Tropical-extratropical interactions and arctic-extratropical interactions conducive to intraseasonal variability of the North Pacific jet stream.

摘要

The autumnal spin up of the Northern Hemisphere (NH) general circulation is characterized by intraseasonal variability in the structure of the North Pacific jet stream (NPJ). The variability in the structure of the NPJ is often associated with large-scale flow reconfigurations over the North Pacific and North America and changes in the NH zonal available potential energy (AZ). This dissertation investigates variability in the structure of the NPJ and the NH AZ in conjunction with tropical--extratropical interactions (TEIs) and arctic--extratropical interactions (AEIs). The former are investigated in association with the El Nino--Southern Oscillation, the Madden--Julian Oscillation, and western North Pacific tropical cyclones (TCs), whereas the latter are investigated in association with upper-tropospheric potential vorticity (PV) disturbances (PVDs).;A climatology of NPJ wind speed maxima for 1979--2008 from the NCEP--NCAR reanalysis demonstrates that variability in the structure of the NPJ can be associated with an increase in the strength of the NPJ, Rossby wave train amplification and dispersion, and persistent downstream upper-tropospheric geopotential height anomalies. NPJ-relative composite analyses and case studies indicate that TEIs and AEIs associated with poleward-displaced TCs and AEIs can be associated with equatorward displaced PVDs, respectively, in the NPJ entrance region can increase horizontal confluence of the nondivergent wind. From a PV perspective, the increase in horizontal confluence is associated with an increase in the magnitude of the upper-tropospheric PV gradient via PV frontogenesis by the nondivergent wind and an increase the strength of the NPJ.;Positive PV advection by the nondivergent wind in the upper troposphere downstream of a PVD can also lead to Rossby wave train amplification in the presence of TC outflow characterized by negative upper-tropospheric PV advection by the irrotational wind in the NPJ equatorward entrance region. The TC outflow can reduce the eastward progression of the PVD, increase the magnitude of the upper-tropospheric PV gradient, and subsequently influence downstream Rossby wave train amplification and dispersion across the North Pacific. Two case studies demonstrate that Rossby wave train dispersion and downstream variability in the large-scale flow are associated with high-impact weather events over North America.