On the assessment of the moisture transport by the Great Plains low-level jet

Low-level jets (LLJs) can be defined as wind corridors of anomalously high wind speed values located within the first kilometre of the troposphere. These structures are one of the major meteorological systems in the meridional transport of moisture on a global scale. In this work, we focus on the southerly Great Plains low-level jet, which plays an important role in the moisture transport balance over the central United States. The Gulf of Mexico is the main moisture source for the Great Plains low-level jet (GPLLJ), which has been identified as a key factor for rainfall modulation over the eastern and central US. The relationship between moisture transport from the Gulf of Mexico to the Great Plains and precipitation has been well documented in previous studies. Nevertheless, a large uncertainty still remains in the quantification of the moisture amount actually carried by the GPLLJ. The main goal of this work is to address this question. For this purpose, a relatively new tool, the regional atmospheric Weather Research and Forecasting Model with 3-D water vapour tracers (WRF-WVT; Insua-Costa and Miguez-Macho, 2018) is used together with the Lagrangian model FLEXPART to estimate the load of precipitable water advected within the GPLLJ. Both models were fed with data from ERA Interim. From a climatology of jet intensity over a 37-year period, which follows a Gaussian distribution, we select five cases for study, representing the mean and 1 and 2 standard deviations above and below it. Results show that the jet is responsible for roughly 70&thinsp;%–80&thinsp;% of the moisture transport occurring in the southern Great Plains when a jet event occurs. Furthermore, moisture transport by the GPLLJ extends to the north-east US, accounting for 50&thinsp;% of the total in areas near the Great Lakes. Vertical distributions show the maximum of moisture advected by the GPLLJ at surface levels and maximum values of moisture flux about 500&thinsp;m above, in coincidence with the wind speed profile.</p

The concurrence of atmospheric rivers and explosive cyclogenesis in the North Atlantic and North Pacific basins

Abstract. The explosive cyclogenesis of extratropical cyclones and the occurrence of atmospheric rivers are characteristic features of a baroclinic atmosphere, and are both closely related to extreme hydrometeorological events in the mid-latitudes, particularly on coastal areas on the western side of the continents. The potential role of atmospheric rivers in the explosive cyclone deepening has been previously analysed for selected case studies, but a general assessment from the climatological perspective is still missing. Using ERA-Interim reanalysis data for 1979–2011, we analyse the concurrence of atmospheric rivers and explosive cyclogenesis over the North Atlantic and North Pacific basins for the extended winter months (ONDJFM). Atmospheric rivers are identified for almost 80 % of explosive deepening cyclones. For non-explosive cyclones, atmospheric rivers are found only in roughly 40 % of the cases. The analysis of the time evolution of the high values of water vapour flux associated with the atmospheric river during the cyclone development phase leads us to hypothesize that the identified relationship is the fingerprint of a mechanism that raises the odds of an explosive cyclogenesis occurrence and not merely a statistical relationship. These new insights on the relationship between explosive cyclones and atmospheric rivers may be helpful to a better understanding of the associated high-impact weather events

Tagging moisture sources with Lagrangian and inertial tracers: application to intense atmospheric river events

Two Lagrangian tracer tools are evaluated for studies on atmospheric moisture sources and pathways. In these methods, a moisture volume is assigned to each particle, which is then advected by the wind flow. Usual Lagrangian methods consider this volume to remain constant and the particle to follow flow path lines exactly. In a different approach, the initial moisture volume can be considered to depend on time as it is advected by the flow due to thermodynamic processes. In this case, the tracer volume drag must be taken into account. Equations have been implemented and moisture convection was taken into account for both Lagrangian and inertial models. We apply these methods to evaluate the intense atmospheric rivers that devastated (i) the Pacific Northwest region of the US and (ii) the western Iberian Peninsula with flooding rains and intense winds in early November 2006 and 20 May 1994, respectively. We note that the usual Lagrangian method underestimates moisture availability in the continent, while active tracers achieve more realistic results

Climatology of Lyapunov exponents: the link between atmospheric rivers and large-scale mixing variability

Large-scale tropospheric mixing and Lagrangian transport properties have been analyzed for the long-term period 1979–2014 in terms of the finite-time Lyapunov exponents (FTLEs). Wind field reanalyses from the European Centre for Medium-Range Weather Forecasts were used to calculate the Lagrangian trajectories of large ensembles of particles. Larger values of the interannual and intra-annual mixing variabilities highlight the El Niño Southern Oscillation, the storm track, or the Intertropical Convergence Zone among other large-scale structures. The mean baroclinic instability growth rate and the mean atmospheric river occurrence show large correlation values with the FTLE climatology as an indication of their influence on tropospheric mixing in the midlatitudes. As a case study, the role that land-falling atmospheric rivers have on large-scale tropospheric mixing and the precipitation rates observed in Saharan Morocco and the British Isles has been analyzed. The atmospheric river contribution to tropospheric mixing is found to decrease from 15 % in Saharan Morocco to less than 5 % for the UK and Ireland regions, in agreement with their contribution to precipitation that is 40 % larger in the former than in the latter region

On the relationship between atmospheric rivers, weather types and floods in Galicia (NW Spain)

Atmospheric rivers (ARs) – long and narrow structures of anomalously high water vapor flux located in the warm sector of extratropical cyclones – have been shown to be closely related to extreme precipitation and flooding. In this paper we analyze the connection between ARs and flooding in the northwestern Spanish region of Galicia under a variety of synoptic conditions represented by the so-called weather types, a classification of daily sea-level pressure patterns obtained by means of a simple scheme that adopts the subjective procedure of Lamb. Flood events are identified from official reports conducted by the Spanish emergency management agency (Protección Civil) from 1979 to 2010. Our results suggest that, although most flood events in Galicia do not coincide with the presence of an overhead AR, ARs are present in the majority of severe cases, particularly in coastal areas. Flood events associated with ARs are connected to cyclonic weather types with westerly and southwesterly flows, which occur mostly in winter months. The link between ARs and severe flooding is not very apparent in inland areas or during summer months, in which case heavy precipitation is usually not frontal in nature but rather convective. Nevertheless, our results show that, in general, the amount of precipitation in flood events in Galicia more than doubles when an AR is present

Evaluation of the moisture sources in two extreme landfalling atmospheric river events using an Eulerian WRF tracers tool

A new 3-D tracer tool is coupled to the WRF model to analyze the origin of the moisture in two extreme atmospheric river (AR) events: the so-called Great Coastal Gale of 2007 in the Pacific Ocean and the Great Storm of 1987 in the North Atlantic. Results show that between 80 and 90 % of moisture advected by the ARs, and a high percentage of the total precipitation produced by the systems have a tropical origin. The tropical contribution to precipitation is in general above 50 % and largely exceeds this value in the most affected areas. Local convergence transport is responsible for the remaining moisture and precipitation. The ratio of tropical moisture to total moisture is maximized as the cold front arrives on land. Vertical cross sections of the moisture content suggest that the maximum in tropical humidity does not necessarily coincide with the low-level jet (LLJ) of the extratropical cyclone. Instead, the amount of tropical humidity is maximized in the lowest atmospheric level in southern latitudes and can be located above, below or ahead of the LLJ in northern latitudes in both analyzed cases

Running a Scientific Conference During Pandemic Times

Despite the COVID-19 pandemic, the science of atmospheric rivers was well served by the organization of a virtual symposium joined by more than 100 researchers. In addition to conveying new science, significant lessons were learned on how to run virtual events.Fil: Garreaud, René. Universidad de Chile; ChileFil: Ralph, M.. University of California; Estados UnidosFil: Wilson, A.. University of California; Estados UnidosFil: Ramos, A. M.. Universidade de Lisboa; PortugalFil: Eiras Barca, J.. Universidad de Vigo; EspañaFil: Steen Larsen, H. C.. University of Bergen; NoruegaFil: Rutz, J.. Nws Western Region; Estados UnidosFil: Albano, C.. Desert Research Institute; Estados UnidosFil: Tilinina, N.. Russian Academy Of Sciences. Shirshov Institute of Oceanology; RusiaFil: Warner, M.. U.S. Army Corps of Engineers; Estados UnidosFil: Viale, Maximiliano. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; ArgentinaFil: Rondanelli, R.. Universidad de Chile; ChileFil: McPhee, J.. Universidad de Chile; ChileFil: Valenzuela, R.. Universidad de O Higgins  (uoh);Fil: Gorodetskaya, I.. Universidade de Aveiro; Portuga

Effects of Atmospheric Rivers

This book is intended to summarize the state of the science of atmospheric rivers (ARs) and itsapplication to practical decision-making and broader policy topics. It is the first book on thesubject and is intended to be a learning resource for professionals, students, and indeed anyonenew to the field, as well as a reference source for all.We first envisioned the book during the heady days of 2013 when the Center for WesternWeather and Water Extremes was being planned and established. However, right from the start,we recognized that the effort required would exceed that of any single or couple of authors, andthat the book would surely benefit from a broad range of perspectives and knowledge from avariety of leaders of atmospheric-river science from around the world. Consequently, the firststep toward this book was to organize workshops addressing various aspects of AR science thatwe were able to co-opt, in part, for recruitment of, and discussions among, possible contributingauthors. This led to the diverse authorship team that ultimately wrote this book, as well asour engagement of an experienced publication and book editing team. Among the strategiesagreed to by the contributing authors, one key decision was that the book would focus mostlyon results that have already been published and would emphasize figures and references fromthose formal publications. Where vital, new information has been developed and incorporated.Each chapter was led by a few expert lead authors recruited by the four of us, and those chapterleads recruited contributions from other experts on the chapter topic. Each chapter wasreviewed by other specialists who were not part of its authorship team, generally including onehighly technical expert and one reviewer intended to represent members of a broader audience.This helped ensure the accuracy of interpretations as well as high standards and accessibilityof presentation. We, the editors of the book, reviewed all chapters at various stages of compositionand layout.Given currently high levels of interest in ARs in the scientific community as well as by thepublic, we hope that the book will be a useful starting place for many readers. Writing a bookabout a topic that is as new and that is advancing as quickly as AR science is today (in 2018)poses many difficult challenges but, with the help of the large team of expert authors who havecontributed, we believe that, with this book, we are providing a firm foundation for futureexpansion and advances in this important field.Fil: Dettinger, Michael D.. United States Geological Survey; Estados UnidosFil: Lavers, David A.. No especifíca;Fil: Compo, Gilbert P.. State University of Colorado at Boulder; Estados UnidosFil: Gorodetskaya, Irina V.. Universidade de Aveiro; PortugalFil: Neff, William. State University of Colorado at Boulder; Estados UnidosFil: Neiman, Paul J.. National Oceanic And Atmospheric Administration; Estados UnidosFil: Ramos, Alexandre M.. Universidade Nova de Lisboa; PortugalFil: Rutz, Jonathan J.. National Weather Service; Estados UnidosFil: Viale, Maximiliano. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; ArgentinaFil: Wade, Andrew J.. University of Reading; Reino UnidoFil: White, Allen B.. National Oceanic And Atmospheric Administration; Estados Unido