Fig. 8: Variability in zonal wave three (ZW3) index. | npj Climate and Atmospheric Science

Fig. 8: Variability in zonal wave three (ZW3) index.

From: Record low sea ice extent in the Weddell Sea, Antarctica in April/May 2019 driven by intense and explosive polar cyclones

Fig. 8

Normalized anomalies of geopotential height at 500 hPa during (a) February‒March 2019, (b) April 2019 and (c) May 2019, relative to the climatology of 1979–2008. Black dot (plus) marks showed the values that exceeded 2 (4) standard deviation from the climatological mean. White dots marked in figure-a represent the locations used for computing amplitudes of ZW3 index in the present study (Methods section ‘Atmospheric reanalysis’, Figure d). Locations used in the previous studies are shown in blue14 and green18 dots. Yellow box represents the Weddell Sea and surrounding region. d Daily changes in ZW3 index (red and blue bars) at three ridges (latitude 50.5°S; longitudes 18°E, 75°W, 172°E). Monthly mean SAM (plus marks) and ZW3 (circles) indices remained in positive phase, with a prevailing pattern of moderate El Niño events (triangles).

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