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PUBLIC RELEASE DATE:
11-Feb-2013

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Contact: Mary Catherine Adams
mcadams@agu.org
202-777-7530
American Geophysical Union
@theagu

AGU Journal Highlights -- Feb. 11, 2013

The following highlights summarize research papers that have been recently published in Geophysical Research Letters (GRL), Journal of Geophysical Research-Earth Surface (JGR-F), and Journal of Geophysical Research-Biogeosciences (JGR-G).

In this release:

1. Global climatology of explosive cyclones

2. For U.S. biomes, climate change will decrease vegetative productivity

3. Lightning detected from space can indicate thundercloud height

4. Storminess helps coastal marshes withstand sea level rise

5. How many lakes are there, and how big are they?

6. Characterizing noise in the global nuclear weapon monitoring system

Anyone may read the scientific abstract for any already-published paper by clicking on the link provided at the end of each Highlight. You can also read the abstract by going to http://onlinelibrary.wiley.com/ and inserting into the search engine the full doi (digital object identifier), e.g. 10.1002/grl.50114. The doi is found at the end of each Highlight below.

Journalists and public information officers (PIOs) at educational or scientific institutions who are registered with AGU also may download papers cited in this release by clicking on the links below.

**Please note** AGU has recently partnered with Wiley, which will now publish AGU's journals. Registered reporters should have received an email from Wiley the week of 7 January with a new login and password, which will allow them to access journal articles for free through the Wiley Online Library at http://onlinelibrary.wiley.com/. If you are a reporter and have not yet registered for a complimentary press subscription, please fill out the form at http://sites.agu.org/sciencepolicy/agu-press-subscriptions/.


1. Global climatology of explosive cyclones

Explosive cyclones, which have rapidly intensifying winds and heavy rain, can seriously threaten life and property. These "meteorological bombs" are difficult to forecast, in part because scientists need a better understanding of the physical mechanisms by which they form. In particular, the large-scale circulation conditions that may contribute to explosive cyclone formation are not well understood.

Black and Pezza analyzed broad-environment energetics in creating a global climatology of explosive cyclones. They identify global hotspots for explosive cyclones and find that explosive cyclones in different geographical locations share a similar characteristic energy-conversion signature that can easily be identified in satellite data. The study could help improve storm track prediction.

Source: Geophysical Research Letters, doi: 10.1002/grl.50114, 2013 http://onlinelibrary.wiley.com/doi/10.1002/grl.50114/abstract

Title: A universal, broad-environment energy conversion signature of explosive cyclones

Authors: Mitchell Timothy Black: School of Earth Sciences, University of Melbourne, Melbourne, Victoria, Australia, and ARC Centre of Excellence for Climate System Science, University of Melbourne, Melbourne, Victoria, Australia;

Alexandre Bernardes Pezza: School of Earth Sciences, University of Melbourne, Melbourne, Victoria, Australia.


2. For U.S. biomes, climate change will decrease vegetative productivity

One recurrently forecast effect of global climate change is that in general, precipitation patterns will become more extreme, with fewer, larger storms and longer dry spells in between. The aftermath of this shift, borne out by the effect the changing water availability will have on vegetative productivity, however, is less well known. Previous research showed that productivity changes with the total annual precipitation, but the measured effect of a shift to a more extreme distribution is less consistent. Research seeking to understand this aspect of the changing precipitation pattern question has typically been conducted through small-scale or short-duration intervention experiments, where the availability of rainwater is artificially manipulated. This makes extrapolating the research to other climes or biomes difficult.

To overcome this difficulty, Zhang et al. conducted an investigation into the observed effect of precipitation variability from 2000 to 2009 on 11 different sites within the continental United States--experimental plots that represented a range of climate and ecological conditions. Using satellite observations of canopy photosynthetic capacity, the authors estimated the aboveground net primary productivity for the experimental sites. Long-term precipitation and temperature records enabled the authors to calculate the occurrence of extreme events. Using their records, the authors could then compare the effect of more or less extreme precipitation patterns for a single site and also compare across experimental sites.

The authors find that for all biomes tested a more extreme precipitation pattern had either a neutral or negative effect on vegetative productivity. Also, extreme rainfall distributions were related to, on average, a 20 percent reduction in rain use efficiency. The decreases were more pronounced for arid grasslands and Mediterranean forests, while mesic grasslands and temperate forests were less affected.

Source: Journal of Geophysical Research-Biogeosciences, doi:10.1029/2012JG002136, 2012 http://dx.doi.org/10.1029/2012JG002136

Title: Extreme precipitation patterns reduced terrestrial ecosystem production across biomes

Authors: Yongguang Zhang, M. Susan Moran, Mark A. Nearing and Guillermo E. Ponce Campos: USDA ARS Southwest Watershed Research Center, Tucson, Arizona, USA;

Alfredo R. Huete: Plant Functional Biology and Climate Change Cluster, University of Technology Sydney, New South Wales, Australia;

Anthony R. Buda: USDA ARS Pasture and Watershed Management Research Unit, University Park, Pennsylvania, USA;

David D. Bosch: USDA ARS Southeast Watershed Research Laboratory, Tifton, Georgia, USA;

Stacey A. Gunter: USDA ARS Southern Plains Range Research Station, Woodward, Oklahoma, USA;

Stanley G. Kitchen: USDA FS Rocky Mountain Research Station, Shrub Sciences Laboratory, Provo, Utah, USA:

W. Henry McNab: USDA FS Southern Research Station, Asheville, North Carolina, USA;

Jack A. Morgan: USDA ARS Rangeland Resources Research Unit, Crops Research Lab, Fort Collins, Colorado, USA;

Mitchel P. McClaran: School of Natural Resources and the Environment, University of Arizona, Tucson, Arizona, USA;

Diane S. Montoya: USDA FS Pacific Southwest Research Station, Arcata, California, USA;

Debra P.C. Peters: USDA ARS Jornada Experimental Range and Jornada Basin Long Term Ecological Research Program, New Mexico State University, Las Cruces, New Mexico, USA;

Patrick J. Starks: USDA ARS Grazinglands Research Laboratory, El Reno, Oklahoma, USA.


3. Lightning detected from space can indicate thundercloud height

High within towering thunderclouds, a distinct form of intracloud lightning, known as "narrow bipolar pulse" discharges, can occur. Like other forms of lightning, narrow bipolar events (NBE) can be either negative or positive discharges. These events are known for their high-powered, short-distance electrical discharges that produce strong emissions of very high frequency radio waves. Previous research has found that since NBEs take place at relatively high altitudes, it is possible to detect them remotely using satellites. To be able to use the detection of narrow bipolar events to measure cloud behavior or storm dynamics, however, requires a better understanding of the relationship between cloud properties and NBEs.

Using a high spatial resolution radar array and a low frequency lightning location system, Wu et al. measured the properties of the NBEs produced by 10 storms near Osaka, Japan, during the summer of 2012. From the sampled storms, the authors identified 232 instances of positive narrow bipolar lightning and 22 negative discharges. The authors find that positive narrow bipolar discharges are typically located deep within the cloud, either in or surrounding the region of deepest convection. Negative NBEs, on the other hand, almost exclusively occur near the cloud tops, with altitudes from 14 to 16 kilometers (about 8.5 to 10 miles).

Based on their observations, the authors suggest that there is a critical cloud height--around 15 kilometers (9 miles) altitude--below which negative narrow bipolar discharges will not occur. As a result of this finding, the authors suggest that the detection of negative NBEs could be used to estimate cloud top height remotely. Or, barring that, they say that the mere detection of negative NBEs can be used for a quick rough assessment of thundercloud height, and hence of its likely severity.

Source: Geophysical Research Letters, doi: 10.1002/grl.50112, 2013 http://onlinelibrary.wiley.com/doi/10.1002/grl.50112/abstract

Title: Spatial relationship between lightning narrow bipolar events and parent thunderstorms as revealed by phased array radar

Authors: Ting Wu, Yuji Takayanagi, Satoru Yoshida, Tsuyoshi Funaki, Tomoo Ushio and Zen Kawasaki: Division of Electrical, Electronic and Information Engineering, Graduate School of Engineering, Osaka University, Suita, Osaka, Japan.


4. Storminess helps coastal marshes withstand sea level rise

Rising sea levels are predicted to threaten many coastal sea marshes around the world in the coming decades as the Earth's climate warms. In addition to accelerating sea level rise, global climate change is predicted to increase the frequency and severity of storms in many places around the world. But few studies have taken into account how an increased storminess might affect the ability of coastal marshes to withstand sea level rise.

Schuerch et al. ran simulations of marshes on the German island of Sylt in the Wadden Sea for the period from 2010 to 2100. They analyzed simulations of 48 sea level rise scenarios and 13 storm scenarios to identify the critical rate of sea level rise that would allow marshes to survive just until 2100.

They find that with no increase in storminess, with constant sea level rise, the maximum rate of sea level rise the marshes could withstand was between 19 and 21 millimeters (about 0.7 and 0.8 inches) per year. But when they took into account storminess, the marshes' ability to withstand sea level rise increased: marshes survived an additional 3 millimeters (0.1 inches) per year of sea level rise if the storminess was caused by increasing frequency of storms, though only an additional 1 millimeter (0.04 inches) per year if the storm intensity, but not frequency, increased.

The authors explain that flooding that occurs with storms tends to transport sediment to the marshes from adjacent areas, helping to build up the marshes; thus the effects of increased storminess on a particular marsh's ability to withstand sea level rise will depend on the availability of erodible fine-grained material near the marsh.

Source: Journal of Geophysical Research-Earth Surface, doi:10.1029/2012JF002471, 2013 http://dx.doi.org/10.1029/2012JF002471

Title: Modeling the influence of changing storm patterns on the ability of a salt marsh to keep pace with sea level rise

Authors: M. Schuerch and A. Vafeidis: "The Future Ocean" Excellence Cluster, Institute of Geography, University of Kiel, Kiel, Germany;

T. Slawig: "The Future Ocean" Excellence Cluster, Institute of Computer Science, University of Kiel, Kiel, Germany;

S. Temmerman: Ecosystem Management Research Group, Department of Biology, University of Antwerp, Antwerp, Belgium.


5. How many lakes are there, and how big are they?

Because of the important role lakes play in regional and local biogeochemical cycling, including carbon storage and emissions, scientists need to know how many lakes of various sizes exist. However, determining the size distribution of lakes is more difficult than it may seem--the smallest lakes are often not recorded on maps. Some researchers have suggested that the number of small lakes is underestimated and have used size distributions to suggest that small lakes dominate the global lake surface area.

Because small lakes are often not included on maps, some researchers have estimated their abundance and size distribution using the assumption that the size distribution of lakes follows a power law. This assumption is supported by the fact that lake coastlines are fractals--zooming in on the coastline reveals more convolutedness, so that the length of the coastline depends on the scale at which it is measured--and fractal geological features typically follow a power law. On the other hand, a recent census of lakes in the United States found that the distribution of small lakes does not actually follow a power law in some regions, suggesting that studies based on assumed power law distributions have significantly overestimated the global number of lakes.

To help resolve the issue Seekell et al. considered lake size distributions in a theoretical fractal geometry framework, focusing on how elevation might affect the lake area distribution. Their calculations indicate that the lake size distribution should follow a power law in flat regions but could deviate from a power law in mountainous regions. They confirm this empirically using lake size data sets from the Adirondack Mountains in New York and the flat island of Gotland in Sweden. Their analysis suggests that small lakes probably do not dominate the total global lake surface area.

Source: Geophysical Research Letters, doi: 10.1002/grl.50139, 2013 http://onlinelibrary.wiley.com/doi/10.1002/grl.50139/abstract

Title: A fractal-based approach to lake size distributions

Authors: David A. Seekell and Michael L. Pace: Department of Environmental Science, University of Virginia, Charlottesville, Virginia, USA;

Lars J. Tranvik: Department of Ecology and Genetics/Limnology, Uppsala University, Evolutionary Biology Centre, Uppsala, Sweden;

Charles Verpoorter: Laboratoire d'Océanologie et des Géosciences, Université de Lille Nord de France, Wimereux, France.


6. Characterizing noise in the global nuclear weapon monitoring system

Under the auspices of the Comprehensive Nuclear-Test-Ban Treaty Organization, a worldwide monitoring system designed to detect the illegal testing of nuclear weaponry has been under construction since 1999. The International Monitoring System is composed of a range of sensors, including detectors for hydroacoustic and seismic signals, and when completed, will include 60 infrasound measurement arrays set to detect low-frequency sound waves produced by an atmospheric nuclear detonation.

The monitoring system's effectiveness, however, is limited because of noise from infrasound signals produced by natural sources, such as wind, surf, and thunder, and by anthropogenic activity, such as mining, industrial operations, and flying aircraft. To improve the identification of atmospheric detonations (or any other signal of interest for the global infrasound network), Matoza et al. have devised a method to eliminate irrelevant sensor noise. Unlike previous research, which treated all noise affecting the infrasound sensors equally, they split the noise into two categories: coherent noise, produced by consistent infrasound sources but that is unrelated to the signals of interest, and incoherent noise, infrasound produced by random sources such as wind.

Analyzing the observations of 39 infrasound stations from April 2005 to December 2010, the authors identify consistent sources of coherent noise, including ocean microbaroms, volcanic eruptions, the sounds of the surf and thunder, and human activity. Identifying the frequencies associated with different noise sources could improve signal processing, which would in turn improve an infrasound array's ability to isolate the signals it is designed to monitor.

Source: Geophysical Research Letters, doi: 10.1029/2012GL054329, 2013 http://onlinelibrary.wiley.com/doi/10.1029/2012GL054329/abstract

Title: Coherent ambient infrasound recorded by the International Monitoring System

Authors: Robin S. Matoza: Institute of Geophysics and Planetary Physics, Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California, USA;

Matthieu Landès and Alexis Le Pichon: CEA/DAM/DIF, Arpajon, France;

Lars Ceranna: BGR, Hannover, Germany;

David Brown: CTBTO, Vienna, Austria.

###

Contact:

Mary Catherine Adams
Phone (direct): 202-777-7530
E-mail: mcadams@agu.org



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