Stratosphere-troposphere coupling in east-coast winter storms

Recent modeling studies reveal a mechanism for coupling of the stratosphere and troposphere through the effect of stratospheric shear on baroclinic wave lifecycles. In a 25-year climatology of over 300 winter storms, we find an association between zonal wind anomalies in the stratosphere and the direction of baroclinic wave propagation and wave breaking. We obtain the approximate wavenumber of the upper tropospheric waves and wavepackets using a wavelet transform. Consistent with previous studies on baroclinic wave lifecycles, composites of tropospheric zonal wind suggest a correlation between the wavenumber and the meridional displacement of the tropospheric zonal jet, with poleward displacement for lower wavenumbers relative to higher wavenumbers. For the higher wavenumbers, generally 7 and above, we find characteristics of the LC2 lifecycle with cyclonic breaking and poleward propagation, while lower wavenumbers exhibit anticyclonic breaking (LC1). The observations show a smoother transition of the lifecycle type with increasing wavenumber than that suggested by theory and idealized modeling. In composites of low wavenumbers with stratospheric zonal wind greater than climatology, the relative poleward displacement of the tropospheric jet increases compared to weaker stratospheric flows. The magnitude of the poleward jet displacement increases with decreasing wavenumber, consistent with the modeling studies.