Bibliography

Total Electron Content Variations during an HSS/CIR driven storm at high and middle latitudes

Geethakumari, Gopika; Aikio, Anita; Cai, Lei; Vanhamaki, Heikki; Pedersen, Marcus; Coster, Anthea; Marchaudon, Aurélie; Blelly, Pierre-Louis; Haberle, Veronika; Maute, Astrid; Ellahouny, Nada; Virtanen, Ilkka; Norberg, Johannes; Soyama, Shin-Ichiro; Grandin, Maxime;

Published by:       Published on: mar

YEAR: 2022     DOI: 10.5194/egusphere-egu22-8194

Ionospheric effects of a solar wind high-speed stream driven geomagnetic storm

Solar wind high-speed streams (HSSs) and associated stream interaction regions (SIRs) typically produce long-lasting, but only moderate or weak geomagnetic storms. In this presentation, we will focus on electron density (Ne) and total electron content (TEC) changes at high to middle latitudes and associated physical processes during a specific HSS/SIR driven storm. The very long-lasting storm was produced by two interacting high-speed streams. Both enhancements, but in specific long-lasting (days) decreases of Ne and TEC are observed by the EISCAT radars and GNSS observations, respectively. Observational data sets also include AMPERE field-aligned current data, SuperDARN convection maps, and TIMED/GUVI observations of the O/N2 ratio.e

Aikio, Anita;

Published by: 44th COSPAR Scientific Assembly. Held 16-24 July      Published on:

YEAR: 2022     DOI:

IPIM Modeling of the Ionospheric F ₂ Layer Depletion at High Latitudes During a High-Speed Stream Event

Our aim is to understand the effect of high-speed stream events on the high-latitude ionosphere and more specifically the decrease of the f_oF₂ frequency during the entire day following the impact. First, we have selected one summertime event, for which a large data set was available: Super Dual Auroral Radar Network (SuperDARN) and European Incoherent SCATter (EISCAT) radars, Troms\o and Sodankylä ionosondes, and the CHAllenging Minisatellite Payload (CHAMP) satellite. We modeled with the IPIM model (IRAP Plasmasphere Ionosphere Model) the dynamics of the ionosphere at Troms\o and Sodankylä using inputs derived from the data. The simulations nicely match the measurements made by the EISCAT radar and the ionosondes, and we showed that the decrease of f_oF₂ is associated with a transition from F₂ to F₁ layer resulting from a decrease of neutral atomic oxygen concentration. Modeling showed that electrodynamics can explain short-term behavior on the scale of a few hours, but long-term behavior on the scale of a few days results from the perturbation induced in the atmosphere. Enhancement of convection is responsible for a sharp increase of the ion temperature by Joule heating, leading through chemistry to an immediate reduction of the F₂ layer. Then, ion drag on neutrals is responsible for a rapid heating and expansion of the thermosphere. This expansion affects atomic oxygen through nonthermal upward flow, which results in a decrease of its concentration and amplifies the decrease of [O]/[N₂] ratio. This thermospheric change explains long-term extinction of the F₂ layer.

Marchaudon, A.; Blelly, P.-L.; Grandin, M.; Aikio, A.; Kozlovsky, A.; Virtanen, I.;

Published by: Journal of Geophysical Research: Space Physics      Published on: 08/2018

YEAR: 2018     DOI: 10.1029/2018JA025744

IPIM Modeling of the Ionospheric F 2 Layer Depletion at High Latitudes During a High-Speed Stream Event

Our aim is to understand the effect of high‐speed stream events on the high‐latitude ionosphere and more specifically the decrease of the f o F 2 frequency during the entire day

Marchaudon, A; Blelly, P-L; Grandin, M; Aikio, A; Kozlovsky, A; Virtanen, I;

Published by: Journal of Geophysical Research: Space Physics      Published on:

YEAR: 2018     DOI: 10.1029/2018JA025744

Radar observations of simultaneous traveling ionospheric disturbances and atmospheric gravity waves

Simultaneous observations of atmospheric gravity waves (AGWs) and traveling ionospheric disturbances (TIDs) measured by an incoherent scatter radar at high latitudes are shown. The measurements were made using a beam swing experiment of the EISCAT UHF radar. The\ F\ region TID is seen as wavefronts in electron density, whereas the\ E\ region AGW is seen in the oscillations of the neutral wind. The wave vector of the TID has a downward component indicating that energy propagates upward. The periods of AGWs and TIDs are approximately the same (52\textendash57min), so it is concluded that the observed gravity wave in the\ E\ region propagates to the\ F\ region causing the TID there. Two interesting properties of the waves are observed. First, the neutral wind oscillations have an amplitude minimum at about 115km. It is suggested that this could be related to the minimum of the vertical refractive index around 120km. Second, in the course of time, the wave vector of the TID turns more in the downward direction, which leads to an increase in the horizontal wave length from 400 to 1450km. A possible explanation is that the background wind increases with altitude and turns the wavefronts more horizontal when distance from a stationary source increases. We suggest that the source is the sunrise terminator, since the horizontal direction of propagation of the TID in the morning hours is from the west, where both the auroral and thunderstorm activity are low.

en, Nygr\; Aikio, A.; Voiculescu, M.; Cai, L.;

Published by: Journal of Geophysical Research: Space Physics      Published on: 05/2015

YEAR: 2015     DOI: 10.1002/2014JA020794

atmospheric gravity wave; incoherent scatter; solar terminator; traveling ionospheric disturbance