On the link between the North Atlantic storm track and precipitation deuterium excess in Reykjavik

Franziska Aemisegger

doi:10.1002/asl.865

Abstract

This study establishes a robust process‐based dynamical link between the variability of the deuterium excess (d) in monthly winter precipitation in Reykjavik and the frequency of strong large‐scale ocean evaporation (SLOE) events in the subpolar North Atlantic. SLOE events are induced by cold advection in the rear of extratropical cyclones. The link between SLOE and d emerges from the fact that a substantial fraction of moisture that precipitates in Reykjavik in winter originates from SLOE events. It is shown that positive anomalies of monthly d co‐occur with positive anomalies in the frequency of SLOE events at the moisture source of Reykjavik precipitation. An intensification and a northeastwards shift of the North Atlantic storm track acts as a driver for the enhanced SLOE frequency in months with positive anomalies in d. This link also implies that in the subpolar North Atlantic, variations of d in monthly (or seasonal) precipitation reveal information about the storm track dynamics in the vicinity of Iceland. Potential implications of this finding for the interpretation of d as a proxy for the location and intensity of storm tracks are discussed.

Highlights

The subpolar North Atlantic (SNA) south of Greenland and Iceland is affected by the frequent passage of extratropical cyclones forming the North Atlantic storm track (Hoskins and Hodges, 2002)
This study proposes a new mechanism linking precipitation d signals with the atmospheric drivers of variability in moisture source conditions at the seasonal to inter-annual timescales
This mechanism involves extratropical cyclones and the associated advection of cold air on their rearwards side. These dry and cold airstreams flowing from subpolar regions towards lower latitudes induce large surface latent heat fluxes as soon as they pass the sea ice edge and reach the open ocean leading to cold air outbreaks (CAOs)

Summary

| INTRODUCTION

The subpolar North Atlantic (SNA) south of Greenland and Iceland is affected by the frequent passage of extratropical cyclones forming the North Atlantic storm track (Hoskins and Hodges, 2002). The atmospheric dynamical drivers of variations in the moisture source controlling factors of d, that is, hs and SST are studied in the SNA In this region, a very large fraction of the water evaporates that later precipitates in Reykjavik (Iceland), where a long time series of precipitation isotopes exists. This context is important for determining the relevant moisture source conditions, the d signature of atmospheric vapour and the d of precipitation For this analysis, 23 years of monthly precipitation isotope data from Reykjavik are used together with the climatology of SLOE events from Aemisegger and Papritz (2018) to address the following two questions: 1. What is the role of the position and intensity of the North Atlantic storm track in modulating the frequency of SLOE events and the meteorological context of moisture uptakes? (section 3.2)

| METHODS

| RESULTS

Findings

| SUMMARY OF PROPOSED MECHANISM AND CONCLUSIONS