Atmospheric blocking and weather extremes over the Euro-Atlantic sector – a review
Weather and Climate Dynamics European Geosciences Union 3:1 (2022) 305-336
Abstract:
The physical understanding and timely prediction of extreme weather events are of enormous importance to society due to their associated impacts. In this article, we highlight several types of weather extremes occurring in Europe in connection with a particular atmospheric flow pattern, known as atmospheric blocking. This flow pattern effectively blocks the prevailing westerly large-scale atmospheric flow, resulting in changing flow anomalies in the vicinity of the blocking system and persistent conditions in the immediate region of its occurrence. Blocking systems are long-lasting, quasi-stationary and self-sustaining systems that occur frequently over certain regions. Their presence and characteristics have an impact on the predictability of weather extremes and can thus be used as potential indicators. The phasing between the surface and the upper-level blocking anomalies is of major importance for the development of the extreme event. In summer, heat waves and droughts form below the blocking anticyclone primarily via large-scale subsidence that leads to cloud-free skies and, thus, persistent shortwave radiative warming of the ground. In winter, cold waves that occur during atmospheric blocking are normally observed downstream or south of these systems. Here, meridional advection of cold air masses from higher latitudes plays a decisive role. Depending on their location, blocking systems also may lead to a shift in the storm track, which influences the occurrence of wind and precipitation anomalies. Due to these multifaceted linkages, compound events are often observed in conjunction with blocking conditions. In addition to the aforementioned relations, the predictability of extreme events associated with blocking and links to climate change are assessed. Finally, current knowledge gaps and pertinent research perspectives for the future are discussed.An NAO-dominated mode of atmospheric circulation drives large decadal changes in wintertime surface climate and snow mass over Eurasia
Environmental Research Letters IOP Publishing 17:4 (2022) 044025
Abstract:
The leading mode of wintertime atmospheric variability over the North Atlantic-North Eurasia sector is dominated by the North Atlantic Oscillation (NAO) and accounts for more than one third of the total variability. This study explores the influences of the leading mode on decadal climate variability of Northern Eurasia. We focus on the little-explored decadal covariations of surface air temperature (SAT), snowfall, snow water equivalent (SWE) and snow cover over the region, using extensive model output from the Coupled Model Intercomparison Project sixth phase. Recent decadal trends (−0.92σ per decade) in the leading mode identified, are found to be largely a manifestation of internal climate variability (at least two thirds from the most conservative estimate). These internally-generated decadal trends strongly contributed to recent trends in SAT, snowfall, SWE and snow cover over Eurasia. External forcings should have played a minor role over Eurasia as they usually suggest opposite decadal trends to those observed. An exception is found for snowfall and SWE in east Eurasia, for which external forcings may have driven a large part of the recent upward trends, equally as important as the NAO-dominated mode. This points to a complex interplay between internally-generated and externally-forced climate variability over Northern Eurasia. Model discrepancies are identified in reproducing the linkages between the leading mode and the Eurasian surface climate variability. The internally-generated variability of this leading mode thus represents a large source of uncertainty in future decadal climate projections over Eurasia and, due to the memory effects of snow, also in modelling springtime climate variability.Understanding climate risk in future energy systems: an energy-climate data hackathon
Bulletin of the American Meteorological Society American Meteorological Society 103:5 (2022) E1321-E1329
Abstract:
What: Approximately 40 participants – with expertise spanning energy, computer science, weather and climate research -– joined a week-long Energy-Climate data “hackathon” in June 2021. It was hosted by the Universities of Oxford and Reading in partnership with the UK Met Office as part of a series of themed hackathons supported by the Met Office and held in the run-up to the UN COP26 conference. Six projects were initiated and developed by teams over the course of the week, supported by access to state-of-the-art computational resources on the UK’s CEDA-JASMIN service, and stimulated by keynote speakers from industry and academia. The hackathon concluded with teams presenting their outputs to a panel of invited experts. Several teams plan to build on their hackathon success in publications, ongoing collaborations and research funding proposals. When: 18th May (half-day “scoping” event) & 21st-25th June 2021 (main hackathon) Where: Online via Zoom and Gather.Town, supported by Slack communication channels Affiliations: Initiated by: University of Oxford Dr Sarah Sparrow, Professor David Wallom, Professor Tim Woollings, & University of Reading Professor David Brayshaw, Dr Hannah Bloomfield, In partnership with the Met Office, the UK’s national meteorological service, and with support from the UK’s CEDA-JASMIN service and Gurobi optimization software.SST-driven variability of the East Asian summer jet on a decadal time-scale in CMIP6 models
Quarterly Journal of the Royal Meteorological Society Wiley 148:743 (2021) 581-598
Abstract:
The East Asian summer jet (EASJ) is an important component of the East Asian summer monsoon system and its variability is correlated with precipitation and surface temperature variations over this region. Whilst many studies have considered the interannual variability of the EASJ, less is known about variations on a decadal time-scale. This study investigates the relationship between decadal EASJ variability and sea surface temperatures (SSTs) and thus the potential predictability that SSTs may provide. Given the relatively short observational record, we make use of the long pre-industrial control simulations in the Coupled Model Intercomparison Project phase 6 (CMIP6) in addition to a large ensemble of atmosphere-only experiments, forced with random SST patterns. We then create an SST-based reconstruction of the dominant modes of EASJ variability in the CMIP6 models, finding a median EASJ–reconstruction correlation for the dominant mode of 0.43. Much of the skill in the reconstruction arises from variations in Pacific SSTs, however the tropical Atlantic also makes a significant contribution. These findings suggest the potential for multi-year predictions of the EASJ, provided that skilful SST forecasts are available.Projections of northern hemisphere extratropical climate underestimate internal variability and associated uncertainty
Communications Earth and Environment Springer Nature 2 (2021) 194