About this Research Topic
Existing numerical weather prediction models still struggle to provide useful weather information at a lead time beyond two weeks. Improving sub-seasonal to seasonal (S2S) forecasts is the focus of several current major international initiatives including the S2S project, sponsored by the World Meteorological Organization. Increasing evidence shows that changes in the stratosphere can in turn affect the troposphere and surface through various chemical, radiative, and dynamical processes. The possible coupling between troposphere and stratosphere opens up a new opportunity for using stratospheric variability as a dynamical tool and a component of empirical models for weather forecasts.
The “downward impact” of the stratospheric variability provides a long lead information (0-60 days) to Arctic oscillation and the associated extreme weather, but such a lead relationship is not found for all cases because of both the large internal variability in the troposphere and the specific stratospheric properties. Even though these stratospheric signals can propagate down, the timing and region of its impact show large case-to-case variability. The quasi-simultaneous relationship between stratospheric anomalies and weather regimes has drawn attention but the predictability of these stratospheric signals and the underlying mechanisms are still not clear.
In this Research Topic we welcome contributions of Original Research Articles, Review Articles, and methodological advances in stratosphere-troposphere coupling and its role in surface weather predictability. The highlight of this Research Topic includes, but is not limited to, the following areas:
• The systematic evaluation and multi-model comparison of the prediction skills of stratospheric variability (including sudden stratospheric warming and final warming events, annular mode, shape, area, intensity of the stratospheric polar vortex, stratospheric meridional mass circulation and meridional heat flux), taking advantage of ensemble hindcasts and real-time forecasts by various forecast systems within the S2S project;
• Studies on understanding the cause of the longer prediction limit of stratosphere than troposphere;
• The assessment of the influence of stratospheric variability (variability at sub-seasonal or shorter timescales, variability at longer timescales such as Quasi-Biennial Oscillation, ozone layer change, water vapor change and the combined variations of stratospheric signals at different timescales) on the dynamical prediction skill of tropospheric and surface weather;
• Investigations on the underlying physical processes governing coupling between the stratosphere and troposphere and the complexity of the “downward impact” of stratosphere on the troposphere and surface weather;
• The exploration of precursory signals from troposphere (e.g., blockings, typhoon, ENSO, tropical convection, sea ice, snow cover, gravity waves and Rossby waves) that are able to force the stratospheric variability;
• New methodology or paradigms of real time S2S forecasts of surface temperature, near surface winds, etc., via utilization of the stratospheric variability.
Keywords: stratosphere-troposphere coupling, S2S predictability, weather, stratosphere, precursor
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