Weather and Climate Dynamics最新文献

{"title":"The composite development and structure of intense synoptic-scale Arctic cyclones","authors":"Alexander F. Vessey, K. Hodges, L. Shaffrey, J. Day","doi":"10.5194/wcd-3-1097-2022","DOIUrl":"https://doi.org/10.5194/wcd-3-1097-2022","url":null,"abstract":"Abstract. Understanding the location and intensity of hazardous weather across the Arctic is important for assessing risks to infrastructure, shipping, and coastal communities. Key hazards driving these risks are extreme near-surface winds, high ocean waves, and heavy precipitation, which are dependent on the structure and development of intense synoptic-scale cyclones. This study aims to describe the typical lifetime, structure, and development of a large sample of past intense winter (DJF) and summer (JJA) synoptic-scale Arctic cyclones using a storm compositing methodology applied to the ERA5 reanalysis. Results show that the composite development and structure of intense summer Arctic cyclones are different from those of intense winter Arctic and North Atlantic Ocean extra-tropical cyclones and from those described in conceptual models of extra-tropical and Arctic cyclones. The composite structure of intense summer Arctic cyclones shows that they typically undergo a structural transition around the time of maximum intensity from having a baroclinic structure to an axi-symmetric cold-core structure throughout the troposphere, with a low-lying tropopause and large positive temperature anomaly in the lower stratosphere. Summer Arctic cyclones are also found to have longer lifetimes than winter Arctic and North Atlantic Ocean extra-tropical cyclones, potentially causing prolonged hazardous and disruptive weather conditions in the Arctic.\u0000","PeriodicalId":383272,"journal":{"name":"Weather and Climate Dynamics","volume":"24 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-09-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125471684","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Modulation of the El Niño teleconnection to the North Atlantic by the tropical North Atlantic during boreal spring and summer","authors":"J. W. Casselman, B. Jiménez-Esteve, D. Domeisen","doi":"10.5194/wcd-3-1077-2022","DOIUrl":"https://doi.org/10.5194/wcd-3-1077-2022","url":null,"abstract":"Abstract. Equatorial Pacific sea surface temperature anomalies (SSTAs) associated with El Niño–Southern Oscillation (ENSO) can influence the North Atlantic European (NAE) region. ENSO tends to be negatively correlated with the North Atlantic Oscillation in winter, while this connection is less clear in boreal spring and summer when the ENSO teleconnection encounters altered background conditions (i.e., a weaker subtropical jet), which can modulate the signal on the way to the NAE region. One such region that modulates the ENSO teleconnection to the NAE region is the tropical North Atlantic (TNA). While several mechanisms exist for this modulation, we center our analysis on the Caribbean region and the Walker cells. In order to isolate the relevant mechanism, we force an idealized atmospheric circulation model with three different seasonally varying sea surface temperature patterns that represent an ENSO event with or without the influence of the TNA, focusing on the decaying phase of ENSO in boreal spring and summer. We find that in boreal spring, the TNA modulates the ENSO teleconnection to the NAE primarily through a propagating Rossby wave train, while in summer, the TNA's influence tends to strengthen the ENSO influence over the NAE sector. Overall, this study offers a deeper understanding of the inter-basin interactions through the Walker cell following an ENSO event and the central role of tropical Atlantic SSTAs in modulating the teleconnection to the NAE region in boreal spring and summer.\u0000","PeriodicalId":383272,"journal":{"name":"Weather and Climate Dynamics","volume":"13 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-09-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128808527","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Predictability of a tornado environment index from El Niño–Southern Oscillation (ENSO) and the Arctic Oscillation","authors":"M. Tippett, C. Lepore, M. L’Heureux","doi":"10.5194/wcd-3-1063-2022","DOIUrl":"https://doi.org/10.5194/wcd-3-1063-2022","url":null,"abstract":"Abstract. El Niño–Southern Oscillation (ENSO) modulates severe thunderstorm activity in the US, with\u0000increased activity expected during La Niña conditions. There is\u0000also evidence that severe thunderstorm activity is influenced by the\u0000Arctic Oscillation (AO), with the positive phase being associated\u0000with enhanced activity. The combined ENSO–AO impact is relevant for\u0000situations such as in early 2021, when persistent, strong positive\u0000and negative AO events occurred during La Niña conditions. Here we\u0000examine the relation of a spatially resolved tornado environment\u0000index (TEI) with ENSO and the AO in climate model forecasts of\u0000February, March, and April conditions over North America. Bivariate\u0000composites on Niño 3.4 and AO indices show that TEI predictability\u0000is high (strong signals and probability shifts) when the ENSO and AO\u0000signals reinforce each other and low when they cancel each\u0000other. The largest increase in the expected value and variance of\u0000TEI occurs when Niño 3.4 is negative, and the AO is\u0000positive. Signal-to-noise ratios are higher during El\u0000Niño–negative AO than during La Niña–positive AO, but\u0000probability shifts are comparable.\u0000","PeriodicalId":383272,"journal":{"name":"Weather and Climate Dynamics","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-09-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130480461","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Supercell convective environments in Spain based on ERA5: hail and non-hail differences","authors":"C. Calvo-Sancho, J. Díaz-Fernández, Yago Martín, P. Bolgiani, M. Sastre, J. J. González-Alemán, D. Santos-Muñoz, J. I. Farrán, María Luisa Martín","doi":"10.5194/wcd-3-1021-2022","DOIUrl":"https://doi.org/10.5194/wcd-3-1021-2022","url":null,"abstract":"Abstract. Severe convective storms, in particular supercells, are\u0000occasionally responsible for a large number of property losses and damage\u0000in Spain. This paper aims to study the synoptic configurations and\u0000pre-convective environments in a dataset of 262 supercells during 2011–2020 in Spain. The events are grouped into supercells with hail (diameter larger than 5 cm) and without hail and the results are compared. ERA5 reanalysis is used to study the synoptic configurations and proximity atmospheric profiles\u0000related to the supercell events at the initial time. In addition,\u0000temperature, convective available potential energy, convective inhibition,\u0000lifting condensation level, level of free convection, height of freezing\u0000level, wind shear and storm-relative helicity are obtained for each event.\u0000Results show that supercells are more frequent on the Mediterranean coast\u0000during the warm season. Some of the variables analyzed present statistically\u0000significant differences between hail and non-hail events. In particular,\u0000supercells with hail are characterized by higher median values of\u0000most-unstable convective available potential energy than supercells without\u0000hail.\u0000","PeriodicalId":383272,"journal":{"name":"Weather and Climate Dynamics","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-09-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129158551","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Dynamics of gap winds in the Great Rift Valley, Ethiopia: emphasis on strong winds at Lake Abaya","authors":"Cornelius Immanuel Weiß, A. Gohm, M. Rotach, T. T. Minda","doi":"10.5194/wcd-3-1003-2022","DOIUrl":"https://doi.org/10.5194/wcd-3-1003-2022","url":null,"abstract":"Abstract. Lake Abaya, located in the Great Rift Valley (GRV) in Ethiopia, is affected by regularly occurring strong winds that cause water waves, which in turn affect the lake's ecology and food web. The driving forces for these winds, however, are yet unexplained. Hence, the main goal of this study is to provide a physical explanation for the formation of these strong winds in the GRV and especially at Lake Abaya. To this aim, two case studies were performed based on measurements, ERA5 reanalysis data and mesoscale numerical simulations conducted with the Weather Research and Forecasting (WRF) model. The simulations revealed that in both cases a gap flow downstream of the narrowest and highest part of the GRV (i.e. the pass) led to high wind speeds of up to 25 m s−1. Two types of gap flow were identified: a north-eastern gap flow and a south-western gap flow. The wind directions are in line with the orientation of the valley axis and depend on the air mass distribution north and south of the valley and the resulting along-valley pressure gradient. The air mass distribution was determined by the position of the Intertropical Convergence Zone relative to the GRV. The colder air mass was upstream of the GRV in both case studies. During the day, the convective boundary layer in the warmer air mass on the downstream side heated up more strongly and quickly than in the colder air mass. The most suitable variable describing the timing of the gap flow was found to be the pressure gradient at pass height, which corresponds roughly to the 800 hPa pressure level. In both cases the gap flow exhibited a strong daily cycle, which illustrates the importance of the thermal forcing due to differential heating over complex terrain in addition to the large-scale forcing due to air mass differences. The start, strength, and the duration of the gap winds within the valley depended on location. For both cases, the strongest winds occurred after sunset and in the ongoing night downstream of the gap and on the corresponding lee slope. The ERA5 reanalysis captures both events qualitatively well but with weaker wind speeds than in the mesoscale numerical simulations. Hence, ERA5 is suitable for a future climatological analysis of these gap flows.\u0000","PeriodicalId":383272,"journal":{"name":"Weather and Climate Dynamics","volume":"124 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-08-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128181300","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Quantifying stratospheric biases and identifying their potential sources in subseasonal forecast systems","authors":"Z. Lawrence, M. Abalos, B. Ayarzagüena, D. Barriopedro, A. Butler, N. Calvo, A. de la Cámara, A. Charlton-Perez, D. Domeisen, E. Dunn‐Sigouin, J. García-Serrano, C. Garfinkel, N. Hindley, L. Jia, M. Jucker, Alexey Y. Karpechko, Hera Kim, A. Lang, Simon H. Lee, P. Lin, M. Osman, F. Palmeiro, J. Perlwitz, I. Polichtchouk, J. Richter, Chen Schwartz, S. Son, Irina Statnaia, M. Taguchi, Nicholas L. Tyrrell, C. Wright, R. Wu","doi":"10.5194/wcd-3-977-2022","DOIUrl":"https://doi.org/10.5194/wcd-3-977-2022","url":null,"abstract":"Abstract. The stratosphere can be a source of predictability for surface weather on timescales of several weeks to months. However, the potential predictive skill gained from stratospheric variability can be limited by biases in the representation of stratospheric processes and the coupling of the stratosphere with surface climate in forecast systems. This study provides a first systematic identification of model biases in the stratosphere across a wide range of subseasonal forecast systems. It is found that many of the forecast systems considered exhibit warm global-mean temperature biases from the lower to middle stratosphere, too strong/cold wintertime polar vortices, and too cold extratropical upper-troposphere/lower-stratosphere regions. Furthermore, tropical stratospheric anomalies associated with the Quasi-Biennial Oscillation tend to decay toward each system's climatology with lead time. In the Northern Hemisphere (NH), most systems do not capture the seasonal cycle of extreme-vortex-event probabilities, with an underestimation of sudden stratospheric warming events and an overestimation of strong vortex events in January. In the Southern Hemisphere (SH), springtime interannual variability in the polar vortex is generally underestimated, but the timing of the final breakdown of the polar vortex often happens too early in many of the prediction systems. These stratospheric biases tend to be considerably worse in systems with lower model lid heights. In both hemispheres, most systems with low-top atmospheric models also consistently underestimate the upward wave driving that affects the strength of the stratospheric polar vortex. We expect that the biases identified here will help guide model development for subseasonal-to-seasonal forecast systems and further our understanding of the role of the stratosphere in predictive skill in the troposphere.\u0000","PeriodicalId":383272,"journal":{"name":"Weather and Climate Dynamics","volume":"120 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-08-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115807155","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Improved teleconnection between Arctic sea ice and the North Atlantic Oscillation through stochastic process representation","authors":"K. Strommen, S. Juricke, F. Cooper","doi":"10.5194/wcd-3-951-2022","DOIUrl":"https://doi.org/10.5194/wcd-3-951-2022","url":null,"abstract":"Abstract. The extent to which interannual variability in Arctic sea ice influences the mid-latitude circulation has been extensively debated. While observational data support the existence of a teleconnection between November sea ice in the Barents–Kara region and the subsequent winter North Atlantic Oscillation, climate models do not consistently reproduce such a link, with only very weak inter-model consensus. We show, using the EC-Earth3 climate model, that while an ensemble of coupled EC-Earth3 simulations shows no evidence of such a teleconnection, the inclusion of stochastic parameterizations to the ocean and sea ice component results in the emergence of a robust teleconnection comparable in magnitude to that observed. While the exact mechanisms causing this remain unclear, we argue that it can be accounted for by an improved ice–ocean–atmosphere coupling due to the stochastic perturbations, which aim to represent the effect of unresolved ice and ocean variability. In particular, the weak inter-model consensus may to a large extent be due to model biases in surface coupling, with stochastic parameterizations being one possible remedy.\u0000","PeriodicalId":383272,"journal":{"name":"Weather and Climate Dynamics","volume":"20 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-08-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123842418","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Jet stream variability in a polar warming scenario – a laboratory perspective","authors":"Costanza Rodda, U. Harlander, M. Vincze","doi":"10.5194/wcd-3-937-2022","DOIUrl":"https://doi.org/10.5194/wcd-3-937-2022","url":null,"abstract":"Abstract. We report on a set of laboratory experiments to investigate the effect of polar warming on the mid-latitude jet stream. Our results show that a progressive decrease in the meridional temperature difference slows down the eastward propagation of the jet stream and complexifies its structure. Temperature variability decreases in relation to the laboratory “Arctic warming” only at locations representing the Earth's polar and mid-latitudes, which are influenced by the jet stream, whilst such a trend is reversed in the subtropical region south of the simulated jet. The reduced variability results in narrower temperature distributions and hence milder extreme events. However, our experiments also show that the frequency of such events increases at polar and mid-latitudes with decreased meridional temperature difference, whilst it decreases towards the subtropics.\u0000Despite missing land–sea contrast in the laboratory model, we find qualitatively similar trends of temperature variability and extreme events in the experimental data and the National Centers for Environmental Prediction (NCEP) reanalysis data.\u0000","PeriodicalId":383272,"journal":{"name":"Weather and Climate Dynamics","volume":"6 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-08-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115371240","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Summertime Rossby waves in climate models: substantial biases in surface imprint associated with small biases in upper-level circulation","authors":"Feifei Luo, F. Selten, K. Wehrli, K. Kornhuber, Philipp Le Sager, W. May, T. Reerink, S. Seneviratne, H. Shiogama, Daisuke Tokuda, Hyungjun Kim, D. Coumou","doi":"10.5194/wcd-3-905-2022","DOIUrl":"https://doi.org/10.5194/wcd-3-905-2022","url":null,"abstract":"Abstract. In boreal summer, circumglobal Rossby waves can promote\u0000stagnating weather systems that favor extreme events like heat waves or\u0000droughts. Recent work showed that amplified Rossby wavenumber 5 and 7 show\u0000phase-locking behavior which can trigger simultaneous warm anomalies in\u0000different breadbasket regions in the Northern Hemisphere. These types of\u0000wave patterns thus pose a potential threat to human health and ecosystems.\u0000The representation of such persistent wave events in summer and their\u0000surface anomalies in general circulation models (GCMs) has not been\u0000systematically analyzed. Here we validate the representation of wavenumbers\u00001–10 in three state-of-the-art global climate models (EC-Earth, CESM, and\u0000MIROC), quantify their biases, and provide insights into the underlying\u0000physical reasons for the biases. To do so, the ExtremeX experiments output\u0000data were used, consisting of (1) historic simulations with a freely running atmosphere with prescribed ocean and experiments that additionally (2) nudge towards the observed upper-level horizontal winds, (3) prescribe soil moisture conditions, or (4) do both. The experiments are used to trace the sources of the model biases to either the large-scale atmospheric\u0000circulation or surface feedback processes. Focusing on wave 5 and wave 7, we show that while the wave's position and magnitude are generally well\u0000represented during high-amplitude (> 1.5 SD) episodes, the\u0000associated surface anomalies are substantially underestimated. Near-surface\u0000temperature, precipitation and mean sea level pressure are typically\u0000underestimated by a factor of 1.5 in terms of normalized standard\u0000deviations. The correlations and normalized standard deviations for surface\u0000anomalies do not improve if the soil moisture is prescribed. However, the\u0000surface biases are almost entirely removed when the upper-level atmospheric\u0000circulation is nudged. When both prescribing soil moisture and nudging the\u0000upper-level atmosphere, then the surface biases remain quite similar to the\u0000experiment with a nudged atmosphere only. We conclude that the near-surface\u0000biases in temperature and precipitation are in the first place related to\u0000biases in the upper-level circulation. Thus, relatively small biases in the\u0000models' representation of the upper-level waves can strongly affect\u0000associated temperature and precipitation anomalies.\u0000","PeriodicalId":383272,"journal":{"name":"Weather and Climate Dynamics","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-08-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129109531","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Pacific Decadal Oscillation modulates the Arctic sea-ice loss influence on the midlatitude atmospheric circulation in winter","authors":"A. Simon, G. Gastineau, C. Frankignoul, V. Lapin, P. Ortega","doi":"10.5194/wcd-3-845-2022","DOIUrl":"https://doi.org/10.5194/wcd-3-845-2022","url":null,"abstract":"Abstract. The modulation of the winter impacts of Arctic sea-ice loss by the Pacific Decadal Oscillation (PDO) is investigated in the IPSL-CM6A-LR\u0000ocean–atmosphere general circulation model. Ensembles of simulations are\u0000performed with constrained sea-ice concentration following the Polar\u0000Amplification Model Intercomparison Project (PAMIP) and initial conditions\u0000sampling warm and cold phases of the PDO. Using a general linear model, we\u0000estimate the simulated winter impact of sea-ice loss, PDO and their combined effects. On the one hand, a negative North Atlantic Oscillation (NAO)-like pattern appears in response to sea-ice loss together with a modest deepening of the Aleutian Low. On the other hand, a warm PDO phase induces a large positive Pacific–North America pattern, as well as a small negative Arctic Oscillation pattern. Both sea-ice loss and warm PDO responses are associated\u0000with a weakening of the poleward flank of the eddy-driven jet, an\u0000intensification of the subtropical jet and a weakening of the stratospheric\u0000polar vortex. These effects are partly additive; the warm PDO phase\u0000therefore enhances the response to sea-ice loss, while the cold PDO phase\u0000reduces it. However, the effects of PDO and sea-ice loss are also partly\u0000non-additive, with the interaction between both signals being slightly\u0000destructive. This results in small damping of the PDO teleconnections under\u0000sea-ice loss conditions, especially in the stratosphere. The sea-ice loss\u0000responses are compared to those obtained with the same model in\u0000atmosphere-only simulations, where sea-ice loss does not significantly alter the stratospheric polar vortex.\u0000","PeriodicalId":383272,"journal":{"name":"Weather and Climate Dynamics","volume":"24 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-08-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131009652","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}