Navigation Links
Global ocean currents explain why Northern Hemisphere is the soggier one
Date:10/20/2013

A quick glance at a world precipitation map shows that most tropical rain falls in the Northern Hemisphere. The Palmyra Atoll, at 6 degrees north, gets 175 inches of rain a year, while an equal distance on the opposite side of the equator gets only 45 inches. Scientists long believed that this was a quirk of the Earth's geometry that the ocean basins tilting diagonally while the planet spins pushed tropical rain bands north of the equator. But a new University of Washington study shows that the pattern arises from ocean currents originating from the poles, thousands of miles away.

The findings, published Oct. 20 in Nature Geoscience, explain a fundamental feature of the planet's climate, and show that icy waters affect seasonal rains that are crucial for growing crops in such places as Africa's Sahel region and southern India.

In general, hotter places are wetter because hot air rises and moisture precipitates out.

"It rains more in the Northern Hemisphere because it's warmer," said corresponding author Dargan Frierson, a UW associate professor of atmospheric sciences. "The question is: What makes the Northern Hemisphere warmer? And we've found that it's the ocean circulation."

Frierson and his co-authors first used detailed measurements from NASA's Clouds and Earth's Radiant Energy System, or CERES, satellites to show that sunlight actually provides more heat to the Southern Hemisphere and so, by atmospheric radiation alone, the Southern Hemisphere should be the soggier one.

After using other observations to calculate the ocean heat transport, the authors next used computer models to show the key role of the huge conveyor-belt current that sinks near Greenland, travels along the ocean bottom to Antarctica, and then rises and flows north along the surface. Eliminating this current flips the tropical rain bands to the south.

The reason is that as the water moves north over many decades it gradually heats up, carrying some 400 trillion (that's four with 14 zeroes after it) watts of power across the equator.

For many years, slanting ocean basins have been the accepted reason for the asymmetry in tropical rainfall.

"But at the same time, a lot of people didn't really believe that explanation because it's kind of a complicated argument. For such a major feature there's usually a simpler explanation," Frierson said.

The ocean current they found to be responsible was made famous in the 2004 movie "The Day After Tomorrow," in which the premise was that the overturning circulation shut down and New York froze over. While a sudden shutdown like in the movie won't happen, a gradual slowing which the recent United Nations report said was "very likely" by 2100 could shift tropical rains south, the study suggests, as it probably has in the past.

The slowdown of the currents is predicted because increasing rain and freshwater in the North Atlantic would make the water less dense and less prone to sinking.

"This is really just another part of a big, growing body of evidence that's come out in the last 10 or 15 years showing how important high latitudes are for other parts of the world," Frierson said.

Frierson's earlier work shows how the changing temperature balance between hemispheres influences tropical rainfall. A recent study by Frierson and collaborators looked at how pollution from the industrial revolution blocked sunlight to the Northern Hemisphere in the 1970s and '80s and shifted tropical rains to the south.

"A lot of the changes in the recent past have been due to air pollution," Frierson said. "The future will depend on air pollution and global warming, as well as ocean circulation changes. That makes tropical rainfall particularly hard to predict."


'/>"/>

Contact: Hannah Hickey
hickeyh@uw.edu
206-543-2580
University of Washington
Source:Eurekalert  

Related biology news :

1. Novo Nordisk and BGI establish global collaboration framework
2. EU-funded study underlines importance of Congo Basin for global climate and biodiversity
3. Global warming threat to coral reefs: Can some species adapt?
4. 1 solution to global overfishing found
5. Young researcher taking fight against global killer to the next level in Vietnam
6. Heightened Security Threats and Economic Issues Provide Fillip to Global Civil and Military Biometrics Market, Says Frost & Sullivan
7. Global Information Inc. Announces Discounted Conference Registration For Bio-IT World Asia and Biodetection Technologies 2012
8. Global effort launched to save turtles from extinction
9. New Biotech and Pharmaceutical Market Research from Global Information Inc Forecasts Strong Growth Coming Out of Recession
10. 2012 Forecast for US Molecular Diagnostics Market Now Available From Global Information Inc.
11. Desert to Rainforest global classroom links future teachers, classrooms in Phoenix and Panama
Post Your Comments:
*Name:
*Comment:
*Email:
Related Image:
Global ocean currents explain why Northern Hemisphere is the soggier one
(Date:3/29/2016)... BOCA RATON, Florida , March 29, 2016 /PRNewswire/ ... ("LegacyXChange" or the "Company") LegacyXChange "LEGX" and SelectaDNA/CSI Protect ... Synthetic DNA in ink used in a variety of ... preventing theft. Buyers of originally created collectibles from athletes ... authenticity through forensic analysis of the DNA. ...
(Date:3/22/2016)... March 22, 2016 ... Sensors Market for Consumer Industry by Type (Image, ... Application (Communication & IT, Entertainment, Home Appliances, ... Forecast to 2022", published by MarketsandMarkets, the ... to reach USD 26.76 Billion by 2022, ...
(Date:3/21/2016)... 22, 2016 Unique technology ... for superior security   Xura, ... of secure digital communications services, today announced it is ... offer enterprise customers, particularly those in the Financial Services ... voice authentication within a mobile app, alongside, and in ...
Breaking Biology News(10 mins):
(Date:6/23/2016)... /PRNewswire/ - FACIT has announced the creation of ... company, Propellon Therapeutics Inc. ("Propellon" or "the Company"), ... portfolio of first-in-class WDR5 inhibitors for the treatment ... represent an exciting class of therapies, possessing the ... cancer patients. Substantial advances have been achieved with ...
(Date:6/23/2016)... June, 23, 2016  The Biodesign Challenge (BDC), a ... ways to harness living systems and biotechnology, announced its ... in New York City . ... students, showcased projects at MoMA,s Celeste Bartos Theater during ... , MoMA,s senior curator of architecture and design, and ...
(Date:6/23/2016)... 2016 Apellis Pharmaceuticals, Inc. today announced ... of its complement C3 inhibitor, APL-2. The trials ... dose studies designed to assess the safety, tolerability, ... in healthy adult volunteers. Forty subjects ... single dose (ranging from 45 to 1,440mg) or ...
(Date:6/23/2016)... ... June 23, 2016 , ... Regulatory Compliance Associates® Inc. (RCA), ... free webinar on Performing Quality Investigations: Getting to Root Cause. ... no charge. , Incomplete investigations are still a major concern to the Regulatory ...
Breaking Biology Technology: