Numerical Simulation of Sudden Stratospheric Warmings

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Abstract
A mechanistic, quasi-geostrophic, semi-spectral model with a self-consistent calculation of the mean zonal flow fields is used to numerically simulate sudden stratospheric warmings generated by a single zonal harmonic (m) planetary wave. The development of a warming depends critically on the two factors which govern the transmission of planetary waves to the upper stratosphere: 1) the strength of the westerly winds in the lower stratosphere and 2) the magnitude of wave damping in the same region. Major warmings can only develop when the prewarming lower stratospheric winds and tropospheric forcing are strong but insufficient to trap the wave at low altitudes. Damping controls the maximum amplitude that a warming can attain and the time constant for its growth rate. The growth rate of a m = 2 warming is accelerated during the westerly zonal wind phase of the quasi-biennial oscillation, but the maximum amplitude of the warming is independent of QBO phase. The evolution of m = 1 and m = 2 warmings a... Abstract A mechanistic, quasi-geostrophic, semi-spectral model with a self-consistent calculation of the mean zonal flow fields is used to numerically simulate sudden stratospheric warmings generated by a single zonal harmonic (m) planetary wave. The development of a warming depends critically on the two factors which govern the transmission of planetary waves to the upper stratosphere: 1) the strength of the westerly winds in the lower stratosphere and 2) the magnitude of wave damping in the same region. Major warmings can only develop when the prewarming lower stratospheric winds and tropospheric forcing are strong but insufficient to trap the wave at low altitudes. Damping controls the maximum amplitude that a warming can attain and the time constant for its growth rate. The growth rate of a m = 2 warming is accelerated during the westerly zonal wind phase of the quasi-biennial oscillation, but the maximum amplitude of the warming is independent of QBO phase. The evolution of m = 1 and m = 2 warmings a...

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