European precipitation connections with large-scale mean sea-level pressure (MSLP) fields

Abstract

To advance understanding of hydroclimatological processes, this paper links spatiotemporal variability in gridded European precipitation and large-scale mean sea-level pressure (MSLP) time series using monthly concurrent correlation. Strong negative (positive) correlation near Iceland and (the Azores) is apparent for precipitation in northwest Europe, confirming a positive North Atlantic Oscillation (NAO) association. An opposing pattern is found for southwest Europe, and the Mediterranean in winter. In the lee of mountains, MSLP correlation is lower reflecting reduced influence of westerlies on precipitation generation. Importantly, European precipitation is shown to be controlled by physically interpretable climate patterns that change in extent and position from month to month. In spring, MSLP-precipitation correlation patterns move and shrink, reaching a minimum in summer, before expanding in the autumn, and forming an NAO-like dipole in winter. These spacetime shifts in correlation regions explain why fixed-point NAO indices have limited ability to resolve precipitation for some European locations and seasons.Key words large-scale climate; precipitation; Europe; ERA-40; NAO; hydroclimatological variability Relations entre les précipitations en Europe et les champs de pression au niveau moyen de la mer à grande échelle Résumé En vue de faire avancer notre compréhension des processus hydro-climatiques, cet article établit des liens entre la variabilité spatio-temporelle des précipitations européennes (distribuées selon un maillage régulier) et la pression atmosphérique au niveau moyen de la mer PNMM (période 1952-2002) en utilisant les corréla-tions existant entre elles. Il s'agit pour les précipitations du Nord-Ouest de l'Europe d'importantes corrélations, négatives près de l'Islande et positives près des Açores, ce qui confirme un lien direct avec l'Oscillation Nord Atlantique (ONA). On trouve une structure inverse pour le Sud-Ouest de l'Europe, et la Méditerranée en hiver. Du côté abrité des montagnes, les corrélations avec la PNMM sont plus faibles, reflétant une moindre influence des vents d'Ouest sur la génération des précipitations. Il est important de noter que les précipitations européennes sont contrôlées par des structures climatiques ayant une interprétation physique et qui changent en étendue et position d'un mois à l'autre. Au printemps, les structures de corrélation entre la PNMM et les précipitations se déplacent et s'amenuisent, atteignant un minimum en été, avant de croître en automne, et de former un dipôle de type ONA en hiver. Les déplacements dans l'espace et le temps des régions de corrélation expliquent pourquoi des indices fixes de type ONA ont, en Europe, une aptitude limitée à expliquer les précipitations de certaines régions et de certaines saisons.

A cyclone climatology of the British‐Irish Isles 1871–2012

“…Correlation between precipitation and cyclone counts was highest during summer. This differs from Lavers et al (), who found that the relationship between mean sea‐level pressure (MSLP) and precipitation across northwest Europe (including the BI) was weaker in summer than in winter. One explanation for this discrepancy is that the storm track is known to be more spatially restricted in summer than winter over the northeast Atlantic (Mesquita et al , ).…”

“…Thus, where cyclone frequency is an important driver of precipitation totals, it is reasonable to expect that regions of significant correlations between rainfall totals and MSLP (which bare the imprint of depression passage) should be similarly constrained. The different period (1957–2002) and spatial resolution (2.5° × 2.5°) of the reanalysis dataset used by Lavers et al () could be another factor. In highlighting the importance of cyclones in driving high precipitation amounts over the BI throughout the year, our results agree with Murphy and Washington (), who, in all seasons, observed a cyclonic pattern in the correlation field centred on the BI when assessing the association between MSLP and the leading empirical orthogonal function of BI rainfall.…”

Revealing Hidden Climate Indices from the Occurrence of Hydrologic Extremes

“…The NAO is an important driver of hydrologic variability in many European regions (Pociask‐Karteczka, ), especially in autumn and winter. It has strong and opposite effects in Northern and Southern Europe, but tends to be less impactful in central regions, including France (Lavers et al, ). Beyond NAO, Renard and Lall () documented that no standard climate index delivered skillful predictions of autumn floods in Mediterranean France.…”

“…However, SCIs also have limitations. For instance, they may focus on capturing a mode of climate variability that is not relevant for hydrologic predictands in the target study region (Lavers et al, 2013). The combined use of several SCIs should account for the fact that distinct SCIs may be strongly related to each other (e.g., Westra et al, 2008;Westra & Sharma, 2009;Westra et al, 2015).…”

A hydrogeomorphic assessment of twenty‐first century floods in the UK

“…For seasonal and monthly rainfall and river flows there are strong positive correlations with the NAO in northern and western locations, especially during the winter half year (October–March), and with increasing altitude (Burt and Howden, ). These patterns weaken during the spring and summer away from the far northwest of Scotland, where extra‐tropical cyclones continue to influence the weather and river discharge (Burt and Howden, ; Lavers et al, ). In contrast, extreme floods in small mountain catchments tend to have a closer association with negative NAO index values (Macklin and Rumsby, ; Foulds et al, ).…”