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AGU Research Spotlight (Sep 22-Sep 29, 2017)

2017-09-29 09:52:15

I. Climate Change

1. How the Micrometeorology of Alpine Forests Affects Snowmelt

A field study in the Swiss Alps showed considerable spatial and temporal variability in forest air and surface temperatures, with implications for snowmelt models.


2. When Less Is More: Opening the Door to Simpler Climate Models

Earth system models are resource intensive and complex. To cut through this complexity, the Community Earth System Model project will now be embracing a hierarchy of simpler climate models.


3. Water World: Sea Level Rise, Coastal Floods and Storm Surges

A special issue of Earth’s Future examines the impacts of sea level rise on coastal areas and showcases a paradigm shift in the modeling of these dynamic systems.


4. Unprecedented Hurricane Season Sees Widespread Damage

This hurricane season has broken multiple records already.


5. Stable Isotopes in Paleoclimate Reanalysis

Second Annual Workshop of the Last Millennium Reanalysis Project; Friday Harbor, Washington, 25–26 October 2016


II. Hazards & Disasters

1. Giant Snails’ Century-Old Shells Recorded Monsoon Rainfall

Researchers explored past precipitation in India using shells from very large land snails collected there in 1918 and preserved in a British museum.


III. Ocean Sciences

1. Faults off Alaska Look Akin to Those Behind 2011 Japan Disaster

In a seismically quiet segment of Alaska’s subduction zone lie faults with structures similar to those of the system that caused the deadly Tohoku earthquake and tsunami.


IV. Geology & Geophysics

1. New Earth and Space Science Preprint Server to Be Launched

An international advisory board drawn from geoscience societies will guide the project initiated by the American Geophysical Union.


V. Hydrology, Cryosphere & Earth Surface

1. The River Basin’s Tale: Carbon Transport Along the Thames

A study finds that population growth during urbanization and World War II–era plowing fed additional carbon into the Thames River Basin.


VI. Space & Planets

1. NASA Fleet Helps Predict Space Weather

Using 8 years of data collected via spacecraft, scientists produce hindcasts of plasma eruptions from the Sun. These will help improve forecasts.


2. Cassini’s Legacy in Print

With over 750 papers published in AGU journals based on Cassini-Huygens mission data, three editors select some of the most noteworthy.


3. Pluto’s Features Receive First Official Names

Names of mountains, plains, valleys, and craters honor human and technological pioneers, Pluto scientists, and underworld mythology from around the world.


VII. Geophysical Research Letters

1. Thaw Depth Determines Dissolved Organic Carbon Concentration and Biodegradability on the Northern Qinghai-Tibetan Plateau

The response of dissolved organic carbon (DOC) flux to permafrost degradation is one of the major sources of uncertainty in predicting the permafrost carbon feedback. We investigated DOC export and properties over two complete flow seasons in a catchment on the northern Qinghai-Tibetan Plateau. DOC concentration and biodegradability decreased systematically as thaw depth increased through the season, attributable to changing carbon sources and degree of microbial processing. Increasing DOC aromaticity and δ13C-DOC indicated shifts toward more recalcitrant carbon sources and greater residence time in soils prior to reaching the stream network. These strong and consistent seasonal trends suggest that gradual active layer deepening may decrease DOC export and biodegradability from permafrost catchments. Because these patterns are opposite observations from areas experiencing abrupt permafrost collapse (thermokarst), the overall impact of permafrost degradation on DOC flux and biodegradability may depend on the proportion of the landscape experiencing gradual thaw versus thermokarst.


2. Ionospheric Gravity Waves Driven by Oceanic Gravity Waves in Resonance: A Modeling Study in Search of Their Spectra

Ionospheric observations associated with the 2011 Tohoku tsunami have revealed gravity waves having spectral characteristics that depend on their proximity to the epicenter. There is a preponderance of medium-scale waves in the vicinity of the epicenter, a significant bifurcation into short- and long-period waves over the Hawaiian archipelago, and a narrow and rich spectrum of waves over the West Coast and inland of the United States (U.S.). Guided by these previous observations, we consider wave sources as triads of nonlinearly interacting oceanic gravity waves, whose wave parameters satisfy resonant conditions. These waves are simulated using a 2-D nonlinear model describing gravity wave propagation in order to explain the observations of tsunamigenic traveling ionospheric disturbances (TIDs) associated with the Tohoku event.


3. Mechanistic Drivers of Reemergence of Anthropogenic Carbon in the Equatorial Pacific

Relatively rapid reemergence of anthropogenic carbon (Cant) in the Equatorial Pacific is of potential importance for its impact on the carbonate buffering capacity of surface seawater and thereby impeding the ocean's ability to further absorb Cantfrom the atmosphere. We explore the mechanisms sustaining Cant reemergence (upwelling) from the thermocline to surface layers by applying water mass transformation diagnostics to a global ocean/sea ice/biogeochemistry model. We find that the upwelling rate of Cant (0.4 PgC yr?1) from the thermocline to the surface layer is almost twice as large as air-sea Cant fluxes (0.203 PgC yr?1). The upwelling of Cant from the thermocline to the surface layer can be understood as a two-step process: The first being due to diapycnal diffusive transformation fluxes and the second due to surface buoyancy fluxes. We also find that this reemergence of Cantdecreases dramatically during the 1982/1983 and 1997/1998 El Ni?o events.


4. Significant Aerosol Influence on the Recent Decadal Decrease in Tropical Cyclone Activity Over the Western North Pacific

Over the past two decades, the number of tropical cyclones (TCs) has decreased markedly in the southeastern part of the western North Pacific (WNP) as a component of the interdecadal variation. This decrease has partially been explained by an internal low-frequency variability of sea surface temperature (SST) in the Pacific, but influences of external forcing remain unclear. Here we show that past changes in sulfate aerosol emissions contributed approximately 60% of the observed decreasing trends in TC genesis frequency in the southeastern WNP for 1992–2011, using multiple simulations by a global climate model. This decrease was mainly attributed to the increased vertical wind shear and decreased low-level vorticity, associated with a trans-basin multidecadal SST change driven by aerosol forcing. The near-future projection shows that the aerosol forcing still has some potential influence on decadal TC change, but the projected decreasing frequency is mainly due to increasing greenhouse gases forcing.


5. A Madden-Julian Oscillation event remotely accelerates ocean upwelling to abruptly terminate the 1997/1998 super El Ni?o

The termination of the superintense 1997/1998 El Ni?o was extraordinarily abrupt. The May 1998 Madden-Julian Oscillation (MJO), a massive complex of stormy tropical clouds, is among possible contributors to the abrupt termination. Despite having been sensationally proposed 18 years ago, the role of the MJO remained controversial and speculative because of the difficulty of sufficiently simulating the El Ni?o and MJO simultaneously. An ensemble simulation series using a newly developed, fully ocean-coupled version of a global cloud system resolving numerical model replicated the specific atmosphere and ocean conditions of May 1998 in unprecedented detail, extending the prediction skill of the MJO to 46 days. Simulation ensemble members with stronger MJO activities over the Maritime Continent experienced quicker sea surface temperature drop in the eastern Pacific, confirming that the easterly winds associated with the remote MJO accelerated ocean upwelling to abruptly terminate the El Ni?o.


6. Connecting tropical climate change with Southern Ocean heat uptake

Under increasing greenhouse gas forcing, climate models project tropical warming that is greater in the Northern than the Southern Hemisphere, accompanied by a reduction in the northeast trade winds and a strengthening of the southeast trades. While the ocean-atmosphere coupling indicates a positive feedback, what triggers the coupled asymmetry and favors greater warming in the northern tropics remains unclear. Far away from the tropics, the Southern Ocean (SO) has been identified as the major region of ocean heat uptake. Beyond its local effect on the magnitude of sea surface warming, we show by idealized modeling experiments in a coupled slab ocean configuration that enhanced SO heat uptake has a profound global impact. This SO-to-tropics connection is consistent with southward atmospheric energy transport across the equator. Enhanced SO heat uptake results in a zonally asymmetric La-Nina-like pattern of sea surface temperature change that not only affects tropical precipitation but also has influences on the Asian and North American monsoons.


VII. AGU Blogs

1. Satellites Show the Lack of Power In Puerto Rico as a Catastrophe Unfolds.

The images and pleas for help coming from Puerto Rico are heartbreaking and increasingly alarming. Media reports this evening are saying that 80% of the island’s crops have been destroyed. Only those with generators have power and mobile signals are sparse and intermittent. Up to 60% of people have no reliable access to clean water, and frankly, I can see no signs that much is being done about it!


2. New study may help identify areas with and without accessible water ice on Mars

New findings reveal deposits on Mars that could be interpreted to be ice-rich may contain little or no ice at all, based on an analysis of radar sounder data for Meridiani Planum—an area on the planet’s equator being explored by the Opportunity rover.


3. Field Glacier, Alaska Retreat, Leads to Glacier Separation

The Field Glacier flows from the northwest side of the Juneau Icefield, and is named for Alaskan glaciologist and American Geographical Society leader William O. Field. Bill also helped initiate the Juneau Icefield Research Program, which Maynard Miller then ably managed for more than 50 years. The JIRP program is still thriving today. In 1981, as a part of JIRP, I had my first experience on this glacier. It was early August and there was new snowfall everyday that week. Jabe Blumenthal, Dan Byrne and myself undertook a ski journey to examine the geology on several of the exposed ridges and peaks, note the burgundy line and X’s on image below.



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