Quantifying Regional Sensitivities to Periodic Events: Application to the MJO

Abstract

As the forecasting community works toward skillfully applying the predictive power of periodic events, it is increasingly useful to quantify regional sensitivities to their influence. We have developed an index to quantify these regional Sensitivities To the Remote Influence of Periodic EventS (STRIPES). Here, periodic events are climate phenomena that smoothly evolve through their life cycles, such as the Madden-Julian Oscillation (MJO). The STRIPES index compiles the information obtained through composite analysis of variables after a periodic event into a single number, which includes information about the life cycle of the event, and for a range of lags with respect to each stage of the event. The STRIPES index quantifies the strength and consistency of a region's response to the remote event. Because the index can be computed for a single point, it can be plotted on a map to show regional variations. We demonstrate the utility of the STRIPES index by applying it to observations of daily geopotential height, maximum temperature, minimum temperature, and precipitation totals for winters between 1974 and 2017. Results for geopotential height show strong sensitivities in the extratropics, indicative of the MJO's remote teleconnections. Results for surface stations over eastern North America highlight regions of enhanced sensitivity that agree well with previous studies. This sensitivity is robust in the sense that it is detectable and significant at the level of individual weather stations. The STRIPES index values for the MJO over North America are generally larger for daily maximum than for daily minimum temperature.