Investigating monsoon-climate connections


Investigating monsoon-climate connections

LASP scientists are participating in a coordinated field campaign to better understand the impacts of chemicals redistributed by the Asian monsoon

The launch of a high-altitude sounding balloon at sunrise.
The launch of a high-altitude sounding balloon. Credit: LASP

This month, a team of international scientists has been involved in a carefully coordinated campaign to study how the Asian summer monsoon—one of the largest and most important meteorological patterns in the world—affects atmospheric chemistry and global climate. Two research groups from the Laboratory for Atmospheric and Space Physics (LASP) at the University of Colorado Boulder are assisting with this effort.

The Asian Summer Monsoon Chemical and CLimate Impact Project (ACCLIP) is supported by the U.S. National Science Foundation (NSF) and is being co-led by NSF’s National Center for Atmospheric Research (NCAR) and NASA. It is based out of the Osan U.S. Air Base in South Korea and involves two research aircraft.

While the monsoon is most often associated with the deluge of moisture it brings to the Asian continent, the ACCLIP research is not focused on the rain that comes down. Instead, the participating scientists are interested in what the powerful circulation of the monsoon pulls back up. Since the monsoon occurs over some of the regions with the worst air quality in the world, scientists think a wide range of pollutants may get sucked high into the atmosphere. The resulting redistribution of chemicals—and their reactions with one another—can have a significant impact on the climate.

 “In recent decades, satellites have revealed that the monsoon creates a distinct layer of chemicals about 10 miles above the Earth, but we know very little about its composition and evolution,” said NCAR scientist Laura Pan, an ACCLIP principal investigator. “ACCLIP gives us an opportunity to sample what’s there, but we know that whatever its composition, it connects to the climate.”

ACCLIP is funded by NSF, NASA, NOAA, and the Office of Naval Research. Additional funding comes from agencies in Europe and Asia. 

Impacts on climate, ozone

ACCLIP’s scientific objectives include an improved understanding of how the Asian summer monsoon transports air from the ground to the top of the troposphere and bottom of the stratosphere miles above Earth’s surface, as well as what chemicals are contained in that air. 

The researchers also want to understand how those chemicals react once they are aloft. For example, some chemical species can transform into aerosols, or tiny particles, once they reach the upper troposphere and lower stratosphere. These aerosols can reflect the Sun’s light back into space, cooling the Earth. Other aerosols, known as “black carbon”, originate from combustion at the surface, and these aerosols absorb the Sun’s radiation and produce a heating effect. Aerosols, as well as water vapor that is also sucked up by the monsoon, can affect cloud formation and brightness, which also impact the climate. The monsoon may also redistribute relatively short-lived greenhouse gases, such as methane, and ozone-depleting substances, such as chlorinated solvents.

Finally, ACCLIP researchers are interested in studying how the pollutants pulled up by the monsoon may affect ozone chemistry in the region of the atmosphere where the protective ozone layer forms. 

To answer these questions, the ACCLIP team is using two research aircraft and high-altitude balloons outfitted with a bevy of scientific instruments. The scientists will also use a group of detailed computer models of chemical transport to guide their flights and test their hypotheses. The results from ACCLIP will ultimately be used to improve these complex models. 

LASP participants

The campaign involves partners from many institutions, including LASP. The ACCLIP balloon team includes four LASP research scientists—Doug Goetz, Lars Kalnajs, Mathew Norgren, and Bruce Kindle—who are making vertical profile measurements of aerosol number concentrations, size distributions, and water vapor concentrations using high-altitude sounding balloons.

During the six-week campaign, the balloon team will launch a total of 20 balloon flights involving four different instrument packages, two of which were designed and built at LASP. According to Kaljnas, these ballooning activities will extend the ACCLIP measurements to altitudes above aircraft flight envelopes to characterize the Asian monsoon’s impact on aerosols from the upper troposphere into the lower stratosphere. 

LASP researchers are also helping to understand which particles the Asian monsoon is injecting into the stratosphere. “Previous work by European scientists has shown that particles rich in ammonia are present above Nepal, and it is a mystery how they got there,” said LASP researcher Brian Toon, who is also a professor in the Atmospheric and Oceanic Sciences department at the University of Colorado Boulder.

Toon’s group is also interested in other aerosols in the upper troposphere and lower stratosphere, which serve as seeds for cirrus clouds. Such clouds are important to the climate, and current models disagree about the abundance of the aerosols they form on. 

Toon’s group is providing daily chemical forecasts for the airplane flight plans and then comparing the resulting data with those forecasts. LASP researcher Yunqian Zhu is helping assess how accurate the forecasts are. “The most exciting thing to me is to see the data fresh from the aircraft,” she said. “This is the first time we know what is actually there for many pollutants. As a model developer, it is exciting and nervous at the same time to know if our model functions well.”

Global participation

The broad participation in ACCLIP—globally, more than 30 institutions are involved in the month-long project—speaks to the strong scientific interest in the project. In fact, researchers, including Pan, have been working for more than a decade to get a field campaign focused on the Asian summer monsoon up and running. These efforts ran into a number of logistical challenges that slowed the effort, including the COVID-19 pandemic. The mission is now moving forward at a U.S. Air Force Base in South Korea.

“For many years, there has been a huge amount of interest in a field campaign to study the Asian summer monsoon because it’s such an important driver of the weather and climate in the northern hemisphere and beyond,” Pan said. “We are thrilled to finally be on our way and grateful to all our institutional partners who have contributed their instruments and expertise to make ACCLIP a success.”

Original article by Laura Snider, NCAR science writer

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