here fixed to 0.8 and the no diffuse radiation is considered. (2012) and are available on the following website: http://epic.awi.de/30060/. Transf., 111, 174–186. Data, 10, 1491–1501. Ho, high performance relies on the assumption of clean snow and, on the quality of the cross-calibration between the upwelling, and downwelling flux acquisitions, which is usually not an is-. Stronger illumination and smaller snow extinction coefficients may correspond to greater euphotic depths in snowpack. https://doi.org/10.1016/j.rse.2009.03.016, 2009. the visible range and closer to 1 in the blue–green range. Until now, however, these improvements and capabilities have not been merged into a unified code base. (a) Measurements of snow density; (b) measurements of snow type; and (c) simulations of snow optical radius from snow density and snow type. (12): When the sun is below the slope, we shall distinguish, two cases, first when the upward-looking sensor is shad-, owed but the neighbouring surface is still illuminated and. wavelength). Opt.. 46, 5529, https://doi.org/10.1364/ao.46.005529, 2007. The diffuse component is, more complex because it includes several contrib, slopes) that can be formulated with a wide range of complex-, which has an angular distribution that depends on the atmo-. measurements. With regard to D and E, the initial Qnet of E is nearly three times as much as that of D. However, the zeu of E is nearly equal to that of D. The snow optical properties account for these exceptional cases. band albedo (the percent of radiation reflected by the surface, vation principle to relate absorption and reflection, such that, common meteorological variable measured using two hori-, zontal radiation sensors, one looking upward and the other. Sect. should raise observer’s attention during data quality checks. The snow grain optical effective radius can be calculated from the snow specific surface area (SSA), as described in Section 2.4. A good correlation is observed for measured concentrations higher than 5 ng g⁻¹ (r²=0.81) despite a clear positive bias. © 2008-2021 ResearchGate GmbH. It provides closer results to empirical values than volume-scattering-based albedo simulations alone. Another possible explanation is that SSA was varying at the, end of the day as suggested in Sect. Strong initial illumination corresponds to a small residual percentage and vice versa. Augé analizza lucidamente il «nuovo umanesimo dei ciclisti», che annulla le differenze di classe, induce all’uguaglianza, riconduce l’esistenza nelle nostre città a tempi e ritmi più sostenibili, trasforma le vie urbane in spazi da ... (b) Sky solid angle (blue shade) used to compute V and neighbourhood solid angle (green). Situazione meteorologica Carmagnola, temperature, pioggia, vento, umidità . is infinite and the slope is infinite except in the top-hill case. Field campaigns in mid-May for 5 of the 6 years of interest provided spatially averaged snow depths and vertical profiles of snow density and specific surface area in the polygon of interest and at other spots in the valley. The grey curves are calculated with the small-slope approximation. Nonetheless, the angular dependence of snow albedo. 0.7–1.0, 1.0–1.2, 1.2–1.5, and 1.5–5.0 μm, respectively). Field data revealed that the heterogeneous spatial distribution of impurities on the snow surface led to differences close to 0.2 on the measured snow albedo within very short distances. Summing the, direct and the two diffuse contributions, the total incident ir, where we have distinguished the direct-hemispherical re-, narios are imaginable depending on the terrain topography, izontal surface and distinguish two cases for the surface type, (Fig. 1983, Warren and Clarke 1990, Tedesco 2015. In absolute terms, small-scale surface roughness can decrease the total albedo by up to about 0.1. The monitoring of snow-covered surfaces on Earth is largely facilitated by the wealth of satellite data available, with increasing spatial resolution and temporal coverage over the last few years. Mathe., 2, 164–168. the difference between the blue and the violet or, red curves) can be large (e.g. 3), meaning, that snow is considered to be a Lambertian surface. Dumont et al. The measured ratio, This equation is interesting per se to get the diffuse-to-total, Another useful derivation is when the diffuse-to-total ratio, is modelled using an atmospheric model, i.e. unattended albedo monitoring with such a parallel setting. https://doi.org/10.1175/jcli-d-19-0318.1, 2020. ror in cryospheric surface radiation measurements at high. to estimate near-surface snow SSA time series, The Cryosphere. Baker et al. If the snow depth is no greater than the euphotic depth, the surface albedo is greatly affected by the underlying surface. A greater, distortion is observed in the morning when the sun is fac-, ing the slope, while the spectrum taken just before the lo-, cal sunset is almost unaffected. 5, second, column). either weaker assumptions or that apply to single acquisitions, the first step is to establish the equations linking measured, albedo to intrinsic albedo accounting for the slope and illumi-, nation conditions. The neighbourhood (i.e. Remote Sens., 28, 963–969, Driemel, A., Augustine, J., Behrens, K., Colle, S., Cox, C., Cuevas-, felin, M., Hodges, G., Hyett, N., Ijima, O., Kallis, A., Knap, W. Mimouni, M., Ntsangwane, L., Ogihara, H., Olano, X., Olefs. We also work at improving the representation of snow phase functi, Abstract. Both multiple reflections and the effective angle effect have more impact with low SSA (2 kg−1). It uses the, diurnal cycle of reflected radiation instead of the albedo to, infer the slope angles, while the sensor tilt is retrieved using, The wide range of possible assumptions shows that many, methods can be valuable depending on the conditions. In the intermediate range, between the, blue and the red ranges, the variations in albedo with wave-, length are driven by the transition from diffuse-dominant to, mostly direct illumination rather than by the variations in the, ice absorption. The first case is, when the measurement is taken on the slope far from the hori-, zontal neighbourhood and far from the top of the slope (here-, inafter case mid-slope or M). Second, the upward and downward looking sensors receive reduced radiation from the sky and the surface respectively, and increased radiation from neighbouring terrain. The BSRN database is the World Radiation Monitoring Center (WRMC). The model is used to explore the albedo sensitivity to surface roughness with varying snow properties and illumination conditions. Miosotis), the Agence Na-, tionale de la Recherche (grant no. However, the presence of macroscopic roughness leads to a systematic decrease in albedo due to two effects: 1) photons are trapped in concavities (multiple reflection effect) and, 2) when the sun is low, the roughness sides facing the sun experience an overall decrease in the local incident angle relative to a smooth surface, promoting higher absorption, whilst the other sides has weak contributions because of the increased incident angle or because they are shadowed (called the effective angle effect here). Res.-Atmos., 123, 8599–8622. Figure 2(b) presents a boxplot for the euphotic depth grouped by month. Measured (plain) and simulated (dashed) albedo acquired on 23 March 2018. https://doi.org/10.1016/j.rse.2009.10.014, 2010. remote sensing?, J. Geophys. (a) Albedo spectra acquired at four selected hours during the day; (b) albedo as a function of time for three selected wavelengths. In the present paper, we point out a new method based on spectral irradiance profile (SIP) measurements which makes it possible to identify the radiative impact of LAPs on visible light extinction in homogeneous layers of the snowpack. Erect shrubs in the Arctic reduce surface albedo when branches protrude above the snow and modify snow properties, in particular specific surface area (SSA). 1983;Warren and Clarke 1990;Tedesco 2015). Res., 99, 18669–18684, mann, C., Picard, G., Arnaud, L., Favier, V. Korkin, S., Kipfstuhl, S., Freitag, J., Hoerhold, M., Zuh, A.. Sentinel-3 Ocean and Land Colour Instrument, Remote Sens.. 11, 19, https://doi.org/10.20944/preprints201906.0162.v1, 2019. sitivity to macroscopic surface roughness using a new ray trac-, ing model, The Cryosphere Discuss., https://doi.org/10.5194/tc-, of solar fluxes over mountain surfaces for applica-. Along with the corrected albedo, both methods provide es-, timates of the two slope angles, which was not possible with, the methods using a single acquisition. Furthermore, spectral dependence complicates the measurements, not to mention the problem of inserting the sensor without disturbing the snowpack (Perovich, 2007). Detailed soil properties are provided. If we can assume that sno, the unknowns, no simple analytical method is devisable, but, the system can be numerically solved with non-linear least, imizing the cost function in this study is performed using, the Python function scipy.optimize.leastsq implementing the, Another method is derived for situations where the snow, surface is known to be free of impurities. Figure 2(c) presents the scatterplot of the relevant surface net solar radiation (Qnet), and Figure 2(d) shows the corresponding boxplot. 2017;Kokhanovsky et al. In addition, SNICAR has been incorporated into the Community Land Model (CLM) version 4 (Oleson et al., 2010). As a corollary, simple small-slope approximation is probably sufficient for, Figure 6 shows a similar calculation for the Autosolexs, measurements taken on 23 March 2018, a day with contin-, uous clear-sky conditions. Ciò che conta è la bicicletta è un appassionante viaggio nella progettazione e nella costruzione della bici dei sogni. (2013) verified this parameterization scheme and found that it performed rather satisfactorily, both qualitatively and quantitatively. The ability of the modified algorithm to include on in radiative transfer models, because using spheres has proved inappropriate. The term "solid-state greenhouse" was suggested for the first of these interesting phenomena. RSRT is coupled to a surface scheme in order to estimate the complete energy budget from which the surface temperature is solved. It assumes a known analytical formula for, the shape of the spectrum, which applies when the type of, impurities is perfectly known (e.g. Prognoză meteo pe ore, condiţii meteo, precipitaţie, punct de rouă, umiditate, vânt de la Weather.com şi The Weather Channel Questa massima del Talmud si presta perfettamente a descrivere la vicenda miracolosa svoltasi dal 1942 al 1945, a Carignano, paese in provincia di Torino, che Gian Piero Bona rivela in questo avvincente romanzo autobiografico. Fur-, ther work should perform a more systematic comparison and, exploration of the sensitivity to input uncertainties of each, Spectral albedo measured with horizontal sensors is very sen-, sitive to the slope of the underlying surface in clear-sk, ditions, first because the illumination received by the slope. second when the neighbouring surface is also in the shadows. Res.-Atmos., 118, 779–786. the correction methods are expected to approach. However, existing albedo measurements over rugged terrain are limited and controversial and remain a major challenge. The theoretical developments and the measured spectra pre-, sented throughout this paper make it clear that the “apparent, albedo” of a slope is not an albedo sensu stricto and must not, be used to compute the energy absorbed by the surface with, parent albedo value is higher than 1, because the calculated, the apparent albedo is not a purely reflective property of the, surface; it also contains the factor converting the ener, well as other terms in the case of large slopes. Accounting for surface roughness improves the model observation agreement by a factor two at 700 nm and 1000 nm (errors of 0.03 and 0.04, respectively), compared to simulations considering a flat smooth surface. The albedo value is more constant in. However, linking measurements of LAP concentration in snow to their actual, Join ResearchGate to discover and stay up-to-date with the latest research from leading experts in, Access scientific knowledge from anywhere. Deep penetration of heat into the snowpack was discussed also by Liston and Winther (2005). data, https://doi.org/10.22008/promice/data/aws, 2019. This equation differs from Eq. Libois, Q., Picard, G., Arnaud, L., Dumont, M., Lafaysse, M., Morin, S., and Lefebvre, E.: Summertime evolution of sno. In the present, cient correction methods, and to this end analytical formula-, tions using simplifying assumptions are preferred over com-, plex models. This approach may improve our understanding of the differences in the albedo between deep and shallow snowpack in GCMs. In turn, any small uncertainty that affects the angular behaviour of, the sensor (e.g. More ad-, vanced calculations can be performed numerically using, multilayer plane-parallel models or Monte Carlo models ac-, counting for 3D cloud effects (Cornet et al., 2010). The diffuse component also includes, the illumination from surrounding mountains, which poten-, tially results from multiple reflections between the surround-, ings and the atmosphere or the surroundings and the con-, sidered point (Lenot et al., 2009). Change, 8, 964–971, https://doi.org/10.1038/s41558-018-, tilayer physically based snowpack model simulating direct and, indirect radiative impacts of light-absorbing impurities in snow, The Cryosphere, 11, 2633–2653, https://doi.org/10.5194/tc-11-. rection in mountainous areas (e.g. A good correlation is observed for measured concentrations higher than 5 ng g⁻¹ (r²=0.81) despite a clear positive bias. applicable to time series of albedo over dirty snow surfaces, makes a stronger assumption to untangle the effect of slope, and impurities. In addi-, tion to albedo, Autosolexs automatically records the diffuse, irradiance using a third light collector shaded by a small rod, following the course of the sun. Red points in (a) and (c) indicate that the solar radiation has already penetrated through to the bottom snow layer completely, and the euphotic depth is marked as its snow depth. https://doi.org/10.5194/tc-7-741-2013, 2013. With the recent advances in modelling LAP–snow interactions, our method could become an attractive alternative to estimate vertical profiles of LAP concentrations in snow. When a single albedo acquisition is available, the most, favourable case is when the slope angles (inclination and, angle) are precisely known. Ideally, the term “albedo” should not be used to refer to the. 21), where, The flat surface case (second panel in Fig. by any of the sensors, whereas the neighbourhood term de-, pends on this term. The solar irradiance absorbed by snow-covered surfaces (or, melt. This paper aims to quantify the impact of surface roughness on albedo and to assess the respective role of these two effects, with (1) observations over varying amounts of surface roughness and (2) simulations using the new rough surface ray-tracing (RSRT) model, based on a Monte Carlo method for photon transport calculation. regions. The correlation coefficient between zeu and Qnet reaches 0.874, which is significant at the 95% confidence level according to the two-tailed Student's t test. snow grain size is derived, was observed for a 2-month period in central The monthly median values of zeu in winter months (December, January, and February) are very close to each other (6.8, 8.8, and 10.5 cm, respectively), while these values are nearly same (24.4 and 24.2 cm) in spring months (March and April). In solar radiation observations, the transmission of the incident radiation can be simplified as follows (Brandt and Warren, To concisely reflect the snow optical properties of a whole snow layer, a mean extinction coefficient (.
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