JOINT BASE LEWIS-McCHORD, Wash. – I’ve looked at clouds from both sides now – from below, on the receiving end of an all-day rain; and from above, where NASA’s flying laboratory is dissecting those rain clouds.
For more than six hours on a rainy Saturday, I rode along as a DC-8 jet bristling with electronic gear took radar and microwave measurements of the clouds hanging over the Olympic Peninsula. The flight is part of a months-long campaign called the Olympic Mountain Experiment, or OLYMPEX, which is being conducted by NASA and the University of Washington.
OLYMPEX is aimed at fine-tuning the algorithms that scientists use to translate the data coming from on-the-ground weather installations and satellites like the recently launched Global Precipitation Measurement Mission Core Observatory into weather and climate projections.
In the process, they’re addressing a scientific problem we’ve known about since Judy Collins first sang about clouds in the ’60s: We really don’t know clouds at all.
“Clouds have been the most important unknown in our climate models,” Simone Tanelli, a researcher from NASA’s Jet Propulsion Laboratory, explained as we flew at an altitude of 39,000 feet. Climate prediction models include mathematical assumptions about cloud reflectivity and how that translates into rainfall and other weather phenomena. But that requires in-depth knowledge about the meteorological processes behind rain.
“If you end up making it rain by the wrong process, you may get the rain right, but the clouds are wrong,” Tanelli said. “And if the clouds are wrong, the radiation’s wrong, and there you go.”
The findings that come out of the OLYMPEX campaign should lead to better climate models as well as better daily forecasts. “Inside the atmospheric models, the building blocks of knowledge are always the same – whether it’s a weather forecast for tomorrow, or a climate forecast for 100 years from now,” Tanelli said.
But those building blocks don’t come easily. It takes time and effort to integrate new sources of data, such as the GPM Core satellite, into the weather modeling algorithms. That’s where the DC-8 plays its part. It’s carrying a dual-frequency scanning radar and a multichannel microwave radiometer, similar to the ones that are on board the satellite but with higher resolution.
The DC-8, which is flying out of Joint Base Lewis-McChord, serves as a stand-in as well as a fact-checker for the satellite. Meanwhile, extra radars and rain gauges have been installed on the ground on the Olympic Peninsula, one of the nation’s rainiest regions. A Cessna Citation business jet has been put into service to fly right through the clouds, and a super-high-flying Lockheed ER-2 aircraft is due to join the OLYMPEX fleet this week.
Saturday’s flight was the DC-8’s third outing for the OLYMPEX campaign, and it was still something of a shakedown cruise. For example, one of the key parts of the CoSMIR radiometer was apparently knocked out of whack during the flight from NASA’s Armstrong Flight Research Center. “We’re still operating nominally,” said Matthew Fritts, CoSMIR’s lead engineer. “It’s just that we had to adjust the mode.”
Fritts and his team planned to fix the problem after Saturday’s flight.
Yet another problem cropped up when one of the computers used by the rain-measuring radar system failed to work, despite multiple trips down to the DC-8’s cargo hold to revive it. Tanelli and his team eventually had to rely on other equipment instead – and miss out on some of the data they were hoping to get. “The game is, don’t make things worse,” he told me. “We’re here for the long game,”
The balky computer would have to be fixed or replaced during the DC-8’s down time.
Even the flight crew experienced a rough patch as they flew back and forth across the Olympics. The seemingly meandering flight path was aimed at collecting specific sets of observations from above the clouds to match up with the observations made by ground stations. During one of the maneuvers, the DC-8 leaned to the side and briefly shook with an ominous rattle.
“What was that about?” NASA mission manager Chris Jennison asked over the headset communication system.
“That’s, uh, trying to turn too short,” came the reply from the cockpit.
The buffeting provided a rare moment of drama during a 6½-hour flight that was sometimes almost soporifically smooth. The DC-8’s cabin has been optimized for science as well as for stretching out, with far fewer seats and far more open space than you’d find on your typical commercial flight.
Most of the 24 crew and passengers spent the time strapped into their seats, peering at the computer screens mounted in front of them. The food and beverage service was strictly BYOS (Bring Your Own Snacks), and the onboard facilities were spartan. One of the plane’s three lavatories had a hand-lettered sign stuck up over the sink, reminding passengers to pull up the spigot to turn off the water.
When they weren’t watching their readouts, passengers milled about the cabin or weathered rounds of media interviews. Some put their feet up and chilled out, or read a book. But few gazed out the DC-8’s windows for very long.
“We’re measuring rain,” Rachael Kroodsma, a researcher from NASA’s Goddard Space Flight Center, explained. “Therefore, all we see out the window is clouds.”
The success of Saturday’s flight hung on several precisely timed moments: Two of them came while the DC-8 was flying over the Pacific Ocean, dozens of miles west of the Washington coast. Each time, it was up to Laura Tudor, a technician from the Colorado-based National Center for Atmospheric Research, to drop a cylinder about the size of a rolled-up newspaper down a tube at the right time.
The cylinders, known as dropsondes, are equipped with parachutes as well as sensors and GPS receivers. They collect atmospheric readings as they descend through the clouds, and beam the data back to the DC-8. “It’s like a weather balloon, but in reverse,” Tudor explained.
Twice during Saturday’s mission, Tudor whirled around in her floor-mounted swivel chair, shoved a dropsonde down the tube and pushed open a valve to let it fly. The operation seemed almost as low-tech as dropping a water balloon, but Tudor said a lot of engineering goes into the operation.
“A lot of it’s troubleshooting, and a lot of it’s building the system,” she told me afterward.
Tanelli also could claim success, despite the computer glitch. The radar system collected data about the structure of rain clouds while the GPM Core satellite was flying over the same spot, and also while the Citation airplane was flying directly below.
“Got it!” he said. “Smack-dab under us!” He asked the mission team to confirm that the Citation was flying at an altitude of 11,000 feet, as indicated by radar – and laughed when the confirmation came.
“See? Radar doesn’t lie,” Tanelli said.
More importantly, the simultaneous readings provided another building block of knowledge for improved atmospheric modeling – just the sort of thing Tanelli was looking for. The radar readings revealed that the rain cloud was composed of disconnected layers, including a mottled formation that Tanelli called “shrapnel stratiform.”
Tanelli stressed that it will take more than one successful flight to get GPM Core ready for prime time.
“Today was a good one, but we have to do it again and again and again,” he told me. “We need to be able to collect enough data to be robust, to show that what we’re seeing is not a random fluke, for example.”
Then our plane headed back to base. We left behind the sunny skies above the clouds and descended through the murk, into the darkness of a rainy November day. I got in my car and drove home on slick, traffic-choked roads for another hour and a half.
I’ve looked at clouds from both sides now – and as we head into a dark and rainy Northwest winter, it doesn’t sound all that bad to visit their bright side, again and again and again.
