I am doing SST experiment , where I have made change in SST_1DEG.f file , The piece of code is in bold attached below.

C ****** PRINT OUT DATA AS A CHECK
IF(NMO.EQ.1) CALL PRINTL ( SST2, MLON, NLAT )

            CALL BILINX( SST2, LONI, LATI, MLON, NLAT
     &                 , SSTMM, XLON, XLAT,   IY,   JX, 1 )
            PRINT *,'XLON,XLAT,SST=', XLON(1,1), XLAT(1,1), SSTMM(1,1)

            DO J=1,JX
            DO I=1,IY
C ************      CHANGE SST HERE ONLY
                IF(I.GE.2.and.I.LE.75.and.J.GE.5.and.J.LE.110) then
                  SSTMM(I,J)=SSTMM(I,J) + 0.5

               ELSE IF(SSTMM(I,J).GT.-100.) then
                  SSTMM(I,J)= SSTMM(I,J) + 273.15
               ELSE
                  SSTMM(I,J) = -9999.
               ENDIF
               if (LSMTYP.eq.'BATS'.and.sstmm(I,J).lt.-5000. .and.
     &             (lu(i,j).gt.13.5.and.lu(i,j).lt.15.5)) then
                 do k=1,20
                   lund(k) = 0.0
                 end do

Now the NAN problem occur when we execute regcm.x scripts. we have change dt value with 20 ,30,40,50,60,70, 80,90,100 and changed the value of abatm 3 times respectively ,In all cases we got same error.

OUT-history written date =    2009070100.00000
BATS variables written at   2009070100 0.333333333333333
Writing rad fields at ktau =            1 2009070100

******* OPENING NEW OUTPUT FILES: 2009070100
OPENING NEW OUT FILE: output/ATM.2009070100
OPENING NEW BAT FILE: output/SRF.2009070100
OPENING NEW RAD FILE: output/RAD.2009070100
     at day =    0.0113, ktau =         50 : 1st, 2nd time deriv of ps = 0.14308E-03 0.96722E-06, no. of points w/convection =    1998
     at day =    0.0229, ktau =        100 : 1st, 2nd time deriv of ps = 0.13989E-03 0.10220E-05, no. of points w/convection =    1814
     at day =    0.0345, ktau =        150 : 1st, 2nd time deriv of ps = 0.14030E-03 0.11685E-05, no. of points w/convection =    1595
     at day =    0.0461, ktau =        200 : 1st, 2nd time deriv of ps = NaN         NaN        , no. of points w/convection =       0
     at day =    0.0576, ktau =        250 : 1st, 2nd time deriv of ps = NaN         NaN        , no. of points w/convection =       0
forrtl: error (69): process interrupted (SIGINT)
Image              PC                Routine            Line        Source
regcm              00000000004DF63B Unknown               Unknown Unknown
regcm              00000000004C7E9C Unknown               Unknown Unknown
regcm              00000000004032DC Unknown               Unknown Unknown
libc.so.6          000000368F21D8B4 Unknown               Unknown Unknown
regcm              00000000004031E9 Unknown               Unknown Unknown

Please look into the problem and reply with your valuable suggestion.

--
Rajesh Kumar Maurya
M.Sc(Tech)- Geophysics(Meteorology); Junior Research Fellow & Research Scholar
Department of Geophysics
Banaras Hindu University
Varanasi 221005