Incoherent scatter spectrum theory for modes propagating perpendicular to the geomagnetic field

Abstract

The short‐term relationship of the equatorial peak electron density and the solar short‐wavelength irradiance is examined using foF2 observations from Jicamarca, Peru and recent solar irradiance measurements from satellites. Solar soft X‐ray measurements from both the Student Nitric Oxide Explorer (SNOE) (1998–2000) and Thermosphere Ionosphere Mesosphere Energetics Dynamics (TIMED) (2002–2004) satellites as well as extreme ultraviolet (EUV) measurements from the TIMED satellite are used. Soft X‐rays show similar or higher correlation with foF2 at short timescales (27 days or less) than EUV does, although the EUV correlation is higher for longer periods. For the short‐term variations, both SNOE and TIMED observations have a higher correlation in the morning (∼0.46) than in the afternoon (∼0.1). In the afternoon, SNOE observations have a higher correlation (∼0.2) with foF2 than the TIMED observations (∼0.1 correlation), which may be due to differences in the solar cycle. At morning times, foF2 has a ∼27‐day variation, consistent with the solar rotation rate. After noon, but not in the morning, a ∼13.5‐day variation consistently appears in foF2. This ∼13.5‐day variation is attributed to geomagnetic influences.