Climate dynamics

Abstract:

Sub-Neptunes, the most common planet type, remain poorly understood. Their atmospheres are expected to be diverse, but their compositions are challenging to determine, even with JWST. Here, we present the first JWST spectroscopic study of the warm sub-Neptune GJ 3090 b (2.13 R⊕, Teq,A = 0.3 ∼ 700 K), which orbits an M2V star, making it a favorable target for atmosphere characterization. We observed four transits of GJ 3090 b: two each using JWST NIRISS/SOSS and NIRSpec/G395H, yielding wavelength coverage from 0.6 to 5.2 μm. We detect the signature of the 10833 Å metastable helium triplet at a statistical significance of 5.5σ with an amplitude of 434 ± 79 ppm, marking the first such detection in a sub-Neptune with JWST. This amplitude is significantly smaller than predicted by solar-metallicity forward models, suggesting a metal-enriched atmosphere that decreases the mass-loss rate and attenuates the helium feature amplitude. Moreover, we find that stellar contamination, in the form of the transit light source effect, dominates the NIRISS transmission spectra, with unocculted spot and faculae properties varying across the two visits separated in time by approximately 6 months. Free retrieval analyses on the NIRSpec/G395H spectrum find tentative evidence for highly muted features and a lack of CH4. These findings are best explained by a high-metallicity atmosphere (>100× solar at 3σ confidence for clouds at ∼μbar pressures) using chemically consistent retrievals and self-consistent model grids. Further observations of GJ 3090 b are needed for tighter constraints on the atmospheric abundances and to gain a deeper understanding of the processes that led to its potential metal enrichment.

Abstract:

Sea ice and snow are crucial components of the cryosphere and the climate system. Both sea ice and spring snow in the Northern Hemisphere (NH) have been decreasing at an alarming rate in a changing climate. Changes in NH sea ice and snow have been linked with a variety of climate and weather extremes including cold spells, heatwaves, droughts and wildfires. Understanding of these linkages will benefit the predictions of climate and weather extremes. However, existing work on this has been largely fragmented and is subject to large uncertainties in physical pathways and methodologies. This has prevented further substantial progress in attributing climate and weather extremes to sea ice and snow change, and will potentially risk the loss of a critical window for effective climate change mitigation. In this review, we synthesize the current progress in attributing climate and weather extremes to sea ice and snow change by evaluating the observed linkages, their physical pathways and uncertainties in these pathways, and suggesting ways forward for future research efforts. By adopting the same framework for both sea ice and snow, we highlight their combined influence and the cryospheric feedback to the climate system. We suggest that future research will benefit from improving observational networks, addressing the causality and complexity of the linkages using multiple lines of evidence, adopting large-ensemble approaches and artificial intelligence, achieving synergy between different methodologies/disciplines, widening the context, and coordinated international collaboration.

Abstract:

The climatological atmospheric circulation is key to establishing the tropical “pattern effect”, whereby cloud feedbacks induced by sea surface temperature (SST) warming depend on the spatial structure of that warming. But how patterned warming‐induced circulation changes affect cloud responses is less clear. Here we use idealized simulations with prescribed SST perturbations to understand the contributions to changes in tropical‐mean cloud radiative effects (CRE) from different circulation regimes. We develop a novel framework based on moist static energy to understand the circulation response, targeting in particular the bulk circulation metric of ascent fraction. Warming concentrated in regions of ascent leads to a strong “upped‐ante” effect and spatial contraction of the ascending region. Our framework reveals substantial contributions to tropical‐mean CRE changes not only from traditional “pattern effect” regimes, but also from the intensification of convection in ascent regions as well as a smaller contribution from cloud changes in convective margins.