Mesoscale Structures in Earth's Magnetotail Observed Using Energetic Neutral Atom Imaging

Automated Detection Algorithm for Mesoscale Heated Regions in TWINS Ion Temperature Maps

Earth's magnetotail plays a critical role in the dynamics of the magnetosphere, particularly during intervals of geomagnetic activity. To improve our understanding of the ion dynamics in this region, energetic neutral atom (ENA) imaging can provide global measurements to place in situ measurements in context and validate simulations. The NASA Two Wide-angle Imaging Neutral-atom Spectrometers mission provided near-continuous observations using ENA imagers. ENA data can be used to calculate maps of equatorial ion temperatures that often show observations of regions of enhanced temperatures associated with phenomena in the magnetotail such as magnetic reconnection and narrow flow channels. We present an algorithm that can be used to search through a collection of these maps to identify intervals with such enhancements for further study. The algorithm results are validated against two sets of related phenomena: (a) a database of dipolarizing flux bundle (DFB) measurements from THEMIS and (b) a list of substorm onsets from SuperMAG. We demonstrate that the algorithm is very good at identifying intervals when there are DFB measurements or substorm onsets as long as there sufficient ENA data. We discuss some potential scientific studies that can result from use of the algorithm. We also show a preliminary application of the algorithm to simulation output to demonstrate the usefulness for other datasets, facilitate comparative studies, and introduce a new method for model validation.

Explicit IMF B y -Dependence of Energetic Protons and the Ring Current

The most important parameter driving the solar wind-magnetosphere interaction is the southward (B _z ) component of the interplanetary magnetic field (IMF). While the dawn-dusk (B _y ) component of the IMF is also known to play an important role, its effects are usually assumed to be independent of its sign. Here we demonstrate for the first time a seasonally varying, explicit IMF B _y -dependence of the ring current and Dst index. Using satellite observations and a global magnetohydrodynamic model coupled with a ring current model, we show that for a fixed level of solar wind driving the flux of energetic magnetospheric protons and the growth-rate of the ring current are greater for B _y  < 0 (B _y  > 0) than for B _y  > 0 (B _y  < 0) in Northern Hemisphere summer (winter). While the physical mechanism of this explicit B _y -effect is not yet fully understood, our results suggest that IMF B _y modulates magnetospheric convection and plasma transport in the inner magnetosphere.