Fig. 4: Radar evolution for NBEs polarity transition.

a Evolution of NBEs. The blue ‘’ presents negative NBEs while the red ‘’ represents positive NBEs. The colored dashed line represents the height variations of radar reflectivity. The dashed gray, blue, and orange lines present the maximum height of 15 dBZ, 30 dBZ, and 40 dBZ derived from the vertical cross-section radar, respectively. b Vertical cross-section radar profile of NBEs during the upwelling stage. The deep red contour shows a large reflectivity echo (>35 dBZ); the dim blue contour indicates a low reflectivity echo (<35 dBZ). NBEs within 10 km of the cross-section line on the plane position indicator (PPI) is overlaid on the vertical cross-section. The red ‘’ presents positive NBEs while the blue ‘’ represents negative NBEs. c Vertical cross-section radar profile of NBEs during the decaying stage. d Variations in the area of reflectivity above 35 dBZ (S_35dBZ) and the volume (V_35dBZ) of reflectivity above 35 dBZ at altitudes higher than 10 km around NBEs activity.