Sub-seasonal to Seasonal Hindcasts of the 2016 Disruption of the Stratospheric Quasi-biennial Oscillation
Abstract
In early 2016 the quasi-biennial oscillation (QBO) in tropical stratospheric winds was disrupted by an anomalous easterly jet centered at ~40 hPa, a development that was completely missed by all operational extended range weather forecast systems. This event and its predictability are investigated through ensemble hindcasts using a global model notable for its sophisticated representation of the upper atmosphere. Key to prediction of this event is simulating the slowly evolving mean winds in the winter subtropics that provide a waveguide for Rossby waves propagating from the winter hemisphere. This presentation shows our continuing effort after Watanabe et al (2018, GRL). The development of the subtropical waveguide in October-November 2015 is affected by the strong El Nino condition, which we demonstrate by ensemble seasonal hindcasts with different prescribed sea surface temperatures. In a series of ensemble hindcasts with initial perturbations, the development and maintenance of the subtropical waveguide, propagation and focus of winter hemisphere Rossby waves into the equatorial lower stratosphere, and the development of the anomalous 40-hPa easterly jet are successfully simulated with a certain probability. Meanwhile, the unprecedented ascent of QBO zonal wind shear above 40 hPa can be reproduced in our hindcasts only when we artificially weaken our model's gravity wave activity during January-February 2016.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.A13I3014W
- Keywords:
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- 3305 Climate change and variability;
- ATMOSPHERIC PROCESSES;
- 3337 Global climate models;
- ATMOSPHERIC PROCESSES;
- 3362 Stratosphere/troposphere interactions;
- ATMOSPHERIC PROCESSES;
- 0550 Model verification and validation;
- COMPUTATIONAL GEOPHYSICS