From the “science is settled” department comes this new paper that points out a correlation between the Interplanetary Magnetic Field (IMF) and polar jet streams, which drive weather events on Earth. This new paper shows that the effects extend even further towards the Equator than before, meaning it will affect weather experienced by a greater portion of Earth’s human population.
Given that the solar magnetic dynamo has been in a slump as of late, and we’ve experienced a very low U.S. tornado season, one wonders if the low tornado numbers are partially related to lack of perturbations induced in the jet stream, which guide storm tracks and fronts.
The effect may also extend to the 2013 Northern Hemisphere hurricane season, which has also been a bust, despite early predictions.
So far the 2013 Accumulated Cyclone Energy (ACE) count for the Northern Hemisphere is 217, about half of what it normally is for this date at 432. Source: WeatherBell, Dr. Ryan Maue
The paper, in Environmental Research Letters is:
The interplanetary magnetic field influences mid-latitude surface atmospheric pressure
M M Lam, G Chisham and M P Freeman
The existence of a meteorological response in the polar regions to fluctuations in the interplanetary magnetic field (IMF) component By is well established. More controversially, there is evidence to suggest that this Sun–weather coupling occurs via the global atmospheric electric circuit. Consequently, it has been assumed that the effect is maximized at high latitudes and is negligible at low and mid-latitudes, because the perturbation by the IMF is concentrated in the polar regions.
We demonstrate a previously unrecognized influence of the IMF By on mid-latitude surface pressure. The difference between the mean surface pressures during times of high positive and high negative IMF By possesses a statistically significant mid-latitude wave structure similar to atmospheric Rossby waves.
Our results show that a mechanism that is known to produce atmospheric responses to the IMF in the polar regions is also able to modulate pre-existing weather patterns at mid-latitudes.
We suggest the mechanism for this from conventional meteorology. The amplitude of the effect is comparable to typical initial analysis uncertainties in ensemble numerical weather prediction. Thus, a relatively localized small-amplitude solar influence on the upper atmosphere could have an important effect, via the nonlinear evolution of atmospheric dynamics, on critical atmospheric processes.
Figure 1 shows the extent:
In the discussion section they write:
To explain the observed correlation of IMF By with surface pressure we propose that the mid-latitude surface pressure is influenced by IMF By via a two-stage process comprising: (i) a change in the polar surface pressure involving the global atmospheric electric circuit [5, 6], and (ii) a resulting change in the mid-latitude surface pressure via conventional meteorology. The first of these two processes, concerning the influence of IMF By fluctuations on the polar surface pressure remains under-explored and controversial [17, 18]. However, our analysis of the surface pressure anomaly field provides new evidence supporting a direct relationship with the ionospheric electric potential.
Figure 3 is a schematic representing this two-stage process: in the Northern Hemisphere, as IMF By switches from dawnward to duskward, the potential difference between the ionosphere and the Earth’s surface, V, and the sea-level pressure p, decrease in the northern polar region. The direct effect on sea-level pressure in the polar regions (figures S3 and S4, available at stacks.iop.org/ERL/8/045001/mmedia), along with the lack of effect on pressure at low latitudes, results in a change in the latitudinal sea-level pressure gradient in mid-latitude regions (figure S5, available at stacks.iop.org/ERL/8/045001/mmedia) associated with an increase in the mean zonal wind U at mid-latitudes. Generalizing the original theory of Rossby waves  to the case of periodic variations in both longitude and latitude , we obtain U = β/(k2 + l2) where k and l are the wavenumbers in the longitudinal and latitudinal directions, respectively. For a fixed value of k (and hence m), an increase in U leads to a decrease in l and an increase in meridional wavelength Lθ. Thus variations in IMF By modify the quasi-stationary Rossby wavenumber (k,l), accounting for the Rossby-wave-like form of . The variations in V,p,U,l and Lθ are reversed in the Southern Hemisphere. More details are in section 2 of the supplementary data (available at stacks.iop.org/ERL/8/045001/mmedia).
Figure 3. Our hypothesis is that the mid-latitude surface pressure is influenced by IMF By via a two-stage process. (i) As IMF By changes from dawnward to duskward, the electric potential difference between the ionosphere and the Earth’s surface, V, and the sea-level pressure p, decrease in the northern polar region; (ii) the mean zonal wind U at mid-latitudes increases resulting in an increase in the meridional wavelength (for simplicity labelled L in this figure; in text referred to as Lθ) of the stationary Rossby wave with an integer number of azimuthal waves m (at co-latitude θ and latitude λ = 90° − θ). The variations in V,p,U and L are reversed in the Southern Hemisphere.
They write in the conclusion section of the paper:
Previously, proposals to link solar wind variations to significant weather or climate variability have been dismissed on the grounds that the magnitude of the energy change in the atmosphere associated with the solar wind variability is far too small to impact the Earth’s system. However, this argument neglects the importance of nonlinear atmospheric dynamics . The amplitudes of the IMF-related changes in atmospheric pressure gradient are comparable with the initial uncertainties in the corresponding zonal wind used in ensemble numerical weather prediction (NWP)  of ~1 m s−1. Such uncertainties are known to be important to subsequent atmospheric evolution and forecasting . Consequently, we have shown that a relatively localized and small-amplitude solar influence on the upper polar atmosphere could have an important effect, via the nonlinear evolution of atmospheric dynamics on critical processes such as European climate and the breakup of Arctic sea ice .
In particular, it affects the structure of the Rossby wavefield, which is key in determining the trajectory of storm tracks . The configuration of the North Atlantic jet stream is particularly susceptible to changes in forcing . In turn, so are the location and the timing of blocking events in this region, in which vortices are shed from the jet stream leading to prolonged periods of low or of high pressure . It has also been proposed that the low-frequency variability of the North Atlantic Oscillation (NAO) arises as a result of variations in the occurrence of upper-level Rossby wavebreaking events over the North Atlantic . The NAO itself is key to climate variability over the Atlantic–European sector stretching from the east coast of the United States to Siberia, and the Arctic to the subtropical Atlantic [28, 25].
Our results may therefore provide part of the explanation for previously observed correlations between Eurasian winter temperatures and solar variability [29, 30], and for the ‘Wilcox effect’ where reductions in the areas of high vorticity in winter storms are seen at times of solar wind heliospheric current sheet crossings  (which are characterized by sharp changes between steady, opposite IMF By states).
To me this is an important discovery, particularly since it manifests itself most strongly at the poles, and the opinion of mainstream climate science is that global warming will show up at the poles more strongly via “polar amplification”.
Full paper in open access here: http://iopscience.iop.org/1748-9326/8/4/045001/article
h/t to Jo Nova