AGU journal highlights - 29 April 2004

04/28/04

Highlights, including authors and their institutions

The following highlights summarize research papers in Geophysical Research Letters (GL) and Journal of Geophysical Research-Atmospheres (JD). The papers related to these Highlights are printed in the next paper issue of the journal following their electronic publication.

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1. Similar nitric acid production during day and night

Nearly the same amount of nitric acid is produced at night as during the day, according to a recent analysis of atmospheric chemistry that compared the diurnal nitric acid production rates. Brown et al. report near-equal rates of nitric acid formation throughout the day, an unexpected finding that they propose is caused by reactions among nitrogen oxides and aerosol particles in the nighttime air. Previous research had not quantified the nighttime production of nitric acid, although other studies attributed a significant portion of daytime nitric acid production to photochemical reactions. The researchers measured the atmospheric chemistry and meteorological conditions over the ocean surface of the New England coast in 2002 to confirm the role of higher oxides of nitrogen that form predominantly in the evening in converting nitrogen oxide to nitric acid. The authors suggest that accurately measuring the diurnal processes is critical to measuring the nitrogen cycle that affects ozone concentrations worldwide.

Title: Nighttime removal of NOx in the summer marine boundary layer

Authors:
Steve S. Brown, H. Stark, M. Aldener, E. J. Williams, B. M. Lerner, J. A. DeGouw, C. Warneke, W. M. Angevine, D. T. Sueper, NOAA Aeronomy Laboratory, Boulder, Colorado, and Cooperative Institute for Research in the Environmental Sciences, University of Colorado, Boulder, Colorado; J. E. Dibb, Institute for the Study of Earth, Oceans and Space, University of New Hampshire, Durham, New Hampshire; M. Vozella, S. Whitlow, Climate Change Research Center, University of New Hampshire, Durham, New Hampshire; R. Jakoubek, A. M. Middlebrook, P. D. Godan, W. C. Kuster, J. F. Meagher, F. C. Fehsenfeld, NOAA Aeronomy Laboratory, Boulder, Colorado; P. K. Quinn, T. S. Bates, NOAA Pacific Marine Environmental Laboratory, Seattle, Washington; A. R. Ravishankara, NOAA Aeronomy Laboratory, Boulder, Colorado, and University of Colorado, Boulder, Colorado.

Source: Geophysical Research Letters (GL) paper 10.1029/2004GL019412, 2004

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2. Possible source of Indian-to-Atlantic Ocean pollution transport

Seasonal episodes of unusually high ozone density over the South Atlantic are likely initiated by pollution sources thousands of miles away in southern Asia. Chatfield et al. attribute individual plumes of ozone in the tropical South Atlantic to emissions from nearby continents, particularly from biomass burning emissions and lightning in the late winter. The authors used satellite observations and detailed balloon-borne ozone snapshots to suggest that the pollution accumulates into thick patches that frequently originate much further to the east. During most periods of unusually high ozone, they note that anthropogenic Indian Ocean pollution is generally transported westward, carried by warm winds from the ground level to clouds and then moving in the upper troposphere across northern Africa to as far as Brazil. The researchers suggest that such Indian-to-Atlantic Ocean pollution shifts contribute up to half of the persistent and unexpectedly high ozone levels observed in the tropical Atlantic.

Title: Convective lofting links Indian Ocean air pollution to paradoxical South Atlantic ozone maxima

Authors:
Robert B. Chatfield, H. Guan, NASA Ames Research Center, Moffett Field, California; A. M. Thompson, J. C. Witte, NASA Goddard Research Center, Greenbelt, Maryland.

Source: Geophysical Research Letters (GL) paper 10.1029/2003GL018866, 2004

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3. Below-ground seismic analysis measures caldera

A seismic profile of the Long Valley caldera in California taken from below ground level indicates the boundaries of the actively growing volcanic dome. Gritto et al. report a patch of decreased porosity rock between approximately 900-2000 meters [3,000-7,000 feet] deep that they inferred by measuring the seismic velocity of downward propagating sound and shear waves. Previous studies to estimate the breadth of the caldera used less effective surface-based

methods that were unable to accurately constrain its size. Researchers had originally sought to measure the caldera in 1980 after a series of earthquakes caused a rapid surface uplift that indicated renewed magma movement below the surface. The researchers identified three distinct seismic zones within the 2000-meter [7,000 foot] hole drilled in the center of the dome from the sound waves, including a decrease in porosity in its lower section that is consistent with previously published temperature records of the same well.

Title: Results of a VSP experiment at the Resurgent Dome, Long Valley caldera, California

Authors:
Roland Gritto, Thomas M. Daley, Lawrence Berkeley National Laboratory, Berkeley, California; Arturo E. Romero, Exxon Production Research Company, Houston, Texas.

Source: Geophysical Research Letters (GL) paper 10.1029/2004GL019451, 2004

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4. Noctilucent clouds likely reduce airborne metals

Ice particles formed in the polar mesosphere during summertime are strongly correlated to reduced potassium levels and may be similarly affecting other atmospheric metals. Lubken and Hoffner present lidar- and radar-based observations suggesting that mesospheric [altitude of 30-80 kilometers, 20-50 miles] ice can significantly reduce the concentration of potassium atoms to the point where the metal nearly disappears. The high-latitude ice particles present distinct radar echoes that are commonly known as noctilucent [night glowing] clouds. The authors report that ice particles form through super-saturated water vapor caused by very low temperatures that occur in the mesosphere during summer and upset the metal-atom balance at altitudes between 81-93 kilometers [50-58 miles]. They suggest that such modification of the boundary layers where the stratosphere and mesosphere interact may significantly influence photochemistry. The researchers also note that the potassium concentration increases later in the year as temperatures increase and the ice particles melt.

Title: Experimental evidence for ice particle interaction with metal atoms at the high latitude summer mesopause region

Authors:
Franz-Josef Lubken, Josef Hoffner, Leibniz Institute for Atmospheric Studies, Kuhlungsborn, Germany.

Source: Geophysical Research Letters (GL) paper 10.1029/2004GL019586, 2004

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5. Using satellite observations to manage air pollution

A new method using satellites to observe surface ozone can allow researchers to better diagnose the cause of the ground-level pollution. Martin et al. suggest that the capabilities of instruments onboard the Global Ozone Monitoring Experiment satellite allow it to detect the ratio of atmospheric formaldehyde to tropospheric nitrogen dioxide, which is an indicator of the sensitivity of surface ozone to anthropogenic emissions. Their findings indicate that, with few exceptions, surface ozone is more sensitive to nitrogen oxide than volatile organic compound emissions throughout polluted regions of the Northern Hemisphere during summer. The surface pollution then becomes more sensitive to volatile organic compounds during fall. The authors report that remote observations can contribute to air pollution management strategies by providing evidence detailing how ground-level ozone responds to reductions of such man-made chemicals. They further note that higher resolution data available in future missions will help researchers resolve existing uncertainties in the atmospheric response to chemicals in urban and suburban areas.

Title: Space-based diagnosis of surface ozone sensitivity to anthropogenic emissions

Authors:
Randall V. Martin, Dalhousie University, Halifax, Nova Scotia, Canada, and Princeton University, Princeton, New Jersey; Arlene Fiore, Princeton University, Princeton, New Jersey; Aaron Van Donkelaar, Dalhousie University, Halifax, Nova Scotia, Canada.

Source: Geophysical Research Letters (GL) paper 10.1029/2004GL019416, 2004

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6. Examining post-seismic slip after Japanese earthquake

Data from Global Positioning System (GPS) satellites indicates that post-seismic slip following the powerful 2003 Tokachi-oki earthquake in Japan was concentrated adjacent to, rather than within, the earthquake rupture zone. Miyazaki et al. examined the displacement at GPS sites on the island of Hokkaido in the month following the 8.0-magnitude earthquake and found a shift of approximately two centimeters [0.8 inches] immediately after the event, which rapidly slowed to nearly one centimeter [0.4 inches] per day for the following two weeks. The authors note that the earthquake occurred in nearly the same area as a strong temblor in 1952, although it is unclear whether past earthquakes have ruptured the post-seismic areas. The researchers suggest that the character of the afterslip movement may reflect variability in a fault zone's frictional properties, noting how such movement increased the stress at the hypocenter of two other Japanese

earthquakes in 1968 and 1973.

Title: Space time distribution of afterslip following the 2003 Tokachi-oki earthquake: Implications for variations in fault zone frictional properties

Authors:
Shinichi Miyazaki, Stanford University, Stanford, California, and Earthquake Research Institute, University of Tokyo, Tokyo, Japan; P. Segall, Stanford University, Stanford, California; J. Fukuda, T. Kato, Earthquake Research Institute, University of Tokyo, Tokyo, Japan.

Source: Geophysical Research Letters (GL) paper 10.1029/2003GL019410, 2004

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7. Seismic recordings beneath a city

A new approach to fault mapping can allow scientists to identify seismically active areas within densely urban areas where traditional profiles are not feasible. Nielsen and Thybo located the 400-700 meter [1,000-2,000 foot] wide Carlsberg Fault near Copenhagen, Denmark, using widely spaced explosions and receivers to detect the speed of sound waves generated by the small dynamite charges. The researchers used three arc-shaped receiver arrays to record the transmission of sound waves generated by detonating small quantities of explosives at 4-7 kilometer [2-4 mile] offsets inside and outside the fault zone and found notable travel time delays and amplitude variations that allowed them to pinpoint the fault. Their interpretation of the disturbances allowed them to identify the concealed Copenhagen Fault without affecting the population or infrastructure of the coastal city. Previous studies had noted a long, shallow fault line between the Danish basin and the Baltic Shield that is responsible for several recent earthquakes, including a 3.0 magnitude quake in 2004.

Title: Location of the Carlsberg Fault zone from seismic controlled-source fan recordings

Authors:
Lars Nielsen, Hans Thybo, Geological Institute, University of Copenhagen, Copenhagen, Denmark.

Source: Geophysical Research Letters (GL) paper 10.1029/2004GL019603, 2004

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8. Clouds likely reduce tropospheric pollution

Clouds may provide a major sink for gaseous methanol in the troposphere,

according to a new paper reporting that cumulus clouds absorb significant quantities of the pollution precursor worldwide. Tabazadeh et al. identified a surprisingly large decrease in methanol from smoke in clouds while conducting research flights that traveled through clouds as opposed to flights passing below them. The researchers studied the organic gas while analyzing the atmospheric effects from biomass burning and noticed that their instruments recorded the rapid loss of methanol and other ozone-forming molecules, corresponding with an increased exposure to clouds. Working from a previous assumption that air masses spend an average of an hour a day in cloudy conditions, the authors believe that clouds may disperse millions of tons of methanol in the atmosphere each year. While the cloud-absorbing effects are less effective for cleaner, pollution-free clouds, they suggest that the processes they observed may have the capacity to reduce tropospheric chemistry globally.

Title: Heterogeneous chemistry involving methanol in tropospheric clouds

Authors:
Azadeh Tabazadeh, H. B. Singh, L. T. Iraci, NASA Ames Research Center, Moffett Field, California; R. J. Yokelson, University of Montana, Missoula, Montana; P. V. Hobbs, University of Washington, Seattle, Washington; J. H. Crawford, NASA Langley Research Center, Hampton, Virginia.

Source: Geophysical Research Letters (GL) paper 10.1029/2003GL018775, 2004

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9. Volcanic eruption modifying Pacific ecosystem

The emission of volcanic gases from the Miyake-jima volcano in Japan has likely modified the marine air quality and affected the open ocean ecosystem over parts of the western North Pacific since its 2000 eruption. Uematsu et al. used satellite images and oceanic observations to identify the atmospheric deposition of sulfur dioxide, ammonia and other aerosol particles from the volcanic eruption located approximately 240 kilometers [150 miles] southwest of Tokyo. They report that the emissions have caused an increase in phytoplankton growth in the previously nutrient-deficient region over the past several years. The still-ongoing eruption has also produced higher than expected amounts of nitrogen in the surrounding seas, which the researchers suggest may be caused by interactions between magma and organic sediment located beneath the volcano as the magma rises from the ground below.

Title: Enhancement of primary productivity in the western North Pacific caused by the eruption of the Miyake-jima Volcano

Authors:
Mitsuo Uematsu, Yasushi Narita, Ocean Research Institute, University of Tokyo, Tokyo, Japan, and Japan Science and Technology Cooperation, Kawaguchi, Saitama, Japan; Mitsuhiro Toratani, Tokai University, Numazu City, Japan; Mizuo Kajino, Disaster Prevention Research Institute, Kyoto University, Kyoto, Japan; Yasuhiro Senga, Tokai University, Shizuoka, Japan; Takashi Kimoto, Kimoto Electric Co., Ltd., Osaka, Japan.

Source: Geophysical Research Letters (GL) paper 10.1029/2003GL018790, 2004

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10. A new type of air pollution: "tar balls"

Researchers have identified a distinct type of carbon-based aerosol particle that represents a potentially significant and previously unrecognized type of air pollution. Posfai et al. report on "tar balls" that commonly occur in the troposphere as a result of biomass and biofuel burning and mix with other forms of airborne pollution to alter the radiant effects from sunlight. The authors observed the combustion particles, which form in a spherical structure readily distinguished from other forms of carbon under an electron microscope, from research flights over Hungary, the Indian Ocean, and southern Africa. The authors note that the tar balls most likely only slightly light-absorbing and thus represent a particle type that forms in the air and contributes to creating atmospheric haze. They suggest that the new information can allow researchers to refine global climate models that simulate the sunlight-blocking effects from airborne pollution.

Title: Atmospheric tar balls: Particles from biomass and biofuel burning

Authors:
Mihaly Posfai, Renata Simonics, Krisztina Arato, University of Veszprem, Veszprem, Hungary; Andras Gelencser, Hungarian Academy of Sciences, Veszprem, Hungary; Jia Li, Arizona State University, Tempe, Arizona; Peter V. Hobbs, University of Washington, Seattle, Washington; Peter R. Buseck, Arizona State University, Tempe, Arizona, and University of Washington, Seattle, Washington.

Source: Journal of Geophysical Research-Atmospheres (JD) paper 10.1029/2003JD004169, 2004

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