Fig. 1: Weak stratospheric wave events in ERA5 reanalysis.
From: Extreme stratospheric wave activity as harbingers of cold events over North America
Composites of days −5, 0, 5, and 10 with respect to the onset of weak stratospheric wave events: a 10 hPa geopotential height (contours at 500 m intervals, 29000 m contour bolded, anomalies shaded). b 100 hPa geopotential height (contours at 200 m intervals, 15200 m contour bolded, anomalies shaded). c 100 hPa vertical component of Plumb wave activity flux (contours at 0.01 m2s−2 intervals, anomalies shaded). d anomalous SLP (contours at 2 hPa intervals) and SAT (shading). The time evolution is smoothed by a 5-day running average (i.e., day −5 is the average of days −7 to −3). The weak wave events are defined by the 5th percentile of the first principal component of the zonally asymmetric component of 10 hPa geopotential height. See details in Methods. Stippling indicates the regions where the anomalies are significant at the 95% confidence level based on the Student’s t-test.
