Relationships between precipitating auroral zone electrons and lower thermospheric nitric oxide densities: 1998 – 2000

Abstract

Data acquired using the Student Nitric Oxide Explorer (SNOE) spacecraft during the years 1998–2000 are presented for nitric oxide (NO) measured at altitudes between 90 and 170 km. These data are compared with energetic electron fluxes (E>25 keV) measured concurrently using a large‐area microchannel plate sensor system (Low‐Energy Ion Composition Analyzer) (LICA) on board the Solar, Anomalous, and Magnetospheric Particle Explorer (SAMPEX) spacecraft. Three geomagnetic storm intervals (in May 1998, September 1998, and October 1998) are examined specifically to determine altitude and latitude variations of NO production as it compares to energetic electron precipitation. A broader statistical analysis is then carried out using daily averages of peak NO densities (at 106 km altitudes) and electron intensities measured by SAMPEX. Northern and Southern Hemisphere data are treated separately within the magnetic latitude bands 60°–70° north and south. We find correlation coefficients of 0.56 (north) and 0.73 (south) for NO density versus SAMPEX electron count rates using two complete years of data. We also use the National Oceanic and Atmospheric Administration (NOAA) “hemispherical power index” to compare with SAMPEX and with SNOE measurements. Correlation coefficients of ∼0.6 are found among all the daily‐averaged quantities, suggesting that perhaps 30–40% of the variance in NO density can be accounted for by the particle measurements used. An analysis and adjustment of NO densities to account for seasonal effects increases the NO correlations with particle intensities to ≳0.7.