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Large biases associated with climate projections are problematic when it comes to their regional application in the assessment of water resources and ecosystems. Here, we demonstrate a method that can reduce systematic biases in regional climate projections. The global and regional climate models employed to demonstrate the technique are the Community Climate System Model (CCSM) and the Weather Research and Forecasting (WRF) model. The method first utilized a statistical regression technique and a global reanalysis dataset to correct biases in the CCSM-simulated variables (e.g., temperature, geopotential height, specific humidity, and winds) that are subsequently used to drive the WRF model. The WRF simulations were conducted for the western United States and were driven with (a) global reanalysis, (b) original CCSM, and (c) bias-corrected CCSM data. The bias-corrected CCSM data led to a more realistic regional climate simulation of precipitation and associated atmospheric dynamics, as well as snow water equivalent (SWE), in comparison to the original CCSM-driven WRF simulation. Since most climate applications rely on existing global model output as the forcing data (i.e., they cannot re-run or change the global model), which often contain large biases, this method provides an effective and economical tool to reduce biases in regional climate downscaling simulations of water resource variables.

Winter precipitation measurement is more problematic in terms of accuracy than measurement of rainfall precipitation that occur during the rest of the year. The results of rainfall measurements during the winter are significantly influenced by wind, both during the accumulation itself and subsequent redistribution of the snow cover. The aim of this work is to analyze automatically measured data from a heated tipping bucket, ultrasonic snow depth sensor for snow measurement and sensors for measuring snow water equivalent, which aims to determine the dependence of the density of new snow on temperature or humidity and consequently to derive the relation that will serve to refine the quantum estimation of winter precipitation. Based on the correlation and regression analysis of the data, the direct dependence between the density of the new snow and air humidity has not been proven, but the dependence between the density of the new snow and the air temperature has already been proven, though not very significant (Spearman's rank corelation rs = 0.39), this dependence explains approximately 9 % of data variability. The resulting calculated snowfall values in the winter seasons of 2016 and 2017 indicate that the heated tipping bucket has underestimated the amount of precipitation by 50% (2016) and 59%...

Póster presentado en: EMS Annual Meeting - European Conference for Applied Meteorology and Climatology 2018, celebrado en Budapest del 3 al 7 de septiembre de 2018.

[Departement_IRSTEA]Territoires [TR1_IRSTEA]SEDYVIN; International audience; Rhododendron ferrugineum L. is a widespread dwarf shrub species growing in high-elevation, alpine environments of the Western European Alps. For this reason, analysis of its growth rings offers unique opportunities to push current dendrochronological networks into extreme environments and way beyond the treeline. Given that different species of the same genus have been successfully used in tree-ring investigations, notably in the Himalayas where Rhododendron spp. has proven to be a reliable climate proxy, this study aims at (i) evaluating the dendroclimatological potential of R. ferrugineum and at (ii) determining the major limiting climate factor driving its growth. To this end, 154 cross-sections from 36 R. ferrugineum individuals have been sampled above local treelines and at elevations from 1800 to 2100 m asl on northwest-facing slopes of the Taillefer massif (French Alps). We illustrate a 195-year-long standard chronology based on growth-ring records from 24 R. ferrugineum individuals, and document that the series is well-replicated for almost one century (1920–2015) with an Expressed Population Signal (EPS) > 0.85. Analyses using partial and moving 3-months correlation functions further highlight that growth of R. ferrugineum is governed by temperatures during the growing season (May–July), with increasingly higher air temperatures favoring wider rings, a phenomenon which is well known from dwarf shrubs growing in circum-arctic tundra ecosystems. Similarly, the negative effect of January–February precipitation on radial growth of R. ferrugineum, already observed in the Alps on juniper shrubs, is interpreted as a result of shortened growing seasons following snowy winters. We conclude that the strong and unequivocal signals recorded in the fairly long R. ferrugineum chronologies can indeed be used for climate–growth studies as well as for the reconstruction of climatic fluctuations in Alpine regions beyond the upper limits of present-day forests.

Six snow depth and total precipitation time series recorded in Western Italian Alps between 960 and 2,177 m a.s.l. have been analyzed to investigate variability and trends over the period 1926–2010. The results outline a significant decrease of snow depth in the period 1951–2010 ranging from −0.2 cm/year in the lowest station up to −1.4 cm/year in the highest one. The contribution to this negative trend comes mainly from spring. These results have been related to the changes in the amount/frequency of total precipitation and to the temperatures analyzed in former studies. The connections between winter precipitation and large-scale atmospheric forcings have been investigated by looking for regular oscillations embedded in the time series. Two different techniques have been used, the MultiTaperMethod and the Monte Carlo Singular Spectral Analysis. Both highlight oscillations corresponding to 2.4–2.7 year periods which are found to be driven by the North Atlantic Oscillation.

Spatial variability of the chemical constituents of winter precipitation on the eastern-western slopes of Mt. Norikura (alt. 3025m) of Japan Northern Alps was examined to clarify the transport process of aerosol that flows over the mountain barrier. The concentrations of chemical constituents in the snow recorded at the upper part of the mountain (above alt. 2420m) make a little difference. However, at the lower part of the mountain (below alt. 2420m), Cl- concentration in the snow on the eastern slope was lower than that on the western slope; non-sea-salt SO42- (nssSO42-), NO3-, nssCa2+, nssMg2+ and NH4+ concentrations on the eastern slope was higher than that on the western slope. The prevailing westerlies raged at the western and alpine parts of the mountain. On the eastern part of the mountain, the easterlies were predominant. We infer that the snow below an altitude of 2420m, in comparison to the other parts of mountain, is under relatively greater influence of the local emission of the chemical constituents., Article, Bulletin of Glaciological Research. 28:17-26 (2010)

In this work, the relationship between atmospheric circulation over Europe and precipitation in Greece is studied during high winter (January-February). Specifically, the 850 hPa relative vorticity centres, affecting or related to precipitation in the various areas of Greece, are defined and the corresponding temporal variability of both parameters is examined. Factor analysis is first applied on both fields, in order to. reduce the dimensionality of the original data sets. Canonical correlation analysis is then applied on the factor analysis results, in order to interrelate the two parameters. It is found that: (i) precipitation over western and northern Greece, the eastern Aegean islands and the western Turkish coasts is mainly controlled by vorticity over Italy and the Gulf of Genoa; (ii) southern Aegean Sea and Crete precipitation is controlled by relative vorticity west of Crete; and (iii) eastern mainland areas precipitation is significantly affected by a vorticity seesaw between Tunisia and the northern Aegean. The temporal variations of precipitation and relative vorticity parameters over the above areas show a precipitation reduction over most Greek stations, combined with enhanced anticyclonic activity over almost the whole Mediterranean during the late 1980s and the early 1990s, a period characterized by high North Atlantic oscillation index values. Finally, cluster analysis is applied on the factor scores time series of precipitation, in order to classify the winter precipitation anomaly patterns into objectively defined clusters. Six main precipitation patterns were revealed and the corresponding relative vorticity mean anomaly regimes over southern Europe indicate the atmospheric circulation characteristics causing these specific patterns. Copyright (C) 2003 Royal Meteorological Society. International Journal of Climatology

El Niño Southern Oscillation (ENSO) is the most important large-scale circulatory phenomenon that causes climatic variability in northern Mexico. The current challenge is to understand its consequences for both local climate and ecological processes of ecosystems. Within this context, we compared the degree of association of three different ENSO indices with local seasonal precipitation ( P ) in northern Mexico, and used dendrochrono - logical series (tree-ring chronologies [TRI]) of Pinus cooperi to assess the impact of forest growth. The results showed a strong association between ENSO, previous winter precipitation and TRI ( r > 0.5, p = 0.05), indicating a positive relationship between warm ENSO phases and subsequent tree growth. The multivariate ENSO index was slightly better at explaining the connection between P and radial growth than other indices. These results could be used to support further research on the effects of ENSO on local climate and forest ecosystems.

Much of the twentieth century multidecadal variability in the relationship between North Atlantic Oscillation (NAO) and winter climate over the North Atlantic–European sector can be linked to the combined effects of the NAO and either the East Atlantic pattern (EA) or the Scandinavian pattern (SCA). Our study documents how different NAO–EA and NAO–SCA combinations influence winter climatic conditions (temperature and precipitation) as a consequence of NAO dipole migrations. Using teleconnectivity maps, we find that the zero-correlated line of the NAO–winter-climate relationship migrates southwards when the EA is in the opposite phase to the NAO, related to a southwestwards migration of the NAO dipole under these conditions. Similarly, a clockwise movement of the NAO–winter-climate correlated areas occurs when the phase of the SCA is opposite to that of the NAO, reflecting a clockwise movement of the NAO dipole under these conditions. Our study provides new insights into the causes of spatial and temporal nonstationarity in the climate–NAO relationships, particularly with respect to winter precipitation. Furthermore, interannual variability in the north–south winter precipitation gradient in the UK appears to reflect the migration of the NAO dipole linked to linear combinations of the NAO and the EA. The study also has important implications for studies of the role of the NAO in modulating the wind energy resource of the UK and Ireland, as well as for the selection of locations for terrestrial proxy archive reconstruction of past states of the NAO. Copyright © 2013 Royal Meteorological Society Science Foundation Ireland Science Foundation Ireland "Research Frontiers Programme" (10/RFP/ GEO2747) and UCD Seed Funding Scheme 2013. I've uploaded the same version that is available on-line but with an author-created format. Please add this publication to the School of Geological Sciences AMS

Icing wind tunnel tests were conducted at the National Research Council Canada's 3 m x 6 m Propulsion and Icing Wind Tunnel (PIWT) located in Ottawa, Ontario, Canada early in 2011 and 2012. These tests were a continuation of the work performed in 2010 on a generic supercritical airfoil representative of a regional-jet type aircraft wing section. Tests nominally consisted of coating the wing with de/anti-icing fluid, applying various levels of precipitation (e.g., snow, ice pellets, freezing rain, or combinations thereof), and simulating a take-off condition in the wind tunnel by accelerating the wind speed and pitching the wing through a desired pitch-profile. The wing performance was evaluated primarily by the measured lift-loss relative to the lift generated by a clean wing. The second phase of testing consisted of test cases similar to the 2010 tests in order to expand the scope of the data sets at various temperatures, while also investigating the effects of the rotation speed and ramp time on lift-loss and the effects of fluids and precipitation on stall. The experimental results were used as guidance for regulators in determining holdover and allowance times for aircraft operating in winter precipitation. © 2012 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved., 4th AIAA Atmospheric and Space Environments Conference 2012, June 25-28, 2012, New Orleans, LA, USA

The paper discusses long-term change in snowfall, rainfall and mixed precipitation viewed in conjunction with air temperature and North Atlantic Oscillation (NAO) in winter (December–February). In the study of contemporary climate change and its effect on the hydrological cycle it is useful to focus on winter precipitation forms. A 146-year secular observation series from Krakow, spanning the period 1863–2008, was used to extract data on the number of days with precipitation and on precipitation amount broken down by form. Statistically significant trends were found in total and mixed precipitation, but not in snowfall and rainfall. The climate warming effect has contributed to a material decrease in the snowfall to total winter precipitation ratio during the second half of the 20th c. The highest impact of air temperature was found in the wintertime variation in number of days with snowfall while the NAO had a significant influence on the frequency and amount of both rainfall and snowfall.

The seasonal characteristics of atmospheric static stability in the Mediterranean region are examined, for the 60-year period 1948-2007 and for the four 15-year sub-periods 1948-1962, 1963-1977, 1978-1992 and 1993-2007. S-Mode and T-Mode Factor Analysis are applied to the mean 5-day values of K static stability index over the Mediterranean region. Three dominant modes are revealed for both, the intra-annual variation and the spatial distribution of K-index. It is found that these modes are connected to the seasonal characteristics of the main atmospheric circulation systems affecting the region and the thermal properties of the Earth's surface (land or sea). The differences among the results of the four sub-periods partially reflect the inter-decadal variations of the strength of the above factors. Theoretical and Applied Climatology

The main climatic characteristics of precipitation in the southern Balkans were examined by applying S-Mode and T-Mode factor analysis (FA) to APHRODITE 0.25 degrees x 0.25 degrees grid point precipitation data for the period 1951-2007. First, S-Mode FA was applied to the seasonal precipitation values and revealed the main modes of interannual variation of precipitation for each season. These modes were found to be connected to specific atmospheric circulation centers of action. Statistically significant negative trends were found for: (1) winter and spring precipitation over northwestern Greece and southern Albania and (2) spring and autumn precipitation over the southern Aegean Sea. Next, T-Mode FA was applied to the 57 yr mean precipitation of 5 d intervals (n = 73) in a year and resulted in 3 main modes of spatial distribution of precipitation: (1) the cold period mode (late November to late March) with maxima in northwestern Greece and the western Asia Minor coasts, (2) the warm period mode (late April to late August), presenting a maximum over the northern continental areas, and (3) the autumn mode (early September to late October) with a maximum found over the northern Ionian Sea. The intra-annual variations of the prevalence degree of these modes are connected to the seasonality of the thermal characteristics of the surface and the overlying atmospheric layers and the main circulation systems affecting the region. Climate Research

The goal of this thesis lies in the identification of possible significant trends in winter temperature and precipitation across Ontario. In this study the trends and variations in several indices of daily winter temperature and precipitation were explored applying least squares regressions and Mann-Kendall test for 13 stations located across Ontario for the period 1939 to 2008. Correlation analysis was also used to detect possible link between winter temperature and winter precipitation variables. Datasets were supplied by Environment Canada. The analysis of the temperature indices indicates a significant upward trend in winter temperature values. Also the analysis of the precipitation indices reveals no significant trend in the winter total precipitation series, decreasing trends in winter snowfall, and increasing trends in winter rainfall. This analysis showed that there has been a significant increase in the number of rainy days, but no significant trend has been detected in the number of snowy days. A downward trend in winter snowfall as a percentage of winter precipitation (S/P), and an upward trend in winter rainfall as a percentage of winter precipitation (R/P) have also been detected. The downward trend in winter S/P is linked to the decreasing trend in the winter snowfall, and the upward trend in R/P is linked to the rising trend in winter rainfall. The trends in inter rainfall and snowfall were found to be correlated with the trend in winter temperatures.

Peculiarities of the atmospheric precipitation regime in medium and high altitudes of the Czechia and Slovakia Abstract The thesis deals with the question of rise in precipitation during winter period in mountain and submontane areas of the former Czechoslovakia. This increase comes out as circumstantial maximum of precipitation in winter period. Some stations have even recorded higher precipitation totals during colder half-years than during warmer half-years. The areas, which experience this phenomenon, differ in this matter from the continental nature of the precipitation in the lower altitudes. The main part of the thesis consists in a background research of the existing expert literature on the topic of increased incidence of winter precipitation, which hasn't been sufficiently discussed so far. The other substantial part of the thesis forms personal research. The research has been made at three stations in the Jizera mountains, i.e. in the area, where the increased incidence of winter precipitation comes out at most. There have been encountered some atmospheric situations triggering extreme precipitation totals in winter, which can't be found to such extent in lower altitudes. The windward of the Jizera mountains combined with the dominant west streaming during winter period is to be regarded as the...

Some aspects oil the intra-annual variability and the seasonal peculiarities of the atmospheric circulation in the Mediterranean region are examined. T-mode, factor analysis is applied on the long-term (1948-2003) 5-day mean Values of relative geostrophic vorticity for the 735-day periods of the year. The analysis is applied for sea-surface and 500-hPa levels. For sea level, two Circulation types are found to be dominant: the type of the warm period and the type of the cold period, characterizing the so-called Mediterranean climate; they are strongly dependent oil the thermal and humidity characteristics of the earth's surface and the position and strength of the sub-tropical (Azores) anti-cyclone. For 500-hPa level, two extra but weaker circulation types are added, prevailing mainly during the transitional seasons and modifying the smooth intra-annual variation of the atmospheric circulation. In this case, the thermal influence of the earth's surface appears to be weaker, while other circulation features, Such Lis blocking activity and/or cut-off lows, seem to play an important role too. Copyright (C) 2007 Royal Meteorological Society. International Journal of Climatology

Any future climate variation forced by human activities will be superimposed on the background of natural climate variation. Therefore, before interpreting the present climate and addressing future climate scenarios some knowledge of past climate is necessary. This thesis offers a rare glimpse into a long record of fluvial activity in Central Sweden and illuminates some of the possible forcing agent behind past (and future) discharge variation. Along the Swedish East Coast varved deposits of sand silt and clay couplets make up a chronology, which extend from the present into the Late Glacial. This chronology is known as the Swedish Time Scale (STS) and the c. 8000 varves were deposited in River Ångermanälven, Central Sweden. Of these varves, the last c. 2000 years are considered secure in terms of coherent chronology and internal thickness variation. A 2000 year long geometric mean varve thickness series was calculated to account for the internal thickness variation, which is postulated to form a proxy for fluvial sediment transport. Geometric mean varve thickness was compared to observed maximum daily annual discharge Qmax (1909-1971 AD) and the relationship expressed in a power equation. Thus, a reconstruction of past discharge for the last 2000 years could be produced. Extreme reconstructed discharge events were shown to be reasonable, considering the range of the observed discharge. Observed Qmax normally occurs during the snowmelt flood. Thus it is reasonable to attribute the variation in reconstructed Qmax to the snowmelt flood and, therefore, to melt water generation. Accumulated observed winter precipitation data from eleven meteorological stations from within and in the vicinity of the Ångermanälven catchment were compared to Qmax. Nine time series shared variation with Qmax and were complied into an average accumulated winter precipitation series. This series shares c. 40% of its variation with Qmax (observed and reconstructed) and it is reasonable to attribute some of the variation in the reconstructed Qmax to snow accumulation changes. The reconstructed Qmax series holds a centennial length waveform, which is interpreted in terms of the late Holocene climate succession, i.e. the Roman Warm Period, Dark Ages Cold Period, Medieval Warm Period, Little Ice Age and Contemporary Warm Period. Non-stationary frequencies in the sub decadal, decadal and centennial bands have been detected in the 2000 year long geometric mean varve series. Sub decadal frequencies are tentatively interpreted as forced by the North Atlantic Oscillation.. Decadal frequencies are interpreted as sunspot forcing. Centennial frequencies are tentative interpreted as Suess cycle forcing. Missing varves in the STS (minimum 500 years) have previously been postulated on the grounds of an independent calibrated radiocarbon calendar age obtained from varve deposits and its correlation to the GRIP Ice Core. However, an evaluation of the STS by cross correlation does not support the presence of a centennial error in the post glacial part of STS. Additional analyses on the relationship between reconstructed discharge and other climate (-derived) proxies have been tested, including temperature, tree rings, atmospheric indices, sea-ice extent, C-14 production variation, global temperature reconstructions and volcanic eruptions. These analyses were mostly internally contradictive and non-conclusive. Denna avhandling handlar om hur man kan utläsa klimatiska signaler från klastiska årsvarviga sediment i Ångermanälven i södra Norrland. Avhandlingen bidrar med kunskap till den pågående diskussionen om klimatets- och den hydrologiska cykelns förändringar, framförallt sett ur ett retrospektiv men den behandlar också frågor om framtiden och en eventuellt ökande växthuseffekt. Varviga sediment förekommer längs den svenska östkusten och i Sveriges norra- och centrala dalgångar. Tillsammans utgör dessa sediment en lång tidsskala, den så kallade Svenska Tidsskalan, som sträcker sig från nutid genom hela vår nuvarande värmetid (Holocen) och in i slutet av den senaste istiden (Senglacial tid). Varven har avsatts i två olika miljöer (1) dels framför den retirerande Fennoskandiska inlandsisen i en issjömiljö och (2) dels i dalgångarna efter att inlandsisen hade dragit sig tillbaka efter isavsmältningen i en lakustrin miljö. Denna avhandling fokuserar främst på varven i Ångermanlandsälvens dräneringsåmråde som har bildats under de senaste ca 2000 åren men den behandlar även de varv avsatta de senaste 8000 åren. Tidsintervallet valdes på grund av att preliminära analyser visat att tidsskalan är tillförlitlig och för att det i sedimenten i mynningen av Ångermanälven finns varv som bildats under denna period. Endast i ett fåtal tidigare undersökningar har förhållandet mellan varvtjocklek och vattenflöde studerats. I denna studie har ett säkert samband mellan varvtjocklek och observerad maximal dagligt årsflöde (Qmax) för åren 1909-1971 upprättats. Förhållandet mellan de två parametrarna har uttryckts med en potensekvation, vilket underlättat beräkningen av Qmax för de senaste 2000 åren. Tidsserier av Qmax har analyserats en efter en. Jag fann bl a en tillfredsställande fördelning av de extrema värdena i jämförelse med observerade dataserier. Qmax visade sig också sammanfalla med vårfloden, vilket betyder att förändringarna i varvtjockleken beror på variationer i snösmältningen. Observerad och rekonstruerad Qmax har korrelerats till observerat snömedeldjup, vilket visar att Qmax är ett resultat av mängden smält nederbörd i form av snö. Detta betyder i sin tur att det finns signaler i varven som leder till variationer atmosfären. I årsnederbördsdata upptäcktes en vintersignal i den s.k. ”North Atlantic Oscillation” (NAO), vilken inte kunde urskiljas i varken Qmax eller varvtjockleken. Jag fann att en hundraårig periodicitet i varvtjockleken sammanfaller med den klassisk Senholocena klimatutveckling d v s med en varm period under romartiden, en kall period mellan ca 500-1000 e. Kr., åter en varm period under Medeltiden följt av ett kallt klimat under den Lilla istiden och slutligen uppvärmningen i vår egen tid. Om det finns en atmosfärisk faktor som påverkar bildningen av varv ska det vara möjligt att sammankoppla varvtjockleken till andra arkiv som påverkas av atmosfären t ex variationer i O18/O16 halten i den Grönländska inlandsisen. Enligt instrumentobservationer och de mekanismer som påverkar NAO, borde det finnas ett omvänt förhållande mellan de två temperaturkänsliga arkiven. Ett sådant förhållande upptäcktes i varvserien under vissa tidsperioder men inte under andra. Detta av- och på förhållande har tolkats som start- och slutsignaler för NAO. Baserat på frekvensanalyser har jag visat att tidsserierna innehåller icke-stationära solvindscyklar men också andra frekvenser. Förutom solvindenscyclisitet, upptäcktes periodiciteter som sträcker sig från tiotals till tusentals år, vilka kan kopplas till variationer I t ex NAO och Suesscykeln. En 1000 års -lång vågform har spekulativt kopplats ihop med Bondcykeln, som hittats i marina sediment. Förutom dessa analyser utfördes ytterligare ett antal analyser för att kunna utreda förhållandet mellan varvtjocklek, Qmax och andra arkiv som kan innehålla indirekt information om klimatets variationer. Dessa arkiv utgjordes av trädringsserier, temperaturserier, atmosfäriska data, isutbredningen på Östersjön, kol-14 serier och data från vulkanutbrott. Slutsatserna från dessa korrelationsanalyser var i huvudsak negativa, d v s jag fann inget samband mellan varvtjocklek och de andra arkiven. Jag har även gjort försök med att korrelera olika varvserier omfattande de senaste ca 8000 åren eftersom tidigare upptäckter visat att kronologin i Svenska Tidsskalan kombinerat med kol-14 dateringar av organiskt material som påträffats i lervarven och tidskalan i en borrkärna från den Gröländska inlandisen (GRIP borrkärnana) inte överensstämmer och att det minst saknas 500 varv i den Svenska Tidsskalan. Mina resultat pekar på att de saknade varven troligtvis inte går att finna i Ångermanälvens avlagringar. Denna avhandling har ökat kunskapen om varv i Ångermanälven på ett flertal olika sätt bl a genom att * sambandet mellan Qmax och vårfloden har utretts * varvdata har omvandlats till vattenflödesserier * en hundraårig periodicsitet har tolkats inom ramen för klassisk Senholocen klimatutveckling * frekvenser sammankopplade till NAO, solvindscykeln och Suesscykeln har upptäckts * tidsskalan har granskats med hjälp av korrelationer och förklarats tillförlitlig * flera olika klimatiska arkiv har testats gentemot varvtjocklek, men dessa studier gav inget nytt ljus åt förståelsen om hur varven i Ångermanlandsälvens dräneringsområde varierar

Ponencia presentada en: III Congreso de la Asociación Española de Climatología “El agua y el clima”, celebrado en Palma de Mallorca del 16 al 19 de junio de 2002. [ES]Se ha realizado un análisis mediante EOFs de datos instrumentales de precipitación invernal (Diciembre, Enero y Febrero) sobre tierra en un entorno de la cuenca mediterránea. Se han identificado los modos de transporte verticalmente integrado de humedad atmosférica asociados a estos EOFs a partir de datos cada seis horas de los Reanálisis. Se han estudiado también los flujos a través de la frontera del área a estudio y en cada punto de red. El primer EOF de precipitación invernal sobre la cuenca mediterránea está asociado a la dinámica del storm-track Atlántico. El segundo EOF representa la redistribución interna de humedad en el seno de la cuenca mediterránea, con el Golfo de Génova suministrando humedad a la atmosfera que precipita sobre el Mediterráneo oriental. Finalmente, el tercer EOF depende de la interacción entre la topografía europea a gran escala con los transportes de humedad. [EN]An EOF analysis of instrumental winter (December, January and February) precipitation data around the Mediterranean basin has been performed. The main modes of variability of the precipitation field have been used to identify the main modes of variability of the vertically integrated moisture transport at each grid point and at the boundaries related to these EOFs. The leading winter precipitation EOF is linked to the dynamics of the Atlantic storm-track. The second EOF, instead, represents the internal redistribution of moisture from the Genoa Gulf to the eastern Mediterranean. Finally, the last mode reflects the interaction of the European topography with the large-scale vertically integrated moisture transport.

This study uses snow events from the Biogenic Aerosols–Effects on Clouds and Climate (BAECC) 2014 campaign to investigate the connection between properties of snow and radar observations. The general hydrodynamic theory is applied to video-disdrometer measurements to retrieve masses of falling ice particles. Errors associated with the observation geometry and the measured particle size distribution (PSD) are addressed by devising a simple correction procedure. The value of the correction factor is determined by comparison of the retrieved precipitation accumulation with weighing-gauge measurements. Derived mass–dimensional relations are represented in the power-law form m = . It is shown that the retrieved prefactor am and exponent bm react to changes in prevailing microphysical processes. From the derived microphysical properties, event-specific relations between the equivalent reflectivity factor Ze and snowfall precipitation rate S (Ze = ) are determined. For the studied events, the prefactor of the Ze–S relation varied between 53 and 782 and the exponent was in the range of 1.19–1.61. The dependence of the factors azs and bzs on the m(D) relation and PSD are investigated. The exponent of the Ze–S relation mainly depends on the exponent of the m(D) relation, whereas the prefactor azs depends on both the intercept parameter N0 of the PSD and the prefactors of the m(D) and υ(D) relations. Changes in azs for a given N0 are shown to be linked to changes in liquid water path, which can be considered to be a proxy for degree of riming.

It has been found that the production of one pound of dry plant substance on soils of average fertility, requires in humid districts not more than five hundred pounds of water, and in arid districts like Utah about seven hundred and fifty pounds. This indicates that the average rainfall of Utah, which is about twelve inches, if properly conserved in the soil, is sufficient to produce annually, without irrigation, from thirty to forty-five bushels of wheat to the acre, or corresponding yields of other crops. The realization of this truth has changed greatly our views of irrigation practices. The beginning of irrigation wisdom is now considered to be the conservation of the natural precipitation, which means that soil must be used as a storage reservoir for water. If the farmer succeeds in bringing the larger portion of the rain and snowfall into the soil, and in keeping it there until crops need it, some success of the crop is assured. Irrigation under such conditions is, as it always should be, supplementary only to the natural precipitation, for the amount of irrigation water needed decreases as the amount of water stored in the soil increases. As the value of the natural precipitation becomes better understood among irrigation farmers, the present supply of irrigation water may be made to cover a more extended area. The progress of irrigation depends very largely upon the degree to which the farmers will care for the natural supply of water that falls upon their farms in the form of rain and snow.

ResumenLa Oscilación del Sur El Niño (ENSO, por sus siglas en inglés) es el principal fenómeno de circulación de gran escala que ocasiona variabilidad climática en el norte de México. El desafío actual consiste en entender sus consecuencias para los procesos climáticos y ecológicos de los ecosistemas. En este contexto, se comparó el grado de asociación de tres diferentes índices de ENSO con la precipitación local (P) en el norte de México, y se utilizaron series dendrocronológicas (cronologías de anillos de crecimiento [TRI, por su siglas en inglés]) de Pinus cooperi para valorar su impacto en el crecimiento forestal. Los resultados mostraron un asociación importante entre ENSO, la precipitación del invierno anterior y el TRI (r>0.5, p = 0.05), lo cual indica que hay una relación directa entre las fases cálidas de ENSO y el crecimiento de los árboles. El índice multivariado de ENSO explicó ligeramente mejor que otros índices la conexión entre P y el crecimiento radial. Estos resultados pueden apoyar futuras investigaciones sobre los efectos de ENSO en el clima local y los ecosistemas forestales.AbstractEl Niño Southern Oscillation (ENSO) is the most important large-scale circulatory phenomenon that causes climatic variability in northern Mexico. The current challenge is to understand its consequences for both local climate and ecological processes of ecosystems. Within this context, we compared the degree of association of three different ENSO indices with local seasonal precipitation (P) in northern Mexico, and used dendrochrono-logical series (tree-ring chronologies [TRI]) of Pinus cooperi to assess the impact of forest growth. The results showed a strong association between ENSO, previous winter precipitation and TRI (r>0.5, p = 0.05), indicating a positive relationship between warm ENSO phases and subsequent tree growth. The multivariate ENSO index was slightly better at explaining the connection between P and radial growth than other indices. These results could be used to support further research on the effects of ENSO on local climate and forest ecosystems.