5:15 PM - 7:15 PM
[PPS05-P05] Variations of Venusian polar atmosphere seen in radio occultation data
Keywords:Venus, cloud-level convection, atmospheric gravity wave, radio occultation
At 50-70km altitudes in the Venusian atmosphere, there is a thick cloud layer composed of H2SO4 and H2O liquid. Around the cloud base, the clouds absorb infrared radiation from the lower atmosphere and then the atmosphere is heated. On the other hand, the atmosphere near the cloud top is cooled by emitting infrared radiation to space. This drives convection in the lower cloud layer(50–55 km altitude). Above the convective layer (around 60 km and higher), atmospheric gravity waves are excited. These waves propagate vertically, transporting energy and momentum between different altitudes, and thus play an important role in Venus' atmospheric dynamics. However, the physical processes governing cloud-level convection and gravity wave activity remain unclear.
In the previous studies, unlike on Earth, radio occultation observations from Venus Express and Akatsuki have shown that the convective layer is thicker at higher latitudes (Tellmann et al. 2009; Ando et al. 2020). It has been suggested that this may be due to reduced solar heating near the cloud top at higher latitudes, which enhances convection at those latitudes (Imamura et al. 2014). Numerical modeling studies (Imamura et al. 2014; Lefèvre et al. 2017) have pointed out that convection may be a source of atmospheric gravity waves. The observed enhancement of gravity wave activity at high latitudes (Tellmann et al. 2012; Ando et al. 2015) could be explained by such latitude-dependent convective activity, though supporting evidence remains insufficient. Additionally, Venus Express radio occultation observations have detected periodic variations in polar atmospheric temperature with a period of approximately 3.1 Earth days, which have been attributed to the propagation of planetary-scale waves (Ando et al. 2017).
In this study, we focus on high-latitude regions, where the convective layer is expected to be thicker, convection stronger, and gravity waves more intense. By analyzing data from near-daily radio occultation data from Venus Express, we aim to:
- Investigate how planetary-scale waves modulate the convective layer structure and gravity wave activity
- Explore the effect of planetary-scale waves on convection and the effect of convection on gravity waves
Our analysis reveals, for the first time, that the tropopause height in the polar atmosphere varies in sync with temperature fluctuations associated with the propagation of planetary-scale waves. Also, although stronger convection was expected to correspond to a higher tropopause and larger gravity wave amplitudes, we found little correlation between the two. This suggests that tropopause height does not necessarily reflect convective intensity or that other mechanisms may play a dominant role in gravity wave excitation.
In the previous studies, unlike on Earth, radio occultation observations from Venus Express and Akatsuki have shown that the convective layer is thicker at higher latitudes (Tellmann et al. 2009; Ando et al. 2020). It has been suggested that this may be due to reduced solar heating near the cloud top at higher latitudes, which enhances convection at those latitudes (Imamura et al. 2014). Numerical modeling studies (Imamura et al. 2014; Lefèvre et al. 2017) have pointed out that convection may be a source of atmospheric gravity waves. The observed enhancement of gravity wave activity at high latitudes (Tellmann et al. 2012; Ando et al. 2015) could be explained by such latitude-dependent convective activity, though supporting evidence remains insufficient. Additionally, Venus Express radio occultation observations have detected periodic variations in polar atmospheric temperature with a period of approximately 3.1 Earth days, which have been attributed to the propagation of planetary-scale waves (Ando et al. 2017).
In this study, we focus on high-latitude regions, where the convective layer is expected to be thicker, convection stronger, and gravity waves more intense. By analyzing data from near-daily radio occultation data from Venus Express, we aim to:
- Investigate how planetary-scale waves modulate the convective layer structure and gravity wave activity
- Explore the effect of planetary-scale waves on convection and the effect of convection on gravity waves
Our analysis reveals, for the first time, that the tropopause height in the polar atmosphere varies in sync with temperature fluctuations associated with the propagation of planetary-scale waves. Also, although stronger convection was expected to correspond to a higher tropopause and larger gravity wave amplitudes, we found little correlation between the two. This suggests that tropopause height does not necessarily reflect convective intensity or that other mechanisms may play a dominant role in gravity wave excitation.