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Atmospheric rivers over eastern US affected by Pacific/North America pattern

March 12th, 2024

Key Findings

  • A significant increase in atmospheric river (AR) frequency is shown during wintertime over the Eastern U.S. in the past four decades.
  • The increase in AR frequency is linked to recent changes in the Pacific/North American teleconnection pattern, accompanied by a poleward shift of the midlatitude jet stream.
  • The linkage between AR frequency and the Pacific/North American teleconnection pattern has been verified in model simulations and has proven effective in predicting AR frequency at both monthly and seasonal scales.

Wenhao Dong, Ming Zhao, Zhihong Tan, V. Ramaswamy. Science Advances. DOI: 10.1126/sciadv.adj332

There is a growing awareness that atmospheric river (AR) activities are responsible for a wide range of environmental and socioeconomic impacts on the West coast of the U.S. The related heavy rainfall, snowfall, and associated floods, especially during winter, have been a focus of many previous studies. This research investigates the impact of AR on the Eastern U.S. (EUS).

ARs in the EUS remain relatively understudied, despite their frequent occurrence and substantial contribution to heavy precipitation and high-impact weather events. The authors examined wintertime AR frequency over the EUS during the past four decades, using multiple observations and a state-of-art high-resolution climate model (AM4) developed at GFDL. These results show that there is a significant increase in AR frequency over EUS during this period.

The increased AR frequency is principally related to the recent changes in the Pacific/North America (PNA) teleconnection pattern, accompanied by a poleward shift of the midlatitude jet stream. Model simulations, using GFDL’s AM4, well capture the observed mean AR and circulation features but fail to simulate their respective trends. Nonetheless, their linkages with the PNA pattern are verified across different realizations, highlighting the critical role of the PNA pattern in regulating the AR variability.

The features of ARs and their hydroclimatic impacts in the EUS remain relatively understudied despite their frequent occurrence there. The linkage identified by the authors between the PNA pattern and AR frequency has important implications for seasonal to subseasonal forecasting of AR and related precipitation over EUS.

Figure 1. a. One typical winter atmospheric river event over the eastern US. Shading shows the integrated vapor transport while vectors represent its meridional and zonal components. b. Winter-mean AR frequency (contour; units: fraction of time) and its linear trend (shading; units: fraction of time per decade) during 1980–2020. c. Correlation map between winter PNA index and winter AR frequency during 1980–2020.. Stipping in (b) and (c) denotes regions with linear trend and correlation coefficient significant at the 95% confidence level.