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observed precipitation patterns, given the sensitivity of the density current and bore occurrence to this factor. Other necessary ingredients for successful numerical simulation include the proper simulation of the waveguide, such as a frontal system acting as a horizontal delimiter, and the strength of the low-level jet, which acts as an important mechanism for trapping vertical wave energy propagation. Acknowledgments We express our appreciation to the University Corporation for Atmospheric Research
observed precipitation patterns, given the sensitivity of the density current and bore occurrence to this factor. Other necessary ingredients for successful numerical simulation include the proper simulation of the waveguide, such as a frontal system acting as a horizontal delimiter, and the strength of the low-level jet, which acts as an important mechanism for trapping vertical wave energy propagation. Acknowledgments We express our appreciation to the University Corporation for Atmospheric Research
convection or cold fronts. The virtual Brunt–Väisälä frequency squared N   2 is given by where the gravitational acceleration g = 9.81 m s −2 and Γ = 9.76 K km −1 is the dry adiabatic lapse rate. From the polarization relation and for wave periods of less than several hours, temperature perturbations T  ′ are proportional to changes in Brunt–Väisälä frequency N ( Fritts et al. 1988 ): where u ′ is the horizontal wind perturbation. Thus, we expect that an increase in atmospheric
convection or cold fronts. The virtual Brunt–Väisälä frequency squared N   2 is given by where the gravitational acceleration g = 9.81 m s −2 and Γ = 9.76 K km −1 is the dry adiabatic lapse rate. From the polarization relation and for wave periods of less than several hours, temperature perturbations T  ′ are proportional to changes in Brunt–Väisälä frequency N ( Fritts et al. 1988 ): where u ′ is the horizontal wind perturbation. Thus, we expect that an increase in atmospheric
1. Introduction While our understanding of mountain waves has advanced significantly over the past five decades, the effect of the atmospheric boundary layer (BL) has been largely ignored in most mountain-wave studies (e.g., Scorer 1949 ; Smith 1980 ), partially because the atmospheric BL is considered shallow relative to the depth of the troposphere, and also because it is difficult to include BL processes in analytical approaches. Over recent years, the influence of the atmospheric BL on
1. Introduction While our understanding of mountain waves has advanced significantly over the past five decades, the effect of the atmospheric boundary layer (BL) has been largely ignored in most mountain-wave studies (e.g., Scorer 1949 ; Smith 1980 ), partially because the atmospheric BL is considered shallow relative to the depth of the troposphere, and also because it is difficult to include BL processes in analytical approaches. Over recent years, the influence of the atmospheric BL on
convectively coupled equatorial atmospheric Kelvin wave (CCKW) over the eastern tropical Atlantic. AEWs, the dominant synoptic weather systems observed over Africa and the tropical Atlantic during Northern Hemisphere boreal summer, are westward-propagating tropical waves that grow along the African easterly jet (AEJ) (e.g., Reed et al. 1977 ; Thompson et al. 1979 ; Avila and Pasch 1992 ; Mekonnen et al. 2006 ). Before reaching the coast of West Africa, the AEWs that later develop into tropical cyclones
convectively coupled equatorial atmospheric Kelvin wave (CCKW) over the eastern tropical Atlantic. AEWs, the dominant synoptic weather systems observed over Africa and the tropical Atlantic during Northern Hemisphere boreal summer, are westward-propagating tropical waves that grow along the African easterly jet (AEJ) (e.g., Reed et al. 1977 ; Thompson et al. 1979 ; Avila and Pasch 1992 ; Mekonnen et al. 2006 ). Before reaching the coast of West Africa, the AEWs that later develop into tropical cyclones
extreme precipitation in North America. In Fig. 2 , SSM/I imagery displays a connection in IWV between the flood event across the Pacific Northwest and deep moisture regions within the near-equatorial intertropical convergence zone (ITCZ) over the central Pacific. Such connections have been well documented for atmospheric rivers affecting the west coast of North America (e.g., Ralph et al. 2004 ; Neiman et al. 2008a , b ). Wave energy propagating into the equatorial east Pacific from the
extreme precipitation in North America. In Fig. 2 , SSM/I imagery displays a connection in IWV between the flood event across the Pacific Northwest and deep moisture regions within the near-equatorial intertropical convergence zone (ITCZ) over the central Pacific. Such connections have been well documented for atmospheric rivers affecting the west coast of North America (e.g., Ralph et al. 2004 ; Neiman et al. 2008a , b ). Wave energy propagating into the equatorial east Pacific from the
jet, and Enomoto et al. (2003) referred to it as the Silk Road pattern. Kosaka et al. (2009) showed using empirical orthogonal function (EOF) analysis that the Silk Road pattern is extracted as principal components of the upper-tropospheric atmospheric variability over southern Eurasia based on monthly dataset of the Japanese 25-Year Reanalysis (JRA-25; Onogi et al. 2007 ), indicating that the wave propagation along the Asian jet is one of the essential factors contributing to East Asian
jet, and Enomoto et al. (2003) referred to it as the Silk Road pattern. Kosaka et al. (2009) showed using empirical orthogonal function (EOF) analysis that the Silk Road pattern is extracted as principal components of the upper-tropospheric atmospheric variability over southern Eurasia based on monthly dataset of the Japanese 25-Year Reanalysis (JRA-25; Onogi et al. 2007 ), indicating that the wave propagation along the Asian jet is one of the essential factors contributing to East Asian
et al. 2006 ; Thorncroft et al. 2008 ). These studies have proposed that AEWs are triggered by convection in the entrance region of the AEJ. Thorncroft et al. (2008) suggest that AEWs rely on the presence of intense upstream convective triggers linked to African topography. We argue here that convectively coupled equatorial atmospheric Kelvin waves (CCKWs) can provide such triggers over African topography by providing a favorable environment for convection and wave growth. This concept
et al. 2006 ; Thorncroft et al. 2008 ). These studies have proposed that AEWs are triggered by convection in the entrance region of the AEJ. Thorncroft et al. (2008) suggest that AEWs rely on the presence of intense upstream convective triggers linked to African topography. We argue here that convectively coupled equatorial atmospheric Kelvin waves (CCKWs) can provide such triggers over African topography by providing a favorable environment for convection and wave growth. This concept
divided into three parts: turbulent momentum flux τ t , WC momentum flux τ w , and viscous momentum flux τ υ . Viscous momentum flux is important only in the lowest millimeters of the atmospheric boundary layer ( Smedman et al. 2003 ) and is neglected in this study. The ratio of the WC momentum flux to the total momentum flux decays with height, as indicated by measurements and numerical simulations ( Sullivan et al. 2008 ; Högström et al. 2015 ). Under growing wave conditions, the WC momentum
divided into three parts: turbulent momentum flux τ t , WC momentum flux τ w , and viscous momentum flux τ υ . Viscous momentum flux is important only in the lowest millimeters of the atmospheric boundary layer ( Smedman et al. 2003 ) and is neglected in this study. The ratio of the WC momentum flux to the total momentum flux decays with height, as indicated by measurements and numerical simulations ( Sullivan et al. 2008 ; Högström et al. 2015 ). Under growing wave conditions, the WC momentum
Abatzolglou , J. T. , and G. Magnusdottir , 2006 : Opposing effects of reflective and nonreflective planetary wave breaking on the NAO. J. Atmos. Sci. , 63 , 3448 – 3457 . Austin , P. C. , and J. V. Tu , 2004 : Bootstrap methods for developing predictive models. Amer. Stat. , 58 , 131 – 137 . Chen , G. , and P. Zurita-Gotor , 2008 : The tropospheric jet response to prescribed zonal forcing in an idealized atmospheric model. J. Atmos. Sci. , 65 , 2254 – 2271 . Chen , G. , I
Abatzolglou , J. T. , and G. Magnusdottir , 2006 : Opposing effects of reflective and nonreflective planetary wave breaking on the NAO. J. Atmos. Sci. , 63 , 3448 – 3457 . Austin , P. C. , and J. V. Tu , 2004 : Bootstrap methods for developing predictive models. Amer. Stat. , 58 , 131 – 137 . Chen , G. , and P. Zurita-Gotor , 2008 : The tropospheric jet response to prescribed zonal forcing in an idealized atmospheric model. J. Atmos. Sci. , 65 , 2254 – 2271 . Chen , G. , I
-level wind fields in the intertropical convergence zone (ITCZ) are strongly influenced by convectively coupled propagating waves on synoptic time scales (e.g., Tai and Ogura 1987 ; Lau and Lau 1990 ; Gu and Zhang 2002 ; Roundy and Frank 2004 ; Serra et al. 2008 ), with the dominant synoptic atmospheric disturbances westward-propagating Pacific easterly waves (PEWs; Chang 1970 ; Reed and Recker 1971 ; Nitta et al. 1985 ; Tai and Ogura 1987 ; Lau and Lau 1990 ; Gu and Zhang 2002 ; Serra and
-level wind fields in the intertropical convergence zone (ITCZ) are strongly influenced by convectively coupled propagating waves on synoptic time scales (e.g., Tai and Ogura 1987 ; Lau and Lau 1990 ; Gu and Zhang 2002 ; Roundy and Frank 2004 ; Serra et al. 2008 ), with the dominant synoptic atmospheric disturbances westward-propagating Pacific easterly waves (PEWs; Chang 1970 ; Reed and Recker 1971 ; Nitta et al. 1985 ; Tai and Ogura 1987 ; Lau and Lau 1990 ; Gu and Zhang 2002 ; Serra and
