New evidence of the influence of the interplanetary magnetic field on middle-latitude surface atmospheric pressure

For the polar regions, results have been published over several decades that indicate a meteorological response to the east-west component of the interplanetary magnetic field (IMF), By. Here we present evidence of a previously unrecognised influence of IMF on mid-latitude surface pressure. We examine the difference, Δp(By), between the mean surface pressure for high and low values of IMF By (e.g., By > 3nT and By < -3nT) using NCEP/NCAR reanalysis data in a 50 year interval (1963-2012) for the whole surface of the Earth at a resolution of 2.5 deg. in latitude and longitude. Similarly we find the difference, Δp(Bz), between the mean surface pressures for high and low values of the north-south component of the IMF, Bz. The Student t-test is used to assess the statistical significance of the results. Both Δp(By) and Δp(Bz) possess a significant mid-latitude wave structure. This structure circles the Earth with a wave number of about 4-5, and is similar in location and structure to the cyclones and anti-cyclones produced by the action of atmospheric Rossby waves on the jet stream. Our results indicate that the mechanism that produces atmospheric responses to IMF in the polar regions is also able to modulate pre-existing weather patterns at mid-latitudes. Our results also confirm those published by Burns et al. in 2008 (J. Geophys. Res. 113 - hereafter B08) who found a statistically-significant dependence of surface pressure variations on IMF By at Antarctic stations for 1995-2005, and at Arctic stations for 1999-2002 (around solar maximum). We extend this work to test whether Δp(By) is consistently positive in the Antarctic and negative in the Arctic over the interval 1963-2012. Lastly, we find a significant correlation of surface pressure with IMF Bz at middle to high latitudes, in contrast to a previous study in J. Geophys. Res. 112, in 2007, by Burns et al. (B07). This may be reconciled by recognising that the amplitude of Δp(Bz) is spatially dependent and that the largest values may not be expected to occur at Vostok, where the results of B07 were obtained. It has been proposed that the observed effect of IMF on the atmosphere occurs as a result of modulation of the current density of the atmospheric circuit via the interplanetary electric field, with subsequent changes in cloud dynamics. An investigation of the effect of (i) a time lag between the IMF and the surface pressure and of (ii) the spatial variation of Δp(By) and Δp(Bz) will be used to consider possible mechanisms that can account for our results.