sees fit, provided that it respects the interface.) presumes that
       the location of each vertical level is given as z (meters above the Earth's
       surface).  If this is the case, vLevelSource and vLevelDestn must be in z.

       Furthermore, that same routine probably presumes that the lowest level
       represents the Earth's surface.  The stateSource values given for that level
       should be true values and not those given by the model (GEM).

       The 'extrapolation' performed by this routine is thus an interpolation
       over the interval between the Earth's surface and the next vertical level.

Author: Jeff Blezius - revised Oct 2003
ARGUMENTS

It can be noted that the arguments to all of the Interp1D_* and Extrap1D_* routines are identical, for ease of switching a call from one to another of them. You should examine the generic description of the arguments. The following are uses of the generic arguments that are specific to this routine:

Input:
extrapGuideDown	maximum wind direction change, in radians, between the surface and the top of the surface layer. This parameter guides the extrapolation. The value of this parameter is typically received from the routine, sltop_uv, of the physical library.
extrapGuideUp	unused
ExtArraysIn	all 6 entries are used
Output:
stateDerivDestn(dst_ijDim, dstNumLevels)	unused
ExtArraysOut	both entries are used

SEE ALSO