The Use of Integrated Enstrophy in Blocking and Flow Regime Transition for Operational Forecasting

More than two decades ago, integrated enstrophy (IE) was shown to be correlated to the positive Lyapunov Exponent in a barotropic flow. Subsequent studies demonstrated that this quantity was similar regionally to that of the entire Northern Hemisphere and was relatively large in association with the onset and decay of blocking. However, these studies demonstrated that relatively high values of IE are not exclusively associated with blocking, but also with hemispheric-scale flow regime transitions as well. Given the relationship to Lyapunov Exponents, this quantity is a measure of flow stability as well as entropy or predictability. Here, the skill of IE in detecting significant changes in the northern hemisphere flow regime using the National Centers for Environmental Prediction (NCEP) North American Ensemble Forecast System (NAEFS) and the Global Ensemble Forecast System (GEFS) are examined using signal detection theory during the winter and spring of 2017-2018. Initial results showed that this tool displayed as a time series and that the ensemble mean has the most skill in identifying these transitions.