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proposed to explain the distinct seasonality in MJO propagation (e.g., Waliser 2006 ; Wang 2012 ). One traditional view of the eastward propagation of the winter MJO maintains through triggering of new convection to the east by frictional moisture convergence in the planetary boundary layer (PBL) associated with the equatorial Kelvin wave response to the MJO convective heating (e.g., Salby et al. 1994 ; Wang and Li 1994 ; Maloney and Hartmann 1998 ). Meanwhile, past work has suggested that
proposed to explain the distinct seasonality in MJO propagation (e.g., Waliser 2006 ; Wang 2012 ). One traditional view of the eastward propagation of the winter MJO maintains through triggering of new convection to the east by frictional moisture convergence in the planetary boundary layer (PBL) associated with the equatorial Kelvin wave response to the MJO convective heating (e.g., Salby et al. 1994 ; Wang and Li 1994 ; Maloney and Hartmann 1998 ). Meanwhile, past work has suggested that
/phenomena in the tropics (e.g., Neale et al. 2008 ; Lau and Waliser 2011 ; Jin et al. 2013 ; Zhang 2013 ; Kim et al. 2014b ) and the impact extends outside of the tropical region. Anomalous MJO-induced upper-level divergence can generate anomalous Rossby wave source (RWS) by producing divergent flow anomalies in the region of the strong absolute vorticity and its gradient associated with the midlatitude North Pacific westerly jet ( Sardeshmukh and Hoskins 1988 ). Rossby waves excited by the tropical
/phenomena in the tropics (e.g., Neale et al. 2008 ; Lau and Waliser 2011 ; Jin et al. 2013 ; Zhang 2013 ; Kim et al. 2014b ) and the impact extends outside of the tropical region. Anomalous MJO-induced upper-level divergence can generate anomalous Rossby wave source (RWS) by producing divergent flow anomalies in the region of the strong absolute vorticity and its gradient associated with the midlatitude North Pacific westerly jet ( Sardeshmukh and Hoskins 1988 ). Rossby waves excited by the tropical
, 376 – 378 , https://doi.org/10.1038/326376a0 . 10.1038/326376a0 Hayashi , Y. , 1979 : A generalized method of resolving transient disturbances into standing and traveling waves by space-time spectral analysis . J. Atmos. Sci. , 36 , 1017 – 1029 , https://doi.org/10.1175/1520-0469(1979)036<1017:AGMORT>2.0.CO;2 . 10.1175/1520-0469(1979)036<1017:AGMORT>2.0.CO;2 Hendon , H. H. , and M. C. Wheeler , 2008 : Some space–time spectral analyses of tropical convection and planetary-scale waves
, 376 – 378 , https://doi.org/10.1038/326376a0 . 10.1038/326376a0 Hayashi , Y. , 1979 : A generalized method of resolving transient disturbances into standing and traveling waves by space-time spectral analysis . J. Atmos. Sci. , 36 , 1017 – 1029 , https://doi.org/10.1175/1520-0469(1979)036<1017:AGMORT>2.0.CO;2 . 10.1175/1520-0469(1979)036<1017:AGMORT>2.0.CO;2 Hendon , H. H. , and M. C. Wheeler , 2008 : Some space–time spectral analyses of tropical convection and planetary-scale waves
. 2020 ). Thus, an adequate representation of WCBs is desirable in NWP and climate models. First introduced by Browning et al. (1973) and Harrold (1973) , WCBs are defined as cyclone-relative airstreams that ascend from the planetary boundary layer to the upper troposphere along vertically sloping isentropic surfaces. Assuming the absence of nonconservative forces, early studies identified WCBs using cyclone-relative streamlines on a wet-bulb potential temperature surface (e.g., Harrold 1973
. 2020 ). Thus, an adequate representation of WCBs is desirable in NWP and climate models. First introduced by Browning et al. (1973) and Harrold (1973) , WCBs are defined as cyclone-relative airstreams that ascend from the planetary boundary layer to the upper troposphere along vertically sloping isentropic surfaces. Assuming the absence of nonconservative forces, early studies identified WCBs using cyclone-relative streamlines on a wet-bulb potential temperature surface (e.g., Harrold 1973
. Atmos. Sci. , 66 , 1665 – 1683 , https://doi.org/10.1175/2008JAS2806.1 . 10.1175/2008JAS2806.1 Horel , J. , and J. M. Wallace , 1981 : Planetary-scale atmospheric phenomena associated with the Southern Oscillation . Mon. Wea. Rev. , 109 , 813 – 828 , https://doi.org/10.1175/1520-0493(1981)109<0813:PSAPAW>2.0.CO;2 . 10.1175/1520-0493(1981)109<0813:PSAPAW>2.0.CO;2 Hoskins , B. J. , and D. Karoly , 1981 : The steady linear response of a spherical atmosphere to thermal and orographic
. Atmos. Sci. , 66 , 1665 – 1683 , https://doi.org/10.1175/2008JAS2806.1 . 10.1175/2008JAS2806.1 Horel , J. , and J. M. Wallace , 1981 : Planetary-scale atmospheric phenomena associated with the Southern Oscillation . Mon. Wea. Rev. , 109 , 813 – 828 , https://doi.org/10.1175/1520-0493(1981)109<0813:PSAPAW>2.0.CO;2 . 10.1175/1520-0493(1981)109<0813:PSAPAW>2.0.CO;2 Hoskins , B. J. , and D. Karoly , 1981 : The steady linear response of a spherical atmosphere to thermal and orographic
