October 6, 2022

Does air pollution make thunderstorms stronger? The goal of the project is to discover

Does air pollution make thunderstorms stronger? The goal of the project is to discover

The rotating radar monitors moving clouds

A rotating radar monitors cloud activity, hoping to image a gathering storm from birth to dissipation. Images: Scott Collis

The sky outside was extremely dark and threatened to rain at any moment – the perfect backdrop for a chat about thunderstorms with Markus van Lier-Valky via Zoom.

Van Lier-Valky He studies clouds and precipitation at the Columbia School of Climate Climate Systems Research Center and NASA’s Goddard Institute for Space Studies. He focuses on the complex interactions of tiny particles and microphysics within clouds that can lead to rain, hail, lightning, and tornadoes.

On stormy days like this, she still feels an inner thrill — “I still think, ‘Oh, thunder!'” she says. – but he also keeps an eye on the weather forecast. A tablet displaying radar data appears briefly on the zoom screen.

Although Van Leer Valky usually works with weather and climate models on computers, he recently returned from field work near Houston, Texas, where he is on a Department of Energy-funded project deploying radar, lidar, radiometers, Aerosol measurements, drones, and a lightning mapping array for studying thunderstorms. The project, called Tracing Aerosol Convection Interactions Experiment (TRACER), in order to improve weather and climate forecasting, aims to understand how thunderstorms form and how particles from air pollution affect their strength and life cycle.

Some research has shown that air pollution makes hurricanes stronger, but it’s a source of contentious debate among scientists.

In the following Q&A, edited for length and clarity, Van Leer-Valky shares more about the project and how she got involved.

A researcher with boy and anvil clouds

Markus van Lier-Valky and his son Oliver visited the field research site in June. In the background, anvil clouds are gathering. Anvils, which are composed of ice particles, form at the upper levels of thunderstorms. Photo: Scott Collis

What are the big questions TRACER is trying to answer?

We’re investigating how aerosols—so, dust and particulate matter—affect the way thunderstorms behave and evolve. The Houston area is a great place to study this because you have this relatively clean air coming in from the bay, and you have a big source of pollution in the Houston metropolitan area and all the companies that refine petrochemicals there, so we can get hurricanes. Let’s compare. It occurs in polluted air versus less polluted air.

Power plant with clouds above

Accumulation of Clouds Over Petrochemical Facilities The TRACER project is investigating how particles from facilities like these affect hurricanes. Photo: Markus van Lier-Valky

Our project revolves around understanding more precisely what happens inside real thunderstorms and trying to come up with the best possible model to compare it to. And then looking at where the differences are and how that might tell us what aspects we don’t understand as well as we think and where we can improve.

Why do we not already understand the role of aerosols?

Much of the advanced radar work has focused on tornadoes, because they cause more damage than simpler, milder thunderstorms, and how their vertical motions develop and interact with cloud particles and precipitation. Less focus has been on gaining observational insight into the fine-grained details of how ice particles interact as they grow and collide with other particles in the atmosphere and how this affects, for example, lightning and electrification and the subsequent evolution of the storm system.

Can studying regular thunderstorms also help us understand tornadoes?

Certainly, there must be that knock-on effect. The better we can understand the microphysics—basically how cloud droplets grow, how they collide to form rain, how liquid particles begin to freeze—the better we can build our predictive models. And ideally, we’d be better able to issue severe weather warnings.

One of the things about microphysics is that when you turn water vapor into a liquid, you release energy. When you freeze a liquid into ice, you release energy. And it is this energy that drives these storms and the strong circulations associated with them. So you have to get these right in the models.

UAV images from the field research site

GoPro footage of TRACER instruments deployed in a field near Houston, TX. Credit: Scott Collis

What is your role in the TRACER project?

Along with Eric Bruning and Kelsey Bruner of Texas Tech University, we proposed deploying additional lightning mapping array sensors. These antennas basically detect the electrical signal produced by the lightning discharge. You have a number of these around an area and they can pinpoint the exact location and time where the discharge is occurring. Even when it’s covered by clouds, you can actually see through the clouds and see exactly how that branch came out.

Lightning is related to the microphysics within the storm — what size ice particles are produced, how many of them are produced — which is related to the rate of atmospheric charging and how much lightning actually occurs.

Some people hypothesized that airborne particles make lightning much stronger. There has been a lot of discussion about this. My colleagues found that although aerosol particles don’t actually affect the strength of updrafts, they do affect the microphysical details of the updraft—changing the size of the cloud and the rain particles it produces. And what that means for lightning is that the size of the ice crystals that may be produced there—the ice crystals that then interact with supercooled water to produce these charging effects—can change significantly. And so even if we don’t see the effect of aerosols on the strength of thunderstorms, we’re kind of in a good position to look at the effects on the fine microphysics that might affect lightning and other features that we see with radar. .

We received funding to add antennas to the existing lightning mapping array in the Houston area, which will improve the accuracy of the network. There is also a lightning modeling component led by Toshi Matsui at Goddard Space Flight Center in Maryland. Most cloud simulations don’t include microphysical charging processes, but this one actually looks at where charging occurs and the simulated cloud carries that charge around and then discharges it to simulate lightning.

Long antenna in a field

Along with his colleagues, van Lier-Valky helped expand the regional lightning mapping array to better understand how air pollution can affect lightning. Photo: Scott Collis

What were you doing when you were on site in June?

I participated in a bit of forecasting efforts. On any given day, the team decides whether or not to release additional sonic balloons to obtain atmospheric conditions, as well as switch the radars to a tracking mode that essentially tracks lightning as it moves. This decision needs to be predicted. So we run our model every day to help with forecasting efforts.

In addition, I was basically a tourist, learning about different aspects of the project. This is my first time in a field campaign, so it was really exciting for me to just get in the field and see what other groups are doing. I visited groups that launched drones. A team from the University of Colorado flew an airplane that flew back and forth along a track to observe horizontal differences in atmospheric conditions. There was also a coptersonde that went up and down in the atmosphere to get details of the lower atmosphere.

Two people with a weather balloon and a probe

Oliver releases a weather balloon with tools hanging below. Photo: Scott Collis

What happens when a storm comes?

There wasn’t much of a storm when I was there, but I did see pictures of one of the groups sheltering under one of their tents when the rain caught them. They must shut down helicopter flights and drones when it occurs to protect their equipment and avoid flying in low visibility. Things like radar, they just keep scanning endlessly.

What happens after the TRACER project?

The field campaign runs until the end of September, and then we start sifting through the mountains of data we’ve collected, running simulations and trying to make sense of the observations. In particular, what we are interested in are cases where we have recorded a thunderstorm from its inception until it dissipates. It would be really great if we could get a certain number of them in relatively clean and unpolluted conditions. So we really need to go through all this data and see what’s there and then adjust the simulations.

What else are you currently working on?

A big part of what I do is developing a new approach to modeling microphysics or clouds and precipitation. Most climate models include certain assumptions about how liquid droplets behave and how their population evolves. Some things are kind of hard to fit into the model and it makes progress a little difficult because in some cases, when you make an approximation or assumption in a weather or climate model, you lose track of it. . You kind of forget you did it, but the uncertainties remain and the effects of that uncertainty remain. So it kind of goes back and says, well, where did that come from? Can we quantify these uncertainties and can we reduce them in a systematic way?

Instead of assumptions, we let observations directly constrain the physics. We consider the minimum Previous information and trying to build it from the ground up to try to get rid of some of the structural fallacies that we think are hindering science. It was funded by the Department of Energy to include in its climate model. We have also received funding from NASA to include it in our two climate models and the National Center for Atmospheric Research Community’s atmospheric model.

It is important to get these things right in climate models. For example, stratocumulus clouds are very important to climate. They are completely liquid clouds that are strongly affected by microscopic events. I saw a recent paper that suggested that these clouds may disappear with a certain degree of warming, which is one of those climate feedbacks that accelerates warming. If you remove them, you remove one of the Earth’s most powerful cooling mechanisms. And if that’s true, then it’s really bad news. We need to make sure our cloud microphysics models are as good as possible, and try to better quantify the remaining uncertainties to refine our expectations for the future effects of global warming.


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