Geophysical Research Letters最新文献

Accurate satellite-based retrieval of boundary-layer water vapor over land is crucial for understanding the Earth-atmosphere system but remains challenging due to the interaction of surface parameters on low-level atmosphere-sensitive channels. This study proposes a novel approach to explicitly extract the upwelling atmospheric radiance ($��R_a�$) from the total radiance ($��R_t�$) observed by the Infrared Atmospheric Sounding Interferometer (IASI), using a Residual Multi-Layer Perceptron model. A modified one-dimensional variational algorithm for surface-free radiances is also developed. The radiance extraction model, trained on simulated IASI radiances, is applied to IASI observations over mainland Australia in January and February of 2022. Validated against ERA5 and radiosonde observations, compared with the traditional $��R_t�$-based method, the $��R_a�$-based atmospheric profile retrievals show distinct improvements in boundary-layer humidity retrieval with at least 20% error reduction. This approach provides a new thought to enhance humidity retrievals from hyperspectral sounders and benefits other quantitative applications such as data assimilation.

Midwestern U.S. extreme precipitation is associated with multiple storm types including mesoscale convective systems (MCSs) and/or training thunderstorms, tropical cyclone (TC) remnants, and winter storms. Anthropogenic warming is expected to increase climatological precipitation globally, however, there may be little correspondence with regional storm-based changes. Furthermore, uncertainty remains in precipitation-temperature scaling due to use of convective parameterization in most global models. In this study, we investigated historically impactful extreme precipitation events from multiple types of Midwest storms using the Weather Research and Forecasting model at convection-permitting resolution. We simulated five-member ensembles of historical hindcasts and experiments representing the storms in the future using the pseudo-global warming method. We found that future precipitation changes depend on storm type, with increases near Clausius-Clapeyron (CC) for winter storms, no consensus for MCSs and/or training thunderstorms, and sub-CC increases for TC remnants. This research highlights the importance of considering storm type in future extreme precipitation projections.

It has been demonstrated that the motion of the Earth's rotational pole with respect to the crust—termed polar motion—is increasingly influenced by barystatic processes, that is, continental-ocean mass redistribution due to melting of polar ice sheets, global glaciers, and variations in terrestrial water storage. However, how these processes might impact polar motion in the $��{21}^{\text{st}}�$ century is not known. Here we investigate this problem under various climatic scenarios, namely, Representative Concentration Pathways (RCP) and Shared Socioeconomic Pathways. We show that the climate-induced polar motion is sensitive to the choice of climatic scenario; under the optimistic RCP2.6, the rotational pole might wander by $��\sim �$12 m with respect to 1900, whereas under the pessimistic RCP8.5 by more than twice as much ($��\sim �$27 m). The most important contributor is the melting of polar ice sheets (Greenland and, to a lesser degree, Antarctica), followed by melting of global glaciers, and variations in terrestrial water storage.

Cyclones at polar latitudes of the Atlantic-Arctic corridor exhibit different thermodynamic characteristics. Midlatitude-origin cyclones, which make up about 14% of wintertime cyclones in the region, are generally warm and moist. The more numerous Arctic-origin cyclones display a wide range in the boundary-layer equivalent potential temperature $��{\theta }_e�$ that depends on both temperature and moisture. This spread includes large positive and negative $��{\theta }_e�$ anomalies, leading to weak signals in composite means. Warm/moist (high-$��{\theta }_e�$) cyclones at polar latitudes are associated with tilted and central jet regimes, steering cyclones of midlatitude-origin into the Barents region or preconditioning the environment for Arctic genesis. Conversely, cold/dry (low-$��{\theta }_e�$) Arctic-origin cyclones form under a jet stream positioned far south, characterized by frequent southern jet regimes. These new insights into the large variability of Barents cyclones have implications for our understanding of genesis mechanisms, cyclone development, and their effect on the climate of the polar regions.

Wetlands are universally recognized as hotspots for nitrogen cycling and gaseous nitrogen emissions. In this study, the fluxes of nitric oxide (NO), nitrogen dioxide (NO₂), ammonia (NH₃), and nitrous oxide (N₂O) were observed seasonally in the mud and waterfront plots of an urban wetland in eastern China using a dynamic flux chamber. The results revealed that the fluxes of NO, NO₂, and NH₃ displayed a diurnal pattern of higher values during the day and lower values at night, which was opposite to that of N₂O. The average annual emissions of NO, NH₃, and N₂O were 0.16 ± 0.04, 0.59 ± 0.03, and 8.81 ± 0.44 kg N ha⁻¹ yr⁻¹, respectively. Conversely, NO₂ exhibited deposition, with an annual flux of 1.51 ± 0.03 kg N ha⁻¹ yr⁻¹. Given the evolving area of urban wetlands, the emissions of gaseous nitrogen, particularly N₂O, deserve substantial attention.

The $��M_2�$ tide displays large seasonal variability in Europe, particularly in the North Sea. The tide is there larger in summer than in winter. However, there is no consensus on the physical drivers leading to such large values, atmosphere circulation and stratification being two good candidates. We analyzed hourly sea level data from observations at 35 tide gauges in Europe. The amplitude of $��M_2�$ seasonal cycle is the largest in the southern North Sea, reaching typically 4–6 cm. This cycle is well reproduced by a barotropic model, forced with the tidal potential and the atmosphere only. This suggests a minor role of the stratification. We show that large seasonal cycles in the southern North Sea are first due to gravitational nonlinear effects. The atmosphere also plays a role, but locally and in a smaller extent.

We demonstrate the global response of the ionosphere to the geomagnetic super storm on 10–11 May 2024. The in situ observations from the Swarm spacecraft show a rapid depletion of plasma density in the dawn and dusk sectors following the storm. The in situ data are further complemented by the ground-based total electron content maps. Both the in situ and the ground-based observations show significant depletion of electron density during the super storm in regions above 50° magnetic latitude. The density depletion originates from a polar hole in the morning high latitude sector. It is suggested that the strong convection speed under substantial solar wind forcing leads to chemical composition changes and rapid recombination in the ionosphere. The region of depleted plasma density is not confined to the polar cap but expands to auroral and mid-latitude regions. The depleted plasma density lasts for about 3 days before it recovers to the pre-storm levels.

Preferential flow (PF) is a relatively rapid water movement that significantly impacts geophysical processes. However, identifying PF and its environmental control mechanisms remains challenging, primarily due to soil spatial heterogeneity. In this study, 20 sensors were installed on two hillslopes with distinct soil thicknesses to monitor moisture at 5-min intervals. PF types were identified based on moisture response sequence to rainfall across layers, and relationships among PF frequency (PFF), soil depth, and rainfall characteristics were determined. Macropore flow was the main PF type, followed by soil‒bedrock interface flow. On the hillslope with deep soil cover, PFF was significantly negatively correlated with soil depth. Comparison, on the hillslope with shallow soil cover, PFF was not influenced by soil depth but more notably controlled by rainfall intensity and antecedent soil moisture. Accordingly, these findings highlight the critical roles of the soil thickness in shaping PF characteristics.

China has made extensive afforestation efforts over the past 40 years. However, ecosystem models simulate only modest vegetation enhancement, creating a significant disparity between documented reforestation efforts and model-based simulations. This fundamental mismatch remains largely unexplored. Here, we conducted a comprehensive analysis using diverse observation data to identify the determinant within Dynamic Global Vegetation Models (DGVMs) that underestimates vegetation growth in China. By developing a high-resolution forest cover change data set, we found that LUH2-GCB, the common land use input for DGVMs, causes models to underestimate afforestation. With a neighborhood comparison analysis, we quantitively demonstrated the predominant role of underestimated afforestation in lowering leaf area index (LAI) trends. Overall, DGVMs underestimated China's afforestation area by an average of 26.88%, leading to a 29.46% underestimation in LAI increase. Our findings confirm a significant greening trend in China and highlight the need for improved land use data representation in DGVMs.

Magnetosonic (MS) waves can be generated by hot Maxwellian ring protons locally within the Martian upper ionosphere, characterized by a weak ambient magnetic field and the presence of cold plasma abundant in heavier ions. A comprehensive study on the resonant instabilities of MS waves making use of the derived growth rates show that ring proton population with energies around 100 eV is optimal for wave generation. Highly oblique propagation leads to sharp harmonic structures at frequencies closer to local proton gyrofrequency. An increase in ring energy, $��{\omega }_{�p�e�}�/�{\Omega }_{�c�e�}�$ ratio, and heavier ion concentration decreases the wave growth rates. When the background ions have very low temperatures, $��O_2^{+}�$ ions lower the growth rate more as compared to $��O^{+}�$ ions. Additionally, the increase in temperatures of cold electrons and ions have opposite effects, with the former increasing the growth rate and the latter decreasing it.