Effects of Polar Wind Outflow on the Storm-time Ring Current
Location
Yosemite National Park
Start Date
2-12-2014 5:40 PM
End Date
2-12-2014 5:55 PM
Description
Ions of ionospheric origin are known to be important in the development of the storm-time ring current. Previous studies have mainly focused on the increased concentration of O+ in the ring current because heavy ions, in contrast with protons, can be easily distinguished from ions of solar wind origin. This study examines the effect of an H+ polar wind outflow on the loss of storm-time ring current. We first conducted two simulations using the coupled LFM-RCM global model, with and without a polar wind outflow, driven by steady IMF Bz at -15 nT. Results show that the maximum energy of the ring current is higher with the H+ outflow than in the baseline run without it. The hypothesis that the increase of ring current energy is due to the reduction of ring-current ions loss was tested by performing four additional simulations with the IMF turning northward after saturation of the ring current in the previous simulations. For two of the simulations, with and without outflow, the RCM’s explicit loss terms (ion charge exchange and strong electron pitch-angle scattering) were disabled; they were enabled in the other two for otherwise identical conditions. The results show that, without the polar wind outflow, the RCM’s loss terms account for only a small fraction of the ring-current loss. With polar wind outflow included, the RCM loss dominated the ring-current loss, but the loss rate is slower than in the case without outflow. The remaining questions are what cause the reduction of the loss and why is the loss reduced after including the outflow. We analyzed the possible mechanisms that may contribute to this result and found that the flux tube interchange motion in the inner magnetosphere is restrained in the outflow run, so a possible explanation would be a reduction in interchange motion reduces the loss of ring-current ions. We are developing additional diagnostics to answer the second question.
Effects of Polar Wind Outflow on the Storm-time Ring Current
Yosemite National Park
Ions of ionospheric origin are known to be important in the development of the storm-time ring current. Previous studies have mainly focused on the increased concentration of O+ in the ring current because heavy ions, in contrast with protons, can be easily distinguished from ions of solar wind origin. This study examines the effect of an H+ polar wind outflow on the loss of storm-time ring current. We first conducted two simulations using the coupled LFM-RCM global model, with and without a polar wind outflow, driven by steady IMF Bz at -15 nT. Results show that the maximum energy of the ring current is higher with the H+ outflow than in the baseline run without it. The hypothesis that the increase of ring current energy is due to the reduction of ring-current ions loss was tested by performing four additional simulations with the IMF turning northward after saturation of the ring current in the previous simulations. For two of the simulations, with and without outflow, the RCM’s explicit loss terms (ion charge exchange and strong electron pitch-angle scattering) were disabled; they were enabled in the other two for otherwise identical conditions. The results show that, without the polar wind outflow, the RCM’s loss terms account for only a small fraction of the ring-current loss. With polar wind outflow included, the RCM loss dominated the ring-current loss, but the loss rate is slower than in the case without outflow. The remaining questions are what cause the reduction of the loss and why is the loss reduced after including the outflow. We analyzed the possible mechanisms that may contribute to this result and found that the flux tube interchange motion in the inner magnetosphere is restrained in the outflow run, so a possible explanation would be a reduction in interchange motion reduces the loss of ring-current ions. We are developing additional diagnostics to answer the second question.