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Abstract Drylands are highly vulnerable to climate change due to their fragile ecosystems and limited ability to adapt. In contrast to the global drying after tropical volcanic eruptions shown previously, we demonstrate that large tropical volcanic eruptions can induce significant two-year hydroclimatic wetting over drylands by employing the last millennium simulations. During this wetting period, which extends from the first to the third boreal winter after the eruption, several hydroclimatic indicators, such as self-calibrating Palmer Drought Severity Index based on the Penman-Monteith equation for potential evapotranspiration (scPDSIpm), standard precipitation evapotranspiration index (SPEI), aridity index (AI), top-10cm soil moisture (SM_10cm), and leaf area index (LAI), show significant positive anomalies over most drylands. The primary contribution to the wetting response is the potential evapotranspiration (PET) reduction resulting from dryland surface cooling and reduced solar radiation, as well as a weak contribution from increased precipitation. The latter is due to the wind convergence into drylands caused by slower tropical cooling compared to drylands. The wetting response of drylands to volcanic eruptions also demonstrates some benefits over the global hydrological slowdown resulting from stratospheric aerosol injection, which replicates the cooling effects of volcanic eruptions to address global warming. 

Abstract Arctic warming has significant environmental and social impacts. Arctic long‐term warming trend is modulated by decadal‐to‐multidecadal variations. Improved understanding of how different external forcings and internal variability affect Arctic surface air temperature (SAT) is crucial for explaining and predicting Arctic climate changes. We analyze multiple observational data sets and large ensembles of climate model simulations to quantify the contributions of specific external forcings and various modes of internal variability to Arctic SAT changes during 1900–2021. We find that the long‐term trend and total variance in Arctic‐mean SAT since 1900 are largely forced responses, including warming due to greenhouse gases and natural forcings and cooling due to anthropogenic aerosols. In contrast, internal variability dominates the early 20th century Arctic warming and mid‐20th century Arctic cooling. Internal variability also explains ∼40% of the recent Arctic warming from 1979 to 2021. Unforced changes in Arctic SAT are largely attributed to two leading modes. The first is pan‐Arctic warming with stronger loading over the Eurasian sector, accounting for 70% of the unforced variance and closely related to the positive phase of the unforced Atlantic Multidecadal Oscillation (AMO). The second mode exhibits relatively weak warming averaged over the entire Arctic with warming over the North American‐Pacific sector and cooling over the Atlantic sector, explaining 10% of the unforced variance and likely caused by the positive phase of the unforced Interdecadal Pacific Oscillation (IPO). The AMO‐related changes dominate the unforced Arctic warming since 1979, while the IPO‐related changes contribute to the decadal SAT changes over the North American‐Pacific Arctic. 

El Niño–Southern Oscillation (ENSO) over the tropical Pacific can affect Arctic climate, but whether it can be influenced by the Arctic is unclear. Using model simulations, we show that Arctic sea ice–air interactions weaken ENSO by about 12 to 17%. The northern North Pacific Ocean warms due to increased absorption of solar radiation under such interactions. The warming excites an anomalous tropospheric Rossby wave propagating equatorward into the tropical Pacific to strengthen cross-equator winds and deepen the thermocline. These mean changes dampen ENSO amplitude via weakened thermocline and zonal advective feedbacks. Observed historical changes from 1921–1960 (with strong sea ice–air interactions) to 1971–2000 (with weak interactions) are qualitatively consistent with the model results. Our findings suggest that Arctic sea ice–air interactions affect both the mean state and variability in the tropical Pacific, and imply increased ENSO amplitude as Arctic sea ice and its interactions with the atmosphere diminish under anthropogenic warming. 

Abstract Multidecadal sea surface temperature (SST) variations in the tropical western Pacific (TWP) have been attributed to nonlinear external forcing and remote influences from the Atlantic Multidecadal Variability (AMV). However, the AMV resulted from both internal variability (IV) and external forcing. Thus, the origins of the TWP SST variations are not well understood. By analyzing observations and model simulations, we show that more than half of the decadal to multidecadal SST variations in TWP during 1920–2020 resulted from external forcing with the forced component correlated with AMV, while the internal component is unrelated to AMV. Furthermore, about 43%–49% of the forced AMV‐like SST variations in TWP result from remote influences of the forced AMV in the Atlantic via atmospheric teleconnection over the North Pacific, with the rest from other remote or local processes. 

Abstract Atmospheric instability affects the formation of convective storms, but how it has changed during recent decades is unknown. Here we analyze the occurrence frequency of stable and unstable atmospheric conditions over land using homogenized radiosonde data from 1979 to 2020. We show that atmospheric stable (unstable) conditions have decreased (increased) significantly by ∼8%–32% (of time) from 1979 to 2020 over most land areas. In boreal summer, the mean positive buoyancy (i.e., convective available potential energy [CAPE]) also increases over East Asia while mean negative buoyancy (i.e., convective inhibition [CIN]) strengthens over Europe and North America from midnight‐dawn for unstable cases. The increased unstable cases and mean CAPE result from increased low‐level specific humidity and air temperature, which increase the buoyancy of a lifted parcel. The stronger CIN results from decreased near‐surface relatively humidity and decreased lapse rate in the lower troposphere. Our results suggest that the atmosphere has become increasingly unstable, which could lead to more convective storms. 

Abstract The diurnal cycle of precipitation plays a crucial role in regulating Earth's water cycle, energy balance, and regional climate patterns. However, the diurnal precipitation across mainland Southeast Asia (MSEA) and the factors influencing its spatial variations are not fully understood. In this study, we investigated diurnal precipitation patterns in summertime (June–August) from 2002 to 2005 over MSEA using ground‐based observations, satellite products, the global ERA5 reanalysis, and high‐resolution simulations from the Weather Research and Forecasting (WRF) Model at 9‐ and 3‐km grid spacing forced by ERA5 hourly data on ∼0.25° grids. Various observation‐based data sets including GHCN‐Daily, Multi‐Source Weighted‐Ensemble Precipitation (MSWEP), Asian Precipitation ‐ Highly‐Resolved Observational Data Integration Towards Evaluation of Water Resources (APHRODITE), and Integrated Multi‐satellite Retrievals for Global Precipitation Measurement (IMERG) were used. In evaluating daily precipitation over MSEA, MSWEP, and APHRODITE data sets show similar patterns in precipitation amount, frequency, and intensity, while IMERG tends to produce higher amounts but with less frequency. ERA5 overestimates light precipitation compared to the other data sets. The WRF simulations generally produce heavier but less frequent light precipitation, with the 3‐km simulation producing less intense precipitation than the 9‐km simulation. A k‐means classification of IMERG data revealed five distinct spatial regimes with varying diurnal precipitation cycles. The WRF simulations closely match these regimes, capturing key diurnal cycles missed by ERA5 over mountainous regions and coastlines. Additionally, convective activities and near‐surface winds influence these cycles, with WRF simulations better representing coastal and mountain precipitation patterns than ERA5. High‐resolution WRF simulations, especially the 3‐km simulation, capture diurnal precipitation more accurately than ERA5, highlighting the importance of employing convection‐permitting models to simulate precipitation diurnal cycles over complex terrain.