5:15 PM - 6:45 PM
[PEM13-P07] Variations in the ozone concentration in the mesosphere observed at Syowa station associated with energetic particles precipitation
Keywords:ozone, mesosphere, EPP(energetic particles precipitation)
In the polar regions, energetic particles precipitation (EPP) occurs associated with solar proton events and magnetic storms. The ionization of atmospheric molecules induced by EPP produce nitrogen and hydrogen oxides in the mesosphere, which could cause destruction of ozone (O3). In order to clarify this issue, Nagoya University has installed a millimeter-wave spectroradiometer at Showa Station in Antarctica and observed nitric oxide (NO) and O3 radiations since 2012. In 2022, simultaneous observations of two O3 emission lines in the 250 GHz band as well as carbon monoxide (CO) emission lines in the 230 GHz band and six NO emission lines in the 250 GHz band were started. We aim to clarify the decrease in O3 concentration in the mesosphere associated with EEP. We are now quantitatively investigating the variations in O3 above the Showa station using data in upwelling phase of this solar cycle. The spectrum observed by the millimeter-wave spectroradiometer on the ground is an integration of O3 radiation over altitudes from the surface to the lower thermosphere. We performed a retrieval of the altitude distribution of O3 volume mixing ratio (VMR) from the radiation spectra to quantitatively estimate the O3 concentration in the mesosphere. In this presentation, we will report the results of adjustments and validations of the retrieval tool developed at Nagoya University. The retrieval tool uses the O3 height distribution obtained by the MLS satellite as an a-priori distribution and estimates the vertical distribution of O3VMR from the model spectrum that best matches the observed spectrum, using the NASA-JPL molecular spectroscopy catalog and the meteorological vertical profile data from MERRA2. Since the altitude distribution of O3 is affected by sunlight, a-priori distributions for daytime and nighttime are switched at times of sunset and sunrise. The observed spectra used for the retrieval are integrated for one hour. When the optical depth varies significantly with time due to weather conditions, the data are excluded from the analysis. Using the data from July 2022 to January 2023, we reveal the following two points. (1)An increase of the O3VMR during the nighttime and a decrease during the daytime at mesospheric altitudes were confirmed. The change of the increase and decrease timing of the O3VMR corresponded to seasonal changes in sunrise and sunset. The daytime decrease is explained by O3 destruction due to photochemical reactions of solar ultraviolet radiation. The VMR in the mesosphere differs by ~6% depending on the choice of the daytime or nighttime a-priori distribution. It is needed to consider the dependence of the VMR on the a-priori distribution when analyzing variability of the VMR across sunrise and sunset. (2) The O3VMR in the mesosphere is a few ppm. Since the pressure broadening of the line spectrum at mesospheric altitudes is small, it is necessary to reproduce the spectral profile near the line center well in the model spectrum to obtain the VMR in the mesosphere accurately. We tried to adjust the model spectral profile with several patterns to compensate for the discrepancy between observation and model spectra near the line center. We found that the estimated mesospheric O3VMR changed by less than 2% among the patterns we tried. In the presentation, we will report on variations in the O3 concentration variations in the mesosphere during solar proton events and magnetic storms.