Research brief: Variations in drivers of cyclone activity may improve forecasting

Using accumulated cyclone energy (ACE) as a measure, ARCCSS researchers modelled the dominant modes that led to variations in tropical cyclone activity in the Pacific. They found that 40% of the total variation in tropical cyclone activity could be ascribed to modes related to the El Niño-Southern Oscillation (ENSO). 

The first mode, which is more active from September-November, was found in the eastern Pacific. The activity there was linked to the build up or decline of El Niño events caused by the build-up or discharge of oceanic heat. 

The second mode occured in the early months of the hurricane season in the central Pacific. It again was in response to El Niños in this central region and the impact they had on atmospheric variability.  

The researchers then were able to model these ENSO modes and other important components of the atmosphere and ocean to reveal how they influenced changes to the location and time of cyclone events in the Pacific. As a result of this work they found four important areas that could act as good seasonal predictors of Pacific tropical cyclone activity in terms of time and location.These predictors were:

  • The subsurface temperatures of the ocean in the east equatorial Pacific during winter,
  • the east-west slope at the base of warm and cold water masses beneath the ocean,
  • the surface conditions of tropical cyclone regions in spring, and
  • the changes in atmospheric activity in the western Pacific  

These results could be used to complement NOAA's official forecast and may add additional time and location information to the forecasts for cyclone seasons in the tropical Pacific. Based on this modelling the researchers forecasted an above average storm season for 2016. This was born out by the observations for that year, with the 2016 season being the 11th most active on record.  

Paper: Modes of hurricane activity variability in the eastern Pacific: Implications for the 2016 season. Geophysical Research Letters.
Picture: Hurricane Ike by NASA. 


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