想要风场与浓度的叠加，为何出两张图？

8-gods

想要出风场与pm浓度叠加，运行后X11下，先出了一张浓度场，点一下才出两者的叠加，我想直接出叠加的图。如果换回eps，只会有前一张图，提示只能出一张图。怎么办？
新手求教！！！
load "/usr/local/ncl/lib/ncarg/nclscripts/csm/gsn_code.ncl"
load "/usr/local/ncl/lib/ncarg/nclscripts/csm/gsn_csm.ncl"
load "/usr/local/ncl/lib/ncarg/nclscripts/csm/contributed.ncl"

begin

fn= "/md3200/storage2/ybchen/Model_Data/WRF/2010/wrfout_d01_2010-01-01_18:00:00.nc"
f=addfile(fn,"r")
fn1="/md3200/storage2/ybchen/CAMxnc/201001PSATareapoint/point/S/CAMx.EA20100102_31pointtest.20100102.avrg.grd01.nc"
f1 = addfile(fn1, "r")
u=f->U(Time|6,bottom_top|0, south_north|:,west_east_stag|:)
v=f->V(Time|6,bottom_top|0, south_north_stag|:,west_east|:)
PSO4f1=f1->PSO4(TSTEP|0,LAY|0,ROW|:,COL|:)
PNO3f1=f1->PNO3(TSTEP|0,LAY|0,ROW|:,COL|:)
PNH4f1=f1->PNH4(TSTEP|0,LAY|0,ROW|:,COL|:)
POAf1=f1->POA(TSTEP|0,LAY|0,ROW|:,COL|:)
PECf1=f1->PEC(TSTEP|0,LAY|0,ROW|:,COL|:)
FPRMf1=f1->FPRM(TSTEP|0,LAY|0,ROW|:,COL|:)
FCRSf1=f1->FCRS(TSTEP|0,LAY|0,ROW|:,COL|:)
SOA1f1=f1->SOA1(TSTEP|0,LAY|0,ROW|:,COL|:)
SOA2f1=f1->SOA2(TSTEP|0,LAY|0,ROW|:,COL|:)
SOA3f1=f1->SOA3(TSTEP|0,LAY|0,ROW|:,COL|:)
SOA4f1=f1->SOA4(TSTEP|0,LAY|0,ROW|:,COL|:)
SOA5f1=f1->SOA5(TSTEP|0,LAY|0,ROW|:,COL|:)
SOA6f1=f1->SOA6(TSTEP|0,LAY|0,ROW|:,COL|:)
SOA7f1=f1->SOA7(TSTEP|0,LAY|0,ROW|:,COL|:)
PCLf1=f1->PCL(TSTEP|0,LAY|0,ROW|:,COL|:)
SOPAf1=f1->SOPA(TSTEP|0,LAY|0,ROW|:,COL|:)
SOPBf1=f1->SOPB(TSTEP|0,LAY|0,ROW|:,COL|:)
pm25f1=PNO3f1+PSO4f1+PNH4f1+POAf1+PECf1+FPRMf1+FCRSf1+SOA1f1+SOA2f1+SOA3f1+SOA4f1+SOA5f1+SOA6f1+SOA7f1+PCLf1+SOPAf1+

filestring_name="2010010100windandpm25"
wks = gsn_open_wks("X11",filestring_name)
clbdft        = "nwt"
gsn_define_colormap(wks,clbdft)

  wtype          = "X11"
  wtype@wkWidth  = 2500
  wtype@wkHeight = 2500

uv_res  = True
pm25_res = True
uv_res@gsnDraw           = False
uv_res@gsnFrame          = False

uv_res=pm25_res
uv_res@gsnAddCyclic             =

uv_res@vcRefMagnitudeF          = 20.0
uv_res@vcRefLengthF             = 0.040
uv_res@vcGlyphStyle             = "WindBarb"
uv_res@vcMinDistanceF           = 0.03
uv_res@vcRefAnnoOrthogonalPosF  = .1
uv_res@vcMonoWindBarbColor = False


pm25_res@gsnSpreadColors   = True
pm25_res@cnFillOn          = True
pm25_res@cnFillMode        = "RasterFill"
pm25_res@cnLinesOn         = False
pm25_res@cnLineLabelsOn    = False
pm25_res@cnInfoLabelOn       = True
pm25_res@cnInfoLabelOrthogonalPosF = -0.04
pm25_res@cnLevelSelectionMode= "AutomaticLevels"

  pm25  = gsn_csm_contour(wks,pm25f1,pm25_res)


  uv = gsn_csm_vector(wks,u(0:159,0:199),v(0:159,0:199),uv_res)
draw(uv)
overlay(pm25,uv)

draw(pm25)
frame(wks)
system("convert -trim "+filestring_name+".eps "+filestring_name+".png")

end