Coherent fluctuations of extratropical geopotential height and tropical convection in intraseasonal time scales

Abstract Coherent fluctuations between extratropical circulation and tropical conviction in the intraseasonal time scale are studied. Possible relationships between 500-mb height field and outgoing longwave radiation (OLR) are examined using correlation, complex EOF and composite techniques. Results show that in the 20-70 day bands data, there is a systematic evolution of extratropical wavetrains from Eurasia across the Pacific to North America and the North Atlantic in the time scale of 5 to 10 days. Over the tropics, the dominant mode of intraseasonal variation in convection is an east-west dipole-like feature which propagates from the western Indian Ocean eastward to the dateline with a quasi-period of 40-50 days. The space-time evolution of these extratropical wavetrains is found to he coherent with the tropical dipolar convection and with the strongest convection over Indonesia/central Pacific in approximate quadrature with the peak phase of the Eurasia and Pacific-North America wavetrains. While the...