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Geothermal heat flow is a key parameter in governing ice dynamics, via its influence on basal melt and sliding, englacial rheology, and erosion. It is expected to exhibit significant lateral variability across Antarctica. Despite this, surface heat flow derived from Earth's interior remains one of the most poorly constrained parameters controlling ice sheet evolution. To obtain a continent‐wide map of Antarctic heat supply at regional‐scale resolution, we estimate upper mantle thermomechanical structure directly from VS. Until now, direct inferences of Antarctic heat supply have assumed constant crustal composition. Here, we explore a range of crustal conductivity and radiogenic heat production values by fitting thermodynamically self‐consistent geotherms to their seismically inferred counterparts. Independent estimates of crustal conductivity derived from VP are integrated to break an observed trade‐off between crustal parameters, allowing us to infer Antarctic geothermal heat flow and its associated uncertainty. Plain Language Summary: The future evolution of the Antarctic Ice Sheet depends on its stability, which describes how sensitive it is to environmental change. A key factor influencing ice sheet stability is how much thermal energy is transferred into its base from Earth's interior: a parameter called geothermal heat flow. If the level of heat supply is high, melting at the base of the ice sheet is encouraged, resulting in enhanced sliding toward outlet glaciers at the continental perimeter. Consequently, ice loss is accelerated, and the likelihood of glacial collapse is increased. Therefore, an accurate map of Antarctic geothermal heat flow, including how this parameter varies from region to region, is needed to produce high quality projections of Antarctic ice mass loss and therefore global sea level change. In this study, we use models of how seismic wave speed varies within Earth to estimate its three‐dimensional temperature structure, as well as its thermal conductivity. These data are used to infer a collection of best‐fitting models of Earth's thermal state, and hence estimate Antarctic geothermal heat flow. Key Points: Demonstration of new methodology for inferring geothermal heat flow from seismological dataS‐ and P‐wave velocity used together to infer and fit geothermsIncorporation of laterally varying crustal conductivity and heat production [ABSTRACT FROM AUTHOR]

Sea surface temperatures (SSTs) vary not only due to heat exchange across the air‐sea interface but also due to changes in effective heat capacity as primarily determined by mixed layer depth (MLD). Here, we investigate seasonal and regional characteristics of the contribution of MLD anomalies to the month‐to‐month variability of SST using observational datasets. First, we propose a metric called Flux Divergence Angle, which can quantify the relative contributions of surface heat fluxes and MLD anomalies to SST variability. Using this metric, we find that MLD anomalies tend to amplify SST anomalies in the extra‐tropics, especially in the eastern ocean basins, during spring and summer. In contrast, MLD anomalies tend to suppress SST anomalies in the eastern tropical Pacific during December‐January‐February. This paper provides the first global picture of the observed importance of MLD anomalies to the local SST variability. Plain Language Summary: Sea surface temperature (SST) is one of the important indicators as well as drivers of climate variability over the globe. SST varies not only due to changes in surface heat fluxes but also due to changes in effective heat capacity as mainly determined by mixed layer depth (MLD). However, the observed characteristics of the latter process associated with the MLD anomalies are limited. In this study, we propose a new metric called "Flux Divergence Angle (FDA)," which can quantify the relative importance of MLD and surface heat flux to the SST variability. Using this metric, we find that the MLD anomalies tend to amplify the local SST variability in the extra‐tropics during spring and summer. On the other hand, MLD anomalies tend to suppress the SST variability in the eastern tropical Pacific during December‐January‐February. This paper provides, for the first time, the global picture of relative importance of MLD anomalies to the SST variability based on observations. Key Points: Relative contributions of mixed layer depth (MLD) and surface heat flux anomalies to sea surface temperature (SST) variability are investigated using the Flux Divergence Angle metricMLD anomalies tend to amplify SST anomalies in the extra‐tropics, especially in eastern part of ocean basin, during the spring and summerMLD anomalies tend to suppress SST anomalies in the eastern tropical Pacific during December‐January‐February [ABSTRACT FROM AUTHOR]

The relationship between outgoing longwave radiation (OLR) and the surface temperature has a major influence on Earth's climate sensitivity. Studies often assume that this relationship is approximately linear, but it is unclear whether the approximation always holds. Here we show that, on seasonal timescales, clear‐sky OLR is a multivalued function of local surface temperature. In many places, the OLR‐temperature relationship is better approximated by a loop than a line and we quantify the resulting "OLR loopiness", that is, how much clear‐sky OLR varies between different seasons with the same surface temperature. Based on offline radiative calculations, in the tropics OLR loops are mainly caused by seasonal variations in relative humidity that are out of phase with surface temperature; in the extratropics, OLR loops are mainly due to variations in lapse rates. Our work provides a mechanism through which Earth's climate feedback can differ between seasonal and long‐term time scales. Plain Language Summary: When the Earth is warmer, it loses more heat to space. The simplest formula describing this relationship is a line with an upwards slope, where the slope determines how much Earth warms from added greenhouse gases. Here, we report that the relationship between local temperature and rate of heat loss to space can be more complicated on seasonal time scales, often taking the form of loops or other curved shapes. We come up with a way to measure how big these loops are, and explain why they happen. Our results underline that Earth's response to seasonal changes is generally different from Earth's response to global warming. Key Points: Monthly outgoing longwave radiation (OLR) is a multivalued function of local surface temperature, exhibiting loops and other complex shapesOLR loops occur both in clear‐sky and all‐sky data, so the behavior is robust to cloudsOLR loops arise because humidity lags surface temperature in the tropics, and lapse rates lead to surface temperature in the extratropics [ABSTRACT FROM AUTHOR]

Searches for phosphine in Venus' atmosphere have sparked a debate. Cordiner et al. (2022, https://doi.org/10.1029/2022gl101055) analyze spectra from the Stratospheric Observatory For Infrared Astronomy (SOFIA) and infer <0.8 ppb of PH3. We noticed that some spectral artifacts arose from non‐essential calibration‐load signals. By‐passing these signals allows simpler post‐processing and a 5.7σ candidate detection, suggesting ∼3 ppb of PH3 above the clouds. Compiling six phosphine results hints at an inverted abundance trend: decreasing above the clouds but rising again in the mesosphere from some unexplained source. However, no such extra source is needed if phosphine is undergoing destruction by sunlight (photolysis), to a similar degree as on Earth. Low phosphine values/limits are found where the viewed part of the super‐rotating Venusian atmosphere had passed through sunlight, while high values are from views moving into sunlight. We suggest Venusian phosphine is indeed present, and so merits further work on models of its origins. Plain Language Summary: Cordiner et al. (2022, https://doi.org/10.1029/2022gl101055) find no phosphine in Venus' atmosphere, using the airborne SOFIA telescope. By‐passing some instrumental effects, we extract a detection with 5.7σ‐confidence from the same data. We can resolve the tension between high and low PH3 abundance values by noticing that the former are from "mornings" in Venus' atmosphere and the latter from "evenings." Sunlight reduces the amount of phosphine in Earth's atmosphere by an order of magnitude, so similarly on Venus, we might expect lower abundances in data taken when the part of the atmosphere observed has passed through sunlight. If the six available data sets can be reconciled in this way, further modeling of possible sources of PH3 (e.g., volcanic, disequilibrium chemistry, extant life) seem worthwhile. Key Points: We recover Venusian phosphine in SOFIA spectra by reducing contaminating signals; the PH3 abundance is ∼3 part‐per billion (ppb)Six recoveries/limits show PH3 depleting between clouds and mesosphere, which would require an unknown re‐formation process or extra sourceRecoveries and upper limits can instead be reconciled by PH3 photolysis, as high/low abundances correspond to Venusian mornings/evenings [ABSTRACT FROM AUTHOR]

Thermal equilibrium in planetary atmospheres occurs at altitudes where the ion, electron, and neutral temperatures are equal. Thermal equilibrium is postulated to occur in the collision‐dominated ionosphere. This postulated altitude is above the lower boundary of all empirical models of planetary ionospheres. Physics‐based model predictions of the altitude cannot be validated due to a lack of adequate simultaneous observations of temperature profiles. This study presents temperature profiles from simultaneous observations on Atmosphere Explorer–C below 140 km and quiet‐time neutral observations from Thermosphere Ionosphere Mesosphere Energy and Dynamics/Global UltraViolet Imager over Millstone Hill. These are compared with profiles from physics‐based models with a discussion of their respective limitations. We conclude that there does not yet exist a quantitative understanding of the ion, electron, and neutral thermalization processes in low‐altitude planetary ionospheres. Progress on this topic requires an adequate database of simultaneous ion, electron, and neutral temperature profiles in the 110–140 km altitude range. Plain Language Summary: Solar radiation ionizes and heats the neutral atmosphere in the process of creating the ionosphere. Heating begins at the altitude where energy carried by photoelectrons produced by solar extreme ultra violet radiation is not absorbed locally. This is the altitude where the ionosphere and neutral atmosphere are no longer in thermal equilibrium. There are numerous ionospheric models predicting the neutral, ion, and electron temperatures (Tn, Ti, and Te) as a function of altitude. These models predict that, in the absence of other heating mechanisms thermal equilibrium where Ti = Ti = Tn occurs below ∼120 km. Temperatures in this altitude range are used as upper boundary conditions for models attempting to describe energy transfer from the upper atmosphere to the ionosphere. Our study shows that ionospheric models of neutral and plasma temperatures cannot be validated in the region of thermal equilibrium because existing observations are sparse and do not have the precision and/or required spatial and temporal resolution. Progress in understanding energy transfer from the atmosphere to the ionosphere requires validated models of the altitude of thermal equilibrium. Key Points: Thermal equilibrium is postulated to be attained at the lowest altitude heated by photoelectrons but has not been observedQuantitative understanding of thermal equilibrium requires observations that validate modelsThere is an ongoing community need for simultaneous neutral, ion, and electron temperature profiles below 140 km altitude [ABSTRACT FROM AUTHOR]

Drainage reorganization generally occurs on geological time scales under unstable river network conditions. A few local‐scale studies indicate that recent climatic changes might accelerate the drainage reorganization process. However, large‐scale drainage reorganization during the modern era is rarely documented. This study examines ongoing drainage reorganization on the endorheic Tibetan Plateau (TP) as a primary result of drastic lake expansion. A total of 11 drainage system reorganization events comprising 24 different lake basins and covering a total area of 61,115 km2 occurred between 2000 and 2018. Assuming the continued growth rate of TP lakes, we project another 20 basins will be reorganized before 2030. These drainage basin reorganizations not only alter hydrological processes in the endorheic TP but may also cause the endorheic‐exorheic transition, leading to the upstream sprawl of the Yangtze River Basin and posing outburst flooding risks on China's key infrastructure such as the Qinghai‐Tibet Railway. Plain Language Summary: Recent climatic changes have intensified the global hydrologic cycle, and have likely accelerated drainage system evolution. We have provided a holistic picture of ongoing drainage reorganization driven by drastic lake expansions on the Tibetan Plateau (TP). Our results indicate that 24 different lake drainage systems have undergone reorganization between 2000 and 2018, and the number of basins is expected to increase to 44 by the year 2030. One notable drainage reorganization is between the endorheic Lake Yanhu and the exorheic Chumaer river, resulting in the upstream expansion of the Yangtze River Basin. These findings provide an increased understanding of ongoing drainage reorganization events driven by climatic changes. Further, this work advances our understanding of the connections between ongoing hydrologic changes and their effect on related geological disasters (e.g., outburst floods) within the TP. Key Points: Rapid lake growths drive large‐scale drainage reorganizations on the Tibetan Plateau24 lake drainage systems have undergone reorganization from 2000 to 2018 and this number is expected to increase to 44 by the year 2030The northern portion of the upstream Yangtze basin has expanded by around 8,400 km2 due to an endorheic‐exorheic transition [ABSTRACT FROM AUTHOR]