Geophysical Research Letters最新文献

Spacecrafts observe signatures of duskside magnetic reconnection in the Earth's magnetotail associated with the presence of oxygen $��\left(O^{+}\right)�$ ions of ionospheric origin. The exact role of $��O^{+}�$ ions in mediating reconnection remains largely unknown due to the local nature of observational techniques. We analyze results from global three-dimensional hybrid (kinetic ions, fluid electrons) simulations of $��O^{+}�$ outflows and demonstrate that oxygen ions, escaping from the top of the ionosphere into the lobes, may cause disruptions on the duskside of the proton-formed magnetotail, adding up to its turbulent, unsteady nature. These $��O^{+}�$ ions are shown to be capable of inducing magnetic flux ropes in the current sheet that thins out toward the dusk flank of the magnetotail due to Hall and ion kinetic effects. Unlike magnetohydrodynamics (MHD) simulations, where dawn-dusk magnetotail asymmetries may develop due to nonuniform ionospheric conductivity, the hybrid simulations demonstrate duskside tail disruptions on much faster ion gyroscales.

Wildfires have broad impacts on the atmosphere, ecology, and society. This study leverages satellite data and chemistry-transport models to analyze the impact of wildfires on trace gases in California during the August-October periods of 2018, 2019, and 2020. During these months, Southern California experiences minimal precipitation, leading to a high Vapor Pressure Deficit, which results in decreased photosynthetic activities. This reduction, combined with increased biomass burning, causes a rise in CO₂ concentrations. Increased CO and CH₄ levels are also seen in TROPOMI retrievals tied to the increase in biomass burning. The CarbonTracker model captures these elevated CO₂ concentrations, though with a reduced amplitude of increased CO₂. Similarly, the GEOS-Chem model successfully simulates high CO levels but underestimates the observed enhancements. These findings will improve the understanding of fire's influence on trace gases and refine future numerical models on surface emissions and transport.

The iron spin crossover in (Mg_1-xFe_x)O ferropericlase causes changes to its physical properties that are expected to affect seismic velocities in Earth's lower mantle. We present new time-resolved pressure-volume measurements of iron-rich ferropericlase (x_Fe = 0.40, 0.59) and combine the results with literature data with x_Fe = 0.04–0.6 to investigate the dependence of ferropericlase elastic properties on iron content. We infer the relationship between unit-cell volume, pressure and iron content directly from the data by training Mixture Density Networks and derive bulk modulus, density and bulk sound velocity from the outputs. This allows us to constrain the effect of the spin crossover on these properties and estimate their uncertainties for different iron contents. Our findings indicate that the spin crossover may significantly alter the physical properties of ferropericlase in iron-enriched regions in the lowermost mantle, with implications for the interpretation of seismic heterogeneities observed near the core-mantle boundary.

The temperature for cloud glaciation importantly determines the initialization of precipitation and lifetime of clouds. The role of anthropogenic pollutants as ice nucleating particles (INPs) to determine the cloud glaciation remains uncertain. In this study, based on satellite radar and lidar observations, the clouds either in pure liquid or mixed-phase with liquid top were statistically analyzed over China during 2006–2019, to obtain the transition freezing temperature (T*) of cloud top where mixed-phase becomes more frequent than pure water, with further validation by the aircraft in situ measurements. Anthropogenic pollution was observed to raise T* up to −9°C, significantly increasing it by approximately 5°C per unit of aerosol optical depth. The results provide regional-scale evidence that anthropogenic pollutants act as efficient INPs, increasing the freezing temperature of mixed-phase clouds.

Terrestrial gamma ray flash (TGF) observations made by the Atmosphere-Space Interaction Monitor (ASIM) have demonstrated that these TGFs are accompanied by a prominent optical pulse from a hot leader channel. It is hard to confidently resolve the true sequence of the events in the source region due to temporal proximity of the involved processes. Here we report a bright long duration TGF together with its associated optical recordings showing clear temporal separation between the TGF and the optical pulse. In this observation the optical pulse is clearly distinct and subsequent relative to the TGF. The corresponding lightning discharge occurred at the very end of the TGF. We conclude that the current surge inside the lightning leader channel cannot be responsible for generation of this TGF. The current surge that produced the associated optical pulse can itself be conditioned by the TGF and may be responsible for the TGF termination.

The Maritime Continent (MC) exhibits a pronounced diurnal cycle in precipitation, with many high-resolution models overestimating the diurnal peak and predicting earlier precipitation over the islands than observed. We hypothesize that part of this model bias comes from ignoring precipitation-induced surface sensible heat flux (Q_P). To test this conjecture, we performed simulations with and without Q_P for April 2009 and June 2006. The inclusion of Q_P reduced the bias in diurnal peak precipitation amplitude by 83% in April 2009 and 23% in June 2006. Similarly, the bias in precipitation peak timing decreased by 26% and 15%, respectively. This bias reduction was even more prominent during periods of heavier rainfall. This improvement in both the amplitude and phase of diurnal precipitation also led to a reduction in bias for total precipitation by ∼10%. These findings suggest that Q_P cannot be neglected over the MC, particularly during heavy precipitation.

Distinct responses in the soil moisture (SM) between the two most severe meteorological droughts in Korea are examined. Although total accumulated precipitation deficit during 1994–1996 drought was slightly less than in the 2013–2017 drought, 1994–1996 drought showed a record-breaking negative SM anomalies, while the accumulated negative SM anomalies during 2013–2017 were less than half of those in 1994–1996. In 1994–1996 case, robust precipitation deficits occurred early in the event, leading to subsequent precipitation shortages under dry conditions. In addition, precipitation deficit was observed not only during wet seasons but also throughout dry seasons. This amplifies the SM response, as the runoff volume remains relatively constant despite reduced precipitation in arid soil conditions, which eventually reduces soil water retention led by the precipitation deficit. Conversely, in 2013–2017 case, precipitation deficit occurred during later period of the event and wet seasons, which leads a moderate SM drying signals.

An accurate center localization in near real-time is critical for tropical cyclone (TC) monitoring and forecasting. This study presents a robust algorithm for localizing typhoon centers using the Chinese geostationary (GEO) meteorological satellite. The results using the Advanced Geostationary Radiation Imager (AGRI) onboard Fengyun-4A (FY-4A) satellite data, achieving a mean absolute error (MAE) of 29.4 km across various typhoon intensities in the Western North Pacific, superior to other baseline methods. By harnessing the multi-spectral imagery from the FY-4A and incorporating an attention mechanism, it significantly boosts the deep learning convolutional neural network's ability to identify typhoon cloud features and their centers, even during their initial and weakest stages, which is laudable because these are the most difficult for center fixing even for human analysts. Remarkably, it requires just a single moment satellite imagery to locate the center of typhoon, enabling automated updates of the typhoon centers in near real-time applications.

Baffin Bay is located between Greenland and several islands of the Canadian Arctic, providing a conduit for the downstream transport of ice and freshwater to the North Atlantic via Davis Strait. Using satellite observations from Sentinel-1, the RADARSAT Constellation Mission, and CryoSat-2, we estimated the sea ice export through Davis Strait and winter ice production in Baffin Bay from 2016 to 2022. The average annual ice export for this 6-year period was 981 ± 193 × 10³ km² for area 816 ± 130 km³ for volume, and 653 ± 130 km³ for solid freshwater, all of which are considerably higher than previously reported estimates. The average winter ice area production upstream of Davis Strait was 758 × 10³ km² and the volume production was 589 km³ indicating that more than 80% of the ice exported out of Baffin Bay was produced locally. Compared to Fram Strait, sea ice fluxes through Davis Strait represent ∼59% of the volume and ∼111% of the area.

The polar cap arc at 1500 MLT (15MLT-PCA) has been considered as an auroral signature of the cusp's duskside boundary and been speculated to be caused by lobe reconnection. However, no observational evidence has been provided to support this speculation. Here we report a 15MLT-PCA event occurred on 29 November 2017 using multi-instrument observations. During the DMSP observed the 15MLT-PCA, Cluster, with its footprints at the root of the 15MLT-PCA, identified two FTEs in the southern hemisphere's lobe region, accompanied by an increase in electron and ion energy from hundreds of eVs to several keVs. AMPERE observed an increase in upward field-aligned currents associated with the 15MLT-PCA. SuperDARN observed a single cell convection with an enhancement of sunward plasma flow near the root of 15MLT-PCA. We suggest that these observations provide the in-situ observational evidence that the 15MLT-PCA is generated by a lobe reconnection at the cusp's duskside boundary.