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The severe storm lasted for over five days in California. The strong atmospheric river hit land, causing intense winds and heavy rain that uprooted trees, flooded streets, and caused mudslides in residential areas.

The storm presented an opportunity for scientists to deploy instruments that measure atmospheric rivers. They were prepared on land and in-flight and used tools attached to parachutes or balloons to collect data directly from the storm’s path.

These compact yet powerful gadgets offer crucial data that can enhance weather predictions, especially with the increasing threat of severe storms due to the climate crisis.

Atmospheric rivers have long been important features of weather systems across the US west and are vital to replenishing the state’s reservoirs and snowpack. But filled with enough moisture to rival flows at the mouth of the Mississippi – and often many times more – the strong systems that carry water across the Pacific also often cause the most destructive floods.

The warming of oceans is intensifying storms, resulting in more danger and higher costs. The recent storms caused the deaths of nine individuals, approximately $11 billion in damage and economic loss, and Los Angeles received half of its yearly rainfall in just a few days.

At present, researchers are hurrying to gain a deeper understanding of these systems before they escalate. This effort is significantly improving the precision of weather forecasts, providing water authorities with more lead time to strategize and allowing communities to receive advance alerts in preparation for darker clouds looming overhead. However, there is still much to be discovered about these systems, particularly as their threats continue to increase.

In the past 30 years, there has been a significant increase in the study of water vapor plumes in the tropical Pacific known as “atmospheric rivers”. Despite this, predictions of where a storm will hit land are still often inaccurate by hundreds of miles, and it remains challenging to forecast the behavior of specific storms.

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Researchers are attempting to decipher the intricate and complex interactions between the ocean, atmosphere, and land, with the goal of gaining greater understanding of when and where storms may occur.

Maike Sonnewald, the head of the computational climate and ocean group at UC Davis, stated that as our knowledge grows, we realize the necessity for additional data on this topic.

Sonnewald, a scientist who combines computer science with oceanography to better understand climate and predict long-term weather patterns, notes that advancements in satellite technology have provided a glimpse into the complex relationship between the ocean and the atmosphere. However, this picture is still incomplete.

According to her, our resolution may not be sufficient for modeling specific details. She further elaborated that the ever-changing nature of the ocean and the significant impact small changes can have on the models make prediction difficult.

“The Earth’s climate is undergoing changes, resulting in increased temperatures, and this is a well-known fact. However, it is the specific details that are difficult to determine,” stated Sonnewald. As the atmosphere warms, it has the ability to hold a significantly larger amount of water vapor, and as the ocean surface temperatures rise, evaporation will occur at a faster rate. This allows scientists to make relatively accurate predictions about how conditions will worsen in the future. The challenge lies in pinpointing when and where these changes will occur.

Within the weather disturbances

Prior to the storm’s arrival, it was evident that it would be strong. As it approached, officials were able to prepare resources and alert residents due to the available data.

According to Alex Lamers, the warning coordination meteorologist for the Weather Prediction Center, global models used by scientists for forecasting are effective in detecting the possibility of a significant storm several days ahead. However, the details of the storm are not clear until it is close.

Lamers emphasized the importance of specific details regarding the intersection of the storm with the coast, the specific mountain ranges affected, and the angle and impact of winds on the mountains and upslope areas.

Satellites have limitations in providing complete information about the ocean. According to the speaker, the Pacific Ocean has a large area and lacks sufficient weather data.

Hence, a group of researchers, headed by Martin Ralph, the original director of the center for western weather and water extremes at the Scripps Institution of Oceanography, initiated collecting data from within the storm systems.

Starting in 2016, the AR recon program has utilized US air force planes, nicknamed “hurricane hunters,” to deploy dropsondes. These instruments are dropped from the plane and collect data as they descend through the atmosphere and into the ocean.

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Each dropsonde is attached to a compact parachute and travels through the sky before landing in the ocean, completing its journey in about 20 minutes. During this time, it provides crucial data to the scientists on board. The dropsondes gather information such as air temperature, pressure, water vapor, and wind speed, acting as an “MRI for an atmospheric river” according to Ralph. This allows researchers to gain a deeper understanding of the system rather than solely relying on satellite images.

In 2023, California experienced a succession of powerful atmospheric river storms. The use of dropsondes improved predictions of intense rainfall by approximately 12%, a feat that would have taken eight more years with conventional methods of data collection, according to researchers.

Ralph emphasized the significance of accurately predicting the strength, location, structure, and water content of an atmospheric river in the model. Any mistakes in these factors can lead to inaccurate forecasts in the future. He also stressed the importance of physically measuring atmospheric rivers in their exact locations.

In addition to the use of parachuting dropsondes, radiosondes, which are traditional weather balloons launched from the ground during storms, also play a crucial role in obtaining a complete understanding of the weather. According to Ralph, while these methods may differ, both are necessary for a highly accurate prediction system.

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The team is using novel technology, such as ARO (airborne radio occultation) developed by Jennifer Haase, a geophysicist and atmospheric scientist at Scripps. Unlike dropsondes that collect data while falling directly below the aircraft, ARO utilizes sensors mounted on the side of the plane to gather horizontal measurements. By analyzing the amount of refraction of GPS signals as they pass through the atmosphere, properties like moisture and temperature can be inferred, providing a more comprehensive understanding of approaching storms.

The initial flights utilizing ARO technology were launched during the winter season, and successfully gathered information from a maximum distance of 186 miles (300km) from the aircraft.

Mitigating the worst disasters

The danger of floods is increasing in California and other areas of the dry American west. Having more accurate information will be crucial in reducing the impact of catastrophic events.

According to Alex Hall, a climate scientist and atmospheric physicist at UCLA, based on the current level of warming, we anticipate that large precipitation events will be approximately 10% more powerful than before the introduction of greenhouse gases into the atmosphere.

“In the future, if we experience double the amount of current warming, there is a frightening possibility that events will be 20% stronger and there may even be new types of events that currently do not exist.”

Ralph sees this situation as a call to take action.

He stated that our advancements in AR reconnaissance and related methods for tracking and forecasting atmospheric rivers will be able to adapt to the ever-changing nature of these storms. This is crucial for mitigating the effects of climate change and helping humans adapt to the changing conditions.

Source: theguardian.com