Presented on May 3, 2023, by
Scripps Institution of Oceanography
La Jolla, CA
Atmospheric rivers (ARs) are large-scale moisture transport systems in the atmosphere, commonly associated with an extratropical cyclone. Two key variables are used to characterize ARs and estimate their impact, that is Integrated Vapor Transport (IVT) and Integrated Water Vapor (IWV). This vertically-integrated approach to atmospheric rivers has limitations related to moisture sourced in the tropics, loosely defined as tropical moisture exports (TMEs). Part of the challenge is understanding how tropical convection fits in this vertically-integrated moisture model, and ultimately how it affects the precipitation caused by this large-scale disturbance. Even though the physical mechanisms behind TMEs are not well understood, many researchers have hypothesized that tropical moisture fluxes can exacerbate the hydrologic impact caused by atmospheric rivers, particularly at landfall. In recent years, the concept of moisture quasi-equilibrium (MQE) has elucidated the average behavior of moisture in the tropics, by setting an anti-correlation between vertically integrated moisture (saturation fraction) and moist convective instability, which depends on vertical temperature anomalies. This moisture feedback mechanism, which has proven to perform significantly well in cloud-resolving models and observations of tropical cyclogenesis, is not unique to the tropics. I propose an alternate approach to characterize tropical moisture exports in atmospheric rivers from the perspective of MQE, and its governing role over moisture convergence and precipitation. I will first describe the ideas that led to the development of the MQE concept, as well as the ideas that led to its application as a tool to understand atmospheric rivers. I will then elaborate on my current research, which explores the role played by TMEs in NE Pacific atmospheric rivers that impact the US West Coast. Results in this study show that the TMEs that evolve in moist convectively stable environments have higher column-integrated moisture (saturation fraction) and a higher precipitation rate, in agreement with MQE. A correlation between saturation fraction and precipitation peaks is also observed in the water vapor budget in atmospheric rivers with TMEs. I finally will discuss how the MQE signal can be used as a tool to predict precipitation extremes at landfall, directly attributed to TMEs, in cases such as the Valentines’ Day AR of 2019.
José was born in Honduras. He became interested in meteorology and atmospheric science in 1998, after Hurricane Mitch made landfall in Honduras and destroyed the majority of the country, leaving an aftermath of 10,000 reported deaths. Following his dream of understanding the atmosphere, particularly extreme weather events, he enrolled in the meteorology BS program at the Universidad de Costa Rica, where he and his mentor Dr. Walter Fernandez published a paper on atmospheric lightning distributions in Costa Rica. He then went on to obtain a MS in lightning physics under the advisory of Dr. Richard Sonnenfeld, and a PhD in atmospheric physics under the advisory of Dr. David Raymond, at the New Mexico Institute of Mining and Technology (NMT). While at NMT, José published a paper and wrote a dissertation on the role of tropical dynamics in early summer atmospheric rivers. In 2021, he was brought to Scripps Institution of Oceanography by Dr. Forest Cannon of the Center for Western Weather and Water Extremes (CW3E) to continue investigating the elusive role of the tropics in winter season NE Pacific atmospheric rivers that affect the U.S. West Coast.