TY - JOUR
T1 - Understanding the Role of Tropical Moisture in Atmospheric Rivers
AU - Hu, Huancui
AU - Dominguez, Francina
N1 - Funding Information: ; ; ; Support for this study has been provided in part by the National Aeronautics and Space Administration (NASA) grant NNX14AD77G. Any opinions, findings, and conclusions or recommendations expressed in this publication are those of the authors and do not necessarily reflect the views of NASA. Hu is also supported by the U.S. Department of Energy Office of Science Biological and Environmental Research as part of the Regional and Global Climate Modeling program. PNNL is operated for the Department of Energy by Battelle Memorial Institute under contract DE‐AC05‐76RL01830. We also acknowledge the data sets we use in this study: MERRA Reanalysis (Rienecker et al., http://goldsmr2.gesdisc.eosdis.nasa.gov/data/s4pa/MERRA/ ), ERA‐Interim Reanalysis (Dee et al., https://apps.ecmwf.int/datasets/data/interim‐full‐daily/levtype=sfc/ ), and Livneh gridded data set (Livneh et al., ftp://ftp.hydro.washington.edu/pub/blivneh/CONUS/Meteorology.nc.v.1.2.1915.2011.bz2 ). Publisher Copyright: ©2019. American Geophysical Union. All Rights Reserved.
PY - 2019/12/27
Y1 - 2019/12/27
N2 - There has been a long-standing debate about whether tropical moisture transport or local moisture convergence plays the dominant role in the development and strength of atmospheric rivers (ARs). In this work, we quantify the contribution of tropical moisture to 29 simulated extreme ARs that affected the U.S. Northwest Coast by “tagging” tropical moisture from the eastern tropical Pacific using water vapor tracers in the Weather Research and Forecast model. From a case study with strong tropical moisture, we find three mechanisms by which tropical moisture can contribute to AR strength: direct contribution of moisture, indirect contributions via thermodynamic feedbacks, and indirect contributions via synoptic-scale dynamic feedbacks. Focusing on these processes, we divide the 29 simulated ARs into two groups (>25% of direct tropical moisture contribution from the eastern tropical Pacific to inland precipitation as DTM-ARs and the other ARs with <25% as OT-ARs) and find that DTM-ARs are characterized by stronger pre-cold-frontal low-level jets and stronger warm air advection. Notably, the ARs with the greatest 2-day precipitation are found to be DTM-ARs but with <50% tropical moisture contributions, indicating a more dominant role of indirect enhancement of local moisture convergence due to tropical moisture than the direct moisture contribution supplying precipitation.
AB - There has been a long-standing debate about whether tropical moisture transport or local moisture convergence plays the dominant role in the development and strength of atmospheric rivers (ARs). In this work, we quantify the contribution of tropical moisture to 29 simulated extreme ARs that affected the U.S. Northwest Coast by “tagging” tropical moisture from the eastern tropical Pacific using water vapor tracers in the Weather Research and Forecast model. From a case study with strong tropical moisture, we find three mechanisms by which tropical moisture can contribute to AR strength: direct contribution of moisture, indirect contributions via thermodynamic feedbacks, and indirect contributions via synoptic-scale dynamic feedbacks. Focusing on these processes, we divide the 29 simulated ARs into two groups (>25% of direct tropical moisture contribution from the eastern tropical Pacific to inland precipitation as DTM-ARs and the other ARs with <25% as OT-ARs) and find that DTM-ARs are characterized by stronger pre-cold-frontal low-level jets and stronger warm air advection. Notably, the ARs with the greatest 2-day precipitation are found to be DTM-ARs but with <50% tropical moisture contributions, indicating a more dominant role of indirect enhancement of local moisture convergence due to tropical moisture than the direct moisture contribution supplying precipitation.
KW - dynamic and thermodynamic feedbacks
KW - precipitation
KW - tropical moisture
KW - water vapor tracer
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U2 - 10.1029/2019JD030867
DO - 10.1029/2019JD030867
M3 - Article
SN - 2169-897X
VL - 124
SP - 13826
EP - 13842
JO - Journal of Geophysical Research Atmospheres
JF - Journal of Geophysical Research Atmospheres
IS - 24
ER -