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1. Introduction Diurnal warm layers (DWLs) form when strong solar radiation and weak-to-moderate winds allow near-surface stratification to develop. In the tropics DWLs appear around 0800 local time (LT), which is 1–2 h after sunrise, as the surface heat flux changes from net ocean cooling to net warming ( Martin 1985 ; Fairall et al. 1996 ; Moulin et al. 2018 ). Heat and momentum trapped in this stratified layer cause sea surface temperature (SST) anomalies of O (0.1–1°C) and near
1. Introduction Diurnal warm layers (DWLs) form when strong solar radiation and weak-to-moderate winds allow near-surface stratification to develop. In the tropics DWLs appear around 0800 local time (LT), which is 1–2 h after sunrise, as the surface heat flux changes from net ocean cooling to net warming ( Martin 1985 ; Fairall et al. 1996 ; Moulin et al. 2018 ). Heat and momentum trapped in this stratified layer cause sea surface temperature (SST) anomalies of O (0.1–1°C) and near
suggests that one single mechanism may not be able to explain the phenomenon in any given region (let alone across the tropics). Closely tied to the activity of the ASM is the boreal summer intraseasonal oscillation (BSISO). A warm-season analog to the boreal winter Madden–Julian oscillation (MJO), the BSISO consists of a convective envelope propagating from the Indian Ocean to the west Pacific (BSISO1; Lee et al. 2013 ; Wang and Xie 1997 ). Associated with this convective envelope is increased cloud
suggests that one single mechanism may not be able to explain the phenomenon in any given region (let alone across the tropics). Closely tied to the activity of the ASM is the boreal summer intraseasonal oscillation (BSISO). A warm-season analog to the boreal winter Madden–Julian oscillation (MJO), the BSISO consists of a convective envelope propagating from the Indian Ocean to the west Pacific (BSISO1; Lee et al. 2013 ; Wang and Xie 1997 ). Associated with this convective envelope is increased cloud
constant, U cr changes by only 0.3 m s −1 for latitudes between 1° and 60° and changes by only 0.5 m s −1 for choices of t between 3 and 7 h. A detailed examination of the sensitivity of Eq. (10) in Fig. 12 shows that within a wide range of plausible input values, U cr is within ±30% of 2.0 m s −1 . Given this limited sensitivity, while also recognizing that variability exists, we consider the 2 m s −1 threshold as a convenient rule of thumb, especially for the tropics, where day length
constant, U cr changes by only 0.3 m s −1 for latitudes between 1° and 60° and changes by only 0.5 m s −1 for choices of t between 3 and 7 h. A detailed examination of the sensitivity of Eq. (10) in Fig. 12 shows that within a wide range of plausible input values, U cr is within ±30% of 2.0 m s −1 . Given this limited sensitivity, while also recognizing that variability exists, we consider the 2 m s −1 threshold as a convenient rule of thumb, especially for the tropics, where day length
1. Introduction Deep convective structures populate the tropics, provide the energetics that drive the large-scale tropical circulation, and interact with superimposed atmospheric waves ( Riehl and Malkus 1957 ; Lorenz 1969 ; Hendon and Liebmann 1991 ; Kiladis and Weickmann 1992 ; Chang 1995 ; Lane et al. 2001 ; Fierro et al. 2009 ). The Madden–Julian oscillation (MJO; Madden and Julian 1971 , 1972 , 1994 ; Zhang 2005 ) is one such disturbance, and while the MJO is commonly defined
1. Introduction Deep convective structures populate the tropics, provide the energetics that drive the large-scale tropical circulation, and interact with superimposed atmospheric waves ( Riehl and Malkus 1957 ; Lorenz 1969 ; Hendon and Liebmann 1991 ; Kiladis and Weickmann 1992 ; Chang 1995 ; Lane et al. 2001 ; Fierro et al. 2009 ). The Madden–Julian oscillation (MJO; Madden and Julian 1971 , 1972 , 1994 ; Zhang 2005 ) is one such disturbance, and while the MJO is commonly defined
tropical area would imply if precipitation were distributed evenly ( Bergemann et al. 2015 ; Ogino et al. 2016 ). Yang and Slingo (2001) found a striking tendency toward offshore propagation of the diurnal cycle across the global tropics. Their hypothesis originally proposed that this propagation was due to diurnally generated gravity waves radiating away from land. This idea has been supported by successive papers, showing very regular patterns of offshore propagation likely due to a gravity wave
tropical area would imply if precipitation were distributed evenly ( Bergemann et al. 2015 ; Ogino et al. 2016 ). Yang and Slingo (2001) found a striking tendency toward offshore propagation of the diurnal cycle across the global tropics. Their hypothesis originally proposed that this propagation was due to diurnally generated gravity waves radiating away from land. This idea has been supported by successive papers, showing very regular patterns of offshore propagation likely due to a gravity wave
ASM is likely modulated by other phenomena at shorter time scales ( Wheeler and McBride 2005 ). While earlier studies have identified the positive contribution by the KWs to the summer monsoon onset over India ( Flatau et al. 2003 ) and SCS ( Straub et al. 2006 ), the potential influence of the KWs on the ASM onset is less discussed. Most studies of the synoptic and subseasonal variability in the tropics focused on the activity of the MJO ( Waliser et al. 2006 ; Zhu et al. 2014 ). The month of
ASM is likely modulated by other phenomena at shorter time scales ( Wheeler and McBride 2005 ). While earlier studies have identified the positive contribution by the KWs to the summer monsoon onset over India ( Flatau et al. 2003 ) and SCS ( Straub et al. 2006 ), the potential influence of the KWs on the ASM onset is less discussed. Most studies of the synoptic and subseasonal variability in the tropics focused on the activity of the MJO ( Waliser et al. 2006 ; Zhu et al. 2014 ). The month of
findings and Sakaeda et al. (2017) may result from our focus on precipitation over Luzon versus their analysis of TRMM rainfall over all land between 15°S and 15°N. Similarly, their findings related to the MJO and DC over Addu Atoll, Maldives, using rainfall from the S-PolKa radar during the Dynamics of the MJO (DYNAMO) field campaign ( Sakaeda et al. 2018 ) may not be valid for other islands within the tropics, especially since several papers have shown that the interaction of the MJO and DC varies
findings and Sakaeda et al. (2017) may result from our focus on precipitation over Luzon versus their analysis of TRMM rainfall over all land between 15°S and 15°N. Similarly, their findings related to the MJO and DC over Addu Atoll, Maldives, using rainfall from the S-PolKa radar during the Dynamics of the MJO (DYNAMO) field campaign ( Sakaeda et al. 2018 ) may not be valid for other islands within the tropics, especially since several papers have shown that the interaction of the MJO and DC varies
. Multiscale Convection-Coupled Systems in the Tropics: A Tribute to Dr. Michio Yanai, Meteor. Monogr. , Vol. 56, Amer. Meteor. Soc., 2.1–2.34, https://doi.org/ 10.1175/AMSMONOGRAPHS-D-15-0013.1 . 10.1175/AMSMONOGRAPHS-D-15-0013.1 Tsai , W.-M. , and C.-M. Wu , 2017 : The environment of aggregated deep convection . J. Adv. Model. Earth Syst. , 9 , 2061 – 2078 , https://doi.org/10.1002/2017MS000967 . 10.1002/2017MS000967 Wang , B. , and Q. Ding , 2008 : Global monsoon: Dominant mode of
. Multiscale Convection-Coupled Systems in the Tropics: A Tribute to Dr. Michio Yanai, Meteor. Monogr. , Vol. 56, Amer. Meteor. Soc., 2.1–2.34, https://doi.org/ 10.1175/AMSMONOGRAPHS-D-15-0013.1 . 10.1175/AMSMONOGRAPHS-D-15-0013.1 Tsai , W.-M. , and C.-M. Wu , 2017 : The environment of aggregated deep convection . J. Adv. Model. Earth Syst. , 9 , 2061 – 2078 , https://doi.org/10.1002/2017MS000967 . 10.1002/2017MS000967 Wang , B. , and Q. Ding , 2008 : Global monsoon: Dominant mode of
convergence in the tropics . J. Atmos. Sci. , 44 , 2418 – 2436 , https://doi.org/10.1175/1520-0469(1987)044<2418:OTROSS>2.0.CO;2 . 10.1175/1520-0469(1987)044<2418:OTROSS>2.0.CO;2 Madden , R. A. , and P. R. Julian , 1971 : Detection of a 40–50 day oscillation in the zonal wind in the tropical Pacific . J. Atmos. Sci. , 28 , 702 – 708 , https://doi.org/10.1175/1520-0469(1971)028<0702:DOADOI>2.0.CO;2 . 10.1175/1520-0469(1971)028<0702:DOADOI>2.0.CO;2 Malkus , J. S. , 1957 : Trade cumulus
convergence in the tropics . J. Atmos. Sci. , 44 , 2418 – 2436 , https://doi.org/10.1175/1520-0469(1987)044<2418:OTROSS>2.0.CO;2 . 10.1175/1520-0469(1987)044<2418:OTROSS>2.0.CO;2 Madden , R. A. , and P. R. Julian , 1971 : Detection of a 40–50 day oscillation in the zonal wind in the tropical Pacific . J. Atmos. Sci. , 28 , 702 – 708 , https://doi.org/10.1175/1520-0469(1971)028<0702:DOADOI>2.0.CO;2 . 10.1175/1520-0469(1971)028<0702:DOADOI>2.0.CO;2 Malkus , J. S. , 1957 : Trade cumulus
.1175/1520-0469(1971)028<0702:DOADOI>2.0.CO;2 Madden , R. A. , and P. R. Julian , 1972 : Description of global-scale circulation cells in the tropics with a 40–50 day period . J. Atmos. Sci. , 29 , 1109 – 1123 , https://doi.org/10.1175/1520-0469(1972)029<1109:DOGSCC>2.0.CO;2 . 10.1175/1520-0469(1972)029<1109:DOGSCC>2.0.CO;2 Mahadevan , A. , G. S. Jaeger , M. Freilich , M. M. Omand , E. L. Shroyer , and D. Sengupta , 2016a : Freshwater in the Bay of Bengal: Its fate and role in air-sea heat exchange
.1175/1520-0469(1971)028<0702:DOADOI>2.0.CO;2 Madden , R. A. , and P. R. Julian , 1972 : Description of global-scale circulation cells in the tropics with a 40–50 day period . J. Atmos. Sci. , 29 , 1109 – 1123 , https://doi.org/10.1175/1520-0469(1972)029<1109:DOGSCC>2.0.CO;2 . 10.1175/1520-0469(1972)029<1109:DOGSCC>2.0.CO;2 Mahadevan , A. , G. S. Jaeger , M. Freilich , M. M. Omand , E. L. Shroyer , and D. Sengupta , 2016a : Freshwater in the Bay of Bengal: Its fate and role in air-sea heat exchange
