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The Forecast Is…Murky: The Uncertainties of Weather Prediction

March 12, 2013


By Cathy Cruise

Predicting weather and climate change has long been a delicate process, and Mason’s Zafer Boybeyi is the first to admit that even with today’s technology, certain aspects of the science remain largely unpredictable.

Zafer Boybeyi

Zafer Boybeyi

An associate professor in Mason’s Department of Atmospheric, Oceanic, and Earth Sciences for the past 15 years, Boybeyi is also director of the Comprehensive Atmospheric Modeling Program (CAMP) within the College of Science. The program, formed in 1997, originally received funding from the Department of Defense to develop emergency response systems for chemical, biological, nuclear, and radiological releases. Over the years, that research has expanded to encompass climate studies, aerosol impacts, severe weather, and natural hazards.

Modeling and Simulation

Numerical modeling—using mathematical models of the atmosphere and oceans to predict weather—has come a long way from efforts that started nearly five decades ago with 1-D and 2-D simulations. Boybeyi says today’s prediction models, particularly those based on the weather scales of a few days, are exceedingly reliable, mainly because of advanced computers and denser observational networks. These networks include conventional systems such as rawinsondes—instruments that measure wind, pressure, temperature, and humidity—and unconventional ones such as radar and satellites.

But weather prediction is quite different from foretelling climate patterns because, says Boybeyi, “you’re making much longer predictions—10, 20, 50 years down the road. The accuracy of those models deviates from the reality as time goes by.”

Researchers are really looking for trends in these model predictions. If a model shows both carbon dioxide levels and temperatures increasing consistently, for example, then a strong correlation must exist between the two. Numerical models are used to interpret those relationships.

“And as we predicted,” Boybeyi says, “when you increase greenhouse gases, you increase global temperature. There’s a strong correlation there, and there’s no doubt about it. How much temperature change will take place? No one has a clear answer for that.”

A Bumpy Ride

In the beginning, modeling presented a learning curve for researchers. But as numerical models became sophisticated, research caught up, reached a point, and then leveled off. Little progress is being made now, mainly because of turbulence, what Boybeyi calls “the one classic, unsolved physics problem.”

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Scientists currently have no way of mathematically defining the random motions involved in turbulence because the atmosphere is both deterministic (i.e., predictable) and chaotic in nature. Therefore, Boybeyi says, “there are both theoretical and practical constraints on what we can do. Think about atmosphere as so many parameters affecting our temperature, density, pressure, and all the weather events that we care about. One parameter affects so many other parameters, and so many other parameters affect others. These nonlinear interactions and relationships are what we fail to understand clearly.”

But in the future, he says, computer advancements will enable modeling to produce higher resolution simulations that will reduce the problem of mathematically defining these random motions, and “resolve explicitly most of the small motions and the nonlinear interactions that exist in the atmosphere.”

Predicting severe weather events also presents an ambiguous challenge. Hurricanes, for instance, have been studied for such a long time, there is now a high level of success in predicting their tracks. But as for predicting their strength, Boybeyi says, “We don’t really do a good job on that. We fail to predict the intensity with accuracy.”

Boybeyi’s group is examining how the Saharan Air Layer (SAL) affects hurricane intensity. The SAL is a mass of dry, dusty air that forms over the Sahara Desert during spring, summer, and fall, and then moves out over the tropical North Atlantic Ocean.

“A recent hypothesis suggests that the Saharan Air Layer, and the dust it carries with it, may cause the intensity prediction problem in the Atlantic region,” Boybeyi says. “That’s a relatively new idea, and people have just started paying attention to that.”

Aerosol Effects

These days, Boybeyi’s group is putting nearly all its efforts into studying the impact of aerosols on climate. Aerosols, or all the particles dispensed in the air including greenhouse gases, have different impacts in the atmosphere. Direct impact, in which aerosols block, scatter, and absorb the short-wave radiation coming from the sun, reduces the amount of solar radiation reaching the ground’s surface and alters the entire energy balance of the atmosphere. Indirect impact occurs when aerosols provide cloud condensation nuclei. This increases the lifetime and thickness of clouds, which delays precipitation. As a result, those clouds can block short-wave radiation and trap long-wave terrestrial radiation.

Boybeyi’s team has also been working on a third, semidirect effect caused by highly absorbing aerosols, such as black carbon. This dark soot soaks up sunlight and generates heat, and aerosols of this type, he says, can “absorb energy and radiation, and increase the atmospheric temperature further. They may play a tremendous role.”

Some of these aerosol impacts contribute to global temperatures in a positive way, and some in a negative way. Which does which is another uncertainty. “Researchers as yet have no clear understanding of their total contribution and which one is the dominant process,” Boybeyi says. “But the polar regions may hold the answers.”

As the earth’s general air circulation pulls in greenhouse gases released from industrialized regions of the world—particularly developing areas such as Asia and parts of Europe—it transports them to the polar regions, where they combine and increase their concentration level. One of Boybeyi’s graduate students, Eric Stofferahn, has been working on aerosol effects on climate in the Alaskan region, through research sponsored by the Department of Energy.

“Our preliminary results indicate that these aerosols play an important role in terms of the vast climate change happening in the polar regions—that of the icebergs melting,” says Boybeyi. “The models predict that in 10 to 20 years, there may be little ice left in those regions during summer months.”

Finally, Boybeyi says long-term, sustainable development of our global society primarily requires an understanding of the interaction between human activities and natural processes (such as climate and climate change), and accurate representation of these natural processes using numerical models. “Unfortunately,” he says, “this remains a challenging problem.”


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