Hurricane‐Like Vortices in Conditionally Unstable Moist Convection

• Published in: Journal of advances in modeling earth systems Vol. 14; no. 7
• Main Authors: Chien, Mu‐Hua, Pauluis, Olivier M., Almgren, Ann S.
• Format: Journal Article
• Language: English
• Published: Washington John Wiley & Sons, Inc 01.07.2022; American Geophysical Union (AGU)
• Subjects: Atmosphere; Atmospheric dynamics; Boundaries; Boussinesq approximation; Cloud microphysics; Convection; Cyclogenesis; Cyclones; Earth atmosphere; ENVIRONMENTAL SCIENCES; Equilibrium; Evaporation; Heat; Hurricanes; idealized simulation; Kinematics; Latent heat; Microphysics; Moist convection; Ocean circulation; Phase transitions; Potential energy; quasi-equilibrium; Radiation; Rayleigh number; Rotation; Thermodynamics; Tropical atmosphere; Tropical cyclogenesis; tropical cyclone; Tropical cyclones; Upwelling; Vortices
• ISSN: 1942-2466; 1942-2466
• DOI: 10.1029/2021MS002846

This study investigates the emergence of hurricane‐like vortices in idealized simulations of rotating moist convection. A Boussinesq atmosphere with simplified thermodynamics for phase transitions is forced by prescribing the temperature and humidity at the upper and lower boundaries. The governing equations are solved numerically using a variable‐density incompressible Navier‐Stokes solver with adaptive mesh refinement to explore the behavior of moist convection under a broad range of conditions. In the absence of rotation, convection aggregates into active patches separated by large unsaturated regions. Rotation modulates this statistical equilibrium state so that the self‐aggregated convection organizes hurricane‐like vortices. The warm and saturated air converges to the center of the vortices, and the latent heat released through the upwelling, forms the warm core structure. These hurricane‐like vortices share characteristics similar to tropical cyclones in the earth's atmosphere. The hurricane‐like vortices occur under conditionally unstable conditions where the potential energy given at the boundaries is large enough, corresponding to a moderate rate of rotation. This regime shares many similar characteristics to the tropical atmosphere indicating that the formation of intense meso‐scale vortices is a general characteristic of rotating moist convection. The model used here does not include any interactions with radiation, wind‐evaporation feedback, or cloud microphysics, indicating that, while these processes may be relevant for tropical cyclogenesis in the Earth atmosphere, they are not its primary cause. Instead, our results confirm that the formation and maintenance of hurricane‐like vortices involve a combination of atmospheric dynamics under the presence of rotation and of phase transitions. Plain Language Summary This paper investigates the emergence of hurricane‐like vortices in a numerical simulation of an idealized atmosphere system. The complicated thermodynamics for water vapor is simplified. The remaining system can still produce a conditionally unstable atmosphere in which unsaturated air parcels experience a stable stratification and unsaturated parcels experience an unstable one. We find hurricane‐like vortices in the presence of rotation. The warm and saturated air converges to the center of the vortices, and the latent heat released through the upwelling forms the warm core structure and easily observed eyewall. The structure of hurricane‐like vortices is analogous to tropical cyclones in the earth's atmosphere. This idealized configuration produces characteristics similar to the tropical atmosphere so that the hurricane‐like vortices can be considered as the outcome of the tropical cyclogenesis, with reasonable simplifications. However, the tropical cyclogenesis here does not require any interactions with radiation, surface flux feedback, or precipitation. Our results confirm that the formation and maintenance of hurricane‐like vortices involve a combination of rotation and thermodynamic forcing. Key Points The impact of rotation on simulations of idealized simulations of moist convection is studied The formation and maintenance of hurricane‐like vortices involve a combination of conditional instability and rotation Rotating moist convection in a conditionally unstable environment should spontaneously generate hurricane‐like vortices