Global electric circuit modulation of winter cyclone vorticity in the northern high latitudes Original Research Article

Small changes in extended winter (November–March) 500 hPa vorticity area index (VAI) values for the 60–80°N latitude band are shown to be positively correlated with changes in a proxy for the high latitude ionosphere-to-surface current density image. The proxy was obtained from low latitude image values, measured at Mauna Loa Observatory (MLO) during the years 1960–1961 and 1977–1982, which were taken as proportional to the global ionospheric potential image. Such MLO image values may also serve as proxies for high latitude image, provided that they are not used during Forbush decreases or during periods of high stratospheric aerosol loading. The MLO data were of sufficient quantity and quality to obtain high latitude image proxies for five northern hemisphere winters. These proxies were used in linear regressions with lagged values of anomalies in the VAI (with lags extending from −150 to +150 days). For the regression analysis using VAI values from the four 1977–1982 winters, the largest image value occurred for a lag of +2 days, and the corresponding regression coefficient was the second largest in magnitude for the 301 day interval. An ANOVA test showed this result to have a statistical significance of greater than 95%. For the regression analysis using data from only the 1960–1961 winter, both the maximum slope and image value occurred for a lag of −3 days. However, the autocorrelation of the VAI has a width of ∼15 days, and the noise associated with the small number of data points for 1960–1961 suggests that the maxima were displaced to negative lags by noise. The overall results are consistent with Tinsley’s hypothesis that higher image values enhance the vorticities of relatively intense winter cyclones when latent heat is important for their development. Electric charge deposited in clouds by image modulates the scavenging rates for both cloud condensation nuclei and ice-forming nuclei. The hypothesis is that these modulate the updraft vigor by the Rosenfeld mechanism, thus increasing the cyclonic vorticity