By Rob Mitchum // October 29, 2015
Every year, scientists get better at modeling the Earth’s climate, making forecasts at higher resolution and further into the future than ever before. But many of these models are still missing a major regulator of the planet’s climate, hanging right over our heads. Clouds play an important cooling role for Earth, shielding the oceans and land from sunlight and influencing weather around the world. In order to study these dynamics and incorporate new details into climate models, atmospheric scientists work in an unusual laboratory: a luxury jet.
This summer, CI fellow Virendra Ghate and CI postdoctoral researcher Chris Schwartz participated in one such airborne study, shuttling between California and Hawaii to collect data from stratocumulus clouds. The Cloud System Evolution in the Trades (CSET) campaign gathered 50 scientists and engineers for this mission, which seeks to understand how the sun-blocking stratocumulus clouds transform into their descendants, cumulus clouds, which block less sunlight. These transitions occur during the regular southwest journey of the clouds from Alaska to Hawaii, along the west coast of the United States, but the impact is global.
“If the cloud covers increase or decrease or if they transition to less patchy or more patchy cumulus, that has everything to do with how much heat the Pacific absorbs and transports all over the globe,” Schwartz said. “If you’re modeling climate and you want to know how the climate is going to respond to increased carbon dioxide forcing, you need to be able to model physically these clouds and their transition.”
Since it’s rather difficult to get a cloud into a laboratory, the CSET team took their laboratory to the clouds. The project used the Gulfstream-V High-performance Instrumented Airborne Platform for Environmental Research (GV HIAPER), a modified business jet owned by the National Science Foundation and operated by the National Center for Atmospheric Research (NCAR). The team loaded up the plane with instruments — including two newer technologies, the HIAPER Cloud Radar (HCR) and the High Spectral Resolution Lidar (HSRL) — and flew above, below, and through stratocumulus clouds to collect information on cloud properties, precipitation, aerosols, and other factors.
These measurements were taken on flights from Sacramento to Kona, Hawaii — after which the researchers enjoyed the nice perk of a free day on the islands. Two days later, the team reversed course back to Sacramento, this time taking measurements from cumulus clouds on the other side of the transition process. Using weather prediction models, the project estimated where the stratocumulus clouds they sampled two days prior would now appear, in order to “trace” the same system along its path.
“It’s not like a bald eagle, you can’t tag it and follow it, but it’s our best guess,” Schwartz said. “We’re sampling basically the same air.”
In total, there were seven round trips made over the summer; an 8-hour flight each leg. Schwartz participated in one trip as an instrument operator, while Ghate acted as mission scientist for one circuit, instructing the pilots on where to fly (including as low as 500 feet above the water) to sample all levels of the clouds and their surroundings.
With the flights finished, it’s now time for the earthbound part of the project. On each leg of the flight, the project collected 2 terabytes of data, creating roughly 26 terabytes for the analysis team to sort through. Some of that work is taking place at Argonne, where the scientists use code written by Schwartz to analyze raw voltages measured by the radar during the flights, calculating the Doppler spectra of cloud and drizzle particles for each volume of air.
That step is nearing completion, Schwartz said, and will help the wider CSET team examine additional compute cloud characteristics such as water content and internal vertical motion. Eventually, these analyses will provide new calculations on the behavior of these clouds that scientists can add to models of global climate and energy use, adding a new layer to our understanding of the Earth’s atmosphere.
CSET was held in July and August of 2015 and was funded through the National Science Foundation (NSF) Physical and Dynamic Meteorology Program. CSET involved the participation of about fifty scientists and engineers and was led jointly by Bruce Albrecht and Paquita Zuidema from the University of Miami, Robert Wood and Chris Bretherton from the University of Washington, and Ghate from EVS.