Abstract Particulate matter (PM) bound cadmium (Cd) deposition on the Earth's surface poses significant ecological risks to humans and the environment. Cd stable isotopes are useful tracers for understanding sources and biogeochemical cycling in the Earth's ecosystems, yet knowledge of atmospheric Cd isotopic compositions remains limited. Here we present measurements of Cd isotopic compositions in fine particulate matter (PM 2.5 ) in five megacities selected to represent different anthropogenic Cd emission structures across China and explore potential atmospheric Cd sources. The mean (±1 SD) δ 114 Cd values of PM 2.5 were −0.231 ± 0.520‰, −0.192 ± 0.265‰, −0.003 ± 0.167‰, 0.005 ± 0.089‰, and 0.090 ± 0.121‰ in Chengdu, Lanzhou, Guangzhou, Jinan, and Beijing, respectively, more negative than δ 114 Cd signatures in the global remote atmosphere. Anticorrelations between δ 114 Cd and anthropogenic emission tracers (i.e., PM 2.5 ‐bound Cd concentrations and enrichment factors), and high Cd/As ratios in Chengdu and Lanzhou, indicate anthropogenic atmospheric Cd emissions mainly from nonferrous metal smelting. No such relationship was observed in other cities, where the δ 114 Cd and Cd/As ratios indicate coal‐fired emissions. Overall, the results of our study suggest that compared with the remote atmosphere, both coal combustion and nonferrous metal smelting cause a shift in PM 2.5 ‐bound Cd toward lighter isotopic compositions, with nonferrous metal smelting characterized by significantly more negative δ 114 Cd values and higher Cd/As ratios. Combined with Cd/As ratios, Cd isotopes provide a promising tool for identifying major anthropogenic atmospheric Cd sources.
Abstract Based on the observational and reanalysis data for winters (December‐January‐February, DJF) of 1962–2022, this study addressed the relationship between the stratospheric polar vortex (SPV) and compound cold‐wet events (CCWEs) in the Yangtze River Basin (YRB). It is found that their relationship varies from an insignificant correlation to a significant negative correlation in the late 1990s. During the latter period, the winter SPV anomaly can excite an Atlantic‐Eurasian teleconnection wave train in the troposphere, which then triggers downstream responses. On one hand, the Siberian high intensifies and the polar front jet weakens, directing strong cold airs southward into the YRB. On the other hand, a baroclinic and meridional dipole‐like pattern of geopotential height anomalies appears over East Asia, with negative geopotential height anomalies extending southward from East Asia to the Indochina Peninsula and the Indian subcontinent. Together with the subtropical jet, this configuration provides favorable conditions for the formation of an inversion layer and dynamic forcing for precipitation, ultimately influencing the CCWE occurrence in the YRB. Further investigation from both observation analyses and model simulations reveals that the interdecadal shift in the dipole pattern of September Arctic sea ice concentration (SIC) from the positive phase to the negative phase (i.e., above‐average SIC in the Barents–Kara Seas and below‐average SIC in the Beaufort‐Chukchi‐East Siberian Seas) plays an important role in the interdecadal strengthening of the stratosphere‐CCWEs relationship since the late 1990s.
Abstract Shallow circulations in the tropics are related to the sea surface temperature distribution, longwave cooling above the boundary layer, and shallow convection in both observations and models. To understand the influences sea surface temperature has on the shallow circulation strength, fixed sea surface temperature distributions are applied in experiments using an idealized general circulation model with uniform insolation and no rotation. The experiments are designed to distinguish the effects of mean sea surface temperature from those of sea surface temperature gradients, creating combinations using global mean SSTs from 299 to 305 K and SST ranges from 2.5 to 15 K. In these simulations, a large‐scale, deep circulation develops connecting the coldest to hottest SSTs. Experiments with sufficiently large sea surface temperature mean or range also exhibit a distinct shallow cell above the boundary layer. This shallow cell is associated with a deep moist layer sloping upwards from the coldest to hottest sea surface temperatures. We find that warming the mean sea surface temperature increases the strength and depth of these shallow circulations primarily by increasing shallow convection over intermediate sea surface temperatures, while increasing the sea surface temperature gradient enhances shallow circulation strength primarily by enhancing longwave cooling above the boundary layer.
Abstract Atmospheric tides in the lower thermosphere play an important role in regulating upper‐atmospheric conditions relevant to space weather. However, their spatial and temporal variability remains poorly understood, apart from seasonal variations. Previous studies have shown that tides can be influenced by meteorological and solar conditions. This study clarifies the relative importance of the El Niño‐Southern Oscillation (ENSO), the Quasi‐Biennial Oscillation (QBO), the Northern and Southern Polar‐night Jet Oscillations (NPJO and SPJO), the Madden‐Julian Oscillation (MJO), and Lyman‐alpha (Ly) radiation to tidal variability in the lower thermosphere. Tides at 80–110 km are derived from hourly temperature and wind fields in the JAGUAR‐DAS Whole neutral Atmosphere Reanalysis (JAWARA) for the period September 2004–August 2025. Rotated empirical orthogonal function analysis is used to identify the dominant modes of de‐seasonalized tidal variability. The resulting principal component time series are used as daily indices of tidal activity and are compared with indices of ENSO, QBO, NPJO, SPJO, MJO, and Ly. Multiple linear regression analysis determines which tides exhibit statistically significant responses to these indices and quantifies their magnitudes. The most pronounced responses include those of the nonmigrating diurnal tide DE3 to ENSO (approximately 4 m in horizontal wind velocity), the migrating diurnal tide DW1 to QBO (∼10 m ), and the migrating semidiurnal tide SW2 to NPJO (∼12 m ) and SPJO (∼7 m ). Tidal responses to MJO and Ly are relatively weak and are therefore not identified with the same level of confidence.
Abstract Multiple observational records indicate a long‐term weakening of the zonal sea surface temperature (SST) gradient in the tropical Atlantic, characterized by enhanced warming in the east. However, the underlying mechanism remains elusive as the concurrent strengthening of the surface southeasterlies and the zonal tilt of the equatorial thermocline would suggest a strengthened zonal gradient through Bjerknes feedback. Here, we demonstrate that this zonal SST gradient weakening is instead driven by local atmospheric adjustments, which are mainly contributed by latent heat flux changes. In the west, intensified surface southeasterlies—linked to a strengthened regional Hadley circulation—suppress local warming by reducing surface relative humidity and increasing surface wind speed. In the east, horizontal moisture convergence increases local relative humidity to enhance local warming. Our findings highlight the critical role of local atmospheric adjustments in shaping the historical tropical Atlantic SST warming pattern, which is distinct from coupled air–sea dynamics.
