In the solar system, Venus is too hot, Mars is too cold, and only Earth has liquid water on the surface. What determines this feature? Did Venus and Mars have liquid water in the past, such as during the early period after planetary formation? What determines the different evolution processes of these planets? Beyond the solar system, thousands of exoplanets have been confirmed. Among them, about 10-20 are potentially habitable. The main target of exoplanet missions is in order to find other habitable or potentially habitable planet(s) and even life on other world(s). Our group is focusing on the atmospheric, oceanic, and ice motions and the climates of different types of planets. The main goal is identifying the locations of the inner edge and the outer edge of the habitable zone, which is crtitical for finding potentially habitable planets and is useful for exoplanet mission designs. Planetary climate and habitability is a complex function of various factors, such as stellar energy, stellar spectrum, planetary size, planetary gravity, planetary orbit (rotation rate, obliquity, eccentricity, etc.), atmospheric composition, surface pressure, greenhouse gas, cloud, dust, aerosol, ocean depth, seawater composition, land-sea distribution, sea ice, ice sheet, and many other factors.
We are also interested in the atmospheric circulation and climate dynamics on Earth and Earth-like planets. The key questions we take are what determines the width and strength of the Hadley cells, what determines the relative humidity of the atmosphere, what sets the spatial pattern and optical thickness of clouds, how does the cloud--radiation--large-scale circulation interaction in the tropics (under no rotation or slow rotation) influence the climate of the planets, how does oceanic circulation influence the inner edge and the outer edge of the habitable zone, how do ice dynamics influence the climate of a (near) snowball Earth and the climate and habitability of planets close to the outer edge of the habitable zone, etc.
The Sun becomes brighter with time, but Earth’s climate is roughly temperate for life during its long-term history; for early Earth, this is known as the Faint Young Sun Problem (FYSP). Besides the carbonate-silicate feedback, recent researches suggest that a long-term cloud feedback may partially solve the FYSP. However, the general circulation models they used cannot resolve convection and clouds explicitly. This study re-investigates the clouds using a near-global cloud-permitting model without cumulus convection parameterization. Our results confirm that a stabilizing shortwave cloud feedback does exist, and its magnitude is ≈6 W m-2 or 14% of the energy required to offset a 20% fainter Sun than today, or ≈10 W m-2 or 16% for a 30% fainter Sun. When insolation increases and meanwhile CO2 concentration decreases, low-level clouds increase, acting to stabilize the climate by raising planetary albedo, and vice versa.
Publication: Mingyu Yan, Jun Yang, Yixiao Zhang, and Han Huang: Cloud Feedback on Earth's Long-Term Climate Simulated by a Near-Global Cloud-Permitting Model, Geophysical Research Letters, 2022, 49, 15, doi:10.1029/2022GL100152.
Using a cloud-resolving model with high resolution (2 km) in a 2D configuration, we study the clouds and circulation on tidally locked aquaplanets. We find that the substellar area is covered by deep convective clouds, the nightside is dominated by low-level clouds, and the two are linked by a global-scale Walker circulation. We further find that the substellar cloud width decreases with uniform surface warming, while increases with a reduction in the day–night surface temperature contrast or an enhancement in the longwave radiative cooling. These relationships can be roughly interpreted in accordance with simple thermodynamic theories. We also make comparisons between our results with previous studies using general circulation models with much coarser resolution.
Publication: Qiyu Song, Jun Yang, Hang Luo, Cheng Li, and Shizuo Fu: Idealized 2D Cloud-resolving Simulations for Tidally Locked Habitable Planets, The Astrophysical Journal, 2022, 934, 149, doi: 10.3847/1538-4357/ac7879.
Under a given global-mean surface temperature, the precipitation is weaker when the surface pressure is higher. In the long-term and global mean, the amount of latent heat that acts to heat the atmosphere is equal to the amount of atmospheric net energy loss. Meanwhile, the value of net latent heat release is equal to the surface precipitation multiplied by the specific heat of water vaporization and the density of liquid water. When air mass increases, the atmospheric net longwave emission decreases because stronger greenhouse effect. Atmospheric shortwave absorption increases because shortwave absorption path of water vapor becomes longer. Meanwhile, surface sensible heat becomes larger because higher air mass. Therefore, atmospheric latent heat decreases with increasing atmospheric mass, and surface precipitation decreases as well.
Publication: Junyan Xiong, Jun Yang, and Ji Nie: Possible Dependence of Climate on Atmospheric Mass: A Convection-Circulation-Cloud Coupled Feedback, Journal of the Atmospheric Sciences, 2020, 77, 11, doi:10.1175/JAS-D-20-0022.1.
Through numerical simulations, we show that oceanic superrotation does occur on tidally locked terrestrial planets around low-mass stars. Its formation (spun up from rest) is associated with surface winds, the equatorward momentum convergence by Rossby waves, and the eastward propagation of Kelvin waves in the ocean. Its maintenance is driven by equatorward momentum transports of coupled Rossby–Kelvin waves in the ocean excited from the uneven stellar radiation distribution. The width of the superrotation is mainly constrained by the Rossby deformation radius in the ocean, while its strength is more complex.
Publication: Yaoxuan Zeng, and Jun Yang: Oceanic Superrotation on Tidally Locked Planets, The Astrophysical Journal, 2021, 909, 172, doi:10.3847/1538-4357/abe12f.
We solve the 1-layer shallow water equations analytically to get the wave patterns on tidally locked planets, and find an wave—jet resonance state. When the speed of zonal jet approaches the phase speed of Kelvin or Rossby waves but with opposite sign, the real phase speed of planetary waves is zero and waves are trapped in the regions of wave source. In this situation, the energy input from the source is maximum, so that wave amplitude is largest.
Publication: Shuang Wang, and Jun Yang: Phase Shift of Planetary Waves and Wave--Jet Resonance on Tidally Locked Planets, The Astrophysical Journal, 2021, 901, 28, doi:10.3847/1538-4357/abcf2a.
Fundations
(1) Effects of background gases concentrations on planetary surface temperature (NSFC 2017-2020);
(2) Estimating the time scale of ocean mixing after the melting of a hard Snowball Earth (NSFC 2017-2019);
(3) Mechanisms for Arctic Warming Amplification and Its Impacts on Mid-latitude Winter Extremes (NSFC 2018-2019);
(4) Hurricanes in three different climate states (NSFC 2021-2023);
(5) Heat Transport in the Atmospheres and Oceans of Rocky Planets: From Hot to Cold (NSFC 2021-2024);
(6) Habitable Hydrogen Worlds: Convection, Cloud, and Observation Characteristics (NSFC, 2023-2026).