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Written by fatih al-farahat in , ,


NASA's JPL: Launch of Aquarius/SAC-D designed to provide monthly global maps of how salt concentration varies on the ocean surface – a key indicator of ocean circulation and its role in climate change, May 2010

Dear Readers,

This might sound to you like the most boring topic known to man, but in fact the measurement of salt concentrations in the ocean indicates its interactions with the atmosphere. They need good measurements to improve their ocean-atmosphere coupled models. For example, at times there is a difference between the salt concentrations in the western Atlantic (around Central America)and the eastern Pacific great enough to very significantly affect weather patterns and where lots of rain falls and where it doesn't. (How's that for layman's language!)

JPL/NASA News


Alan Buis 818-354-0474
Jet Propulsion Laboratory, Pasadena, Calif.
Alan.buis@jpl.nasa.gov

Sandra Torrusio 011-54-11-4331-0074, ext. 288
Comisión Nacional de Actividades Espaciales, Buenos Aires, Argentina
storrusio@conae.gov.ar

News release: 2009-149                                                                      Oct. 1, 2009

International Science Teams Selected for Aquarius/SAC-D Mission

PASADENA, Calif. – NASA and Argentina's Comisión Nacional de Actividades Espaciales (CONAE), with support from the Argentine Ministry of Science, Technology and Innovative Production (MinCyT), have selected additional members of the international scientific investigating team for the Aquarius/Satélite de Aplicaciones Científicas (SAC)-D mission, scheduled to launch in 2010. The new team members include two from NASA's Jet Propulsion Laboratory, Pasadena, Calif.

The joint minimum three-year mission will carry a suite of instruments into space onboard the Argentine-built SAC-D spacecraft. NASA's sensor, Aquarius, is the primary instrument on the mission. Aquarius is designed to provide monthly global maps of how salt concentration varies on the ocean surface – a key indicator of ocean circulation and its role in climate change. Seven CONAE-sponsored instruments will provide environmental data for a wide range of applications, including natural hazards, land processes, epidemiological studies and air quality issues.

NASA and CONAE conducted a joint solicitation and selection of scientific investigations and innovative application demonstration projects using Aquarius/SAC-D observations. NASA selected 15 projects that it will fund over the next four years for a total of $8 million. CONAE/MinCyT selected 15 Argentine projects with participation of scientists from Chile and Brazil, which will be funded for a total of $1.3 million. An additional 10 proposals were selected from scientists in Italy and Japan.

The primary focus of the selected projects is to prepare the scientific community to use Aquarius/SAC-D observations to better understand the interactions between global ocean circulation, the water cycle and Earth's climate. Several projects will concentrate on socio-economic applications of the mission's observations in such areas as fishery management, disease and flood forecasting, and monitoring volcanic eruptions and fires.

The principal investigators for the NASA-funded projects are:

- William Asher, University of Washington, Seattle
- Frederick Bingham, University of North Carolina, Wilmington
- Shannon Brown, NASA's Jet Propulsion Laboratory, Pasadena, Calif.
- Antonio Busalacchi, University of Maryland, College Park
- Ichiro Fukumori, Jet Propulsion Laboratory, Pasadena, Calif.
- Arnold Gordon, Lamont-Doherty Earth Observatory, Columbia University, Palisades, N.Y.
- Thomas Jackson, U. S. Department of Agriculture, Beltsville, Md.
- W. Linwood Jones, University of Central Florida, Orlando
- Roger Lang, George Washington University, Washington, D.C.
- William Large, National Center for Atmospheric Research, Boulder, Colo.
- Nikolai Maximenko, University of Hawaii, Honolulu
- Rui Ponte, Atmospheric and Environmental Research, Inc., Cambridge, Mass.
- Stephen Riser, University of Washington, Seattle
- Douglas Vandemark, University of New Hampshire, Durham
- Frank Wentz, Remote Sensing Systems, Santa Rosa, Calif.

The principal investigators for the CONAE/MinCyT-funded projects are:

- Miguel Bertolami, National University of the Patagonia San Juan Bosco, Chubut, Argentina
- Marcelo Cassini, National University of Luján, Buenos Aires, Argentina
- Carlos Cotlier, National University of Rosario, Santa Fe, Argentina
- Dora Goniadzki, National Water Institute, Buenos Aires, Argentina
- Raúl Guerrero, National Institute for Fisheries Research and Development, Buenos Aires, Argentina
- Haydee Karszenbaum, University of Buenos Aires, Buenos Aires, Argentina
- Maite Narvarte, Marine Biology Institute Alte. Storni, Chubut, Argentina
- Alberto Piola, Naval Hydrographic Service, Buenos Aires, Argentina
- Gloria Pujol, National Meteorological Service, Buenos Aires, Argentina
- Mirta Raed, National University of Luján, Buenos Aires, Argentina
- Raúl Rivas, National University of Centro, Buenos Aires, Argentina
- Cristina Rodriguez, Mariscope Chilena Department of Oceanography, Puerto Montt, Chile
- Hector Salgado, Naval Hydrographic Service, Buenos Aires, Argentina
- Paola Salio, National University of Buenos Aires, Buenos Aires, Argentina
- Cristina Serafini, National University of Luján, Buenos Aires, Argentina

NASA is providing the Aquarius instrument (which was built by JPL), along with launch services and Aquarius science data processing. JPL manages the Aquarius mission for NASA. NASA's Goddard Space Flight Center, Greenbelt, Md., is providing the Aquarius instrument radiometer. CONAE is providing the SAC-D spacecraft; additional instruments, including optical and thermal cameras, a microwave radiometer and other specific sensors (with participation from Italy, France, Canada and various Argentine institutions); and mission operations.

Launch of Aquarius/SAC-D onboard a Delta II rocket is scheduled for no earlier than May 2010 from Vandenberg Air Force Base in California.

For more information on the Aquarius/SAC-D mission, visit: http://aquarius.nasa.gov and http://www.conae.gov.ar/satelites/sac-d.html . JPL is managed for NASA by the California Institute of Technology in Pasadena.

Written by fatih al-farahat in


Julian P. Sachs et al., Nature Geoscience, June 2009: Southward movement of the Pacific intertropical convergence zone AD 1400–1850

Nature Geoscience, 2 (2009) 519-525, published online 28 June 2009; doi:10.1038/ngeo554

Southward movement of the Pacific intertropical convergence zone AD 1400–1850

Julian P. Sachs1,*, Dirk Sachse1,4, Rienk H. Smittenberg1,4, Zhaohui Zhang1,4, David S. Battisti2 and Stjepko Golubic3

Tropical rainfall patterns control the subsistence lifestyle of more than one billion people. Seasonal changes in these rainfall patterns are associated with changes in the position of the intertropical convergence zone, which is characterized by deep convection causing heavy rainfall near 10° N in boreal summer and 3° N in boreal winter. Dynamic controls on the position of the intertropical convergence zone are debated, but palaeoclimatic evidence from continental Asia, Africa and the Americas suggests that it has shifted substantially during the past millennium, reaching its southernmost position some time during the Little Ice Age (AD 1400–1850). However, without records from the meteorological core of the intertropical convergence zone in the Pacific Ocean, quantitative constraints on its position are lacking. Here we report microbiological, molecular and hydrogen isotopic evidence from lake sediments in the Northern Line Islands, Galápagos and Palau indicating that the Pacific intertropical convergence zone was south of its modern position for most of the past millennium, by as much as 500 km during the Little Ice Age. A colder Northern Hemisphere at that time, possibly resulting from lower solar irradiance, may have driven the intertropical convergence zone south. We conclude that small changes in Earth's radiation budget may profoundly affect tropical rainfall.

  1. School of Oceanography, University of Washington, Seattle, WA 98195, USA
  2. Department of Atmospheric Sciences, University of Washington, Seattle, WA 98195, USA
  3. Biological Science Center, Boston University, Boston, MA 02215, USA
  4. Present addresses: DFG-Leibniz Center for Surface Process and Climate Studies, Institut für Geowissenschaften, Universität Potsdam, 14476 Potsdam, Germany (D.S.); Geological Institute, ETH Zürich, 8092 Zürich, Switzerland (R.H.S.); Department of Earth Sciences, Nanjing University, Nanjing, 210093, China (Z.Z.)

*Correspondence, e-mail: jsachs@u.washington.edu

Link to abstract: http://www.nature.com/ngeo/journal/v2/n7/abs/ngeo554.html

Written by fatih al-farahat in


Intertropical Convergence Zone, the Earth's most prominent rainfall feature creeping northward

Earth's most prominent rainfall feature creeping northward

ScienceDaily, July 1, 2009 — The rain band near the equator that determines the supply of freshwater to nearly a billion people throughout the tropics and subtropics has been creeping north for more than 300 years, probably because of a warmer world, according to research published in the July issue of Nature Geoscience.

If the band continues to migrate at just less than a mile (1.4 km) a year, which is the average for all the years it has been moving north, then some Pacific islands near the equator – even those that currently enjoy abundant rainfall – may be drier within decades and starved of freshwater by midcentury or sooner. The prospect of additional warming because of greenhouse gases means that situation could happen even sooner.

The findings suggest "that increasing greenhouse gases could potentially shift the primary band of precipitation in the tropics with profound implications for the societies and economies that depend on it," the article says.

"We're talking about the most prominent rainfall feature on the planet, one that many people depend on as the source of their freshwater because there is no groundwater to speak of where they live," says Julian Sachs, associate professor of oceanography at the University of Washington and lead author of the paper. "In addition many other people who live in the tropics but farther afield from the Pacific could be affected because this band of rain shapes atmospheric circulation patterns throughout the world."

The band of rainfall happens at what is called the intertropical convergence zone. There, just north of the equator, trade winds from the northern and southern hemispheres collide at the same time heat pours into the atmosphere from the tropical sun. Rain clouds 30,000 ft. thick in places proceed to dump as much as 13 ft. (4 m) of rain a year in some places. The band stretching across the Pacific is generally between 3 and 10 degrees north of the equator depending on the time of year. It has recently been hypothesized that the intertropical convergence zone does not reside in the southern hemisphere for reasons having to do with the distribution of land masses and locations of major mountain ranges in the world, particularly the Andes mountains, that have not changed for millions of years.

The new article presents surprising evidence that the intertropical convergence zone hugged the equator some 350 years ago during Earth's "Little Ice Age," which lasted from 1400 to 1850.

The authors analyzed the record of rainfall in lake and lagoon sediments from four Pacific islands at or near the equator.

One of the islands they studied, Washington Island, is about 5 degrees north of the equator. Today it is at the southern edge of the intertropical convergence zone and receives nearly 10 ft. (2.9 m) of rain a year. But cores reveal a very different Washington Island in the past: It was arid, especially during the little ice age.

Among other things, the scientists looked for evidence in sediment cores of salt-tolerant microbes. On Washington Island they found that evidence in 400- to 1,000-year-old sediment underlying what is now a freshwater lake. Such organisms could only have thrived if rainfall was much reduced from today's high levels on the island. Additional evidence for changes in rainfall were provided by ratios of hydrogen isotopes of material in the sediments that can only be explained by large changes in precipitation.

Sediment cores from Palau, which lies about 7 degrees north of the equator and in the heart of the modern convergence zone, also revealed arid conditions during the Little Ice Age.

In contrast, the researchers present evidence that the Galapagos Islands, today an arid place on the equator in the Eastern Pacific, had a wet climate during the little ice age.

They write, "The observations of dry climates on Washington Island and Palau and a wet climate in the Galapagos between about 1420-1560/1640 provide strong evidence for an intertropical convergence zone located perennially south of Washington Island (5° N) during that time and perhaps until the end of the eighteenth century."

If the zone at that time experienced seasonal variations of 7 degrees latitude, as it does today, then during some seasons it would have extended southward to at least the equator, Sachs says. This has been inferred previously from studies of the intertropical convergence zone on or near the continents, but the new data from the Pacific Ocean region is clearer because the feature is so easy to identify there.

The remarkable southward shift in the location of the intertropical convergence zone during the little ice age cannot be explained by changes in the distribution of continents and mountain ranges because they were in the same places in the little ice age as they are now. Instead, the co-authors point out that the Earth received less solar radiation during the little ice age, about 0.1% less than today, and speculate that may have caused the zone to hover closer to the equator until solar radiation picked back up.

"If the intertropical convergence zone was 550 km, or 5 degrees, south of its present position as recently as 1630, it must have migrated north at an average rate of 1.4 km – just less than a mile – a year," Sachs says. "Were that rate to continue, the intertropical convergence zone will be 126 km – or more than 75 miles – north of its current position by the latter part of this century."

Link: http://www.sciencedaily.com/releases/2009/07/090701135535.htm

Written by fatih al-farahat in , ,


G. Leduc et al., Nature, 445: Moisture transport across Central America as a positive feedback on abrupt climatic changes

Nature 445, 908-911 (22 February 2007); doi:10.1038/nature05578; received 18 October 2006; accepted 4 January 2007.

Moisture transport across Central America as a positive feedback on abrupt climatic changes

Guillaume Leduc, Laurence Vidal, Kazuyo Tachikawa, Frauke Rostek, Corinne Sonzogni, Luc Beaufort and Edouard Bard (CEREGE, UMR6635, CNRS Université Paul Cézanne Aix-Marseille III, Collège de France, Europôle de l'Arbois, BP 80, 13545 Aix-en-Provence Cedex 04, France)

Abstract

Moisture transport from the Atlantic to the Pacific ocean across Central America leads to relatively high salinities in the North Atlantic Ocean1 and contributes to the formation of North Atlantic Deep Water2. This deep water formation varied strongly between Dansgaard/Oeschger interstadials and Heinrich events—millennial-scale abrupt warm and cold events, respectively, during the last glacial period3. Increases in the moisture transport across Central America have been proposed to coincide with northerly shifts of the Intertropical Convergence Zone and with Dansgaard/Oeschger interstadials, with opposite changes for Heinrich events4. Here we reconstruct sea surface salinities in the eastern equatorial Pacific Ocean over the past 90,000 years by comparing palaeotemperature estimates from alkenones and Mg/Ca ratios with foraminiferal oxygen isotope ratios that vary with both temperature and salinity. We detect millennial-scale fluctuations of sea surface salinities in the eastern equatorial Pacific Ocean of up to two to four practical salinity units. High salinities are associated with the southward migration of the tropical Atlantic Intertropical Convergence Zone, coinciding with Heinrich events and with Greenland stadials5. The amplitudes of these salinity variations are significantly larger on the Pacific side of the Panama isthmus, as inferred from a comparison of our data with a palaeoclimate record from the Caribbean basin6. We conclude that millennial-scale fluctuations of moisture transport constitute an important feedback mechanism for abrupt climate changes, modulating the North Atlantic freshwater budget and hence North Atlantic Deep Water formation.

Correspondence and requests for materials should be addressed to G.L. (e-mail: leduc@cerege.fr) and E.B. (e-mail: bard@cerege.fr).

Link to abstract: http://www.nature.com/nature/journal/v445/n7130/abs/nature05578.html