2:30 PM - 2:45 PM
[PEM13-28] Mechanisms for thermospheric zonal mean wind responses to doubled CO2 concentration
Keywords:Thermosphere, Aeronomy, CO2, Tide
The thermosphere is cooling with increasing CO2 concentration, while the troposphere is warming. Several numerical models have predicted this thermospheric cooling trend and also show that this trend leads to a thermospheric density drop. Although the thermal cooling process due to increased CO2 concentration is established well, the dynamical response in the thermosphere remains unclear. Liu et al. (2020) explored doubled CO2 concentration effect on the thermospheric circulation with the whole atmosphere model GAIA (Ground-to-topside Atmosphere Ionosphere model for Aeronomy). The simulation results revealed a strengthening of the zonal mean meridional wind and a change in the zonal wind in June.
This study explored mechanisms for the thermospheric zonal mean wind responses to doubled CO2 concentration reported by Liu et al. (2020). We applied the zonal mean momentum balance analysis with the same simulation data as Liu et al. (2020). The analysis shows that an increase in zonal mean zonal ion drag due to the doubled CO2 concentration dominantly contributes to the strengthening of the southward wind in the northern (summer) hemisphere and latitudes north of 35°S (~15 ms-1 at maximum). Southward of 35°S, the zonal pressure gradient force and the meridional advection of zonal wind strengthens the southward wind by 4-10 ms-1 in total. On the other hand, the zonal wind is mainly altered by increasing meridional pressure gradient force (~15 ms-1 at maximum), which is due to a latitudinally asymmetric drop of the neutral density. The meridional advection of meridional wind also contributes to strengthening the westward wind in the tropic region and northern high latitudes above 50°N by 2-10 ms-1. The meridional advections of zonal and meridional winds are 50-95% attributed to their diurnal tidal component with wavenumber 1 (DW1). Our result suggests that the DW1 tide generated in-situ has an important role in strengthening the westward wind at summer middle latitudes and southward wind at winter high latitudes due to increasing CO2 concentration. In contrast, the increases in the vertical advections, which were 50-95% attributed to gravity waves, were less than 4 ms-1, and hence do not have a key role in strengthening the wind.
This study explored mechanisms for the thermospheric zonal mean wind responses to doubled CO2 concentration reported by Liu et al. (2020). We applied the zonal mean momentum balance analysis with the same simulation data as Liu et al. (2020). The analysis shows that an increase in zonal mean zonal ion drag due to the doubled CO2 concentration dominantly contributes to the strengthening of the southward wind in the northern (summer) hemisphere and latitudes north of 35°S (~15 ms-1 at maximum). Southward of 35°S, the zonal pressure gradient force and the meridional advection of zonal wind strengthens the southward wind by 4-10 ms-1 in total. On the other hand, the zonal wind is mainly altered by increasing meridional pressure gradient force (~15 ms-1 at maximum), which is due to a latitudinally asymmetric drop of the neutral density. The meridional advection of meridional wind also contributes to strengthening the westward wind in the tropic region and northern high latitudes above 50°N by 2-10 ms-1. The meridional advections of zonal and meridional winds are 50-95% attributed to their diurnal tidal component with wavenumber 1 (DW1). Our result suggests that the DW1 tide generated in-situ has an important role in strengthening the westward wind at summer middle latitudes and southward wind at winter high latitudes due to increasing CO2 concentration. In contrast, the increases in the vertical advections, which were 50-95% attributed to gravity waves, were less than 4 ms-1, and hence do not have a key role in strengthening the wind.