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Climate impact of the Atlantic Multidecadal Variability (AMV) on the Northern Eurasia is poorly documented in literature due to the lack of observations in space, limited by the local fighting weather conditions, and in time, i.e. the analysed timescale is too long compared to the observational record (~120 years). To overcome this limitation, an idealized modelling approach designed in CMIP6 Decadal Climate Prediction Project is applied, based on the CMCC-CM2-SR5 coupled model: the North Atlantic sea surface temperature are continuously nudged towards the positive (negative) AMV anomalies to simulate the warm (cold) AMV phase. An ensemble of 32 members is performed for each experiment, in which all the forcings are set at the pre-industrial values for a 10-year integration time.Model results shows that, during Boreal summer, a positive phase of the AMV induces a circumglobal east-west wave train across the entire Northern Hemisphere. Enhanced westerly winds alters the climatological upper-troposphere circulation, advecting moisture from the North Atlantic Ocean along the northern part of the Eurasian continent. In particular, over Siberia, an anomalous geopotential dipole promotes the poleward movement of specific humidity from the Pacific Ocean, converging at high latitudes with the aforementioned westerly flux. Moisture anomalies regionally contribute to May-to-August rainfall, intensifying multidecadal precipitation over Scandinavia and Eastern Russia. Interestingly, rainfall rises by 10% of its climatology over Siberia, where the AMV-induced moisture fluxes converges.Furthermore, this study also points out that the AMV has a role in modulating the freshwater balance of the Arctic Ocean, due to the anomalous precipitation over the Siberian rivers' watersheds (Ob', Yenisei and Lena). Siberia is a key region for the hydrological cycle of the Arctic Ocean and the catchment areas of these three large rivers accounts for about 46% of the Arctic freshwater input provided by terrestrial sources. We find a decrease of sea surface salinity (about 12% of model climatology, broadly consistent with the anomalous river discharge) in the proximity of the river mouths during positive-AMV years.These results disclose the potential predictability of precipitation over northern Eurasian via tropical-extratropical pathway, associated with multidecadal fluctuations of the North Atlantic sea surface temperatures, in agreement with recent observational studies.This work is supported by EUCP (European Climate Prediction system) under Horizon 2020, grant agreement 776613. [ABSTRACT FROM AUTHOR]

In this study the relationship between the poleward transport of moisture and heat by atmospheric eddies and North Atlantic weather regimes is assessed in reanalysis data. Weather regimes are patterns of large scale atmospheric circulation that are often regarded as recurrent, quasi-stationary states of the atmospheric flow. Transport of heat by transient atmospheric eddies is a key component of the heat budget of the Arctic and high latitude regions. Recent studies suggest that heat transport into the pole happens in "bursts" of warm air. Time scales involved are between the midlatitude baroclinic life cycle and the sub-seasonal range. In our work, the four optimal North Atlantic weather regimes, namely the two phases of the NAO, Atlantic ridge and Scandinavian blocking, are identified, then their relationship with storminess, baroclinicity and transport of moist static energy (MSE) by transient synoptic and intraseasonal eddies is analysed. The focus of the analysis is on the extended winter season and on the lower troposphere. We demonstrate that the spatial distribution of aforementioned quantities is substantially modulated by the occurrence of weather regimes and that the convergence of the MSE flux into the pole is significantly affected. Particular emphasis is posed on link between Scandinavian blocking and heat flux convergence in the Nordic Seas. The link between WRs and surface temperature, sea ice cover, snow cover and soil moisture is also documented and the implications of our findings for sub-seasonal predictability and systematic errors in coupled models are discussed. Applications of the proposed approach to seasonal forecast systems (Blue-Action) and multi-model frameworks (PRIMAVERA) is ongoing. This study is supported by the Blue-Action project (European Union's Horizon 2020 research and innovation programme, grant: 727852) [ABSTRACT FROM AUTHOR]

The Kuroshio Extension (KE) is the eastward-flowing, free, inertial meandering jet formed by the confluence of the Kuroshio and Oyashio western boundary currents. The KE jet is known for its low-frequency variability (LFV) which connects a zonally elongated, fairly stable and energetic meandering jet (elongated state) and a much weaker, highly variable and convoluted jet with a reduced zonal penetration (contracted state). The LFV of the KE is therefore often referred to as being bimodal (Qiu, 2002). The nature of this variability is still under debate; some authors suggest that non-linear internal oceanic mechanisms can play a fundamental role in the phenomenon (Pierini, 2006) but there is also evidence from the observations that the KE LFV is connected with changes in atmospheric patterns of variability as the Aleutian Low and the North Pacific Oscillation (Nathan J. and Mantua Steven R. Hare, 2002; Qiu B., 2003; L. Ceballos et al, 2009; S. Pierini, 2014; M. Newman et al, 2016). In the first part of our analysis, we assess the impact of model resolution on the low-frequency variability of the KE jet. Results from two present-climate coupled simulations differing by their atmospheric component resolution are compared. For this analysis, results from the CMCC-CM2 model are used, under the CMIP6 HighResMIP protocol. Several aspects of the KE LFV are inspected, including the KE bimodality and the role of ocean weather (mesoscale oceanic eddies) in modulating the air-sea interactions. In the second part of the work, the role of the intrinsic variability and atmospherically-forced variability of the KE LFV is investigated taking advantage of the OCCIPUT ensemble of 1/4° global oceanic hindcasts provided by the Institut des Géosciences de l'Environnement (IGE). This dataset is built in order to simulate simultaneously both contributions (intrinsic and forced) and to allow their separation via ensemble statistics. [ABSTRACT FROM AUTHOR]

A large inter-annual variability exists in the strength of the Northern stratospheric polar-vortex in the extra-tropics. Variations of the polar vortex are influenced by external factors and by internal atmospheric dynamics. Part of variability may be linked to the sudden stratospheric warming (SSWs) in the extra-tropics and to the quasi-biennial oscillation (QBO) in the equatorial stratosphere which appears to affect the zonal mean circulation. SSW correspond to extreme 'polar vortex events' influencing the Arctic Oscillation and mid-latitude extreme weather. The QBO is the major wind variability source in the tropical lower stratosphere.We examine the decadal variability and predictability of the climate system, associated with these processes occurring in the stratosphere. We base our analysis on a set of near-term predictions performed with state-of-the-art stratosphere-resolving climate models, initialized with an estimated state of the ocean and atmosphere. We conclude that the atmosphere initialization has a key role on the variability and predictability of stratospheric processes providing evidence that a proper initialization of the QBO might be beneficial not only for the predictability of the tropics but also in the extra-tropics. [ABSTRACT FROM AUTHOR]

It is well established that climate model projections indicate a tendency towards more extreme daily rainfall events. It is however uncertain how this changing intensity translates at the sub-daily time scales. The main goal of the present study is to examine possible differences in projected changes in intense precipitation events over Europe at the daily and sub-daily (3-hourly) time scales using a state-of-the-science climate model. There are large differences in intense precipitation projections when comparing the results at the daily and sub-daily time scales. Over north-eastern Europe, projected precipitation intensification at the 3-hour scale is lower than at the daily scale. On the other hand, Spain and the western seaboard exhibit an opposite behaviour, with stronger intensification at the daily rather than 3-hour scale. While the mean properties of the precipitation distributions are independent of the analysed frequency, projected precipitation intensification exhibit regional differences. [ABSTRACT FROM AUTHOR]