Figure 3 : Circulation drivers of spring frost timing.

From: Observed variations in U.S. frost timing linked to atmospheric circulation patterns

Figure 3

(a) Correlation between the day of year with last spring frost in the North region (SN) and mean March–May 500-hPa geopotential height at each grid point (ZMAM). The atmospheric teleconnection that captures this ZMAM pattern is referred to as CSN, and is the second principal component of ZMAM within the grey box. The CSN spatial pattern is contoured in black at 5 m per standard deviation of the CSN index with negative values dashed and the zero contour suppressed. On all maps, centres of action for the PNA are indicated by small filled white and black circles. (b) SN (black) and the CSN time series (blue). (c) Correlation between ZMAM and the day of year with last spring frost in the Central region (SC). The associated circulation mode (CSC) is the second principal component of ZMAM within the grey box. (d) SC (black) and the CSC time series (blue). (e) Correlation between ZMAM and the day of year with last spring frost in the South region (SS). The associated circulation mode (CSS) is the third principal component of ZMAM within the grey box. (f) SS (black) and the CSS time series (blue). (g) Correlation between ZMAM and the day of year with last spring frost in the West region (SW). The associated circulation mode (CSW) is the first principal component of ZMAM within the grey box. (h) SW (black) and the CSW time series (blue).