Case study of the mesospheric and lower thermospheric effects of solar X-ray flares: coupled ion-neutral modelling and comparison with EISCAT and riometer measurements

Abstract

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 NO x 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 10 8 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.

Effects of the September 2005 Solar Flares and Solar Proton Events on the Middle Atmosphere in WACCM

“…Solar flares also influence the mesosphere and thermosphere (Donnelly, 1976;Enell et al, 2008;Tsurutani et al, 2009;Woods et al, 2004). Depending on the flare's spectral irradiance and class (e.g., Le et al, 2016;Tsurutani et al, 2005) and the solar zenith angle (Le et al, 2007), photoionization of the atmosphere by solar flares can occur at altitudes from approximately 80 km up through the layers of the ionosphere.…”

New incoherent scatter diagnostic methods for the heated D-region ionosphere

“…In the present work an experimental version (SIC 7.2), developed as part of the work presented by Enell et al (2008), was applied for modelling the background altitude profiles of N e , λ and m i . Only solar radiation and electron precipitation were considered as ionisation sources.…”

Heuristic model of solar X-ray spectrum according to satellite data for geophysical applications

“…This allows us to compute T=T XR (R), where R=W XL /W XS , from measured W XL and W XS , and then to get C ME . Enell et al [2008] used the spectrum proposed in [Culhane, Acton, 1970]…”

“…These events have been analyzed in [Korsunskaja, 2015]. Enell et al [2008] employed a method for reconstructing the hard X-ray (HXR) spectrum from GOES XL and XS measurements, using the results obtained by Garcia [1994]. The author has shown that these measurements can be used to reconstruct parameters of the temperature spectrum of the type…”