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experiment with the particular system. Yang et al. (2008b) have briefly shown the improvement in simulating the Asian summer monsoon from resolution T62 to resolution T126 over the Tibetan Plateau and the tropical Indian Ocean, but the discussion was based on the results from two free runs. Achuthavarier and Krishnamurthy (2010) claimed that the improvement in monsoon simulation with model resolution was only marginal. Many of the studies reviewed above have also analyzed the features of monsoons
experiment with the particular system. Yang et al. (2008b) have briefly shown the improvement in simulating the Asian summer monsoon from resolution T62 to resolution T126 over the Tibetan Plateau and the tropical Indian Ocean, but the discussion was based on the results from two free runs. Achuthavarier and Krishnamurthy (2010) claimed that the improvement in monsoon simulation with model resolution was only marginal. Many of the studies reviewed above have also analyzed the features of monsoons
, 1994 : The life cycle of the Madden–Julian oscillation . J. Atmos. Sci. , 51 , 2225 – 2237 . Hendon , H. H. , and M. C. Wheeler , 2008 : Some space–time spectral analyses of tropical convection and planetary-scale waves . J. Atmos. Sci. , 65 , 2936 – 2948 . Kalnay , E. , and Coauthors , 1996 : The NCEP/NCAR 40-Year Reanalysis Project . Bull. Amer. Meteor. Soc. , 77 , 437 – 471 . Kikuchi , K. , and B. Wang , 2010 : Spatiotemporal wavelet transform and the multiscale
, 1994 : The life cycle of the Madden–Julian oscillation . J. Atmos. Sci. , 51 , 2225 – 2237 . Hendon , H. H. , and M. C. Wheeler , 2008 : Some space–time spectral analyses of tropical convection and planetary-scale waves . J. Atmos. Sci. , 65 , 2936 – 2948 . Kalnay , E. , and Coauthors , 1996 : The NCEP/NCAR 40-Year Reanalysis Project . Bull. Amer. Meteor. Soc. , 77 , 437 – 471 . Kikuchi , K. , and B. Wang , 2010 : Spatiotemporal wavelet transform and the multiscale
1. Introduction Convection-coupled waves are an integral part of atmospheric variability in the tropics (e.g., Gruber 1974 ; Takayabu 1994 ; Wheeler and Kiladis 1999 ). Numerous studies have found that they modulate precipitation, atmospheric momentum transport. and tropical cyclone (TC) activity (e.g., Liebmann et al. 1994 ; Lin et al. 2005 ; Bessafi and Wheeler 2006 ). Accurate assessment of climatological wave activity is essential for a complete description of tropical circulation and
1. Introduction Convection-coupled waves are an integral part of atmospheric variability in the tropics (e.g., Gruber 1974 ; Takayabu 1994 ; Wheeler and Kiladis 1999 ). Numerous studies have found that they modulate precipitation, atmospheric momentum transport. and tropical cyclone (TC) activity (e.g., Liebmann et al. 1994 ; Lin et al. 2005 ; Bessafi and Wheeler 2006 ). Accurate assessment of climatological wave activity is essential for a complete description of tropical circulation and
that enters the stratosphere through the tropical tropopause undergoes a freeze-drying process near the CPT ( Brewer 1949 ), the amount of water vapor transported into the stratosphere is highly dependent on thermal characteristics of the CPT ( Holton et al. 1995 ; Mote et al. 1996 ). It is known that small changes in water vapor in the stratosphere can drive significant changes in the climate below by modifying the global radiation budget ( Holton et al. 1995 ; de F. Forster and Shine 1999
that enters the stratosphere through the tropical tropopause undergoes a freeze-drying process near the CPT ( Brewer 1949 ), the amount of water vapor transported into the stratosphere is highly dependent on thermal characteristics of the CPT ( Holton et al. 1995 ; Mote et al. 1996 ). It is known that small changes in water vapor in the stratosphere can drive significant changes in the climate below by modifying the global radiation budget ( Holton et al. 1995 ; de F. Forster and Shine 1999
1. Introduction During ENSO mature winter, the sea surface temperature anomalies (SSTAs) in the tropical Indian Ocean (TIO) evolve to a basin-scale uniform mode, referred to as Indian Ocean basin mode (IOBM) ( Klein et al. 1999 ; Huang and Kinter 2002 ; Krishnamurthy and Kirtman 2003 ). The IOBM is generally seen as a response to ENSO remote forcing ( Klein et al. 1999 ; Venzke et al. 2000 ; Alexander et al. 2002 ; Lau and Nath 2003 ). The warm SSTA in the equatorial central
1. Introduction During ENSO mature winter, the sea surface temperature anomalies (SSTAs) in the tropical Indian Ocean (TIO) evolve to a basin-scale uniform mode, referred to as Indian Ocean basin mode (IOBM) ( Klein et al. 1999 ; Huang and Kinter 2002 ; Krishnamurthy and Kirtman 2003 ). The IOBM is generally seen as a response to ENSO remote forcing ( Klein et al. 1999 ; Venzke et al. 2000 ; Alexander et al. 2002 ; Lau and Nath 2003 ). The warm SSTA in the equatorial central
trapped, zonally propagating tropical circulations. Later, Takayabu (1994) and Wheeler and Kiladis (1999) explicitly demonstrated the existence of coupled anomalies of deep convection and large-scale circulation in the tropics. Now these waves are well known to compose a nonnegligible fraction of submonthly tropical variability ( Kiladis et al. 2009 ; Straub et al. 2010 ). Recent studies revealed remarkable self-similar vertical dynamical–thermodynamical wave structures among CCEWs and the Madden
trapped, zonally propagating tropical circulations. Later, Takayabu (1994) and Wheeler and Kiladis (1999) explicitly demonstrated the existence of coupled anomalies of deep convection and large-scale circulation in the tropics. Now these waves are well known to compose a nonnegligible fraction of submonthly tropical variability ( Kiladis et al. 2009 ; Straub et al. 2010 ). Recent studies revealed remarkable self-similar vertical dynamical–thermodynamical wave structures among CCEWs and the Madden
1. Introduction The multiscale nature of circulation in the tropical western North Pacific (WNP) has become an interesting subject in recent years (e.g., Holland 1995 ; Hsu 2005 ). These multiscale features include monsoon circulation, intraseasonal oscillation (ISO), 3–8-day synoptic waves, and tropical cyclones (TCs). It has been reported in numerous studies that TCs tend to form and develop in the favorable condition provided by the large-scale tropical circulation (e.g., Carr and
1. Introduction The multiscale nature of circulation in the tropical western North Pacific (WNP) has become an interesting subject in recent years (e.g., Holland 1995 ; Hsu 2005 ). These multiscale features include monsoon circulation, intraseasonal oscillation (ISO), 3–8-day synoptic waves, and tropical cyclones (TCs). It has been reported in numerous studies that TCs tend to form and develop in the favorable condition provided by the large-scale tropical circulation (e.g., Carr and
1. Introduction Tropical cyclones commonly form when sea surface temperatures are warm and when large-scale environmental conditions (e.g., low-moderate vertical wind shear, increased low-to-midlevel moisture, and sufficient low-level cyclonic relative vorticity) are favorable for tropical cyclogenesis ( Gray 1968 , 1988 , 1998 ). Such conditions are known to vary on different time scales. At multidecadal time scales, the environment over the Atlantic has been shown to vary with the Atlantic
1. Introduction Tropical cyclones commonly form when sea surface temperatures are warm and when large-scale environmental conditions (e.g., low-moderate vertical wind shear, increased low-to-midlevel moisture, and sufficient low-level cyclonic relative vorticity) are favorable for tropical cyclogenesis ( Gray 1968 , 1988 , 1998 ). Such conditions are known to vary on different time scales. At multidecadal time scales, the environment over the Atlantic has been shown to vary with the Atlantic
troposphere and poleward mass transport in the upper troposphere. The HC is fundamentally important to the global climate system, because its ascending and descending branches determine the climate of various tropical regions and play a role in influencing the climate at middle and high latitudes (e.g., Lindzen 1994 ; Chang 1995 ; Hou 1998 ). Therefore, the HC has important impacts on global climate ( Diaz and Bradley 2004 ). In recent years, there has been growing interest in the variations of the HC
troposphere and poleward mass transport in the upper troposphere. The HC is fundamentally important to the global climate system, because its ascending and descending branches determine the climate of various tropical regions and play a role in influencing the climate at middle and high latitudes (e.g., Lindzen 1994 ; Chang 1995 ; Hou 1998 ). Therefore, the HC has important impacts on global climate ( Diaz and Bradley 2004 ). In recent years, there has been growing interest in the variations of the HC
this region. This paper considers how the MJO modulates the intraseasonal variability of African easterly wave (AEW) activity over Africa and tropical cyclogenesis activity over the main development region (MDR; 5°–25°N, 15°–60°W). The WAM is modulated by interactions across different spatial and temporal scales over West Africa and the eastern Atlantic basin. Janicot and Sultan (2001) and Sultan et al. (2003) identified two dominant frequency bands for the intraseasonal variability in WAM
this region. This paper considers how the MJO modulates the intraseasonal variability of African easterly wave (AEW) activity over Africa and tropical cyclogenesis activity over the main development region (MDR; 5°–25°N, 15°–60°W). The WAM is modulated by interactions across different spatial and temporal scales over West Africa and the eastern Atlantic basin. Janicot and Sultan (2001) and Sultan et al. (2003) identified two dominant frequency bands for the intraseasonal variability in WAM
