The Effect of a Kona Low on the Eastern Pacific Valentine’s Day (2019) Atmospheric River

Abstract A high-impact atmospheric river (AR) event that made landfall on the U.S. West Coast on Valentine’s Day of 2019 and produced widespread flooding in California is examined. The U.S. Naval Research Laboratory cloud resolving and high-resolution Coupled Ocean–Atmosphere Mesoscale Prediction Sy...

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Bibliographic Details
Published inMonthly weather review Vol. 150; no. 4; pp. 863 - 882
Main Authors Chen, Sue, Reynolds, Carolyn A., Schmidt, Jerome M., Papin, Philippe P., Janiga, Matthew A., Bankert, Richard, Huang, Andrew
Format Journal Article
LanguageEnglish
Published Washington American Meteorological Society 01.04.2022
Subjects
Anticyclones
Case studies
Clouds
Cold
Cyclones
Flooding
Landslides & mudslides
Life cycle
Life cycles
Mesoscale phenomena
Precipitation
Rain
Seasons
Surface flow
Vertical wind shear
Water vapor
Water vapour
Weather
Wind shear
Hawaii
United States > US
California
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Summary:Abstract A high-impact atmospheric river (AR) event that made landfall on the U.S. West Coast on Valentine’s Day of 2019 and produced widespread flooding in California is examined. The U.S. Naval Research Laboratory cloud resolving and high-resolution Coupled Ocean–Atmosphere Mesoscale Prediction System (COAMPS) captures the main features impacting the life cycle and structure of the Valentine’s Day AR. Analysis of the model-simulated AR reveals the complex processes leading up to the initial northeastward surge of the water vapor and enhanced near-surface flow associated with this AR. These include the preexistence of a mesoscale cold-core kona low, a mesoscale anticyclone, and a strong low-level convergence in the corridor between the kona low and mesoscale anticyclone where the environment becomes supersaturated in a region of weak vertical wind shear. Model sensitivity experiments show that the eastward progression and magnitude of the AR water vapor surge are strongly sensitive to the magnitude of kona low circulation. Experiments with the kona low circulation amplitude reduced to less than 25% showed that the AR is not able to reach the U.S. West Coast. These results help to identify key new aspects of an important player—the kona low—and its significant contributions to the overall AR characteristics of this particular observed event.
ISSN:0027-0644
1520-0493
DOI:10.1175/MWR-D-21-0182.1