Off the Radar: Rivers in the Sky – Understanding Atmospheric Rivers

Episode Release Date: December 3, 2024
Host: Emily Gracey, Meteorologist at The National Weather Desk
Guest: Dr. Marty Ralph, Director of the Center for Western Weather and Water Extremes at the Scripps Institution of Oceanography

Introduction to Atmospheric Rivers

In the December 3, 2024 episode of Off the Radar, Meteorologist Emily Gracey delves into the complex and impactful phenomenon known as atmospheric rivers (ARs). These colossal streams of water vapor significantly influence weather patterns, particularly on the U.S. West Coast, bringing both relief and challenges through heavy rainfall, flooding, and even mudslides.

Defining Atmospheric Rivers

Emily introduces Dr. Marty Ralph, a pivotal figure in atmospheric river research, emphasizing his role in bringing ARs to the forefront of meteorological studies. Dr. Ralph explains:

“It’s literally a river in the sky, but it’s a river of water vapor pushed along by the wind... an average AR is about 500 miles across and a thousand miles long” (06:07).

This definition highlights the immense scale and significance of ARs compared to their terrestrial counterparts.

The Evolution of Atmospheric River Research

Dr. Ralph recounts the history of AR research, noting that although the term emerged in the early 1990s, it wasn't until 2003 that ARs gained substantial attention. His pivotal moment occurred in 1998 during a field campaign called Caljet, where satellite imagery first revealed the pronounced water vapor ribbons characteristic of ARs. Dr. Ralph states:

“In 2003, I noticed the AR paper and it became obvious that this was a super important phenomenon” (01:00).

Recognizing the critical role ARs play in weather systems, Dr. Ralph established the Center for Western Weather and Water Extremes in 2013, expanding the research team to around 100 multidisciplinary experts.

Developing the Atmospheric River Scale

A significant contribution from Dr. Ralph and his team is the creation of a standardized scale to rank atmospheric rivers based on their intensity and duration. Emily inquires about the development process:

“We boiled it down to the duration of the AR and the intensity of it over a point” (14:23).

This scale allows for consistent communication of AR impacts, aiding meteorologists, policymakers, and the public in understanding and preparing for severe weather events. Dr. Ralph elaborates:

“If the duration of the AR is 24 to 48 hours, that would make it an AR3. If it lasts more than 48 hours, we promote it to AR4” (19:31).

Global Presence and Impact

While ARs are most studied on the U.S. West Coast, Dr. Ralph emphasizes their global presence, affecting regions such as Western Canada, Europe, South America, Australia, New Zealand, and Southern Africa. He mentions:

“They produce the majority of flooding in Mediterranean climates” (07:00).

This widespread influence underscores the necessity for comprehensive AR research and forecasting to mitigate both water scarcity and disaster risks.

Atmospheric River Reconnaissance and Data Collection

A cornerstone of advancing AR understanding is the deployment of reconnaissance flights to gather in situ data. Dr. Ralph discusses the evolution of AR reconnaissance missions:

“By 2020, AR Reconnaissance became the core element of the National Winter Season Operations Plan” (29:03).

These missions involve flying specialized aircraft equipped with dropsondes and other sensors to measure water vapor transport and other critical parameters within ARs. Dr. Ralph shares his personal experience flying:

“When you drop the sun through it, it might be pumping away at like 25 Mississippi rivers worth of water vapor transport” (35:31).

Additionally, advancements such as airborne radio occultation and the use of ocean buoys enhance the precision and scope of AR data collection.

Interplay Between Atmospheric Rivers and Climate Phenomena

The conversation explores the relationship between ARs and larger climate patterns like El Niño and La Niña. Contrary to common perceptions, Dr. Ralph points out:

“We really haven’t been able to show that El Niño or La Niña significantly impact ARs” (24:11).

Instead, ARs themselves play a critical role in modifying the typical effects of these climate phenomena, particularly in regions like Southern California.

Atmospheric Rivers and Extreme Weather Events

Dr. Ralph explains the connection between ARs and severe weather, such as bomb cyclones. He notes:

“60% of all bomb cyclones have an antecedent AR present” (45:26).

This relationship underscores ARs as vital contributors to the development and intensification of powerful weather systems, amplifying their impact on affected regions.

Future Directions and Research

Looking ahead, Dr. Ralph emphasizes the ongoing efforts to improve AR forecasting, particularly on subseasonal timescales. Current research focuses on enhancing prediction models to better anticipate AR occurrences weeks in advance, leveraging phenomena like the Madden-Julian Oscillation and the Quasi-Biennial Oscillation.

He concludes with a call to action for early-career scientists to engage in AR research:

“Atmospheric rivers are really important for water in many parts of the world... there’s a lot of opportunity for early career people to get into this field” (43:21).

Conclusion

Emily Gracey's interview with Dr. Marty Ralph provides an in-depth exploration of atmospheric rivers, shedding light on their definition, global significance, and the innovative methods used to study them. Dr. Ralph’s pioneering work has not only advanced scientific understanding but also equipped communities with the knowledge to better prepare for and respond to these powerful atmospheric phenomena. For listeners eager to comprehend the complexities of weather systems beyond the conventional narratives, this episode offers valuable insights and underscores the critical role of atmospheric rivers in shaping our environment.

Notable Quotes:

• Dr. Marty Ralph (06:07): “It’s literally a river in the sky, but it’s a river of water vapor pushed along by the wind... an average AR is about 500 miles across and a thousand miles long.”

• Dr. Marty Ralph (01:00): “In 2003, I noticed the AR paper and it became obvious that this was a super important phenomenon.”

• Dr. Marty Ralph (14:23): “We boiled it down to the duration of the AR and the intensity of it over a point.”

• Dr. Marty Ralph (35:31): “When you drop the sun through it, it might be pumping away at like 25 Mississippi rivers worth of water vapor transport.”

• Dr. Marty Ralph (45:26): “60% of all bomb cyclones have an antecedent AR present.”

• Dr. Marty Ralph (43:21): “Atmospheric rivers are really important for water in many parts of the world... there’s a lot of opportunity for early career people to get into this field.”

For more enlightening discussions on weather, climate, and related topics, follow Off the Radar on Apple Podcasts, Spotify, or your preferred podcast platform.