  In the exploration of global-scale features of the Earth's aurora, little
attention has been given to the radial component of the Interplanetary Magnetic
Field (IMF). This study investigates the global auroral response in both
hemispheres when the IMF is southward and lies in the $\textit{xz}$ plane. We
present a statistical study of the average auroral response in the 12-24
magnetic local time (MLT) sector to an $\textit{x}$ component in the IMF. Maps
of auroral intensity in both hemispheres for two IMF $\mathit{B}_{x}$ dominated
conditions($ \pm $ IMF $\mathit{B}_{x}$) are shown during periods of negative
IMF $\mathit{B}_{z}$, small IMF $\mathit{B}_{y}$, and local winter. This is
obtained by using global imaging from the Wideband Imaging Camera on the IMAGE
satellite. The analysis indicates a significant asymmetry between the two IMF
$\mathit{B}_{x}$ dominated conditions in both hemispheres. In the Northern
Hemisphere the aurora is brighter in the 15-19 MLT region during negative IMF
$\mathit{B}_{x}$. In the Southern Hemisphere the aurora is brighter in the
16-20 MLT sector during positive IMF $\mathit{B}_{x}$. We interpret the results
in the context of a more efficient solar wind dynamo in one hemisphere. Both
the intensity asymmetry and its location are consistent with this idea. This
has earlier been suggested from case studies of simultaneous observations of
the aurora in both hemispheres, but hitherto never been observed to have a
general impact on global auroral brightness in both hemispheres from a
statistical study. The observed asymmetries between the two IMF
$\mathit{B}_{x}$ cases are not large; however, the difference is significant
with a 95% confidence level. As the solar wind conditions examined in the study
are rather common (37% of the time) the accumulative effect of this small
influence may be important for the total energy budget.
