Geophysical Research Letters最新文献

Intense convective mixing in the central North Atlantic is a major gateway for dissolved organic matter (DOM) into the deep ocean, sustaining elevated dissolved organic carbon (DOC) concentrations. Rapid down-slope transport on adjacent Irish and Hebrides Margins represents another, less-explored mechanism contributing to the deep-sea DOM reservoir. Our analyses of solid-phase extractable DOM (SPE-DOM) in bottom waters in this region showed 7–11 μM higher DOC concentration and 190–330 years youngerSPE-DOM radiocarbon ages compared to similar depths in the open eastern North Atlantic. We estimated a down-slope DOC flux of 43 Tg C yr⁻¹ from the Irish and Hebrides shelves. During transport, conservative mixing, dominated by physical rather than biological/chemical processes, determined the molecular DOM composition, while minor particulate organic matter degradation introduced less-refractory DOM with terrigenous characteristics. Thus, rapid down-slope transport emerges as an efficient conduit for delivering fresh DOM into the deep ocean.

Synoptic climatology, which connects atmospheric circulation with regional environmental conditions, is pivotal to understanding climate dynamics. While regional climate models (RCMs) can reproduce key mesoscale precipitation patterns, biases related to synoptic circulation from the driving model, typically global climate models (GCMs), often remain unaddressed. This study examines the influence of correcting systematic bias in RCM boundaries on the representation of Australian synoptic systems. We utilize a structural self-organizing map to evaluate the frequency, persistence, and transitions of daily synoptic systems. Our findings reveal that an RCM with multivariate bias-corrected boundaries improves the representation of synoptic systems compared to the driving GCM, or an RCM with uncorrected or simply bias-corrected boundaries, particularly in reference to the frequency of systems identified. This demonstrates that appropriately correcting RCM boundary conditions helps correct many of the circulation errors inherited from the driving GCM but not all.

An outstanding question in the geological evolution of the Chilean Andes is the cause of the westward shift and relocation of magmatism from the High Andes (HA) to the Coastal Cordillera (CC) during the Late Triassic, Pre–Andean stage. The spatiotemporal distribution of Permian–Triassic–Jurassic igneous rocks in northern-central Chile (20°S–32°S) reveals a significant westward magmatic shift of ∼120 km during the Norian time. Despite diverse proposed models, the precise geodynamic mechanism behind this shift remains unclear. To address this, we used 2D numerical modeling to investigate two contrasting scenarios: (a) subduction rollback and (b) subduction transference/jump and reinitiation by terrane accretion. Our modeling results strongly support Scenario B, where mantle density and the size of the oceanic plateau are crucial for triggering subduction jump and reinitiation. This model aligns with geological and geophysical evidence and offers new insights into unraveling the Pre– and Early–Andean evolution.

Urban heat stress is a critical issue, particularly in cities where dense infrastructure and limited green space exacerbate temperature extremes. This study investigates the impact of greenery (EVI2), canopy cover (CC), impervious cover (IC), and water bodies on heat index in Chicago using high-resolution data from the Heat Watch campaign. We find that EVI2, CC and proximity to water body significantly reduce heat while IC increases heat, particularly in the afternoon when solar radiation is intense. Additionally, the effective radius that land cover impacts heat is smaller in the afternoon. The combined effect analysis indicates that enhancing total greenness, not just canopy cover, is the most effective strategy to reduce heat. This study underscores the importance of strategic vegetation management, highlighting the critical role of integrated approaches in reducing urban heat.

The present study analyzes novel observations of vertical wind $��\left(�w�\right)�$ in the tropical upper troposphere-lower stratosphere obtained from a radar wind profiler in Cochin, India. Between December 2022 and April 2023, 63 consecutive 4 hr curtains of $��w�$ were measured with a vertical spacing of 180 m and a sampling time step of 44 s, thus resolving almost the whole spectrum of vertical motions. Spectra of $��w�$ strongly vary with altitude. They are generally flat up to the local Brunt-Väisälä frequency (BVF), but sometimes exhibit a peak of $��w�$ variance closer to BVF, a feature which may be attributed to trapped gravity waves. At other times and locations, the $��w�$ profiles reveal Kelvin-Helmholtz billows. Finally, the variability of $��w�$ variance over the 4 month campaign period is investigated. Using brightness temperature from geostationary satellites as a convective proxy, it is found that $��w�$ variance is highly correlated with fluctuations in convective activity.

Sea surface temperature anomaly (SSTA) of ocean eddies induces an anomalous air-sea turbulent heat flux that acts to dampen SSTA. A two-dimensional SSTA model explores the effect of air-sea turbulent heat flux, parameterized as SSTA damping, in shaping eddy SSTA patterns. Increased SSTA damping transitions the SSTA pattern from a monopole to dipole, indicating the balance between eddy stirring of the background SST gradient and SSTA damping. The SSTA dipole pattern increases the correlation of eddy velocity and SSTA, but SSTA damping weakens the SSTA, resulting in an optimal damping rate maximizing lateral eddy surface heat transport. Globally, the SSTA damping rate increases toward the equator. In mid-latitude and high-latitude regions (e.g., the Kuroshio, the Gulf Stream, and the Southern Ocean), eddy SSTAs are monopoles, while the tropics and subtropics exhibit dipole SSTA patterns due to higher damping rates, facilitating greater lateral eddy heat transport when the SSTA is large.

Previous work has shown that estimates of climate sensitivity vary over time in response to abrupt CO₂ forcing in climate model simulations. The energy fluxes that drive warming in response to increasing CO₂ also influence precipitation, which prompts the question: Does the precipitation response therefore also vary over time? We investigate by examining the response of precipitation to warming forced by greenhouse gases—the hydrological sensitivity—in a set of millennial-length climate simulations with multiple climate models, Long Run Model Intercomparison Project (LongRunMIP). We compare hydrological sensitivity calculated from three different timescales of the simulations: years 1–20, 21–150, and 151–1000. We show that the hydrological sensitivity lacks a consistent dependence on timescale, in contrast to climate sensitivity. Decomposition of the surface energy budget reveals that the relative muting of the multi-model mean hydrological sensitivity is driven by surface downwelling shortwave flux.