Browsing by Subject "precipitation"

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  • Luoto, Tomi P.; Kivila, E. Henriikka; Kotrys, Bartosz; Plociennik, Mateusz; Rantala, Marttiina; Nevalainen, Liisa (2020)
    Independent Arctic records of temperature and precipitation from the same proxy archives are rare. Nevertheless, they are important for providing detailed information on long-term climate changes and temperature-precipitation relationships in the context of large-scale atmospheric dynamics. Here, we used chironomid and cladoceran fossil assemblages to reconstruct summer air-temperature and water-level changes, during the past 400 years, in a small lake located in Finnish Lapland. Temperatures remained persistently cold over the Little Ice Age (LIA), but increased in the 20th century. After a cooler phase in the 1970s, the climate rapidly warmed to the record-high temperatures of the most recent decades. The lake-level reconstruction suggested persistently wet conditions for the LIA, followed by a dry period between similar to 1910 and 1970 CE, when the lake apparently became almost dry. Since the 1980s, the lake level has returned to a similar position as during the IAA. The temperature development was consistent with earlier records, but a significant local feature was found in the lake-level reconstruction the LIA appears to have been continuously wet, without the generally depicted dry phase during the 18th and 19th centuries. Therefore, the results suggest local precipitation patterns and enforce the concept of spatially divergent LIA conditions.
  • Gedefaw, Melakeneh G.; Geli, Hatim M. E.; Abera, Temesgen (2021)
    Rangelands provide significant socioeconomic and environmental benefits to humans. However, climate variability and anthropogenic drivers can negatively impact rangeland productivity. The main goal of this study was to investigate structural and productivity changes in rangeland ecosystems in New Mexico (NM), in the southwestern United States of America during the 1984-2015 period. This goal was achieved by applying the time series segmented residual trend analysis (TSS-RESTREND) method, using datasets of the normalized difference vegetation index (NDVI) from the Global Inventory Modeling and Mapping Studies and precipitation from Parameter elevation Regressions on Independent Slopes Model (PRISM), and developing an assessment framework. The results indicated that about 17.6% and 12.8% of NM experienced a decrease and an increase in productivity, respectively. More than half of the state (55.6%) had insignificant change productivity, 10.8% was classified as indeterminant, and 3.2% was considered as agriculture. A decrease in productivity was observed in 2.2%, 4.5%, and 1.7% of NM's grassland, shrubland, and ever green forest land cover classes, respectively. Significant decrease in productivity was observed in the northeastern and southeastern quadrants of NM while significant increase was observed in northwestern, southwestern, and a small portion of the southeastern quadrants. The timing of detected breakpoints coincided with some of NM's drought events as indicated by the self-calibrated Palmar Drought Severity Index as their number increased since 2000s following a similar increase in drought severity. Some breakpoints were concurrent with some fire events. The combination of these two types of disturbances can partly explain the emergence of breakpoints with degradation in productivity. Using the breakpoint assessment framework developed in this study, the observed degradation based on the TSS-RESTREND showed only 55% agreement with the Rangeland Productivity Monitoring Service (RPMS) data. There was an agreement between the TSS-RESTREND and RPMS on the occurrence of significant degradation in productivity over the grasslands and shrublands within the Arizona/NM Tablelands and in the Chihuahua Desert ecoregions, respectively. This assessment of NM's vegetation productivity is critical to support the decision-making process for rangeland management; address challenges related to the sustainability of forage supply and livestock production; conserve the biodiversity of rangelands ecosystems; and increase their resilience. Future analysis should consider the effects of rising temperatures and drought on rangeland degradation and productivity.
  • Kok, L.; van Zyl, P. G.; Beukes, J. P.; Swartz, J-S; Burger, R. P.; Ellis, Suria; Josipovic, M.; Vakkari, V.; Laakso, L.; Kulmala, M. (2021)
    Relatively limited data have been published on the chemical composition of wet deposition for South Africa, which is considered an important source region for atmospheric pollutants. Concentrations and wet deposition fluxes of ionic species determined in rain samples collected from December 2014 to April 2018 at a regional site, Welgegund, are presented, and contextualised by wet deposition composition in the northeastern interior of South Africa. 89% of rain samples collected during the sampling period complied with the data quality objectives of the World Meteorological Organisation. The total ionic concentration of rainwater at Welgegund was similar to that at two regional sites located within proximity of industrial activities. The pH of rainwater (4.80) was comparable to that determined at two rural background sites, which indicated increased neutralisation. Similarly to the other sites located in the South African interior, SO42- was the most abundant species in rain, with concentrations thereof in the same order as SO42- levels determined at the two industrially influenced sites. Lower sulphur and nitrogen fluxes at Welgegund were attributed to lower average annual rainfall. The anthropogenic (industrial) source group had the largest contribution to wet deposition chemical composition, which signified the influence of major source regions in the South African interior that impact Welgegund. Relatively large contributions were also calculated from marine and crustal sources. The influence of agricultural activities was also evident, while biomass burning had the lowest contribution due to open biomass burning occurring mainly during the dry season
  • Eyres, Alison; Eronen, Jussi T.; Hagen, Oskar; Boehning-Gaese, Katrin; Fritz, Susanne A. (2021)
    Climatic niches describe the climatic conditions in which species can persist. Shifts in climatic niches have been observed to coincide with major climatic change, suggesting that species adapt to new conditions. We test the relationship between rates of climatic niche evolution and paleoclimatic conditions through time for 65 Old-World flycatcher species (Aves: Muscicapidae). We combine niche quantification for all species with dated phylogenies to infer past changes in the rates of niche evolution for temperature and precipitation niches. Paleoclimatic conditions were inferred independently using two datasets: a paleoelevation reconstruction and the mammal fossil record. We find changes in climatic niches through time, but no or weak support for a relationship between niche evolution rates and rates of paleoclimatic change for both temperature and precipitation niche and for both reconstruction methods. In contrast, the inferred relationship between climatic conditions and niche evolution rates depends on paleoclimatic reconstruction method: rates of temperature niche evolution are significantly negatively related to absolute temperatures inferred using the paleoelevation model but not those reconstructed from the fossil record. We suggest that paleoclimatic change might be a weak driver of climatic niche evolution in birds and highlight the need for greater integration of different paleoclimate reconstructions.
  • Selmer, Ilka; Karnetzke, Julia; Kleemann, Christian; Lehtonen, Mari; Mikkonen, Kirsi S.; Kulozik, Ulrich; Smirnova, Irina (2019)
  • Liu, Zhiyong; Chen, Lei; Smith, Nicholas G.; Yuan, Wenping; Chen, Xiaohong; Zhou, Guoyi; Alam, Syed Ashraful; Lin, Kairong; Zhao, Tongtiegang; Zhou, Ping; Chu, Chengjin; Ma, Hanqing; Liu, Jianquan (2019)
    The directionality of the response of gross primary productivity (GPP) to climate has been shown to vary across the globe. This effect has been hypothesized to be the result of the interaction between multiple bioclimatic factors, including environmental energy (i.e., temperature and radiation) and water availability. This is due to the tight coupling between water and carbon cycling in plants and the fact that temperature often drives plant water demand. Using GPP data extracted from 188 sites of FLUXNET2015 and observation-driven terrestrial biosphere models, we disentangled the confounding effects of temperature, precipitation and carbon dioxide on GPP, and examined their long-term effects on productivity across the globe. Based on the FLUXNET2015 data, we observed a decline in the positive effect of temperature on GPP, while the positive effects of precipitation and CO2 were becoming stronger during 2000-2014. Using data derived from terrestrial biosphere models between 1980 and 2010 we found similar effects globally. The modeled data allowed us to investigate these effects more thoroughly over space and time. In arid regions, the modeled response to precipitation increased since 1950, approximately 30 years earlier than in humid regions. We further observed the negative effects of summer temperature on GPP in arid regions, suggesting greater aridity stress on productivity under global warming. Our results imply that aridity stress, triggered by rising temperatures, has reduced the positive influence of temperature on GPP, while increased precipitation and elevated CO2 may alleviate negative aridity impacts.
  • Moiseev, Dmitry; Lautaportti, Susanna; Alku, Laura; Tabakova, Ksenia; O'Connor, Ewan; Leskinen, Matti; Kulmala, Markku (2019)
    Abstract: Eleven years of dual-polarization weather radar data, complemented by satellite and lidar observations, were used to investigate the origin of areas of localized intensification of precipitation spotted in the vicinity of Helsinki-Vantaa airport. It was observed that existing precipitation is enhanced locally on spatial scales from a few kilometers to several tens of kilometers. The precipitation intensity in these localized areas was 6-14 times higher than the background large-scale precipitation rate. Surface observations and dual-polarization radar data indicate that snowflakes within the ice portion of the falling precipitation in the intensification regions are larger and more isotropic than in the surrounding precipitation. There appears to be an increase in the ice particle number concentration within the intensification region. The observed events were linked to arriving or departing air traffic. We advocate that the mechanism responsible for intensification is aircraft-produced ice particles boosting the aggregation growth of snowflakes. Plain Language Summary: By analyzing 11 years of dual-polarization weather radar observations in the Helsinki region, we have discovered that airplanes landing in or departing from the Helsinki-Vantaa airport could locally increase precipitation rate by as much as 14 times. The observed phenomenon is related to the hole-punch clouds, which are also forming with the help of airplanes. The reported observations allow us to have a better understanding of precipitation formation processes that take place in ice and mixed phase clouds. They show that falling ice crystals from upper clouds could seed lower clouds and therefore increase rain or snowfall intensity through the process called snowflake aggregation. During snowflake aggregation bigger faster falling particles are formed by ice particles colliding and sticking together.
  • Merkouriadi, Ioanna; Leppäranta, Matti; Järvinen, Onni (2017)
    The interannual variability of the air temperature, precipitation and snow conditions were examined in the Finnish Arctic region based on data from the period 1946-2012. The purpose of this work was to describe the climatology of the region and to examine long-term variations in the climatic parameters. This information is essential for both environmental and socioeconomic aspects of the Finnish Arctic region. The air temperature, precipitation and snow depth records from nine weather stations were analysed in order to study the evolution of the winter duration (sub-zero temperature days), precipitation, snow cover duration and snow depth. The climatological description was based on the most recent 30-year period record available (1982-2011). Since 1946, air temperature has increased significantly by 0.4 degrees C/decade. Significant precipitation trends reached up to 35 mm/decade. For the most part there were no significant trends in snow depth and snow cover duration.
  • Gregow, Hilppa; Ruosteenoja, Kimmo; Juga, Ilkka; Näsman, Sigbritt; Mäkelä, Miika; Laapas, Mikko; Jylhä, Kirsti (2011)
    Raportteja - Rapporter - Reports 2011:5
    Raportissa on arvioitu ilmastonmuutoksen vaikutusta Suomen maaperän talviaikaiseen jäätymiseen lämpösummien perusteella. Laskelmat kuvaavat roudan paksuutta nimenomaisesti lumettomilla alueilla, esimerkiksi teillä, joilta satanut lumi aurataan pois. Luonnossa lämpöä eristävän lumipeitteen alla routaa on ohuemmin kuin tällaisilla lumettomilla alueilla. Toisaalta luonnollisessa ympäristössä paikalliset erot korostuvat johtuen mm. maalajeista ja kasvillisuudesta. Roudan paksuudet laskettiin ensin perusjakson 1971–2000 ilmasto-oloissa talviaikaisten säähavaintotietoihin pohjautuvien lämpötilojen perusteella. Sen jälkeen laskelmat toistettiin kolmelle tulevalle ajanjaksolle (2010–2039, 2040–2069 ja 2070–2099) kohottamalla lämpötiloja ilmastonmuutosmallien ennustamalla tavalla. Laskelman pohjana käytettiin 19 ilmastomallin A1B-skenaarioajojen keskimäärin simuloimaa lämpötilan muutosta. Tulosten herkkyyden arvioimiseksi joitakin laskelmia tehtiin myös tätä selvästi heikompaa ja voimakkaampaa lämpenemisarviota käyttäen. A1B-skenaarion mukaisen lämpötilan nousun toteutuessa nykyisiä mallituloksia vastaavasti routakerros ohenee sadan vuoden aikana Pohjois-Suomessa 30–40 %, suuressa osassa maan keski- ja eteläosissa 50–70 %. Jo lähivuosikymmeninä roudan ennustetaan ohentuvan 10–30 %, saaristossa enemmän. Mikäli lämpeneminen toteutuisi voimakkaimman tarkastellun vaihtoehdon mukaisesti, roudan syvyys pienenisi tätäkin enemmän. Roudan paksuuden vuosienvälistä vaihtelua ja sen muuttumista tulevaisuudessa pyrittiin myös arvioimaan. Leutoina talvina routa ohenee enemmän kuin normaaleina tai ankarina pakkastalvina. Päivittäistä sään vaihtelua simuloineen säägeneraattorin tuottamassa aineistoissa esiintyi kuitenkin liian vähän hyvin alhaisia ja hyvin korkeita lämpötiloja. Siksi näitten lämpötilatietojen pohjalta laskettu roudan paksuuskin ilmeisesti vaihtelee liian vähän vuodesta toiseen. Kelirikkotilanteita voi esiintyä myös kesken routakauden, jos useamman päivän suojasää ja samanaikainen runsas vesisade pääsevät sulattamaan maata. Tällaiset routakauden aikana sattuvat säätilat näyttävätkin yleistyvän lähivuosikymmeninä. Vuosisadan loppua kohti ne sen sijaan maan eteläosissa jälleen vähenevät, koska routakausi lyhenee oleellisesti. Tulevia vuosikymmeniä koskevien ilmastonmuutosennusteiden ohella routaa ja kelirikon esiintymistä on periaatteessa mahdollista ennustaa myös lähiaikojen sääennusteita hyödyntäen. Pitkät, viikkojen tai kuukausien mittaiset sääennusteet eivät tosin ole ainakaan vielä erityisen luotettavia, mutta myös lyhyemmistä ennusteista voisi olla hyötyä mm. tienpitoa suunniteltaessa.
  • Makkonen, Ulla; Saarnio, Karri; Ruoho-Airola, Tuija; Hakola, Hannele (Ilmatieteen laitos, 2016)
    Raportteja - Rapporter - Reports 2016:2
    Tiivistelmä Itämeren pahimpana ongelmana pidetään typpi- ja fosforikuormituksen aiheuttamaa rehevöitymistä. Typpeä ja fosforia joutuu Itämereen paitsi valumana rantavaltioista myös merkittävissä määrin ilman kautta. Ilmaperäisen typpilaskeuman määrää ja sen kehitystä on selvitetty mittauksin ja mallinnuksen avulla 1980-luvulta lähtien, mutta ilmaperäistä fosforikuormaa Itämereen on mitattu vain sateen mukana laskeutuvan märkälaskeuman osalta muutamilla asemilla. Hiukkasiin sitoutuneesta kuivalaskeumasta ei mittaustietoa ole julkaistu lainkaan, eikä Itämeren ympärysvaltioilla ole käytettävissään menetelmää ilmaperäisen fosforikuorman hiukkasosuuden seuraamiseksi. Tässä työssä kehitettiin ja testattiin menetelmät ilmakehästä sadeveden mukana tulevan sekä ilmakehän hiukkasiin sitoutuneen fosfaatin sekä kokonaisfosforin määrittämiseksi. Menetelmäkehitys sisälsi näytteenkeruumenetelmät, näytteen esikäsittelymenetelmät sekä kemialliset analyysimenetelmät. Menetelmiä testattiin Utön saarella Saaristomeren ulkolaidalla vuosien 2013–2015 aikana. Utön saarella toimii Ilmatieteen laitoksen mittausasema, jonka mittaustulokset edustavat ilmanlaadun tausta-arvoja pohjoisella Itämerellä. Testattuina fosforin ja fosfaatin kuiva- ja märkälaskeuman näytteenkeruumenetelminä toimivat olemassa olevat ja laajasti käyttöönotetut EMEP-protokolliin perustuvat menetelmät. Näytteiden kokonaisfosforipitoisuuden määritysmenetelmään sovellettiin olemassa olevaa ISO-standardiin perustuvaa spektrometristä menetelmää. Vesiliukoisen fosfaatin pitoisuuden määrittämiseen hyödynnettiin käytössä olevaa ISO-standardiin perustuvaa ionikromatografista menetelmää, jota laajennettiin sisältämään fosfaatin määritys muiden epäorgaanisten ionien kanssa samassa analyysissä. Havaittiin, että sekä märkä- että kuivalaskeumanäytteiden sisältämät kokonaisfosfori- ja fosfaattipitoisuudet olivat erittäin alhaisia, usein pitoisuudet olivat lähellä analyysimenetelmien määritysrajoja tai niiden alle. Kuitenkin mittausjakson ajalta saatiin riittävä määrä määritystuloksia, joiden avulla voidaan laskea aiempaa luotettavampi arvio vuotuisesta ilmaperäisestä fosforikuormituksesta Itämereen. Työssä tutkittiin Utön saaren mittausasemalla suoritetun intensiivikampanjan aikana mahdollisuutta määrittää hiukkasissa olevan fosfaatin pitoisuutta jatkuvatoimisella ionikromatografilla. Menetelmän herkkyys osoittautui kuitenkin riittämättömäksi ilmakehän hiukkasten fosfaattipitoisuuden määrittämiseen. Käytetyt menetelmät on esitelty tässä raportissa siten, että menetelmät voidaan ottaa käyttöön muillakin mittausasemilla ja laboratorioissa sadeveden ja ilmakehän hiukkasten sisältämien fosfaatin ja kokonaisfosforin pitoisuuksien määrittämiseksi, ja siten ilmaperäisen fosforin kuormitusta voidaan arvioida luotettavammin ja laajemmin Itämeren alueella. Abstract Eutrophication caused by nitrogen and phosphorus load is generally thought as the most severe problem of the Baltic Sea. Nitrogen and phosphorus end up in the Baltic Sea not only by run-off from the coastal countries of the Baltic Sea but to an important extent also from the atmosphere. The amount of atmospheric nitrogen load and its development have been determined using measurements and models since the 1980’s. The atmospheric phosphorus load to the Baltic Sea has been measured earlier only from the wet deposition from the collected rain water samples from a few sites around the Baltic Sea; no published data exists about the particle bound dry deposition of phosphorus. The coastal countries of the Baltic Sea haven’t got any method in use to measure the particle bound phosphorus deposition. In this work, methods for determining the concentrations of phosphate and total phosphorus in atmospheric precipitation and particulate matter were developed and tested. The method development included the sampling, sample pre-treatment, and chemical analysis techniques. The methods were tested onsite on the Utö Island in the outskirts of the Archipelago Sea during the years 2013–2015. The monitoring station on the Utö Island is operated by the Finnish Meteorological Institute. The measurements on the station represent the background air quality of the northern Baltic Sea area. The existing and widely used sampling methods based on the EMEP protocols were tested for the sampling of dry and wet deposition of phosphorus and phosphate. A spectrometric method based on an ISO standard was applied for determination of the total phosphorus concentration of the samples. For the determination of dissolved phosphate, an ion chromatographic method based on an ISO standard was extended to include the analysis of phosphate with the main inorganic ions. It was discovered that the concentrations of total phosphorus and dissolved phosphate in the dry and wet deposition samples were very low; the concentrations were often close to the determination limits of the used analytical methods or even below those. Nevertheless, a sufficiency of samples were determined to be able to estimate the yearly atmospheric phosphorus load to the Baltic Sea more reliably than earlier. In addition, feasibility of measuring the concentration of particle-bound phosphate using a semi-continuous ion chromatograph was tested in the Utö Island during an intensive campaign. However, the sensitivity of the analyser was not sufficient to measure the low atmospheric concentrations of phosphate. The used methods are presented in this report so that they can be taken into use in other sampling sites and laboratories to determine the concentrations of phosphate and total phosphorus in the precipitation and in the atmospheric particulate matter. Thus, more reliable estimates of the atmospheric phosphorus load to the Baltic Sea could be calculated more widely.
  • Leikola, Matti (Suomen metsätieteellinen seura, 1971)
  • Kellomäki, Seppo; Pohjapelto, Pirkko (Suomen metsätieteellinen seura, 1976)
  • Salgado, Ana; DiLeo, Michelle; Saastamoinen, Marjo (2020)
    1. Understanding species' habitat preferences are crucial to predict organisms' responses to the current climate crisis. In many insects, maternal habitat selection for oviposition essentially determines offspring performance. Whether future changes in climatic conditions may generate mismatches between oviposition preference and offspring performance, when mothers continue to prefer microhabitats that might threaten offspring survival, is an open question. 2. To address this gap, we tested if oviposition preferences of the Glanville fritillary butterfly Melitaea cinxia females put offspring at risk when plants are under drought stress conditions. Mainly, we focus on identifying the microhabitat determinants for oviposition and the variation of conditions experienced by the sessile offspring, using field observations from 12 populations collected over 2015–2018. These data are combined with 10 years of larval nest and precipitation data to understand within-population patterns of habitat selection. We tested whether the preferred microhabitats maximized the extended larval performance (i.e. overwinter survival). 3. We found that females preferentially oviposited in microhabitats with higher host plant abundance and higher proportion of host plants with signs of drought stress. In most years, larval nests had higher survival in these drought-stressed microhabitats. However, in an extremely dry year, only two nests survived over the summer. 4. Our results highlight that a failure to shift habitat preference under extreme climate conditions may have drastic consequences for the survival of natural populations under changing climatic conditions.
  • Gregow, Erik (2018)
    Finnish Meteorological Institute Contributions 142
    Observations have been and are an important part of today's meteorological developments. Surface observations are very useful as they are, providing weather information for a point location. ough they do not give much information, if any, on what happens between the stations across a larger area. With models one can create an analysis of the meteorological situation, i.e. calculate and estimate what happens between these fixed observation points. Remote-sensing data, such as radar and satellite, are being processed and the output is given over a domain as an analysed product of their measurements. For example, radar gives a plot of where the rain is located, i.e. an analysis of the current precipitation. With a series of radar images, a human (subjectively) or a computer objectively) can process this information to estimate where the rain will move and be located within the next few minutes (even hours), i.e. a short forecast also called "nowcast". is applies to some extent also for other observations, such as satellite data (cloud propagation). But for most quantities (such as temperature, wind, etc) it is significantly harder to make such a nowcast, since these are influenced by many other factors and there is no linear development of them. Therefore, there are forecast models that solve physical and dynamic equations, so that one can estimate the future weather for the coming hours and days. A prerequisite for generating a forecast of high quality is to capture the initial weather conditions as best as possible. This is done using observations and they are introduced into the forecast model through different techniques, where the model creates its own analysis as the initial step. There remain problems since forecast models often are affected by physical disagreements, as the dynamic conditions are not in balance. This results in the model having a spin-up effect, where the meteorological quantities are not yet in balance with each other and the resulting weather conditions are not always reliable during the first hours. Hence, a lot of research is spent on how to reduce this spin-up effect and on the use of nowcast models, in order to deliver the best model results for the first few hours of the forecast period. In this dissertation, the research work has been to improve the meteorological analysis, algorithms and functionality, using the Local Analysis and Prediction System (LAPS) model. Different kinds of observations were used and their interdependencies have been studied, in order to combine and merge information from variousinstruments. Primarily focus has been to improve the estimation of precipitation accumulation and meteorological quantities that affect wind energy. The LAPS developments have been used for several end-users and nowcasting applications, and experimentally as initial conditions for forecast modelling. The studies have been concentrated on Finland and nearby sea areas, with the available datasets for this domain. By combining surface-station measurements, radar and lightning information, one can improve the precipitation-amount estimations. The use of lightning data further improves the estimates and gives the advantage of having additional data outside radar coverage, which can potentially be very useful for example over sea areas. In addition, the improved LAPS analyses (cloud-related quantities) and a newly developed model (LOWICE), calculating the electricity production during wintertime (taking into account the icing of wind turbine rotor blades which reduces efficiency), have shown good results.
  • Päivänen, Juhani (Suomen metsätieteellinen seura, 1974)
  • Moisseev, Dmitri; von Lerber, Annakaisa; Tiira, Jussi (2017)
    Ground-based observations of ice particle size distribution and ensemble mean density are used to quantify the effect of riming on snowfall. The rime mass fraction is derived from these measurements by following the approach that is used in a single ice-phase category microphysical scheme proposed for the use in numerical weather prediction models. One of the characteristics of the proposed scheme is that the prefactor of a power law relation that links mass and size of ice particles is determined by the rime mass fraction, while the exponent does not change. To derive the rime mass fraction, a mass-dimensional relation representative of unrimed snow is also determined. To check the validity of the proposed retrieval method, the derived rime mass fraction is converted to the effective liquid water path that is compared to microwave radiometer observations. Since dual-polarization radar observations are often used to detect riming, the impact of riming on dual-polarization radar variables is studied for differential reflectivity measurements. It is shown that the relation between rime mass fraction and differential reflectivity is ambiguous, other factors such as change in median volume diameter need also be considered. Given the current interest on sensitivity of precipitation to aerosol pollution, which could inhibit riming, the importance of riming for surface snow accumulation is investigated. It is found that riming is responsible for 5% to 40% of snowfall mass. The study is based on data collected at the University of Helsinki field station in Hyytiala during U.S. Department of Energy Biogenic Aerosols Effects on Clouds and Climate (BAECC) field campaign and the winter 2014/2015. In total 22 winter storms were analyzed, and detailed analysis of two events is presented to illustrate the study.
  • Mason, S. L.; Chiu, C. J.; Hogan, R. J.; Moisseev, D.; Kneifel, S. (2018)
    Retrievals of ice and snow are made from Ka- and W-band zenith-pointing Doppler radars at Hyytiala, Finland, during the snow experiment component of the Biogenic Aerosols: Effects on Clouds and Climate (2014) field campaign. In a novel optimal estimation retrieval, mean Doppler velocity is exploited to retrieve a density factor parameter, which modulates the mass, shape, terminal velocity, and backscatter cross sections of ice particles. In a case study including aggregate snow and graupel we find that snow rate and ensemble mean ice density can be retrieved to within 50% of in situ measurements at the surface using dual-frequency Doppler radar retrievals. While Doppler measurements are essential to the retrieval of particle density, the dual-frequency ratio provides a strong constraint on particle size. The retrieved density factor is strongly correlated with liquid water path, indicating that riming is the primary process by which the density factor is modulated. Using liquid water path as a proxy for riming, profiles classified as unrimed snow, rimed snow, and graupel exhibit distinct features characteristic of aggregation and riming processes, suggesting the potential to make estimates of process rates from these retrievals. We discuss the potential application of the technique to future satellite missions. Plain Language Summary Ground-based radar measurements of ice clouds and snow are used to estimate the size, number, and density of snowflakes. Doppler velocity measurements of particle fall speeds are used to estimate the mass and shape of the snow particles. The properties of snow estimated using radar compare well against measurements of particles at the surface and estimates of the amount of liquid water in the atmosphere; the presence of liquid water relates to the potential for riming, in which snowflakes increase in density and fall speed by collecting and freezing liquid droplets. More accurate estimates of snow density from ground-based and satellite radars help to improve global estimates of precipitation and snow accumulation and the representation of clouds and snow in weather and climate models.
  • 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.
  • Nissinen, Anne; Haapalainen, Minna; Ojanen, Hannu; Pirhonen, Minna; Jauhiainen, Lauri (2021)
    Carrot cultivation in Europe is suffering from infections with "Candidatus Liberibacter solanacearum" (CLso), a psyllid-transmitted bacterial pathogen. In this study, field experiments were carried out in Finland to separately measure the effects of psyllid feeding damage and CLso infection on the carrot root growth and to reveal the dynamics of the spreading of CLso within the field. Most of the experiments were carried out during the summers 2016 and 2017, and a follow-up sampling was performed in 2018. Carrot psyllid (Trioza apicalis) flight activity was monitored and carrots were sampled at 25 points within the field. Early in the season a clear spatial correlation was found between the sampling sites showing the psyllid feeding damage, that is, leaf-curling, up to the range of 40-60 m, indicating aggregation behaviour of the psyllids. No CLso infections were detected in the first sampling, which was performed before the psyllid flight peak in both years. Later, a positive correlation between the psyllid feeding damage and the CLso titre was observed. An increase in the CLso titre occurred approximately a month after the psyllid flight peak, and this increase correlated with the accumulating effective temperature sum. In 2016, both the psyllid feeding damage and CLso infection had a significant effect on the carrot root weight. The effect of CLso titre on root weight was nonlinear, that is, it intensified rapidly at the highest bacterial titres. During the colder summer of 2017 the CLso titres did not reach high enough levels in the plants to cause substantial visible symptoms and root growth reduction. Thus, it seems that in the Nordic conditions the effect of CLso infection on carrot yield is strongly dependent on the weather conditions during the growing season.