Colorado State University atmospheric scientists recently embarked on partner field campaigns to study weather phenomena over the Philippines and surrounding sea. The complex processes at play in this part of the world affect southeastern portions of continental Asia, and even weather in the United States. Ultimately, the observations CAMP²Ex scientists took by plane and PISTON researchers made by ship will improve weather and climate forecasts.

CAMP²Ex, the Cloud, Aerosol and Monsoon Processes Philippines Experiment, monitored the impact of smoke and pollution on cloud and aerosol processes. PISTON, or the Propagation of Intra-Seasonal Tropical OscillatioNs, observed how oceanic convective systems organize and evolve in the tropical atmosphere. The two international field teams conducting these studies will be able to compare findings for more comprehensive results.

Flight delays

CAMP²Ex originally was scheduled to take to the sky in 2018, but the campaign had to be delayed a year due to aircraft issues. Once off the ground, flight scientist and Professor Susan van den Heever and her crew aboard the NASA P-3B science aircraft collected a wealth of data that will enhance our understanding of aerosol and cloud processes.

“The campaign was a tremendous success,” van den Heever said. “We flew 19 P-3 science flights. We obtained observations of shallow maritime cumulus clouds, deeper congestus clouds, tropical linear cloud systems, and cold pools within polluted and clean environments, allowing us to examine the impacts of aerosols on these cloud types and processes.”

Industrial growth in Southeast Asia has led to changes in atmospheric composition and precipitation. Biomass burning in Malaysia and Borneo produces smoke, while China creates large quantities of sulfates and other pollution, and the urban center of Manila also yields high concentrations of aerosols. All of the resulting particles filling the air influence cloud processes, precipitation, and how incoming solar radiation interacts with clouds and the surface. CAMP²Ex’s three-part mission is to examine the impacts of aerosols on cloud processes, precipitation and radiation; the way in which the atmospheric environment alters these impacts; and how clouds subsequently affect the aerosols.

To accomplish these goals, a suite of remote-sensing and in-situ instruments on board NASA’s P-3 and a SPEC, Inc. Lear Jet measured the microphysical and chemical properties of clouds as the aircraft passed through, below, above and around them. Scientists aboard the P-3 dropped almost 200 dropsondes from the tail of the plane to measure vertical profiles of temperature, moisture and wind.

“We are hoping that this vertical characterization of the environment will help us to better understand the role of temperature, moisture and wind shear in controlling or modulating aerosol-cloud interactions,” van den Heever said.

The two CAMP²Ex aircraft worked in tandem, with the Lear Jet frequently collecting in-situ data within the cloud, while the P-3 flew above it gathering co-located remote-sensing observations.

By sea

Meanwhile, the R/V Sally Ride, a U.S. research vessel operated by Scripps Institution of Oceanography, complemented the aircraft observations from below. As the ship steamed around the Pacific Ocean east of the Philippines, its crew of scientists measured air and sea interactions using radiosondes launched via weather balloons and the SEA-POL C-band polarimetric radar, designed and built at CSU under the direction of Professors Steven Rutledge and V. Chandrasekar.

“Our interest is in documenting the evolution, organization and diurnal cycle of convection in relation to larger-scale variability in the tropical atmosphere,” said research scientist Brenda Dolan, who oversaw atmospheric operations for the Sally Ride. “We are able to do this at very high spatial and temporal resolution with the SEA-POL radar.”

Dolan coordinated missions with the CAMP²Ex flight scientists as they flew around the Sally Ride, sampling clouds and aerosols. Associate Professor Michael Bell’s research group provided daily weather forecasts for PISTON, while graduate student Sean Freeman did the same for CAMP²Ex, ensuring both ship and plane collected the best data and steered clear of typhoons.

Soundings launched from the ship eight times a day characterized the atmospheric thermodynamic state, while dual-polarized measurements taken with SEA-POL provided insights into the growth processes of convective cells. These PISTON observations, made by Professor Rutledge’s research group, offer context for CAMP²Ex’s research.

“Such co-located datasets allow us to obtain better observations near the surface and aloft, and are tremendously valuable in enhancing our understanding of aerosol and cloud processes, as well as evaluating these processes in numerical models,” van den Heever said.

Professors Bell, Rutledge, van den Heever, Eric Maloney and their research groups all contributed to PISTON, which set sail for the first time in August 2018.

Gauging pollution’s effects

With increasing air pollution and agricultural and deforestation fires generating aerosol particles that alter clouds, it is important to understand how those particles are influencing weather and ultimately climate, in the region and around the world. Filipinos have anecdotally observed a decrease in annual precipitation in recent decades, suggesting that a shift as a result of enhanced particle loading already is underway.

“Do more polluted environments produce populations of raindrops below cloud base that have a greater number of larger raindrops than those in cleaner environments?” van den Heever said. “Our numerical model, RAMS, as well as several other numerical models, suggest this is the case, and we need observations to evaluate this process. This process has important implications for surface precipitation rates as well as evaporation rates, and hence tropical cold pools.”

NASA, the U.S. Naval Research Laboratory (NRL), and the Manila Observatory worked closely to launch the NASA-funded CAMP²Ex. The CSU Department of Atmospheric Science continues to collaborate with scientists from NRL and the Manila Observatory, and plans to host visits from Observatory students next year. PISTON was funded by the U.S. Office of Naval Research.