The impact of an extreme solar event on the middle atmosphere: a case study

A possible impact of an extreme solar particle event (ESPE) on the middle atmosphere is studied for present-day climate and geomagnetic conditions. We consider an ESPE with an occurrence probability of about 1 per millennium. In addition, we assume that the ESPE is followed by an extreme geomagnetic storm (GMS), and we compare the contribution of the two extreme events. The strongest known and best-documented ESPE of 774/5 CE is taken as a reference example and established estimates of the corresponding ionization rates are applied. The ionization rates due to the energetic particle precipitation (EPP) during an extreme GMS are upscaled from analyzed distributions of electron energy spectra of observed GMSs. The consecutive buildup of NOx and HOx by ionization is modeled in the high-top 3D chemistry circulation model KArlsruhe SImulation Model of the middle Atmosphere (KASIMA), using specified dynamics from ERA-Interim analyses up to the stratopause. A specific dynamical situation was chosen that includes an elevated stratosphere event during January and maximizes the vertical coupling between the northern polar mesosphere–lower thermosphere region and the stratosphere; it therefore allows us to estimate a maximum possible impact. The particle event initially produces about 65 Gmol of NOy, with 25 Gmol of excess NOy even after 1 year. The related ozone loss reaches up to 50 % in the upper stratosphere during the first weeks after the event and slowly descends to the mid-stratosphere. After about 1 year, 20 % ozone loss is still observed in the northern stratosphere. The GMS causes strong ozone reduction in the mesosphere but plays only a minor role in the reduction in total ozone. In the Southern Hemisphere (SH), the long-lived NOy in the polar stratosphere, which is produced almost solely by the ESPE, is transported into the Antarctic polar vortex, where it experiences strong denitrification into the troposphere. For this special case, we estimate a NO3 washout that could produce a measurable signal in ice cores. The reduction in total ozone causes an increase of the UV erythema dose of less than 5 %, which maximizes in spring for northern latitudes of 30∘ and in summer for northern latitudes of about 60∘

Impact of chlorine ion chemistry on ozone loss in the middle atmosphere during very large solar proton events

Solar coronal mass ejections can accelerate charged particles, mostly protons, to high energies, causing solar proton events (SPEs). Such energetic particles can precipitate upon the Earth\u27s atmosphere, mostly in polar regions because of geomagnetic shielding. Here, SPE-induced chlorine activation due to ion chemistry can occur, and the activated chlorine depletes ozone in the polar middle atmosphere. We use the state-of-the-art 1D stacked-box Exoplanetary Terrestrial Ion Chemistry (ExoTIC) model of atmospheric ion and neutral composition to investigate such events in the Northern Hemisphere (NH). The Halloween SPE that occurred in late October 2003 is used as a test field for our study. This event has been extensively studied before using different 3D models and satellite observations. Our main purpose is to use such a large event that has been recorded by the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) on the Environmental Satellite (ENVISAT) to evaluate the performance of the ion chemistry model. Sensitivity tests were carried out for different model settings with a focus on the chlorine species of HOCl and ClONO2 as well as O3 and reactive nitrogen, NOy. The model simulations were performed in the Northern Hemisphere at a high latitude of 67.5∘ N, inside the polar cap. Comparison of the simulated effects against MIPAS observations for the Halloween SPE revealed rather good temporal agreement, also in terms of altitude range for HOCl, O3 and NOy. For ClONO2, good agreement was found in terms of altitude range. The model showed ClONO2 enhancements after the peak of the event. The best model setting was the one with full ion chemistry where O(1D) was set to photo-chemical equilibrium. HOCl and ozone changes are very well reproduced by the model, especially for nighttime. HOCl was found to be the main active chlorine species under nighttime conditions, resulting in an increase of more than 0.2 ppbv. Further, ClONO2 enhancements of 0.2–0.3 ppbv have been observed during both daytime and nighttime. Model settings that compared best with MIPAS observations were applied to an extreme solar event that occurred in AD 775, presumably once in a 1000-year event. With the model applied to this scenario, an assessment can be made about what is to be expected at worst for the effects of a SPE on the middle atmosphere, concentrating on the effects of ion chemistry compared to crude parameterizations. Here, a systematic analysis comparing the impact of the Halloween SPE and the extreme event on the Earth\u27s middle atmosphere is presented. As seen from the model simulations, both events were able to perturb the polar stratosphere and mesosphere with a high production of NOy and HOx. Longer-lasting and stronger stratospheric ozone loss was seen for the extreme event. A qualitative difference between the two events and a long-lasting impact on HOCl and HCl for the extreme event were found. Chlorine ion chemistry contributed to stratospheric ozone losses of 2.4 % for daytime and 10 % for nighttime during the Halloween SPE, as seen with time-dependent ionization rates applied to the model. Furthermore, while comparing the Halloween SPE and the extreme scenario, with ionization rate profiles applied just for the event day, the inclusion of chlorine ion chemistry added ozone losses of 10 % and 20 % respectively

Energetic Particle Precipitation during Extreme Space Weather Events

Here we provide a selection of extreme geomagnetic storms of the last century based on NOAA classification which lead to the energetic particle precipitation (EPP). EPP of such geomagnetic storms can cause power outages, communication failures, and navigation problems as well as impact on the environment and the ozone level. Studies of historical extreme geomagnetic storms together with EPP for large space weather events in the space era can help to reconstruct the parameters of extreme events of past centuries

Polar particle flux distribution and its spatial extent

Context: The main challenge in atmospheric ionisation modelling is that sparse measurements are used to derive a global precipitation pattern. Typically this requires intense interpolation or scaling of long-term average maps. In some regions however, the particle flux might be similar and a combination of these regions would not limit the results even though it would dramatically improve the spatial and temporal data coverage. Aims: The paper intends to statistically analyse the particle flux distribution close to the geomagnetic poles labelled as Polar Particle Flux Distribution (PPFD) and identify similar distributions in neighbouring bins. Those bins are grouped and the size of the PPFD area is estimated. The benefit is that single measurements within the PPFD area should be able to represent the particle flux for the whole area at a given time. Methods: We use spatially binned energetic particle flux distributions measured by POES and Metop spacecraft during 2001–2018 to identify a Kp-dependent area with a similar flux distribution as the one found close to the geomagnetic poles (|magn.lat| > 86°). First, the particle flux is mapped on a magnetic local time (MLT) vs. magnetic latitude grid. In the second step, the gridded data is split up according to Kp levels (forming the final bins). Third, the particle flux in every bin has been recalculated in order to replace zero-count rates with rates based on longer measurement periods which results in a more realistic low flux end of the particle distribution. Then the binned flux distributions are compared to the PPFD. A “Δ-test” indicates the similarity. A threshold for the Δ-test is defined using the standard deviation of Δ-test values inside the (|magn.lat| > 86°) area. Bins that meet the threshold are attributed as PPFD area. Results: PPFDs and the corresponding PPFD areas have been determined for all investigated particle channels, covering an energy range of 154 eV–300 keV for electrons and 154 eV–2.5 MeV for protons. Concerning low energy channels a gradual flux increase with rising Kp has been identified. High energy channels show a combination of background population and solar particle event (SPE) population that adds up with increasing Kp. The size of the PPFD area depends on particle species, energy and geomagnetic disturbance, as well as MLT. The main findings are: a) There are small but characteristic hemispheric differences. b) Only above a certain energy threshold do the PPFD areas increase with particle energy. c) A clear enlargement with rising Kp is identified – with exceptions for very low Kp. d) The centre of the PPFD area is shifted towards midnight and moves with Kp. Asymmetries of the boundaries could be explained by auroral intensity. e) For low-energy particles the main restriction of the PPFD area seems to be the auroral precipitation

The impact of an extreme solar event on the middle atmosphere:a case study

Abstract A possible impact of an extreme solar particle event (ESPE) on the middle atmosphere is studied for present-day climate and geomagnetic conditions. We consider an ESPE with an occurrence probability of about 1 per millennium. In addition, we assume that the ESPE is followed by an extreme geomagnetic storm (GMS), and we compare the contribution of the two extreme events. The strongest known and best-documented ESPE of 774/5 CE is taken as a reference example and established estimates of the corresponding ionization rates are applied. The ionization rates due to the energetic particle precipitation (EPP) during an extreme GMS are upscaled from analyzed distributions of electron energy spectra of observed GMSs. The consecutive buildup of NOx and HOx by ionization is modeled in the high-top 3D chemistry circulation model KArlsruhe SImulation Model of the middle Atmosphere (KASIMA), using specified dynamics from ERA-Interim analyses up to the stratopause. A specific dynamical situation was chosen that includes an elevated stratosphere event during January and maximizes the vertical coupling between the northern polar mesosphere–lower thermosphere region and the stratosphere; it therefore allows us to estimate a maximum possible impact. The particle event initially produces about 65 Gmol of NOy, with 25 Gmol of excess NOy even after 1 year. The related ozone loss reaches up to 50 % in the upper stratosphere during the first weeks after the event and slowly descends to the mid-stratosphere. After about 1 year, 20 % ozone loss is still observed in the northern stratosphere. The GMS causes strong ozone reduction in the mesosphere but plays only a minor role in the reduction in total ozone. In the Southern Hemisphere (SH), the long-lived NOy in the polar stratosphere, which is produced almost solely by the ESPE, is transported into the Antarctic polar vortex, where it experiences strong denitrification into the troposphere. For this special case, we estimate a NO₃ washout that could produce a measurable signal in ice cores. The reduction in total ozone causes an increase of the UV erythema dose of less than 5 %, which maximizes in spring for northern latitudes of 30∘ and in summer for northern latitudes of about 60∘

Heppa III Intercomparison Experiment on Electron Precipitation Impacts: 2. Model-Measurement Intercomparison of Nitric Oxide (NO) During a Geomagnetic Storm in April 2010

Precipitating auroral and radiation belt electrons are considered to play an important part in the natural forcing of the middle atmosphere with a possible impact on the climate system. Recent studies suggest that this forcing is underestimated in current chemistry-climate models. The HEPPA III intercomparison experiment is a collective effort to address this point. In this study, we apply electron ionization rates from three data-sets in four chemistry-climate models during a geomagnetically active period in April 2010. Results are evaluated by comparison with observations of nitric oxide (NO) in the mesosphere and lower thermosphere. Differences between the ionization rate data-sets have been assessed in a companion study. In the lower thermosphere, NO densities differ by up to one order of magnitude between models using the same ionization rate data-sets due to differences in the treatment of NO formation, model climatology, and model top height. However, a good agreement in the spatial and temporal variability of NO with observations lends confidence that the electron ionization is represented well above 80 km. In the mesosphere, the averages of model results from all chemistry-climate models differ consistently with the differences in the ionization-rate data-sets, but are within the spread of the observations, so no clear assessment on their comparative validity can be provided. However, observed enhanced amounts of NO in the mid-mesosphere below 70 km suggest a relevant contribution of the high-energy tail of the electron distribution to the hemispheric NO budget during and after the geomagnetic storm on April 6.ISSN:0148-0227ISSN:2169-938