Tucson Standard

Earth's atmosphere, while invisible to the naked eye, is a dynamic entity composed of layers with distinct characteristics. Understanding these layers is crucial for meteorologists in predicting air quality. The planetary boundary layer, which interacts directly with the Earth's surface, and the mixing layer, containing thoroughly mixed air that cools with elevation, usually share similar heights. Lidar laser technology has been effective in detecting these heights by measuring light scattering and absorption by aerosol particles.

However, under certain conditions, the mixing layer can be significantly lower than the planetary boundary layer—a phenomenon known as decoupling. Traditional lidar methods have struggled to measure both layers' heights in such scenarios. Recognizing this gap, a team of researchers from the University of Arizona developed a new technique combining scientific insights and an updated computer algorithm to enhance lidar's capability in detecting atmospheric layers.

The research was funded by a $30 million NASA award granted to a UArizona-led project in 2018. Led by Armin Sorooshian from the Department of Chemical and Environmental Engineering, the team collected data on aerosols, clouds, and meteorology over the northwestern Atlantic Ocean using lidar and other airborne instruments. This funding was part of NASA's Earth Venture Class program aimed at exploring lesser-understood Earth system processes.

Xubin Zeng from UArizona’s Department of Hydrology and Atmospheric Sciences highlighted how the height of the planetary boundary layer varies globally—averaging just over 3,000 feet but reaching over 13,000 feet during hot desert summers and shrinking below 500 feet at polar regions. Sometimes an inversion layer traps air beneath it within the mixing layer.

"On a clear day in wintertime Tucson," Zeng noted, "you can see a brownish fog trapped near the surface by warm air above—an inversion."

Lidar traditionally measures atmospheric inversion height or cloud tops at the top of this boundary layer but has been limited until now. The revised algorithm allows lidar data to identify both lower and higher inversion layers through gaps between clouds or clear skies.

The accuracy of this new method was validated against data collected from weather balloons dropped from aircraft. These balloons provided temperature, humidity, and wind information during their descent.

"From this comparison," said Yike Xu from UArizona’s Department of Hydrology and Atmospheric Sciences, "we verified that our new techniques are a reliable way of determining the height of the planetary boundary layer and mixing layer."

While initially conducted over the Atlantic Ocean, Zeng stated that this method could be applied globally with implications for climate change mitigation efforts. For instance, attempts to brighten low-level clouds off California's coast using aerosols may be less effective if released when atmospheric layers are decoupled.

"If they release aerosols when decoupled," Xu explained, "the aerosols can't overcome the boundary between layers to reach clouds," reducing their impact on cloud-whitening solar radiation management.

Zeng’s team hopes their findings will support future satellite missions focusing on these atmospheric phenomena within the next decade.