[A-AS10] Stratosphere-troposphere (Atmospheric) Processes And their Role in Climate

[AAS10-04] Seasonal variability and annual trends of wind and turbulence parameters from MU radar data in the tropo-stratosphere (1987-2022)

Haruka Uchimoto¹, *Hubert LUCE¹, Hiroyuki Hashiguchi¹, Mamoru Yamamoto¹, Noriyuki Nishi², Manabu D. Yamanaka³, Toshitaka Tsuda¹ (1.Research Institute for Sustainable Humanosphere, 2.Faculty of Science, Fukuoka University, 3.Kobe University)

Keywords:atmospheric turbulence, ST radar, climate change, seasonal variability

For almost 40 years, the 46.5 MHz Middle and Upper atmosphere (MU) radar (Shigaraki Observatory, 35°N, 136°E) has been operating a few days a month for routine observations of the lower atmosphere (2-20 km). We used radar and radiosonde data collected from 1987 to 2022 to re-examine the characteristics of seasonal variations in atmospheric turbulence parameters, such as the turbulence kinetic energy dissipation rate ε , and to identify possible climatological trends that may be related to the current climate change. This study has been made in the light of recent advances in models based on Doppler spectrum width to derive ε and in our understanding of the radar backscattering mechanisms. The monthly average of ε shows a maximum in the upper troposphere mainly in spring and a minimum in the low and middle troposphere in summer. Turbulent activity is minimal in the lower stratosphere, but shows a strong increase in winter up to at least 20 km, resulting from short (a few hours to a day) and intense events, probably due to increased gravity wave activity. These features are well supported by an analysis of seasonal variations in the Richardson number Ri, a rough turbulence indicator, calculated from radiosonde data at nearby weather stations: the seasonal and height enhancements of ε coincide with Ri minima, as expected when turbulence is generated by shear and convective instabilities. The potential of the MU radar to provide climatological trends over almost 4 decades has been tested from comparisons between radar wind, radiosondes and ERA5 re-analysis data. The results are mixed because the various trends, positive or negative according to the datasets, are small and not fully consistent. However, the preliminary results for turbulence intensity do not show any detectable changes that would indicate an increase or decrease in ε over the last 20 years in the troposphere due to the climate change.