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concludes with further discussion in section 5 . 2. Theoretical considerations How can we, then, explain the MJO in terms the dry dynamics? Under the linear limit, the large-scale tropical atmospheric dynamics consists of a set of the equatorial waves ( Matsuno 1966 ; Yano and Bonazzola 2009 ). Thus, if the MJO is to be explained in terms of the linear dynamics, it must be explained in terms of the slowest-propagating equatorial planetary-scale waves: the Kelvin or the Rossby wave. At first sight, the
concludes with further discussion in section 5 . 2. Theoretical considerations How can we, then, explain the MJO in terms the dry dynamics? Under the linear limit, the large-scale tropical atmospheric dynamics consists of a set of the equatorial waves ( Matsuno 1966 ; Yano and Bonazzola 2009 ). Thus, if the MJO is to be explained in terms of the linear dynamics, it must be explained in terms of the slowest-propagating equatorial planetary-scale waves: the Kelvin or the Rossby wave. At first sight, the
; Powell and Houze 2015a ; Zhang et al. 2017 ; Chen and Zhang 2019 ). Evidence is accumulating to indicate that such planetary Kelvin waves are linked to a large class of MJOs that initiate over the Indian Ocean ( Kikuchi and Takayabu 2003 ; Matthews 2008 ; Haertel et al. 2015 ; Powell and Houze 2015a ). It is postulated that the Kelvin waves force anomalous lifting, thereby reducing large-scale subsidence and promoting midtropospheric moistening and cloud development during the onset phases of
; Powell and Houze 2015a ; Zhang et al. 2017 ; Chen and Zhang 2019 ). Evidence is accumulating to indicate that such planetary Kelvin waves are linked to a large class of MJOs that initiate over the Indian Ocean ( Kikuchi and Takayabu 2003 ; Matthews 2008 ; Haertel et al. 2015 ; Powell and Houze 2015a ). It is postulated that the Kelvin waves force anomalous lifting, thereby reducing large-scale subsidence and promoting midtropospheric moistening and cloud development during the onset phases of
–Julian Oscillation, Kelvin wave, and equatorial Rossby wave . J. Atmos. Sci. , 64 , 4400 – 4416 . Molinari , J. , and D. Vollaro , 2000 : Planetary- and synoptic-scale influences on eastern Pacific tropical cyclogenesis. Mon. Wea. Rev., 128, 3296–3307 . Nakazawa , T. , 1988 : Tropical super clusters within intraseasonal variations over the western Pacific . J. Meteor. Soc. Japan , 66 , 823 – 839 . Ray , P. , and C. Zhang , 2010 : A case study of the mechanics of extratropical influence
–Julian Oscillation, Kelvin wave, and equatorial Rossby wave . J. Atmos. Sci. , 64 , 4400 – 4416 . Molinari , J. , and D. Vollaro , 2000 : Planetary- and synoptic-scale influences on eastern Pacific tropical cyclogenesis. Mon. Wea. Rev., 128, 3296–3307 . Nakazawa , T. , 1988 : Tropical super clusters within intraseasonal variations over the western Pacific . J. Meteor. Soc. Japan , 66 , 823 – 839 . Ray , P. , and C. Zhang , 2010 : A case study of the mechanics of extratropical influence
1. Introduction The tropical atmosphere consists of weather systems spanning a wide range of spatial and temporal scales. At the planetary scale, the Madden–Julian oscillation (MJO) is found to be the dominant mode of intraseasonal variability with typical periods of 20–100 days ( Madden and Julian 1971 , 1972 ; Zhang 2005 ). The active phase of an MJO is characterized by enhanced deep convection and intense precipitation that propagates eastward at a speed around 5 m s −1 . Within the MJO
1. Introduction The tropical atmosphere consists of weather systems spanning a wide range of spatial and temporal scales. At the planetary scale, the Madden–Julian oscillation (MJO) is found to be the dominant mode of intraseasonal variability with typical periods of 20–100 days ( Madden and Julian 1971 , 1972 ; Zhang 2005 ). The active phase of an MJO is characterized by enhanced deep convection and intense precipitation that propagates eastward at a speed around 5 m s −1 . Within the MJO
radiation (OLR), confirmed the planetary scale of the MJO ( Weickmann 1983 ; Murakami and Nakazawa 1985 ; Lau and Chan 1986 ; Li and Zhou 2009 ). Studies also show that the oscillation is more broadband than the original 40–50-day period identified by Madden and Julian (1971) and can span a range of 20–100 days (e.g., Krishnamurti and Subrahmanyam 1982 ; Annamalai and Slingo 2001 ; Lau and Waliser 2005 ; Zhang 2005 ; Li and Wang 2005 , Waliser 2006 ). As the most significant variability
radiation (OLR), confirmed the planetary scale of the MJO ( Weickmann 1983 ; Murakami and Nakazawa 1985 ; Lau and Chan 1986 ; Li and Zhou 2009 ). Studies also show that the oscillation is more broadband than the original 40–50-day period identified by Madden and Julian (1971) and can span a range of 20–100 days (e.g., Krishnamurti and Subrahmanyam 1982 ; Annamalai and Slingo 2001 ; Lau and Waliser 2005 ; Zhang 2005 ; Li and Wang 2005 , Waliser 2006 ). As the most significant variability
wave-CISK propagate faster than the MJO, and the shortest waves are the most unstable to wave-CISK ( Hendon 2005 ). Frictional wave-CISK predicts slower waves destabilized by boundary layer moist static energy convergence. Convectively coupled equatorial Kelvin, Rossby, and inertia–gravity waves are observed with higher frequencies and smaller scales that do not match the planetary scale of the MJO ( Wheeler and Kiladis 1999 ). Quasi-equilibrium models assume that latent heating above precipitation
wave-CISK propagate faster than the MJO, and the shortest waves are the most unstable to wave-CISK ( Hendon 2005 ). Frictional wave-CISK predicts slower waves destabilized by boundary layer moist static energy convergence. Convectively coupled equatorial Kelvin, Rossby, and inertia–gravity waves are observed with higher frequencies and smaller scales that do not match the planetary scale of the MJO ( Wheeler and Kiladis 1999 ). Quasi-equilibrium models assume that latent heating above precipitation
wave dynamics with a wave–conditional instability of the second kind (wave-CISK)-type parameterization of convective heating (e.g., Lau and Peng 1987 ). The most unstable wave in such a simplified system is normally at a small wavelength, which is different from the observed planetary-scale circulation associated with MJOs. To remedy the scale selection problem, Wang (1988) and Wang and Li (1994) added friction-induced boundary layer convergence in the wave-CISK framework. In the wave
wave dynamics with a wave–conditional instability of the second kind (wave-CISK)-type parameterization of convective heating (e.g., Lau and Peng 1987 ). The most unstable wave in such a simplified system is normally at a small wavelength, which is different from the observed planetary-scale circulation associated with MJOs. To remedy the scale selection problem, Wang (1988) and Wang and Li (1994) added friction-induced boundary layer convergence in the wave-CISK framework. In the wave
Bretherton 2001 ; Tung and Yanai 2002a , b ; Lin et al. 2005 ). Using Doppler radar data, Houze et al. (2000) identified strong midlevel inflow in the stratiform regions of mesoscale convective systems (MCSs) during the westerly onset and in regions of strong westerly winds associated with the Kelvin–Rossby wave pattern. They postulated that the mesoscale inflow transports easterly momentum downward, reducing the westerlies near the surface in the westerly onset region, while in the strong westerly
Bretherton 2001 ; Tung and Yanai 2002a , b ; Lin et al. 2005 ). Using Doppler radar data, Houze et al. (2000) identified strong midlevel inflow in the stratiform regions of mesoscale convective systems (MCSs) during the westerly onset and in regions of strong westerly winds associated with the Kelvin–Rossby wave pattern. They postulated that the mesoscale inflow transports easterly momentum downward, reducing the westerlies near the surface in the westerly onset region, while in the strong westerly
MJO and high-frequency tropical wave modes are discussed in section 5 and conclusions summarized in section 6 . 2. Model description The baseline code used for all simulations is the prototype version of SPCAM, version 3.0, as archived [ https://svn.sdsc.edu/repo/cmmap/cam3_sp (rev. 80)] by the Center for Multiscale Modeling of Atmospheric Processes. The global scale is represented by a version of CAM that slightly predates the CAM3.0 release. Global dynamics are formulated spectrally, with a
MJO and high-frequency tropical wave modes are discussed in section 5 and conclusions summarized in section 6 . 2. Model description The baseline code used for all simulations is the prototype version of SPCAM, version 3.0, as archived [ https://svn.sdsc.edu/repo/cmmap/cam3_sp (rev. 80)] by the Center for Multiscale Modeling of Atmospheric Processes. The global scale is represented by a version of CAM that slightly predates the CAM3.0 release. Global dynamics are formulated spectrally, with a
a role in alternate theories for convective organization, including those based on frictionally driven convergence ( Wang 1988 ; Seo and Wang 2010 ; Hsu and Li 2012 ), or boundary layer moisture convergence as a Kelvin-wave response ( Wang and Rui 1990 ; Maloney and Hartmann 1998 ; Hsu and Li 2012 ). Here, we are concerned only with the convective–dynamical interactions, not with its application to the MJO or other large-scale circulations at this point. Furthermore, while our initial
a role in alternate theories for convective organization, including those based on frictionally driven convergence ( Wang 1988 ; Seo and Wang 2010 ; Hsu and Li 2012 ), or boundary layer moisture convergence as a Kelvin-wave response ( Wang and Rui 1990 ; Maloney and Hartmann 1998 ; Hsu and Li 2012 ). Here, we are concerned only with the convective–dynamical interactions, not with its application to the MJO or other large-scale circulations at this point. Furthermore, while our initial
