Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Long-term increase in rainfall seen in tropics

28.08.2007
NASA scientists have detected the first signs that tropical rainfall is on the rise with the longest and most complete data record available.

Using a 27-year-long global record of rainfall assembled by the international scientific community from satellite and ground-based instruments, the scientists found that the rainiest years in the tropics between 1979 and 2005 were mainly since 2001. The rainiest year was 2005, followed by 2004, 1998, 2003 and 2002, respectively.

"When we look at the whole planet over almost three decades, the total amount of rain falling has changed very little. But in the tropics, where nearly two-thirds of all rain falls, there has been an increase of 5 percent," says lead author Guojun Gu, a research scientist at Goddard Space Flight Center in Greenbelt, Md. The rainfall increase was concentrated over tropical oceans, with a slight decline over land.

Climate scientists predict that a warming trend in Earth's atmosphere and surface temperatures would produce an accelerated recycling of water between land, sea and air. Warmer temperatures increase the evaporation of water from the ocean and land and allow air to hold more moisture. Eventually, clouds form that produce rain and snow.

"A warming climate is the most plausible cause of this observed trend in tropical rainfall," says co-author Robert F. Adler, senior scientist at Goddard's Laboratory for Atmospheres. Adler and Gu are now working on a detailed study of the relationship between surface temperatures and rainfall patterns to further investigate the possible link. The study appears in the Aug. 1, 2007, issue of the American Meteorological Society's Journal of Climate.

Obtaining a global view of our planet's rainfall patterns is a challenging work-in-progress. Only since the satellite era have regular estimates of rainfall over oceans been available to supplement the long-term but land-limited record from rain gauges. Just recently have the many land- and space-based data been merged into a single global record endorsed by the international scientific community: the Global Precipitation Climatology Project, sponsored by the World Climate Research Program. Adler's research group at NASA produces the project’s monthly rainfall updates, which are available to scientists worldwide.

Using this global record, Gu, Adler and their colleagues identified a small upward trend in overall tropical rainfall since 1979, but their confidence was not high that this was an actual long-term trend rather than natural year-to-year variability. So they took another look at the record and removed the effects of the two major natural phenomena that change rainfall: the El Niño–Southern Oscillation and large volcanic eruptions.

El Niño is a cyclical warming of the ocean waters in the central and eastern tropical Pacific that generally occurs every three to seven years and alters weather patterns worldwide. Volcanoes that loft debris into the upper troposphere and stratosphere create globe-circling bands of aerosol particles that slow the formation of precipitation by increasing the number of small cloud drops and temporarily shielding the planet from sunlight, which lowers surface temperatures and evaporation that fuels rainfall. Two such eruptions – El Chicon in Mexico and Mount Pinatubo in the Philippines – occurred during the 27-year period.

The scientists found that during El Niño years, total tropical rainfall did not change significantly but more rain fell over oceans than usual. The two major volcanoes both reduced overall tropical rainfall by about 5 percent during the two years following each eruption. With these effects removed from the rainfall record, the long-term trend appears more clearly in both the rainfall data over land and over the ocean.

According to Adler, evidence for the rainfall trend is holding as more data come in. The latest numbers for 2006 show another record-high year for tropical rainfall, tying 2005 as the rainiest year during the period.

"The next step toward firmly establishing this initial indication of a long-term tropical rainfall trend is to continue to lengthen and improve our data record," says Adler, who is project scientist of the Tropical Rainfall Measuring Mission (TRMM), a joint mission between NASA and the Japan Aerospace Exploration Agency. The three primary instruments on TRMM are currently providing the most detailed view of rainfall ever provided from space. Adler's group has been incorporating TRMM rainfall data since 1997 into the global rainfall record.

NASA plans to extend TRMM's success of monitoring rainfall over the tropics to the entire globe with the Global Precipitation Measurement mission, scheduled for launch in 2013. This international project will provide measurements of both rain and snow around the world with instruments on a constellation of spacecraft flying in different orbits.

Lynn Chandler | EurekAlert!
Further information:
http://www.nasa.gov/centers/goddard/news/topstory/2007/rainfall_increase.html

More articles from Ecology, The Environment and Conservation:

nachricht How fires are changing the tundra’s face
12.12.2017 | Gesellschaft für Ökologie e.V.

nachricht Using drones to estimate crop damage by wild boars
12.12.2017 | Gesellschaft für Ökologie e.V.

All articles from Ecology, The Environment and Conservation >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Long-lived storage of a photonic qubit for worldwide teleportation

MPQ scientists achieve long storage times for photonic quantum bits which break the lower bound for direct teleportation in a global quantum network.

Concerning the development of quantum memories for the realization of global quantum networks, scientists of the Quantum Dynamics Division led by Professor...

Im Focus: Electromagnetic water cloak eliminates drag and wake

Detailed calculations show water cloaks are feasible with today's technology

Researchers have developed a water cloaking concept based on electromagnetic forces that could eliminate an object's wake, greatly reducing its drag while...

Im Focus: Scientists channel graphene to understand filtration and ion transport into cells

Tiny pores at a cell's entryway act as miniature bouncers, letting in some electrically charged atoms--ions--but blocking others. Operating as exquisitely sensitive filters, these "ion channels" play a critical role in biological functions such as muscle contraction and the firing of brain cells.

To rapidly transport the right ions through the cell membrane, the tiny channels rely on a complex interplay between the ions and surrounding molecules,...

Im Focus: Towards data storage at the single molecule level

The miniaturization of the current technology of storage media is hindered by fundamental limits of quantum mechanics. A new approach consists in using so-called spin-crossover molecules as the smallest possible storage unit. Similar to normal hard drives, these special molecules can save information via their magnetic state. A research team from Kiel University has now managed to successfully place a new class of spin-crossover molecules onto a surface and to improve the molecule’s storage capacity. The storage density of conventional hard drives could therefore theoretically be increased by more than one hundred fold. The study has been published in the scientific journal Nano Letters.

Over the past few years, the building blocks of storage media have gotten ever smaller. But further miniaturization of the current technology is hindered by...

Im Focus: Successful Mechanical Testing of Nanowires

With innovative experiments, researchers at the Helmholtz-Zentrums Geesthacht and the Technical University Hamburg unravel why tiny metallic structures are extremely strong

Light-weight and simultaneously strong – porous metallic nanomaterials promise interesting applications as, for instance, for future aeroplanes with enhanced...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

See, understand and experience the work of the future

11.12.2017 | Event News

Innovative strategies to tackle parasitic worms

08.12.2017 | Event News

AKL’18: The opportunities and challenges of digitalization in the laser industry

07.12.2017 | Event News

 
Latest News

Long-lived storage of a photonic qubit for worldwide teleportation

12.12.2017 | Physics and Astronomy

Multi-year submarine-canyon study challenges textbook theories about turbidity currents

12.12.2017 | Earth Sciences

Electromagnetic water cloak eliminates drag and wake

12.12.2017 | Power and Electrical Engineering

VideoLinks
B2B-VideoLinks
More VideoLinks >>>