An imaging riometer for ionospheric studies

Browne, S. E.; Hargreaves, J. K.; Honary, B.

doi:10.1049/ecej:19950505

Cited by 84 publications

(91 citation statements)

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“…The ''Churchill line'' of seven riometers labelled in Figure 1 lies close to the 94°W geographic meridian (±2°) from Taloyoak (talo) in the north to Pinawa (pina) in the south. These data were complemented by measurements from the zenithal beam of the Imaging Riometer for Ionospheric Studies (IRIS) (Browne et al 1995;Honary et al 2011) operated by Lancaster University at Kilpisjärvi, Finland in conjunction with the Sodankylä Geophysical Observatory (SGO). The data were processed using the Multi-Instrument Analysis (MIA) software package (Marple & Honary 2004).…”

Section: Riometer Measurementsmentioning

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: Riometer Measurementsmentioning

confidence: 99%

“…where the measured absorption remains greater than 0.1 dB). Details of the generation of the QDC are described for the NORSTAR riometers in a University of Calgary report (NORSTAR 2014) and for the IRIS riometer at Kilpisjärvi using a variant of the percentile technique of Browne et al (1995) described by Rodger et al (2013, p. 7815).…”

Section: Excluded Datamentioning

confidence: 99%

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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“…Canadian data is supplied from what was the CANOPUS project (Rostocker et al, 1995); each of the stations is equipped with a broad beam (∼60 • ), 30 MHz riometer (pointing to the zenith) as well as a 3-component fluxgate magnetometer, which provide data at 5 s resolution. The riometer data from Finland have been supplied by a chain of widebeam riometers, operated by Sodankylä Geophysical Observatory (SGO), and from a widebeam instrument co-located with the Imaging Riometer for Ionospheric Studies (IRIS), operated by Lancaster University (UK) (Browne et al, 1995). IRIS data is taken at 1-s resolution but has been averaged to 5 s here and the SGO chain provides data at 1-min resolution.…”

Section: Instrumentationmentioning

confidence: 99%

Energetic electron precipitation during sawtooth injections

Kavanagh

Donovan

et al. 2007

Ann. Geophys.

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Abstract. We present simultaneous riometer observations of cosmic noise absorption in the nightside and dawn-noon sectors during sawtooth particle injections during 18 April 2002. Energetic electron precipitation (>30 keV) is a feature of magnetospheric substorms and cosmic radio noise absorption acts as a proxy for qualitatively measuring this precipitation. This event provides an opportunity to compare the absorption that accompanies periodic electron injections with the accepted paradigm of substorm-related absorption. We consider whether the absorption is consistent with the premise that these injections are quasi-periodic substorms and study the effects of sustained activity on the level of precipitation. Four consecutive electron injection events have been identified from the LANL (Los Alamos National Laboratory) geosynchronous data; the first two showing that additional activity can occur within the 2-4 h sawtooth periodicity. The first three events have accompanying absorption on the nightside that demonstrate good agreement with the expected pattern of substorm-absorption: discrete spike events with poleward motion at the onset followed by equatorward moving structures and more diffuse absorption, correlated with optical observations. Dayside absorption is linked to gradient-curvature drifting electrons observed at geostationary orbit and it is shown that low fluxes can lead to a lack of absorption as precipitation is suppressed; precipitation begins when the drifting electron flux surpasses some critical level following continuous injections of electrons from the magnetotail. In addition it is shown that the apparent motion of absorption determined from an azimuthal chain of riometers exhibits an acceleration that may be indicative of an energisation of the drifting electron population.

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“…Increase in the convective electric field and auroral particle precipitation produce intense currents in the ionosphere, which are monitored through magnetic field measurements (Singh et al, 2012;Behera et al, 2015). Changes in the ionosphere are also monitored using an Imaging Riometer, which measures the strength of the 38.2 MHz galactic radio waves that impinge on the Earth's atmosphere, and thereby gives information on the changes in absorption of this signal due to changes in the ionospheric electron density (Browne et al, 1995). Apart from the dramatic short term changes in the geomagnetic field recorded at Antarctica, which may be attributed to external causes, it has emerged that the Earth's complex main magnetic field, which has its origin in the fluid outer core of the Earth at a depth of about 300 Ashwini K Sinha et al 2900 km below the surface of the Earth, is also undergoing a systematic rapid decline as observed in the Antarctic region (Pathan et al, 2009).…”

Section: Introductionmentioning

confidence: 99%

India's Contribution to Geomagnetism and Allied Studies in Antarctica-A Review

Sinha

2017

Proceedings of the Indian National Science Academy

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In this paper, we review the progress in Geomagnetism and allied areas based on the past thirty five Indian Antarctic expeditions and summarize the scientific results obtained in the last decade. Various dynamic processes in the near-Earth space environment, driven by the transient changes in geomagnetic field such as storms and substorms, severely affect the space weather over the Polar Regions. Magnetopsheric substorms lead to the intensification of ionospheric currents and auroral outbursts within the auroral oval, causing energetic charged particles in the auroral region to come down to D-region ionosphere, which is reflected as Cosmic Noise Absorption (CNA) as monitored by imaging RIOmeter at Indian Antarctic station, Maitri (Geog. 70.75 o S, 11.73 o E; Geom. 66.84 o S, 56.29 o E). A systematic rapid decline in The Earth's complex main magnetic field at Maitri (~110 nT/yr) is important for monitoring the evolution of reverse magnetic flux patches due to physical processes occurring in the outer core of the Earth. The Global Electric Circuit (GEC) studies were started to understand the solar-terrestrial relationship and associated changes in surface weather and the near-earth electrical environment. Schumann resonances (SRs), the AC part of GEC reveal a strong UT variation of amplitude in seasonal as well as yearly time scales. The observed diurnal variation is explained in terms of the dominant thunderstorm activity centered over the three convectively active regions, viz. Asia/Maritime Continent (Indonesia), South America and Africa.The velocity and strain distribution of Schirmarchaer Glacier was investigated during two GPS campaigns in the year 2003 and 2004. The studies indicate that the horizontal velocity is in the range of 1.89-10.88 ma -1 with an average velocity of 6.21 ma -1 .

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An imaging riometer for ionospheric studies

Cited by 84 publications

References 0 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

Energetic electron precipitation during sawtooth injections

India's Contribution to Geomagnetism and Allied Studies in Antarctica-A Review

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