x轴的标签和坐标轴的数字重叠在一起了咋办？

601337653

各位前辈，我刚学ncl，想试着画几张图，画的过程中遇到点问题想请教下大家，图如下，x轴的标签longitude和坐标重叠在一起了，y轴的就不会，这是什么原因？应该要怎么设置呢？脚本如下：（ps：填色部分太丑，大家不要见怪哈）
load"$NCARG_ROOT/lib/ncarg/nclscripts/csm/gsn_code.ncl"
load"$NCARG_ROOT/lib/ncarg/nclscripts/csm/gsn_csm.ncl"
load"$NCARG_ROOT/lib/ncarg/nclscripts/csm/contributed.ncl"
load"$NCARG_ROOT/lib/ncarg/nclscripts/csm/shea_util.ncl"
begin
f=addfile("c:/hgt.2003.nc","r")
b=addfile("$NCARG_ROOT/lib/ncarg/data/cdf/landsea.nc","r")
hgt=short2flt(f->hgt(0,5,:,:))
oro=landsea_mask(b->LSMASK,hgt&lat,hgt&lon)
land_only=mask(hgt,oro.eq.0,False)
copy_VarMeta(hgt,land_only)
wks=gsn_open_wks("png","hgt")
gsn_define_colormap(wks,"rainbow")
hgt@units="dgam"
hgt&lon@units="degrees-east"
hgt&lat@units="degrees-north"
res=True
res@gsnAddCyclic=False
res@cnLevelSelectionMode="ManualLevels"
res@gsnMaximize=True
res@mpMinLatF=0
res@mpMaxLatF=90
res@mpMinLonF=40
res@mpMaxLonF=160
res@cnMinLevelValF=5000
res@cnMaxLevelValF=5880
res@cnLevelSpacingF=40
res@gsnSpreadColors=True
res@gsnSpreadColorStart=30
res@cnFillOn=True
res@cnLinesOn=False
res@lbBoxLinesOn=False
res@lbOrientation="Vertical"
res@tiMainString="500hpa"
res@tiXAxisString="longitude"
res@tiYAxisString="latitude"
res@gsnLeftString="hgt"
res@gsnCenterString=" "
res@tmXBLabelFontHeightF = 0.02
res@tmYLLabelFontHeightF = 0.02
plot=gsn_csm_contour_map(wks,land_only,res)
end

cc4936

res@pmTickMarkDisplayMode = "Always"