The following highlights summarize research papers that have recently been published in Geophysical Research Letters (GRL).
In this release:
- Heat from Pacific stoked Arctic melting
- Satellite radar can gauge hurricane wind speed
- Nitrogen constraints may accelerate climate change
- Mysterious seafloor magnetic anomaly explained
- Cloud processes improve climate simulations
- Icy spokes in Saturn’s ring analyzed
1. Heat from Pacific stoked Arctic melting
The causes of the 2007 record-breaking Arctic sea ice loss are not well understood. To investigate the source of the heat that melted so much ice, Woodgate et al. study the role of heat transported to the Arctic from the Pacific Ocean. The authors use observations from in situ moorings and satellite sea surface temperature measurements to quantify the heat flux through the Bering Strait into the Arctic. They find that a substantial amount of heat is transferred through the Bering Strait and that this amount is highly variable from year to year. In 2007, both the amount of water flowing through the strait and the temperatures were at record highs, the authors report. They note that the 2007 heat flux through the Bering Strait was twice the 2001 heat flux and was enough to account for a third of the Arctic sea ice lost in 2007.
The 2007 Bering Strait oceanic heat flux and anomalous Arctic sea-ice retreat
Rebecca A. Woodgate and Ron Lindsay: Applied Physics Laboratory, University of Washington, Seattle, Washington, USA;
Tom Weingartner: Institute of Marine Science, University of Alaska Fairbanks, Fairbanks, Alaska, USA.
Geophysical Research Letters (GRL) paper 10.1029/2009GL041621, 2009
2. Satellite radar can gauge hurricane wind speed
Spaceborne microwave sensors could complement wind measurements from weather ships and instrumented buoys, which are not well distributed over the entire ocean. Radar scattering off the sea surface can be a useful new tool in determining hurricane wind speeds and monitoring wave breaking, according to a new study. Previous theories had predicted that radar returns would have a different dependence on wind speed when bounced off gentle waves than when bounced off breaking waves, but this had not been observed to work for radar waves in general. However, analyzing data from the RADARSAT 2 satellite, Hwang et al. find that depolarized radar returns, in which radar waves are sent with one polarization and the return waves are received in the perpendicular polarization, do show the predicted different wind speed dependence for breaking and gentle waves. The authors conclude that polarimetric radar offers a method for monitoring wave breaking from space. Furthermore, the high sensitivity of depolarized radar returns to wind speeds could provide more accurate monitoring of hurricane wind speeds.
Depolarized radar return for breaking wave measurement and hurricane wind retrieval
Paul A. Hwang: Remote Sensing Division, Naval Research Laboratory, Washington, D. C., USA;
Biao Zhang and William Perrie: Fisheries and Oceans Canada, Bedford Institute of Oceanography, Dartmouth, Nova Scotia, Canada.
Geophysical Research Letters (GRL) paper 10.1029/2009GL041780, 2009
3. Nitrogen feedbacks may accelerate climate change
Studies have shown that nitrogen can affect the carbon cycle and hence global climate. Nitrogen affects carbon-climate interactions in several ways. As atmospheric carbon dioxide concentrations increase, the amount of carbon dioxide plants take up should rise, but nitrogen constrains the amount of carbon dioxide plants can use. On the other hand, rising temperatures increase organic matter decomposition, making more nitrogen available for increased plant growth, which results in increased carbon storage. Using land surface model simulations, Zaehle et al. investigate the overall effect of nitrogen dynamics on carbon and climate. The authors first compare their model with ecosystem level experimental studies to verify that the model reproduces observed effects, and then use the model to estimate how nitrogen might influence the future global carbon cycle and climate. Overall, the authors find that nitrogen dynamics substantially decrease terrestrial carbon storage, and thus increase atmospheric carbon dioxide concentrations, potentially accelerating climate change. Predictions of future climate change need to account for the potential impacts of nitrogen dynamics on the global carbon cycle.
Terrestrial nitrogen feedbacks may accelerate future climate change
Sönke Zaehle: Max Planck Institute for Biogeochemistry, Jena, Germany;
Pierre Friedlingstein: QUEST, Department of Earth Sciences, University of Bristol, Bristol, UK and LSCE, UMR, CEA, CNRS, Gif-sur-Yvette, France;
Andrew D. Friend: Department of Geography, University of Cambridge, Cambridge, UK.
Geophysical Research Letters (GRL) paper 10.1029/2009GL041345, 2009
4. Mysterious seafloor magnetic anomaly explained
Newly formed seafloor adopts the Earth’s magnetic field orientation and strength at the time of its solidification. As the seafloor spreads, a pattern of magnetic anomalies emerges, providing a continuous record of the Earth’s past magnetic field. But in some places the pattern of magnetic reversals is not regular or clear. One such zone is the Atlantic M-anomaly Smooth Zone (AMSZ), an area of ocean crust in the North Atlantic, formed during the Late Jurassic-Early Cretaceous (about 130-145 million years ago). In this zone, magnetic anomalies are smoother than elsewhere and do not match well with magnetic anomaly patterns in different locations from the same time period. Scientists had thought that the AMSZ was caused by slow seafloor spreading; however, Tominaga and Sager reexamine the magnetic anomalies in the AMSZ and find that slow spreading rates alone do not account for the smooth zone. Instead, the authors suggest that a lower supply of melted material during slow spreading periods results in the formation of a thinner crustal basalt layer or a tectonically unroofed nonbasaltic magnetic source layer. This anomalous crust has weaker, less coherent magnetization, creating the smoother anomaly pattern observed in the AMSZ.
Origin of the smooth zone in early Cretaceous North Atlantic magnetic anomalies
Masako Tominaga and William W. Sager: Department of Oceanography, Texas A&M University, College Station, Texas, USA.
Geophysical Research Letters (GRL) paper 10.1029/2009GL040984, 2009
5. Cloud processes improve climate simulations
As the world undergoes global climate change, accurate climate simulations are especially important for understanding and predicting future changes. Most current coupled ocean-atmosphere general circulation models to do not include explicit representation of some physical processes such as cloud formation, but instead parameterize these processes, leading to uncertainties. In fact, clouds are one of the largest sources of uncertainties in climate models. To find out if including detailed cloud resolving models can improve climate simulations, Stan et al. analyze atmosphere-ocean general circulation simulations with and without explicit representation of cloud processes. The authors compare results of both simulations with observations and find that the simulation with an embedded cloud resolving model performs better. In particular, including the cloud processes improves the accuracy of simulation of seasonal precipitation patterns, the Madden-Julian Oscillation, the Asian monsoon, and the El Niño-Southern Oscillation. The authors conclude that explicit representation of clouds in a general circulation model is essential for accurate simulation of climate phenomena.
An ocean-atmosphere climate simulation with an embedded cloud resolving model
Cristiana Stan: Center for Ocean-Land-Atmosphere Studies, Calverton, Maryland, USA;
Marat Khairoutdinov: School of Marine and Atmospheric Sciences, Stony Brook University, Stony Brook, New York, USA;
Charlotte A. DeMott and David A. Randall: Department of Atmospheric Science, Colorado State University, Fort Collins, Colorado, USA;
V. Krishnamurthy, David M. Straus and James L. Kinter III: Center for Ocean-Land-Atmosphere Studies, Calverton, Maryland, USA, and Department of Atmospheric, Oceanic and Earth Sciences, George Mason University, Fairfax, Virginia, USA;
J. Shukla: Department of Atmospheric, Oceanic and Earth Sciences, George Mason University,
Fairfax, Virginia, USA and Institute of Global Environment and Society, Calverton, Maryland, USA.
Geophysical Research Letters (GRL) paper 10.1029/2009GL040822, 2009
6. Icy spokes in Saturn’s ring analyzed
In Saturn’s largest ring, the B ring, radial spokes sometimes form across the ring. These spokes appear to be a seasonal phenomenon and can become visible and then fade within a few hours. The spokes were first observed by the Voyager spacecraft in 1980, but scientists still do not fully understand how these spokes form and evolve. To learn more, D’Aversa et al. use instruments on the Cassini spacecraft to observe the infrared spectrum emitted by these spokes. The authors’ measurements suggest that the spokes are composed entirely of water ice, including a substantial number of grains at least a micrometer in radius. Scientists had believed the spokes were composed mainly of smaller ice grains. This new information will help scientists as they reconsider the formation mechanism for these strange spokes.
The spectrum of a Saturn ring spoke from Cassini/VIMS
E. D’Aversa, G. Bellucci, F. Altieri, F. G. Carrozzo, and F. Tosi: Istituto di Fisica dello Spazio Interplanetario, INAF, Rome, Italy;
P. D. Nicholson and M. M. Hedman: Astronomy Department, Cornell University, Ithaca, New York, USA;
R. H. Brown: Lunar and Planetary Laboratory, University of Arizona, Tucson, Arizona, USA;
M. R. Showalter: SETI Institute, Mountain View, California, USA;
G. Filacchione: Istituto di Fisica Spaziale e Fisica Cosmica, INAF, Rome, Italy.
Geophysical Research Letters (GRL) paper 10.1029/2009GL041427, 2009
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