Auroral radio absorption: The prediction question

Hargreaves, J. K.

doi:10.1016/j.asr.2009.10.026

Cited by 12 publications

(18 citation statements)

References 34 publications

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“…The analysis shows the exponential frequency dependence of the absorption with -1.5 power coefficient (Fig.4B). This value corresponds well with the data of other observations and models [16,17,18,19,4] and allows to use the proposed model for detecting and estimating the absorption level over the large noise dataset obtained at EKB ISTP SB RAS radar in 2013-2018.…”

Section: Resultssupporting

confidence: 84%

“…The radar field of view is about 1 million square kilometers and is shown in Fig.1A. In regular mode, the radar operates in 16 discrete directions (beams) with 1-2 minute temporal resolution, with 45 km spatial resolution, and at the operating frequencies [8][9][10][11][12][13][14][15][16][17][18][19][20] MHz. The radar transmits sequences of short sounding pulses and processes the received signals, scattered from surface and ionospheric irregularities.…”

Section: Introductionmentioning

confidence: 99%

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Noise level forecasts at 8–20 MHz and their use for morphological studies of ionospheric absorption variations at EKB ISTP SB RAS radar

Berngardt¹

2020

Advances in Space Research

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In this paper, a method is described for using 8-20MHz noise absorption effect for realtime detecting radiowave absorption periods. The method is based on two empirical autoregression models of noise dynamics. The first (rough) prediction model is based on radar measurements of daily minimal noise dynamics averaged over 28-days with specially calculated weight coefficients. The second (fine) prediction model uses real-time scaling of rough model. The scaling is based on the comparison of this model with the experimental noise observations during previous 5 days. The models are based on the whole EKB ISTP SB RAS radar dataset (2013)(2014)(2015)(2016)(2017)(2018). The rough model allows one to estimate the boundary beyond which the noise variations can be associated with absorption periods with a high degree of certainty. A joint analysis of simultaneous data on neighboring radar beams and at several frequencies reduces the detection errors, and allows to identify absorption events with a higher degree of confidence. Use of fine model allows to estimate absorption. The technique is validated by frequency dependence of absorption during two-frequency measurements. The found frequency dependence has an average exponent of the order of -1.5, which is in good agreement with the literature data and the data obtained earlier in analysis of solar X-ray flares. The use of the detection technique at EKB radar shows that most probable absorption over absorption events is about -0.65dB. Analysis of absorption of different amplitudes shows that low-intensity absorption events (0..-1.3dB) have slight local time dependence and mostly observed at north directions. For the storng absorption events (stronger than -1.3dB) the local time dynamics correlates well with noise level dynamics, and usually fills the whole radar field-of-view.

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Section: Resultssupporting

confidence: 84%

Section: Introductionmentioning

confidence: 99%

Noise level forecasts at 8–20 MHz and their use for morphological studies of ionospheric absorption variations at EKB ISTP SB RAS radar

Berngardt¹

2020

Advances in Space Research

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“…This in turn makes it a useful tool for study of the dynamics of the D and E regions. Traditionally, there are several techniques in use (Davies, 1969;Hunsucker & Hargreaves, 2002), including constant power 2-to 6-MHz transmitters (URSI A1 and A3 methods; see, e.g., Sauer & Wilkinson, 2008;Schumer, 2010), riometry using cosmic radio space sources at 30-50 MHz (URSI A2 method; Hargreaves, 2010), and imaging riometry (Detrick & Rosenberg, 1990). Recently, a large, spatially distributed network of riometers has been deployed to monitor absorption (Rogers & Honary, 2015).…”

Section: Introductionmentioning

confidence: 99%

Global Diagnostics of Ionospheric Absorption During X‐Ray Solar Flares Based on 8‐ to 20‐MHz Noise Measured by Over‐the‐Horizon Radars

et al. 2019

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An analysis of noise attenuation during 80 solar flares between 2013 and 2017 was carried out at frequencies 8–20 MHz using 34 Super Dual Auroral Radar Network radars and the EKB ISTP SB RAS radar. The attenuation was determined on the basis of noise measurements performed by the radars during the intervals between transmitting periods. The location of the primary contributing ground sources of noise was found by consideration of the propagation paths of radar backscatter from the ground. The elevation angle for the ground echoes was determined through a new empirical model. It was used to determine the paths of the noise and the location of its source. The method was particularly well suited for daytime situations, which had to be limited for the most part to only two crossings through the D region. Knowing the radio path was used to determine an equivalent vertical propagation attenuation factor. The change in the noise during solar flares was correlated with solar radiation lines measured by GOES/XRS, GOES/EUVS, SDO/AIA, SDO/EVE, SOHO/SEM, and PROBA2/LYRA instruments. Radiation in the 1 to 8 Å and near 100 Å are shown to be primarily responsible for the increase in the radionoise absorption, and by inference, for an increase in the D and E region density. The data are also shown to be consistent with a radar frequency dependence having a power law with an exponent of −1.6. This study shows that a new data set can be made available to study D and E regions.

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“…[] suggest a lower limit of 0.2 dB for reliability, consistent with the 0.2 dB threshold employed in this study. It can be noted that the literature suggests that deviations from the QDC causing an absorption value of > 1 dB are of note [i.e., Foppiano and Bradley , ; Hargreaves , ].…”

Section: Riometer Datamentioning

confidence: 99%

“…Riometers are passive radio antennas that measures background cosmic radio noise emanating from extraterrestrial sources (i.e., stars and galaxies) to gauge the opacity of the ionosphere to radio noise [Little and Leinbach, 1959;Davies, 1990;Browne et al, 1995]. Riometers operate in the VHF band in the 20-60 MHz range [Kavanagh et al, 2004;Hargreaves, 2010], typically at~30 MHz, and measure voltage which changes in response to received energy. Radio noise from fixed cosmic sources is regular.…”

Section: Introductionmentioning

confidence: 99%

Examination of the relationship between riometer-derived absorption and the integral proton flux in the context of modeling polar cap absorption

Fiori

Danskin

2016

Space Weather

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Energetic protons can penetrate into the ionosphere increasing ionization in the D region causing polar cap absorption that may potentially block high‐frequency radio communications for transpolar flights. The protons are guided by the geomagnetic field into the high‐latitude polar cap region. Riometers monitor variations in ionospheric absorption by observing the level of background cosmic radio noise. Current polar cap absorption modeling techniques are based on the linear relationship between absorption and the square root of the integral proton flux, which has previously only been demonstrated using data from a single high‐latitude polar station. The proportionality constant describing this relationship is evaluated for two different polar cap absorption events occurring 7–11 March 2012 and 23 January 2012 to 1 February 2012. Examination of the proportionality constant using data from riometers distributed between 60° and 90° magnetic latitude reveals a previously unreported latitudinal dependence for data at magnetic latitudes of ≤66.8° on the dayside and ≤70.8° on the nightside. Incorporating the latitudinal dependence into the current D Region Absorption Prediction absorption model improves the agreement between measurement‐derived and modeled parameters by increasing the correlation coefficient between data sets, reducing the root‐mean‐square error, and reducing the bias.

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Auroral radio absorption: The prediction question

Cited by 12 publications

References 34 publications

Noise level forecasts at 8–20 MHz and their use for morphological studies of ionospheric absorption variations at EKB ISTP SB RAS radar

Noise level forecasts at 8–20 MHz and their use for morphological studies of ionospheric absorption variations at EKB ISTP SB RAS radar

Global Diagnostics of Ionospheric Absorption During X‐Ray Solar Flares Based on 8‐ to 20‐MHz Noise Measured by Over‐the‐Horizon Radars

Examination of the relationship between riometer-derived absorption and the integral proton flux in the context of modeling polar cap absorption

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