Geosciences Dept. Seminar: The Downward Influence of Sudden Stratospheric Warmings
Dr. Ian White, HUJI
Sudden stratospheric warmings (SSWs) are understood to have a significant downward influence on the tropospheric circulation below. However, the mechanism(s) by which this downward influence occurs are not well understood, nor are the factors governing the magnitude of the downward influence. It is particularly difficult to attempt to understand this coupling process as nonlinear tropospheric feedbacks effectively bury the mechanisms by which the stratospheric anomaly is initially communicated downward to the troposphere. Here, we use the recently-developed moist idealised model of the atmosphere to attempt to understand the mechanisms and factors governing this downward coupling. This model of ‘intermediate complexity’ is particularly suited to this study as it incorporates the radiation scheme that is utilised by operational forecast systems, including both the ECMWF and NCEP. The radiation scheme also allows us to force the model with a realistic ozone profile, and thus to simulate realistic radiative timescales in the stratosphere. From a control run with a realistic climatology, we perform an ensemble of spin-off runs with imposed high-latitude stratospheric warm-blobs. These imposed warmings have varying strengths and durations which allow us to examine the sensitivity of the tropospheric response to the magnitude and persistence of the stratospheric warming. The experiment setup also allows us to examine the stratosphere-troposphere coupling at both short lags (i.e., close to the forcing), and at longer lags, the latter of which are generally thought to be dominated by synoptic-wave feedbacks.
Seminar Organizer: Prof. Eyal Haifetz