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AGU Research Spotlight (Aug 10-Aug 16, 2018)

2018-08-17 08:55:37

I.Climate Change

1.Why Trace Metals Cling to the Ocean's Skin

Metals within the millimeter-thick sea surface microlayer may impact ocean health and climate.


2.How Much Land Surface Is Under Water at Any Given Time?

Measurement of inundation extent in rivers, lakes, reservoirs, and wetlands is of vital importance to addressing scientific and societal problems ranging from flood prediction to quantification of the global carbon cycle. Boundaries between dry land and open water extend for long distances, and they change over time, so ground-based measurement of inundation extent is difficult. Instead, remote sensing is a promising way to comprehensively monitor surface water extent at large spatial scales.


3.Brown Carbon from Increased Shipping Could Harm Arctic Ice

Emission from a ship’s engine gives clues to how much light-absorbing molecules may build up on and above snow and sea ice. Such emissions are likely to increase as more ships venture into the Arctic.


II.Hazards & Disasters

1.Radar Data Highlights Areas Damaged by Wildfire and Debris Flows

Synthetic aperture radar data post-processing can be used to analyze changes in the landscape, providing a useful tool for disaster response.


2.Bhutan Earthquake Opens Doors to Geophysical Studies

A multinational research team discovered an underestimated earthquake hazard during their 7-year exploration of the unique geodynamics of the eastern Himalayas in Bhutan.


3.K?lauea Eruption Abruptly Slows Down

Volcanologists say it's too soon to know whether the sudden drop in activity signals the end of the eruption or just a pause.


III.Planetary Sciences

1.Evidence of Regional Deposition in Mars's South Polar Deposits

Shallow Radar correlation of discrete units in one of the Red Planet's largest ice reservoirs suggests that its material was emplaced as a single, regional deposit.


IV.Space & Planets

1.First Spacecraft to Touch the Sun Awaiting Launch

The Parker Solar Probe will study the Sun's corona and its electric and magnetic fields, as well as the mechanisms that drive the solar wind, all from behind an advanced protective heat shield.


V.Geophysical Research Letters

1.The seasonal cycle of the South Indian Ocean subtropical gyre circulation as revealed by Argo and satellite data

The seasonal variability in volume transport of the South Indian Ocean subtropical gyre is characterized for the first time. Only 3 complete hydrographic crossings of the gyre have been conducted over a 22 year period, with an upcoming repeat in 2019. Changes to geostrophic transport and thermocline properties imply a strengthening of the gyre from 1987 ‐ 2002. However, some of this strengthening could result from aliasing of seasonal variability. We use data from Argo, satellite altimetry, and an Agulhas Current transport proxy at 34° S to quantify the seasonal variability of the upper 2000 m volume transport. A semi‐annual cycle is revealed, with peak‐to‐peak amplitude of 6.4 ± 3.1 Sv and dominated by annual anomalies in quadrature near the eastern and western boundaries. Seasonal aliasing does not account for the observed gyre strengthening.


2.Shifts in Precipitation Accumulation Extremes during the Warm Season over the United States

Precipitation accumulations, integrated over precipitation events in hourly data, are examined from 1979 to 2013 over the contiguous United States during the "warm" season (May‐October). As expected from theory, accumulation distributions have a characteristic shape, with an approximate power law decrease with event size followed by an exponential drop at a characteristic cutoff scale sL for each location. This cutoff is a predictor of the highest accumulation percentiles, and of a similarly defined daily precipitation cutoff PL. Comparing 1997‐2013 and 1979‐1995 periods, there are significant regional increases in sL in several regions. This yields distribution changes that are weighted disproportionately toward extreme accumulations. In the Northeast for example, risk ratio (conditioned on occurrence) for accumulations larger than 109mm increases by a factor of 2‐4 (5th‐95th). These changes in risk ratio as a function of size, and connection to underlying theory, have counterparts in the observed daily precipitation trends.


3.Whistler wave generation by anisotropic tail electrons during asymmetric magnetic reconnection in space and laboratory

Whistler wave generation near the magnetospheric separatrix during reconnection at the dayside magnetopause is studied with data from the Magnetospheric Multiscale (MMS) mission. The dispersion relation of the whistler mode is measured for the first time near the reconnection region in space, which shows that whistler waves propagate nearly parallel to the magnetic field line. A linear analysis indicates that the whistler waves are generated by temperature anisotropy in the electron tail population. This is caused by loss of electrons with a high velocity parallel to the magnetic field to the exhaust region. There is a positive correlation between activities of whistler waves and the lower‐hybrid drift instability (LHDI) both in laboratory and space, indicating the enhanced transport by LHDI may be responsible for the loss of electrons with a high parallel velocity.


4.Autonomous biogeochemical floats detect significant carbon dioxide outgassing in the high‐latitude Southern Ocean

Although the Southern Ocean is thought to account for a significant portion of the contemporary oceanic uptake of carbon dioxide (CO2), flux estimates in this region are based on sparse observations that are strongly biased towards summer. Here we present new estimates of Southern Ocean air‐sea CO2 fluxes calculated with measurements from biogeochemical profiling floats deployed by the Southern Ocean Carbon and Climate Observations and Modeling (SOCCOM) project during 2014‐2017. Compared to ship‐based CO2 flux estimates, the float‐based fluxes find significantly stronger outgassing in the zone around Antarctica where carbon‐rich deep waters upwell to the surface ocean. Although interannual variability contributes, this difference principally stems from the lack of autumn and winter ship‐based observations in this high‐latitude region. These results suggest that our current understanding of the distribution of oceanic CO2 sources and sinks may need revision and underscore the need for sustained year‐round biogeochemical observations in the Southern Ocean.


VI.AGU Blogs

1.Diving robots find Antarctic winter seas exhale surprising amounts of carbon dioxide

More than 100 oceanic floats are now diving and drifting in the Southern Ocean around Antarctica during the peak of winter. These instruments are gathering data from a place and season that remains very poorly studied, despite its important role in regulating the global climate.


2.Amazon pirating water from neighboring Rio Orinoco

The Amazon River is slowly stealing a 40,000-square-kilometer (25,000-square-mile) drainage basin from the upper Orinoco River, according to new research suggesting this may not be the first time the world’s largest river has expanded its territory by poaching from a neighbor. The rare conjunction could help researchers understand how river systems evolve and how the Amazon Basin grew to dominate the South American continent.



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