Poleward water vapor transport in the midlatitudes mainly occurs in meandering filaments of intense water vapor transport, spanning thousands of kilometers long and hundreds of kilometers wide and moving eastward. The water vapor filaments are known as atmospheric rivers (ARs). They can cause extreme wind gusts, intense precipitation, and flooding along densely populated coastal regions. Many recent studies about ARs focused on the statistical analyses of ARs, but a process-level understanding of ARs remains elusive. In a preprint, we show that ARs are streams of air with enhanced vapor kinetic energy (VKE) and derive a governing equation for Integrated VKE (IVKE) to understand what contributes to the evolution of ARs. We find that ARs grow mainly because of potential energy conversion to kinetic energy, decay largely owing to condensation and turbulence, and the eastward movement is primarily due to horizontal advection of VKE. Our VKE framework complements the integrated vapor transport framework, which is popular for identifying ARs but lacks a prognostic equation for understanding the physical processes.
Humid air is lighter than dry air at the same temperature and pressure because the molecular weight of water vapor is less than that of dry air. This effect is known as vapor buoyancy (VB). In this work we use a 3D general circulation model (GCM) to show that VB warms the tropical free troposphere and leads to a significant increase in outgoing longwave radiation (OLR). This radiative effect increases with climate warming, causing a negative climate feedback there. We call this the VB feedback. Notably, 1D, 2D, and 3D models consistently indicate that the VB feedback strengthens with warming.
Also see Yang et al. (2022), Yang and Seidel (2023), Seidel and Yang (2020), and Yang and Seidel (2020).
The Madden-Julian Oscillation (MJO) has long been a mystery in tropical atmospheric dynamics. A paper in GRL uses the E3SM-MMF, a superparameterized climate model, to investigate whether radiative feedbacks are essential for simulating the MJO. Through vertically resolved MSE diagnoses and mechanism-denial experiments, the study demonstrates that the MJO can still self-emerge and maintain its characteristic structures even in the absence of radiative feedbacks.
Previous research showed that radiative feedbacks are essential to the spontaneous development of convective aggregation (CSA) in idealized atmosphere models. A paper in GRL finds that the contribution of radiative feedbacks decreases with warming and that, in warm climates, CSA occurs without radiative feedbacks. This result agrees with the vertically resolved moist static energy diagnosis.
The molar mass of water vapour is less than that of dry air, making humid air lighter than dry air at the same temperature and pressure. This effect is known as vapour buoyancy and has been considered negligibly small in large-scale climate dynamics. A paper in Nature Geoscience shows that vapour buoyancy has a similar magnitude to thermal buoyancy in the tropical free troposphere. We further show that vapour buoyancy makes cold air rise and increases subtropical stratiform low clouds by up to 70% of its climatological value. However, some widely used climate models fail to represent vapour buoyancy in the governing equations. This flaw leads to inaccurate simulations of cloud distributions—the largest uncertainty in predicting climate change.