Viewing sea level anomaly forecasts from a coastal wave guide perspective

Mr Andy Taylor1, Dr Gary Brassington1

1Bureau of Meteorology, Docklands, Australia

Abstract:

Coastal sea level anomalies are too often associated with solely local weather effects.  However nuisance flooding is often connected to remote forcing.  We describe an approach to reduce numerical forecast data to “coastal waveguide” coordinates as one way to help raise the profile of non-local sea level drivers.  The method is informed by the literature on coastally trapped waves (CTW).

All discussion is limited to the Australian mainland but the approach is generally relevant to regions where CTWs influence sea level. The approach does not produce new forecasts, but aims to focus forecaster attention on aspects of sea level forecasts prominent on the long Australian coast.  The approach also explicitly addresses spatial issues associated with measuring coastal paths.  Coastal paths are scale-dependent and forecast models discretise the coastal boundary differently.  A well defined coastal path provides a frame of reference for the objective interpretation of CTW properties. The relevance of coastally trapped signals and remote forcing is documented in the oceanographic literature, but is effectively unknown to the general public and rarely mentioned in press reports of sea level events such as nuisance flooding.

Routine presentation of forecast guidance in waveguide coordinates could contribute to the transfer of oceanographic research understanding into forecast narratives. In addition, the approach can facilitate quantitative forecast evaluations that target CTW properties. Two ocean forecast systems are contrasted in this framework for the Australian mainland. One year of daily forecasts are compared, with indications that model baroclinicity is of practical relevance.


Biography:

Research and operational aspects of ocean forecasting at the Bureau of Meteorology.