Evaluating the Meteorological Conditions Associated With Dusty Atmospheric Rivers

January 6, 2022

Recent CW3E PhD graduate student, Dr. Kara Voss, along with co-authors Dr. F. Martin Ralph and Dr. Amato T. Evan (CW3E/Scripps Institution of Oceanography), recently published an article in Journal of Geographic Research: Atmospheres, titled “Evaluating the Meteorological Conditions Associated With Dusty Atmospheric Rivers”. The paper contributes to the goals of CW3E’s 2019-2024 Strategic Plan to support Atmospheric River (AR) Research and Applications by advancing our scientific understanding of the development of dusty ARs.

This study aims to understand the drivers of ARs embedded within dusty environments, or “dusty ARs,” defined by Voss et al. as the top 100 AR days in later winter and early spring (February–April) from 2001 through 2018, compared to ARs in more pristine environments. Dust has the potential to increase precipitation from ARs by initiating ice formation in clouds at relatively warm temperatures. Utilizing an 18-year record of the dust content of AR surroundings combined with satellite, reanalysis, and observational meteorological data, the study investigates the following questions: What meteorological features are associated with dusty ARs a) over dust source regions and b) over the North Pacific, and how do these meteorological features differ from features associated with pristine ARs, defined here as the bottom 100 AR days in late winter and early spring (February–April) when ranked by dust score?

The study finds dusty ARs to be associated with transport of dust from the east Asian coast to North America. Dusty ARs are characterized by conditions that are especially conducive to transport of dust across the Pacific; namely, enhanced mid- to upper-tropospheric westerly winds over Asian dust source regions and over the Pacific. In contrast, ARs in more pristine environments are associated with a persistent ridge over the central Pacific, which blocks zonal westerly flow, as well as continental dust. The study also notes that while trans-Pacific dust is largely confined to the 600–200 hPa levels as it is transported across the Pacific, as it nears the storms impacting the western U.S. this dust flows downward along post-cold frontal isentropic surfaces into the AR environment in the lower troposphere. The conceptual model presented in Figure 1 summarizes the steps in the development of dusty ARs, suggested by Voss et al.’s findings.

While complex questions remain regarding the relative impacts of dusty ARs, this study fills a critical research gap in our understanding of these events, offering insight to the conditions and drivers that lead to their development.

Figure 1: Conceptual model of the development of a dusty AR. The mustard yellow meandering arrow represents transported dust. The blue and red circles represent high and low mid- and upper-level geo-potential heights, respectively, and the broken blue arrows indicate the direction of movement of the trough. The blue solid arrow represents the North Pacific Jet. The panel in the top right corner represents forced descent of dust from near 400 hPa to 800 hPa across the cold-frontal region of the extra-tropical cyclone.

Voss, K. K., Evan, A. T., & Ralph, F. M. (2021). Evaluating the meteorological conditions associated with dusty atmospheric rivers. Journal of Geophysical Research: Atmospheres, 126, e2021JD035403. https://doi. org/10.1029/2021JD035403