Irina Mironova

Energetic particle precipitation (EPP) during geomagnetic storms plays a significant role in accelerating ozone depletion in the high-latitude upper atmosphere. During the January 2026 geomagnetic storm with a sudden commencement reached NOAA G4 level following an X1.9-class solar flare on January 18 and a fast coronal mass ejection arrived at Earth. The storm commenced on January 19, producing an AE index up to 2,597 nT and a severe storm levels globally (NOAA Kp 8-). The storm persisted through January 20, producing a | Dst | index minimum of 236 nT, characteristic of an intense event. The Aura Microwave Limb Sounder (MLS) instrument provides simultaneous measurements of chemical species from the upper troposphere to the mesosphere, enabling detailed investigation of energetic particle precipitation effects on atmospheric composition. Using data from MLS/Aura collected in January 2026, we have analyzed the HO 2 , HNO 3 , and ozone variability over the high-latitude bands between 60 o and 80 o in both the Northern and Southern Hemispheres. MLS/Aura observations show EPP influence in both hemispheres, with it being more pronounced in the Northern Hemisphere. Instantaneous EPP-induced ozone depletion up to 70% is observed in the altitudinal range from 0.01 hPa to 0.1 hPa, and after this EPP ozone did not recover until the end of the month.

On January 16–22, 2005 huge fluxes of high-energy charged particles came from the Sun through magnetosphere to our Earth. Charged particles mostly solar protons and magnetospheric electrons affect the atmosphere by inducing additional ionization sources in ionosphere and atmosphere. Ionization plays main role in the formation of ozone-depleting odd oxides of nitrogen (NO_x) and hydrogen (HO_x). Here we study the energetic particle impact on the chemical properties of the stratosphere and mesosphere in the Northern Hemisphere using MLS Aura data obtained during January 16–22, 2005. We show how strong can be depleted the polar ozone layer in mesosphere and change the chemistry from the mesosphere to the stratosphere during geoeffective coronal mass ejections and magnetic storms.

The high latitude Earth’s atmosphere is ionized via direct solar radiation. This results in the formation of positively charged ions through, e.g., photoionization and the ionization of NO. A one-dimensional chemical and climatic model with interactive neutral and ionic chemistry is used to track the ionic compositions of the D region of the ionosphere on daily and seasonal scales. It is found that ion clusters dominate the total ion content up to altitudes of 95 km in winter and 80 km in summer.

Energetic electron precipitation (EEP) into the Earth’s atmosphere/ionosphere caused by various physical mechanisms and recorded by various instruments are studied separately. EEP events detected in balloon observations in the Murmansk region and from low-orbit Meteor-M2 satellite were used to estimate EEP effects on the atmosphere/ionosphere. Satellite energy channels from hundreds of keV to MeV were used to reconstruct the EEP energy spectra. To determine the atmospheric-ionospheric response to EEP during geomagnetic disturbances, calculated ionization rates were used based on spectra obtained from both satellites and balloon observations. The EEP spectra from satellites and balloon observations have practically the same slope, and only the particle flux intensity changes. The ionization rates throughout the altitude range on the last day of substorm activity are lower than during substorm activity maximum.

Solar proton events (SPEs) affect the Earth’s atmosphere, causing additional ionization in the high-latitude mesosphere and stratosphere. Ionization rates from such solar proton events maximize in the stratosphere, but the formation of ozone-depleting nitrogen and hydrogen oxides begins at mesospheric altitudes. The destruction of mesospheric ozone is associated with protons with energies of about 10 MeV and higher and will strongly depend on the intensity of the flux of these particles. Most studies investigating the impact of SPEs on the characteristics of the middle atmosphere have been based on either simulations or reanalysis datasets, and some studies have used satellite observations to validate model results. We study the impact of SPEs on cold-season ozone loss in both the northern and southern hemispheres using Aura MLS mesospheric ozone measurements over the 2004 to 2024 period. Here, we show how strongly SPEs can deplete polar mesospheric ozone in different hemispheres and attempt to evaluate this dependence on the intensity of solar proton events. We found that moderate SPEs consisting of protons with an energy of more than 10 MeV and a flux intensity of more than 100 pfu destroy mesospheric ozone in the northern hemisphere up to 47% and in the southern hemisphere up to 33%. For both hemispheres, the peak of winter ozone loss was observed at about 76 km. In the northern hemisphere, maximum winter ozone loss was observed on the second day after a solar proton event, but in the southern hemisphere, winter ozone depletion was already detected on the first day. In the southern hemisphere, mesospheric ozone concentrations return to pre-event levels on the ninth day after a solar proton event, but in the northern hemisphere, even on the tenth day after a solar proton event, the mesospheric ozone layer may not be fully recovered. The strong SPEs with a proton flux intensity of more than 1000 pfu lead to a maximum winter ozone loss of up to 85% in the northern hemisphere, and in the southern hemisphere winter, ozone loss reaches 73%.