Journal of Geophysical Research: Space Physics, 2013
ABSTRACT [1] In this paper, we analyze Two Wide-angle Imaging Neutral-atom Spectrometers (TWINS) ... more ABSTRACT [1] In this paper, we analyze Two Wide-angle Imaging Neutral-atom Spectrometers (TWINS) stereo observations of energetic neutral atoms (ENAs) produced from the low altitude emission (LAE) region during the interval 1130–1146 UT on 6 April 2010. Geometrical calculations determine the geophysical locations of pixels at or near the LAE limb and the associated uncertainties. For our event, the two TWINS imagers observed a broad (8.4–9.2 h wide in magnetic local time (MLT)) region of LAEs on the opposing limb, possibly containing an ion boundary near dusk. The most intense LAEs were detected in a narrow range of magnetic latitude (67°–74°) and pitch angle (112°–116°). We implement a simplified thick-target approximation (TTA) to obtain ion spectra from TWINS LAEs and perform a validation study using a conjunction of the TWINS-observed LAE crescents with a simultaneous NOAA 17 polar-orbit pass slightly west of the TWINS LAEs. Since TTA is limited to the brightest portion of LAEs, we apply our analysis for pixels with at least 30% of the peak value. TWINS ion spectra are calculated for individual pixels spanning several hours of MLT. The spectra exhibit a pronounced local time dependence. For more westward MLT (and more equatorward latitude), there is a shift toward spectra that are more energetic and peaked. This spatial dependence is consistent with ion drift theory and previous observations. The peaked LAE-derived ion spectra of 6 April 2010 are notably different than those observed during much weaker disturbances, but are consistent with LAE observations from similar activity levels. These results demonstrate that with proper caution in interpreting the results, TWINS ENA imaging resolves MLT-dependent (and to a limited extent, latitude-dependent) low-altitude ion spectral shape information, simultaneously across a broad range of MLT. This study advances previous results that considered much coarser MLT structure in LAEs and augments previous statistical spectral analysis of in situ data.
Both the Medium Energy Neutral Atom (MENA) and High Energy Neutral Atom (HENA) imagers onboard th... more Both the Medium Energy Neutral Atom (MENA) and High Energy Neutral Atom (HENA) imagers onboard the IMAGE spacecraft have been able to observe ENA emissions from the plasma sheet. The MENA observations showed enhanced emissions associated with high solar wind densities during magnetospheric storm intervals. The HENA observations showed decreases of emissions from the plasma sheet following dipolarization associated with
HO Funsten · F. Allegrini · P. Bochsler · G. Dunn · S. Ellis · D. Everett · MJ Fagan · SA Fuselie... more HO Funsten · F. Allegrini · P. Bochsler · G. Dunn · S. Ellis · D. Everett · MJ Fagan · SA Fuselier · M. Granoff · M. Gruntman · AA Guthrie · J. Hanley · RW Harper · D. Heirtzler · P. Janzen · KH Kihara · B. King · H. Kucharek · MP Manzo · M. Maple · K. Mashburn · DJ McComas · E. ...
The moderate storm of 22 July 2009 is the largest measured during the extended solar minimum betw... more The moderate storm of 22 July 2009 is the largest measured during the extended solar minimum between December 2006 and March 2010. We present observations of this storm made by the two wide-angle imaging neutral-atom spectrometers (TWINS) mission. The TWINS mission measures energetic neutral atoms (ENAs) using sensors mounted on two separate spacecrafts. Because the two spacecrafts' orbital planes are
We examine the evolution of the ring current during the main and early recovery phases of three g... more We examine the evolution of the ring current during the main and early recovery phases of three geomagnetic storms driven by corotating interaction regions. The equatorial energy density profiles of 5–30 keV ions are calculated from deconvolved energetic neutral atom images from the Two Wide-Angle Imaging Neutral-Atom Spectrometers mission. The energy density in the ring current is enhanced by almost
ABSTRACT The moderate storm of 22 July 2009 (Dst of ~-80 nT) was accompanied by a sudden increase... more ABSTRACT The moderate storm of 22 July 2009 (Dst of ~-80 nT) was accompanied by a sudden increase of the strength of the interplanetary magnetic field (IMF), multiple rotations of the IMF clock angle during the storm, and rapid changes in the proton density. During this storm the Two Wide-angle Imaging Neutral-atom Spectrometer (TWINS) mission continuously imaged the inner magnetosphere, with periods of stereoscopic imaging, using Energetic Neutral Atoms (ENAs). TWINS measures the incident flux and velocity of ENAs, and can also determine the fraction of the incident flux that is due to hydrogen (H) and oxygen (O) ENAs. This study presents mass-separated ENA maps from 22 July 2009 as they vary with the solar wind drivers. For the time periods when good stereoscopic viewing is available we will also be showing the first stereoscopic mass-separated ENA images of the inner magnetosphere.
Journal of Geophysical Research: Space Physics, 2013
ABSTRACT [1] In this paper, we analyze Two Wide-angle Imaging Neutral-atom Spectrometers (TWINS) ... more ABSTRACT [1] In this paper, we analyze Two Wide-angle Imaging Neutral-atom Spectrometers (TWINS) stereo observations of energetic neutral atoms (ENAs) produced from the low altitude emission (LAE) region during the interval 1130–1146 UT on 6 April 2010. Geometrical calculations determine the geophysical locations of pixels at or near the LAE limb and the associated uncertainties. For our event, the two TWINS imagers observed a broad (8.4–9.2 h wide in magnetic local time (MLT)) region of LAEs on the opposing limb, possibly containing an ion boundary near dusk. The most intense LAEs were detected in a narrow range of magnetic latitude (67°–74°) and pitch angle (112°–116°). We implement a simplified thick-target approximation (TTA) to obtain ion spectra from TWINS LAEs and perform a validation study using a conjunction of the TWINS-observed LAE crescents with a simultaneous NOAA 17 polar-orbit pass slightly west of the TWINS LAEs. Since TTA is limited to the brightest portion of LAEs, we apply our analysis for pixels with at least 30% of the peak value. TWINS ion spectra are calculated for individual pixels spanning several hours of MLT. The spectra exhibit a pronounced local time dependence. For more westward MLT (and more equatorward latitude), there is a shift toward spectra that are more energetic and peaked. This spatial dependence is consistent with ion drift theory and previous observations. The peaked LAE-derived ion spectra of 6 April 2010 are notably different than those observed during much weaker disturbances, but are consistent with LAE observations from similar activity levels. These results demonstrate that with proper caution in interpreting the results, TWINS ENA imaging resolves MLT-dependent (and to a limited extent, latitude-dependent) low-altitude ion spectral shape information, simultaneously across a broad range of MLT. This study advances previous results that considered much coarser MLT structure in LAEs and augments previous statistical spectral analysis of in situ data.
Both the Medium Energy Neutral Atom (MENA) and High Energy Neutral Atom (HENA) imagers onboard th... more Both the Medium Energy Neutral Atom (MENA) and High Energy Neutral Atom (HENA) imagers onboard the IMAGE spacecraft have been able to observe ENA emissions from the plasma sheet. The MENA observations showed enhanced emissions associated with high solar wind densities during magnetospheric storm intervals. The HENA observations showed decreases of emissions from the plasma sheet following dipolarization associated with
HO Funsten · F. Allegrini · P. Bochsler · G. Dunn · S. Ellis · D. Everett · MJ Fagan · SA Fuselie... more HO Funsten · F. Allegrini · P. Bochsler · G. Dunn · S. Ellis · D. Everett · MJ Fagan · SA Fuselier · M. Granoff · M. Gruntman · AA Guthrie · J. Hanley · RW Harper · D. Heirtzler · P. Janzen · KH Kihara · B. King · H. Kucharek · MP Manzo · M. Maple · K. Mashburn · DJ McComas · E. ...
The moderate storm of 22 July 2009 is the largest measured during the extended solar minimum betw... more The moderate storm of 22 July 2009 is the largest measured during the extended solar minimum between December 2006 and March 2010. We present observations of this storm made by the two wide-angle imaging neutral-atom spectrometers (TWINS) mission. The TWINS mission measures energetic neutral atoms (ENAs) using sensors mounted on two separate spacecrafts. Because the two spacecrafts' orbital planes are
We examine the evolution of the ring current during the main and early recovery phases of three g... more We examine the evolution of the ring current during the main and early recovery phases of three geomagnetic storms driven by corotating interaction regions. The equatorial energy density profiles of 5–30 keV ions are calculated from deconvolved energetic neutral atom images from the Two Wide-Angle Imaging Neutral-Atom Spectrometers mission. The energy density in the ring current is enhanced by almost
ABSTRACT The moderate storm of 22 July 2009 (Dst of ~-80 nT) was accompanied by a sudden increase... more ABSTRACT The moderate storm of 22 July 2009 (Dst of ~-80 nT) was accompanied by a sudden increase of the strength of the interplanetary magnetic field (IMF), multiple rotations of the IMF clock angle during the storm, and rapid changes in the proton density. During this storm the Two Wide-angle Imaging Neutral-atom Spectrometer (TWINS) mission continuously imaged the inner magnetosphere, with periods of stereoscopic imaging, using Energetic Neutral Atoms (ENAs). TWINS measures the incident flux and velocity of ENAs, and can also determine the fraction of the incident flux that is due to hydrogen (H) and oxygen (O) ENAs. This study presents mass-separated ENA maps from 22 July 2009 as they vary with the solar wind drivers. For the time periods when good stereoscopic viewing is available we will also be showing the first stereoscopic mass-separated ENA images of the inner magnetosphere.
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Papers by P. Valek