Exploring the influence of the North Pacific Ocean Rossby wave sources on interannual variability of summer precipitation and surface temperature over the Northern Hemisphere

Ramón Fuentes-Franco,Federico Graef,David Docquier,Torben Koenigk,Klaus Wyser

doi:10.5194/egusphere-egu21-3270

Abstract

&lt;p&gt;The influence of Rossby wave sources (RWS) emitted on the Northeastern Pacific Ocean (NePO) in the Northern Hemisphere during summer is analysed in the ERA5 reanalysis and a large ensemble performed with the EC-Earth3 model. Using extreme years composites of precipitation, surface temperature and geopotential height, we found a causal influence of the Rossby waves generated over the NePO on a global climate response. Both the reanalysis ERA5 and the EC-Earth3 large ensemble show that RWS triggers wave-like patterns arising from the upper troposphere NePO region. We show that an increased Rossby wave sources intensity is related with a) negative temperature anomalies over western North America, b) positive temperature anomalies over eastern North America, c) increased precipitation over Northern Europe during summer and d) sea-ice concentration decrease in the Arctic.&amp;#160; We also show that the North Atlantic plays a very important role hindering or permitting that Rossby waves generated in the Pacific reach the Atlantic and modulate the atmospheric conditions over Europe. Such conditions were found in ERA5 and EC-Earth3 large ensemble during colder and icier conditions over the North Atlantic.&lt;/p&gt;

Highlights

Circumglobal Rossby waves influence strongly the meandering of the jet stream in the mid-latitudes around the globe, and they have been associated with strong variability of precipitation during summer (Kornhuber et al 2019) and winter seasons (Scaife et al 2017b, Dunstone et al 2018, Li et al 2019)
During summer, in the Northern Hemisphere the Rossby wave sources (RWS) maxima are located over the Eastern Pacific extending from the central Pacific to the North American coasts (PacCal), the subtropical North Atlantic (TNA), the Mediterranean area (Medit), Middle East (MidEast) (Figure 1b)
The consistency of the results coming from reanalysis and the EC-Earth large ensemble provides strong support for a causal influence of the Rossby waves generated over the Northeastern Pacific ocean on a global climate response

Summary

Introduction

Circumglobal Rossby waves influence strongly the meandering of the jet stream in the mid-latitudes around the globe, and they have been associated with strong variability of precipitation during summer (Kornhuber et al 2019) and winter seasons (Scaife et al 2017b, Dunstone et al 2018, Li et al 2019). Rossby waves appear in the atmosphere as a result of vertical motion and upper‐tropospheric divergence in the tropics causing in turn anomalous upper-level vorticity. Due to the strong impact of Rossby waves on the extratropical weather and climate, it is relevant to study the geographical places that act as sources. In this context, Nie et al (2019) analysed the observed average spatial location of the RWS during winter and summer, finding that during winter, the main RWS in the Northern Hemisphere are located in East Asia, subtropical central and eastern Pacific, North America, subtropical North Atlantic, Mediterranean, and Arabian regions; while during summer over the Mediterranean, Arabian, and over the Eastern Pacific close to North America. Nie et al (2019) assessed how some CMIP5 models simulate the intensity and location of RWS in the historical period, finding that CMIP5 models can capture the basic geographical distribution of RWS, but most models overestimate the RWS intensity in the subtropics and underestimate the RWS in the midlatitudes

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