We present the first evidence for a lower S-wave velocity (Vs ~3.3 to 3.5 km/s) at 8-17 km depth underlying a 4 km thick high-velocity zone with Vs >3.8 km/s beneath the west coast and the neighbouring parts of the Deccan Volcanic Province, India, coinciding with the last phase of volcanism. The velocity structure is derived from joint inversion of receiver function from 9 seismographs operated along ~106 km long W-E profile with the surface wave dispersion data. The low-velocity layer possibly represents the horizontally elongated frozen magma reservoir, the source for the magma eruption at ~65 million years produced due to the interaction of the Reunion hotspot with India. The shallow, high-velocity layer could be basaltic mafic intrusions responsible for the production of massive CO2 degassing. The Moho deepens beneath the west coast to ~45 km due to 10-15 km of underplating as a consequence of magma upwelling.

On Jan. 15, 2022, the Hunga Tonga-Hunga Ha’apai (HT) eruption injected SO2 and water into the middle stratosphere. Shortly after the eruption, the water vapor anomaly moved northward toward and across the equator. This northward movement appears to be due to a Rossby wave forced by the excessive IR water vapor cooling. Following the early eruption stage, persistent mid-stratospheric water vapor and aerosol layers were mostly confined to Southern Hemisphere (SH) tropics (Eq. to 30°S). However, during the spring of 2022, the westerly phase of the tropical quasi-biennial oscillation (QBO) descended through the tropics. The HT water vapor and aerosol anomalies were observed to again split across the equator coincident with the descent of the QBO shear zone. This split occurred because of the enhanced meridional transport circulation associated with the QBO. Neither transport event can be reproduced using MERRA2 assimilated winds.

Mesoscale eddies play an important role in both momentum and heat balances in the Southern Ocean. Previous studies have documented an increasing intensity of the Southern Ocean eddy field during recent decades; however, it is still unclear whether the mesoscale eddies with different lifetimes have different temporal variations. Using satellite altimeter observations from 1993 to 2020, we find that the increasing trend in the intensity of eddies is dominated by long-lived eddies (with lifetimes ≥ 90 days), whose amplitude has increased at a rate of ~2.8% per decade; the increase is concentrated downstream of topography. In contrast, short-lived eddies (with lifetimes < 90 days) do not appear to have a significant trend in their amplitudes since the early 1990s. An energy conversion analysis indicates that the increased baroclinic instabilities of the mean flows associated with topography are responsible for the amplitude increase of the long-lived eddies.

The non-linear reliance of channel steepness on erosion rates can be reconciled by the stochastic-threshold incision model that incorporates river incision threshold and discharge probability distribution into erosion efficiency. Here, we explored the usage of the model in river longitudinal profile inversion, by assuming time-dependent tectonic forcing and a linear exponent that relates channel incision to slope. We developed an analytical solution to the model equation and an inverse scheme to retrieve relative uplift rate history, whose validity was based on the theoretical demonstration on knickpoint preservation. Application of the inverse scheme to the main trunks of the Dadu River basin in the eastern Tibetan Plateau produced a history with two-phase increases in the uplift/incision rates, which is similar to the results from low-temperature thermochronology. Thus, our analytical procedures provide new insights into the link of tectonic uplift and river profile evolution, when channel steepness depends on erosion rates non-linearly. 

Products derived from remote sensing reflectances ($R_{rs}(\lambda)$), e.g. chlorophyll, phytoplankton carbon, euphotic depth, or particle size, are widely used in oceanography. Problematically, $R_{rs}(\lambda)$ may have fewer degrees of freedom (DoF) than measured wavebands or derived products. A global sea surface hyperspectral $R_{rs}(\lambda)$ dataset has DoF=4. MODIS-like multispectral equivalent data also have DoF=4, while their SeaWiFS equivalent has DoF=3. Both multispectral-equivalent datasets predict individual hyperspectral wavelengths’ $R_{rs}(\lambda)$ within nominal uncertainties. Remotely sensed climatological multispectral $R_{rs}(\lambda)$ have DoF=2, as information is lost by atmospheric correction, shifting to larger spatiotemporal scales, and/or more open-ocean measurements, but suites of $R_{rs}(\lambda)$-derived products have DoF=1. These results suggest that remote sensing products based on existing satellites’ $R_{rs}(\lambda)$ are not independent and should not be treated as such, that existing $R_{rs}(\lambda)$ measurements hold unutilized information, and that future multi- or especially hyper-spectral algorithms must rigorously consider correlations between $R_{rs}(\lambda)$ wavebands.

Ice cliff distribution plays a major role in determining the melt of debris-covered glaciers but its controls are largely unknown. We assembled a dataset of 37537 ice cliffs and determined their characteristics across 86 debris-covered glaciers within High Mountain Asia (HMA). We complemented this dataset with the analysis of 202 cliff formation events from multi-temporal UAV observations for a subset of glaciers. We find that 38.9% of the cliffs are stream-influenced, 19.5% pond-influenced and 19.7% are crevasses. Surface velocity is the main predictor of cliff distribution at both local and glacier scale, indicating its dependence on the dynamic state and hence evolution stage of debris-covered glacier tongues. Supraglacial ponds contribute to maintaining cliffs in areas of thicker debris, but this is only possible if water accumulates at the surface. Overall, total cliff density decreases exponentially with debris thickness as soon as debris gets thicker than 10 cm.

A document by Linying Gao. Click on the document to view its contents.

A document by Robert Lewis Walker. Click on the document to view its contents.

Atmospheric motion vectors (AMVs), known as cloud track winds, have positive impacts on global numerical weather forecasts (NWP). In this study, AMVs retrieved from Fengyun-2G and Fengyun-4A are compared in their data quality and impacts on the typhoon forecasts in order to investigate the differences between the first and second generation of the geostationary meteorological satellites of China. This report conducted data evaluation and assimilation-forecasting experiments on FY-2G and FY-4A atmospheric motion vector (AMVs), respectively. The results show that the AMVs data of FY-4A are of better quality than those of FY-2G and assimilating the AMVs of FY-2G and FY-4A have a neutral to slightly positive impacts on typhoon forecasts, which is quite encouraging for the operational use in the future.

This study summarizes paleomagnetic secular variation (PSV) in five published Holocene records from Eastern North America. We have developed 100-year increment time series for the declinations and inclinations for all sites and compared their directional variability. We see evidence of ten correlatable features in both inclination and declination. We focus on the clockwise or counter-clockwise motion of paleomagnetic directions (termed circularity) in these PSV records. We have first calculated the incremental rate and direction of motion (clockwise or counter-clockwise) for each record over the last 4000-8000 years. We have separately looked for discernable looping in individual records. We estimate the loop sizes, durations, and circularity direction. We see the same pattern of circularity in both measurement techniques. There are seven intervals of oscillating circularity and looping in all five sites. Both techniques suggest a distinctive oscillating, teeter-totter like, behavior to PSV circularity that must be due to the pattern of fluid flow in the outer core. This teeter-totter behavior is unbalanced with more time spent in clockwise motion than in counter-clockwise motion. We think the teeter-totter oscillation may be due to torsional oscillation in the outer core fluid flow. The loops have a distribution of sizes and durations with smaller loops being shorter in duration and bigger loops having longer durations. All five PSV records show 5 intervals of ~102 yr significant acceleration in circularity rate and PSV rate combined with change in circularity direction. These features are broadly analogous to historic geomagnetic jerks.