res@vcMonoVectorLineColor无效？

601337653

请问大家，我在用ncl画矢量图时，用到res@vcMonoVectorLineColor，可是ncl提示warning:vcMonoVectorLineColor is not a valid resource in uv1_vector at this time，为什么是无效的呢？和版本有关吗，我是6.0.0的，以下是脚本，大家帮忙看看
load"$NCARG_ROOT/lib/ncarg/nclscripts/csm/gsn_code.ncl"
load"$NCARG_ROOT/lib/ncarg/nclscripts/csm/gsn_csm.ncl"
begin
f=addfile("c:/uwnd.1991.nc","r")
h=addfile("c:/vwnd.1991.nc","r")
uwnd=f->uwnd(0,5,:,:)
vwnd=h->vwnd(0,5,:,:)
speed=sqrt(uwnd^2+vwnd^2)
wks=gsn_open_wks("png","uv1")
gsn_define_colormap(wks,"rainbow")
res=True
res@gsnDraw=False
res@gsnFrame=False
res@gsnMaximize=True
res@gsnLeftString="uv"
res@gsnRightString="m/s"
res@gsnAddCyclic=True
res@vcRefMagnitudeF=20
res@vcRefLengthF=0.09
res@vcGlyphStyle="CurlyVector"
res@vcMonoVectorLineColor=False
res@gsnSpreadColors=True
res@gsnSpreadColorStart=30
plot=gsn_csm_vector(wks,uwnd(::4,::4),vwnd(::4,::4),res)
end