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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.

The paper reviews recent advances in studies of electric discharges in the stratosphere and mesosphere above thunderstorms, and their effects on the atmosphere. The primary focus is on the sprite discharge occurring in the mesosphere, which is the most commonly observed high altitude discharge by imaging cameras from the ground, but effects on the upper atmosphere by electromagnetic radiation from lightning are also considered. During the past few years, co-ordinated observations over Southern Europe have been made of a wide range of parameters related to sprites and their causative thunderstorms. Observations have been complemented by the modelling of processes ranging from the electric discharge to perturbations of trace gas concentrations in the upper atmosphere. Observations point to significant energy deposition by sprites in the neutral atmosphere as observed by infrasound waves detected at up to 1000 km distance, whereas elves and lightning have been shown significantly to affect ionization and heating of the lower ionosphere/mesosphere. Studies of the thunderstorm systems powering high altitude discharges show the important role of intracloud (IC) lightning in sprite generation as seen by the first simultaneous observations of IC activity, sprite activity and broadband, electromagnetic radiation in the VLF range. Simulations of sprite ignition suggest that, under certain conditions, energetic electrons in the runaway regime are generated in streamer discharges. Such electrons may be the source of X-and Gamma-rays observed in lightning, thunderstorms and the so-called Terrestrial Gamma-ray Flashes (TGFs) observed from space over thunderstorm regions. Model estimates of sprite perturbations to the global atmospheric electric circuit, trace gas concentrations and atmospheric dynamics suggest significant local perturbations, and possibly significant meso-scale effects, but negligible global effects.

Abstract. Transient luminous events, such as red sprites, occur in the middle atmosphere in the electric field above thunderstorms. We here address the question whether these processes may be a significant source of odd nitrogen and affect ozone or other important trace species. A well-established coupled ion-neutral chemical model has been extended for this purpose and applied together with estimated rates of ionisation, excitation and dissociation based on spectroscopic ratios from ISUAL on FORMOSAT-2. This approach is used to estimate the NO x and ozone changes for two type cases.The NO x enhancements are at most one order of magnitude in the streamers, which means a production of at most 10 mol per event, or (given a global rate of occurrence of three events per minute) some 150-1500 kg per day. The present study therefore indicates that sprites are insignificant as a global source of NO x . Local effects on ozone are also negligible, but the local enhancement of NO x may be significant, up to 5 times the minimum background at 70 km in extraordinary cases.

[1] Ground-based zenith sky UV-visible measurements of stratospheric bromine monoxide (BrO) slant column densities are compared with simulations from the SLIMCAT three-dimensional chemical transport model. The observations have been obtained from a network of 11 sites, covering high and midlatitudes of both hemispheres. This data set gives for the first time a near-global picture of the distribution of stratospheric BrO from ground-based observations and is used to test our current understanding of stratospheric bromine chemistry. In order to allow a direct comparison between observations and model calculations, a radiative transfer model has been coupled to the chemical model to calculate simulated slant column densities. The model reproduces the observations in general very well. The absolute amount of the BrO slant columns is consistent with a total stratospheric bromine loading of 20 ± 4 ppt for the period 1998-2000, in agreement with previous estimates. The seasonal and latitudinal variations of BrO are well reproduced by the model. In particular, the good agreement between the observed and modeled diurnal variation provides strong evidence that the BrO-related bromine chemistry is correctly modeled. A discrepancy between observed and modeled BrO at high latitudes during events of chlorine activation can be resolved by increasing the rate constant for the reaction BrO + ClO ! BrCl + O 2 to the upper limit of current recommendations. However, other possible causes of the discrepancy at high latitudes cannot be ruled out.