Exploring Linkages between Teleconnections and the Formation of Persistent Flow Regimes

The study and identification of weather regimes have been applied extensively in an attempt to better understand large-scale midlatitude flow patterns. While the dynamics underpinning any given weather regime will vary, teleconnection patterns are often useful at understanding the formation of weather regimes on a subseasonal-to-seasonal timescale. Certain modes of low-frequency variability in the atmosphere allow for windows of opportunity for improved forecasts at longer lead times. However, these windows are limited to a few instances each season and can be difficult to anticipate more than a week or two in advance. The purpose of this study is to assess the usefulness of established (e.g., the MJO) and nascent (e.g., position of the North Pacific jet stream or NPJ) teleconnections for predicting the formation of amplified and persistent flow regimes (PFR) during boreal winter.

PFRs are identified as periods of widespread persistent anomalies as defined by Dole and Gordon (1983) and updated by Miller et al. (2020) using CFSR reanalysis data for DFJ from 1979–2022. All PFRs are aggregated into five groups using k-means clustering of the 500-hPa geopotential height data at the start of each PFR. The teleconnections used in this study are the MJO as defined in Wheeler and Hendon (2004) and the NPJ phase as defined in Winters et al. (2019). Initial work will identify select phases of each index that exhibit increased occurrence frequency in periods leading up to the formation of each composite PRF. These results will be complemented with an assessment of statistical significance through a bootstrap resampling method. The above relationships will be reversed to assess the likelihood of a particular PFR forming at various time lags after a given phase of the MJO or NPJ to translate the initial PRF–teleconnection relationships into ones which have use for forecasting. The third and final component of this study is to compare composites of select phases of the MJO and NPJ that do and do not result in a PFR in an attempt to link the statistical results to improved dynamical understanding of the teleconnection relationships.