Wave Sources, Energy Propagation and Conversion for Anomalous Rossby Wave Activities Along the West Asian Jet Stream

Characteristics of the wave sources, energy propagation and conversion for anomalous Rossby wave activities (RWAs) along the West Asian jet stream (WAJS) in summer are examined based on the NCEP/NCAR (National Centers for Environmental Prediction/National Center for Atmospheric Research) reanalysis data from 1958 to 2003, using the vorticity source equation, the Eliassen-Palm (EP) flux, and the wave energy equation under diabatic heating. The study aims to find the dynamical causes for RWA anomalies along the WAJS and to improve the understanding of mid-high latitude circulation anomalies. The results show that the negative vorticity source and the strong EP flux divergence over the Mediterranean Sea and the North Atlantic-Scandinavian Peninsula area act as the wave sources for RWA anomalies along the WAJS.When the intensity and position of the wave sources are anomalous, the excited eastward-propagating RWA along the WAJS also behaves anomalously. In strong (weak) years of RWA, Rossby waves excited by the strong divergence of EP fluxes over the Iceland Scandinavian Peninsula area (east to the Scandinavian Peninsula) propagate eastward and southeastward. The eastward propagating waves become strengthened (weakened) after turning southeastward near the Ural Mountains and then entering the Asian subtropical westerly jet stream (ASWJS) over the Caspian SeaAral SeaXinjiang. The southeastward propagating waves also strengthen (weaken) after directly entering the ASWJS over the eastern Mediterraneanthe Black Sea. Furthermore, the divergence of EP fluxes over the Mediterranean also strengthens (weakens) in the strong (weak) years, so they jointly bring about the strong (weak) RWA along the WAJS. Finally, the perturbation available potential energy (PAPE) along the WAJS (15-60°E) produced by diabatic heating, is far greater than the conversion from the kinetic energy of the basic flow into the perturbation kinetic energy and from the available potential energy of the basic flow into PAPE. The RWA along the WAJS looks stronger (weaker) than normal when the PAPEs produced by diabatic heating over the Iranian Plateau and West Asia significantly strengthen (weaken), and therefore they are also the energy sources of RWA anomalies.