"E181" . . . . "The surface called \"surface\" means the lower boundary of the atmosphere. \"Northward\" indicates a vector component which is positive when directed northward (negative southward). \"Downward\" indicates a vector component which is positive when directed downward (negative upward). \"Downward northward\" indicates the ZY component of a tensor. A downward northward stress is a downward flux of northward momentum, which accelerates the lower medium northward and the upper medium southward. The surface downward stress is the windstress on the surface." . "Climate and Forecast (CF)" . . "surface downward northward stress" .