NASA Study Links Severe Storm Increases, Global Warming

12.19.08



Extremely high clouds, known as deep convective clouds, are typically associated with severe storms and rainfall. In this AIRS image of Hurricane Katrina, taken August 28, 2005, the day before Katrina made landfall in Louisiana, the eye of the storm was surrounded by a "super cluster" of 528 deep convective clouds (depicted in dark blue). The temperatures of the tops of such clouds are colder than 210 degrees Kelvin (-82 degrees Fahrenheit).


PASADENA, Calif. -- The frequency of extremely high clouds in Earth's tropics -- the type associated with severe storms and rainfall -- is increasing as a result of global warming, according to a study by scientists at NASA's Jet Propulsion Laboratory, Pasadena, Calif.

In a presentation today to the fall meeting of the American Geophysical Union in San Francisco, JPL Senior Research Scientist Hartmut Aumann outlined the results of a study based on five years of data from the Atmospheric Infrared Sounder (AIRS) instrument on NASA's Aqua spacecraft. The AIRS data were used to observe certain types of tropical clouds linked with severe storms, torrential rain and hail. The instrument typically detects about 6,000 of these clouds each day. Aumann and his team found a strong correlation between the frequency of these clouds and seasonal variations in the average sea surface temperature of the tropical oceans.

For every degree Centigrade (1.8 degrees Fahrenheit) increase in average ocean surface temperature, the team observed a 45-percent increase in the frequency of the very high clouds. At the present rate of global warming of 0.13 degrees Celsius (0.23 degrees Fahrenheit) per decade, the team inferred the frequency of these storms can be expected to increase by six percent per decade.

Climate modelers have long speculated that the frequency and intensity of severe storms may or may not increase with global warming. Aumann said results of the study will help improve their models.

"Clouds and rain have been the weakest link in climate prediction," said Aumann. "The interaction between the daytime warming of the sea surface under clear-sky conditions and increases in the formation of low clouds, high clouds and, ultimately, rain is very complicated. The high clouds in our observations?typically at altitudes of 20 kilometers (12 miles) and higher?present the greatest difficulties for current climate models, which aren't able to resolve cloud structures smaller than about 250 kilometers (155 miles) in size."

Aumann said the results of his study, published recently in Geophysical Research Letters, are consistent with another NASA-funded study by Frank Wentz and colleagues in 2005. That study found an increase in the global rain rate of 1.5 percent per decade over 18 years, a value that is about five times higher than the value estimated by climate models that were used in the 2007 report of the Intergovernmental Panel on Climate Change.

Source: NASA

Star Light, Star Bright, Its Explanation is Out of Sight

01.06.09



A mysterious flash of light from somewhere near or far in the universe is still keeping astronomers in the dark long after it was first detected by NASA’s Hubble Space Telescope in 2006. It might represent an entirely new class of stellar phenomena, say researchers.

Astronomers commonly observe intense flashes of light from a variety of stellar explosions and outbursts, such as novae and supernovae. Hubble discovered the cosmic flash on February 26, 2006. It steadily rose in brightness for 100 days, and then dimmed back to oblivion after another 100 days.

The rise and fall in brightness has a signature that simply has never been recorded for any other type of celestial event. Supernovae peak after no more than 70 days, and gravitational lensing events are much shorter. Therefore, this observation defies a simple explanation, reports Kyle Barbary of the Lawrence Berkeley National Laboratory (LBNL) in Berkeley, Calif. He is describing the bizarre Hubble observation at the 213th meeting of the American Astronomical Society in Long Beach, Calif. “We have never seen anything like it,” he concludes.

The spectral fingerprints of light coming from the object, cataloged as SCP 06F6, also have eluded identification as being due to any specific element. One guess is that the features are redshifted molecular carbon absorption lines in a star roughly one billion light-years away.

But searches through various astronomical survey catalogs for the source of the light have not uncovered any evidence for a star or galaxy at the location of the flash. The Supernova Cosmology Project at LBNL discovered it serendipitously in a search for supernovae.

Hubble was aimed at a cluster of galaxies 8 billion light-years away in the spring constellation Bootes. But the mystery object could be anywhere in between, even in the halo of our own Milky Way galaxy.

Papers published by other researchers since the event was reported in June 2006, have suggested a bizarre zoo of possibilities: the core collapse and explosion of a carbon rich star, a collision between a white dwarf and an asteroid, or the collision of a white dwarf with a black hole.

But Barbary does not believe that any model offered so far fully explains the observations. “I don’t think we really know what the discovery means until we can observe similar objects in the future.”

All-sky surveys for variable phenomena, such as those to be conducted with the planned Large Synoptic Survey Telescope, may ultimately find similar transient events in the universe.

Source: NASA