Cosmic noise absorption accompanying geomagnetic storm sudden commencements

Ortner, J.; Hultqvist, B.; Brown, R. R.; Hartz, T. R.; Holt, O.; Landmark, B.; Hook, J. L.; Leinbach, H.

doi:10.1029/jz067i011p04169

Cited by 61 publications

(31 citation statements)

References 15 publications

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“…It is well known that at the time of a Sudden Commencement a sudden burst of particle precipitation occurs that gives rise to a short-lasting intense increase in riometer absorption, known as Sudden Commencement Absorption (SCA; Ortner et al, 1962). This is also observed in the event presented.…”

Section: Introductionmentioning

confidence: 50%

Observations of ionospheric flows and particle precipitation following a Sudden Commencement

Nielsen¹,

Honary

2000

Ann Geophysicae

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Abstract. On May 4, 1998, at 0227 UT an interplanetary shock crossed the WIND spacecraft, and half an hour later a Sudden Commencement occurred. Coinciding with the Sudden Commencement a rapid intensi®cation of the¯ux of particle precipitation into the ionosphere was observed. Evidence is presented that the ionospheric electric ®elds were in¯uenced by the associated dynamic variations of the ionospheric conductivities. Following the initial phase the ionospheric¯ow speeds increased rapidly over the next 20 min to more than 2000 m/s, in agreement with an increased eective coupling of the solar wind energy to the magnetosphere following the interplanetary shock that caused the Sudden Commencement. These strong¯ows were meandering in latitude, a type of plasma¯ow modulation that has been reported before to occur during Omega band events: a string of alternating ®eld-aligned currents propagating eastward. The riometer absorption was found to be at a minimum in regions associated with outward directed ®eld aligned currents. The riometer absorption regions (the regions of particle precipitation) were drifting with E´B drift speed of the ionospheric electrons.

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Section: Introductionmentioning

confidence: 50%

Observations of ionospheric flows and particle precipitation following a Sudden Commencement

Nielsen¹,

Honary

2000

Ann Geophysicae

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“…Ortner et al, 1962;Brown et al, 1972). No significant CNA is detected by any of the riometers following the SC.…”

Section: Precipitation Prior To Substorm Onsetmentioning

confidence: 96%

The driving mechanisms of particle precipitation during the moderate geomagnetic storm of 7 January 2005

et al. 2007

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Abstract. The arrival of an interplanetary coronal mass ejection (ICME) triggered a sudden storm commencement (SSC) at ∼09:22 UT on the 7 January 2005. The ICME followed a quiet period in the solar wind and interplanetary magnetic field (IMF). We present global scale observations of energetic electron precipitation during the moderate geomagnetic storm driven by the ICME. Energetic electron precipitation is inferred from increases in cosmic noise absorption (CNA) recorded by stations in the Global Riometer Array (GLO-RIA). No evidence of CNA was observed during the first four hours of passage of the ICME or following the sudden commencement (SC) of the storm. This is consistent with the findings of Osepian and Kirkwood (2004) that SCs will only trigger precipitation during periods of geomagnetic activity or when the magnetic perturbation in the magnetosphere is substantial. CNA was only observed following enhanced coupling between the IMF and the magnetosphere, resulting from southward oriented IMF. Precipitation was observed due to substorm activity, as a result of the initial injection and particles drifting from the injection region. During the recovery phase of the storm, when substorm activity diminished, precipitation due to density driven increases in the solar wind dynamic pressure (P dyn ) were identified. A number of increases in P dyn were shown to drive sudden impulses (SIs) in the geomagnetic field. While many of these SIs appear coincident with CNA, SIs without CNA were also observed. During this period, the threshold of geomagnetic activity required for SC driven precipitation was exceeded. This implies that solar wind density driven SIs occurring during storm recovery can drive a different response in particle precipitation to typical SCs.

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“…Ortner et al (1962) reported that SCAs were located around the central line of the auroral zone. Increased electron density at altitudes 80-100 km has also been detected by the EISCAT radar during several SC events (Yahnin et al, 1995;Manninen et al, 1996) indicating the wide energy range of precipitating electrons.…”

Section: Introductionmentioning

confidence: 99%

Geomagnetic disturbances on ground associated with particle precipitation during SC

Safargaleev

Kozlovsky²,

Honary

et al. 2010

Ann. Geophys.

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Abstract.We have examined several cases of magnetosphere compression by solar wind pressure pulses using a set of instruments located in the noon sector of auroral zone. We have found that the increase in riometric absorption (sudden commencement absorption, SCA) occurred simultaneously with the beginning of negative or positive magnetic variations and broadband enhancement of magnetic activity in the frequency range above 0.1 Hz. Since magnetic variations were observed before the step-like increase of magnetic field at equatorial station (main impulse, MI), the negative declinations resembled the so-called preliminary impulse, PI. In this paper a mechanism for the generation of PI is introduced whereby PI's generation is linked to SCA -associated precipitation and the local enhancement of ionospheric conductivity leading to the reconstruction of the ionospheric current system prior to MI. Calculation showed that PI polarity depends on orientation of the background electric field and location of the observation point relative to ionospheric irregularity. For one case of direct measurements of electric field in the place where the ionospheric irregularity was present, the sign of calculated disturbance corresponded to the observed one. High-resolution measurements on IRIS facility and meridional chain of the induction magnetometers are utilized for the accurate timing of the impact of solar wind irregularity on the magnetopause.

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Cosmic noise absorption accompanying geomagnetic storm sudden commencements

Cited by 61 publications

References 15 publications

Observations of ionospheric flows and particle precipitation following a Sudden Commencement

Observations of ionospheric flows and particle precipitation following a Sudden Commencement

The driving mechanisms of particle precipitation during the moderate geomagnetic storm of 7 January 2005

Geomagnetic disturbances on ground associated with particle precipitation during SC

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