Wave trains of 10 30-day meridional wind variations over the north pacific during summer

Abstract

The present study investigates the intraseasonal oscillations over the North Pacific during summer based on the ERA-Interim reanalysis dataset. It is shown that the main component of intraseasonal variations in meridional wind is dominated by 10 30-day variability. Zonally oriented wave trains are identified over the North Pacific at this band, with a zonal wavenumber 6. The wave trains exhibit an equivalent-barotropic structure, with the maximumamplitude in the upper troposphere, and are manifested as quasi-stationary Rossby waves with the energy dispersing eastward. The wave trains do not show a phase-locking feature; that is, they have no preferred geographical locations in the zonal direction. Furthermore, energy analyses suggest that the intraseasonal waves gain energy through baroclinic energy conversion, while the barotropic energy conversion plays a negligible role. The present results have implications for better understanding and forecasting weather and climate in North America, since the intraseasonal waves over the North Pacific may act as precursory signals for extreme events occurring over North America.