The influence of solar wind on extratropical cyclones: Wilcox effect revisited

A sun-weather correlation, namely the link between solar magnetic sector boundary passage by the Earth and tropospheric vorticity area index (VAI), that was found by Wilcox et al. (1974) and shown to be statistically significant by Hines and Halevy (1977) is revisited. Using the ECMWF ERA-40 re-analysis dataset for a period from 1963 to 2002, we have verified these results for the northern as well as the southern hemisphere winters. The Wilcox effect is corroborated by a correlation with coronal holes where the fast solar wind originates. Ground-based measurements of the green coronal emission line (Fe XIV, 530.3 nm) are used in the superposed epoch analysis keyed by the times of sector boundary passage to show a one-to-one correspondence between the mean VAI variations and coronal holes. The VAI is modulated by high-speed solar wind streams with a delay of 1-2 days. Prikryl et al. (2007) have proposed a mechanism invoking solar-wind-generated auroral atmospheric gravity waves influencing the growth of extratropical cyclones. It is observed that severe extratropical storms and explosive cyclogenesis tend to occur within a few days of the arrival of high-speed solar wind.

Hines, C. O. and Halevy, I., 1977: On the reality and nature of a certain sun-weather correlation. J. Atmos. Sci., 34, 382–404.

Prikryl, P., 2007: Do auroral atmospheric gravity waves influence mesoscale processes, extratropical and tropical cyclones? The 12th Conference on Mesoscale Processes, Waterville Valley, NH, Paper 11.5.

Wilcox et al., 1974: Influence of solar magnetic sector structure on terrestrial atmospheric vorticity. J. Atmos. Sci., 31, 581–588.