Projecting Northern Hemisphere Flow Regime Transition Using Integrated Enstrophy

Emily Klaus,Patrick Market,Anthony Lupo,Joshua Kastman,Michael Bodner

doi:10.3390/atmos11090915

Abstract

Integrated enstrophy (IE) is the square of vorticity integrated over an entire hemisphere at a particular level in the atmosphere. Previous work has shown this quantity is correlated to the positive Lyapunov Exponent for hemispheric flow, and as such is a measure of flow stability or predictability. In this study, IE is calculated at 500 hPa over an area that encompasses 0° to 70° in the Northern Hemisphere. The data sets used were the 500 hPa initial and forecast fields for the Global Ensemble Forecasting System (GEFS) (on a 1 × 1 latitude-longitude grid) provided by the National Oceanic and Atmospheric Administration (NOAA) Weather Prediction Center (WPC) and the National Centers for Environmental Prediction/NOAA reanalyses (on a 2.5 × 2.5 latitude-longitude grid) archived in Boulder, CO. The GEFS forecast fields were provided every 24 h out to 240 h. By examining these forecasts over a year, it was found here that significant changes in the calculated IE values, as quantitatively determined, are a good predictor of flow regime transition, and 34 cases were found. We also found that the model IE forecasts identified these regime transitions reliably out to about seven days, however, the probability of detection and the skill decreased after this time. Additionally, a threshold for changes in IE was found for the cases studied here.

Highlights

Earth’s atmosphere is a turbulent, ever-changing system whose future states can be difficult to forecast (e.g., [1])
We found that the model Integrated enstrophy (IE) forecasts identified these regime transitions reliably out to about seven days, the probability of detection and the skill decreased after this time
Planetary scale flow patterns in the NH, such as teleconnection regimes or those associated with atmospheric blocking anticyclones, have been found to have positive correlations between the weather and climate of the North Pacific and the mid-western and eastern USA [3,4,5]

Summary

Introduction

Earth’s atmosphere is a turbulent, ever-changing system whose future states can be difficult to forecast (e.g., [1]). Planetary scale flow patterns in the NH, such as teleconnection regimes or those associated with atmospheric blocking anticyclones, have been found to have positive correlations between the weather and climate of the North Pacific and the mid-western and eastern USA [3,4,5]. Knowing when these patterns may reoccur and how they affect certain regions upstream or downstream would be applicable in long-range forecasting (e.g., [6,7]). Atmospheric predictability is limited by, at least in part, an incomplete representation, or even a full understanding of relevant physical processes in the atmosphere (e.g., [8])

Methods

Results

Conclusion