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subroutine getfields(firststep,itime,indexf,idiff,nstop)
C i i o o o
********************************************************************************
* *
* This subroutine manages the 3 data fields to be kept in memory. *
* During the first time step of petterssen it has to be fulfilled that the *
* first data field must have |wftime|<itime, i.e. the absolute value of wftime*
* must be smaller than the absolute value of the current time in [s]. *
* The other 2 fields are the next in time after the first one. *
* Pointers (memind) are used, because otherwise one would have to resort the *
* wind fields, which costs a lot of computing time. Here only the pointers are*
* resorted. *
* *
* Author: A. Stohl *
* *
* 29 April 1994 *
* *
********************************************************************************
* *
* Variables: *
* firststep .true. for first time step of petterssen, else .false. *
* idiff [s] time difference between the two wind fieldse read in *
* indj indicates the number of the wind field to be read in *
* indmin remembers the number of wind fields already treated *
* memind(3) pointer, on which place the wind fields are stored *
* memtime(3) [s] times of the wind fields, which are kept in memory *
* itime [s] current time since start date of trajectory calculation *
* ldirect 1 for forward trajectories, -1 for backward trajectories*
* nstop > 0, if trajectory has to be terminated *
* nx,ny,nuvz,nwz field dimensions in x,y and z direction *
* uu(0:nxmax-1,0:nymax-1,nuvzmax,3) wind components in x-direction [m/s] *
* vv(0:nxmax-1,0:nymax-1,nuvzmax,3) wind components in y-direction [m/s] *
* ww(0:nxmax-1,0:nymax-1,nwzmax,3)wind components in z-direction [deltaeta/s] *
* tt(0:nxmax-1,0:nymax-1,nuvzmax,3) temperature [K] *
* ps(0:nxmax-1,0:nymax-1,3) surface pressure [Pa] *
* *
* Constants: *
* idiffnorm normal time difference between 2 wind fields *
* idiffmax maximum allowable time difference between 2 wind fields *
* *
********************************************************************************
include 'includepar'
include 'includecom'
integer indj,indmin,l,itime,indexf,idiff,nstop,memhelp
logical firststep
save indmin
data indmin/1/
C Check, if wind fields are available for the current time step
***************************************************************
if ((ldirect*wftime(1).ge.ldirect*itime).or.
+(ldirect*wftime(numbwf).le.ldirect*itime)) then
write(*,*) 'FLEXTRA WARNING: NO WIND FIELDS ARE AVAILABLE.'
write(*,*) 'A TRAJECTORY HAS TO BE TERMINATED.'
nstop=4
return
endif
******************************************************************************
C For the first time step of petterssen, arrange the wind fields in such a way
C that 1st wind field is before itime and 2nd and 3rd are after itime.
******************************************************************************
if (firststep) then
if ((ldirect*memtime(1).lt.ldirect*itime).and.
+ (ldirect*memtime(2).ge.ldirect*itime)) then
C The right wind fields are already in memory -> don't do anything
******************************************************************
continue
else if ((ldirect*memtime(2).lt.ldirect*itime).and.
+ (ldirect*memtime(3).ge.ldirect*itime)) then
C Current time is between 2nd and 3rd wind field
C -> Resort wind field pointers, so that current time is between 1st and 2nd
****************************************************************************
memhelp=memind(1)
do 10 l=1,2
memind(l)=memind(l+1)
10 memtime(l)=memtime(l+1)
memind(3)=memhelp
C Read a new wind field and store it on place memind(3)
*******************************************************
do 30 indj=indmin,numbwf-2
if ((ldirect*wftime(indj).lt.ldirect*itime).and.
+ (ldirect*wftime(indj+1).ge.ldirect*itime)) then
call readwind(indj+2,memind(3))
call readwind_nests(indj+2,memind(3))
memtime(3)=wftime(indj+2)
goto 40
endif
30 continue
40 indmin=indj
else
C No wind fields, which can be used, are currently in memory
C -> read all 3 wind fields
************************************************************
do 50 indj=indmin,numbwf-1
if ((ldirect*wftime(indj).lt.ldirect*itime).and.
+ (ldirect*wftime(indj+1).ge.ldirect*itime)) then
memind(1)=1
call readwind(indj,memind(1))
call readwind_nests(indj,memind(1))
memtime(1)=wftime(indj)
memind(2)=2
call readwind(indj+1,memind(2))
call readwind_nests(indj+1,memind(2))
memtime(2)=wftime(indj+1)
memind(3)=3
call readwind(indj+2,memind(3))
call readwind_nests(indj+2,memind(3))
memtime(3)=wftime(indj+2)
goto 60
endif
50 continue
60 indmin=indj
endif
indexf=1
idiff=abs(memtime(2)-memtime(1))
*****************************************************************************
C For 2nd step of petterssen all necessary data fields are already in memory.
C Just look, if current temporal position is between the first two fields or
C between the 2nd and 3rd field.
*****************************************************************************
else
if ((ldirect*memtime(1).lt.ldirect*itime).and. !between 1st and 2nd
+ (ldirect*memtime(2).ge.ldirect*itime)) then
indexf=1
idiff=abs(memtime(2)-memtime(1))
else if ((ldirect*memtime(2).lt.ldirect*itime).and. !between 2nd and 3rd
+ (ldirect*memtime(3).ge.ldirect*itime)) then
indexf=2
idiff=abs(memtime(3)-memtime(2))
endif
endif
C Check the time difference between the wind fields. If it is too
C big, terminate the trajectory.
******************************************************************
if (idiff.gt.idiffmax) nstop=3
return
end
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