C&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&
      SUBROUTINE VDIFQ(LMHK,KTM,DTQ2,Q2,EL,Z)
C     ******************************************************************
C     *                                                                *
C     *  VERTICAL DIFFUSION                                            *
C     *                                                                *
C     ******************************************************************
C-----------------------------------------------------------------------
      INCLUDE "parmeta"
#include "sp.h"
C-----------------------------------------------------------------------
                             P A R A M E T E R
     &(LP1=LM+1,LM1=LM-1,LM2=LM-2)
                             P A R A M E T E R
     &(ESQ=0.20,ELZ0=0.)
C-----------------------------------------------------------------------
                             D I M E N S I O N
     & Q2    (LM)
                             D I M E N S I O N
     & EL    (LM1)
     &,Z     (LP1)
                             D I M E N S I O N
     & CM    (LM2),CR    (LM2),RSQ2  (LM2),AKQ   (LM2),DTOZ  (LM2)
C-----------------------------------------------------------------------
C***********************************************************************
      DTDIF=DTQ2/FLOAT(KTM)
      LMHM=LMHK-1
      LMH2=LMHK-2
      LMHP=LMHK+1
C-----------------------------------------------------------------------
                             DO 300 KT=1,KTM
C-----------------------------------------------------------------------
          DO 100 L=1,LMH2
      DTOZ(L)=(DTDIF+DTDIF)/(Z(L)-Z(L+2))
      AKQ(L)=SQRT((Q2(L)+Q2(L+1))*0.5)*(EL(L)+EL(L+1))*0.5*ESQ
     &      /(Z(L+1)-Z(L+2))
      CR(L)=-DTOZ(L)*AKQ(L)
 100  CONTINUE
C
      CM(1)=DTOZ(1)*AKQ(1)+1.
      RSQ2(1)=Q2(1)
C-----------------------------------------------------------------------
          DO 110 L=2,LMH2
      CF=-DTOZ(L)*AKQ(L-1)/CM(L-1)
      CM(L)=-CR(L-1)*CF+(AKQ(L-1)+AKQ(L))*DTOZ(L)+1.
      RSQ2(L)=-RSQ2(L-1)*CF+Q2(L)
 110  CONTINUE
C-----------------------------------------------------------------------
      DTOZS=(DTDIF+DTDIF)/(Z(LMHM)-Z(LMHP))
      AKQS=SQRT((Q2(LMHM)+Q2(LMHK))*0.5)*(EL(LMHM)+ELZ0)*0.5*ESQ
     &    /(Z(LMHK)-Z(LMHP))
C
      CF=-DTOZS*AKQ(LMH2)/CM(LMH2)
C-----------------------------------------------------------------------
      Q2(LMHM)=(DTOZS*AKQS*Q2(LMHK)-RSQ2(LMH2)*CF+Q2(LMHM))
     &        /((AKQ(LMH2)+AKQS)*DTOZS-CR(LMH2)*CF+1.)
C
          DO 120 IVI=1,LMH2
      L=LMHM-IVI
      Q2(L)=(-CR(L)*Q2(L+1)+RSQ2(L))/CM(L)
 120  CONTINUE
C-----------------------------------------------------------------------
 300                         CONTINUE
C-----------------------------------------------------------------------
                             RETURN
                             END