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Large Electron Densities in the Early Morning Equatorial Ionosphere Observed with UV Instruments from Space
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  • Robert Schaefer,
  • Larry Paxton,
  • Yongliang Zhang,
  • Hyosub Kil,
  • Giuseppe Romeo,
  • Brian Wolven,
  • Justin Yonker
Robert Schaefer
Johns Hopkins University Applied Physics Laboratory

Corresponding Author:robert.schaefer@jhuapl.edu

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Larry Paxton
Johns Hopkins University Applied Physics Laboratory
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Yongliang Zhang
Johns Hopkins University Applied Physics Laboratory
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Hyosub Kil
Johns Hopkins University Applied Physics Laboratory
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Giuseppe Romeo
Johns Hopkins University Applied Physics Laboratory
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Brian Wolven
Johns Hopkins University Applied Physics Laboratory
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Justin Yonker
Johns Hopkins University Applied Physics Laboratory
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Abstract

The equatorial ionosopheric anomalies (EIA) at night are the slowly recombining remnants of the dayside ionosphere, and charged particle densities slowly decay during the course of the night. Thus the electron density in ionosphere in the early morning (0300-0400 Local time) is usually very low and the ionospheric UV 135.6 nm O+ recombination emission is rarely detectable from current UV remote sensing instruments. However, there are times when the EIA have unusually high density even during these morning times and are observable by the DMSP/SSUSI and TIMED/GUVI instruments. By using other UV ‘colors’ - 130.4 nm (from monatomic Oxygen) and N2 Lyman Birge Hopfield bands - we can establish that this emission is definitely from the ionosphere recombination emission. We will show examples of this phenomenon, and correlate these occurrences to geomagnetic storm events. We estimate the electron density in the early morning EIA and compare with other ionosphere observations and climatological models. In the figure below, we show the 135.6 nm radiance seen by DMSP F16 SSUSI as it crosses the equator around 210 degrees longitude (over the Pacific Ocean) at 03:45 local time. The equatorial anomaly peaks are clearly visible in the SSUSI data. These radiances are background subtracted, which is not perfect and introduces a small (-1 Rayleigh) bias to the resulting radiances. DMSP = Defense Meteorological Satellite Program, SSUSI = Special Sensor Ultraviolet Spectrographic Imager; TIMED = Thermosphere, Ionosphere, Mesosphere Energetics and Dynamics, GUVI = Global UltraViolet Imager