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تسجيل مستخدم جديد3D convection-resolving model of temperate, tidally-locked exoplanets
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A large fraction of known terrestrial-size exoplanets located in the Habitable Zone of M-dwarfs are expected to be tidally-locked. Numerous efforts have been conducted to study the climate of such planets, using in particular 3-D Global Climate Models (GCM). One of the biggest challenges in simulating such an extreme environment is to properly represent the effects of sub-grid convection. Most GCMs use either a simplistic convective-adjustment parametrization or sophisticated (e.g., mass flux scheme) Earth-tuned parametrizations. One way to improve the representation of convection is to study convection using Convection Resolving numerical Models (CRMs), with an fine spatial resolution . In this study, we developed a CRM coupling the non-hydrostatic dynamical core WRF with the radiative transfer and cloud/precipitation models of the LMD-Generic climate model to study convection and clouds on tidally-locked planets, with a focus on Proxima b. Simulations were performed for a set of 3 surface temperatures (corresponding to three different incident fluxes) and 2 rotation rates, assuming an Earth-like atmosphere. The main result of our study is that while we recover the prediction of GCMs that (low-altitude) cloud albedo increases with increasing stellar flux, the cloud feedback is much weaker due to transient aggregation of convection leading to low partial cloud cover.
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lly locked (i.e., synchronously rotating) terrestrial planets with oceans, strong convergence and convection produce optically thick clouds over the substellar area. One obvious weakness of these studies is that clouds are parameterized based on the knowledge on Earth, and whether it is applicable to exoplanetary environment is unknown. Here we use a cloud-resolving model (CRM) with high resolution (2 km) in a two-dimensional (2D) configuration to simulate the clouds and circulation on tidally locked aqua-planets. We confirm that the substellar area is covered by deep convective clouds, the nightside is dominated by low-level stratus clouds, and these two are linked by a global-scale overturning circulation. We further find that a uniform warming of the surface causes the width of convection and clouds to decrease, but a decrease of day-night surface temperature contrast or an increase of longwave radiative cooling rate causes the width of convection and clouds to increase. These relationships can be roughly interpreted based on some simple thermodynamic theories. Comparing the results between CRM and GCM, we find that the results are broadly similar although there are many significant differences. Future work is required to use 3D CRM(s) with realistic radiative transfer and with the Coriolis force to examine the clouds and climate of tidally locked planets.
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