Fig. (8) The dd1000 versus dd850 (geostrophic direction; “geo dir” in figures) at 12Z: a) PT-W JJA, example for the “Low troposphere Inversion” 1st category; b) HN DJF, “not well-defined” 2nd category c) CLN-D DJF 3rd “Cyclone activity” category. Note the significantly different ranges of axes for each graph.