Geophysical Research Letters最新文献

Aerosol from the Hunga Tonga-Hunga Ha'apai (HT-HH) volcanic eruption (20.6°S) in January 2022 were not incorporated into the austral polar vortex until the following year, March 2023. Within the polar vortex in situ profiles of aerosol size spectra were completed in the austral autumns of 2019 and 2023, from McMurdo Station, Antarctica (78˚S), 30 months prior to and 15 months after the HT-HH eruption. The measurements indicate that the HT-HH impact on aerosol size was primarily confined to particles with diameters >0.5 μm leading to differences in aerosol mass, surface area, and extinction from factors of 2–4 at the volcanic layer's peak below 20 km, increasing to ratios of 5–10 above 20 km. Effective radius, with radiative and microphysical implications, increased from ∼0.2 to ∼0.3 μm. An Earth system model with a modal aerosol package compares favorably with the in situ measurements of the HT-HH aerosol impact.

Groundwater level records in North America are relatively short (<60 years), preventing long-term analysis of historical changes in groundwater levels associated with drought. In this study, tree ring widths are used to reconstruct groundwater levels in three regions in the North American Cordillera: Central British Columbia (BC), Canada, the Southern Interior Region of BC, and the San Luis Valley in Colorado, USA. Periods with severe drought conditions, identified using regime shift and threshold analyses were: 1890–1900 and 1950–1970 in Colorado, around 1920–1940 in the BC Interior, and 1935–1945 in Central BC. The groundwater level reconstructions are correlated with several climate indices and have similar regime shifts as identified in streamflow and drought records. The groundwater level reconstructions are strongly related to winter snowpack, suggesting that the observed trend of declining snowpack in recent years may lead to declining groundwater availability in these regions.

Using a Green's function-like approach, this study identifies optimal atmospheric heat sources for the two leading modes of South Asian Summer Monsoon (SASM) interannual variability. Optimal heating for the first mode, characterized by a lower-level anomalous anticyclone over northern Bay of Bengal (BOB), is distributed over the Arabian Sea and tropical eastern Indian Ocean (EIO)-Maritime Continent, with cooling over the BOB-western North Pacific. In contrast, heating over the tropical southwestern Indian Ocean and equatorial Atlantic, along with cooling over the tropical EIO-western Pacific, optimally drives the second mode, featuring an anomalous anticyclone over central-northern India. El Niño/Southern Oscillation indirectly influences SASM by triggering heat sources resembling these optimal patterns. Other sea surface temperatures (SSTs), like those over equatorial Atlantic, can also generate similar heating structures, causing corresponding SASM anomalies. This suggests that the impact of SST modes on SASM depends on the similarity of induced heat sources to optimal patterns.

Mesoscales, which couple small to large scales, and vice-versa, are critical to the magnetosphere-ionosphere coupling. Optical and radar measurements indicate that dynamical mesoscale features are present in the ionosphere, however quantifying their contribution to the overall dynamics remains a challenge. We use a new ionospheric data assimilation technique, Lompe (Local mapping of the polar ionospheric electrodynamics), to specify ionospheric electrodynamics using a wide variety of input data and a priori assumptions about the physical nature of the ionospheric electric field. We isolate the terms of the ionospheric Ohm's law and find that mesoscale structures in the FACs are driven by Hall gradients, while the larger scale patterns are associated with the divergence of the electric field. We calculate the relative contribution of mesoscales to the overall FAC patterns during a magnetospheric substorm, and find that in the nightside, mesoscale FACs contribute up to 60% of the total.

The capability to observe temporal changes on Io's surface at optical wavelengths has recently been demonstrated by Conrad et al. (2024, https://doi.org/10.1029/2024GL108609) using new instrumentation at the Large Binocular Telescope. Monitoring of Io's surface morphology would be impactful since preexisting metrics of the degree, location and composition of Io's plume activities are severely limited. Relationships with external data sets appear especially fruitful. Comparisons with spatially resolved data on gas distributions and thermal hots spots would better characterize composition and chemistry in Io's volcanic plumes. Comparisons with measurements remote from Io are posed to advance our understanding of atmospheric escape and how eruptions connect to transient enhancements at disparate size and time scales in the extended neutral clouds and plasma torus.

Atmospheric turbulence over the Arctic sea-ice surface has been understudied due to the lack of observational data. In this study, we focus on the turbulence kinetic energy (TKE) over sea ice and distinguish its two different vertical structures, the “Surface” type and the “Elevated” type, using observations during the Multidisciplinary drifting Observatory for the Study of Arctic Climate expedition (MOSAiC). The “Surface” type has the maximum TKE near the surface (at 2 m), while the “Elevated” type has the maximum TKE at a higher level (6 m). The TKE budget analysis indicates that the “Elevated” type is caused by the increased shear production of TKE at 6 m. In addition, spectral analysis reveals that the contribution to TKE by horizontal large eddies is enhanced in the “Elevated” type. Finally, how the vertical structure of TKE affects the parameterization of turbulent momentum flux is discussed.

Turbulent vertical velocity measurements are scarce in regions prone to convection such as the Labrador Sea, which hinders our understanding of deep convection dynamics. Vertical velocity, $��w�$, is retrieved from wintertime glider deployments in the convective region. From $��w�$, downward convective plumes of dense waters are identified. These plumes only cover a small fraction of the convective area. Throughout the convective area, the standard deviation of $��w�$ agrees with scaling relations for the atmospheric surface and boundary layers. It initially depends on surface buoyancy loss in winter, and later, on wind stress after mid-March. Both periods are characterized by positive turbulent vertical buoyancy flux. During convective periods in winter, the positive buoyancy flux is mostly forced by surface heat loss. After mid-March, when buoyancy loss to the atmosphere is reduced, the positive buoyancy flux results from a restratifying upward freshwater flux, potentially of lateral origins and without much atmospheric influence.