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NEWS | Feb. 26, 2018

NRL Meteorologists Re-examine Cirrus Clouds, Help Improve Weather Predicting for Warfighters

By Michael R. Hart

MONTEREY, Calif. – It’s a late-summer morning on California’s rugged central coast and Dr. James Campbell, a meteorologist at the U.S. Naval Research Laboratory Meteorological Division here, sits in his office – complete with a ceiling-high shelfful of books and picturesque window view of sand dunes, desert and clear-blue skies.

With more than 20 years of experience, Campbell’s professional life is brimming with all things concerning climate, atmosphere, weather -- and clouds. Clouds have been Campbell’s objects of attention most recently – cirrus clouds, specifically.

These aren’t the big, cotton ball-looking formations that can be amazing on clear, summer afternoons. Cirrus clouds -- formed from freezing, super-cooled water droplets -- are thinner. They float 16,000 to 45,000 feet above the earth -- wispy looking and translucent, resembling tufts of smoke.

Campbell and his team are in the first year of a three-year endeavor of researching and observing cirrus clouds, the “forgotten” clouds, as Campbell calls them, via a project termed Radiative Effects of Thin Cirrus. REThinC is an in-depth project NRL meteorologists are undertaking, with assistance from NASA and their research aircraft.

“We’ve all looked up at the sky on a beautiful sunny day and [have seen] ice crystal streaks across the sky,” Campbell began. “Optical displays in the sky caused by cirrus clouds, like ice halos, have captivated ground observers since the beginnings of civilization.

“REThinC is about engaging the atmospheric sciences community and drawing attention back toward basic physical questions about ice that, unlike liquid water clouds, have yet to be really addressed.”
For instance, “over the last 20 years, we’ve learned that cirrus clouds are twice as common as we had thought, as far back as the late 1990s,” Campbell explained.

“We recognize now that we were missing what we now call “thin” cirrus clouds.”

Typical weather satellite sensors, like the ones used by meteorologists on the evening news, struggle “seeing” thin cirrus because of the translucency, according to Campbell, because objects on the ground or other clouds below them overwhelm their appearance.

“What’s unique, though, is that we’ve found that despite being so “thin” and diffuse, cirrus clouds exert a significant effect on the Earth’s climate because of their overwhelming prevalence, compared with denser liquid water clouds,” he continued. “REThinC is designed to better understand how these very thin clouds are uniquely influencing climate.”

Campbell said that unlike many liquid water cloud forms, cirrus clouds are found worldwide and throughout the year.

“Our goal with RETHinC is to further our understanding of how cirrus contribute to climate in terms of its radiative balance with the Sun,” he said. “It’s about raising basic awareness of cirrus clouds as a whole. They are critical contributors to many climatic processes.

The Navy is quite interested in cirrus clouds’ climate influence and is invested in predicting weather, both for the warfighter and for understanding environmental threats to our country, said Campbell, who most recently collected field measurements of cirrus clouds using NASA’s WB-57 aircraft near Ellington Air Force Base, in Houston.

Here's how the research works: Because ice crystals are so unusually small (typically less than 0.1 mm), lidar (similar to radar, but it is lasers instead of radio waves that project wavelengths about a 1,000 times smaller than what your local weatherman uses) is used to monitor cirrus clouds from the ground and space-based platforms and then evaluate their radiative properties.

Aircraft flying between 50-60,000 feet, place sensors that measure the Sun and Earth’s simultaneous energies during daytime above and below cirrus clouds to understand what the impact is of a given cloud relative to if it wasn’t there in the first place.

“The cloud “forcing” effect helps us understand the net impact on net top-of-the-atmosphere energy balance, which tells us whether or not a cloud is causing a net cooling or warming of the atmosphere,” Campbell explained. “What is unique about cirrus clouds is they are the only cloud that can cause a net warming OR cooling at the top of the atmosphere during the day, depending on the characteristics of a given cloud layer and the position of the Sun.

“Cirrus clouds are a part of this net warming system. A better understanding of how cirrus clouds impact the radiation balance of the earth, for instance, will lead to better weather and climate models that ensure tactical superiority and the safety of our country as a whole,” said Campbell.

One example of where REThinC may lead, according to Campbell, is a better understanding of how cirrus clouds can help improve Navy and Marine Corps operational weather models. “This will help improve medium-term weather predictions (7-10 days),” he said.

“Furthermore, many routine satellite-based ocean and atmospheric measurements used in prediction models, like sea surface temperatures, temperature and water vapor profiles, aerosol properties and even the basic solar reflectance off of the planet’s surface, are susceptible to thin cirrus contamination and bias.

Campbell emphasized that bringing the “forgotten” clouds back into the light for a reexamination will only help Navy and Marine Corps operators in the future.

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