Climate dynamics

Abstract:

Previous studies have found inconsistent responses of the North Atlantic jet to Arctic sea-ice loss. The response of wintertime atmospheric circulation and surface climate over the North Atlantic-European region to future Arctic sea-ice loss under 2°C global warming is analyzed, using model output from the Polar Amplification Model Intercomparison Project. The models agree that the North Atlantic jet shifts slightly southward in response to sea-ice loss, but they disagree on the sign of the jet speed response. The jet response induces a dipole anomaly of precipitation and storm track activity over the North Atlantic-European region. The changes in jet latitude and speed induce distinct regional surface climate responses, and together they strongly shape the North Atlantic-European response to future Arctic sea-ice loss. Constraining the North Atlantic jet response is important for reducing uncertainty in the North Atlantic-European precipitation response to future Arctic sea-ice loss.

Abstract:

Climate model simulations that restore SSTs in the North Atlantic have been used to explore the climate impacts of Atlantic Multidecadal Variability (AMV). However, despite simulations and observations exhibiting similar North Atlantic SST anomalies, experiments with active SST-restoring in the Tropical North Atlantic exhibit strong positive surface heat-fluxes out of the ocean with warm SST anomalies, which is not replicated in other simulations or observations. The upward surface heat-fluxes that are systematically driven by the active SST-restoring in the Tropical North Atlantic are found to be crucial for generating a strong local precipitation response and the associated remote impact on the Pacific Walker circulation; these are both absent in other simulations. The results of this study strongly suggest that experiments employing SST-restoring (or prescribed SSTs) in the Tropical North Atlantic exaggerate the influence of the Atlantic on patterns of global climate anomalies and its role in recent multidecadal SST trends.

Abstract:

<jats:title>Abstract</jats:title> <jats:p>The implications of the water vapor runaway greenhouse phenomenon for water-rich sub-Neptunes are developed. In particular, the nature of the postrunaway equilibration process for planets that have an extremely high water inventory is addressed. Crossing the threshold from subrunaway to superrunaway conditions leads to a transition from equilibrated states with cold, deep liquid oceans and deep interior ice-X phases to states with hot supercritical fluid interiors. There is a corresponding marked inflation of radius for a given mass, similar to the runaway greenhouse radius inflation effect noted earlier for terrestrial planets, but in the present case the inflation involves the entire interior of the planet. The calculation employs the AQUA equation-of-state database to simplify the internal structure calculation. Some speculations concerning the effect of H<jats:sub>2</jats:sub> admixture, silicate cores, and hot- versus cold-start evolution trajectories are offered. Observational implications are discussed though the search for the mass–radius signature of the phenomena considered is limited by degeneracies and by lack of data.</jats:p>

Abstract:

<jats:title>Abstract</jats:title> <jats:p>The gas giant HD 80606 b has a highly eccentric orbit (e ∼ 0.93). The variation due to the rapid shift of stellar irradiation provides a unique opportunity to probe the physical and chemical timescales and to study the interplay between climate dynamics and atmospheric chemistry. In this work, we present integrated models to study the atmospheric responses and the underlying physical and chemical mechanisms of HD 80606 b. We first run three-dimensional general circulation models (GCMs) to establish the atmospheric thermal and dynamical structures for different atmospheric metallicities and internal heat. Based on the GCM output, we then adopted a 1D time-dependent photochemical model to investigate the compositional variation along the eccentric orbit. The transition of the circulation patterns of HD 80606 b matched the dynamics regimes in previous works. Our photochemical models show that efficient vertical mixing leads to deep quench levels of the major carbon and nitrogen species and the quenching behavior does not change throughout the eccentric orbit. Instead, photolysis is the main driver of the time-dependent chemistry. While CH4 dominates over CO through most of the orbits, a transient state of [CO]/[CH4] &amp;gt; 1 after periastron is confirmed for all metallicity and internal heat cases. The upcoming JWST Cycle 1 GO program will be able to track this real-time CH4–CO conversion and infer the chemical timescale. Furthermore, sulfur species initiated by sudden heating and photochemical forcing exhibit both short-term and long-term cycles, opening an interesting avenue for detecting sulfur on exoplanets.</jats:p>