Interannual and intraseasonal variations of convective activities in the tropical western Pacific during summer and their impact on the Northern Hemisphere circulation are investigated by using satellite cloud amount, sea surface temperature (SST) and geopotential data for 7 years (1978)(1979)(1980)(1981)(1982)(1983)(1984).During summers when SST in the tropical western Pacific is about 1.0* warmer than normal, active convection regions consisting of a number of typhoons and tropical depressions are shifted northeastward from the normal position near Philippines to the subtropical western Pacific around 20*N and cloud amounts both in the middle latitudes and in the equatorial regions are greatly suppressed. A high pressure anomaly with little vertical tilt predominates in middle latitudes extending from East China, through Japan Islands to North Pacific during these summers.Analyses of 5-day mean cloud amount reveal that the convective activity is largely modulated by the intraseasonal variations (ISV). The amplitude of ISV of convective activity in the Philippine Sea around 15*N-20*N is more intensified in warm SST summers than in cold SST summers resulting in stronger season mean convective activities in the former than in the latter.Correlation computations between 5-day mean tropical cloud amount and 500mb geopotential height show that there exist wave trains of geopotential height emanating from the heat source region near Philippines to North America. Daily analyses of geopotential height indicate that these wave trains appear to be generated when convective activities in the Philippine Sea become intense and that the amplification occurs downstream from the western Pacific to the west coast of North America taking about 5 days.It is concluded that Rossby waves are generated by the tropical heat source associated with ISV, and high pressure anomalies over East Asia and Northwest Pacific during warm SST summers can be understood as the results of frequent occurrence of Rossby wave generation.

Analyses of the global sea surface temperature (SST) were performed to examine year to decadescale variations of SST. It is found that the tropical SST, especially in the central and eastern Pacific

Convection-associated disturbance systems that propagate westward over the equatorial Pacific with a period of 3-5 days are studied utilizing the GMS IR equivalent blackbody temperature (TBB) data and the ECMWF global analysis data. The period of analysis is JJA 1980JJA -1989JJA excluding 1984. Spectral analysis, lag-correlation analysis and composite analysis are utilized for the study.The dominance of 3-5 day variations with convective activity is statistically confirmed in the equatorial Pacific ITCZ region for the boreal summer season. It is shown, in a climatological sense, that these convective variations are associated with mixed Rossby-gravity (MRG)-wave-type disturbances in the central Pacific near the dateline, while they are associated with tropical depression (TD)-type disturbances in the tropical western north Pacific. It is suggested that the changes of dominant disturbance types are attributed to variations in large-scale environmental conditions, such as the mean vertical wind shear, the speed of mean zonal wind as well as the SST distribution. This hypothesis is supported by comparing disturbance structures in an El Nino year with those in a La Nina year at the same longitude. The convection and wave convergence exhibit relatively "loose" coupling. The vertical phase structure for MRG waves coincides with the result of Yanai et al. (1968) and what was proposed by Hayashi (1970). However, it is not clear that the system can be described in the framework of wave-CISK. The characteristics of TD-type disturbances, on the other hand, coincide with the classical "easterly waves" as described by Reed & Recker (1971) and exhibit "tight" coupling with convection. They do not correspond to any linear equatorial waves. It is shown that both types of disturbances obtain the kinetic energy through energy conversion from the available potential energy.

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The power spectra of the meridional component of the wind from the ground to the 30-km level at 17 stations in the tropical and sub-tropical Pacific are studied based on special upper wind observations taken during the period April through July 1962.In equatorial latitudes, the power spectra show a peak at a period close to 4 days corresponding to the passage of "equatorial waves" in the lower tropospheric easterlies. A very large spectral density is found at the periods 4 to 5 days throughout the upper troposphere and the lower stratosphere where the mean wind is from the west. The peak spectral density reaches a maximum at about the 17-km level near the tropopause. The spectral density gradually decreases with height in the stratosphere where the mean wind is from the east.In sub-tropical latitudes, large disturbance energy is associated with the upper tropospheric westerlies and a large portion of the spectral density is contained in the wave period longer than 5 days. A sharp suppression of the spectral density takes place at the lower boundary of the stratospheric easterlies.From the computation of the coherence and the phase difference of the meridional component of the wind, the vertical and horizontal structure of the disturbances is studied. The large horizontal extent and the westward inclination of phase lines of the disturbances in the upper troposphere and in the lower stratosphere are revealed. The horizontal coherence of the lower tropospheric disturbances in the east-west direction is very low. The phase lines of the lower tropospheric disturbances are inclined eastward with height. The average wavelength of the disturbances at various levels is estimated from the relation between the phase difference and the longitudinal difference of the stations.