Greenland clouds offer clues to potential climate change impacts

The cloud cover over the Greenland Ice Sheet is the focus of University of Colorado post-doctorate researcher Ryan Neely’s ongoing project. He’s using novel LiDAR data collection techniques to better understand how clouds and other particles suspended in the air affect the ice sheet’s energy budget. Photo: Ryan Neely On a cold, crisp day hundreds of clouds drift over the Greenland Ice Sheet. These clouds play an important role in the region’s energy balance, affecting everything from air temperature to ice melt and precipitation.

University of Colorado post-doctorate researcher Ryan Neely is using a sophisticated LiDAR system installed at Summit Station to collect data that will shed light on the properties, structure and formation of the clouds above the ice sheet, as well as other particles suspended in the air.

Neely (left) and his student Robert Stillwell (right) next to the LiDAR system, which is stowed behind the black safety curtain. Credit: Ryan Neely

“My goal is to really try to understand the energy budget and how clouds impact the energy budget over the Greenland Ice Sheet. I’m particularly interested in how ice crystals, ice clouds, the types of particles we see and how they orient themselves impact the budget,” Neely explained.

His research is especially relevant as the tiny particles and clouds he’s studying may have a huge impact on Greenland’s ice cover as air temperatures increase due to climate change.

“As the temperatures warm up with climate change and with changes in cloud cover, we’ll need to understand how much energy is coming in or out, and whether that will accelerate melting of the ice sheets. So we’re trying to understand the small processes and how they will change in time with climate change,” he said.

Some of the haloes seen over the Greenland Ice Sheet that Neely and his team hope to measure with the LiDAR. Credit: Ryan Neely

Neely’s multi-year project, High Resolution, Active Remote Sensing of Cloud Microphysics at Summit, Greenland with Polarized Raman Lidar, which is funded by the National Science Foundation (NSF), is part of the larger body of research taking place at the ICECAPS Observatory at Summit, Greenland. The ICECAPS Observatory is home to a suite of sophisticated instruments used by dozens of scientists to collect real-time cloud and atmospheric date.

(Check out Field Notes’ recent coverage of other ongoing projects at the ICECAPS Observatory.)

Roles of Clouds

Neely and his colleagues are interested in more than just clouds. Every particle in the air—from water and ice to bits of volcanic ash and dirt to even microbes—impact the formation of clouds and how sunlight interacts with the ice sheet below.

“Aerosols are key for cloud formation. They act as nuclei because the water droplets or ice particles must have something to start the formation of a cloud,” Neely said. “Depending on what other particles are in the air besides water, they can actually change whether a cloud has ice particles or liquid.”

Virtually every characteristic of a cloud, including its composition and thickness, has an impact on the energy balance above the Greenland Ice Sheet. For instance, a really thick cloud can block the majority of radiation from reaching the ground. Along with thickness, a cloud’s composition—liquid or ice—can also affect how light reaches the surface and how much is bounced back to space.

Clouds can also act as a blanket, trapping heat and keeping the surface warm.

“Have you ever noticed how on a cloudy day it can be a little warmer than you may have expected? Well, the reason is that the clouds are blocking the long-wave radiation from escaping,” Neely explained.

Atmospheric Studies via a Beam of Light

Neely is using a LiDAR system stationed at the ICECAPS Observatory to study these different cloud properties. The instrument is programmed to collect data 24/7 and streams it back to his research lab in Boulder, Colorado where Neely downloads new data daily.

The LiDAR system shoots out a single beam of polarized light into the sky. Once the LiDAR beam encounters a cloud or particle, Neely is able to calculate a cloud’s height based on the time it took for the LiDAR pulse to bounce back. Changes in the polarization of the LiDAR beam tell him if the particles are liquid or ice, as well as how they are oriented.

“We use the LiDAR to look at the clouds as they go by a single point. So we are measuring the point right above us all the time. As clouds move, we get a profile versus time that shows the bottom layer of a thick cloud. If it’s a thinner cloud, we can see higher in to the profile.”

New and Possibly Pioneering Cloud Research

A diagram of horizontally-oriented versus non-oriented crystals. The orientation of crystals can influence how radiation is reflected onto the ice sheet and back in to space. Source: Ryan Neely

Neely and his graduate student Robert Stillwell just returned from the observatory where they upgraded the LiDAR system to collect data on how crystals are oriented.

“We’re interested to see how and why the crystals become horizontally oriented. When they are oriented this way, they act as tiny mirrors, which makes them much more efficient at reflecting radiation back down to the surface, and eventually back up in to space,” he said. “This is a new thing we are doing. No one is really doing anything like this anywhere else in the world except for Summit.”

More to Come

Neely and his team just completed the fifth year of data collection for this project and have some solid data to analyze under their belts. They recently received additional funding from the National Science Foundation to start a new, five-year project that will complement his cloud microphysics work.

Their plan is to build a bigger LiDAR system at Summit that can constantly measure temperature and water vapor above the ice sheet. This new LiDAR, dubbed SuPR LiDAR, will have the biggest laser ever operated in Greenland.

“It’s also a polarized LiDAR, but it uses a different aspect of light and different techniques to measure temperature and water vapor. This is a big need right now. It’s the one thing Summit doesn’t have,” Neely said.

Once installed in July 2015, SuPR will help give scientists a more complete picture of how clouds are changing as the weather changes and fast-moving fronts crisscross the region. —Alicia Clarke