The Effect of Storm Driver and Intensity on Magnetospheric Ion Temperatures. Issue 9 (18th September 2017) - Keesee, Amy M.
Abstract: Energy deposited in the magnetosphere during geomagnetic storms drives ion heating and convection. Ions are also heated and transported via internal processes throughout the magnetosphere. Injection of the plasma sheet ions to the inner magnetosphere drives the ring current and, thus, the storm intensity. Understanding the ion dynamics is important to improving our ability to predict storm evolution. In this study, we perform superposed epoch analyses of ion temperatures during storms, comparing ion temperature evolution by storm driver and storm intensity. The ion temperatures are calculated using energetic neutral atom measurements from the Two Wide‐Angle Imaging Neutral‐Atom Spectrometers (TWINS) mission. The global view of these measurements provide both spatial and temporal information. We find that storms driven by coronal mass ejections (CMEs) tend to have higher ion temperatures throughout the main phase than storms driven by corotating interaction regions (CIRs) but that the temperatures increase during the recovery phase of CIR‐driven storms. Ion temperatures during intense CME‐driven storms have brief intervals of higher ion temperatures than those during moderate CME‐driven storms but have otherwise comparable ion temperatures. The highest temperatures during CIR‐driven storms are centered at 18 magnetic local time and occur on the dayside for moderate CME‐driven storms. During the second half of the main phase, ion temperatures tend to decrease in the postmidnight to dawn sector for CIR storms, but an increase is observed for CME storms. This increase begins with a sharp peak in ion temperatures for intense CME storms, likely a signature of substorm activity that drives the increased ring current. Plain Language Summary: During geomagnetic storms, ions in the magnetosphere are heated and move around to different regions. Understanding where, when, and how this heating occurs is important to being able to forecast the effects of these storms. In this study, we create ion temperature maps during geomagnetic storms using data from the NASA TWINS mission. We categorize the storms based on what causes them and how strong they are and then perform a study of the average ion temperatures during each type of storm. We find that the differences in ion temperatures between the storm types tend to be caused by differences in the strength of the electric field that moves the ions. Key Points: Superposed epoch analyses of ion temperatures calculated from TWINS energetic neutral atom data are performed Ion temperatures are compared by storm driver and storm intensity Temperatures are higher during coronal mass ejection storms until the recovery phase when they increase for corotation interaction region storms