The role of the Pacific Decadal Oscillation and ocean-atmosphere interactions in driving US temperature predictability

Sem Vijverberg,Dim Coumou

doi:10.1038/s41612-022-00237-7

Abstract

Heatwaves can have devastating impact on society and reliable early warnings at several weeks lead time are needed. Previous studies showed that north-Pacific sea surface temperatures (SST) can provide long-lead predictability for eastern US temperature, mediated by an atmospheric Rossby wave. The exact mechanisms, however, are not well understood. Here we analyze two different Rossby waves associated with temperature variability in western and eastern US, respectively. Causal discovery analyses reveal that both waves are characterized by positive ocean-atmosphere feedbacks at daily timescales. Only for the eastern US, a long-lead causal link from SSTs to the Rossby wave exists, which generates summer temperature predictability. We show that this SST forcing mechanism originates from the evolution of the winter-to-spring Pacific Decadal Oscillation (PDO). During pronounced winter-to-spring PDO phases (either positive or negative) eastern US summer temperature forecast skill more than doubles, providing a temporary window of enhanced long-lead predictability.

Highlights

Quasi-stationary or recurrent Rossby waves in boreal summer play an important role in the development of high impact heat waves[1,2].Such Rossby waves create persistent clear-sky high pressure systems, which, in combination with soil desiccation and land-atmosphere feedbacks, can lead to extreme heatwaves such as seen in Russia 20103,4 and the United States 20125
Quantifying ocean-atmosphere coupling of Rossby Waves Figure 1a, b shows that western (Tw) and eastern (TE) United States (US) summer temperatures strongly correlate with two distinct Rossby wave patterns, here called the western (RWW) and eastern Rossby waves (RW) (RWE)
We show that two different Rossby waves are important drivers of temperature variability in western and eastern US, respectively (Fig. 1a, b)

Summary

Introduction

Quasi-stationary or recurrent Rossby waves in boreal summer play an important role in the development of high impact heat waves[1,2] Such Rossby waves create persistent clear-sky high pressure systems, which, in combination with soil desiccation and land-atmosphere feedbacks, can lead to extreme heatwaves such as seen in Russia 20103,4 and the United States 20125. Understanding the role of mid-latitude ocean-atmosphere interactions in generating and maintaining Rossby waves is needed to improve subseasonal-to-seasonal (S2S) predictions[14–16] and climate change projections[17–19]. The atmosphere responds to this negative vorticity anomaly by moving air equatorward, mainly at the downstream edge of the warm ridge This adjustment can lead to a downstream Rossby wave response consisting of alternating highs and lows[25]

Methods

Results

Conclusion