Abstract
AbstractThe Empirical Canadian High Artic Ionospheric Model (E‐CHAIM) provides the four‐dimensional ionosphere electron density at northern high latitudes (>50° geomagnetic latitude). Despite its emergence as the most reliable model for high‐latitude ionosphere density, there remain significant deficiencies in E‐CHAIM's representation of the lower ionosphere (below ∼200 km) due to a sparsity of reliable measurements at these altitudes, particularly during energetic particle precipitation events. To address this deficiency, we have developed a precipitation component for E‐CHAIM to be driven by satellite‐based far‐ultraviolet (FUV) imager data. Satellite observations of FUV emissions may be used to infer the characteristics of energetic particle precipitation and subsequently calculate the precipitation‐enhanced ionization rates and ionosphere densities. In order to demonstrate the improvement of E‐CHAIM's ionosphere density representation with the addition of a precipitation component, this paper presents comparisons of E‐CHAIM precipitation‐enhanced densities with ionosphere density measurements of three auroral region incoherent scatter radars (ISRs) and one polar cap ISR. Calculations for 29,038 satellite imager and ISR conjunctions during the years 2005–2019 revealed that the root‐mean‐square difference between E‐CHAIM and ISR measurements decreased by up to 2.9 × 1010 ele/m3 (altitude dependent) after inclusion of the precipitation component at auroral sites, and by 2.6 × 109 ele/m3 in the polar cap. Improvements were most substantial in the winter season and during active auroral conditions. The sensitivity of precipitation‐enhanced densities to uncertainties inherent to the calculation method was also examined, with the bulk of the errors due to uncertainties in FUV imager data and choice of distribution function for precipitation energy spectra.
Highlights
The precipitation of energetic electrons and ions of magnetospheric and solar origin play a significant role in governing the structure and dynamic behavior of the high latitude ionosphere
In order to demonstrate the improvement of Empirical Canadian High Artic Ionospheric Model (E-CHAIM)'s ionosphere density representation with the addition of a precipitation component, this paper presents comparisons of E-CHAIM precipitation-enhanced densities with ionosphere density measurements of three auroral region incoherent scatter radars (ISRs) and one polar cap ISR
We examine the feasibility of deriving precipitation enhanced profiles for E-CHAIM based on auroral far ultraviolet (FUV) emission observations of the Defense Meteorological Satellite Program (DMSP) Special Sensor Ultraviolet Spectrographic Imager (SSUSI; Paxton et al, 1992) and the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) Global Ultraviolet Imager (GUVI; Humm et al, 1998)
Summary
The precipitation of energetic electrons and ions of magnetospheric and solar origin play a significant role in governing the structure and dynamic behavior of the high latitude ionosphere. E-CHAIM is a significant improvement over other models such as the International Reference Ionosphere (IRI) at high latitudes, providing, for example, improvements of up to 60% in NmF2 in the polar cap (Themens et al, 2017) Despite this improvement, E-CHAIM has limitations in its representation of the bottomside ionosphere, generally underestimating bottomside densities and performing poorly during energetic particle precipitation events (Themens, Jayachandran, & McCaffrey, 2019). The energy flux and mean energy of precipitating electrons govern the atmospheric ionization rate and altitude of ionization, respectively, and are available as high-level GUVI and SSUSI data products. GUVI and SUSSI data are used to characterize precipitating electron populations with mean energies of 0–20 keV, and subsequently calculate precipitation-enhanced ionosphere densities for E-CHAIM This energy range primarily impacts altitudes in the range of 100–200 km.
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