TY - JOUR
T1 - Three-dimensional structure of mass-weighted isentropic time-mean meridional circulations
AU - Kanno, Yuki
AU - Iwasaki, Toshiki
N1 - Funding Information:
Acknowledgments. This study is supported in part by the Japanese Ministry of Education, Culture, Sports, Science and Technology through Grant-in-Aid 15H02129 and by the Social Implementation Program on Climate Change Adaptation Technology (SI-CAT). YK is supported by the Japan Society for the Promotion of Science through a Grant-in-Aid for Research Fellows (16J01722). The authors thank Dr. Takenari Kinoshita for kindly providing codes to calculate the PRSD in the 3D TEM framework, Dr. Hidenori Aiki for fruitful discussions, and two anonymous reviewers and Dr. Walter Robinson for their valuable comments that have led to an improved manuscript.
Publisher Copyright:
© 2018 American Meteorological Society.
PY - 2018/6/1
Y1 - 2018/6/1
N2 - The present study develops a diagnostic framework for investigating the three-dimensional (3D) structure of mass-weighted isentropic time-mean (T-MIM) meridional circulations and conducts a preliminary analysis of the winter hemispheres. The T-MIM meridional velocity can unfold, in the zonal direction, time-averaged two-dimensional (2D) mass-weighted isentropic zonal means. Furthermore, the T-MIM velocity can be decomposed into the unweighted isentropic time-mean (uTM) velocity and the temporal eddy-correlated transport velocity, the so-called bolus velocity. The bolus velocity greatly contributes to the 2D extratropical direct circulation in the troposphere and to the Brewer-Dobson circulation in the stratosphere. The 3D bolus velocity seems to reflect the geographical distributions of baroclinic instability wave activity. In the boreal winter, both low-level equatorward flows and upper-level poleward flows are located around the North Pacific and North Atlantic storm tracks. In the austral winter, low-level equatorward flows extend zonally across the midlatitudes. In the subtropics, the 3D bolus velocity is found to be significant in the upper branch of the Hadley circulation. A zonal momentum equation is formulated to examine the 3D momentum balance of the meridional circulation in the T-MIM framework. In the extratropics, the uTM and bolus meridional velocities are in geostrophic balance with the stationary and transient components of the 3D Eliassen-Palm (EP) flux divergence, respectively. The pressure gradient force of transient baroclinic instability waves balances with the low-level equatorward flows of the bolus velocity in the storm tracks.
AB - The present study develops a diagnostic framework for investigating the three-dimensional (3D) structure of mass-weighted isentropic time-mean (T-MIM) meridional circulations and conducts a preliminary analysis of the winter hemispheres. The T-MIM meridional velocity can unfold, in the zonal direction, time-averaged two-dimensional (2D) mass-weighted isentropic zonal means. Furthermore, the T-MIM velocity can be decomposed into the unweighted isentropic time-mean (uTM) velocity and the temporal eddy-correlated transport velocity, the so-called bolus velocity. The bolus velocity greatly contributes to the 2D extratropical direct circulation in the troposphere and to the Brewer-Dobson circulation in the stratosphere. The 3D bolus velocity seems to reflect the geographical distributions of baroclinic instability wave activity. In the boreal winter, both low-level equatorward flows and upper-level poleward flows are located around the North Pacific and North Atlantic storm tracks. In the austral winter, low-level equatorward flows extend zonally across the midlatitudes. In the subtropics, the 3D bolus velocity is found to be significant in the upper branch of the Hadley circulation. A zonal momentum equation is formulated to examine the 3D momentum balance of the meridional circulation in the T-MIM framework. In the extratropics, the uTM and bolus meridional velocities are in geostrophic balance with the stationary and transient components of the 3D Eliassen-Palm (EP) flux divergence, respectively. The pressure gradient force of transient baroclinic instability waves balances with the low-level equatorward flows of the bolus velocity in the storm tracks.
KW - Atmospheric circulation
KW - Cold air surges
KW - Isentropic analysis
KW - Planetary waves
KW - Transport
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U2 - 10.1175/JAS-D-17-0154.1
DO - 10.1175/JAS-D-17-0154.1
M3 - Article
AN - SCOPUS:85048403943
VL - 75
SP - 2029
EP - 2047
JO - Journals of the Atmospheric Sciences
JF - Journals of the Atmospheric Sciences
SN - 0022-4928
IS - 6
ER -