The following highlights summarize research papers that have been recently published or are "in press" (accepted, but not yet published) in Journal of Geophysical Research-Atmospheres (JGR-D) and Geophysical Research Letters (GRL).
In this release:
1. Warming's water changes locked in for decades
2. An increase in tropical cyclones? Data disagree.
3. More evidence ice is common on Moon
4. Explaining record low atmospheric trait during solar lull
5. Satellites as ammonia-pollution trackers?
6. Linking atmospheric chemistry and climate
7. Does the ocean influence atmospheric response to ozone depletion?
8. Mercury flyby spots solar wind-related waves
Anyone may read the scientific abstract for any already-published paper (not papers "in press") by clicking on the link provided at the end of each Highlight. You can also read the abstract by going to http://www.agu.org/pubs/search_options.shtml and inserting into the search engine the full doi (digital object identifier), e.g. 10.1029/2010GL043730. The doi is found at the end of each Highlight below.
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1. Warming's water changes locked in for decades
One of the most significant direct effects of global warming is an alteration of the hydrological cycle affecting the world's water supplies, floods, and droughts. Most studies assume that if human-induced temperature changes were reversed, the hydrological cycle would revert to its prewarming state.
However, a new study reveals that climate change mitigation will not quickly return the hydrological cycle to its previous state. Wu et al. use climate model simulations to show how the hydrological cycle could react to changes in future amounts of carbon dioxide (CO2) in the atmosphere. They simulate the effects of a steady rise in CO2 levels to more than 1000 parts per million (ppm), followed by a decrease to pre-industrial levels of around 280 ppm.
The simulations reveal that even a dramatic reduction of CO2 would not immediately reverse long-term changes to global precipitation already stored in the system. In fact, changes to the hydrological cycle would continue to intensify for several decades because accumulated heat in the ocean would continue to affect precipitation patterns long after global temperatures were brought back down. For instance, high-latitude regions would receive more rainfall, while the Amazon, Australia, and western Africa would become drier for decades after CO2 reductions were implemented, the researchers find.
The authors point out that when considering climate mitigation strategies, the effects on precipitation need to be carefully considered. The more heat that is stored in the ocean, the greater will be the commitment to long-lasting changes to the water cycle.
Title: Temporary acceleration of the hydrological cycle in response to a CO2 rampdown
Authors: Peili Wu, Richard Wood, Jeff Ridley, Jason Lowe: Met Office Hadley Centre, Exeter, UK.
Source:
Geophysical Research Letters (GRL) paper 10.1029/2010GL043730, 2010
http://dx.doi.org/10.1029/2010GL043730
2. An increase in tropical cyclones? Data disagree.
It has been hotly debated recently whether global warming has led to an increase in tropical cyclone activity in the western North Pacific over the past several decades. One complicating factor in the debate is that different data sets show different trends in tropical cyclone activity.
To learn more, Song et al. compare three best track data sets from the Joint Typhoon Warning Center (JTWC), the Regional Specialized Meteorological Center (RSMC) Tokyo Typhoon Center, and the Shanghai Typhoon Institute (STI). They examine differences in track, intensity, and frequency of tropical cyclones that were simultaneously recorded in all three data sets from 1945 to 2007, along with the associated long-term trends. The study finds that differences in the tropical cyclone tracks among the data sets are small, but the three data sets estimate storm intensity differently. The JTWC data set tends to classify category 2-3 cyclones as category 4-5, while the others do not. Furthermore, the JTWC data set shows an upward trend in annual frequency of category 4-5 cyclones and potential destructiveness from 1977 to 2007; this trend does not appear in the other two data sets.
The researchers believe that the discrepancies among the data sets are likely caused by the different algorithms used to determine tropical cyclone intensity. The authors suggest that given the significant differences in intensity in these data sets, it is important to better understand the mechanisms behind the possible tropical cyclone intensity change and to further validate the data sets with observations.
Title: Trend Discrepancies among Three Best-Track Datasets of the Western North Pacific Tropical Cyclones
Authors: Jin-Jie Song and Yuan Wang: School of Atmospheric Sciences, and Key Laboratory of Mesoscale Severe Weather/MOE, Nanjing University, P. R. China;
Liguang Wu: Key Laboratory of Meteorological Disaster of Ministry of Education, Nanjing University of Information Science and Technology, P. R. China.
Source:
Journal of Geophysical Research-Atmospheres (JGR-D) paper 10.1029/2009JD013058, 2010
http://dx.doi.org/10.1029/2009JD013058
3. More evidence ice is common on Moon
In October 2009, NASA's LCROSS mission smashed into a crater on the Moon and clearly detected water there, confirming other studies that suggested that water ice existed on the Moon. Scientists can learn more about lunar water by studying the abundance and distribution of hydrogen. Hydrogen has been detected near the lunar poles, but scientists were not certain whether this hydrogen was in the form of water ice or in other compounds such as molecular hydrogen. If hydrogen exists in a volatile compound such as water, it would only remain stable in cold, permanently shaded regions such as deep craters.
To map the lunar polar hydrogen distribution, Teodoro et al. use an image reconstruction algorithm applied to existing data from the Lunar Prospector, which detected low energy neutrons—an indication of the presence of hydrogen. They compare their hydrogen distribution map with a map of permanently shadowed crater locations derived from altimetry measurements from the KAGUYA (aka SELENE) spacecraft.
The results show that the hydrogen distribution is not uniform near the lunar poles. Rather, hydrogen is concentrated in permanently shadowed craters, indicating that a significant amount of lunar hydrogen is likely to be in the form of water ice. The researchers estimate that there could be about 5 × 1011 kilograms of water ice in craters near the lunar poles. The study adds to and expands upon other evidence showing that water ice is common on the Moon, which could be important for future lunar exploration.
Title: The spatial distribution of lunar polar hydrogen deposits after KAGUYA (SELENE)
Authors: L.F.A. Teodoro: Eloret Corporation, NASA Ames Research Center, Moffett Field, California, USA;
V.R. Eke: Institute for Computational Cosmology, Department of Physics, Durham University, Science Laboratories, South Road, Durham, UK;
R.C. Elphic: Planetary Systems Branch, Space Sciences and Astrobiology Division, MS 245-3, NASA Ames Research Center, Moffett Field, California, USA.
Source:
Geophysical Research Letters (GRL) paper 10.1029/2010GL042889, 2010
http://dx.doi.org/10.1029/2010GL042889
4. Explaining record low atmospheric trait during solar lull
The total mass density of the upper thermosphere (~200 to 600 kilometers in altitude, or 124 to 373 miles) was lower during the 2008 solar minimum than at any other time during the space age. Using historical records of thermospheric density, Emmert et al. compare the behavior of the thermosphere during the recent solar minimum with its behavior during previous solar minima.
Solar irradiance at extreme ultraviolet (EUV) wavelengths heats the thermosphere, causing it to expand. During a solar minimum, EUV irradiance is lower than it is during more active times in the solar cycle, producing a cooler, contracted thermosphere and decreased density at a given altitude.
Solar EUV irradiance during the recent prolonged solar minimum was somewhat lower on average than during the prior minimum, but the researchers find that this can only explain about one third of the density difference. The remaining density anomalies (departures from climatologically expected values) began in 2005 and are attributable to lower-than-expected upper thermospheric temperatures and low concentrations of atomic oxygen near the base of the thermosphere. Previous research indicates that at least part of this change can be accounted for by enhanced cooling due to increased levels of atmospheric carbon dioxide, the primary cooling agent of the thermosphere.
To account for the remaining unexplained anomalously low density, the researchers hypothesize that changes in the chemical and dynamical processes of the underlying mesosphere and lower thermosphere may play a role. They note that more research is needed to clarify the sources of the observed density anomalies. The density is important because it affects the amount of drag on satellites.
Title: Record-low thermospheric density during the 2008 solar minimum
Authors: J. T. Emmert, J. L. Lean: Space Science Division, Naval Research Laboratory, Washington, D.C., USA;
J. M. Picone: Department of Physics and Astronomy, George Mason University, Fairfax, Virginia, USA.
Source:
Geophysical Research Letters (GRL) paper 10.1029/2010GL043671, 2010
http://dx.doi.org/10.1029/2010GL043671
5. Satellites as ammonia-pollution trackers?
Emissions of ammonia, which come mainly from agriculture, have increased in recent decades and are likely to continue to rise as the world's population grows and demand for food increases. Ammonia pollutes the air, increases creation of particulate matter, and contributes to deposition of reactive nitrogen in sensitive ecosystems. Ground-based ammonia measurements are sparse, and although some monitoring of atmospheric ammonia has been conducted with infrared sounders from space, so far these observations have been limited and errors are often high.
To investigate the feasibility of using satellite-based monitoring of ammonia, Clarisse et al. use a case study of the San Joaquin Valley in California, a major agricultural region known for poor air quality. The researchers analyze infrared satellite soundings taken twice daily for a year to determine the conditions under which such measurements are sensitive enough to detect atmospheric ammonia levels near Earth's surface. They find that ammonia concentrations can best be measured when there is both a high concentration of ammonia and a large temperature difference between the Earth's surface and the boundary-level air. In particular, the researchers find that the sensitivity to ammonia in the San Joaquin Valley is greatest for daytime measurements from March to October and for nighttime measurements in March, October, and November. Their study indicates that current emission inventories coupled with atmospheric models underestimate ammonia concentrations in the San Joaquin Valley by as much as a factor of 10.
Title: Satellite monitoring of ammonia: A case study of the San Joaquin Valley.
Authors: Lieven Clarisse, Daniel Hurtmans, Federico Karagulian, Martin Van Damme and Pierre-Francois Coheur: Spectroscopie de l'Atmosphere, Service de Chimie Quantique et Photophysique, Universite Libre de Bruxelles (U.L.B.), Brussels, Belgium;
Mark W. Shephard: Atmospheric and Environmental Research, Inc., Lexington, Massachusetts, USA;
Frank Dentener: European Commission, Joint Research Centre (JRC), I-21027 Ispra, Italy;
Karen Cady-Pereira: Atmospheric and Environmental Research, Inc., Lexington, Massachusetts, USA;
Cathy Clerbaux: Spectroscopie de l'Atmosphere, Service de Chimie Quantique et Photophysique, Universite Libre de Bruxelles (U.L.B.), Brussels, Belgium and UPMC Univ. Paris 6; Universite Versailles St.-Quentin; CNRS/INSU, LATMOS-IPSL, Paris, France.
Source:
Journal of Geophysical Research-Atmospheres (JGR-D) paper 10.1029/2009JD013291, 2010
http://www.agu.org/journals/pip/jd/2009JD013291-pip.pdf
6. Linking atmospheric chemistry and climate
Accurately predicting climate change involves a thorough knowledge of how perturbations in the Earth's radiation balance influence temperature and other climate variables. These feedbacks alter the Earth's capability to absorb incoming solar radiation, and they involve water vapor, clouds, and ice and snow effects. Traditionally, changes in atmospheric chemistry induced by changes in climate have not been fed back into climate models to further change the climate itself. Thus, studies that evaluate the effect of reducing emissions typically assume a constant climate state rather than an evolving one, neglecting the effects of how changing atmospheric compositions influence climate.
Noting that climate models, though increasingly sophisticated, have not yet successfully coupled feedbacks between climate and atmospheric chemistry in a comprehensive way, Raes et al. develop a framework to help models better fuse these interrelated concepts together. When applying this framework to a specific model, they find that although atmospheric chemistry has only a small effect on climate sensitivity on a planetary scale, locally atmospheric chemistry can influence climate sensitivity by 20 percent. Further, climate processes can significantly amplify the relationship between emissions and burdens of air pollutants. As a result, climate, through feedback processes, exacerbates air pollution.
Title: Atmospheric chemistry-climate feedbacks
Authors: Frank Raes: Joint Research Centre, European Commission, Ispra, Italy; also at Departments of Environmental Science and Engineering, and Chemical Engineering, California Institute of Technology, Pasadena, California;
Hong Liao: State Key Laboratory of Atmospheric Boundary Layer Physics and Atmospheric Chemistry, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, People's Republic of China;
Wei-Ting Chen: Jet Propulsion Laboratory, Pasadena, California;
John H. Seinfeld: Departments of Environmental Science and Engineering, and Chemical Engineering, California Institute of Technology, Pasadena, California.
Source:
Journal of Geophysical Research-Atmospheres (JGR-D) paper 10.1029/2009JD013300, 2010
http://dx.doi.org/10.1029/2009JD013300
7. Does the ocean influence the atmosphere's response to ozone depletion?
Southern Hemisphere weather patterns have changed significantly over the past few decades. Modeling studies have shown that these changes can be mainly attributed to stratospheric ozone depletion. However, the ozone layer is predicted to slowly recover over the next several decades, and climate modelers would like to predict how the atmosphere will respond to this recovery.
It is known that the ocean influences the atmosphere: wind-induced changes to the ocean feed back on the atmosphere, making atmospheric fluctuations more persistent. It is anticipated that such atmosphere-ocean interaction will affect the atmosphere's response to ozone changes. The basic question is: do ocean-atmosphere interactions need to be included in climate models that project the atmosphere's response to ozone recovery? Currently, the majority of these models do not include this interaction.
To help answer this question, Sigmond et al. ran carefully constructed climate model experiments to determine the impact of the ocean on the atmospheric response to ozone depletion. They find that although atmosphere-ocean interactions affect the persistence of atmospheric fluctuations, atmosphere-ocean interactions do not have a discernible influence on the atmospheric response to stratospheric ozone depletion. Therefore, the researchers conclude that it may not be essential for global climate models to explicitly simulate ocean-atmosphere interactions to obtain reliable projections of Southern Hemisphere atmospheric change following ozone recovery.
Title: Does the ocean impact the atmospheric response to stratospheric ozone depletion?
Authors: M. Sigmond: Department of Physics, University of Toronto, Toronto, Ontario, Canada;
J.C. Fyfe and J. F. Scinocca: Canadian Centre for Climate Modelling and Analysis, Environment Canada, Victoria, British Columbia, Canada.
Source:
Geophysical Research Letters (GRL) paper 10.1029/2010GL043773, 2010
http://dx.doi.org/10.1029/2010GL043773
8. Mercury flyby spots solar wind-related waves
Kelvin-Helmholtz waves, the surface waves that form when two fluids with different speeds move past each other, can be created along the magnetopause when solar wind plasma interacts with a planet's magnetosphere. These waves have previously been observed in Earth's magnetosphere. Now they have been observed in Mercury's magnetosphere as well.
On 29 September 2009, the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft flew by the planet Mercury for the third time. During MESSENGER's previous flybys, no Kelvin-Helmholtz waves were detected. However, during the third flyby, multiple magnetopause crossings were observed. Boardsen et al. report that during this flyby, the spacecraft observed 15 magnetopause crossings along the inbound duskside. The quasiperiodic crossings were recorded over a 2-minute period in which the spacecraft traveled a distance of 0.2 Mercury radii. The multiple crossings, along with measurements of the magnetic field direction, indicated that the edge of Mercury's magnetic field had formed a highly steepened surface wave pattern characteristic of Kelvin-Helmholtz waves.
Sharply-rolled Kelvin-Helmholtz waves along Earth's magnetopause are believed to allow charged particles in the solar wind to enter Earth's magnetic field, which normally shields the planet from solar wind particles; the researchers suggest that a similar mechanism could be occurring on Mercury.
Title: Observations of Kelvin-Helmholtz Waves along the Dusk-side Boundary of Mercury's Magnetosphere during MESSENGER's Third Flyby
Authors: Scott Boardsen: Heliophysics Science Division, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA and Goddard Earth Sciences and Technology Center, University of Maryland, Baltimore County, Baltimore, MD 21228, USA;
K. A. T. Sundberg, L. G. Blomberg: Space and Plasma Physics, School of Electrical Engineering, Royal Institute of Technology (KTH), Stockholm, Sweden;
James A. Slavin: Heliophysics Science Division, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA;
Brian J. Anderson, Haje Korth: Johns Hopkins University Applied Physics Laboratory, Laurel, MD 20723, USA;
Sean C. Solomon: Department of Terrestrial Magnetism, Carnegie Institution of Washington, Washington, DC 20015, USA.
Source:
Geophysical Research Letters (GRL) paper 10.1029/2010GL043606, 2010
http://dx.doi.org/10.1029/2010GL043606
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