Geophysical Research Letters最新文献

Pulse-like infrasound accompanying volcanic phenomena sometimes suggests interaction with water at the crater. We focus on pulse-like infrasound observed at Semisopochnoi Island in the Aleutian Arc, Alaska, during the phreatomagmatic activity on 13 July 2021. Overflight observations confirmed a small, ephemeral water lake on the crater floor in June 2021. We examined temporal variations in pulse-like infrasound activity, seismoacoustic amplitudes, and spectral characteristics. Pulse-like infrasound activity gradually became intermittent and waned at the end of the day. Seismic-infrasonic amplitude ratio decreased, while the infrasound frequency index increased with time. These results suggest less interaction with water due to drying out of the vent. Satellite observations also show increased ground surface temperatures inside the crater from 13 to 14 July. Numerical simulation suggests a significant topographic effect on the waveform and spectrum of the pulse-like infrasound, which should be considered before interpreting the source process.

Quantifying how and where climate change will alter meteorological drought properties is a priority to inform adaptation policies. Here we use the standardized precipitation index to portray future changes in the climatological properties of moderate drought events projected by the latest generation of Earth system models. Beyond the assessment of their mean frequency and intensity, other metrics are explored including length of drought intervals, drought duration, starting date and severity. Two extended 6-month seasons are distinguished starting in October and April, respectively. Consistent changes in drought properties are projected across timescales and seasons. Regional “dry spots” are identified, such as northern South America and the Caribbean Islands, where the median model response shows the largest increase in drought severity, mostly as a result of prolonged duration. Yet, there are many regions where the inter-model spread remains substantial and cannot be reduced by the application of global and regional observational constraints.

The Kuroshio Extension (KE) exhibits pronounced decadal variability, influencing marine ecosystems, fisheries, and regional climate. However, how anthropogenic warming affects this variability remains uncertain due to limited satellite records and model resolution constraints. Based on an eddy-resolving historical-and-future transient climate simulation, we find that the KE decadal variability weakens significantly under a high-emissions scenario. This weakening likely results from a disruption of the coupled ocean-atmosphere delayed oscillation, which involves basin-scale atmospheric circulation both forcing and responding to KE variations. Specifically, warming-induced strengthening of atmospheric stratification likely suppresses the thermodynamic adjustment, including the deep-reaching updraft and associated mid-to-upper tropospheric responses, typically triggered by oceanic mesoscale warming during the KE stable state. Such suppression disrupts the coupled ocean-atmosphere delayed oscillation, contributing to the weakened KE decadal variability. Our findings imply that the KE system might be less predictable under future warming.

Transient luminous events (TLEs), such as sprites, have been investigated via observations and simulations for decades. Recent TLE research has focused on effects leading to the delay of a sprite from its parent lightning flash. Here we investigate a sprite with by far the longest recorded delay to date, a delay of almost a full second (916.6 ± 16.6 ms) from the onset of the parent flash, as observed from the ISS during the ILAN-ES campaign on 6 February 2024. Based on meteorological, satellite, and ground-based ELF data, we reconstruct a realistic charge configuration for the parent thunderstorm. We input this reconstructed charge configuration to a 3D quasi-electrostatic model in order to simulate regions of possible sprite inception as a function of time corresponding to this sprite event following the lightning. We demonstrate how the observed delayed sprite could have been incepted by a prolonged piecewise pattern of the current in the parent flash.

Thermal tides are global oscillations driven by periodic solar heating that strongly influence circulation and vertical coupling in the Martian atmosphere. Previous studies have focused on the first and second migrating harmonics, while recent work has revealed higher-frequency harmonics in surface pressure records. However, these detections are limited to single locations, and spacecraft observations have only confirmed global structure up to the third harmonic. Here, we present the first planetary-scale characterization of migrating thermal tides up to the eighth harmonic as observed in remotely sensed temperature observations from the Emirates Mars Mission, sampling the lower atmosphere, and surface pressure measurements from the Curiosity and Perseverance landers. We examine the latitudinal and seasonal structure and show that high-frequency migrating tides have deep vertical structure with little phase variation with height, suggestive of near-resonant Lamb wave structure. Nearly identical seasonal amplitude-phase evolution across the longitudinally separated landers, indicate dominance of migrating tides.

Sea surface temperature (SST) anomalies in the Kuroshio Extension (KE) region have been increasingly recognized as playing a key role in shaping the extratropical air–sea interactions. However, the extent to which such extratropical SST forcing can influence large-scale atmospheric circulation and surrounding SST remains uncertain, particularly given strong atmospheric internal variability. Here, we investigate the atmospheric response to idealized positive SST anomalies in the KE region using large-ensemble atmospheric general circulation model experiments. The imposed forcing generates a robust sea-level pressure anomaly over and downstream of the KE, leading to surface westerly wind anomalies extending into the subtropical North Pacific. Despite substantial atmospheric internal variability over the Aleutian Low region, these subtropical wind anomalies consistently emerge across the ensemble. Our results suggest that SST forcing in the KE region can modulate air–sea interactions not only locally but also across a broader region extending equatorward.

The large annual carbon source over northern tropical Africa (NTA), inferred from satellite CO₂, remains highly debated. Using observing system simulation experiments with Orbiting Carbon Observatory-2 (OCO-2) sampling, we show that seasonally dependent sampling can lead to overestimated annual fluxes. These biases arise when prior flux seasonal cycle differs from the assumed truth. Since OCO-2 provides more observations during the non-growing season, posterior fluxes are more constrained in that period. When prior fluxes underestimate the seasonal amplitude, the posterior carbon sink during the growing season is underestimated, leading to a net positive bias. This effect is supported by real OCO-2 data, where we hypothesize that underestimating fire emissions during non-growing season and weaker seasonality of prior fluxes may contribute to overestimated annual fluxes. Our results highlight the need to improve prior flux estimates and expand observational coverage during the growing season to reduce biases in regional carbon budget assessments over NTA.