Tropical Cyclones in a Reduced Rossby Wave Breaking Environment

Abstract:

Hurricanes are capable of causing devastating damage to the coastlines they affect. Seasonal forecasting aids in estimating this damage ahead of time. Forecasts for the 2013 North Atlantic hurricane season were successful in predicting the number of storms for the season fairly accurately, but drastically overestimated the intensity of these storms. A previously proposed reason for this is an increased occurrence of Rossby wave breaking in the western part of the North Atlantic. This increase would dry the tropical atmosphere, preventing or reducing hurricane intensification.

To investigate this hypothesis, the ICOsahedral Nonhydrostatic atmosphere model ICON is used in limited area mode. To change the behavior of Rossby waves, the boundary conditions north of 25°N are gradually shifted towards a 30-day running mean with increasing latitude. While this method does reduce the humidity in the tropical North Atlantic at some times, this is not a persistent feature. However, there are differences in intensity distribution and great differences in storm track positions when compared to reference simulations with 6-hourly boundary conditions.

Both the merit of the experimental setup and the changes to hurricane activity will be dicussed.