5:15 PM - 7:15 PM
[PEM10-P21] Variations in the ozone concentration in the mesosphere observed at Syowa Station associated with energetic particle precipitation
Keywords:ozone, mesosphere, energetic particle precipitation
We report variations in ozone (O3) concentrations in the mesosphere above Syowa Station, Antarctica, caused by energetic particle precipitation (EPP) associated with a major magnetic storm in May 2024. Additionally, we report a statistical analysis of the relationship between mesospheric O3 and geomagnetic activity over five months, from July to October 2022 and May 2024. The goal is to clarify the decrease in O3 concentration in the mesosphere associated with the EPP. In the polar regions, EPP are associated with solar proton events and magnetic storms. The ionization of atmospheric molecules induced by the EPP produces nitrogen oxide and hydrogen oxide in the mesosphere, which can cause O3 destruction.
We used a millimeter-wave spectroradiometer installed by Nagoya University at Syowa Station in Antarctica. The millimeter-wave spectra observed on the ground were integrations of O3 radiation over altitudes from the surface to the lower thermosphere. We retrieved the altitude distribution of the O3 volume mixing ratio (VMR) from the radiation spectra to quantitatively estimate the O3 concentration in the mesosphere.
In the case of the major magnetic storm of May 2024, the O3 column amounts were compared with the EPP and NO column amounts in the mesosphere. After the magnetic storm started on May 10th, an increase in proton flux from 10 MeV to over 100 MeV was observed from May 10th to 20th. During this period, the PANSY radar observed signatures of EPP, and a monotonic decrease in O3 column amounts was observed from dusk to dawn, particularly from May 10th to 11th. A comparison of the NO column amounts in the mesosphere showed an overall inverse correlation with the O3 column amounts. However, during the significant decrease in O3 column amounts from May 10th to 11th, the NO column amounts showed little increase, which was an unexpected feature, as NO typically acts as a catalyst in the O3 destruction reaction. A detailed analysis was conducted to determine the cause of the decrease from May 10th to 11th. The data from the GOES satellite showed that the solar proton flux began increasing gradually around LT 12:00 on May 9th and peaked around LT 20:50 on May 10th. The riometer data at Syowa Station indicated an intense EPP at LT 20:10 on May 10th, followed by weaker precipitation until LT 21:40. It can be inferred that the EPP occurred over Syowa Station from May 10th to 11th, leading to a decrease in the O3 column amounts in the mesosphere. To investigate the origin of the EPP, the rTEC keogram over Tromso, Norway, located near the magnetic conjugate of the Syowa Station, was examined. The auroral oval appeared over Tromso around LT 20:00 on May 10th following the onset of the magnetic storm, and then moved toward lower latitudes. The auroral oval moved back over Tromso from lower latitudes at LT 03:00 on May 11th. Therefore, during the period when the O3 column amounts decreased, Syowa Station was likely located inside the polar cap region. This suggests that the decrease in the O3 column amount from May 10th to 11th was likely caused by solar protons.
In the statistical analysis covering a total of five months from July to October 2022 and May 2024, the correlation between the O3 column amounts in the mesosphere and geomagnetic activity over Syowa Station was investigated. The K-index of Syowa Station was used as an indicator of geomagnetic activity. The results did not show a statistically significant correlation between mesospheric O3 column amounts and geomagnetic activity. Although the statistical analysis did not demonstrate a significant relationship between the EPP and O3 column amounts in the mesosphere, a case study of a major magnetic storm in May 2024 indicated that energetic proton precipitation led to O3 concentration destruction in the mesosphere.
We used a millimeter-wave spectroradiometer installed by Nagoya University at Syowa Station in Antarctica. The millimeter-wave spectra observed on the ground were integrations of O3 radiation over altitudes from the surface to the lower thermosphere. We retrieved the altitude distribution of the O3 volume mixing ratio (VMR) from the radiation spectra to quantitatively estimate the O3 concentration in the mesosphere.
In the case of the major magnetic storm of May 2024, the O3 column amounts were compared with the EPP and NO column amounts in the mesosphere. After the magnetic storm started on May 10th, an increase in proton flux from 10 MeV to over 100 MeV was observed from May 10th to 20th. During this period, the PANSY radar observed signatures of EPP, and a monotonic decrease in O3 column amounts was observed from dusk to dawn, particularly from May 10th to 11th. A comparison of the NO column amounts in the mesosphere showed an overall inverse correlation with the O3 column amounts. However, during the significant decrease in O3 column amounts from May 10th to 11th, the NO column amounts showed little increase, which was an unexpected feature, as NO typically acts as a catalyst in the O3 destruction reaction. A detailed analysis was conducted to determine the cause of the decrease from May 10th to 11th. The data from the GOES satellite showed that the solar proton flux began increasing gradually around LT 12:00 on May 9th and peaked around LT 20:50 on May 10th. The riometer data at Syowa Station indicated an intense EPP at LT 20:10 on May 10th, followed by weaker precipitation until LT 21:40. It can be inferred that the EPP occurred over Syowa Station from May 10th to 11th, leading to a decrease in the O3 column amounts in the mesosphere. To investigate the origin of the EPP, the rTEC keogram over Tromso, Norway, located near the magnetic conjugate of the Syowa Station, was examined. The auroral oval appeared over Tromso around LT 20:00 on May 10th following the onset of the magnetic storm, and then moved toward lower latitudes. The auroral oval moved back over Tromso from lower latitudes at LT 03:00 on May 11th. Therefore, during the period when the O3 column amounts decreased, Syowa Station was likely located inside the polar cap region. This suggests that the decrease in the O3 column amount from May 10th to 11th was likely caused by solar protons.
In the statistical analysis covering a total of five months from July to October 2022 and May 2024, the correlation between the O3 column amounts in the mesosphere and geomagnetic activity over Syowa Station was investigated. The K-index of Syowa Station was used as an indicator of geomagnetic activity. The results did not show a statistically significant correlation between mesospheric O3 column amounts and geomagnetic activity. Although the statistical analysis did not demonstrate a significant relationship between the EPP and O3 column amounts in the mesosphere, a case study of a major magnetic storm in May 2024 indicated that energetic proton precipitation led to O3 concentration destruction in the mesosphere.