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[1] We have studied the short-term effect of the October-November 2003 series of solar proton events on the middle atmosphere. Using the proton flux measurements from the GOES-11 satellite as input, we modeled the effect of the precipitating particles between 26 October and 6 November with a one-dimensional ion and neutral chemistry model. Then we compared the results with ground-based radio propagation measurements, as well as with NO 2 and ozone profiles made by the GOMOS satellite instrument. The very low frequency signal experiences up to À7 dB absorption during the largest solar proton event, subsequently varying with time of day during the recovery phase. The model and radio propagation observations show very good agreement, suggesting that the model is capturing the impact of solar protons on the ionosphere. The model results show order-of-magnitude changes in odd hydrogen and odd nitrogen concentrations, as well as ozone depletion varying from 20% at 40 km altitude to more than 95% at 78 km. The magnitude and altitude distribution of ozone depletion is found to depend not only on the flux and energy of the protons but also on the diurnal cycle of atomic oxygen and ozone-depleting constituents so that the largest depletions of ozone are seen during sunrise and sunset. The after-event recovery of ozone is altitude-dependent because of the differences in the recovery of odd hydrogen and odd nitrogen and also because of a relatively faster ozone production at higher altitudes. The modeled and measured NO 2 profiles agree well at altitudes 35-60 km, particularly during times of large concentrations observed after the solar proton event onset. A comparison of the time series of ozone depletion shows a good agreement between the model and observations.

For some time theoretical modeling has shown that electromagnetic ion cyclotron (EMIC) waves should play an important role in the loss of relativistic electrons from the radiation belts, through precipitation into the atmosphere. Up to now there has been limited experimental evidence for relativistic electron precipitation driven by EMIC waves. In this paper we present case studies of events showing EMIC waves, observed by ground‐based pulsation magnetometers, which are linked to strong responses in a subionospheric precipitation monitor. This response is consistent with precipitation occurring near the plasmapause, where EMIC waves may resonate with relativistic electrons. At the same time there is only a weak response in a co‐located riometer chain, as expected for relativistic electron precipitation that penetrates deeply into the atmosphere.

Abstract. While several model estimates predict cooling of the upper atmosphere as a result of increasing concentrations of greenhouse gases, direct observational evidence of such a trend is scarce and partly susceptible, because the relevant data series do not cover sufficiently long time periods. We study the long-term data set from the ionosonde station at Sodankyl•i (67.4 ø N, 26.7 ø E), which has been operated during almost 4 solar cycles. We find a close to linear decrease in the altitude of the F2 layer peak during the last 39 years, when the effect of solar cycle variations is removed from the data. This local trend is qualitatively consistent with the model predictions of a cooling of the lower thermosphere.

[1] AARDDVARK data from a radio wave receiver in Sodankylä, Finland have been used to monitor transmissions across the auroral oval and just into the polar cap from the very low frequency communications transmitter, call sign NAA (24.0 kHz, 44°N, 67°W, L = 2.9), in Maine, USA, since 2004. The transmissions are influenced by outer radiation belt (L = 3-7) energetic electron precipitation. In this study, we have been able to show that the observed transmission amplitude variations can be used to determine routinely the flux of energetic electrons entering the upper atmosphere along the total path and between 30 and 90 km. Our analysis of the NAA observations shows that electron precipitation fluxes can vary by 3 orders of magnitude during geomagnetic storms. Typically when averaging over L = 3-7 we find that the >100 keV POES "trapped" fluxes peak at about 10 6 el. cm −2 s −1 sr −1 during geomagnetic storms, with the DEMETER >100 keV drift loss cone showing peak fluxes of 10 5 el. cm −2 s −1 sr −1 , and both the POES >100 keV "loss" fluxes and the NAA ground-based >100 keV precipitation fluxes showing peaks of ∼10 4 el. cm −2 s −1 sr −1 . During a geomagnetic storm in July 2005, there were systematic MLT variations in the fluxes observed: electron precipitation flux in the midnight sector (22-06 MLT) exceeded the fluxes from the morning side (0330-1130 MLT) and also from the afternoon sector (1130( -1930. The analysis of NAA amplitude variability has the potential of providing a detailed, near real-time, picture of energetic electron precipitation fluxes from the outer radiation belts.