Browsing by Subject "WEATHER"

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  • Korhonen, Natalia; Hyvärinen, Otto; Kämäräinen, Matti; Richardson, David S.; Järvinen, Heikki; Gregow, Hilppa (2020)
    The strength of the stratospheric polar vortex influences the surface weather in the Northern Hemisphere in winter; a weaker (stronger) than average stratospheric polar vortex is connected to negative (positive) Arctic Oscillation (AO) and colder (warmer) than average surface temperatures in northern Europe within weeks or months. This holds the potential for forecasting in that timescale. We investigate here if the strength of the stratospheric polar vortex at the start of the forecast could be used to improve the extended-range temperature forecasts of the European Centre for Medium-Range Weather Forecasts (ECMWF) and to find periods with higher prediction skill scores. For this, we developed a stratospheric wind indicator (SWI) based on the strength of the stratospheric polar vortex and the phase of the AO during the following weeks. We demonstrate that there was a statistically significant difference in the observed surface temperature in northern Europe within the 3-6 weeks, depending on the SWI at the start of the forecast. When our new SWI was applied in post-processing the ECMWF's 2-week mean temperature reforecasts for weeks 3-4 and 5-6 in northern Europe during boreal winter, the skill scores of those weeks were slightly improved. This indicates there is some room for improving the extended-range forecasts, if the stratosphere-troposphere links were better captured in the modelling. In addition to this, we found that during the boreal winter, in cases where the polar vortex was weak at the start of the forecast, the mean skill scores of the 3-6 weeks' surface temperature forecasts were higher than average.
  • Petäjä, T.; Järvi, L.; Kerminen, V. -M.; Ding, A. J.; Sun, J. N.; Nie, W.; Kujansuu, J.; Virkkula, A.; Yang, X. -Q.; Fu, C. B.; Zilitinkevich, S.; Kulmala, M. (2016)
    Severe air pollution episodes have been frequent in China during the recent years. While high emissions are the primary reason for increasing pollutant concentrations, the ultimate cause for the most severe pollution episodes has remained unclear. Here we show that a high concentration of particulate matter (PM) will enhance the stability of an urban boundary layer, which in turn decreases the boundary layer height and consequently cause further increases in PM concentrations. We estimate the strength of this positive feedback mechanism by combining a new theoretical framework with ambient observations. We show that the feedback remains moderate at fine PM concentrations lower than about 200 mu g m(-3), but that it becomes increasingly effective at higher PM loadings resulting from the combined effect of high surface PM emissions and massive secondary PM production within the boundary layer. Our analysis explains why air pollution episodes are particularly serious and severe in megacities and during the days when synoptic weather conditions stay constant.
  • Marke, Tobias; Crewell, Susanne; Schemann, Vera; Schween, Jan H.; Tuononen, Minttu (2018)
    Low-level-jet (LLJ) periods are investigated by exploiting a long-termrecord of ground-based remote sensing Doppler wind lidar measurements supported by tower observations and surface flux measurements at the Julich Observatory for Cloud Evolution (JOYCE), a midlatitude site in western Germany. LLJs were found 13% of the time during continuous observations over more than 4 yr. The climatological behavior of the LLJs shows a prevailing nighttime appearance of the jets, with a median height of 375 m and a median wind speed of 8.8 ms(-1) at the jet nose. Significant turbulence below the jet nose only occurs for high bulk wind shear, which is an important parameter for describing the turbulent characteristics of the jets. The numerous LLJs (16% of all jets) in the range of wind-turbine rotor heights below 200 m demonstrate the importance of LLJs and the associated intermittent turbulence for wind-energy applications. Also, a decrease in surface fluxes and an accumulation of carbon dioxide are observed if LLJs are present. A comprehensive analysis of an LLJ case shows the influence of the surrounding topography, dominated by an open pit mine and a 200-m-high hill, on the wind observed at JOYCE. High-resolution large-eddy simulations that complement the observations show that the spatial distribution of the wind field exhibits variations connected with the orographic flow depending on the wind direction, causing high variability in the long-term measurements of the vertical velocity.
  • Landauer, Mia; Goodsite, Michael Evan; Juhola, Sirkku (2018)
    The tourism sector is affected by climate change. Nordic tourism destinations have also experienced changes, such as changing precipitation patterns, lack of snow in winter and shifts in seasons. The sector has to implement adaptation strategies but it is unclear whether the current public climate policy is sufficient to support considering adaptation actions. We reviewed national climate strategies of the Nordic countries from the perspectives of tourism, but excluding the transport sector. We also reviewed Nordic national tourism strategies from the perspective of climate change, particularly the extent to which they address climate adaptation. We found out that the national climate strategies do not pay enough attention to tourism adaptation needs, nor do the national tourism strategies present adaptation actions that tourism actors could consider. To connect these national-level strategies, there is a need to review adaptation actions for tourism within the national adaptation framework supported by research based evidence. Next, by means of Nordic cooperation, guidance for both public and private tourism actors within and across Nordic countries can be provided. This can enhance the competitiveness and resilience of the Nordic tourism supply and contribute to the development of economically, environmentally and socially sustainable tourism in the region.
  • Lehikoinen, Aleksi; Linden, Andreas; Karlsson, Mans; Andersson, Arne; Crewe, Tara L.; Dunn, Erica H.; Gregory, George; Karlsson, Lennart; Kristiansen, Vidar; Mackenzie, Stuart; Newman, Steve; Roer, Jan Erik; Sharpe, Chris; Sokolov, Leonid V.; Steinholtz, Asa; Stervander, Martin; Tirri, Ina-Sabrina; Tjornlov, Rune Skjold (2019)
    Climate change has been shown to shift the seasonal timing (i.e. phenology) and distribution of species. The phenological effects of climate change on living organisms have often been tested using first occurrence dates, which may be uninformative and biased. More rarely investigated is how different phases of a phenological sequence (e.g. beginning, central tendency and end) or its duration have changed over time. This type of analysis requires continuous observation throughout the phenological event over multiple years, and such data sets are rare. In this study we examined the impact of temperature on long-term change of passage timing and duration of the spring migration period in birds, and which species' traits explain species-specific variation. Data used covered 195 species from 21 European and Canadian bird observatories from which systematic daily sampling protocols were available. Migration dates were negatively associated with early spring temperature and timings had in general advanced in 57 years. Short-distance migrants advanced the beginning of their migration more than long-distance migrants when corrected for phylogenic relatedness, but such a difference was not found in other phases of migration. The advancement of migration has generally been greater for the beginning and median phases of migration relative to the end, leading to extended spring migration seasons. Duration of the migration season increased with increasing temperature. Phenological changes have also been less noticeable in Canada even when corrected for rate of change in temperature. To visualize long-term changes in phenology, we constructed the first multi-species spring migration phenology indicator to describe general changes in median migration dates in the northern hemisphere. The indicator showed an average advancement of one week during five decades across the continents (period 1959-2015). The indicator is easy to update with new data and we therefore encourage future research to investigate whether the trend towards longer periods of occurrence or emergence in spring is also evident in other migratory populations. Such phenological changes may influence detectability in monitoring schemes, and may have broader implications on population and community dynamics.
  • Seitola, Teija; Silen, Johan; Järvinen, Heikki (2015)
    In this article, we introduce a new algorithm called randomised multichannel singular spectrum analysis (RMSSA), which is a generalisation of the traditional multichannel singular spectrum analysis (MSSA) into problems of arbitrarily large dimension. RMSSA consists of (1) a dimension reduction of the original data via random projections, (2) the standard MSSA step and (3) a recovery of the MSSA eigenmodes from the reduced space back to the original space. The RMSSA algorithm is presented in detail and additionally we show how to integrate it with a significance test based on a red noise null-hypothesis by Monte-Carlo simulation. Finally, RMSSA is applied to decompose the 20th century global monthly mean near-surface temperature variability into its low-frequency components. The decomposition of a reanalysis data set and two climate model simulations reveals, for instance, that the 2-6 yr variability centred in the Pacific Ocean is captured by all the data sets with some differences in statistical significance and spatial patterns.
  • Hautsalo, Juho; Jauhiainen, Lauri; Hannukkala, Asko; Manninen, Outi; Vetelainen, Merja; Pietila, Leena; Peltoniemi, Kirsi; Jalli, Marja (2020)
    Fusarium head blight (FHB) and the mycotoxins produced by its causal agents in oats (Avena sativaL.) have become a growing problem in northern countries over the last decades. The development of resistant cultivars would offer a highly needed and economical solution to the problem. To tackle the high genotypexenvironment interaction of FHB, a combined analysis was carried out on eight greenhouse and 13 field experiments inoculated with DON-producingFusariumspecies. Our data included 406 oat genotypes consisting of Nordic cultivars, breeding lines and potentially resistant gene bank accessions. High variation in the DON accumulation estimates in the material shows that the selection of genotypes with better resistance would be valuable. The greenhouse and field studies resulted in significantly different oat genotype susceptibility rankings for both DON andFusariuminfected kernels. The results obtained from the field experiments have more practical relevance for farmers and breeders for the identification of DON resistant cultivars than greenhouse screenings. Days to maturity and the plant height of the genotypes both significantly affected theFusariuminfections and DON in the field. The relationship betweenFusariuminfected kernels, DONand germination capacity provide an insight into the composition of genotypes with resistance. The core set of 30 oat genotypes, which were phenotyped in several experiments, provides valuable examples of both highly susceptible and moderately resistant oat genotypes.
  • Luomaranta, Anna M; Aalto, Juha; Jylhä, Kirsti (2019)
    Snow conditions in high-latitude regions are changing in response to climate warming, and these changes are likely to accelerate as the warming proceeds. Here, we analyse daily gridded snow depth, temperature and precipitation data from Finland over the period 1961-2014 to discover the ongoing changes in monthly average snow depths (SN) and several snow-related indices. Our results indicate that regional differences of changes in snow conditions can be relatively large, even within such a small district as Finland. Moreover, the interannual variation of the various snow indices was found to be larger in southern Finland than in northern Finland. The largest decrease in snow depth occurred in the southern, western and central parts of Finland in late winter and early spring. This decrease was driven by increasing mixed and liquid precipitation and, especially in spring, increasing temperature. In northern Finland, the decreasing trend of snow depth was most evident in spring, but no change occurred during winter months, although the amount of solid precipitation was found to increase in December-February. In the same months, temperature and the amount of mixed and liquid precipitation increased, likely counteracting the effects of the increasing solid precipitation on snow depth. The annual maximum snow depth that typically occurs in March was found to decrease in over 85% of Finland's area, most strongly in western coastal areas. In almost half of Finland's area, this decrease occurred despite increasing solid precipitation. Our findings highlight the complexity of the responses of snow conditions to climatic variability in northern Europe.
  • Kämäräinen, Matti; Uotila, Petteri; Karpechko, Alexey; Hyvärinen, Otto; Lehtonen, Ilari; Räisänen, Jouni (2019)
    A statistical learning approach to produce seasonal temperature forecasts in western Europe and Scandinavia was implemented and tested. The leading principal components (PCs) of sea surface temperature (SST) and the geopotential at the 150-hPa level (GPT) were derived from reanalysis datasets and used at different lags (from one to five seasons) as predictors. Random sampling of both the fitting years and the potential predictors together with the Least Absolute Shrinkage and Selection Operator regression (LASSO) was used to create a large ensemble of statistical models. Applying the models to independent test years shows that the ensemble performs well over the target areas and that the ensemble mean is more accurate than the best individual ensemble member on average. Skillful results were especially found for summer and fall, with the anomaly correlation coefficient values ranging between 0.41 and 0.68 for these seasons. The correct simulation of decadal trends, using sufficiently long time series for fitting (70 years), and the use of lagged predictors increased the prediction skill. The decadal-scale variability of SST, most importantly the Atlantic multidecadal oscillation (AMO), and different PCs of GPT are the most important individual predictors among all predictors. Both SST and GPT bring equally much predictive power, although their importance is different in different seasons.
  • Jonauskaite, Domicele; Abdel-Khalek, Ahmed; Abu-Akel, Ahmad; Al-Rasheed, Abdulrahman Saud; Antonietti, Jean-Philippe; Ásgeirsson, Árni Gunnar; Atitsogbe, Kokou Amenyona; Barma, Marodégueba; Barratt, Daniel; Bogushevskaya, Victoria; Bouayed Meziane, Maliha Khadidja; Chamseddine, Amer; Charernboom, Thammanard; Chkonia, Eka; Ciobanu, Teofil; Corona, Violeta; Creed, Allison; Dael, Nele; Daouk, Hassan; Dimitrova, Nevena; Doorenbos, Cornelis B.; Fomins, Sergejs; Fonseca-Pedrero, Eduardo; Gaspar, Augusta; Gizdic, Alena; Griber, Yulia A.; Grimshaw, Gina; Hasan Aya, Ahmed; Havelka, Jelena; Hirnstein, Marco; Karlsson, Bodil S.A.; Kim, Jejoong; Konstantinou, Nikos; Laurent, Eric; Lindeman, Marjaana; Manav, Banu; Marquardt, Lynn; Mefoh, Philip; Mroczko-Wąsowicz, Aleksandra; Mutandwa, Phillip; Muthusi, Steve; Ngabolo, Georgette; Oberfeld, Daniel; Papadatou-Pastou, Marietta; Perchtold, Corinna M.; Pérez-Albéniz, Alicia; Pouyan, Niloufar; Rashid Soron, Tanjir; Roinishvili, Maya; Romanyuk, Lyudmyla; Salgado Montejo, Alejandro; Sultanova, Aygun; Tau, Ramiro; Uusküla, Mari; Vainio, Suvi; Vargas-Soto, Veronica; Volkan, Eliz; Wąsowicz, Grażyna; Zdravković, Sunčica; Zhang, Meng; Mohr, Christine (2019)
    Across cultures, people associate colours with emotions. Here, we test the hypothesis that one driver of this cross-modal correspondence is the physical environment we live in. We focus on a prime example – the association of yellow with joy, – which conceivably arises because yellow is reminiscent of life-sustaining sunshine and pleasant weather. If so, this association should be especially strong in countries where sunny weather is a rare occurrence. We analysed yellow-joy associations of 6625 participants from 55 countries to investigate how yellow-joy associations varied geographically, climatologically, and seasonally. We assessed the distance to the equator, sunshine, precipitation, and daytime hours. Consistent with our hypotheses, participants who live further away from the equator and in rainier countries are more likely to associate yellow with joy. We did not find associations with seasonal variations. Our findings support a role for the physical environment in shaping the affective meaning of colour.
  • Ruosteenoja, Kimmo; Markkanen, Tiina; Räisänen, Jouni (2020)
    Global warming acts to prolong thermal summers and shorten winters. In this work, future changes in the lengths and timing of four thermal seasons in northern Europe, with threshold temperatures 0 and 10 degrees C, are derived from bias-adjusted output data from 23 CMIP5 global climate models. Three future periods and two Representative Concentration Pathway (RCP) scenarios are discussed. The focus is on the period 2040-2069 under RCP4.5, which approximately corresponds to a 2 degrees C global warming relative to the preindustrial era. By the period 2040-2069, the average length of the thermal summer increases by nearly 30 days relative to 1971-2000, and the thermal winter shortens by 30-60 days. The timing of the thermal springs advances while autumns delay. Within the model ensemble, there is a high linear correlation between the modelled annual-mean temperature increase and shifts in the thermal seasons. Thermal summers lengthen by about 10 days and winters shorten by 10-24 days per 1 degrees C of local warming. In the mid-21st century, about two-thirds of all summers (winters) are projected to be very long (very short) according to the baseline-period standards, with an anomaly greater than 20 days relative to the late-20th century temporal mean. The proportion of years without a thermal winter increases remarkably in the Baltic countries and southern Scandinavian peninsula. Implications of the changing thermal seasons on nature and human society are discussed in a literature review.