Collision frequency and transport properties of electrons in the ionosphere

Aggarwal, K. M.; Nath, N.; Setty, Chandan

doi:10.1016/0032-0633(79)90004-7

Cited by 48 publications

(38 citation statements)

References 55 publications

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“…(4), a(h) is proportional to the electron-neutral collision frequency ν en , which tends to increase as the electron temperature increases. However, since variations of electron temperature are small at the altitude below the D-region, ν en also has only minor variations in this region (Aggarwal et al, 1979). Yet, in the polar region, geomagnetic activities can sometimes increase electron temperature in the E-region excessively.…”

Section: Discussionmentioning

confidence: 99%

Energy distribution of precipitating electrons estimated from optical and cosmic noise absorption measurements

et al. 2004

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Abstract. This study is a statistical analysis on energy distribution of precipitating electrons, based on CNA (cosmic noise absorption) data obtained from the 256-element imaging riometer in Poker Flat, Alaska (65.11 • N, 147.42 • W), and optical data measured with an MSP (Meridian Scanning Photometer) over 79 days during the winter periods from 1996 to 1998. On the assumption that energy distributions of precipitating electrons represent Maxwellian distributions, CNA is estimated based on the observation data of auroral 427.8-nm and 630.0-nm emissions, as well as the average atmospheric model, and compared with the actual observation data. Although the observation data have a broad distribution, they show systematically larger CNA than the model estimate. CNA determination using kappa or double Maxwellian distributions, instead of Maxwellian distributions, better explains the distribution of observed CNA data. Kappa distributions represent a typical energy distribution of electrons in the plasma sheet of the magnetosphere, the source region of precipitating electrons. Pure kappas are more likely during quiet times -and quiet times are more likely than active times. This result suggests that the energy distribution of precipitating electrons reflects the energy distribution of electrons in the plasma sheet.

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Section: Discussionmentioning

confidence: 99%

Energy distribution of precipitating electrons estimated from optical and cosmic noise absorption measurements

et al. 2004

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“…We notice, however, that this value is still smaller than that observed (0.8 dB), resulting in a difference by a factor of 5-6. This discrepancy may arise if the theoretical electron-ion collision frequency, used in formula (2), is too small compared with the experimentally determined value (see Setty et al, 1970;Aggarwal et al, 1979; and the suggestion by Wang et al, 1994).…”

Section: Discussionmentioning

confidence: 97%

“…They indicated that the smaller values are due to a difference, by a factor as high as 4, between the ν e-i calculated by formula (2) above, and the experimentally measured collision frequencies (Setty et al, 1970, Aggarwal et al, 1979.…”

Section: Discussionmentioning

confidence: 98%

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Daytime ionospheric absorption features in the polar cap associated with poleward drifting F-region plasma patches

2014

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Absorption of radio waves in the polar ionosphere near the magnetic noon was observed on October 8, 1991, by the 30 MHz imaging riometer at Ny-Alesund, Svalbard (invariant latitude 76.1°). These observations showed that the initially widespread absorption features became localized and enhanced in the high-latitude sector of the field of view, and followed a poleward motion. This behavior occurred quasi-periodically and repeated every 10-20 min. Simultaneous observations by EISCAT "Polar" experiments showed that nine discrete plasma patches, with F-region electron density enhanced by an order of 10 6 el/cm 3 , drifted poleward from the polar cusp to the cap during the same period. This coincidence suggested that the ionospheric absorption was associated with F-region plasma patches in the polar cap. Theoretical absorption values of 0.14 dB, estimated using the electron densities and the electronion collision frequencies from the EISCAT F-region plasma data, are smaller than the observed values (<0.8 dB). This discrepancy may be related to the difference between the theoretically-and experimentally-determined collision frequencies, as indicated by Wang et al. (1994). These localized, enhanced, and poleward drifting absorption features over Ny-Alesund may be explained as F-region plasma patches produced by a magnetosheathlike particle precipitation into the cusp, and as small-scale irregularities caused by density gradients of the patches drifting into the polar cap.

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“…(11) applies to all elements of the vector. ν was derived from Table 3a of Aggarwal et al (1979) and it was assumed to be dependent only on the altitude z.…”

Section: Projection To Observational Datamentioning

confidence: 99%

Feasibility study on Generalized-Aurora Computed Tomography

et al. 2011

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Abstract. Aurora Computed Tomography (ACT) is a method for retrieving the three-dimensional (3-D) distribution of the volume emission rate from monochromatic auroral images obtained simultaneously by a multi-point camera network. We extend this method to a Generalized-Aurora Computed Tomography (G-ACT) that reconstructs the energy and spatial distributions of precipitating electrons from multi-instrument data, such as ionospheric electron density from incoherent scatter radar, cosmic noise absorption (CNA) from imaging riometers, as well as the auroral images. The purpose of this paper is to describe the reconstruction algorithm involved in this method and to test its feasibility by numerical simulation. Based on a Bayesian model with prior information as the smoothness of the electron energy spectra, the inverse problem is formulated as a maximization of posterior probability. The relative weighting of each instrument data is determined by the crossvalidation method. We apply this method to the simulated data from real instruments, the Auroral Large Imaging System (ALIS), the European Incoherent Scatter (EISCAT) radar at Tromsø, and the Imaging Riometer for Ionospheric Study (IRIS) at Kilpisjärvi. The results indicate that the differential flux of the precipitating electrons is well reconstructed from the ALIS images for the low-noise cases. Furthermore, we demonstrate in a case study that the ionospheric electron density from the EISCAT radar is useful for improving the reconstructed electron flux. On the other hand, the incorporation of CNA data into this method is difficult at this stage, because the extension of energy range to higher energy causes a difficulty in the reconstruction of the low-energy electron flux. Nevertheless, we expect that this method may be useCorrespondence to: Y.-M. Tanaka (ytanaka@nipr.ac.jp) ful in analyzing multi-instrument data and, in particular, 3-D data, which will be obtained in the upcoming EISCAT 3D.

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Collision frequency and transport properties of electrons in the ionosphere

Cited by 48 publications

References 55 publications

Energy distribution of precipitating electrons estimated from optical and cosmic noise absorption measurements

Energy distribution of precipitating electrons estimated from optical and cosmic noise absorption measurements

Daytime ionospheric absorption features in the polar cap associated with poleward drifting F-region plasma patches

Feasibility study on Generalized-Aurora Computed Tomography

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