1. Reading ancient ocean temperatures from a shark's tooth
2. Study finds no evidence of unexplained solar absorption by clouds
3. Better understanding lightning "branching"
4. Weather modification in space may be feasible
5. Natural ecosystems shape future climate change
6. Tropical winds stir up ocean carbon cycle
7. Linking equatorial winds to El Niño onset
8. Method proposed to measure ocean turnover
9. How big are magnetic explosions in space?
10. Finding cavities in the upper ionosphere

Fossilized shark teeth have helped researchers decipher tropical sea surface temperatures during the Cretaceous period, approximately 144-65 million years ago. Puceat et al. analyzed the composition of the tooth enamel from fossils during different Cretaceous stages and determined that sea temperatures were at times nearly 5-10 degrees Celsius [9-20 degrees Fahrenheit] warmer than the modern ocean in high-latitude locations. The researchers used the oxygen isotope ratio from phosphate in the modern ocean to project the water temperatures that surrounded the fish while their teeth were formed. The study marks the first use of phosphate analysis to estimate ocean temperatures during the time period, leading the authors to conclude that the sea temperatures were far more varied than original predictions. The researchers found that over the 80 million-year-long Cretaceous period, subtropical sea surface temperatures varied from cool in the early portions of the period to warmer during its midpoint, followed by a progressive cooling until the end of the period.

Title: Thermal evolution of Cretaceous Tethyan marine waters inferred from oxygen isotope composition of fish tooth enamels

Authors: 
Emmanuelle Puceat, Gilles Dromart, Stephane Reboulet, Patricia Grandjean, National Center for Scientific Research, Claude Bernard Lyon 1 University, Villeurbanne, France;
Christophe Lecuyer, National Center for Scientific Research, Claude Bernard Lyon 1 University, Villeurbanne, France and University Institute of France, Paris, France;
Simon M. F. Sheppard, National Center for Scientific Research, Higher Teacher Training School of Lyon, Lyon, France.

Source: Paleoceanography (PA) paper 10.1029/2002PA000823, 2003
 

The most thorough study to date of solar energy absorption by clouds has found no evidence of an anomalous absorption between observations and theoretical models, a finding that may help settle a longstanding controversy about the phenomenon's existence. Ackerman et al. used multiple measures of solar radiation from airplane observations and research equipment on the ground from the federal Atmospheric Radiations Measurement Program in Oklahoma. The authors compared the data from ground and air measurements with model calculations of solar absorption on two cloudless and three cloudy days, finding that the measures agreed with each other within their range of uncertainties. The authors have made their data and research methods available, including measurements from one specific date when the difference between measured and calculated atmospheric absorption exceeded the uncertainty range, which the researchers explain by proposing that particles between the clouds and ground were responsible for the additional energy loss. Because their experiment did not show the absorption, the researchers suggest that the previously unexplained energy loss may not exist.

Title: Quantifying the magnitude of anomalous solar absorption

Authors:
Thomas P. Ackerman, Donna M. Powell, Roger T. Marchand, Pacific Northwest National Laboratory, Richland, Washington.

Source: Journal of Geophysical Research-Atmospheres (JGR-D) paper 10.1029/2002JD002674, 2003

An analysis of lightning behavior suggests that voltage differences deep within clouds guide the altitudes of horizontal movement, or branching, during a lightning flash. Coleman et al. provide the first comparison of in-cloud voltage to individual lightning paths, finding evidence that voltage "potential wells" affect the breakdown paths of lightning flashes within clouds. The authors propose that horizontal branching within the wells is a way for a lightning flash to extract electrical energy from a cloud. Using a three-dimensional lightning mapping technique and balloon measurements, the researchers compared observations from dozens of flashes during two mountain thunderstorms in New Mexico to voltage and charge measurements inferred from the in situ data. Their measurements support the hypothesis that voltage within the cloud determines the lightning behavior.

Title: Effects of charge and electrostatic potential on lightning propagation

Authors:
Leonidas M. Coleman, T. C. Marshall, M. Stolzenburg, University of Mississippi, University, Mississippi;
T. Hamlin, P. R. Krehbiel, W. Rison, R. J. Thomas, New Mexico Institute of Mining and Technology, Socorro, New Mexico.

Source: Journal of Geophysical Research-Atmospheres (JGR-D) paper 10.1029/2002JD002718, 2003

The controlled release of very low frequency waves can help mitigate episodes of sudden and unexpected changes in the Earth's inner radiation belt that can adversely affect communications and space-based systems. Inan et al. investigated the requirements for such a satellite-based very low frequency (VLF) transmitter, considering the power, frequency and location needed to maximize the influence of the waves on energetic electrons found in the radiation belt and nearer to the planet. They found that injecting approximately 50 kilowatts of power into the magnetosphere at frequencies of a few kilohertz can produce so-called whistler waves that hasten the precipitation of such radiation. Radiation belts are constantly filled with energetic electrons, but the particles' descent is enhanced by scattering during periods of solar and magnetic storms. The researchers found that VLF signals injected from a satellite within the radiation belt are far more efficient than ground-based transmitters and can be used to artificially change the population of energetic electrons in the magnetosphere [the confines of Earth's magnetic field]..

Title: Controlled precipitation of radiation belt electrons

Authors:
Umran S. Inan, T. F. Bell, J. Bortnik, Stanford University, Stanford, California;
J. M. Albert, Boston College, Chestnut Hill, Massachusetts.

Source: Journal of Geophysical Research-Space Physics (JGR-A) paper 10.1029/2002JA009580, 2003

A new simulation that incorporates wildfires provides what the authors suggest is a more realistic modeling scenario for examining fire's impact on the climate and predicts that natural change may be as important to the environment as man-made influences. Bachelet et al. examined two climate change scenarios that predict a rapid warming trend in the United States over the next 100 years and describe the resulting environmental results. Their analysis of a possible future suggests that changes in the frequency of natural events like wildfires and drought will produce an increase in carbon levels nationwide, with particularly evident changes to the rainfall and vegetation distribution throughout the conterminous United States and particularly in the Southeastern forests and Southwestern desert. The researchers conclude that while man-made changes in land use have significantly affected the carbon cycle over the past 100 years, natural effects like wildfires also play a key role in driving carbon dynamics.

Title: Simulating past and future dynamics of natural ecosystems in the United States

Authors:
Dominique Bachelet, Raymond J. Drapek, James M. Lenihan, Oregon State University, Corvallis, Oregon;
Ronald P. Neilson, U.S. Forest Service, Corvallis, Oregon;
Thomas Hickler, Martin T. Sykes, Benjamin Smith, University of Lund, Lund, Sweden;
Stephen Sitch, Kirsten Thonicke, Potsdam Institute for Climate Impact Research, Potsdam, Germany.

Source: Global Biogeochemical Cycles (GBC) paper 10.1029/2001GB001508, 2003

Evidence from a 2000 study indicates that trade wind-generated cyclonic eddies significantly affect the carbon cycle that feeds microbial life in Hawaiian waters. Bidigare et al. measured the plankton biomass and carbon export rates within a persistent cold-core cyclonic eddy, finding levels within the eddy's center that were approximately two to three times higher than in adjacent waters. The authors propose that the eddies act as a pump to enhance the nutrient concentrations in the upper ocean, which increases the carbon export rate from the subtropical marine ecosystem. They conclude that their multidisciplinary study using satellite and shipboard observations demonstrates that eddies and similar features enhance the efficiency of the biological pump near Hawaii and in other comparable environments.

Title: Influence of a cyclonic eddy on microheterotroph biomass and carbon export in the lee of Hawaii

Authors:
Robert R. Bidigare, Claudia Benitez-Nelson, Carrie L. Leonard, David G. Foley, University of Hawaii at Manoa, Honolulu, Hawaii;
Paul D. Quay, University of Washington, Seattle, Washington;
Michael L. Parsons, University of Hawaii-Hilo, Hilo, Hawaii;
Michael P. Seki, National Marine Fisheries Service, National Oceanic and Atmospheric Administration, Honolulu, Hawaii.

Source: Geophysical Research Letters (GRL) paper 10.1029/2002GL016393, 2003

A new analysis suggests that anomalous equatorial wind patterns from the Indian to the Pacific Ocean may be used to provide an earlier prediction of the El Niño and La Niña weather effects. Clarke and Van Gorder note that El Niño is typically preceded by strong, warm seasonal wind anomalies, which amplify as they blow eastward into the western Pacific and eventually lead to a full El Niño pattern just over a year later. A similar eastward-moving pattern for wind anomalies also affects ocean heat levels and occurs before a La Niña. By keeping track of the wind patterns and the amount of heat in the upper equatorial Pacific Ocean, the authors suggest that scientists can study the development of the El Niño and La Niña patterns and better forecast the events.

Title: Improving El Niño prediction using a space-time integration of Indo-Pacific winds and equatorial Pacific upper ocean heat content

Authors:
Allan J. Clarke, Stephen Van Gorder, Florida State University, Tallahassee, Florida.

Source: Geophysical Research Letters (GRL) paper 10.1029/2002GL016673, 2003

A team of researchers has suggested a method for the first measurements of the meridional overturning circulation in the North Atlantic. Hirschi et al. suggest that a set of moorings placed deep within a section of the ocean could help accurately measure the strength and vertical structure of water turnover there. Currently, scientists most often use hydrographic data from ship-based recordings, which do not provide a continuous look at the circulation over time. Other proposals to measure the turnover have also faced significant limitations preventing their use. Instead, the authors propose a concept for continuous observation of the Atlantic overturning circulation using a string of underwater observation posts that would provide a profile of the water density. That information could be combined with measurements of the wind stress on the water's surface and observations of the flow through the Florida Strait obtained from submerged telephone cables.

Title: A monitoring design for the Atlantic meridional overturning circulation

Authors:
Joël Hirschi, J. Baehr, J. Marotzke, J. Stark, S. Cunningham, Southampton Oceanography Centre, Southampton, United Kingdom;
J.-O. Beismann, Institute for Oceangraphy, Kiel, Germany.

Source: Geophysical Research Letters (GRL) paper 10.1029/2002GL016776, 2003

Researchers are closer to understanding what controls the size of sudden magnetic explosions in outer space near the Earth after a powerful new computer model has simulated the explosions. Shay et al. analyzed the phenomenon known as magnetic reconnection, in which magnetic energy is explosively converted into fast-moving plasma flows and heat. Previous research had noted that the size and energy release from the explosions in the Earth's magnetotail showed significant variation, and earlier computer studies examined only a tiny fraction of the planet's larger physical systems. The magnetosphere temporarily stores magnetic energy and large releases of the magnetic currents can affect Earth conditions. The authors found that magnetic reconnection, and thus the size and strength of explosion, depend on how strongly the magnetotail is compressed. They conclude that their findings for the predicted size of the energy release for smaller explosions are consistent with existing satellite observations.

Title: Inherently three dimensional magnetic reconnection: A mechanism for bursty bulk flows?

Authors:
Michael A. Shay, J. F. Drake, M. Swisdak, W. Dorland, University of Maryland, College Park, Maryland;
B. N. Rogers, Dartmouth College, Hanover, New Hampshire.

Source: Geophysical Research Letters (GRL) paper 10.1029/2002GL016267, 2003

Researchers have identified gaps in the ionosphere known as hybrid cavities at higher altitudes in Earth's atmosphere than have previously been reported. Tjulin et al. used data from the Viking and Cluster satellites to locate these pockets, which are temporary low-density regions in the upper sky that can be identified by low-frequency sound waves. Previous analyses from spacecraft data had not previously observed any of the features above, but had found the unusual cavities in lower portions of the Earth's atmosphere. The authors looked, however, at the seldom-used background density and electric field measurements from existing satellite information and found density depletions that indicated the formations. They suggest that their findings represent a new way for space plasma to organize and structure itself both within Earth's magnetosphere and beyond, concluding that further investigations will likely yield additional examples of the cavities and may help predict their formation.

Title: Lower hybrid cavities in the inner magnetosphere

Authors: Anders Tjulin, A. I. Eriksson, M. Andre, Uppsala University, Uppsala, Sweden.

Source: Geophysical Research Letters (GRL) paper 10.1029/2003GL016915, 2003

*****
Ordering information for science writers

Journalists and public information officers of educational and scientific institutions (only) may receive one or more of the papers cited in the Highlights by sending a message to Emily Crum at ecrum@agu.org, indicating which one(s). Include your name, the name of your publication, and your phone and fax number. State whether you prefer to receive the paper(s) as pdf attachments by email or as a fax.

Others should send a request to service@agu.org, citing the doi of the paper (number beginning 10.1029/....), to order a copy of the paper.

The Highlights and the papers to which they refer are not under AGU embargo.

Contact: 
Emily Crum
American Geophysical Union
2000 Florida Avenue, N.W.
Washington, DC 20009
U.S.A.

Phone (direct): +1 (202) 777-7513
Phone (toll-free in North America): (800) 966-2481 x513 
Fax: +1 (202) 328-0566
Email: ecrum@agu.org
        ###