The effective recombination coefficient of electrons in the ionosphere between 50 and 150 km

Gledhill, J. A.

doi:10.1029/rs021i003p00399

Cited by 63 publications

(75 citation statements)

References 60 publications

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“…The latter is expressed as a eff N e 2 where a eff is the effective recombination coefficient. Examples of the altitude profile a eff (z) during solar proton events are presented in Figure 2 based on measurements from various sources (Vickrey et al 1982;Gledhill 1986;). The profile is broadly exponential with distinct scale heights of h E~5 1 km in the E-region (90-120 km) (Vickrey et al 1982), and h Dd~6 .1 km and h Dn~4 .3 km in the day and night D-region, respectively (Gledhill 1986).…”

Section: Type 2 (Full-profile) Pca Modelsmentioning

confidence: 99%

“…Examples of the altitude profile a eff (z) during solar proton events are presented in Figure 2 based on measurements from various sources (Vickrey et al 1982;Gledhill 1986;). The profile is broadly exponential with distinct scale heights of h E~5 1 km in the E-region (90-120 km) (Vickrey et al 1982), and h Dd~6 .1 km and h Dn~4 .3 km in the day and night D-region, respectively (Gledhill 1986). These profiles, which were applied in the PCA model of Patterson et al (2001), are best-fit values from observations that can range over several orders of magnitude at 50 km altitude.…”

Section: Type 2 (Full-profile) Pca Modelsmentioning

confidence: 99%

“…The parameters to be optimised were the scale heights h Dd and h Dn of a eff in the day-and nighttime D-region, respectively. The initial estimates of h Dd and h Dn were those determined by Gledhill (1986). An example of initial and optimised parameters and the associated model error and correlation statistics is presented in Table 7 for optimisation using data for all 94 SPEs recorded at the Taloyoak riometer.…”

Section: Optimisation Of Type 2 Pca Modelsmentioning

confidence: 99%

“…2.5). Altitude (km) E−region [Vickrey, 1982] Day SPE (Eqn 5, [Gledhill, 1986]) Night SPE (Eqn 4, [Gledhill, 1986]) Night aurora (Eqn 3, [Gledhill, 1986] where v is the solar-zenith angle. In (Sauer & Wilkinson 2008), v c = 90°and the half-width of the day-night transition, Dv = 10°.…”

Section: Type 1 (Energy Threshold) Pca Modelsmentioning

confidence: 99%

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Assimilation of real-time riometer measurements into models of 30 MHz polar cap absorption

Rogers

Honary

2015

J. Space Weather Space Clim.

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Space weather events may adversely affect high frequency (HF) radio propagation, hence the ability to provide nowcasting and forecasting of HF radio absorption is key for industries that rely on HF communications. This paper presents methods of assimilating 30 MHz radio absorption measurements into two types of ionospheric polar cap absorption (PCA) model to improve their performance as nowcasting tools. Type 1 models calculate absorption as m times the square root of the flux of solar protons above an energy threshold, E t . Measurements from 14 riometers during 94 solar proton events (1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010) are assimilated by optimising the day and night values of m by linear regression. Further non-linear optimisations are demonstrated in which parameters such as E t are also optimised and additional terms characterise local time and seasonal variations. These optimisations reduce RMS errors by up to 36%. Type 2 models incorporate altitude profiles of electron and neutral densities and electron temperatures. Here the scale height of the effective recombination coefficient profile in the D-region is optimised by regression. Furthermore, two published models of the rigidity cut-off latitude (CL) are assessed by comparison with riometer measurements. A small improvement in performance is observed by introducing a 3-h lag in the geomagnetic index K p in the CL models. Assimilating data from a single riometer in the polar cap reduces RMS errors below 1 dB with less than 0.2 dB bias. However, many highlatitude riometers now provide absorption measurements in near-real time and we demonstrate how these data may be assimilated by fitting a low-order spherical harmonic function to both the measurements and a PCA model with optimised parameters.

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Section: Type 2 (Full-profile) Pca Modelsmentioning

confidence: 99%

Section: Type 2 (Full-profile) Pca Modelsmentioning

confidence: 99%

Section: Optimisation Of Type 2 Pca Modelsmentioning

confidence: 99%

Section: Type 1 (Energy Threshold) Pca Modelsmentioning

confidence: 99%

See 2 more Smart Citations

Assimilation of real-time riometer measurements into models of 30 MHz polar cap absorption

Rogers

Honary

2015

J. Space Weather Space Clim.

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“…α eff is the effective dissociative recombination coefficient. The program uses formulas derived from Vickrey et al (1982) and Gledhill (1986) to calculate α eff . We should point out that we have not included diffusive transport in the equation as this is negligible at the heights contributing to the conductances.…”

Section: Deriving the Conductance Values From The Energy Spectramentioning

confidence: 99%

Instantaneous ionospheric global conductance maps during an isolated substorm

et al. 2002

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Abstract. Data from the Polar Ionospheric X-ray Imager (PIXIE) and the Ultraviolet Imager (UVI) on board the Polar satellite have been used to provide instantaneous global conductance maps. In this study, we focus on an isolated substorm event occurring on 31 July 1997. From the PIXIE and the UVI measurements, the energy spectrum of the precipitating electrons can be derived. By using a model of the upper atmosphere, the resulting conductivity values are generated. We present global maps of how the 5 min timeaveraged height-integrated Hall and Pedersen conductivities vary every 15 min during this isolated substorm. The method presented here enables us to study the time development of the conductivities, with a spatial resolution of ∼700 km. During the substorm, a single region of enhanced Hall conductance is observed. The Hall conductance maximum remains situated between latitudes 64 and 70 corrected geomagnetic (CGM) degrees and moves eastward. The strongest conductances are observed in the pre-midnight sector at the start of the substorm expansion. Toward the end of the substorm expansion and into the recovery phase, we find the Hall conductance maximum in the dawn region. We also observe that the Hall to Pedersen conductance ratio for the regions of maximum Hall conductance is increasing throughout the event, indicating a hardening of the electron spectrum. By combining PIXIE and UVI measurements with an assumed energy distribution, we can cover the whole electron energy range responsible for the conductances. Electrons with energies contributing most to the Pedersen conductance are well covered by UVI while PIXIE captures the high energetic component of the precipitating electrons affecting the Hall conductance. Most statistical conductance models have derived conductivities from electron precipitation data below approximately 30 keV. Since the intensity of the shortest UVI-wavelengths (LBHS) decreases significantly at higherCorrespondence to: A. Aksnes (arve.aksnes@fi.uib.no) electron energies, the UVI electron energy range is more or less comparable with the energy ranges of the statistical models. By calculating the conductivities from combined PIXIE and UVI measurements to compare with the conductivities from using UVI data only, we observe significant differences in the Hall conductance. The greatest differences are observed in the early evening and the late morning sector. We therefore suggest that the existing statistical models underestimate the Hall conductance.

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First modulation of high‐frequency polar mesospheric summer echoes by radio heating of the ionosphere

Senior

Mahmoudian

Pinedo

et al. 2014

Geophysical Research Letters

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The first high‐frequency (HF, 8 MHz) observations of the modulation of polar mesospheric summer echoes (PMSE) by artificial radio heating of the ionosphere are presented and compared to observations at 224 MHz and model predictions. The experiments were performed at the European Incoherent Scatter facility in northern Norway. It is shown that model results are in qualitative and partial quantitative agreement with the observations, supporting the prediction that with certain ranges of ice particle radii and concentration, PMSE at HF radar wavelengths can be enhanced by heating due to the dominance of dust charging over plasma diffusion.

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The effective recombination coefficient of electrons in the ionosphere between 50 and 150 km

Cited by 63 publications

References 60 publications

Assimilation of real-time riometer measurements into models of 30 MHz polar cap absorption

Assimilation of real-time riometer measurements into models of 30 MHz polar cap absorption

Instantaneous ionospheric global conductance maps during an isolated substorm

First modulation of high‐frequency polar mesospheric summer echoes by radio heating of the ionosphere

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