Some observations of short-duration cosmic noise absorption events in nearly conjugate regions at high magnetic latitude

Abstract. Two case studies of upper mesospheric and lower thermospheric (UMLT) high-latitude effects of solar X-ray flares are presented. Sodankylä Ion-neutral Chemistry Model (SIC) electron density profiles agree with D-region EISCAT and riometer observations, provided that the profiles of the most variable ionisable component, nitric oxide, are adjusted to compensate for NOx production during preceding geomagnetically active periods. For the M6-class flare of 27 April 2006, following a quiet period, the agreement with cosmic noise absorption observed by the Sodankylä riometers was within reasonable limits without adjustment of the [NO] profile. For the major (X17-class) event of 28 October 2003, following high auroral activity and solar proton events, the NO concentration had to be increased up to on the order of 108 cm−3 at the D-region minimum. Thus [NO] can in principle be measured by combining SIC with observations, if the solar spectral irradiance and particle precipitation are adequately known. As the two case events were short and modelled for high latitudes, the resulting neutral chemical changes are insignificant. However, changes in the model ion chemistry occur, including enhancements of water cluster ions.

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Relation between lower ionospheric electron density profiles and cosmic noise absorption during auroral zone disturbances.

Journal of geomagnetism and geoelectricity ◽

10.5636/jgg.27.113 ◽

1975 ◽

Vol 27 (2) ◽

pp. 113-129 ◽

Cited By ~ 6

Author(s):

Shigeru MIYAZAKI

Keyword(s):

Electron Density ◽

Auroral Zone ◽

Ionospheric Electron Density ◽

Density Profiles ◽

Noise Absorption ◽

Electron Density Profiles ◽

Cosmic Noise

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Pulsating aurora and cosmic noise absorption associated with growth-phase arcs

Annales Geophysicae ◽

10.5194/angeo-36-59-2018 ◽

2018 ◽

Vol 36 (1) ◽

pp. 59-69 ◽

Cited By ~ 7

Author(s):

Derek McKay ◽

Noora Partamies ◽

Juha Vierinen

Keyword(s):

Growth Phase ◽

Optical Emission ◽

Border Region ◽

Emission Region ◽

Expansion Phase ◽

Phase Dynamics ◽

Noise Absorption ◽

Initial Stage ◽

Cosmic Noise

Abstract. The initial stage of a magnetospheric substorm is the growth phase, which typically lasts 1–2 h. During the growth phase, an equatorward moving, east–west extended, optical auroral arc is observed. This is called a growth-phase arc. This work aims to characterize the optical emission and riometer absorption signatures associated with growth-phase arcs of isolated substorms. This is done using simultaneous all-sky camera and imaging riometer observations. The optical and riometric observations allow determination of the location of the precipitation within growth-phase arcs of low- (<10 keV) and high- (> 10 keV) energy electrons, respectively. The observations indicate that growth-phase arcs have the following characteristics: The peak of the cosmic noise absorption (CNA) arc is equatorward of the optical emission arc. This CNA is contained within the region of diffuse aurora on the equatorward side. Optical pulsating aurora are seen in the border region between the diffuse emission region on the equatorward side and the bright growth-phase arc on the poleward side. CNA is detected in the same region. There is no evidence of pulsations in the CNA. Once the equatorward drift starts, it proceeds at constant speed, with uniform separation between the growth-phase arc and CNA of 40±10 km. Optical pulsating aurora are known to be prominent in the post-onset phase of a substorm. The fact that pulsations are also seen in a fairly localized region during the growth phase shows that the substorm expansion-phase dynamics are not required to closely precede the pulsating aurora. Keywords. Ionosphere (auroral ionosphere)

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