The Impact of Strong Negative Arctic Oscillations on the 2009-2010 and 2010-11 Florida Dry Seasons

For over 10 years the lead author has investigated the influence of the El Niño Southern Oscillation (ENSO), the North Atlantic Oscillation (NAO), the Pacific/ North American Pattern (PNA), and the Arctic Oscillation (AO) on storminess, rainfall and temperature during the Florida dry season (1 November through 30 April). The ENSO phase was found to have the greatest impact on dry season storminess and rainfall and the AO a small impact. Seasonal forecasts of these parameters have been quite successful during La Niña or El Niño phases, but less so during ENSO-neutral conditions when other teleconnections can dominate. ENSO's relationship to temperature has been found to be much weaker and the AO was found to have the greatest impact on temperature during the Florida dry season, particularly minimum temperature. Since the AO is not predicted at long range the dry season forecasts for temperature are based primarily on the ENSO signal. Conventional thinking has been that strong El Niño's (cooler) or La Nina's (warmer) would provide the dominant influence on temperature with modification by the other teleconnections.

The occurrence of extremely strong negative Arctic Oscillations that totally dominated dry season temperature in Florida during the back- to-back strong El Nino of 2009-10 and strong La Nina of 2010-11 was unprecedented in modern history. The environmental impact to Florida from these two record negative AO events was profound. An updated statistical analysis using logistic regression will be presented to re-confirm the strong relationship between dry season minimum temperature and the AO for ten Florida Cities. Case studies of the impact of the negative AO on the 2009-10 and 2010-11 dry seasons will be presented to illustrate how the expected impacts of a strong El Nino and strong La Nina were modified by the negative AO's. Finally, the development of an “AO Event” definition and climatology, and documentation of their impacts on Florida will be explored. Such information would be helpful in assessing risk in a future climate that might include more frequent negative AO events.