Researchers Studying Effects of Aerosols on Storms in Houston Area
A team of atmospheric scientists from around the nation is descending on the Houston area for the next 14 months to seek answers to a vexing question: Do tiny specks of soot, dust, smoke and other particles suspended in Earth鈥檚 atmosphere help determine the severity of thunderstorms? The knowledge gained may make weather forecasts more accurate and provide crucial data for improving predictions about how aerosols may affect Earth鈥檚 future climate.
鈥淲e鈥檙e a coastal environment, so it鈥檚 particularly challenging to forecast the weather.鈥
James Flynn, research associate professor in the UH Department of Earth and Atmospheric Sciences
The Houston deployment will also provide detailed data on local air quality. As an extensive field study in a metropolitan area, it will give scientists a unique opportunity to explore the effects of industry, vehicle emissions, and the built environment on weather and climate.
鈥淲e want to know how aerosols, the tiny particles that water condenses onto to form cloud droplets, influence the physics of deep convective clouds鈥攖he kind that often pack lightning and pour rain鈥攁nd then how those same weather conditions affect the local aerosol characteristics and urban air quality,鈥 said Michael Jensen, a meteorologist at the U.S. Department of Energy鈥檚 (DOE) Brookhaven National Laboratory and principal investigator for the TRACER field campaign. TRACER is short for TRacking Aerosol Convection interactions ExpeRiment, a study being carried out by DOE鈥檚 Atmospheric Radiation Measurement (ARM) user facility.
Working in close collaboration with researchers at the 葫芦影业, TRACER scientists from Brookhaven, Los Alamos National Laboratory, and other institutions will collect data on aerosols and atmospheric characteristics for a full year. The team will deploy a suite of instruments supplied and operated by ARM at four locations just outside the city.
During an intensive study period from June through September 2022, additional partners from the National Science Foundation, NASA, the Texas Commission on Environmental Quality, and other agencies will join the team to catch the peak of Houston鈥檚 summer storm season.
With a humid subtropical climate, numerous isolated convective storms, and a range of industrial and natural aerosol sources, Houston is the perfect place for the study.
鈥淲e鈥檙e a coastal environment, so it鈥檚 particularly challenging to forecast the weather,鈥 said James Flynn, research associate professor in the 葫芦影业 Department of Earth and Atmospheric Sciences in the College of Natural Sciences and Mathematics. 鈥淲e have a lot of thunderstorms; we have pollution and some natural sources of fine particles.鈥
Examples include dust, sea salt, particles emitted by diesel engines, soot from combustion processes at power plants and refineries, lots of urban road traffic, and even smoke from wildfires in California and Colorado.
Some research suggests that such aerosols can change the lifecycle of clouds, delaying the onset of precipitation. If that happens, as clouds grow, water droplets may get bigger. 鈥淎nd when they do fall, it鈥檚 a gully washer,鈥 Flynn said.
TRACER data will improve understanding of these processes鈥攁nd our ability to predict when the deluges will occur.
ARM Deployment
The ARM instruments, housed in 10 mobile shipping containers, are collectively known as 鈥渢he first ARM Mobile Facility,鈥 or AMF1. Many of these instruments, including an Aerosol Observing System outfitted at Brookhaven Lab, have traveled to locations around the world from the Arctic to the tropics to collect atmospheric data.
鈥淭his is the first deployment of the ARM Mobile Facility in an urban coastal environment,鈥 said Sally McFarlane, DOE program manager for ARM. 鈥淭he warm, moist air from the Gulf of Mexico helps drive the formation of a lot of isolated, moderately strong storms鈥攖he ones that are probably ripe to be impacted by aerosols. Those coastal conditions and Houston鈥檚 mix of industrial and natural aerosol sources make the area an ideal laboratory for studying aerosol-cloud interactions.鈥
鈥淭his is one of those projects that is very applicable to everyday life here in Houston.鈥
James Flynn, research associate professor, UH College of Natural Sciences and Mathematics
An ARM team will set up the containers, each housing racks of instruments and intake vents, near Galveston Bay鈥攁n area with lots of industry, refineries, and transportation. Several of the containers also host sophisticated radars (which use radio waves) and lidars (which use laser light pulses) to measure the height, depth, and amount of water in clouds鈥攁mong other important variables. Additional meteorological instruments will operate in an adjacent instrument field. Collectively these tools will track cloud properties; the size, number, and chemical composition of aerosols; precipitation; and variables such as temperature and humidity that affect atmospheric stability.
Sampling Throughout the Atmosphere
Over the course of the year, the ARM team will also launch more than a thousand weather balloons carrying additional battery-powered sensors, called radiosondes, aloft. The balloons will travel through and above the clouds, to an altitude up to 17 kilometers (nearly 56,000 feet)鈥攐ften making it to the stratosphere鈥攕ending additional data on temperature, humidity, pressure, and winds back to the research station below.
Some balloon-borne instruments will also measure the concentration of ozone through the depth of the atmosphere.
鈥淲e鈥檒l use these ozone measurements to learn about air quality and how thunderstorms redistribute air between the surface and aloft,鈥 Flynn said. Surface ozone is generated when chemicals emitted as part of automobile exhaust and industrial processes react with sunlight. So, when storms transport air from the surface upward through the atmosphere, the pollutant can serve as a tracer for TRACER.
Land, Sea, Atmospheric Interactions
During the intensive study period next summer, scientists from TRACER and partner agencies will also deploy additional equipment near the town of Guy, Texas, southwest of the city. Two tethered balloon systems, one at the site in Guy and one at Smith Point on the east side of Galveston Bay, will carry instruments to measure winds, small aerosol particles, and ozone in the lowest layers of the atmosphere. The measurements on the shore of Galveston Bay will provide important information about how the bay influences the local atmospheric circulation. Meanwhile, the instruments in Guy will collect data in a more rural location.
鈥淲e expect to see lower aerosol concentrations, so this site will serve as a contrast to the AMF1 site and allow comparison of the cloud and precipitation characteristics under these very different conditions,鈥 McFarlane said.
Between the two main land sites, a scanning ARM precipitation radar in Pearland will track the properties of clouds.
鈥淭his radar will collect data on cloud properties, including the velocity of vertical updrafts that affect how fast clouds grow, form ice, and produce rain and lightning. It will operate during the entire study period,鈥 Jensen said.
Then, during the intensive study period, using unique observational techniques, the radar will be able to look at finer details in the clouds鈥攊ncluding the size and shape of the cloud droplets and whether they are ice or liquid. 鈥淚t will be able to look at the atmosphere over each site as they are experiencing different aerosol conditions,鈥 Jensen said.
The radar will be driven by software developed by Brookhaven scientist Pavlos Kollias and programmed using artificial intelligence (AI) and existing data sets. 鈥淭his software allows the radar to select the storms we think are going to develop and move over the sites, and then zoom in and scan at high resolution to explore details of how aerosols are impacting the precipitation drops in there,鈥 Jensen said.
Sharing and Applying Data
All data collected by ARM will be freely available to anyone who wants to analyze it.
鈥淲e hope the things we learn here, the processes within convective activity, how pollution impacts storms, will be applicable in other major urban areas that have a lot of convection,鈥 Flynn said. 鈥淲ith a lot of projects, you鈥檙e really getting down to some real core science. People sometimes aren鈥檛 sure why it matters. This is one of those projects that is very applicable to everyday life here in Houston.鈥
The research will be applicable beyond the Houston area as well. DOE鈥檚 Atmospheric System Research (ASR) program has already committed to fund 10 TRACER projects led by university-based researchers.
鈥淭RACER鈥檚 scientific objectives are aligned with ASR鈥檚 focus on cloud, aerosol, precipitation, and radiation processes,鈥 said Jeff Stehr, a DOE program manager for ASR. 鈥淐onvective clouds occur all around the world, but there are still many questions about how they are affected by their environment. TRACER will improve our understanding of how these clouds form, grow, and decay in and around a coastal urban environment. The initial set of ASR-funded projects involve research teams from around the country, and will add measurements as well as modeling to the TRACER campaign.鈥
Data collected by TRACER will also be helpful for understanding processes relevant to how hurricanes form and how long they last.
And while weather and climate operate on different timescales, they鈥檙e both about 鈥渢he physics of Earth鈥檚 atmosphere,鈥 Jensen said. 鈥淯nderstanding storms is important for understanding climate because storms redistribute heat and moisture through the atmosphere. And that redistribution is affected by small-scale processes in the atmosphere including interactions with aerosols. That鈥檚 what we struggle with in the models of climate and weather.鈥
鈥淭RACER will fill in some of the missing data to help us improve those models.鈥
TRACER is funded by DOE鈥檚 Office of Science.
- Karen McNulty Walsh, Brookhaven National Laboratory