Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

NASA Detects Trends in Rainfall Traits from Drizzles to Downpours

07.03.2007
Breaking news in recent years has been swamped with stories of extreme weather -- flash floods in East Asia, prolonged drought in Africa, destructive hurricanes like Hurricane Katrina, heavy monsoon rainfall in South Asia, and an historic heat wave in Europe.

The effects of these weather crises have been devastating, and their frequency seemingly on the rise. With an understanding that the societal effect of increased rainfall is huge, researchers have had a key question at the center of a debate among them: Are rain-producing weather events increasing worldwide, and if so, what is the relationship, if any, between their growth and climate change?

To detect long-term global rainfall trends, scientists have to overcome major challenges. Since two-thirds of the Earth is covered by oceans, estimating oceanic rainfall relies on satellite remote sensing. However, satellite rainfall estimates are well known to have large uncertainties, because they depend on algorithms derived from assumptions based on incomplete knowledge of the physics of rainfall. Also, long-term rainfall records may have consistency problems because they are made up of segments from different sensors on different satellite orbits, each having their own measurement features.

Therefore, up to now, detection of long-term global rainfall has been considered a "mission impossible," yet the need to know whether trends in rainfall exist is urgent because of how enormously it affects people everywhere. A recent NASA study published in the International Journal of Climatology in January resolves this problem by using a new technique to confirm that extremely heavy rainfall in the tropics is indeed on the rise as suspected.

Researchers used a technique based on the concept of a "probability distribution function" (PDF), a measure of the likelihood that rain will fall with a given intensity over a given area and for a chosen period of time (for example, the entire tropics over 25 years from 1979 to 2003 for this study. The authors then computed the trend for each rain intensity level, ranging from very light to extremely heavy rain. What they found was that the trends showed a systematic pattern, i.e., positive for heavy and light rain, and negative for moderate rain. Essentially, they found there is a noticeable change in the PDF, even though the mean rainfall does not change very much.

"This study makes for a very compelling story in solving a science puzzle," said William Lau, chief of the Laboratory for Atmospheres at NASA's Goddard Space Flight Center, Greenbelt, Md., and a climatologist who is the senior author of the study. "We did this by simply asking the right question. The technique is actually very simple. Instead of looking at trends in total rain, we look for possible signals in different categories of rain, defined by its intensity. It's changes in the traits that make up total rainfall that are most telling, not necessarily total rainfall itself."

Lau and his coauthor used data from both the Climate Precipitation Center's Merged Analysis of Precipitation (CMAP) and the Global Precipitation Climatology Project (GPCP), which blends outdoor rain gauges and rainfall estimates culled from satellite algorithms. They also used data from independent historical gauge records, and from NASA's Tropical Rainfall Measuring Mission (TRMM) satellite to confirm and interpret their results. Their study is focused on the tropics. Their results show that even though there are discrepancies in total rainfall, the change in the characteristics of rainfall are consistent among all the sets of data they looked at.

"Simply put, I'd compare this problem to trying to figure out why your bank account has an apparent error compared to your own records. You'd review the individual items affecting the total balance to see whether certain withdrawal or deposit items were smaller or larger than you'd believed," said Lau, an expert in atmospheric dynamics with an emphasis on tropical climates. "By doing so, you may be able to find a 'pattern' that tells you whether it is your income, your spending habits, or whether it is the bank that actually messed up your balance. Our goal has been to find out what causes the large credits and debits that are throwing the balance off. We must use this itemized approach to solve the rainfall estimation problem, because we know the rain total (the net balance) is wrong.

"The individual items count in solving this puzzle," Lau added. "Because drizzles occur more frequently, and are associated with clouds that cover large areas, they can control the radiance energy from the sun more effectively. That makes drizzles just as important as downpours and the range of rainfall in between."

Taken separately, neither TRMM data alone, available for only the last 10 years, nor data from other satellites available only as far back as 1979, are long enough to confirm a relationship between rainfall and climate change, which requires at least 30-40 years of consistent data. According to Lau, it's asking the right question, using the right methodology, and a combination of information sources that has given researchers a clear picture of how rainfall is changing in a warmer climate.

"It's the small signals in rainfall that tell us the big things," said Lau.

Lynn Chandler | EurekAlert!
Further information:
http://www.nasa.gov

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Fizzy soda water could be key to clean manufacture of flat wonder material: Graphene

Whether you call it effervescent, fizzy, or sparkling, carbonated water is making a comeback as a beverage. Aside from quenching thirst, researchers at the University of Illinois at Urbana-Champaign have discovered a new use for these "bubbly" concoctions that will have major impact on the manufacturer of the world's thinnest, flattest, and one most useful materials -- graphene.

As graphene's popularity grows as an advanced "wonder" material, the speed and quality at which it can be manufactured will be paramount. With that in mind,...

Im Focus: Exotic quantum states made from light: Physicists create optical “wells” for a super-photon

Physicists at the University of Bonn have managed to create optical hollows and more complex patterns into which the light of a Bose-Einstein condensate flows. The creation of such highly low-loss structures for light is a prerequisite for complex light circuits, such as for quantum information processing for a new generation of computers. The researchers are now presenting their results in the journal Nature Photonics.

Light particles (photons) occur as tiny, indivisible portions. Many thousands of these light portions can be merged to form a single super-photon if they are...

Im Focus: Circular RNA linked to brain function

For the first time, scientists have shown that circular RNA is linked to brain function. When a RNA molecule called Cdr1as was deleted from the genome of mice, the animals had problems filtering out unnecessary information – like patients suffering from neuropsychiatric disorders.

While hundreds of circular RNAs (circRNAs) are abundant in mammalian brains, one big question has remained unanswered: What are they actually good for? In the...

Im Focus: RAVAN CubeSat measures Earth's outgoing energy

An experimental small satellite has successfully collected and delivered data on a key measurement for predicting changes in Earth's climate.

The Radiometer Assessment using Vertically Aligned Nanotubes (RAVAN) CubeSat was launched into low-Earth orbit on Nov. 11, 2016, in order to test new...

Im Focus: Scientists shine new light on the “other high temperature superconductor”

A study led by scientists of the Max Planck Institute for the Structure and Dynamics of Matter (MPSD) at the Center for Free-Electron Laser Science in Hamburg presents evidence of the coexistence of superconductivity and “charge-density-waves” in compounds of the poorly-studied family of bismuthates. This observation opens up new perspectives for a deeper understanding of the phenomenon of high-temperature superconductivity, a topic which is at the core of condensed matter research since more than 30 years. The paper by Nicoletti et al has been published in the PNAS.

Since the beginning of the 20th century, superconductivity had been observed in some metals at temperatures only a few degrees above the absolute zero (minus...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Call for Papers – ICNFT 2018, 5th International Conference on New Forming Technology

16.08.2017 | Event News

Sustainability is the business model of tomorrow

04.08.2017 | Event News

Clash of Realities 2017: Registration now open. International Conference at TH Köln

26.07.2017 | Event News

 
Latest News

Nagoya physicists resolve long-standing mystery of structure-less transition

21.08.2017 | Materials Sciences

Chronic stress induces fatal organ dysfunctions via a new neural circuit

21.08.2017 | Health and Medicine

Scientists from the MSU studied new liquid-crystalline photochrom

21.08.2017 | Materials Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>