Emergence of sprite streamers from screening-ionization waves in the lower ionosphere

Unlucky strike

ISTOCKPHOTO / C. SPENCER

The combined global land and ocean surface temperature for September 2009 was 0.62 °C (1.12 °F) above the 20^th century average of 15.0 °C (59.0 °F). This was the second warmest September on record, behind 2005, and the 33^rd consecutive September with a global temperature above the 20^th Century average. The last below-average September occurred in 1976.

• +0.13 °C/decade (UAH)
• +0.18 °C/decade (UAH

Nature Geoscience, published online 23 August 2009; doi: 10.1038/ngeo607

Quantification of the troposphere-to-ionosphere charge transfer in a gigantic jet

Steven A. Cummer¹, Jingbo Li¹, Feng Han¹, Gaopeng Lu¹, Nicolas Jaugey¹, Walter A. Lyons² and Thomas E. Nelson²

Gigantic jets blast electricity into upper atmosphere

The gigantic jet observed by Steven Cummer and his team. The thunderstorm that produced this jet was over 300 kilometres away, below the visible horizon (Image: Steven Cummer)

See YouTube video: Gigantic jets

by Michael Marshall, New Scientist, August 23, 2009

The ancient Greeks might have thought Zeus was furious with heaven itself. The power of lightning strikes that shoot upwards from storm clouds has been measured for the first time – and they turn out to be every bit as powerful as normal lightning.

First caught on camera in 2003, "gigantic jets" shoot upwards from thunderclouds and can reach altitudes above 80 kilometres. But it wasn't until 21 July last year that Steven Cummer at Duke University in Durham, North Carolina, and his colleagues managed to measure the electrical discharge from a single gigantic jet, released from tropical storm Cristobal.

"No one had been very close to one with the right radio instrumentation before," Cummer says. "So we didn't know whether they just petered out without doing anything much, or whether they actually took some charge and dumped it somewhere."

Electric jet

The jet came out of a high storm cloud, beginning at an altitude of about 14 kilometres, and shot upwards for a further 75 kilometres.

At those heights, the atmosphere is a much better electrical conductor than at ground level because of ionising radiation from space. As a result, the jet was able to discharge 144 coulombs of charge into the upper atmosphere in about 1 second.

This is comparable to the charge transferred by a large cloud-to-ground lightning strike.

"It's fantastic that they see such a high charge transfer between the thundercloud and the ionosphere," says Victor Pasko of Pennsylvania State University in University Park.

Changing weather

Gigantic jets could be important for our ability to predict lightning strikes.

"There is this newly identified path for discharging the thunderstorm, and a lot of charge can be moved," says Cummer. "In storms that can produce gigantic jets, it might influence what other lightning is happening in the storm."

This time, however, the team found no difference in the rate of ordinary lightning strikes around the time of the gigantic jet. "I'm surprised they saw no drop in lightning rates before or after the jet – but that might be because of the sheer size of the storm," says Pasko.

Gigantic jets are one of a host of new atmospheric phenomena discovered in recent years. Other examples are sprites and blue jets.

Journal reference: Nature Geoscience, DOI: 10.1038/ngeo607 (in press)

Link: http://www.newscientist.com/article/dn17664-gigantic-jets-blast-electricity-into-upper-atmosphere.html

Cyclones spurt water into stratosphere, feeding global warming

ScienceDaily (April 21, 2009) — Scientists at Harvard University have found that tropical cyclones readily inject ice far into the stratosphere, possibly feeding global warming.

"Since water vapor is an important greenhouse gas, an increase of water vapor in the stratosphere would warm the Earth's surface," says David M. Romps, a research associate in Harvard's Department of Earth and Planetary Science. "Our finding that tropical cyclones are responsible for many of the clouds in the stratosphere opens up the possibility that these storms could affect global climate, in addition to the oft-mentioned possibility of climate change affecting the frequency and intensity of tropical cyclones."

Romps and co-author Zhiming Kuang, assistant professor of climate science in Harvard's Faculty of Arts and Sciences, were intrigued by earlier data suggesting that the amount of water vapor in the stratosphere has grown by roughly 50 percent over the past 50 years. Scientists are currently unsure why this increase has occurred; the Harvard researchers sought to examine the possibility that tropical cyclones might have contributed by sending a large fraction of their clouds into the stratosphere.

Using infrared satellite data gathered from 1983 to 2006, Romps and Kuang analyzed towering cloud tops associated with thousands of tropical cyclones, many of them near the Philippines, Mexico, and Central America. Their analysis demonstrated that in a cyclone, narrow plumes of miles-tall storm clouds can rise so explosively through the atmosphere that they often push into the stratosphere.

Romps and Kuang found that tropical cyclones are twice as likely as other storms to punch into the normally cloud-free stratosphere, and four times as likely to inject ice deep into the stratosphere.

"It is ... widely believed that global warming will lead to changes in the frequency and intensity of tropical cyclones," Romps and Kuang write in Geophysical Research Letters. "Therefore, the results presented here establish the possibility for a feedback between tropical cyclones and global climate."

Typically, very little water is allowed passage through the stratosphere's lower boundary, known as the tropopause. Located some 6 to 11 miles above the Earth's surface, the tropopause is the coldest part of the Earth's atmosphere, making it a barrier to the lifting of water vapor into the stratosphere: As air passes slowly through the tropopause, it gets so cold that most of its water vapor freezes out and falls away.

But if very deep clouds, such as those in a tropical cyclone that can rise through the atmosphere at speeds of up to 40 miles per hour, can punch through the tropopause too quickly for this to happen, they can deposit their ice in the warmer overlying stratosphere, where it then evaporates.

"This suggests that tropical cyclones could play an important role in setting the humidity of the stratosphere," Romps and Kuang write.

Romps and Kuang's research was funded by the Eppley Foundation and NASA.

Geophysical Research Letters, 36, L03803; doi:10.1029/2008GL036076.

Cause of the widening of the tropical belt since 1958

Jian Lu (Advanced Study Program, National Center for Atmospheric Research, Boulder, CO, USA; and Center for Ocean-Land-Atmosphere Studies, Calverton, MD, USA), Clara Deser (National Center for Atmospheric Research, Boulder, CO, USA), and Thomas Reichler (Department of Meteorology, University of Utah, Salt Lake City, UT, USA)

Journal of Geophysical Research -- Atmospheres, 113, D24103; doi:10.1029/2008JD010114.

Exploring the stratospheric/tropospheric response to solar forcing

D. Rind (NASA Goddard Institute for Space Studies, Columbia University, New York, NY, USA), J. Lean (Naval Research Laboratory, Washington, DC, USA), and J. Lerner, P. Lonergan and A. Leboissitier (Center for Climate Systems Research, Columbia University, New York, NY, USA)

Water Vapor Confirmed As Major Player In Climate Change

ScienceDaily, Nov. 18, 2008 — Water vapor is known to be Earth's most abundant greenhouse gas, but the extent of its contribution to global warming has been debated. Using recent NASA satellite data, researchers have estimated more precisely than ever the heat-trapping effect of water in the air, validating the role of the gas as a critical component of climate change.

With new observations, the scientists confirmed experimentally what existing climate models had anticipated theoretically. The research team used novel data from the Atmospheric Infrared Sounder (AIRS) on NASA's Aqua satellite to measure precisely the humidity throughout the lowest 10 miles of the atmosphere. That information was combined with global observations of shifts in temperature, allowing researchers to build a comprehensive picture of the interplay between water vapor, carbon dioxide, and other atmosphere-warming gases. The NASA-funded research was published recently in the American Geophysical Union's Geophysical Research Letters.

"Everyone agrees that if you add carbon dioxide to the atmosphere, then warming will result," Dessler said. "So the real question is, how much warming?"

The answer can be found by estimating the magnitude of water vapor feedback. Increasing water vapor leads to warmer temperatures, which causes more water vapor to be absorbed into the air. Warming and water absorption increase in a spiraling cycle.

Water vapor feedback can also amplify the warming effect of other greenhouse gases, such that the warming brought about by increased carbon dioxide allows more water vapor to enter the atmosphere.

"The difference in an atmosphere with a strong water vapor feedback and one with a weak feedback is enormous," Dessler said.

Climate models have estimated the strength of water vapor feedback, but until now the record of water vapor data was not sophisticated enough to provide a comprehensive view of at how water vapor responds to changes in Earth's surface temperature. That's because instruments on the ground and previous space-based could not measure water vapor at all altitudes in Earth's troposphere -- the layer of the atmosphere that extends from Earth's surface to about 10 miles in altitude.

AIRS is the first instrument to distinguish differences in the amount of water vapor at all altitudes within the troposphere. Using data from AIRS, the team observed how atmospheric water vapor reacted to shifts in surface temperatures between 2003 and 2008. By determining how humidity changed with surface temperature, the team could compute the average global strength of the water vapor feedback.

"This new data set shows that as surface temperature increases, so does atmospheric humidity," Dessler said. "Dumping greenhouse gases into the atmosphere makes the atmosphere more humid. And since water vapor is itself a greenhouse gas, the increase in humidity amplifies the warming from carbon dioxide."

Specifically, the team found that if Earth warms 1.8 degrees Fahrenheit, the associated increase in water vapor will trap an extra 2 Watts of energy per square meter (about 11 sq. ft.).

"That number may not sound like much, but add up all of that energy over the entire Earth surface and you find that water vapor is trapping a lot of energy," Dessler said. "We now think the water vapor feedback is extraordinarily strong, capable of doubling the warming due to carbon dioxide alone."

Because the new precise observations agree with existing assessments of water vapor's impact, researchers are more confident than ever in model predictions that Earth's leading greenhouse gas will contribute to a temperature rise of a few degrees by the end of the century.

"This study confirms that what was predicted by the models is really happening in the atmosphere," said Eric Fetzer, an atmospheric scientist who works with AIRS data at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "Water vapor is the big player in the atmosphere as far as climate is concerned."

Claim That Simulated Temperature Trends For Tropics Inconsistent With Observations Is Flawed, Experts Argue

CLICK TO ENLARGE (Credit: Image courtesy of DOE/Lawrence Livermore National Laboratory)

ScienceDaily (Oct. 10, 2008) — A team led by Livermore scientists has helped reconcile the differences between simulated and observed temperature trends in the tropics.

Using state-of-the-art observational datasets and results from computer model simulations archived at Lawrence Livermore National Laboratory, LLNL researchers and colleagues from 11 other scientific institutions have refuted a recent claim that simulated temperature trends in the tropics are fundamentally inconsistent with observations. This claim was based on the application of a flawed statistical test and the use of older observational datasets.

Climate model experiments invariably predict that human-caused greenhouse gas increases should lead to more warming in the tropical troposphere (the lowest layer of the atmosphere) than at the tropical land and ocean surface. This predicted “amplification” behavior is in accord with basic theoretical expectations.

Until several years ago, however, most satellite and weather balloon records suggested that the tropical troposphere had warmed substantially less than the surface.

For nearly a decade, this apparent discrepancy between simulations and reality was a major conundrum for climate scientists. The discrepancy was at odds with the overwhelming body of other scientific evidence pointing toward a “discernible human influence” on global climate.

A paper published online last year in the International Journal of Climatology claimed to show definitively that “models and observations disagree to a statistically significant extent” in terms of their tropical temperature trends. This claim formed the starting point for an investigation by a large team of climate modelers and observational data specialists, which was led by LLNL’s Benjamin Santer.

In marked contrast to the earlier claim, Santer’s international team found that there is no fundamental discrepancy between modeled and observed trends in tropical temperatures.

“We’ve gone a long way toward reconciling modeled and observed temperature trends in the problem area of the tropics,” said Santer, the lead author of a paper now appearing online in the International Journal of Climatology.

There are two reasons for this reconciliation.

First, the analysis that reported disagreement between models and observations had applied an inappropriate statistical test, which did not account for the statistical uncertainty in observed warming trends. This uncertainty arises because the human-caused component of recent temperature changes is not perfectly known in any individual observed time series – it must be estimated from data that are influenced by both human effects and the “noise” of natural climate variability. Examples of such “noise” include large El Niño and La Niña events, which have pronounced effects on the year-to-year variability of tropical temperatures.

The Livermore-led consortium applied this inappropriate test to randomly generated data. The test revealed a strong bias in the method toward “detecting” differences that were not real.

The consortium modified the test to correctly account for uncertainty in estimating temperature trends from noisy observational data. With this modified test, there were no longer pervasive, statistically significant differences between simulated and observed tropical temperature trends.

The second reason for the reconciliation of models and observations was the availability of new and improved observational datasets, both for surface and tropospheric temperatures. The developers of these datasets used different procedures to identify and adjust for biases (such as those caused by changes over time in the instruments and platforms used to measure temperature).

Access to multiple, independently produced datasets provided the LLNL-led consortium with a valuable perspective on the inherent uncertainty in observations. Many of the recently developed observational datasets showed larger warming aloft than at the surface, and were more consistent with climate model results.

Even with improved datasets, there are still important uncertainties in observational estimates of recent tropospheric temperature trends that may never be fully resolved, and are partly a consequence of historical observing strategies, which were geared toward weather forecasting rather than climate monitoring.

“We should apply what we learned in this study toward improving existing climate monitoring systems, so that future model evaluation studies are less sensitive to observational ambiguity,” Santer said.

Other researchers in this international consortium were Karl Taylor, Peter Gleckler and Stephen Klein (all at Livermore); Peter Thorne at the United Kingdom Meteorological Office Hadley Centre; Leo Haimberger at the University of Vienna; Tom Wigley and Doug Nychka at the National Center for Atmospheric Research; John Lanzante at the National Oceanic and Atmospheric Administration (NOAA)/Geophysical Fluid Dynamics Laboratory; Susan Solomon at the NOAA/Earth System Research Laboratory; Melissa Free at the NOAA/Air Resources Laboratory; Phil Jones at the University of East Anglia; Tom Karl at the NOAA/National Climatic Data Center; Carl Mears and Frank Wentz at Remote Sensing Systems; Gavin Schmidt at the NASA/Goddard Institute for Space Studies; and Steve Sherwood at Yale University.

LLNL researchers were supported by the Office of Biological and Environmental Research in the U.S. Department of Energy's Office of Science.