Possible connections are studied between the monthly average values of the wind angular moment module and anomalу of the globally averaged surface temperature and change in radiative forcing. The existence of statistically significant positive linear correlation between these characteristics is shown. The results obtained are in accordance with the conclusions of the theory of similarity of planetary atmospheres.
The possibility that Arctic sea ice loss weakens mid-latitude westerlies, promoting more severe cold winters, has sparked more than a decade of scientific debate, with apparent support from observations but inconclusive modelling evidence. Here we show that sixteen models contributing to the Polar Amplification Model Intercomparison Project simulate a weakening of mid-latitude westerlies in response to projected Arctic sea ice loss. We develop an emergent constraint based on eddy feedback, which is 1.2 to 3 times too weak in the models, suggesting that the real-world weakening lies towards the higher end of the model simulations. Still, the modelled response to Arctic sea ice loss is weak: the North Atlantic Oscillation response is similar in magnitude and offsets the projected response to increased greenhouse gases, but would only account for around 10% of variations in individual years. We further find that relationships between Arctic sea ice and atmospheric circulation have weakened recently in observations and are no longer inconsistent with those in models. ; D.M.S., R.E., L.H., L.S.G., T.J., T.S., X.L., and P.O. were supported by the EU H2020 APPLICATE project (GA727862). The Met Office contribution was also supported by the Met Office Hadley Centre Climate Programme funded by BEIS and Defra and by the UK-China Research and Innovation Partnership Fund through the Met Office Climate Science for Service Partnership (CSSP) China as part of the Newton Fund. J.A.S was supported by NERC grants NE/P006760/1, NE/R005125/1 and NE/V005855/1. G.M and Y.P. were supported by the US Department of Energy, grant number DE-SC0019407. L.S.G was also supported by the Research council of Norway INES project (270061), and the Norwegian e-infrastructure for Research and Education (UNINETT Sigma2) through projects NN2345K, NS2345K and NS9034K. E.M. and D.M. acknowledge the support of the German Federal Ministry of Education and Research through the JPI Climate/JPI Oceans NextG-Climate Science-ROADMAP (FKZ: 01LP2002A) project and of the European Union's Horizon 2020 Programme through the Blue-Action Project (GA727852); and the use of resources from the DKRZ bm0966 and bm1190 projects. C. Deser acknowledges support from the National Center for Atmospheric Research, which is a major facility sponsored by the US National Science Foundation under cooperative agreement 1852977. M.M. was supported by MEXT through the Integrated Research Program for Advancing Climate Models (JPMXD0717935457) and ArCS II (JPMXD1420318865) programs, and by the Environment Research and Technology Development Fund (JPMEERF20192004). J.G.-S. and P.O. were supported by the Spanish Ramón y Cajal' programme (RYC-2016-21181, RYC-2016-22772). B.H. was jointly funded by the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No. XDA19070404) and the National Natural Science Foundation of China (Grant Nos. 42030602, 91837101). G.G. was supported by the EU H2020 Blue–Action (GA727852) project and uses the HPC resources of TGCC under the allocations 2018-R0040110492 and 2019-A0060107732 made by GENCI. J.S. acknowledges the project L4 of the Collaborative Research Centre TRR 181 Energy Transfers in Atmosphere and Ocean funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Project 274762653. ; Peer Reviewed ; "Article signat per 31 autors/es: D. M. Smith, R. Eade, M. B. Andrews, H. Ayres, A. Clark, S. Chripko, C. Deser, N. J. Dunstone, J. García-Serrano, G. Gastineau, L. S. Graff, S. C. Hardiman, B. He, L. Hermanson, T. Jung, J. Knight, X. Levine, G. Magnusdottir, E. Manzini, D. Matei, M. Mori, R. Msadek, P. Ortega, Y. Peings, A. A. Scaife, J. A. Screen, M. Seabrook, T. Semmler, M. Sigmond, J. Streffing, L. Sun & A. Walsh " ; Postprint (published version)
Abstract The paper discusses the impact of the atmospheric circulation on the long-term variability of liquid, mixed and solid precipitation. The three precipitation forms were characterised by their totals, the number of days when they prevailed, and the contribution of each to the overall precipitation totals. Trends, as a background to further analysis, were calculated with regard to each characteristic of each precipitation form. The most significant increases were recorded in the contribution of liquid precipitation to the overall precipitation totals in September and in the mixed precipitation totals in December and November. Arctic Oscillation (AO) was found to have only a minor influence on the long-term variability of precipitation characteristics. The AO phase could to some degree account for the observed variation in the number of days with liquid precipitation. On the other hand, the direction of the local advection could account for considerably more of this variability and also the variability in liquid precipitation totals.
Abstract. The climate characteristics of summer human thermal discomfort in Athens and its connection to atmospheric circulation are studied for the period 1954–2012. The human thermal discomfort is examined in terms of the Predicted Mean Vote (PMV) discomfort index for calm and light wind (3 ms-1) conditions. Its inter-annual variability is characterised by a significant increase from the middle 1980s to the end of the study period. The onset and the cessation of the discomfort period are found to take place around the beginning of July and the end of August respectively, but from middle 1980s the dates of onset and cessation have slightly moved earlier and later, respectively, leading to a longer summer discomfort period. The connection between human thermal discomfort and atmospheric circulation is studied by examining the distribution of discomfort cases across six objectively defined circulation types over Europe, based on Athens weather characteristics. High values of the PMV discomfort index are mainly associated with two typical high-summer pressure patterns with the intensity of discomfort depending on the pressure gradient over the Aegean Sea. On the contrary, low PMV discomfort index values prevail mainly on days typified by the other four circulation types, which are more frequent during May, June, and September.
Abstract. Deep persistent slab avalanches are capable of destroying infrastructure and are usually unsurvivable for those who are caught. Formation of a snowpack conducive to deep persistent slab avalanches is typically driven by meteorological conditions occurring in the beginning weeks to months of the winter season, and yet the avalanche event may not occur for several weeks to months later. While predicting the exact timing of the release of deep persistent slab avalanches is difficult, onset of avalanche activity is commonly preceded by rapid warming, heavy precipitation, or high winds. This work investigates the synoptic drivers of deep persistent slab avalanches at three sites in the western USA with long records: Bridger Bowl, Montana; Jackson, Wyoming; and Mammoth Mountain, California. We use self-organizing maps to generate 20 synoptic types that summarize 5899 daily 500 mbar geopotential height maps for the winters (November–March) of 1979/80–2017/18. For each of the three locations, we identify major and minor deep persistent slab avalanche seasons and analyze the number of days represented by each synoptic type during the beginning (November–January) of the major and minor seasons. We also examine the number of days assigned to each synoptic type during the 72 h preceding deep persistent slab avalanche activity for both dry and wet slab events. Each of the three sites exhibits a unique distribution of the number of days assigned to each synoptic type during November–January of major and minor seasons and for the 72 h period preceding deep persistent slab avalanche activity. This work identifies the synoptic-scale atmospheric circulation patterns contributing to deep persistent slab instabilities and the patterns that commonly precede deep persistent slab avalanche activity. By identifying these patterns, we provide an improved understanding of deep persistent slab avalanches and an additional tool to anticipate the timing of these difficult-to-predict events.
Abstract. We present an analysis of daily extreme precipitation events for the extended winter season (October–March) at 20 Mediterranean coastal sites covering the period 1950–2006. The heavy tailed behaviour of precipitation extremes and estimated return levels, including associated uncertainties, are derived applying a procedure based on the Generalized Pareto Distribution, in combination with recently developed methods. Precipitation extremes have an important contribution to make seasonal totals (approximately 60% for all series). Three stations (one in the western Mediterranean and the others in the eastern basin) have a 5-year return level above 100 mm, while the lowest value (estimated for two Italian series) is equal to 58 mm. As for the 50-year return level, an Italian station (Genoa) has the highest value of 264 mm, while the other values range from 82 to 200 mm. Furthermore, six series (from stations located in France, Italy, Greece, and Cyprus) show a significant negative tendency in the probability of observing an extreme event. The relationship between extreme precipitation events and the large scale atmospheric circulation at the upper, mid and low troposphere is investigated by using NCEP/NCAR reanalysis data. A 2-step classification procedure identifies three significant anomaly patterns both for the western-central and eastern part of the Mediterranean basin. In the western Mediterranean, the anomalous southwesterly surface to mid-tropospheric flow is connected with enhanced moisture transport from the Atlantic. During ≥5-year return level events, the subtropical jet stream axis is aligned with the African coastline and interacts with the eddy-driven jet stream. This is connected with enhanced large scale ascending motions, instability and leads to the development of severe precipitation events. For the eastern Mediterranean extreme precipitation events, the identified anomaly patterns suggest warm air advection connected with anomalous ascent motions and an increase of the low- to mid-tropospheric moisture. Furthermore, the jet stream position (during ≥5-year return level events) supports the eastern basin being in a divergence area, where ascent motions are favoured. Our results contribute to an improved understanding of daily precipitation extremes in the cold season and associated large scale atmospheric features.
Abstract Climate change over the territory of the Atlantic-European sector during the recent decades is studied with reference to changes in the largescale atmospheric circulation. The classification of synoptic patterns (from the class of most probably to the class of least probable fields) is given for winter and summer for the last three decades, starting from 1974-1983. The synoptic pattern of the most probable class of field sea-level pressure shows high pressure over Europe in 1974-2005, which from decade to decade occupies more and more territory in summer and winter. The high temporal stability of predominant synoptic patterns is responsible for long-lived events of extreme warm and dry weather in winter and in summer for heat waves and droughts. The synoptic patterns corresponding to such dangerous weather conditions as extreme cold, strong precipitation, glaze ice, strong winds, hail etc. are discussed as well.
In: Messori , G , van Wees , D , Pausata , F S R , Acosta Navarro , J C , Hannachi , A & Dentener , F J 2018 , ' The impact of future atmospheric circulation changes over the Euro-Atlantic sector on urban PM 2.5 concentrations ' , Tellus, Series B : Chemical and Physical Meteorology , vol. 70 , no. 1 , pp. 1-22 . https://doi.org/10.1080/16000889.2018.1468704
Air quality management is strongly driven by legislative aspects related to the exceedance of air quality limit values. Here, we use the Norwegian Climate Centre's Earth System Model to assess the impact of a future scenario of maximum feasible aerosol emission abatement and increasing greenhouse gases (RCP4.5) on urban PM 2.5 concentrations in Europe. Daily PM 2.5 concentrations are assessed using a novel downscaling method which allows us to compute exceedances of current and planned air quality thresholds. For the latter, we assume that future ambitious emission reductions are likely to be accompanied by stricter air quality thresholds. The changes in PM 2.5 concentrations are discussed in the context of the large-scale atmospheric changes observed relative to the present-day climate. Our results show a more positive North Atlantic Oscillation mean state in the future, combined with a large eastward shift of both North Atlantic sea-level pressure centres of action. This is associated with more frequent mid-latitude blocking and a northward shift of the jet stream. These changes favour higher than expected anthropogenic urban PM 2.5 concentrations in Southern Europe, while they have the opposite effect on the northern half of the continent. In the future scenario, PM concentrations in substantial parts of Southern Europe are found to exceed the World Health Organisation Air Quality Guideline daily limit of 25 μg/m 3 on 25 to over 50 days per year, and annual guidelines of 10 µg/m 3 on more than 80% of the 30 years analysed in our study. We conclude that alterations in atmospheric circulation in the future, induced by stringent maximum feasible air pollution mitigation as well as GHG emissions, will negatively influence the effectiveness of these emission abatements over large parts of Europe. This has important implications for future air quality policies.
In the past decades, boreal summers have been characterized by an increasing number of extreme weather events in the Northern Hemisphere extratropics, including persistent heat waves, droughts and heavy rainfall events with significant social, economic and environmental impacts. Many of these events have been associated with the presence of anomalous large-scale atmospheric circulation patterns, in particular persistent blocking situations, i.e., nearly stationary spatial patterns of air pressure. To contribute to a better understanding of the emergence and dynamical properties of such situations, we construct complex networks representing the atmospheric circulation based on Lagrangian trajectory data of passive tracers advected within the atmospheric flow. For these Lagrangian flow networks, we study the spatial patterns of selected node properties prior to, during and after different atmospheric blocking events in Northern Hemisphere summer. We highlight the specific network characteristics associated with the sequence of strong blocking episodes over Europe during summer 2010 as an illustrative example. Our results demonstrate the ability of the node degree, entropy and harmonic closeness centrality based on outgoing links to trace important spatio-temporal characteristics of atmospheric blocking events. In particular, all three measures capture the effective separation of the stationary pressure cell forming the blocking high from the normal westerly flow and the deviation of the main atmospheric currents around it. Our results suggest the utility of further exploiting the Lagrangian flow network approach to atmospheric circulation in future targeted diagnostic and prognostic studies. ; This project has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No813844. RVD has been additionally supported by the Federal Ministry for Education and Research of Germany (BMBF) via the JPI Climate/JPI Oceans project ROADMAP (grant no. 01LP2002B). CL and EHG also acknowledge support from MINECO/AEI/FEDER through the María de Maeztu Program for Units of Excellence in R&D (MDM-2017-0711, Spain). ; No
Using the daily records derived from the synoptic weather stations and the NCEP/NCAR and ERA-Interim reanalysis data, the variability of the winter haze pollution (indicated by the mean visibility and number of hazy days) in the Beijing–Tianjin–Hebei (BTH) region during the period 1981 to 2015 and its relationship with the atmospheric circulations at middle–high latitude were analyzed in this study. The winter haze pollution in BTH had distinct inter-annual and inter-decadal variabilities without a significant long-term trend. According to the spatial distribution of correlation coefficients, six atmospheric circulation indices ( I 1 to I 6 ) were defined from the key areas in sea level pressure (SLP), zonal and meridional winds at 850 hPa (U850, V850), geopotential height field at 500 hPa (H500), zonal wind at 200 hPa (U200), and air temperature at 200 hPa (T200), respectively. All of the six indices have significant and stable correlations with the winter visibility and number of hazy days in BTH. In the raw (unfiltered) correlations, the correlation coefficients between the six indices and the winter visibility (number of hazy days) varied from 0.57 (0.47) to 0.76 (0.6) with an average of 0.65 (0.54); in the high-frequency ( < 10 years) correlations, the coefficients varied from 0.62 (0.58) to 0.8 (0.69) with an average of 0.69 (0.64). The six circulation indices together can explain 77.7 % (78.7 %) and 61.7 % (69.1 %) variances of the winter visibility and the number of hazy days in the year-to-year (inter-annual) variability, respectively. The increase in I c (a comprehensive index derived from the six individual circulation indices) can cause a shallowing of the East Asian trough at the middle troposphere and a weakening of the Siberian high-pressure field at sea level, and is then accompanied by a reduction (increase) of horizontal advection and vertical convection (relative humidity) in the lowest troposphere and a reduced boundary layer height in BTH and its neighboring areas, which are favorable for the formation of haze pollution in BTH winter, and vice versa. The high level of the prediction statistics and the reasonable mechanism suggested that the winter haze pollution in BTH can be forecasted or estimated credibly based on the optimized atmospheric circulation indices. Thus it is helpful for government decision-making departments to take action in advance in dealing with probably severe haze pollution in BTH indicated by the atmospheric circulation conditions.
Using the daily records derived from the synoptic weather stations and the NCEP/NCAR and ERA-Interim reanalysis data, the variability of the winter haze pollution (indicated by the mean visibility and number of hazy days) in the Beijing–Tianjin–Hebei (BTH) region during the period 1981 to 2015 and its relationship with the atmospheric circulations at middle–high latitude were analyzed in this study. The winter haze pollution in BTH had distinct inter-annual and inter-decadal variabilities without a significant long-term trend. According to the spatial distribution of correlation coefficients, six atmospheric circulation indices (I1 to I6) were defined from the key areas in sea level pressure (SLP), zonal and meridional winds at 850 hPa (U850, V850), geopotential height field at 500 hPa (H500), zonal wind at 200 hPa (U200), and air temperature at 200 hPa (T200), respectively. All of the six indices have significant and stable correlations with the winter visibility and number of hazy days in BTH. In the raw (unfiltered) correlations, the correlation coefficients between the six indices and the winter visibility (number of hazy days) varied from 0.57 (0.47) to 0.76 (0.6) with an average of 0.65 (0.54); in the high-frequency ( < 10 years) correlations, the coefficients varied from 0.62 (0.58) to 0.8 (0.69) with an average of 0.69 (0.64). The six circulation indices together can explain 77.7 % (78.7 %) and 61.7 % (69.1 %) variances of the winter visibility and the number of hazy days in the year-to-year (inter-annual) variability, respectively. The increase in Ic (a comprehensive index derived from the six individual circulation indices) can cause a shallowing of the East Asian trough at the middle troposphere and a weakening of the Siberian high-pressure field at sea level, and is then accompanied by a reduction (increase) of horizontal advection and vertical convection (relative humidity) in the lowest troposphere and a reduced boundary layer height in BTH and its neighboring areas, which are favorable for the formation of haze pollution in BTH winter, and vice versa. The high level of the prediction statistics and the reasonable mechanism suggested that the winter haze pollution in BTH can be forecasted or estimated credibly based on the optimized atmospheric circulation indices. Thus it is helpful for government decision-making departments to take action in advance in dealing with probably severe haze pollution in BTH indicated by the atmospheric circulation conditions.
More than 90% of oceanic heat enters the Arctic Ocean with the Norwegian Current. In this paper we examine the mechanisms of variability of the oceanic heat flux in the Norwegian Current (across the Svinoy section in the southern Norwegian Sea) in 1993–2019. GLORYS oceanic reanalysis with a spatial resolution of 1/12° is used. It is found that the variability of oceanic heat flux is associated with that of water transport, which, in turn, is associated with variability of the sea level gradient across the Norwegian Current. It is shown that an increase in water transport of the Norwegian Current is a result of a decrease of the atmospheric pressure over the central part of the Norwegian Sea. The latter intensifies the southwesterly winds along the Scandinavian Peninsula. The sea level gradients across the Norwegian Current, formed by the winds, are primarily associated with Ekman pumping towards the coast, as well as with the wind stress curl. Both have a significant impact on the variability of water transport through the section. Another factor is variability of the steric sea level gradient, which significantly affects the water transport during the period of a rapid temperature rise of in the Norwegian Current (1995–2005).
