ncl给图片的某一区域添加方框

gres                 = True
gres@gsLineThicknessF = 2.5 
gres@gsLineColor       = "black"
;gres@gsFillOpacityF=0.1
; gres@tfPolyDrawOrder = "Draw"  ; this can be used for polylines, polymarkers, or polygons
;SATE 40°N~75°N, 60°E~150°E
lat1 = (/75,  75, 40, 40, 75/)
lon1 = (/150, 60, 60, 150,150/)
;SATw  40°N~75°N, 30°W~120°W
lat2 = (/75,  75, 40, 40, 75/)
lon2 = (/-120, -30, -30, -120,-120/)

delete(gres@gsLineColor  )
gres@gsLineColor       = "red"
dum(0) = gsn_add_polyline(wks,plot(0),lon1,lat1,gres)
delete(gres@gsLineColor  )
gres@gsLineColor       = "blue"
dum(1) = gsn_add_polyline(wks,plot(0),lon2,lat2,gres)
delete(gres@gsLineColor  )
gres@gsLineColor       = "red"
dum(2) = gsn_add_polyline(wks,plot(1),lon1,lat1,gres)
delete(gres@gsLineColor  )
gres@gsLineColor       = "blue"
dum(3) = gsn_add_polyline(wks,plot(1),lon2,lat2,gres)
delete(gres@gsLineColor  )
gres@gsLineColor       = "red"
dum(4) = gsn_add_polyline(wks,plot(2),lon1,lat1,gres)
delete(gres@gsLineColor  )
gres@gsLineColor       = "blue"
dum(5) = gsn_add_polyline(wks,plot(2),lon2,lat2,gres)