Analytical estimate for low-altitude ENA emissivity

摘要: We formulate the first analytical model for energetic neutral atom (ENA) emissivity that partially corrects global viewing geometry dependence of low-altitude emissions (LAEs) observed by Two Wide-angle Imaging Neutral-atom Spectrometers (TWINS). The correction requires pitch angle distribution (PAD) and geophysical location ENAs. To estimate PAD, we create an energy-dependent model, based on a Monte Carlo simulation. account energy binning integrating PAD over each bin. finite angular pixels computing as integral range sampled pixel. investigate uncertainty in TWINS performing nine variations calculation. Using TWINS 2 ENA imaging data from 1131 to 1145 UT 6 April 2010, derive emissivity-corrected ion fluxes two pixel sizes: 4° 1°. evaluate method, compare TWINS-derived simultaneous situ National Oceanic Atmospheric Administration (NOAA) 17 satellite. TWINS-NOAA agreement flux is improved up factor 7, compared uncorrected flux. highest 1° are 2 higher than pixels, consistent with pixel-derived artificially low because subpixel structures smoothed out, indicating possible slight advantage oversampling instrument-measured LAE signal. Both NOAA decrease westward 2000 magnetic local time. comparison indicates precipitation oval comprises multiple smaller-scale (3–5° latitude) structures.