Climate dynamics

Abstract:

Interactions between magma oceans and overlying atmospheres on young rocky planets leads to an evolving feedback of outgassing, greenhouse forcing, and mantle melt fraction. Previous studies have predominantly focused on the solidification of oxidized Earth-similar planets, but the diversity in mean density and irradiation observed in the low-mass exoplanet census motivate exploration of strongly varying geochemical scenarios. We aim to explore how variable redox properties alter the duration of magma ocean solidification, the equilibrium thermodynamic state, melt fraction of the mantle, and atmospheric composition. We develop a 1D coupled interior-atmosphere model that can simulate the time-evolution of lava planets. This is applied across a grid of fixed redox states, orbital separations, hydrogen endowments, and C/H ratios around a Sun-like star. The composition of these atmospheres is highly variable before and during solidification. The evolutionary path of an Earth-like planet at 1 AU ranges between permanent magma ocean states and solidification within 1 Myr. Recently solidified planets typically host H 2 O - or H 2 -dominated atmospheres in the absence of escape. Orbital separation is the primary factor determining magma ocean evolution, followed by the total hydrogen endowment, mantle oxygen fugacity, and finally the planet's C/H ratio. Collisional absorption by H 2 induces a greenhouse effect which can prevent or stall magma ocean solidification. Through this effect, as well as the outgassing of other volatiles, geochemical properties exert significant control over the fate of magma oceans on rocky planets.

Abstract:

<jats:title>Abstract</jats:title> <jats:p>It is widely accepted that Arctic Amplification (AA) - enhanced Arctic warming relative to global warming - will increasingly moderate cold-air outbreaks to the midlatitudes. Yet, some recent studies also argue that AA over the last three decades to the rest of the present century may potentially contribute to more frequent severe winter weather including continued disruptive cold spells. To prepare society for future extremes, it is necessary to resolve whether AA and severe midlatitude winter weather are coincidental or physically linked. Severe winter weather events in the northern continents are often related to a range of stratospheric polar vortex configurations and atmospheric blocking, but these dynamical drivers are complex and still not fully understood. Here we review recent research advances and paradigms including a nonlinear theory of atmospheric blocking that helps to explain the location, timing and duration of AA/midlatitude weather connections, as well as studies of the polar vortex’s zonal asymmetric and intra-seasonal variations, its southward migration over continents, and its surface impacts. We highlight novel understanding of stratospheric polar vortex variability – polar vortex stretching and a stratosphere-troposphere oscillation – that have remained mostly hidden in the predominant research focus on sudden stratospheric warmings. A physical explanation of the two-way vertical coupling process between the polar vortex and blocking highs, taking into account local surface conditions, remains elusive. We conclude that evidence exists for tropical preconditioning of Arctic-midlatitude climate linkages. Recent research using very large-ensemble climate modelling provides an emerging opportunity to robustly quantify internal atmospheric variability when studying the potential response of midlatitude cold-air outbreaks to AA and sea-ice loss.</jats:p>

Abstract:

Purpose of Review: Extratropical jets and associated storm tracks significantly influence weather and regional climate across various timescales. Understanding jet responses to climate change is essential for reliable regional climate projections. This review serves two main purposes: (1) to provide an accessible overview of extratropical jet dynamics and a comprehensive examination of current challenges and uncertainties in predicting jet responses to greenhouse gas increases and (2) to suggest innovative experiments to advance our understanding of these responses. Recent Findings: While successive generations of climate model ensembles consistently project a mean poleward shift of the midlatitude zonal-mean maximum winds, there remains considerable intermodel spread and large uncertainty across seasonal and regional jet responses. Of particular note is our limited understanding of how these jets respond to the intricate interplay of multiple concurrent drivers, such as the strong warming in polar and tropical regions, and the relative importance of each factor. Furthermore, the difficulty of simulating processes requiring high resolution, such as those linked to sharp sea surface temperature gradients or diabatic effects related to tropical convection and extratropical cyclones, has historically hindered progress. Summary: We advocate for a collaborative effort to enhance our understanding of the jet stream response to climate change. We propose a series of new experiments that take advantage of recent advances in computing power and modelling capabilities to better resolve small-scale processes such as convective circulations, which we consider essential for a good representation of jet dynamics.