Emissions, Thunderstorms, & Climate Change

Smoke from wildfires in California and Colorado can make it hotter in Budapest. Isoprene, a naturally occurring hydrocarbon, rising in a summer mist from the forests of the Southeastern U.S., can damage the ozone layer that protects earth from harmful ultra violet radiation.

NASA’s Earth Science Division will employ three different aircraft and a fleet of satellites over the Southeastern U.S. this summer to collect data for a project called SEAC4RS, Studies of Emissions, Atmospheric Composition, Clouds and Climate Coupling by Regional Surveys. Quite a mouthful, meaning the researchers will examine the process of how localized pollutants change the composition of thunderstorms and invade the upper atmosphere, and how that impacts the global climate cycle.

In a prior study conducted by scientists at NASA’s Pacific Northwest Laboratory in June, 2012, it was found that locally-occurring contaminants such as car exhaust, factory smoke, and methane from cow manure rise with heat updrafts into the clouds of summer thunderstorms.  Sucked up in the form of tiny aerosol particles, local pollutants mix with the water in the cloud when it condenses to form a thunderhead. The pollution then acts to divide the water droplets inside the storm cloud, making them too small to create rain.  Polluted storm clouds, instead of bringing cool rain, become heat traps, gradually reflecting stored heat back to earth.

In the new SEAC4RS study, earth’s atmosphere will be probed from top to bottom with aircraft, satellite, and ground-based sensors at the critical time of year when regional air pollution and natural emissions pump gases and particles high into the atmosphere, with potentially global consequences for Earth’s climate.

Brian Toon of the University of Colorado, the study’s lead scientist, states, “In summertime across the United States, emissions from seasonal fires, metropolitan areas, and vegetation are moved upward by thunderstorms and the North American Monsoon. When these chemicals get into the stratosphere, they can affect the whole Earth. They may also influence thunderstorm behavior. We hope to better understand how all these things interact.”

Data will be collected from specialized instruments on (1) a fleet of formation-flying satellites known as NASA’s A-Train, (2) an ER-2 high-altitude aircraft that flies to the edge of space, (3) a DC-8 flying at lower levels, and (4) a specialty aircraft that measures cloud properties. A network of ground-based sensors will also be used.

By analyzing the collected data, the scientists expect to achieve a more precise understanding of how manmade and natural pollutants affect global climate:  What happens when polluted clouds travel with a weather system? Which pollution particles are absorbed by clouds, and which go directly into the stratosphere, and in what amounts? What happens when the jet stream carries stratospheric pollution around the world? Knowing more about this process should help us find more and better ways to reduce emissions and slow the pace of global warming.

Thunderstorms Warm the Planet

Summer thunderstorms can cool us off with welcome rain, but at the same time contribute to long-term global warming. The reason for this seeming contradiction, according to a study being led by Dr. Jiwen Fan of Pacific Northwest National Laboratory, lies in the way thunderstorm clouds are formed.

A building thunderhead pulls in strong updrafts of warm air rising from the ground, plus whatever natural and man-made pollutants are present in the local environment. In addition to the warm air, the updrafts suck in tiny aerosol droplets of everything from factory smoke to car exhaust to methane from cow manure. These pollutants mix with the water in the cloud when it cools and condenses to form the thunderhead. As the cool air in the cloud sinks, it becomes part of a convective cycle, sweeping into the warm updrafts coming from the ground and bringing more pollutants into the cloud.

The pollution serves to divide the natural water droplets within the thunderhead, making them too small to create rain. Instead, the droplets migrate to the top of the cloud where they freeze and absorb more water, increasing the overall size of the cloud. The research showed that these pollution-heavy clouds create stronger storms than those with little or no pollution. They spread out over a larger area and create larger anvils at the top, also acting as heat traps, gradually reflecting the stored heat back to earth. In general, the findings show that cleaner clouds produce more rain, while dirty clouds produce more heat.

The cloud research project, which is still ongoing, is a collaboration of scientists at Pacific Northwest National Laboratory in Richland, Washington, Hebrew University in Jerusalem, and the University of Maryland.