quit
ncl

  f   = addfile("air.day.ltm.nc","r")
  TT := f->air                             ; (time | 365] x [lat | 73] x [lon | 144]
  TT  = TT-273.15
  TT@units = "degC"
 
  ymd = cd_calendar(TT&time, -2)   ; yyyymmdd

  t  = TT                                                ; local [deleted upon exit]
  if (.not.isatt(t,"_FillValue"))
      t@_FillValue = 1e20
  end if

  dimt = dimsizes(t)
  rankt= dimsizes(dimt)
  ntim = dimt(0)

  testValue=0  ;;;;;pick the testvalue





if (rankt.eq.3) then                               ; T[*][*][*] => T(time,lat,lon)
      nlat = dimt(1)
      mlon = dimt(2)
      it3   = new((/nlat,mlon/), "integer", -999)
      copy_VarCoords(t(0,:,:),it3)
      it3@long_name = "temporal index for Cross-Over"
      if (.not.(all(t.le.testValue) .or. all(t.ge.testValue))) then
          do nl=0,nlat-1
            do ml=0,mlon-1
               t3= t(:,nl,ml)
               if (.not.(all(t3.le.testValue) .or. all(t3.ge.testValue))) then
                   t3= where(t3.ge.testValue, t3@_FillValue, t3); 
                   t3 = where(.not.ismissing(t3),testValue,t3)   
                   it3(nl,ml) = dim_maxind(t3,0)                ; !!!!!indices of last occurence of testValue
               end if
            end do
          end do
          return(it3)
      end if
  end if           


if (rankt.eq.3) then                               ; T[*][*][*] => T(time,lat,lon)
      nlat = dimt(1)
      mlon = dimt(2)
      it   = new((/nlat,mlon/), "integer", -999)
      copy_VarCoords(t(0,:,:),it)
      it@long_name = "temporal index for Cross-Over"
      if (.not.(all(t.le.testValue) .or. all(t.ge.testValue))) then
          do nl=0,nlat-1
            do ml=0,mlon-1
               t1 = t(:,nl,ml)
               if (.not.(all(t1.le.testValue) .or. all(t1.ge.testValue))) then
                   t1= where(t1.le.testValue, t1@_FillValue, t1); 
                   t1 = where(.not.ismissing(t1),testValue,t1)      
                   it(nl,ml) = dim_minind(t1,0)                ; !!!!!indices of 1st occurence of testValue
               end if
            end do
          end do
          return(it)
      end if
  end if           
 
 test=it3-it       ;;;;;;;;test the indices
 printMinMax(test,0)
 
  dimITT = dimsizes(it)
  nlat   = dimITT(0)
  mlon   = dimITT(1)
  lat    = TT&lat
  lon    = TT&lon
date=new((/73,144/),float)
  do nl=0,nlat-1
    do ml=0,mlon-1
       nt  = it(nl,ml)
       if (.not.ismissing(nt)) then
         date(nl,ml)=ymd(nt)
		 ; print("("+nl+","+ml+"): ("+lat(nl)+","+lon(ml)+")  nt="+nt+"  ymd="+ymd(nt)+"  TT(nt,nl,ml)="+TT(nt,nl,ml))
       else
	       date(nl,ml)=-999
           ;print("("+nl+","+ml+") has no cross-over")
       end if
    end do
  end do