Browsing by Subject "OPTICAL-PROPERTIES"

Sort by: Order: Results:

Now showing items 21-40 of 44
  • Lu, Peng; Cao, Xiaowei; Li, Guoyu; Huan, Wenfeng; Leppäranta, Matti; Arvola, Lauri; Huotari, Jussi; Li, Zhijun (2020)
    To improve the understanding of the seasonal evolution of the mass and heat budget of ice-covered lakes in the cold and arid climate zone, in-situ observations were collected during two winters (2016-2017 and 2017-2018) in Lake Wuliangsuhai, Inner Mongolia, China. The mean snow thickness was 5.2 and 1.6 cm in these winters, due to low winter precipitation. The mean ice thickness was 50.9 and 36.1 cm, and the ice growth rate was 3.6 and 2.1 mm day(-1) at the lower boundary of ice. Analyses of mass and heat balance data from two winters revealed that the surface heat budget was governed by solar radiation and terrestrial radiation. The net heat flux loss of the ice was 9-22 W m(-2), affected by the snow and ice thickness. Compared to boreal lakes, Lake Wuliangsuhai received more solar radiation and heat flux from the water. The ice temperature had a strong diurnal variation, which was produced by the diurnal cycles of solar radiation, and air and water temperatures. These results expand our knowledge of the evolution of mass and heat balance in temperate lakes of mid-latitude arid areas.
  • Hong, Juan; Xu, Hanbing; Tan, Haobo; Yin, Changqing; Hao, Liqing; Li, Fei; Cai, Mingfu; Deng, Xuejiao; Wang, Nan; Su, Hang; Cheng, Yafang; Wang, Lin; Petäjä, Tuukka; Kerminen, Veli-Matti (2018)
    Simultaneous measurements of aerosol hygroscopicity and particle-phase chemical composition were performed at a suburban site over the Pearl River Delta region in the late summer of 2016 using a self-assembled hygroscopic tandem differential mobility analyzer (HTDMA) and an Aerodyne quadruple aerosol chemical speciation monitor (ACSM), respectively. The hygroscopic growth factor (HGF) of the Aitken mode (30 nm, 60 nm) and accumulation mode (100 nm, 145 nm) particles were obtained under 90% relative humidity (RH). An external mixture was observed for particles of every size during this study, with a dominant mode of more-hygroscopic (MH) particles, as aged aerosols dominated due to the anthropogenic influence. The HGF of lesshygroscopic (LH) mode particles increased, while their number fractions decreased during the daytime due to a reduced degree of external mixing that probably resulted from the condensation of gaseous species. These LH mode particles in the early morning or late afternoon could be possibly dominated by carbonaceous material emitted from local automobile exhaust during rush hours. During polluted days with air masses flowing mainly from the coastal areas, the chemical composition of aerosols had a clear diurnal variation and a strong correlation with the mean HGF. Closure analysis was carried out between the HTDMA-measured HGF and the ACSM-derived hygroscopicity using various approximations for the hygroscopic growth factor of organic compounds (HGF(org)). Considering the assumptions regarding the differences in the mass fraction of each component between PM1 and 145 nm particles, the hygroscopicity-composition closure was achieved using an HGF(org) of 1.26 for the organic material in the 145 nm particles and a simple linear relationship between the HGForg and the oxidation level inferred from the O : C ratio of the organic material was suggested. Compared with the results from other environments, HGF(org) obtained from our measurements appeared to be less sensitive to the variation of its oxidation level, which is, however, similar to the observations in the urban atmosphere of other megacities in China. This finding suggests that the anthropogenic precursors or the photooxidation mechanisms might differ significantly between the suburban and urban atmosphere in China and those in other background environments. This may lead to different characteristics of the oxidation products in secondary organic aerosols (SOA) and therefore to a different relationship between the HGF(org) and its O : C ratio.
  • Hussein, Tareq; Boor, Brandon E.; dos Santos, Vanessa N.; Kangasluoma, Juha; Petäjä, Tuukka; Lihavainen, Heikki (2017)
    Air pollution research and reports have been limited in the Middle East, especially in Jordan with respect to aerosol particle number concentrations. In this study, we utilized a simple "mobile setup" to measure, for the first time, the spatial variation of aerosol concentrations in Eastern Mediterranean. The mobile setup consisted of portable aerosol instruments to measure particle number concentrations (cut off sizes 0.01, 0.02, 0.3, 0.5, 1, 2.5, 5, and 10 mu m), particle mass concentrations (PM1, PM2.5, and PM10), and black carbon concentration all situated on the back seat of a sedan car. The car was driven with open windows to ensure sufficient cabin air ventilation for reliable outdoor aerosol sampling. Although the measurement campaign was two days long, but it provided preliminary information about aerosols concentrations over a large spatial scale that covered more than three quarters of Jordan. We should keep in mind that the presented concentrations reflect on road conditions. The submicron particle concentrations were the highest in the urban locations (e.g., Amman and Zarqa) and inside cities with heavy duty vehicles activities (e.g., Azraq). The highest micron particle concentrations were observed in the southern part of the country and in places close to the desert area (e.g., Wadi Rum and Wadi Araba). The average submicron concentration was 4.9 x 10(3)-120 x 10(3) cm-3 (5.7-86.7 mu g m(-3)) whereas the average micron particle concentration was 1-11 cm(-3) (8-150 mu g m(-3), assume rho(p) = 1 g cm(-3)). The main road passing through Jafr in the eastern part of Jordan exhibited submicron concentration as low as 800 cm(-3). The PM10 concentration consisted of about 40-75% as PM1. The black carbon (BC) concentration variation was in good agreement with the PM1 as well as the submicron particle number concentration.
  • Coen, Martine Collaud; Andrews, Elisabeth; Alastuey, Andres; Arsov, Todor Petkov; Backman, John; Brem, Benjamin T.; Bukowiecki, Nicolas; Couret, Cedric; Eleftheriadis, Konstantinos; Flentje, Harald; Fiebig, Markus; Gysel-Beer, Martin; Hand, Jenny L.; Hoffer, Andras; Hooda, Rakesh; Hueglin, Christoph; Joubert, Warren; Keywood, Melita; Kim, Jeong Eun; Kim, Sang-Woo; Labuschagne, Casper; Lin, Neng-Huei; Lin, Yong; Myhre, Cathrine Lund; Luoma, Krista; Lyamani, Hassan; Marinoni, Angela; Mayol-Bracero, Olga L.; Mihalopoulos, Nikos; Pandolfi, Marco; Prats, Natalia; Prenni, Anthony J.; Putaud, Jean-Philippe; Ries, Ludwig; Reisen, Fabienne; Sellegri, Karine; Sharma, Sangeeta; Sheridan, Patrick; Sherman, James Patrick; Sun, Junying; Titos, Gloria; Torres, Elvis; Tuch, Thomas; Weller, Rolf; Wiedensohler, Alfred; Zieger, Paul; Laj, Paolo (2020)
    In order to assess the evolution of aerosol parameters affecting climate change, a long-term trend analysis of aerosol optical properties was performed on time series from 52 stations situated across five continents. The time series of measured scattering, backscattering and absorption coefficients as well as the derived single scattering albedo, backscattering fraction, scattering and absorption Angstrom exponents covered at least 10 years and up to 40 years for some stations. The non-parametric seasonal Mann-Kendall (MK) statistical test associated with several pre-whitening methods and with Sen's slope was used as the main trend analysis method. Comparisons with general least mean square associated with autoregressive bootstrap (GLS/ARB) and with standard least mean square analysis (LMS) enabled confirmation of the detected MK statistically significant trends and the assessment of advantages and limitations of each method. Currently, scattering and backscattering coefficient trends are mostly decreasing in Europe and North America and are not statistically significant in Asia, while polar stations exhibit a mix of increasing and decreasing trends. A few increasing trends are also found at some stations in North America and Australia. Absorption coefficient time series also exhibit primarily decreasing trends. For single scattering albedo, 52 % of the sites exhibit statistically significant positive trends, mostly in Asia, eastern/northern Europe and the Arctic, 22 % of sites exhibit statistically significant negative trends, mostly in central Europe and central North America, while the remaining 26 % of sites have trends which are not statistically significant. In addition to evaluating trends for the overall time series, the evolution of the trends in sequential 10-year segments was also analyzed. For scattering and backscattering, statistically significant increasing 10-year trends are primarily found for earlier periods (10-year trends ending in 2010-2015) for polar stations and Mauna Loa. For most of the stations, the present-day statistically significant decreasing 10-year trends of the single scattering albedo were preceded by not statistically significant and statistically significant increasing 10-year trends. The effect of air pollution abatement policies in continental North America is very obvious in the 10-year trends of the scattering coefficient - there is a shift to statistically significant negative trends in 2009-2012 for all stations in the eastern and central USA. This long-term trend analysis of aerosol radiative properties with a broad spatial coverage provides insight into potential aerosol effects on climate changes.
  • Proestakis, Emmanouil; Amiridis, Vassilis; Marinou, Eleni; Georgoulias, Aristeidis K.; Solomos, Stavros; Kazadzis, Stelios; Chimot, Julien; Che, Huizheng; Alexandri, Georgia; Binietoglou, Ioannis; Daskalopoulou, Vasiliki; Kourtidis, Konstantinos A.; de Leeuw, Gerrit; Ronald, J. van der A. (2018)
    We present a 3-D climatology of the desert dust distribution over South and East Asia derived using CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation) data. To distinguish desert dust from total aerosol load we apply a methodology developed in the framework of EARLINET (European Aerosol Research Lidar Network). The method involves the use of the particle linear depolarization ratio and updated lidar ratio values suitable for Asian dust, applied to multiyear CALIPSO observations (January 2007-December 2015). The resulting dust product provides information on the horizontal and vertical distribution of dust aerosols over South and East Asia along with the seasonal transition of dust transport pathways. Persistent high D_AOD (dust aerosol optical depth) values at 532 nm, of the order of 0.6, are present over the arid and semi-arid desert regions. Dust aerosol transport (range, height and intensity) is subject to high seasonality, with the highest values observed during spring for northern China (Taklimakan and Gobi deserts) and during summer over the Indian subcontinent (Thar Desert). Additionally, we decompose the CALIPSO AOD (aerosol optical depth) into dust and non-dust aerosol components to reveal the non-dust AOD over the highly industrialized and densely populated regions of South and East Asia, where the non-dust aerosols yield AOD values of the order of 0.5. Furthermore, the CALIPSO-based short-term AOD and D_AOD time series and trends between January 2007 and December 2015 are calculated over South and East Asia and over selected subregions. Positive trends are observed over northwest and east China and the Indian subcontinent, whereas over southeast China trends are mostly negative. The calculated AOD trends agree well with the trends derived from Aqua MODIS (Moderate Resolution Imaging Spectroradiometer), although significant differences are observed over specific regions.
  • Asmala, Eero; Haraguchi, Lumi; Jakobsen, Hans H.; Massicotte, Philippe; Carstensen, Jacob (2018)
    Incubation experiments were performed to examine the processing of fresh autochthonous dissolved organic matter (DOM) produced by coastal plankton communities in spring and autumn. The major driver of observed DOM dynamics was the seasonally variable inorganic nutrient status and characteristics of the initial bulk DOM, whereas the characteristics of the phytoplankton community seemed to have a minor role. Net accumulation of dissolved organic carbon (DOC) during the 18-days experiments was 3.4 and 9.2 A mu mol l(-1) d(-1) in P-limited spring and N-limited autumn, respectively. Bacterial bioassays revealed that the phytoplankton-derived DOC had surprisingly low proportions of biologically labile DOC, 12.6% (spring) and 17.5% (autumn). The optical characteristics of the DOM changed throughout the experiments, demonstrating continuous heterotrophic processing of the DOM pool. However, these temporal changes in optical characteristics of the DOM pool were not the same between seasons, indicating seasonally variable environmental drivers. Nitrogen and phosphorus availability is likely the main driver of these seasonal differences, affecting both phytoplankton extracellular release of DOM and its heterotrophic degradation by bacteria. These findings underline the complexity of the DOM production and consumption by the natural planktonic community, and show the importance of the prevailing environmental conditions regulating the DOM pathways.
  • Lu, Peng; Cheng, Bin; Leppäranta, Matti; Li, Zhijun (2018)
    Summary The partitioning of solar radiation in the Arctic sea ice during the melt season is investigated using a radiative transfer model containing three layers of melt pond, underlying sea ice, and ocean beneath ice. The wavelength distribution of the spectral solar irradiance clearly narrowed with increasing depth into ice, from 350–900 nm at the pond surface to 400–600 nm in the ocean beneath. In contrast, the net spectral irradiance is quite uniform. The absorbed solar energy is sensitive to both pond depth (Hp) and the underlying ice thickness (Hi). The solar energy absorbed by the melt pond (Ψp) is proportional only to Hp. However, the solar energy absorbed by the underlying ice (Ψi) is more complicated due to the counteracting effects arising from the pond and ice to the energy absorption. In September, Ψp decreased by 10% from its August value, which is attributed to more components in the shortwave band (<530 nm) of the incident solar radiation in September relative to August. The absorption coefficient of the sea ice only enhances the absorbed energy in ice, while an increase in the ice scattering coefficient only enhances the absorbed energy in the melt pond, although the resulted changes in Ψp and Ψi are smaller than that in the albedo and transmittance. The energy absorption rate with depth depends strongly on the incident irradiance and ice scattering, but only weakly on pond depth. Our results are comparable to previous field measurements and numerical simulations. We conclude that the incident solar energy was largely absorbed by the melt pond rather than by the underlying sea ice.
  • Arnaud, M.; Atrio-Barandela, F.; Aumont, J.; Baccigalupi, C.; Banday, A. J.; Barreiro, R. B.; Battaner, E.; Benabed, K.; Benoit-Levy, A.; Bernard, J. T.; Bersanelli, M.; Bielewicz, P.; Bonaldi, A.; Bond, J. R.; Borril, J.; Bouchet, E. R.; Bueini, C. S.; Burigana, C.; Cardoso, J. -F; Casassus, S.; Catalano, A.; Cerrigone, L.; Chamballu, A.; Chiang, H. C.; Colombi, S.; Colombo, L. P. L.; Couchot, F.; Crill, B. P.; Curto, A.; Cuttaia, E.; Davies, R. D.; Davis, R. J.; de Bernardis, P.; de Rosa, A.; de Zotti, G.; Delabrouille, J.; Dickinson, C.; Diego, J. M.; Donzelli, S.; Dore, O.; Dupac, X.; Ensslin, T. A.; Eriksen, H. K.; Finelli, E.; Juvela, M.; Keihanen, E.; Keskitalo, R.; Kurki-Suonio, H.; Suur-Uski, A. -S.; Valiviita, J. (2015)
  • Herranen, Joonas; Lazarian, A.; Hoang, Thiem (2019)
    The radiative torque (RAT) mechanism is the most promising way of explaining observed polarization arising from aligned grains. We explore the efficiency of the grain alignment by an anisotropic radiation flow for an extensive ensemble of grain shapes, grain sizes (a), and wavelength (lambda). We calculate the distribution of the ratios of the amplitudes of the two major components of the RATs, which is an essential parameter that is used in the theory of RAT alignment in Lazarian & Hoang. While this distribution is different for the different classes of grain shapes that we considered, the most probable values of the parameter are centered in the range of q(max) similar to 0.5-1.5. The functional form from the calculated RATs is in good agreement with the analytical model. We find that the RAT efficiency scales as (lambda/a)(-2.6) for lambda greater than or similar to 1.8a, which has a slightly shallower slope than previously found in LH07. This increases the power of predictions obtained with the RAT theory. We also confirm that superparamagnetic inclusions are necessary for achieving high degrees of alignment, and constrain the parameter space describing the requirements for achieving these alignment degrees.
  • Vakkari, Ville; Kerminen, Veli-Matti; Beukes, Johan Paul; Tiitta, Petri; van Zyl, Pieter G.; Josipovic, Miroslav; Venter, Andrew D.; Jaars, Kerneels; Worsnop, Douglas R.; Kulmala, Markku; Laakso, Lauri (2014)
  • Chen, Xuemeng; Paatero, Jussi; Kerminen, Veli-Matti; Riuttanen, Laura; Hatakka, Juha; Hiltunen, Veijo; Paasonen, Pauli; Hirsikko, Anne; Franchin, Alessandro; Manninen, Hanna E.; Petäjä, Tuukka; Viisanen, Yrjo; Kulmala, Markku (2016)
    Radon-222 (Rn-222) has traditionally been used as an atmospheric tracer for studying air masses and planetary boundary-layer evolution. However, there are various factors that influence its atmospheric concentration. Therefore, we investigated the variability of the atmospheric radon concentration in response to the vertical air mixing and spatial transport in a boreal forest environment in northern Europe. Long-term Rn-222 data collected at the SMEAR II station in southern Finland during 2000-2006 were analysed along with meteorological data, mixing layer height retrievals and air-mass back trajectory information. The daily mean atmospheric radon concentration followed a log-normal distribution within the range <0.1-11 Bq m(-3), with the geometric mean of 2.5 Bq m(-3) and a geometric standard deviation of 1.7 Bq m(3). In spring, summer, autumn and winter, the daily mean concentrations were 1.7, 2.7, 2.8 and 2.7 Bq m(-3), respectively. The low, spring radon concentration was especially attributed to the joint effect of enhanced vertical mixing due to the increasing solar irradiance and inhibited local emissions due to snow thawing. The lowest atmospheric radon concentration was observed with northwesterly winds and high radon concentrations with southeasterly winds, which were associated with the marine and continental origins of air masses, respectively. The atmospheric radon concentration was in general inversely proportional to the mixing layer height. However, the ambient temperature and small-scale turbulent mixing were observed to disturb this relationship. The evolution of turbulence within the mixing layer was expected to be a key explanation for the delay in the response of the atmospheric radon concentration to the changes in the mixing layer thickness. Radon is a valuable naturally-occurring tracer for studying boundary layer mixing processes and transport patterns, especially when the mixing layer is fully developed. However, complementing information, provided by understanding the variability of the atmospheric radon concentration, is of high necessity to be taken into consideration for realistically interpreting the evolution of air masses or planetary boundary layer.
  • Khriachtchev, Leonid; Ossicini, Stefano; Iacona, Fabio; Gourbilleau, Fabrice (2012)
  • Kukli, Kaupo; Kemell, Marianna; Heikkilä, Mikko J.; Castan, Helena; Duenas, Salvador; Mizohata, Kenichiro; Ritala, Mikko; Leskelä, Markku (2020)
    Amorphous SiO2-Nb2O5 nanolaminates and mixture films were grown by atomic layer deposition. The films were grown at 300 degrees C from Nb(OC2H5)(5), Si-2(NHC2H5)(6), and O-3 to thicknesses ranging from 13 to 130 nm. The niobium to silicon atomic ratio was varied in the range of 0.11-7.20. After optimizing the composition, resistive switching properties could be observed in the form of characteristic current-voltage behavior. Switching parameters in the conventional regime were well defined only in a SiO2:Nb2O5 mixture at certain, optimized, composition with Nb:Si atomic ratio of 0.13, whereas low-reading voltage measurements allowed recording memory effects in a wider composition range.
  • Cao, Xiaowei; Lu, Peng; Leppäranta, Matti; Arvola, Lauri; Huotari, Jussi; Shi, Xiaohong; Li, Guoyu; Li, Zhijun (2021)
    Spectral albedo and light transmittance through snow, ice, and water were measured in Lake Wuliangsuhai (40 degrees 36 '-41 degrees 30 ' N, 108 degrees 43 '-108 degrees 70 ' E), Inner Mongolia, China, during winter 2016. Data on the weather, structure of lake ice, and geochemistry of water were also collected during the 60-day field program. The study lake is shallow (mean depth 1.0-1.5 m) with a large wetland area. Compared with polar lakes, solar elevation is higher, snow accumulation is much lower, and the ice has more sediment. The ice was all congelation ice with a mean thickness of 36.6 cm, corresponding to a mean air temperature of -9.6 degrees C. The mean daily broadband albedo and photosynthetically active radiation (PAR) band transmittance were 0.54 and 0.08 (bare ice), 0.74 and 0.04 (new snow), and 0.30 and 0.12 (melting period), respectively. The level of light allowed photosynthesis to occur to the bottom of the lake. The ice acted as a grey filter for the sunlight with a mean attenuation coefficient of 2.1 m(-1). These results expand our knowledge of the evolution of light transfer through ice and snow cover and its role in the ecology of lakes in temperate and arid areas.
  • Moschos, Vaios; Kumar, Nivedita K.; Dällenbach, Kaspar; Baltensperger, Urs; Prevot, Andre S. H.; El Haddad, Imad (2018)
    The impact of brown carbon (BrC) on climate has been widely acknowledged but remains uncertain, because either its contribution to absorption is being ignored in most climate models or the associated mixed emission sources and atmospheric lifetime are not accounted for. In this work, we propose positive matrix factorization as a framework to apportion the contributions of individual primary and secondary organic aerosol (OA) source components of BrC absorption, by combining long-term aerosol mass spectrometry (AMS) data with concurrent ultraviolet-visible (UV-vis) spectroscopy measurements. The former feature time-depend ent factor contributions to OA mass, and the latter consist of wavelength-dependent absorption coefficients. Using this approach for a full-year case study, we estimate for the first time the mass absorption efficiency (MAE) of major light-absorbing water soluble OA components in the atmosphere. We show that secondary biogenic OA contributes negligibly to absorption despite dominating the mass concentration in the summer. In contrast, primary and secondary wood burning emissions are highly absorbing up to 500 nm. The approach allowed us to constrain their MAE within a confined range consistent with previous laboratory work, which can be used in climate models to estimate the impact of BrC from these emissions on the overall absorption.
  • Markiet, Vincent; Hernandez-Clemente, Rocio; Mõttus, Matti (2017)
    The photochemical reflectance index (PRI) is a proxy for light use efficiency (LUE), and is used in remote sensing to measure plant stress and photosynthetic downregulation in plant canopies. It is known to depend on local light conditions within a canopy indicating non-photosynthetic quenching of incident radiation. Additionally, when measured from a distance, canopy PRI depends on shadow fraction-the fraction of shaded foliage in the instantaneous field of view of the sensor-due to observation geometry. Our aim is to quantify the extent to which sunlit fraction alone can describe variations in PRI so that it would be possible to correct for its variation and identify other possible factors affecting the PRI-sunlit fraction relationship. We used a high spatial and spectral resolution Aisa Eagle airborne imaging spectrometer above a boreal Scots pine site in Finland (Hyytiala forest research station, 61 degrees 50'N, 24 degrees 17'E), with the sensor looking in nadir and tilted (off-nadir) directions. The spectral resolution of the data was 4.6 nm, and the spatial resolution was 0.6 m. We compared the PRI for three different scatter angles (beta = 19 degrees, 55 degrees and 76 degrees defined as the angle between sensor and solar directions) at the forest stand level, and observed a small (0.006) but statistically significant (p <0.01) difference in stand PRI. We found that stand mean PRI was not a direct function of sunlit fraction. However, for each scatter angle separately, we found a clear non-linear relationship between PRI and sunlit fraction. The relationship was systematic and had a similar shape for all of the scatter angles. As the PRI-sunlit fraction curves for the different scatter angles were shifted with respect to each other, no universal curve could be found causing the observed independence of canopy PRI from the average sunlit fraction of each view direction. We found the shifts of the curves to be related to a leaf structural effect on canopy scattering: the ratio of needle spectral reflectance to transmittance. We demonstrate that modeling PRI-sunlit fraction relationships using high spatial resolution imaging spectroscopy data is suitable and needed in order to quantify PRI variations over forest canopies.
  • Lim, Saehee; Lee, Meehye; Kim, Sang-Woo; Laj, Paolo (2018)
    Black carbon (BC) and brown carbon (BrC) aerosols that are released from the combustion of fossil fuels and biomass are of great concern because of their light-absorbing ability and great abundance associated with various anthropogenic sources, particularly in East Asia. However, the optical properties of ambient aerosols are dependent on the mixing state and the chemical composition of absorbing and non-absorbing aerosols. Here we examined how, in East Asian outflows, the parameters of the aerosol optical properties can be altered seasonally in conjunction with the mixing state and the chemical composition of aerosols, using 3-year aerosol measurements. Our findings highlight the important role played by sulfate in East Asia during the warm season in both enhancing single scattering albedo (SSA) and altering the absorption properties of aerosols-enhancing mass absorption cross section of BC (MAC(BC)) and reducing MAC of BrC (MAC(BrC),(370)). Therefore we suggest that in global radiative forcing models, particular attention should be paid to the consideration of the accurate treatment of the SO2 emission changes in the coming years in this region that will result from China's air quality policy.
  • Lu, Peng; Leppäranta, Matti; Cheng, Bin; Li, Zhijun; Istomina, Larysa; Heygster, Georg (2018)
    Pond color, which creates the visual appearance of melt ponds on Arctic sea ice in summer, is quantitatively investigated using a two-stream radiative transfer model for ponded sea ice. The upwelling irradiance from the pond surface is determined and then its spectrum is transformed into RGB (red, green, blue) color space using a colorimetric method. The dependence of pond color on various factors such as water and ice properties and incident solar radiation is investigated. The results reveal that increasing underlying ice thickness H-i enhances both the green and blue intensities of pond color, whereas the red intensity is mostly sensitive to H-i for thin ice (H-i <1.5 m) and to pond depth H-p for thick ice (H-i > 1.5 m), similar to the behavior of meltpond albedo. The distribution of the incident solar spectrum F-0 with wavelength affects the pond color rather than its intensity. The pond color changes from dark blue to brighter blue with increasing scattering in ice, and the influence of absorption in ice on pond color is limited. The pond color reproduced by the model agrees with field observations for Arctic sea ice in summer, which supports the validity of this study. More importantly, the pond color has been confirmed to contain information about meltwater and underlying ice, and therefore it can be used as an index to retrieve H-i and H-p. Retrievals of H-i for thin ice (H-i <1 m) agree better with field measurements than retrievals for thick ice, but those of H-p are not good. The analysis of pond color is a new potential method to obtain thin ice thickness in summer, although more validation data and improvements to the radiative transfer model will be needed in future.
  • Song, Chengfang; Shan, Shengdao; Yang, Chao; Zhang, Cheng; Zhou, Xiaoqing; Ma, Qi; Yrjälä, Kim; Zheng, Huabao; Cao, Yucheng (2020)
    Dissolved organic matter (DOM) has an important effect on soil fertility, activity of microorganisms and transport of contaminants. In this study, DOM released by the hydrochar and biochar prepared under various conditions from pig manure, was assessed using a combination of UV–Visible spectroscopy, fluorescence excitation-emission (EEM) spectrophotometry and 1H-nuclear magnetic resonance (1H NMR). The dissolved organic carbon (DOC) extracted from the hydrochar and biochar ranged from 3.34–11.96% and 0.38–0.48%, respectively, and the highest DOM was released by HCK0.5 (180 °C and 0.5% KOH). The aliphatic compounds were most common in DOM which mainly included three humic acid-like and one protein-like substance. The hydrochar-DOM had a larger molecular weight and lower aromaticity than biochar-DOM, but the effect of temperature on the DOM characteristics of hydrochar and biochar was opposite. The acidic treatment increased the content of functional groups containing oxygen and nitrogen in hydrochar-DOM, and alkaline treatment increased the content of aliphatic compounds. The results obtained are beneficial to select carbonation process and guide the rational application of hydrochar and biochar from pig manure in soil remediation field.
  • Rontu, Laura; Gleeson, Emily; Räisänen, Petri; Nielsen, Kristian Pagh; Savijärvi, Hannu; Sass, Bent Hansen (2017)
    This paper provides an overview of the HLRADIA shortwave (SW) and longwave (LW) broadband radiation schemes used in the HIRLAM numerical weather prediction (NWP) model and available in the HARMONIE-AROME mesoscale NWP model. The advantage of broadband, over spectral, schemes is that they can be called more frequently within the model, without compromising on computational efficiency. In mesoscale models fast interactions between clouds and radiation and the surface and radiation can be of greater importance than accounting for the spectral details of clear-sky radiation; thus calling the routines more frequently can be of greater benefit than the deterioration due to loss of spectral details. Fast but physically based radiation parametrizations are expected to be valuable for high-resolution ensemble forecasting, because as well as the speed of their execution, they may provide realistic physical perturbations. Results from single-column diagnostic experiments based on CIRC benchmark cases and an evaluation of 10 years of radiation output from the FMI operational archive of HIRLAM forecasts indicate that HLRADIA performs sufficiently well with respect to the clear-sky downwelling SW and longwave LWfluxes at the surface. In general, HLRADIA tends to overestimate surface fluxes, with the exception of LW fluxes under cold and dry conditions. The most obvious overestimation of the surface SW flux was seen in the cloudy cases in the 10-year comparison; this bias may be related to using a cloud inhomogeneity correction, which was too large. According to the CIRC comparisons, the outgoing LW and SW fluxes at the top of atmosphere are mostly overestimated by HLRADIA and the net LW flux is underestimated above clouds. The absorption of SW radiation by the atmosphere seems to be underestimated and LW absorption seems to be overestimated. Despite these issues, the overall results are satisfying and work on the improvement of HLRADIA for the use in HARMONIE-AROME NWP system is ongoing. In a HARMONIE-AROME 3-D forecast experiment we have shown that the frequency of the call for the radiation parametrization and choice of the parametrization scheme makes a difference to the surface radiation fluxes and changes the spatial distribution of the vertically integrated cloud cover and precipitation.