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Diurnal variations in atmospheric convection, dynamic/thermodynamic fields, and heat/moisture budgets over the equatorial Pacific warm pool region are analyzed based on data collected from different observation platforms during the Intensive Observation Period of the Tropical Ocean Global Atmosphere Coupled Ocean-Atmosphere Response Experiment (TOGA COARE). Results reveal that the diurnal variations in rainfall/convection over the TOGA COARE region can be classified into three distinct stages: warm morning cumulus, afternoon convective showers, and nocturnal convective systems. Afternoon rainfall comes mostly from convective cells, but the nocturnal rainfall is derived from deeper convective cells and large areas of stratiform clouds. Results further show that afternoon convective showers are more evident in the large-scale undisturbed periods when the diurnal SST cycle is strong, but the nocturnal convective systems and morning cumulus are more enhanced in the disturbed periods when more moisture is available. The primary cause of the nocturnal rainfall maximum is suggested to be associated with more (less) available precipitable water in the night (day) due to the diurnal radiative cooling/heating cycle and the resultant change in tropospheric relative humidity.

The western North Pacific Subtropical High (WNPSH) in summer exhibits significant 2–3 years and 3–5 years oscillations with interdecadal variability. The 2–3‐year oscillation is most evident after 1990. It is accompanied by anomalous meridional overturning circulation characterized by warm SST anomalies (SSTA) and ascending motion in the maritime continent and anomalous descending motion near the Philippine Sea, and by evolving warm to cold SSTA in the central‐eastern Pacific from the preceding winter to the summer. The 3–5‐year oscillation is most pronounced during the 1980s. It is accompanied by anomalous descending motion over the maritime continent and warm SSTA in the central‐eastern equatorial Pacific that persists from the preceding winter to the summer; the complementary cooling and descending motion in the western Pacific are related to anomalous east‐west circulation associated with ENSO.

The variability of observed tropical cyclone (TC) activity (i.e., genesis, track, and landfall) in the western North Pacific (WNP) is examined in relation to the various categories of the Madden-Julian oscillation (MJO) during summer (June-September) for the period 1979-2004. The MJO categories are defined based on the empirical orthogonal function analysis of outgoing longwave radiation data.The number of TCs increases when the MJO-related convection center is located in the WNP. The axis of a preferable genesis region systematically shifts like a seesaw in response to changes in the large-scale environments associated with both the eastward and northward propagation of the MJO and the intraseasonal variability of the WNP subtropical high. Furthermore, the authors show that the density of TC tracks in each MJO category depends on the systematic shift in the main genesis regions at first order. Also, the shift is affected by the prevailing large-scale steering flows in each MJO category. When the MJO-related convection center is found in the equatorial Indian Ocean (the tropical WNP), a dense area of tracks migrates eastward (westward). The effects of extreme ENSO events and the variations occurring during ENSO neutral years are also examined.A statistical analysis of TC landfalls by MJO category is applied in seven selected subareas: the Philippines,

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