Enhanced Tropospheric Wave Forcing of Two Anticyclones in the Prephase of the January 2009 Major Stratospheric Sudden Warming Event

Abstract

Tropospheric forcing of planetary wavenumber 2 is examined in the prephase of the major stratospheric sudden warming event in January 2009 (MSSW 2009). Because of a huge increase in Eliassen–Palm fluxes induced mainly by wavenumber 2, easterly angular momentum is transported into the Arctic stratosphere, deposited, and then decelerates the polar night jet. In agreement with earlier studies, the results reveal that the strongest eddy heat fluxes, associated with wavenumber 2, occur at 100 hPa during the prephase of MSSW 2009 in ERA-Interim. In addition, moderate conditions of the cold phase of ENSO (La Niña) contribute to the eddy heat flux anomaly. It is shown that enhanced tropospheric wave forcing over Alaska and Scandinavia is caused by tropical processes in two ways. First, in a climatological sense, La Niña contributes to an enhanced anticyclonic flow over both regions. Second, the Madden–Julian oscillation (MJO) has an indirect influence on the Alaskan ridge by enhancing eddy activity over the North Pacific. This is manifested in an increase in cyclone frequency and associated warm conveyor belt outflow, which contribute to the maintenance and amplification of the Alaskan anticyclone. The Scandinavian ridge is maintained by wave trains emanating from the Alaskan ridge propagating eastward, including an enhanced transport of eddy kinetic energy. The MSSW 2009 is an extraordinary case of how a beneficial phasing of La Niña and MJO conditions together with multiscale interactions enhances tropospheric forcing for wavenumber 2–induced zonal mean eddy heat flux in the lower stratosphere.

Processes governing the amplification of ensemble spread in a medium‐range forecast with large forecast uncertainty

“…Our PV framework builds on the PV perspective of midlatitude dynamics (Hoskins et al, 1985) and provides a quantitative partitioning of the dynamics into individual processes, including the influence of near-tropopause Rossby-wave dynamics, baroclinic growth, and moist processes. The PV framework has recently been applied to quantify the governing processes of Rossby-wave packets (Piaget et al, 2015;Teubler and Riemer, 2016) and a large-amplitude ridge (Schneidereit et al, 2017). The PV framework has also been applied to a case study of error growth in an operational ECMWF forecast and to study upscale error growth in dedicated numerical experiments (Baumgart et al, 2019).…”

“…; Teubler and Riemer, ) and a large‐amplitude ridge (Schneidereit et al . ). The PV framework has also been applied to a case study of error growth in an operational ECMWF forecast (Baumgart et al .…”

Rossby Wave Propagation into the Northern Hemisphere Stratosphere: The Role of Zonal Phase Speed

“…Before the event, a wave 2 pattern dominated the Northern Hemisphere tropopause-level flow, with anticyclonic anomalies over western North America and Scandinavia. These ridges were colocated with blocking anticyclones and are suggested to have played a role in exciting upward propagating wave packets (Ayarzaguena et al, 2011;Harada et al, 2010;Schneidereit et al, 2017) by projecting onto the climatological planetary-scale wave 1 and wave 2 patterns.…”

Dynamics of Anomalous Stratospheric Eddy Heat Flux Events in an Idealized Model

“…The troposphere dominates view involves an anomalous tropospheric wave source while the stratosphere dominates view involves a preconditioned stratospheric zonal-mean flow but neither specifies their origin. Wave-wave interactions could generate the tropospheric wave source directly via interactions between wavenumbers (Scinocca and Haynes 1998;Schneidereit et al 2017;Lee et al 2019) or indirectly such that tropospheric waves modify the zonal-mean flow impinging on surface topography (Charney and Eliassen 1949). Wave-wave interactions could be mediated by the stratospheric zonal-mean flow such that stratospheric waves precondition the polar vortex for upward wave propagation or resonance (McIntyre 1982;Palmer and Hsu 1983;Albers and Birner 2014).…”