What controls the isotopic composition of Greenland surface snow?

International audienceWater stable isotopes in Greenland ice core data provide key paleoclimatic information, and have been compared with precipitation isotopic composition simulated by isotopically enabled atmospheric models. However, post-depositional processes linked with snow metamorphism remain poorly documented. For this purpose, monitoring of the isotopic composition (d18O, dD) of near-surface water vapor, precipitation and samples of the top (0.5 cm) snow surface has been conducted during two summers (2011-2012) at NEEM, NW Greenland. The samples also include a subset of 17O-excess measurements over 4 days, and the measurements span the 2012 Greenland heat wave. Our observations are consistent with calculations assuming isotopic equilibrium between surface snow and water vapor. We observe a strong correlation between near-surface vapor d18O and air temperature (0.85 ± 0.11‰ °C-1 (R = 0.76) for 2012). The correlation with air temperature is not observed in precipitation data or surface snow data. Deuterium excess (d-excess) is strongly anti-correlated with d18O with a stronger slope for vapor than for precipitation and snow surface data. During nine 1-5-day periods between precipitation events, our data demonstrate parallel changes of d18O and d-excess in surface snow and near-surface vapor. The changes in d18O of the vapor are similar or larger than those of the snow d18O. It is estimated using the CROCUS snow model that 6 to 20% of the surface snow mass is exchanged with the atmosphere. In our data, the sign of surface snow isotopic changes is not related to the sign or magnitude of sublimation or deposition. Comparisons with atmospheric models show that day-to-day variations in near-surface vapor isotopic composition are driven by synoptic variations and changes in air mass trajectories and distillation histories. We suggest that, in between precipitation events, changes in the surface snow isotopic composition are driven by these changes in near-surface vapor isotopic composition. This is consistent with an estimated 60% mass turnover of surface snow per day driven by snow recrystallization processes under NEEM summer surface snow temperature gradients. Our findings have implications for ice core data interpretation and model-data comparisons, and call for further process studies. © Author(s) 2014

Triple isotopic composition of oxygen in surface snow and water vapor at NEEM (Greenland)

International audienc

The influence of volcanic eruptions on weather regimes over the North Atlantic simulated by ECHAM5/MPI-OM ensemble runs from 800 to 2000 CE

International audienceThe volcanic fingerprint on the winter North Atlantic atmospheric circulation and climate is analyzed in six ensemble runs of ECHAM5/MPI-OM covering 800–2000 CE, both for equatorial and Northern Hemisphere (NH) eruptions. Large volcanic eruptions influence climate on both annual and decadal time scales due to dynamic interactions of different climate components in the Earth's system. It is well known that the North Atlantic Oscillation (NAO) tends to shift towards its positive phase during winter in the first 1–2 years after large tropical volcanic eruptions, causing warming over Europe, but other North Atlantic weather regimes have received less attention. Here we investigate the four dominant weather regimes in the North Atlantic: The negative and positive phase of NAO as well as the Atlantic Ridge, Scandinavian blocking. The volcanic fingerprint is detected as a change in the frequency of occurrence and anomalies in the wind and temperature fields as well as in the sea ice cover. We observe a strong significant increase in the frequency of Atlantic Ridge in the second year after equatorial eruptions that precede the NAO+ detected in year 3–5 as a result of a strong zonal wind anomalies in year 1–2. Evidence for a stronger polar vortex is detected in years 12–14 where NAO+ is detected both as a frequency increase and in the wind and temperature fields. A short-term response is also detected 2–4 years after NH eruptions. The longterm signal after NH eruptions indicate a weak polar vortex around a decade after an eruption. Although the signal after NH eruptions is weaker our results stress the need for further studies. The simulated atmospheric response recorded in ECHAM5 after volcanic eruptions suggest a more dynamic response than previously thought. The methodology used can also be applied to other forcing scenario, for example for future climate projections where the aim is to search for a long-term climate signal

Global and Regional Perspectives

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: Rutz, Jonathan J.. National Weather Service; Estados UnidosFil: Guan, Bin. University of California at Los Angeles; Estados UnidosFil: Bozkurt, Deniz. Universidad de Chile. Facultad de Ciencias Físicas y Matemáticas; ChileFil: Gorodetskaya, Irina V.. University Of Alveiro; PortugalFil: Gershunov, Alexander. University of California at San Diego. Scripps Institution of Oceanography; Estados UnidosFil: Lavers, David A.. European Centre for Medium-Range Weather Forecasts; Reino UnidoFil: Mahoney, Kelly. National Oceanic And Atmospheric Administration; Estados UnidosFil: Moore, B.. University of Colorado; Estados UnidosFil: Neff, William. University of Colorado; Estados UnidosFil: Neiman, Paul J.. National Oceanic And Atmospheric Administration; Estados UnidosFil: Ralph, Martin F.. University of California at San Diego. Scripps Institution of Oceanography; Estados UnidosFil: Ramos, Alexander M.. Universidade Nova de Lisboa; PortugalFil: Steen Larsen, H.C.. University of Bergen; NoruegaFil: Tsukernik, Maria. Brown University; Estados UnidosFil: Valenzuela, Raúl. Universidad de Chile. Facultad de Ciencias Físicas y Matemáticas; ChileFil: 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: Wernli, H.. Institute for Atmospheric and Climate Science; Suiz