17:15 〜 18:45
[PPS04-P09] Characteristics of gravity waves and thermal tides derived from LIR images with radiative transfer modeling
★Invited Papers
キーワード：Venus, Radiative transfer, Akatsuki, Infrared image, Radio occultation, Gravity waves
Although Venus is a terrestrial planet sharing similar size and mass with the Earth, the atmospheric circulation of Venus is yet to be fully understood. Above the surface, the sulfuric acid clouds are located at about 48-70 km altitudes, covering the entire surface. At the cloud-top level, the global zonal wind shows predominantly westward with a maximum speed of about 100 m s-1, namely superrotation, which is about 60 times faster than the rotation of Venus. Gravity waves are thought to play crucial roles in maintenance of the superrotation.
However, the details of the gravity waves on Venus remain unknown. Previous analysis highlighted on short-vertical wavelength gravity waves using radio occultation data[1], while we anticipate providing a new perspective for studying the gravity waves with longer vertical wavelengths. In this study, we are developing an algorithm to retrieve the amplitude of gravity waves including stationary waves and thermal tides, based on Longwave Infrared Camera (LIR) on board Akatsuki. With the collaborative observation of radio occultation and 2-μm Camera (IR2), we estimated perturbations associated with gravity waves.
In this study, the infrared radiance was calculated based on line-by-line radiative transfer codes following Sato et al.[2]. We adopted temperature and pressure profiles for equatorial regions (<30o) from The International Venus Reference Atmosphere[3] and the cloud particle density model from Haus et al.[4]. The extinction cross-section of cloud particles was calculated by the Mie scattering model with parameters corresponding to 75% H2SO4 aerosol particles. Gaseous absorption includes H2O, CO2, CO, SO2, HF, and OCS. Their vertical profiles were taken from Marcq et al.[5], and spectral line data was taken from the HITRAN2020 database[6].
The influence of gravity waves on the infrared radiance includes perturbations of temperature and particle density. We assumed a constant cloud particle mixing ratio of a certain air parcel, and thus the fluctuation of cloud particles can be derived from the fluctuation of temperature by linear theory of gravity waves[7]. The vertical wavelength and growth rate of thermal tides and stationary waves were estimated from radio occultation and linear theory, respectively. The upper scale height of cloud particles was modified by fitting the model’s result of thermal tides with the LIR observation.
Responses of the atmosphere to gravity waves were described by the linear theory. Our model gives consistent results with other observations. Horizontal wind perturbation induced by semidiurnal thermal tides was calculated and compared with cloud tracking results. Cloud top altitude perturbation associated with stationary waves was yielded and compared with IR2 results.
However, this model still needs to be polished. More sensitivity tests are needed to prove the credibility of our model. The 3D gravity wave structure should be constructed to estimate the meridional energy propagation of gravity waves. Eventually, we aim to estimate the angular moment transported by gravity waves and assess the contribution of gravity waves to global circulation.
Reference:
[1] Mori, R., Imamura, T., et al. (2021). Gravity Wave Packets in the Venusian Atmosphere Observed by Radio Occultation Experiments: Comparison With Saturation Theory. Journal of Geophysical Research: Planets, 126(9).
[2] Sato, T. M., Sagawa, H., et al. (2014). Cloud top structure of Venus revealed by Subaru/ COMICS mid-infrared images. Icarus, 243, 386-399.
[3] Seiff, A., Schofield, J. T., et al. (1985). Models of the structure of the atmosphere of Venus from the surface to 100 kilometers altitude. Advanced in Space Research, 5(11), 3-58.
[4] Haus, R., Kappel, D., Arnold, G. (2013). Self-consistent retrieval of temperature profiles and cloud structure in the northern hemisphere of Venus using VIRTIS/VEX and PMV/VENERA-15 radiation measurements. Planetary and Space Science 89, 77-101.
[5] Marcq, E., Bézard, B., et al. (2005). Latitudinal variations of CO and OCS in the lower atmosphere of Venus from near-infrared nightside spectro-imaging. Icarus, 179, 375-386.
[6] I.E. Gordon, L.S. Rothman, et al. (2022). The HITRAN2020 molecular spectroscopic database. Journal of Quantitative Spectroscopy and Radiative Transfer, 277, 107949.
[7] D. C. Fritts, M. J. Alexander (2003). Gravity wave dynamics and effects in the middle atmosphere. Reviews of Geophysics, 41.
However, the details of the gravity waves on Venus remain unknown. Previous analysis highlighted on short-vertical wavelength gravity waves using radio occultation data[1], while we anticipate providing a new perspective for studying the gravity waves with longer vertical wavelengths. In this study, we are developing an algorithm to retrieve the amplitude of gravity waves including stationary waves and thermal tides, based on Longwave Infrared Camera (LIR) on board Akatsuki. With the collaborative observation of radio occultation and 2-μm Camera (IR2), we estimated perturbations associated with gravity waves.
In this study, the infrared radiance was calculated based on line-by-line radiative transfer codes following Sato et al.[2]. We adopted temperature and pressure profiles for equatorial regions (<30o) from The International Venus Reference Atmosphere[3] and the cloud particle density model from Haus et al.[4]. The extinction cross-section of cloud particles was calculated by the Mie scattering model with parameters corresponding to 75% H2SO4 aerosol particles. Gaseous absorption includes H2O, CO2, CO, SO2, HF, and OCS. Their vertical profiles were taken from Marcq et al.[5], and spectral line data was taken from the HITRAN2020 database[6].
The influence of gravity waves on the infrared radiance includes perturbations of temperature and particle density. We assumed a constant cloud particle mixing ratio of a certain air parcel, and thus the fluctuation of cloud particles can be derived from the fluctuation of temperature by linear theory of gravity waves[7]. The vertical wavelength and growth rate of thermal tides and stationary waves were estimated from radio occultation and linear theory, respectively. The upper scale height of cloud particles was modified by fitting the model’s result of thermal tides with the LIR observation.
Responses of the atmosphere to gravity waves were described by the linear theory. Our model gives consistent results with other observations. Horizontal wind perturbation induced by semidiurnal thermal tides was calculated and compared with cloud tracking results. Cloud top altitude perturbation associated with stationary waves was yielded and compared with IR2 results.
However, this model still needs to be polished. More sensitivity tests are needed to prove the credibility of our model. The 3D gravity wave structure should be constructed to estimate the meridional energy propagation of gravity waves. Eventually, we aim to estimate the angular moment transported by gravity waves and assess the contribution of gravity waves to global circulation.
Reference:
[1] Mori, R., Imamura, T., et al. (2021). Gravity Wave Packets in the Venusian Atmosphere Observed by Radio Occultation Experiments: Comparison With Saturation Theory. Journal of Geophysical Research: Planets, 126(9).
[2] Sato, T. M., Sagawa, H., et al. (2014). Cloud top structure of Venus revealed by Subaru/ COMICS mid-infrared images. Icarus, 243, 386-399.
[3] Seiff, A., Schofield, J. T., et al. (1985). Models of the structure of the atmosphere of Venus from the surface to 100 kilometers altitude. Advanced in Space Research, 5(11), 3-58.
[4] Haus, R., Kappel, D., Arnold, G. (2013). Self-consistent retrieval of temperature profiles and cloud structure in the northern hemisphere of Venus using VIRTIS/VEX and PMV/VENERA-15 radiation measurements. Planetary and Space Science 89, 77-101.
[5] Marcq, E., Bézard, B., et al. (2005). Latitudinal variations of CO and OCS in the lower atmosphere of Venus from near-infrared nightside spectro-imaging. Icarus, 179, 375-386.
[6] I.E. Gordon, L.S. Rothman, et al. (2022). The HITRAN2020 molecular spectroscopic database. Journal of Quantitative Spectroscopy and Radiative Transfer, 277, 107949.
[7] D. C. Fritts, M. J. Alexander (2003). Gravity wave dynamics and effects in the middle atmosphere. Reviews of Geophysics, 41.