Fig. 1: The relationship of the NWPSH across different months.
From: The interdecadal variations of cross-month correlation feature of the NWPSH
a–d The standard deviation of the 850hPa geopotential height field (unit: \({\rm{gpm}}\)) for June, July, August, and the summer mean, respectively. The purple box denotes the region for defining the NWPSH index. e The 21-year sliding correlation of the NWPSH index between June and August (purple solid line), June and July (red solid line), and July and August (blue solid line). Horizontal (vertical) gray dashed line indicates the 95% confidence level threshold for the 21-year sliding correlation (2005, the dividing year for the two periods). The purple numbers in the upper left (upper right) corner show the correlation coefficient and confidence level between the June and August NWPSH indices during 1979–2005 (2006–2024).
