Variation of (A), (C) zonal mean temperature between 10 and 20 km and at 2.5 km, respectively, as a function of season and latitude and (B), (D) RMS(T’) between 10 and 20 km and at 2.5 km, respectively, as a function of season and latitude. In (A), the solid black contours are the zonal-average zonal wind (m s⁻¹). In (A) and (B), the 140 K and 170 K contours are in solid white and dashed–dotted white, respectively. In (C) and (D), the white contour is the 150 K contour, and the black dashed–dotted contour is the approximate edge of the seasonal polar ice cap.