Browsing by Subject "Precipitation"

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  • Camenisch, Chantal; Jaume-Santero, Fernando; White, Sam; Pei, Qing; Hand, Ralf; Rohr, Christian; Brönnimann, Stefan (2022)
    Although collaborative efforts have been made to retrieve climate data from instrumental observations and paleoclimate records, there is still a large amount of valuable information in historical archives that has not been utilized for climate reconstruction. Due to the qualitative nature of these datasets, historical texts have been compiled and studied by historians aiming to describe the climate impact in socioeconomic aspects of human societies, but the inclusion of this information in past climate reconstructions remains fairly unexplored. Within this context, we present a novel approach to assimilate climate information contained in chronicles and annals from the 15th century to generate robust temperature and precipitation reconstructions of the Burgundian Low Countries, taking into account uncertainties associated with the descriptions of narrative sources. After data assimilation, our reconstructions present a high seasonal temperature correlation of similar to 0.8 independently of the climate model employed to estimate the background state of the atmosphere. Our study aims to be a first step towards a more quantitative use of available information contained in historical texts, showing how Bayesian inference can help the climate community with this endeavor.
  • Korkiakoski, Mika; Maatta, Tiia; Peltoniemi, Krista; Penttila, Timo; Lohila, Annalea (2022)
  • Ahmad, Faraaz; Morris, Katherine; Law, Gareth T.W.; Taylor, Kevin G.; Shaw, Samuel (2021)
    Understanding the speciation and fate of radium during operational discharge from the offshore oil and gas industry into the marine environment is important in assessing its long term environmental impact. In the current work, Ra-226 concentrations in marine sediments contaminated by produced water discharge from a site in the UK were analysed using gamma spectroscopy. Radium was present in field samples (0.1-0.3 Bq g(-1)) within International Atomic Energy Agency activity thresholds and was found to be primarily associated with micron sized radiobarite particles (
  • Pfeifer, Marion; Gonsamo, Alemu; Disney, Mathias; Pellikka, Petri; Marchant, Rob (2012)
  • Zhang, Jinru; Li, Haoran; Zeng, Yong; Yang, Lianmei; Li, Jiangang (2022)
    The macro- and microphysical characteristics of wintertime precipitating clouds and non-precipitating clouds over the West Tianshan Mountains, China, were analyzed with the use of Ka-band radar and weighing rain gauge observations. The data were collected from January to February 2019, December 2019, and from December 2020 to February 2021. Snowfall clouds mainly ranged from 0.15 similar to 2.50 km and had a reflectivity (Z) of mostly 10 33 dBZ. Non-snowfall clouds were primarily distributed within the height range of 2 similar to 8 km, and the Z values were within the range of - 22 similar to 15 dBZ. Compared with non-snowfall clouds, snowfall clouds have a higher particle water content (M) but a similar radial velocity (V). Light and moderate snowfall clouds were mainly located at heights of 0.15 similar to 3.50 km and had Z values concentrated from 5 similar to 24 dBZ. Heavy snowfall clouds were characterized by a Z of 5 similar to 30 dBZ below 3.5 km. The proportion of clouds with an M value> 0.1 g.m(-3) below 2 km was noticeably higher for heavy snow events than for light and moderate snow events. The differences in the distributions and values of snowfall cloud V values were small among the different snow types, and descending motions occurred below 6 km, with V ranging - 1.4 similar to - 0.3 m.s(-1). The heights of the non-snowfall cloud top and base during the day were lower than those at night. The snowfall cloud top did not show noticeable diurnal variations. The cloud top and base heights of the non-snowfall clouds both showed a single-peak distribution. The cloud top values of snowfall clouds exhibited bimodal distributions.
  • Kneifel, Stefan; von Lerber, Annakaisa; Tiira, Jussi; Moisseev, Dmitri; Kollias, Pavlos; Leinonen, Jussi (2015)
    Recently published studies of triple-frequency radar observations of snowfall have demonstrated that naturally occurring snowflakes exhibit scattering signatures that are in some cases consistent with spheroidal particle models and in others can only be explained by complex aggregates. Until recently, no in situ observations have been available to investigate links between microphysical snowfall properties and their scattering properties. In this study, we investigate for the first time relations between collocated ground-based triple-frequency observations with in situ measurements of snowfall at the ground. The three analyzed snowfall cases obtained during a recent field campaign in Finland cover light to moderate snowfall rates with transitions from heavily rimed snow to open-structured, low-density snowflakes. The observed triple-frequency signatures agree well with the previously published findings from airborne radar observations. A rich spatiotemporal structure of triple-frequency observations throughout the cloud is observed during the three cases, which often seems to be related to riming and aggregation zones within the cloud. The comparison of triple-frequency signatures from the lowest altitudes with the ground-based in situ measurements reveals that in the presence of large (>5 mm) snow aggregates, a bending away in the triple-frequency space from the curve of classical spheroid scattering models is always observed. Rimed particles appear along an almost horizontal line in the triple-frequency space, which was not observed before. Overall, the three case studies indicate a close connection of triple-frequency signatures and snow particle structure, bulk snowfall density, and characteristic size of the particle size distribution.
  • Hohenthal, Johanna; Venäläinen, Ari; Ylhäisi, Jussi S.; Jylhä, Kirsti; Käyhkö, Jukka (Ilmatieteen laitos, 2014)
    Raportteja - Rapporter - Reports 2014:1
    In spite of the relatively humid climate of Northern Europe, prolonged meteorological dry spells do occasionally cause problems for the water supply in different sectors of society. During recent decades, total annual precipitation has increased in the region, especially during winter. A linear change in total precipitation does not necessarily indicate a change in the occurrence of meteorological drought across different time scales. In this study, temporal changes of meteorological summer (May-August) dry spells (MDS) and dry days (MDD) are analysed using measured precipitation observations from 12 weather stations located around Northern Europe. The statistics studied are the number of MDDs (<1.0 and <0.1 mm) per selected periods, plus the lengths of the longest MDSs during which the total accumulated precipitation remains under certain thresholds, namely 10 and 100 mm. The results suggest that, in general, the lengths of the longest MDSs and the numbers of MDDs do not differ remarkably between the stations, median value being 26/80 days (<10/<100 mm rain) and 87/70 days (<1.0/<0.1 mm/day), respectively. A distinct exception is Bergen, in Norway, where the lengths of the longest MDSs are shorter (19 and 41 days, on average) and the numbers of MDDs lower (ca. 64 and 50 days) than at the other stations. During the period of homogeneous instrumental precipitation observations, the occurrence of summer MDSs and MDD have remained the same at most of the stations. Only a few statistically significant increasing temporal trends appear in the time series of MDDs in the southern parts of the region. In the north, one statistically significant decreasing trend has been detected.
  • Räsänen, Matti; Aurela, Mika; Vakkari, Ville; Beukes, Johan P.; Tuovinen, Juha-Pekka; van Zyl, Pieter G.; Josipovic, Miroslav; Siebert, Stefan J.; Laurila, Tuomas; Kulmala, Markku; Laakso, Lauri; Rinne, Janne; Oren, Ram; Katul, Gabriel (2022)
    The role of precipitation (P) variability with respect to evapotranspiration (ET) and its two components, transpiration (T) and evaporation (E), from savannas continues to draw significant research interest given its relevance to a number of ecohydrological applications. Our study reports on 6 years of measured ET and estimated T and E from a grazed savanna grassland at Welgegund, South Africa. Annual P varied significantly with respect to amount (508 to 672 mm yr(-1)), with dry years characterized by infrequent early-season rainfall. T was determined using annual water-use efficiency and gross primary production estimates derived from eddy-covariance measurements of latent heat flux and net ecosystem CO2 exchange rates. The computed annual T for the 4 wet years with frequent early wet-season rainfall was nearly constant, 326 +/- 19 mm yr(-1) (T/ET=0.51), but was lower and more variable between the 2 dry years (255 and 154 mm yr(-1), respectively). Annual T and T/ET were linearly related to the early wet-season storm frequency. The constancy of annual T during wet years is explained by the moderate water stress of C4 grasses as well as trees' ability to use water from deeper layers. During extreme drought, grasses respond to water availability with a dieback-regrowth pattern, reducing leaf area and transpiration and, thus, increasing the proportion of transpiration contributed by trees. The works suggest that the early-season P distribution explains the interannual variability in T, which should be considered when managing grazing and fodder production in these grasslands.
  • Sukselainen, Leena Kristiina; Kaakinen, Anu; Eronen, Jussi Tuomas; Passey, Benjamin H.; Harrison, Terry; Zhaoqun, Zhang; Fortelius, Mikael (2017)
    Damiao, Inner Mongolia, has three main fossil horizons representing the early, middle, and late Miocene. The middle Miocene locality DM01 is the only primate locality from the region and also represents the latest occurrence of pliopithecoids in northern China. The presence of pliopithecoid primates in central Asia after the middle Miocene climatic optimum seems to contradict the general trend of strengthening climatic zonality and increasing aridity. To investigate this enigma, we employ faunal similarity, ecometrics, and stable isotope analysis. Our results support previous inferences concerning the presence of locally humid environments within the increasingly arid surroundings that characterized central Asia. Hypsodonty, estimated mean annual precipitation (MAP), local sedimentology, and large mammal fossils suggest more humid and possibly more forested and wooded environments for the DM01 locality. We compared our results with the adjacent fossil-rich middle Miocene Tunggur localities. However, the small mammal fauna and isotope data are consistent with a mosaic of forest and grassland environment for all Damiao localities. Based on our results, Tunggur may have been too seasonal or not sufficiently humid for pliopithecids. This is supported by the higher mean hypsodonty and lower estimated MAP estimates, as well as slightly higher d13C values. We suggest that DM01, the driest known Asian pliopithecid locality, may have been a more humid refugium within a generally drier regional context.
  • Guan, Yanlong; Lu, Hongwei; Yin, Chuang; Xue, Yuxuan; Jiang, Yelin; Kang, Yu; He, Li; Heiskanen, Janne (2020)
    Extensive research has focused on the response of vegetation to climate change, including potential mechanisms and resulting impacts. Although many studies have explored the relationship between vegetation and climate change in China, research on spatiotemporal distribution changes of climate regimes using natural vegetation as an indicator is still lacking. Further, limited information is available on the response of vegetation to shifts in China's regional climatic zones. In this study, we applied Mann-Kendall, and correlation analysis to examine the variabilities in temperature, precipitation, surface soil water, normalised difference vegetation index (NDVI), and albedo in China from 1982 to 2012. Our results indicate significant shifts in the distribution of Koppen-Geiger climate classes in China from 12.08% to 18.98% between 1983 and 2012 at a significance level of 0.05 (MK). The percentage areas in the arid and continental zones expanded at a rate of 0.004%/y and 0.12%/y, respectively, while the percentage area in the temperate and alpine zones decreased by -0.05%/y and - 0.07%/y. Sensitivity fitting results between simulated and observed changes identified temperature to be a dominant control on the dynamics of temperate (r(2)= 0.98) and alpine (r(2)= 0.968) zones, while precipitation was the dominant control on the changes of arid (r(2) = 0.856) and continental (r(2) = 0.815) zones. The response of the NDVI to albedo infers a more pronounced radiative response in temperate (r = -0.82, p
  • Virman, Meri; Bister, Marja; Sinclair, Victoria; Räisänen, Jouni; Järvinen, Heikki (2020)
    A recent study based on observations has shown that after precipitation over tropical oceans rather shallow temperature structures occur in the lower troposphere and that their magnitude depends on climatological low- to midtropospheric humidity. As any process that produces temperature perturbations in the lower troposphere can be of great significance for the formation of atmospheric deep convection, the vertical temperature structure associated with evaporation of stratiform precipitation and its sensitivity to low- to midtropospheric humidity are studied by conducting three-dimensional, high-resolution, idealized simulations with the Advanced Research version of the Weather Research and Forecasting (WRF) Model. In the simulations, rainwater with mixing ratio and number concentration characteristic of stratiform precipitation associated with mesoscale convective systems is added in a large round area at roughly 560 hPa. Evaporative cooling and subsidence warming below result in a cold anomaly at roughly 560–750 hPa and, especially, a warm anomaly at roughly 750–900 hPa. The cold-over-warm anomalies are stronger with smaller low- to midtropospheric relative humidity in the initial conditions, with the maximum magnitude of the warm anomaly ranging between 0.7 and 1.2 K. The temperature anomalies propagate to the environment and still remain present after precipitation stops. The results show that evaporation of stratiform precipitation alone can lead to temperature structures, which are on the same order of magnitude as the observed ones, that potentially inhibit subsequent convection by increasing convective inhibition. Therefore, the representation of microphysical processes affecting the location, amount, and vertical and horizontal distribution of stratiform precipitation and its evaporation in numerical models requires special attention.