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Winter (December to March) precipitation is the major source of rainfed agriculture, storage, and perennial water flow in the western river system of Pakistan. Hence, this study uses precipitation data and variables of land–ocean and atmosphere from the Pakistan Meteorological Department and European Centre for Medium-Range Weather Forecasts (ECMWF) and fifth-generation reanalysis data (ERA5), respectively, to investigate the changes in winter precipitation and its sensitivity to different land–ocean and atmosphere variables, which are rarely investigated in Pakistan. Non-parametric techniques, such as the modified Mann–Kendal, Sen slope, kernel density-based probability function (PDF), empirical orthogonal function (EOF), and correlation analysis, were used to assess the changes and modes of variability in winter precipitation. The overall seasonal precipitation showed a significant decreasing trend with a (−0.1 mm d−1 yr−1) in the seasonal mean and monthly precipitation, except in February which showed a significant increase (>0.11 mm d−1 yr−1). The highest decrease in daily precipitation (0.60) with the central Pacific and Indian Ocean’s basin-wide sea surface temperature, corroborating the influence of ENSO-induced meridional/zonal deviation of Hadley–Walker circulations. The Hadley and Walker cells affect the south-westerlies’ jet stream strength, impacting the water vapor transport and precipitation over Pakistan. These changes in the precipitation magnitude will affect rain-fed agriculture, especially the Rabi cropping pattern and perennial river flow.

Актуальность работы обусловлена необходимостью анализа методов, используемых для оценки снегозапасов в речных бассейнах и прогнозирования половодья. В условиях недостаточности гидрометеорологической информации для прогноза объёма и максимальных уровней половодья, как правило, используются статистические модели, основанные на корреляционной зависимости параметров стока от снегозапасов, либо уравнения множественной линейной регрессии. При этом нет обоснованного сравнения традиционных методов прогноза, основанных на расчете суммы зимних осадков (снегозапасов), и статистических моделей множественной регрессии. Цель: сравнительный анализ методик расчета сумм зимних осадков в бассейне по традиционно применяемым высотным зависимостям и по авторской методике при помощи орографической добавки к скорости вертикальных движений воздушных масс; сравнительный анализ традиционных статистических методов прогноза и моделей множественной линейной регрессии на примере бассейна реки Амыл. Методы: комплексный географо-гидрометеорологический анализ; выявление зависимостей по данным многолетних гидрометеорологических наблюдений с использованием методов математической статистики (корреляционный и регрессионный анализ); моделирование снегозапасов с использованием орографической добавки к скорости вертикальных движений. Результаты. В результате использования двух разных подходов к определению сумм зимних осадков (по высотным зависимостям и с помощью орографической добавки к скорости вертикальных движений воздушных масс) получены идентичные статистические зависимости с близкими коэффициентами детерминации. Разработаны модели прогноза объема стока и максимальных уровней половодья на основе парной корреляции и с использованием множественного регрессионного анализа. Сравнительный анализ традиционных методов прогноза слоя стока, основанных на расчете суммы зимних осадков (снегозапасов), и статистических моделей множественной регрессии также показал идентичность результатов. Для прогноза максимальных уровней воды, вызванных таянием снега, предпочтительнее использование однофакторных зависимостей. The study topicality relates to the analysis of available methods for assessing snow reserves in river basins and forecasting floods. To predict runoff volume and maximum flood levels, statistical models resting on the correlation dependence of runoff parameters on snow reserves or multiple linear regression equations are usually used in the absence of sufficient hydrometeorological information. An important point is that there are no justified comparisons of traditional forecasting methods based on calculations of winter precipitation amount (snow reserves) and statistical models of multiple regression. The aim of the study is to carry out the comparative analysis of methods for calculating winter precipitation amounts in the basin by means of traditionally applied altitude dependencies and the author's estimation method using orographic correction to the velocity of vertical movements of air masses; to carry out the comparative analysis of traditional statistical forecasting methods and models of multiple linear regression by the example of the Amyl River basin. Methods: comprehensive geographical and hydrometeorological analysis; dependence establishment based on long-term hydrometeorological observations using methods of mathematical statistics (correlation and regression analysis); snow reserves simulation with the use of orographic correction to the velocity of vertical movements. Results. By altitude dependencies and the author's assessment considering orographic correction to the velocity of vertical movements of air masses, two different approaches to estimate of winter precipitation amounts suggest similar statistical dependences with close values of determination coefficients. Models for predicting runoff volumes and maximum flood stages based on pair correlation and multiple regression analysis were developed. The comparative analysis of traditional methods for forecasting runoff layers based on calculations of winter precipitation amount (snow reserves) and statistical models of multiple regression also showed similar results. The applied onefactor dependencies turned out to be the best in forecasting snowmelt-induced maximum levels.

Актуальность работы связана с необходимостью совершенствования методик среднесрочных прогнозов половодья в условиях недостаточности гидрометеорологической информации. Цель: оценка возможности использования пространственно распределенных моделей атмосферных осадков для прогнозирования объема стока половодья; разработка стохастических моделей для прогноза объема и максимальных расходов половодья с использованием данных наблюдений сети Росгидромета и распределенных атмосферных осадков по данным реанализа и данных дистанционного зондирования земли высокого пространственного разрешения. Методы: геоинформационный, комплексный географо-гидрометеорологический анализ, статистические методы (корреляционный и регрессионный анализ). Результаты. Выполнена оценка атмосферного увлажнения бассейна р. Чумыш с использованием данных пространственно распределенных моделей атмосферных осадков и материалов наблюдений на метеорологических станциях; проанализирована связь сумм осадков с объемом стока и максимальными расходами половодья. Сравнительная оценка полученных зависимостей позволила выбрать наиболее значимые предикторы для построения уравнения множественной линейной регрессии. Разработана статистическая модель для прогноза объема и максимальных расходов половодья реки Чумыш в створе пгт Тальменка с использованием данных наблюдений сети Росгидромета и реанализов высокого пространственного разрешения. The relevance of the study stems from the necessity to refine the methods of medium-term flood forecasts when sufficient hydrometeorological data are not available. The purpose of the work is to assess probable application of spatially distributed precipitation models to forecast runoff volume of flood, to develop stochastic models for predicting flood volume and its maximum discharge using hydrometeorological observation data, distributed precipitation datasets from reanalysis and remote sensing data of high spatial and temporal resolution. Methods include geoinformation, complex geographical and hydrometeorological analysis, statistical methods (correlation and regression analysis). Results. The Chumysh basin moistening was estimated due to the data from spatially distributed precipitation models and hydrometeorological observation data; the relationship of total precipitation with runoff volume and maximum flood discharge was analyzed. A comparative evaluation of the obtained dependencies made it possible to identify key predictors for deriving the multiple linear regression equation. The statistical model was developed for predicting volumes and maximum discharges of Chumysh flood at Talmenka settlement using hydrometeorological observation data and reanalysis ones of high spatial and temporal resolution.

Актуальность работы обусловлена воздействием изменений климата на гидрологические режимы рек южной Сибири, увеличением повторяемости опасных гидрологических явлений. Наблюдаемые и прогнозируемые изменения в режимах половодий вызываются множеством факторов и требуют различных подходов для характеристики типов этих изменений. Цель: стохастическое моделирование сумм твердых осадков в исследуемом бассейне р. Абакан, установление их связи с максимальными уровнями воды в р. Абакан периода половодья в условиях пространственно-временной изменчивости гидрометеорологических факторов. Методы: комплексный географо-гидрометеорологический анализ, выявление зависимостей по данным многолетних гидрометеорологических наблюдений с использованием методов математической статистики, а также методики оценки количества осадков в бассейне с учетом орографический добавки к скорости вертикальных движений во фронтальной зоне, разработанной В. П. Галаховым. Результаты. Основным фактором формирования максимальных уровней периода половодья является количество зимних осадков. Обильные жидкие осадки на спаде половодья могут вносить значительные коррективы в максимальные уровни. Однако для бассейнов горных рек юга Западной и Восточной Сибири в последние десятилетия в связи с климатическими изменениями отмечается влияние условий промерзания почвогрунтов в осенний период на формирование максимальных уровней вследствие снеготаяния. Для бассейнов со значительной долей предгорных равнин в отдельные годы возможно уменьшение максимальных уровней периода половодья. Для бассейнов, имеющих в основном горный ландшафт, подобного эффекта не наблюдается. Разработана методика расчета сумм зимних ежегодных осадков в бассейне Абакана, учитывающая физические особенности формирования осадков в горах, в частности орографическую добавку к скорости вертикальных движений. На примере независимых данных показано, что алгоритмы расчета максимальных уровней за счет снеготаяния, основанные на регрессионных зависимостях, не всегда дают адекватные результаты. Необходима их корректировка с учетом процессов промерзания на предгорной равнине. Для получения общей статистической зависимости требуются дополнительные данные наблюдений. The study topicality relates to the effect of climate changes and increased recurrence of dangerous hydrological events on rivers of southern Siberia. The observed and predicted changes in flood regimes are caused by a variety of factors and require different approaches in order to characterize the types of these changes. The aim of the study is stochastic modeling of solid precipitation total in the Abakan river basin, establishing relationship between precipitation and maximum water levels in the Abakan river during the flood period under spatial and temporal variability of hydrometeorological factors. Methods: comprehensive geographical and hydrometeorological analysis, dependence establishment based on long-term hydrometeorological observations using mathematical statistics methods, methods (developed by V. P. Galakhov) for estimating precipitation total in the basin with regard for orographic correction to the velocity of vertical movements in the frontal zone. Results. The crucial factor in the formation of maximum flood levels is winter precipitation amount. Heavy rainfalls during flood recession may significantly influence the maximum water levels. However, climate changes of recent decades in river mountain basins of southwestern and eastern Siberia are evidence of dependences between autumn soil freezing and formation of snowmelt-induced maximum stages. In some years during the flood period, decreased maximum water levels are probable in basins with prevailing foothill plains, unlike those with overwhelmingly mountainous landscapes. We have developed a method for calculating winter annual precipitation total in the Abakan basin taking into account physical features of precipitation formation in the mountains, in particular the orographic correction to the velocity of vertical movements. The independent data suggest that algorithms for calculating snowmelt-induced maximum stages based on regression dependencies do not always give adequate results, therefore updating with regard for freezing processes in the foothill plain is required. Besides, extra observation data are called for obtaining the general statistical dependence.

The study topicality relates to the effect of climate changes and increased recurrence of dangerous hydrological events on rivers of southern Siberia. The observed and predicted changes in flood regimes are caused by a variety of factors and require different approaches in order to characterize the types of these changes. The aim of the study is stochastic modeling of solid precipitation total in the Abakan river basin, establishing relationship between precipitation and maximum water levels in the Abakan river during the flood period under spatial and temporal variability of hydrometeorological factors. Methods: comprehensive geographical and hydrometeorological analysis, dependence establishment based on long-term hydrometeorological observations using mathematical statistics methods, methods (developed by V.P. Galakhov) for estimating precipitation total in the basin with regard for orographic correction to the velocity of vertical movements in the frontal zone. Results. The crucial factor in the formation of maximum flood levels is winter precipitation amount. Heavy rainfalls during flood recession may significantly influence the maximum water levels. However, climate changes of recent decades in river mountain basins of southwestern and eastern Siberia are evidence of dependences between autumn soil freezing and formation of snowmelt-induced maximum stages. In some years during the flood period, decreased maximum water levels are probable in basins with prevailing foothill plains, unlike those with overwhelmingly mountainous landscapes. We have developed a method for calculating winter annual precipitation total in the Abakan basin taking into account physical features of precipitation formation in the mountains, in particular the orographic correction to the velocity of vertical movements. The independent data suggest that algorithms for calculating snowmelt-induced maximum stages based on regression dependencies do not always give adequate results, therefore updating with regard for freezing processes in the foothill plain is required. Besides, extra observation data are called for obtaining the general statistical dependence.

This study presents results from regular observation of permanent and summer-persisting firn-ice bodies in the highest parts of the Dinaric Alps. The sizes of six small glaciers and two snow patches on the Prokletije Massif (in Albania) and the Durmitor Massif (in Montenegro) were measured from 2011 to 2018. In recent years, specific cycles of interannual behavior have been observed: a year of considerable snow accumulation (a »recharge« phase), followed by two to four years of gradual decrease (a »wastage« phase). At present, the small glaciers studied exist in unbalanced conditions, which in the long term may lead to their degradation. Progressive warming makes short-term cycle minimums increasingly severe. Their retreat after the summer of 2017 was probably the most pronounced since the Little Ice Age, and small glaciers are on the verge of extinction.

According to the forecast of IPCC (Intergovernmental Panel of the Climate Change), an increase in precipitation is expected in this century in the Arctic. The main reason is intensification of evaporation from waters of the Arctic Ocean opening due to the intensive melting of sea ice. It is supposed that these changes will be most severe in winters in the Arctic regions, which are subject to significant anthropogenic load. In this respect, the intensively developed Nadym Lowland may be considered as a promising area for researches. The results of our study showed that the circulation conditions (primarily cyclones coming from the North Atlantic under the Eastern (E) circulation form of the G.Ya. Vangenheim–A.A. Girs classification) significantly influence on the isotopic composition of precipitation in this region. Thus, in the cold period of 2016–2017, the isotopic composition of precipitation changed for δ18О by 21 ‰, and for δD by 167 ‰ (weighted average values δ18О = −22.3 ‰, δD = −172.6 ‰, and dexc = 5.6 ‰). The use of the dew point temperature at the moment of precipitation in the calculations of the isotopic-temperature dependences allows obtaining the following coupling equation: δ18О = 0.67Tdp − 15.2 (R2 = 0.67). On the basis of the joint analysis of synoptic, trajectory and isotopic data, the main regions-sources of atmospheric moisture, precipitated in the Nadym Lowland during the cold period of 2016–2017, were determined. The major contributions were made by the Atlantic Ocean (35.7%), the North Atlantic Ocean and the Arctic Ocean (30.4%), and the Black Sea-Caspian region (20%). The last one is characterized by the most weighted isotopic composition. Inland source regions have contributed the least to precipitation (slightly larger 10%), and their lightweight isotopic composition is related to cryogenic fractionation.

The India–Burma troughs (IBTs) with different shapes (i.e., narrow and wide IBT-like circulations) can significantly affect winter precipitation over different regions in southern China through modulating the paths of water vapor transportation ahead of the IBTs. The effect of the wide/narrow IBT- (WIBT/NIBT-) like circulation cannot be depicted by traditional IBT indices that mainly focus on the IBT’s intensity. This study defines the WIBT and NIBT indices, which can effectively distinguish different water vapor transportation in front of the WIBT and NIBT and relevant water vapor convergence and therefore successfully reflect different distributions of winter precipitation anomalies over southern China. Further exploration reveals that a Rossby wave from the Mediterranean Sea to the Bay of Bengal (BoB) contributes to the variability of the NIBT, while the El Niño–Southern Oscillation (ENSO) can modulate the variability of the WIBT by stimulating the Matsuno–Gill response. The WIBT and NIBT indices should be considered as important supplements to the traditional IBT indices, which are favorable to more detailed diagnosis and prediction of winter climate over southern China.

The measurement of winter precipitation represents one of the largest uncertainties in the calculation of the hydrological balance. Manual measurement of winter precipitation is time- consuming, costly in terms of personnel and money, and is for this reason not often carried out. The measurement of winter precipitation using a heated rain gauge is in turn affected by wind and partly by the increased evaporation caused by heating. Therefore, automatic snow depth measurement is increasingly used and is becoming more affordable over time. This paper deals with the analysis of automatically measured data from a heated rain gauge, from ultrasonic or laser sensors for snow depth measurements, and from sensors for snow water equivalent measurements in order to find the dependence of new snow density on air temperature and on air humidity. Subsequently, a multiple linear regression equation was derived to calculate the density of new snow, which, together with the new snow accretion, was used to calculate snowfall totals. In addition, alternative winter precipitation was calculated and measured by sensors to calculate the snow water value as well as reference winter precipitation measured by a rain gauge from a manned station. The accuracy of these three precipitation alternatives was assessed using the...

This study reveals an intensified impact of winter (November–February mean) Arctic Oscillation (AO) on simultaneous precipitation over the mid–high latitudes of Asia (MHA) since the early 2000s. The unstable relationship may be related to the changes in the tropospheric AO mode and the subtropical jet. Further analyses suggest that their changes may be attributable to the interdecadal changes in the stratospheric polar vortex. During 2002–2017, the anomalously weak stratospheric polar vortex is accompanied by intensified upward-propagating tropospheric planetary-scale waves anomalies. Subsequently, the stratospheric geopotential height anomalies over the North Atlantic high-latitudes propagate downward strongly, causing the changes in the tropospheric AO mode, that is, the positive height anomalies over the North Atlantic high-latitudes are stronger and extend southward, corresponding to the stronger and eastward extension of negative height anomalies over the North Atlantic mid-latitudes. Thus, the Rossby wave source anomalies over Baffin Bay and the Black Sea are strong, and correspondingly so too are their subsequently excited the Rossby waves anomalies. Meanwhile, the planetary-scale waves anomalies propagate weakly along the low-latitude waveguide, causing the intensified and southward shift of the subtropical jet. Therefore, the strong Rossby waves anomalies propagate eastward to the MHA. By contrast, during 1979–1999, the strong stratospheric polar vortex anomaly is accompanied by weak upward-propagating planetary-scale waves anomalies, resulting in weaker height anomalies over the North Atlantic mid–high latitudes. Consequently, the anomalous Rossby waves are weak. In addition, the subtropical jet weakens and shifts northward, which causes the Rossby waves anomalies to dominate over the North Atlantic, and thereby the impact of winter AO on simultaneous precipitation over the MHA is weak.

High latitude and altitude environments are universally recognized as particularly sensitive to environmental changes and the current climate warming is inducing remarkable transformations on vegetation assemblage in these temperature-limited regions. However, next to the wealth of studies describing the effect of rising growing season temperature on trees, much less is known about the concurrent effects of precipitation and snowpack dynamics on the other key component of alpine vegetation represented by prostrate life forms. Selecting the most widespread shrub species in the North Hemisphere, we assembled a monospecific (Juniperus communis L.) network of 7 sites overarching the European Alps, measured the annual growth on >330 individuals and assessed the climate-growth associations for the last century (1910–2010) adopting a new model estimating the solid fraction of precipitation from unique highly-resolved daily climate records. Despite the high space-time variability of the yearly precipitation amount and distribution across the region, our analysis found a prominent, consistent and negative role of winter precipitation for shrub growth. Moreover, this crucial role of snow is maintained even in recent years, despite the persistent and significant warming trend. The presence of this underrated key factor for Alpine long-lived vegetation will require a thorough consideration. For the prostrate life form, not only temperature but also the solid fraction of winter precipitation should be considered to improve the projections of future growth trajectories.

Número monográfico dedicado al "18th EMS Annual Meeting: European Conference for Applied Meteorology and Climatology 2018" We describe a methodology for ensemble member’s weighting of operational seasonal forecasting systems (SFS) based on an enhanced prediction of a climate driver strongly affecting meteorological parameters over a certain region. We have applied it to the North Atlantic Oscillation (NAO) influence on the Iberian Peninsula winter precipitation. The first step in the proposed approach is to find the best estimation of winter NAO. Skill and error characteristics of forecasted winter NAO index by different Copernicus SFS are analysed in this study. Based on these results, a bias correction scheme is proposed and implemented for the ECMWF System 5 ensemble mean of NAO index, and then a modified NAO index pdf based on Gaussian errors is formulated. Finally, we apply the statistical estimation theory to achieve the Best linear unbiased estimate of winter NAO index and its uncertainty. For this purpose, two a priori estimates are used: the bias corrected NAO index Gaussian pdf from ECMWF System 5, and a skilful winter NAO index prediction based on teleconnection with snow cover advance with normal distributed errors. The second step of the proposed methodology is to employ the enhanced NAO index pdf estimates for ensemble member’s weighting of a SFS based on a single dynamical model. The new NAO pdfs obtained in this work have been used to improve the skill of the ECMWF System 5 to predict both NAO index and precipitation over the Iberian Peninsula. We show the improvement of NAO prediction, and of winter precipitation forecasts over our region of interest, when members are weighted with the bias corrected NAO index Gaussian pdf based on ECMWF System 5 compared with the usual approach based on equiprobability of ensemble members. Forecast skill is further enhanced if the Best NAO index pdf based on an optimal combination of the two a priori NAO index estimates is used for ensemble member’s weighting. The research leading to these results has received funding from MEDSCOPE project. MEDSCOPE is cofunded by the European Commission as part of ERA4CS, an ERANET initiated by JPI Climate, grant agreement no. 690462.

In order to construct a statistical downscaling model to reproduce regional precipitation pattern from sea level pres-sure (SLP) pattern for the use of global warming studies, the characteristic of winter precipitation in the Kyushu region are analyzed in relation to the pressure pattern in East Asia. Principal component analysis was performed on SLP data col-lected every six hours, and cluster analysis was performed in the principal component space using the principal compo-nent scores. For each sea level pressure patterns obtained, the precipitation rate was calculated for each precipitation threshold (i.e., mainly from 1 to 5 mm, in 1 mm increments) at each AMeDAS and SDP (Surface Daily Data Observation Point) sta-tion in the Kyushu region, and the regional characteristics of precipitation patterns are examined. 1) In case of the cyclone approaching (Gp.HLa.Dec) to Japan, the precipitation rate becomes high on the east side of the Kyushu mountain range, and low on the west side. 2) Under the influence of two cyclones, when Japan becomes a low pressure area (Gp.La.Dec) progressing to the typical winter pressure system, precipitation rate over the regions except Oita prefecture and Miyazaki prefecture are high. 3) When the cyclones passes through the south coast of Japan (Gp.Lb.Dec), the precipita-tion rate is high in the northwestern side of the Kyushu mountain range and low in the southeastern side and Nagasaki prefecture. 4) In case of the typical winter pressure pattern (Gp.SAd.Jan), the precipitation rate is low on the east side of the Kyushu mountainous area and at Izuhara, Ariake Sea coast, and inland region. Although Kyushu district are examined in this study, this statistical downscaling technique can be applied to all over Japan.

На основании 16 пробных площадей проанализировано накопление зимних осадков под пологом древостоев различного состава и под линиями электропередач в условиях подзоны южной тайги Урала. Данные о высоте и плотности снежного покрова получены на основе снегомерной съемки, выполненной в конце марта, т.е. при максимальной высоте снежного покрова. При проведении исследований использовались снегомерная рейка и весовой снегомер ВС-43. Установлено, что максимальный запас снеговой воды к моменту начала снеготаяния накапливается под пологом лиственничников с примесью сосны в составе древостоя. Значительные запасы снеговой воды накапливаются также под пологом березняков и под линиями электропередач при их расположении с севера на юг. Средняя высота снежного покрова варьируется от 33,5 до 54,9 см, что свидетельствует о защите нижних ярусов насаждения от вымерзания. В целях накопления зимних осадков в насаждениях подзоны южной тайги целесообразно формировать смешанные насаждения с примесью к сосне лиственницы и березы. Указанные насаждения в лесопарках будут способствовать не только повышению устойчивости и рекреационной привлекательности насаждений, но и обеспечат максимальное накопление зимних осадков. Последнее будет способствовать накоплению грунтовых вод и водности реки Исеть., The study conducts an analysis of the accumulation of winter precipitation under the canopy of stands of various compositions and on power lines in 16 sample areas in the southern taiga subzone of the Urals. The data on the height and density of the snow cover were obtained on the basis of a snow measurement survey carried out at the end of March, i.e. at the maximum height of the snow cover. The authors of the study used a snow measuring rail and a weight snow meter VS-43. The research establishes that the maximum supply of snow water at the time of the beginning of snowmelt accumulates under the canopy of larch trees with an admixture of pine in the composition of the stands. Significant reserves of snow water also accumulate under the canopy of birch forests and on power lines when they are located from north to south. The average height of the snow cover varies from 33.5 to 54.9 cm, which indicates the protection of the lower layers of vegetation from freezing. In order to accumulate winter precipitation in the stands of the southern taiga subzone, it is advisable to form mixed plantings with an admixture of larch and birch to pine. These plantings in forest parks will not only increase the stability and recreational attractiveness of the stands but also ensure the maximum accumulation of winter precipitation. The latter, in turn, will contribute to the accumulation of groundwater and the water Level of the Iset river., Международный научно-исследовательский журнал, Выпуск 7 (109) 2021, Pages 128-131

To improve solid precipitation monitoring in the hydrology and meteorology field, 1-min precipitation data observed by the PARticle SIze VELocity (PARSIVEL) disdrometer in Nanjing, eastern China, from February 2014 to February 2019 for all days with solid precipitation, were used to study the microphysical characteristics of winter precipitation. In this study, the empirical V-D (velocity&ndash, diameter) relationships and observed surface temperature are used for matching precipitation types, and the precipitation data are divided into rain, graupel, wet snow and dry snow. The results show that dry snow and wet snow have maximum Dm (mass-weighted mean diameter) and minimum log10Nw (normalized intercept parameter), while rain shows the opposite. Additionally, the &mu, &Lambda, (shape parameter&ndash, slope parameter) curve of dry snow and wet snow is very close, and the &mu, value of dry snow and wet snow is higher than that of graupel and higher than that of rain for the same &Lambda, value. Furthermore, the Ze-S (equivalent reflectivity factor&ndash, precipitation intensity) relationships among different types of precipitation are significantly different. If only the Ze-S relationship of rain is used for quantitative precipitation estimation (QPE), then, for small precipitation intensity, solid precipitation will be overestimated, while, for large precipitation intensity, it will be underestimated.

Over the past three decades, several general circulation models of the atmosphere and ocean (atmospheric and oceanic general circulation models – GCMs) have been improved by modeling the hydrological cycle with the use of isotopologues (isotopes of water) HDO and H2 18O. Input parameters for the GCM models taking into account changes in the isotope composition of atmospheric precipitation were, above all, the results obtained by the network GNIP – Global Network of Isotopes in Precipitation. At different times, on the vast territory of Russia there were only about 40 simultaneously functioning stations where the sampling of atmospheric precipitation was performed. In this study we present the results of the isotope composition of samples taken on the foothills of the Altai during two winter seasons of 2014/15 and 2015/16. Values of the isotope composition of precipitation changed in a wide range and their maximum fluctuations were 25, 202 and 18‰ for δ18О, dexc and δD, respectively. The weighted-mean values of δ18О and δD of the precipitation analyzed for the above two seasons were close to each other (−21.1 and −158.1‰ for the first season and −21.1 and −161.9‰ for the second one), while dexc values differed significantly. The comparison of the results of isotope analysis of the snow cover integral samples with the corresponding in the time interval the weighted-mean values of precipitation showed high consistency. However, despite the similarity of values of δ18О and δD, calculated for precipitation and snow cover, and the results, interpolated in IsoMAP (from data of the GNIP stations for 1960–2010), the dexc values were close to mean annual values of IsoMAP for only the second winter season. According to the trajectory analysis (the HYSPLIT model), the revealed differences between both, the seasons, and the long-term average values of IsoMAP, were associated with a change of main regions where the air masses carrying precipitation were formed, namely, the North Atlantic (the winter season of 2014/15) and the inland areas with open ice-free water bodies (the season of 2015/16). Thus, with the correct interpretation of the results, the data on the snow cover isotope composition on the Altai foothills can be used as an alternative data sources instead of the GNIP data.

The influence of the large-scale atmospheric circulation on winter precipitation over the Mediterranean region is studied with the use of monthly 2.5° × 2.5° ERA-Interim 500 and 1000 hPa geopotential heights and GPCP-v2.3 precipitation, for the period 1980–2017. At first, Principal Component Analysis (PCA) is applied both to geopotential heights and precipitation datasets and the main modes of inter-annual variations are found. Then, these modes are investigated through Canonical Correlation Analysis (CCA) to identify the centers of action of the lower and the middle troposphere that control precipitation variability over the Mediterranean region. Three statistically significant canonical pairs are found. The first one, in the North Atlantic, controls precipitation over western Asia Minor, northern Libya and the western Iberian Peninsula. Τhe second mode corresponds to the see-saw between Greenland and central Europe and controls precipitation over the northern Mediterranean region. The third one is located north of Britain and controls precipitation over NW Africa and northern France. For each canonical pair, the mean geopotential heights and precipitation anomaly patterns for the four (10%) years with the highest and the lowest canonical scores are constructed, confirming the results of CCA. Moreover, the correlation between the canonical scores and the indices of the large-scale atmospheric oscillations, namely the North Atlantic Oscillation (NAO), the Arctic Oscillation (AO), the North Sea – Caspian Pattern (NCP) and the East Atlantic/West Russia Pattern (EA/WR), was studied.

Urban modification of precipitation regimes is well documented in the urban climate literature. Studies investigating urbanization and non-convective precipitation, specifically winter precipitation, are limited. The theoretical framework here argues that the collective influence of urbanization extends beyond traditional city limits and the surrounding rural areas and can impact regional climate in non-adjacent cities. This paper utilizes the weather research and forecasting model (WRF-ARW) to simulate a cold-season synoptic system over the Northeastern United States over a variety of urban land surface scenarios. This case study centers on the potential boundary layer urban heat island effect on the lower troposphere and its ability to impact winter precipitation type at the local to regional scales. Results show a significant reduction in temperatures near the modified surface and subtle reductions over adjacent urban areas. When surface wind speeds are less than 5 ms−1, the boundary layer heat island increases air temperatures on the order of 3–4 °C at altitudes up to 925 mb. When combined with encroaching warm air near 850 mb during transitional precipitation events, the boundary layer heat island increases the thickness of the melting layer and consequently exposes falling hydrometeors to longer melting duration and phase change. Model simulations also show regional connections through remote temperature and relative humidity changes in urban areas removed from reforested areas.

Previous investigations have reported that the impacts of the preceding climate signal in the Southern Hemisphere can extend to Northern Hemisphere middle latitudes during the following season. This study suggests that the positive (negative) boreal autumn south Pacific Ocean dipole (SPOD) sea surface temperature anomalies are usually followed by reduced (increased) precipitation in the following winter over the North American monsoon (NAM) region. The positive autumn SPOD has the potential to regulate the southward fluctuation of the eddy-driven westerly jet in the southern Pacific Ocean, and exert the Rossby wave train stretching across the Pacific Ocean to transport the related energy into the NAM region. This finally results in anomalous high pressure in the troposphere over the NAM region. The related sinking motion and the water vapor conditions further affect the precipitation variability in these regions. This entire process can be referred to as a &ldquo, coupled oceanic&ndash, atmospheric bridge&rdquo, in which the &ldquo, oceanic bridge&rdquo, is the SPOD and the &ldquo, is the response of atmospheric circulation in the Pacific Ocean.

Using ERA-interim Reanalysis data and observational data, the intraseasonal oscillation of the winter rainfall in southern China is studied. The mean square deviation of daily precipitation is used to express precipitation variability, and winter precipitation variability over southern China is determined to be highly correlated with sea surface temperature (SST) in central and eastern tropical Pacific, the dominant period of the precipitation is 10&ndash, 30 days, which reflects quasi-biweekly oscillation. Examination of 1000 hPa geopotential height suggests that key low-pressure systems affecting the intraseasonal precipitation come from Lake Baikal, but with different travel paths. In El Ni&ntilde, o years, key low-pressure systems converge with other low-pressure systems and move southeastward until reaching South China, while in La Ni&ntilde, a years, only one low-pressure system can reach southern China. Meanwhile, the explosive development of the low-pressure system is mainly caused by the joint effects of thermal advection and vorticity advection in El Ni&ntilde, o, and only vorticity advection accounted for the dominant status in La Ni&ntilde, a. Multiscale analysis shows that the meridional distribution of intraseasonal circulation plays an important role on the thermal transmission and brings strong warm advection from low latitudes to high latitudes in El Ni&ntilde, o.

Winter precipitation over South China tended to be much higher than normal for the spring El Ni&ntilde, o events during 1979&ndash, 2016. For the spring El Ni&ntilde, o events, the meridional and zonal circulations served as a bridge, linking the warmer sea surface temperature (SST) in the eastern equatorial Pacific (EEP) and South China winter precipitation. This possible physical process can be described as follows: During boreal winter, a positive SST anomaly in the EEP was concurrent with strong anomalous convection activity over South China via anomalous Walker circulation, an anomalous Hadley Cell along 110&deg, &ndash, 130&deg, E, and a zonal westward teleconnection wave train pattern at 700 hPa in the Northern Hemisphere. In addition, an anomalous pumping effect at 200 hPa contributed to the convective activity. Meanwhile, the western Pacific subtropical high moved southwards and strengthened at 500 hPa, and abnormal southwesterly winds brought plentiful water vapor to South China at 850 hPa. All these factors favored an increase in precipitation over South China. For the summer El Ni&ntilde, o events, the aforementioned anomalies were weaker, which resulted in a precipitation close to normal over South China.

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)

Reconstructions of mean July temperature (Tjul) and winter precipitation (Pw) for the last 11/500 years on the Folgefonna peninsula are presented. Tjul was reconstructed using pollen-climate transfer functions and Pw was reconstructed based on the exponential relationship between mean solid winter precipitation and ablation-season temperature at the equilibrium-line altitude (ELA) with a reconstructed former ELA, using Tjul as the proxy for ablation-season temperature. The reconstructions from the Folgefonna peninsula suggest that the early Holocene was relatively cool and dry until c. 8000 cal. yr BP, followed by a warm and humid mid-Holocene until c. 4000 cal. yr BP with inferred Tjul above 12°C and Pw reaching as high as 225% of the present day. Subsequent to c. 4000 cal. yr BP a reduction is seen in both inferred Tjul and Pw with large fluctuations during the last 500 years. In addition, new calculations of Pw from two glaciers (Hardangerjøkulen and Jostedalsbreen) in southern Norway are presented. The results show that Pw varied in phase at all glaciers, probably as a response to the same climate forcing factor. During the early Holocene a major shift is suggested between winds from the west and the east.

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

This article proposes and presents a novel approach to the characterization of winter precipitation and modeling of radar observables through a synergistic use of advanced optical disdrometers for microphysical and geometrical measurements of ice and snow particles (in particular, a multi-angle snowflake camera—MASC), image processing methodology, advanced method-of-moments scattering computations, and state-of-the-art polarimetric radars. The article also describes the newly built and established MASCRAD (MASC + Radar) in-situ measurement site, under the umbrella of CSU-CHILL Radar, as well as the MASCRAD project and 2014/2015 winter campaign. We apply a visual hull method to reconstruct 3D shapes of ice particles based on high-resolution MASC images, and perform “particle-by-particle” scattering computations to obtain polarimetric radar observables. The article also presents and discusses selected illustrative observation data, results, and analyses for three cases with widely-differing meteorological settings that involve contrasting hydrometeor forms. Illustrative results of scattering calculations based on MASC images captured during these events, in comparison with radar data, as well as selected comparative studies of snow habits from MASC, 2D video-disdrometer, and CHILL radar data, are presented, along with the analysis of microphysical characteristics of particles. In the longer term, this work has potential to significantly improve the radar-based quantitative winter-precipitation estimation.

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.

Glaciers and small ice caps respond rapidly to climate perturbations (mainly winter precipitation, and summer temperature), and the mass-balance of glaciers located in western Norway is governed mainly by winter precipitation (Pw). Records of past Pw can offer important insight into long-term changes in atmospheric circulation, but few proxies are able to accurately capture winter climate variations in Scandinavia. Reconstructions of equilibrium-line-altitude (ELA) variations from glaciers that are sensitive to changes in Pw therefore provide a unique opportunity to quantify past winter climate in this region. Here we present a new, Holocene glacier activity reconstruction for the maritime ice cap Ålfotbreen in western Norway, based on investigations of distal glacier-fed lake sediments and modern mass balance measurements (1963–2010). Several lake sediment cores have been subject to a suite of laboratory analyses, including measurements of physical parameters such as dry bulk density (DBD) and loss-on-ignition (LOI), geochemistry (XRF), surface magnetic susceptibility (MS), and grain size distribution, to identify glacial sedimentation in the lake. Both radiocarbon (AMS 14C) and 210Pb dating were applied to establish age-depth relationships in the sediment cores. A novel approach was used to calibrate the sedimentary record against a simple ELA model, which allowed reconstruction of continuous ELA changes for Ålfotbreen during the Neoglacial (when Ålfotbreen was present, i.e. the last ∼1400 years). Furthermore, the resulting ELA variations were combined with an independent summer temperature record to calculate Neoglacial Pw using the ‘Liestøl equation’. The resulting Pw record is of higher resolution than previous reconstructions from glaciers in Norway and shows the potential of glacier records to provide high-resolution data reflecting past variations in hydroclimate. Complete deglaciation of the Ålfotbreen occurred ∼9700 cal yr BP, and the ice cap was subsequently absent or very small until a short-lived glacier event is seen in the lake sediments ∼8200 cal yr BP. The ice cap was most likely completely melted until a new glacier event occurred around ∼5300 cal yr BP, coeval with the onset of the Neoglacial at several other glaciers in southwestern Norway. Ålfotbreen was thereafter absent (or very small) until the onset of the Neoglacial period ∼1400 cal yr BP. The ‘Little Ice Age’ (LIA) ∼650–50 cal yr BP was the largest glacier advance of Ålfotbreen since deglaciation, with a maximum extent at ∼400–200 cal yr BP, when the ELA was lowered approximately 200 m relative to today. The late onset of the Neoglacial at Ålfotbreen is suggested to be a result of its low altitude relative to the regional ELA. A synthesis of Neoglacial ELA fluctuations along the coast of Norway indicates a time-transgressive trend in the maximum extent of the LIA, which apparently seems to have occurred progressively later as we move northwards. We suggest that this trend is likely due to regional winter precipitation differences along the coast of Norway. publishedVersion

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.