Comparison of TWINS Images of Low-Altitude ENA Emissions With DMSP Precipitating Ion Fluxes

Details Comparison of TWINS Images of Low-Altitude ENA Emissions With DMSP Precipitating Ion Fluxes Comparison of TWINS Images of Low-Altitude ENA Emissions With DMSP Precipitating Ion Fluxes

May 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agusmsm72a..02b&link_type=abstract

American Geophysical Union, Spring Meeting 2009, abstract #SM72A-02

Physics

2716 Energetic Particles: Precipitating, 2730 Magnetosphere: Inner, 2788 Magnetic Storms And Substorms (7954), 7837 Neutral Particles (2151)

Scientific paper

Despite the low levels of geomagnetic activity over the past year, ENA cameras on both TWINS spacecraft have been detecting strong low-altitude emission (LAE) of energetic neutral atoms (ENAs) in the range 1-30 keV/nuc. The emission appears to come from auroral latitudes. The TWINS image pixels (4°× 4°) cannot resolve the auroral zone in latitude (MLAT), but do allow a resolution ~ 3h in local time (MLT) under favorable viewing conditions. We have been comparing the ENA spectra in the LAE to the precipitating ion spectra 0.3-40 keV/Q measured in situ by DMSP at the same UT and as near as possible to the MLT of the ENA emission. We present comparisons of TWINS and DMSP spectra during the modest geomagnetic activity during the 24-hour period of 11 October 2008. Assuming the source to be precipitating protons, we estimate the proton spectrum implied by the TWINS ENA spectrum using the "thick target" calculations for multiple charge-exchange transport in the monatomic oxygen exosphere at altitudes below 500km [Roelof; Nair and Roelof; this Special Session]. The spectra often show good agreement in terms of spectral shape, though the TWINS spectra can be up to a factor of ten lower in intensity than the DMSP spectra. This is consistent with the large (4°× 4°) TWINS pixel size compared to the narrow latitudinal extent of the auroral oval.

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