Airborne in the Arctic

This blog post is part of a series of first-hand stories from NASA scientists, visualizers and educators that were created for Earth Science Week 2015: Visualizing Earth Systems. Read all the blogs and find educational resources for all ages at: http://ift.tt/1OKWxQV. Four turboprop engines roar to life under the autumnal Alaskan sun, and we begin to taxi to the main runway of Eielson Air Force Base. After extensive pre-flight configurations, our science payload is primed for our eight-hour mission. Without delay, the engines' roar becomes a howl as we hurtle down the nearly three-mile stretch of runway until that near-weightless moment we become airborne. Our mission into the clouds of the arctic is underway. Clouds are important drivers of Earth's climate by regulating the amount of sunlight that is absorbed at the ground versus what is reflected back into space. You've probably experienced this firsthand when sitting outside on a hot and sunny summer day when a fluffy cumulus cloud crosses the sky between you and the sun. The respite that you feel from the heat of the sun's rays means that that energy is no longer reaching you at the surface. At the lower latitudes where most of us live, these thick, stratiform and cumuliform clouds have a cooling effect because the white cloud reflects the sun's energy back to space instead of being absorbed by the dark brown soil, green trees and plants, or the blue ocean waters. The story is much more complicated at the high latitudes where the frozen ice surface is also very bright white and reflective. Under these conditions, clouds can actually have a net warming effect because they reflect a similar or smaller amount of the incoming sunlight, but also trap more of the outgoing heat radiation and keep it close to the surface (like a blanket.) The exact balance between heating and cooling depends on the cloud properties - droplet number and size - and where the clouds are located in the atmosphere (high or low altitude as well as overlying dark water or bright ice.) Unraveling these effects is important for understanding how the Earth's radiation balance and climate exist now and how they are likely to change in the future. Differentiating the impacts of low-level clouds versus Arctic sea ice on sunlight from space is hard, because to a passive satellite sensor orbiting many hundreds of kilometers above the Earth's surface, both the ice and cloud look very similar. To best visualize this system, we must go to the Arctic with scientific research aircraft to measure the cloud properties just below, above, and within the clouds themselves. This was precisely the motivation behind the NASA Arctic Radiation - IceBridge Sea and Ice Experiment (ARISE), which was conducted in the Alaskan Arctic from September-October, 2014. ARISE carried out 14 science flights aboard the NASA Wallops Flight Facility C-130 Hercules aircraft, which was outfitted with a comprehensive suite of scientific instrumentation including a laser altimeter for measuring the sea ice surface properties, in situ cloud probes, and a sun photometer and two radiometers (SSFR, BBR) for measuring the surface, aerosol, and cloud radiative properties. An example 8-hour flight track is shown for the September 7th science flight in the Google Map below. The aircraft was based at Eielson Air Force Base near Fairbanks, AK, and began each flight by transiting approximately 2 hours north to the vicinity of the ice edge in the Beaufort Sea. On the 7th, the aircraft flew a series of parallel, horizontal legs to cover a single satellite grid box of the overflying NASA Clouds and the Earth's Radiant Energy System (CERES) satellite. These measurements help CERES scientists to understand how small-scale variability in ice and cloud extent and properties affect their satellite-based retrievals. Google map showing the flight track of the NASA C-130 aircraft during a research flight conducted on 7 September 2014 north of the Alaskan coast. Before wrapping up the research flight on the 7th and beginning our 2-hour transit back to Fairbanks, we descended into the low-level clouds to measure their microphysical properties with the in situ cloud probes. The video below shows what it's like to measure an Arctic cloud from inside it! The left side of the video shows the real-time data time series from our research instruments that we are continuously monitoring in flight. The top-right imagery is from the forward-facing camera in the C-130 cockpit. The bottom-right imagery is from the downward-facing, nadir camera mounted on the bottom of the aircraft. In the video, we start out above the clouds in a shallow descent. The altitude data trace is trending down, but nothing has registered yet on any of the cloud probe instrumentation. Looking at the lower-right, downward-facing camera, we can see the sea ice on the surface periodically, which tells us that these clouds are somewhat broken up. As the pilots lower us below about 400 meters altitude, we enter the clouds, but they continue to descend looking for the cloud bottom. On this day, the clouds extended down so close to the ice surface that we were unable to safely get below them, so the pilots climbed back up to a comfortable altitude in the cloud for a level altitude leg. Looking at the color map of CDP Droplet Diameters, we can see some interesting changes in the cloud droplet size distribution with altitude around 23:12:30 UTC - the droplet sizes get smaller at the lower altitude closer to cloud base! Within the cloud on the level leg (23:12:30-23:17:30 UTC), the forward-looking camera (top-right) is pretty socked in with opaque white cloud; although, every once in a while we see a glimpse of blue sky above. Similarly, on the downward-facing camera (bottom-right), we see thin wisps of clouds punctuated by periodic breaks in the cloud structure and clear visibility of the sea ice below. Now looking at the data, we see this constant up/down pattern in the CDP Cloud Droplet Number Concentration (red trace) and the Cloud Liquid and Total Water Content (LWC in blue and TWC in black). This structure in the data is due to the aircraft cutting across the parallel streaks of low clouds. The video ends with the pilots ascending out of the cloud. Manning the scientific instrument displays, which allow me to see real-time variations in the atmospheric composition has to be my favorite part of ARISE aircraft studies! Quite simply, there's never a dull moment when you're sitting inside of an airplane travelling across cities, states, or countries, and encountering different air masses along the way. -- Rich Moore, Research Physical Scientist (NASA Langley Research Center)

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