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AGU Research Spotlight (Dec 22-Dec 28, 2016)

2016-12-30 10:09:57

I. Science Policy

1.White House Issues Ambitious Arctic Research Plan

The plan focuses on improving the well-being of Arctic residents and better understanding the components of the Arctic system.


II.Atmospheric Sciences

1.How Global Warming's Effect on Clouds May Make It Rain Harder

More clustering of clouds due to higher temperatures increases the likelihood of heavy downpours.


III.Space & Planets

1.The Curious Case of Titan's Missing Clouds

Two instruments, one region on Titan: One instrument saw clouds, the other didn't—what's going on?


IV.Hydrology, Cryosphere & Earth Surface

1.Measurements and Models of Reactive Transport in Geological Media

Author Brian Berkowitz answers questions about his recently published article and the scientific and societal implications of his findings.


V. Ocean Sciences

1.Notorious Ocean Current Is Far Stronger Than Previously Thought

The Antarctic Circumpolar Current is the only ocean current to circle the planet and the largest wind-driven current on Earth. It's also 30% more powerful than scientists realized.


VI. Geophysical Research Letters

1. Radiative forcing of carbon dioxide, methane, and nitrous oxide: A significant revision of the methane radiative forcing

New calculations of the radiative forcing (RF) are presented for the three main well-mixed greenhouse gases, methane, nitrous oxide, and carbon dioxide. Methane's RF is particularly impacted because of the inclusion of the shortwave forcing; the 1750–2011 RF is about 25% higher (increasing from 0.48?W?m?2 to 0.61?W?m?2) compared to the value in the Intergovernmental Panel on Climate Change (IPCC) 2013 assessment; the 100?year global warming potential is 14% higher than the IPCC value. We present new simplified expressions to calculate RF. Unlike previous expressions used by IPCC, the new ones include the overlap between CO2 and N2O; for N2O forcing, the CO2overlap can be as important as the CH4 overlap. The 1750–2011 CO2 RF is within 1% of IPCC's value but is about 10% higher when CO2 amounts reach 2000?ppm, a value projected to be possible under the extended RCP8.5 scenario.


2. Effect of a sheared flow on iceberg motion and melting

Icebergs account for approximately half the freshwater flux into the ocean from the Greenland and Antarctic ice sheets and play a major role in the distribution of meltwater into the ocean. Global climate models distribute this freshwater by parameterizing iceberg motion and melt, but these parameterizations are presently informed by limited observations. Here we present a record of speed and draft for 90 icebergs from Sermilik Fjord, southeastern Greenland, collected in conjunction with wind and ocean velocity data over an 8?month period. It is shown that icebergs subject to strongly sheared flows predominantly move with the vertical average of the ocean currents. If, as typical in iceberg parameterizations, only the surface ocean velocity is taken into account, iceberg speed and basal melt may have errors in excess of 60%. These results emphasize the need for parameterizations to consider ocean properties over the entire iceberg draft.


3. Interhemispheric transport of light neutral species in the thermosphere

A mechanistic description of neutral species transport is presented, reconciling two long-standing yet ostensibly incompatible interpretations of the “wind-induced diffusion” of thermospheric constituents. Regarding the creation and sustainment of anomalous winter distributions of light species (e.g., atomic oxygen or helium), the theory of Reber and Hays (1973) cites vertical advection as the main cause while Mayr et al. (1978) cite horizontal transport—both in the presence of a diffusively separated atmosphere. We demonstrate that these theories are not at odds with each other. Instead, they describe two coherent aspects of a single process: convergent (divergent) horizontal motion increases downwelling (upwelling), thereby transporting light constituents both horizontally and vertically simultaneously. Such a connection between horizontal and vertical transport is straightforward and well established for the mass-averaged circulation. Yet this connection has remained obscure for a single minor species entrained within the flow, in part due to the appearance of the composition equation when expressed in a Eulerian frame of reference. Concrete evidence is presented in terms of model equations and diagnostics, establishing a direct link between the horizontal and vertical transport of an atmospheric constituent. Consequently, we are able to show that winter accumulations of light species arise from an interhemispheric migration operating on seasonal timescales, rather than from their redistribution within the vertical column. This new understanding has implications for the timescales at play in both theFregion ionosphere and lower exosphere, two regions profoundly impacted by light neutral species.


4. Monsoon circulations and tropical heterogeneous chlorine chemistry in the stratosphere

Model simulations presented in this paper suggest that transport processes associated with the summer monsoons bring increased abundances of hydrochloric acid into contact with liquid sulfate aerosols in the cold tropical lowermost stratosphere, leading to heterogeneous chemical activation of chlorine species. The calculations indicate that the spatial and seasonal distributions of chlorine monoxide and chlorine nitrate near the monsoon regions of the northern hemisphere tropical and subtropical lowermost stratosphere could provide indicators of heterogeneous chlorine processing. In the model, these processes impact the local ozone budget and decrease ozone abundances, implying a chemical contribution to longer-term northern tropical ozone profile changes at 16–19?km.


5. Modulation of Bjerknes feedback on the decadal variations in ENSO predictability

Clear decadal variations exist in the predictability of the El Ni?o–Southern Oscillation (ENSO), with the most recent decade having the lowest ENSO predictability in the past six decades. The Bjerknes Feedback (BF) intensity, which dominates the development of ENSO, has been proposed to determine ENSO predictability. Here we demonstrate that decadal variations in BF intensity are largely a result of the sensitivity of the zonal winds to the zonal sea level pressure (SLP) gradient in the equatorial Pacific. Furthermore, the results show that during low-ENSO predictability decades, zonal wind anomalies over the equatorial Pacific are more linked to SLP variations in the off-equatorial Pacific, which can then transfer this information into surface temperature and precipitation fields through the BF, suggesting a weakening in the ocean-atmosphere coupling in the tropical Pacific. This result indicates that more attention should be paid to off-equatorial processes in the prediction of ENSO.


6. Influence of sea ice on ocean water vapor isotopes and Greenland ice core records

A warming climate results in sea ice loss and impacts to the Arctic water cycle. The water isotope parameter deuterium excess, a moisture source proxy, can serve as a tracer to help understand hydrological changes due to sea ice loss. However, unlocking the sea ice change signal of isotopes from ice cores requires understanding how sea ice changes impact deuterium excess, which is unknown. Here we present the first isotope data linking a gradient of sea ice extents to oceanic water vapor deuterium excess values. Initial loss of sea ice extent leads to lower deuterium excess moisture sources, and then values progressively increase with further ice loss. Our new process-based interpretation suggests that past rapid (1–3?years) Greenland ice core changes in deuterium excess during warming might not be the result of abrupt atmospheric circulation shifts, but rather gradual loss of sea ice extent at northern latitude moisture sources.


7. Contemporary glacier retreat triggers a rapid landslide response, Great Aletsch Glacier, Switzerland

The destabilization and catastrophic failure of landslides triggered by retreating glaciers is an expected outcome of global climate change and poses a significant threat to inhabitants of glaciated mountain valleys around the globe. Of particular importance are the formation of landslide-dammed lakes, outburst floods, and related sediment entrainment. Based on field observations and remote sensing of a deep-seated landslide, located at the present-day terminus of the Great Aletsch Glacier, we show that the spatiotemporal response of the landslide to glacier retreat is rapid, occurring within a decade. Our observations uniquely capture the critical period of increase in slope deformations, onset of failure, and show that measured displacements at the crown and toe regions of the landslide demonstrate a feedback mechanism between glacier ice reduction and response of the entire landslide body. These observations shed new light on the geomorphological processes of landslide response in paraglacial environments, which were previously understood to occur over significantly longer time periods.



1.Random temperature fluctuations may have made Earth habitable

Random temperature fluctuations in the mantle and on the planet’s surface could be the reason Earth is a habitable world with moving tectonic plates while other terrestrial planets in the solar system are inhospitable worlds, according to new research.


2.Commercial oyster farming could help increase biodiversity in Delaware Bay, scientists say

Commercial oyster aquacultures can restore lost biodiversity by cleaning up polluted waterways, according to new research. A new study finds oyster farms in the Delaware Bay increased biodiversity when introduced into the waterway and could possibly restore the bay to its previous, healthier state, according to the researchers.


3.Hot springs in California host snapshot of early Earth conditions

Conditions in the hot alkaline springs of Paoha Island in Mono Lake, California, could be similar to Earth’s pre-oxygen environment billions of years ago, according to new research. Studying the springs could help scientists better understand microbial biodiversity as it evolved in the early Earth atmosphere.


4.Horse hair can help improve accuracy of climate data

In a new study, researchers used horsehair to determine that latitude influences certain climate measurements. The finding could help scientists find other factors potentially affecting climate measurements and to better understand how to compare climate records from different locations, according to the study’s authors.


5.Humidity may cloud sediment deposits used to study storms

Using sediment as an indicator of past hurricanes may not work well in hot, humid environments, a new study finds. The finding could change the way scientists hunt for evidence of past storms, according to the study’s authors.



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