The influence of internal atmospheric variability on the ionosphere response to a geomagnetic storm

The Whole Atmosphere Community Climate Model eXtended is used to investigate the extent to which neglecting the realistic day-to-day lower atmospheric variability introduces uncertainty in the ionosphere response to an idealized geomagnetic storm. A 10-member ensemble is generated by adding small temperature perturbations in the lower atmosphere 30days prior to the imposed geomagnetic storm. Chaotic divergence, and internal atmospheric variability, leads to the geomagnetic storm occurring under an arbitrarily different, though climatically similar, atmospheric state for each ensemble member. The intra-ensemble variability, which we characterize by the ensemble standard deviation, of the day-to-day change in total electron content is generally similar to 10%-20% during geomagnetically quiet time. During an idealized storm with a K-p of 7 the ensemble standard deviation of the change in total electron content increases to similar to 20%-40% at low and middle latitudes, with localized regions exceeding 100%. Examination of individual ensemble members illustrates that they all capture the same large-scale features of the storm time changes in the ionosphere but can exhibit notable (50%) differences regionally, especially during later stages of the storm. The results thus demonstrate that in order to accurately capture smaller-scale features of the upper atmosphere response to geomagnetic storms, it is necessary to include the effects of lower atmosphere variability.