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Atmospheric rivers (ARs) bring concentrated rainfall and flooding to the western United States (US) and are hypothesized to have supported sustained hydroclimatic changes in the past. However, their ephemeral nature makes it challenging to document ARs in climate models and estimate their contribution to hydroclimate changes recorded by time-averaged paleoclimate archives. We present new climate model simulations of Heinrich Stadial 1 (HS1; 16,000 years before the present), an interval characterized by widespread wetness in the western US, that demonstrate increased AR frequency and winter precipitation sourced from the southeastern North Pacific. These changes are amplified with freshwater fluxes into the North Atlantic, indicating that North Atlantic cooling associated with weakened Atlantic Meridional Overturning Circulation (AMOC) is a key driver of HS1 climate in this region. As recent observations suggest potential weakening of AMOC, our identified connection between North Atlantic climate and northeast Pacific AR activity has implications for future western US hydroclimate.
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This content will become publicly available on December 16, 2026
Adaptive Sampling of the Upper Ocean by Autonomous Floats During Atmospheric River Precipitation
Atmospheric rivers (ARs) are elongated structures in the atmosphere that transport water vapor from the tropics to mid‐ and high‐latitudes in highly episodic events. ARs are a major source of precipitation in the western United States and many other regions of the world and play a role in air‐sea exchanges of heat and freshwater in the subtropics. For the first time, an experiment was designed to observe (open) ocean changes during AR precipitation, using profiling floats in the northeast subtropical Pacific. Results show upper ocean freshening and cooling with AR precipitation (lasting several hours), especially when surface winds are low ( m/s). ARs contribute 70%–90 of the total winter precipitation in the subtropical northeast Pacific: a salt budget analysis (using ECCO) shows that precipitation over winter is the main driver of ocean freshening in the top 25–30 m and contributes by to the integrated changes in the top m.
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- PAR ID:
- 10711947
- Publisher / Repository:
- Wiley
- Date Published:
- Journal Name:
- Geophysical Research Letters
- Volume:
- 52
- Issue:
- 23
- ISSN:
- 0094-8276
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Atmospheric rivers (ARs) bring concentrated rainfall and flooding to the western United States (US) and are hypothesized to have supported sustained hydroclimatic changes in the past. However, their ephemeral nature makes it challenging to document ARs in climate models and estimate their contribution to hydroclimate changes recorded by time-averaged paleoclimate archives. We present new climate model simulations of Heinrich Stadial 1 (HS1; 16,000 years before the present), an interval characterized by widespread wetness in the western US, that demonstrate increased AR frequency and winter precipitation sourced from the southeastern North Pacific. These changes are amplified with freshwater fluxes into the North Atlantic, indicating that North Atlantic cooling associated with weakened Atlantic Meridional Overturning Circulation (AMOC) is a key driver of HS1 climate in this region. As recent observations suggest potential weakening of AMOC, our identified connection between North Atlantic climate and northeast Pacific AR activity has implications for future western US hydroclimate.more » « less
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