Comparison between CNA and energetic electron precipitation: simultaneous observation by Poker Flat Imaging Riometer and NOAA satellite

Abstract

Abstract. The cosmic noise absorption (CNA) is compared with the precipitating electron flux for 19 events observed in the morning sector, using the high-resolution data obtained during the conjugate observations with the imaging riometer at Poker Flat Research Range (PFRR; 65.11 • N, 147.42 • W), Alaska, and the low-altitude satellite, NOAA 12. We estimate the CNA, using the precipitating electron flux measured by NOAA 12, based on a theoretical model assuming an isotropic pitch angle distribution, and quantitatively compare them with the observed CNA. Focusing on the eight events with a range of variation larger than 0.4 dB, three events show high correlation between the observed and estimated CNA (correlation coefficient (r 0 )>0.7) and five events show low correlation (r 0 <0.5). The estimated CNA is often smaller than the observed CNA (72% of all data for 19 events), which appears to be the main reason for the low-correlation events. We examine the assumption of isotropic pitch angle distribution by using the trapped electron flux measured at 80 • zenith angle. It is shown that the CNA estimated from the trapped electron flux, assuming an isotropic pitch angle distribution, is highly correlated with the observed CNA and is often overestimated (87% of all data). The underestimate (overestimate) of CNA derived from the precipitating (trapped) electron flux can be interpreted in terms of the anisotropic pitch angle distribution similar to the loss cone distribution. These results indicate that the CNA observed with the riometer may be quantitatively explained with a model based on energetic electron precipitation, provided that the pitch angle distribution and the loss cone angle of the electrons are taken into account.

Direct Comparison Between Magnetospheric Plasma Waves and Polar Mesosphere Winter Echoes in Both Hemispheres

“…In the Southern Hemisphere, an enhancement of cosmic noise absorption (CNA) in the ionosphere was observed with the imaging riometer at SYO just after the onset (Figure 4g), which indicates precipitation of electrons with E of several tens to several hundreds of kiloelectron volts (e.g., Tanaka et al, 2005 and their references). The imaging riometer at SYO measures two-dimensional distribution of CNA at a frequency of 38.2 MHz (Figure 1b).…”

“…The energetic electrons penetrate the upper atmosphere and deposit energy through ionization, dissociation, and excitation of atmospheric constituents. They cause auroral optical emissions in the ionospheric E region at an altitude of 90-150 km (corresponding to precipitation of electrons with energy E of several to several tens of kiloelectron volts), absorption of cosmic radio noise in the ionospheric D region at 60-90 km (E of several tens to several hundreds of kiloelectron volts), and backscatter radar echoes from the mesosphere at 50-80 = km (E of several tens of kiloelectron volts to several megaelectron volts; cf., Figure 4a in this paper; S. Kasahara, Miyoshi, et al, 2018;Miyoshi et al, 2010;Nishimura et al, 2010;Nishiyama et al, 2018;Tanaka et al, 2005). In particular, special attention has been paid to the precipitation of relativistic electrons with E greater than 500 keV because they reach an altitude lower than 70 km.…”

Relationship between Na layer and CNA variations observed at Syowa, Antarctic

“…The CNA increase indicates enhancements of D region electron densities, and then such enhancements imply more precipitation (larger energy flux) of the energetic particles (cf. Tanaka et al 2005), which would consist of mainly 10-100-keV electrons. MLT features of such energetic electrons were investigated by satellite observations (Lam et al 2010).…”

Interplanetary medium condition effects in the South Atlantic Magnetic Anomaly: A case study

“…Although the main relationship mostly investigated is that between CNA and the flux of precipitating energetic electrons, the proton data are also relevant since protons are known to be able to contribute to ionization and consequently to an increase of CNA (Shirochkov et al, 2004;Tanaka et al, 2005).…”