Effects of solar elevation and cloudiness on snow albedo at the South Pole

Carroll, John J.; Fitch, Bruce W.

doi:10.1029/jc086ic06p05271

Cited by 95 publications

(78 citation statements)

References 16 publications

(13 reference statements)

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“…Several observational and modeling studies have found that sastrugi can cause a slight decrease in the albedo compared to flat snow (Warren et al, 1998;Carroll and Fitch, 1981;Zhuravleva and Kokhanovsky, 2011). This is due to the effective decrease in the solar zenith angle compared to the flat snow.…”

Section: Sastrugi and Brdf Of Snowmentioning

confidence: 99%

Accounting for the effects of sastrugi in the CERES clear-sky Antarctic shortwave angular distribution models

Corbett

2015

Atmos. Meas. Tech.

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Abstract. The Cloud and the Earth's Radiant Energy System (CERES) instruments on NASA's Terra, Aqua and Soumi NPP satellites are used to provide a long-term measurement of Earth's energy budget. To accomplish this, the radiances measured by the instruments must be inverted to fluxes by the use of a scene-type-dependent angular distribution model (ADM). For permanent snow scenes over Antarctica, shortwave (SW) ADMs are created by compositing radiance measurements over the full viewing zenith and azimuth range. However, the presence of small-scale wind blown roughness features called sastrugi cause the BRDF (bidirectional reflectance distribution function) of the snow to vary significantly based upon the solar azimuth angle and location. This can result in monthly regional biases between −12 and 7.5 Wm −2 in the inverted TOA (top-of-atmosphere) SW flux. The bias is assessed by comparing the CERES shortwave fluxes derived from nadir observations with those from all viewing zenith angles, as the sastrugi affect fluxes inverted from the oblique viewing angles more than for the nadir viewing angles. In this paper we further describe the clearsky Antarctic ADMs from Su et al. (2015). These ADMs account for the sastrugi effect by using measurements from the Multi-Angle Imaging Spectro-Radiometer (MISR) instrument to derive statistical relationships between radiance from different viewing angles. We show here that these ADMs reduce the bias and artifacts in the CERES SW flux caused by sastrugi, both locally and Antarctic-wide. The regional monthly biases from sastrugi are reduced to between −5 and 7 Wm −2 , and the monthly-mean biases over Antarctica are reduced by up to 0.64 Wm −2 , a decrease of 74 %. These improved ADMs are used as part of the Edition 4 CERES SSF (Single Scanner Footprint) data.

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Section: Sastrugi and Brdf Of Snowmentioning

confidence: 99%

Accounting for the effects of sastrugi in the CERES clear-sky Antarctic shortwave angular distribution models

Corbett

2015

Atmos. Meas. Tech.

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“…In contrast, there is no diurnal variation of albedo on cloudy days that are dominated by diffuse solar radiation, and it is thus reasonable to approximate albedo by a daily average value assuming no metamorphic changes of the snow surface microstructure during the day (Pirazzini, 2004). Albedo is also known to increase with cloud cover due to spectral variations (Brock, 2004;Carroll and Fitch, 1981;Jonsell et al, 2003;Cutler and Munro, 1996;Oerlemans and Knap, 1998). As has been noted by Warren and Wiscombe (1980) and Wiscombe and Warren (1980), the responses of all commercial pyranometers deviate from a proper "cosine law" making them usually less sensitive at large incident zenith angles.…”

Section: Albedo Over Snow and Ice Surfacesmentioning

confidence: 99%

Correction of broadband snow albedo measurements affected by unknown slope and sensor tilts

et al. 2016

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Abstract. Geometric effects induced by the underlying terrain slope or by tilt errors of the radiation sensors lead to an erroneous measurement of snow or ice albedo. Consequently, artificial diurnal albedo variations in the order of 1-20 % are observed. The present paper proposes a general method to correct tilt errors of albedo measurements in cases where tilts of both the sensors and the slopes are not accurately measured or known. We demonstrate that atmospheric parameters for this correction model can either be taken from a nearby well-maintained and horizontally levelled measurement of global radiation or alternatively from a solar radiation model. In a next step the model is fitted to the measured data to determine tilts and directions of sensors and the underlying terrain slope. This then allows us to correct the measured albedo, the radiative balance and the energy balance. Depending on the direction of the slope and the sensors a comparison between measured and corrected albedo values reveals obvious over-or underestimations of albedo. It is also demonstrated that differences between measured and corrected albedo are generally highest for large solar zenith angles.

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“…In this framework Pirazzini (2004) expresses the importance of minimizing the sampling bias over sastrugi fields by collecting a large number of samples at various places or over a long time span (Carroll and Fitch, 1981) or by increasing the height of the sensor above the surface, so that the irradiance measured will also be more representative of the effective reflectance of the surface (Warren et al, 1998). For penitentes, however, the ISRT models shows that the albedo uncertainty for individual measurements still is ±0.04 at 4 m above the surface.…”

Section: Implications For Interpretation Of Albedo Measurementsmentioning

confidence: 99%

“…Firstly, sastrugis lower the averaged incidence angle, which reduces the albedo due to the strong dependence of albedo on the incidence angle of incoming radiation (Warren, 1982). This effect depends on the sun's azimuth position relative to the sastrugi axis, as perpendicular insolation results in an albedo decrease between 2 and 4 % relative to parallel insolation (Carroll and Fitch, 1981;Kuhn, 1974). Secondly, multiple reflections between the walls cause light trapping in the trough.…”

Section: Introductionmentioning

confidence: 99%

Albedo over rough snow and ice surfaces

2014

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Abstract. Both satellite and ground-based broadband albedo measurements over rough and complex terrain show several limitations concerning feasibility and representativeness. To assess these limitations and understand the effect of surface roughness on albedo, firstly, an intrasurface radiative transfer (ISRT) model is combined with albedo measurements over different penitente surfaces on Glaciar Tapado in the semiarid Andes of northern Chile. Results of the ISRT model show effective albedo reductions over the penitentes up to 0.4 when comparing the rough surface albedo relative to the albedo of the flat surface. The magnitude of these reductions primarily depends on the opening angles of the penitentes, but the shape of the penitentes and spatial variability of the material albedo also play a major role.Secondly, the ISRT model is used to reveal the effect of using albedo measurements at a specific location (i.e., apparent albedo) to infer the true albedo of a penitente field (i.e., effective albedo). This effect is especially strong for narrow penitentes, resulting in sampling biases of up to ±0.05. The sampling biases are more pronounced when the sensor is low above the surface, but remain relatively constant throughout the day. Consequently, it is important to use a large number of samples at various places and/or to locate the sensor sufficiently high in order to avoid this sampling bias of surface albedo over rough surfaces.Thirdly, the temporal evolution of broadband albedo over a penitente-covered surface is analyzed to place the experiments and their uncertainty into a longer temporal context. Time series of albedo measurements at an automated weather station over two ablation seasons reveal that albedo decreases early in the ablation season. These decreases stabilize from February onwards with variations being caused by fresh snowfall events. The 2009/2010 and 2011/2012 seasons differ notably, where the latter shows lower albedo values caused by larger penitentes. Finally, a comparison of the ground-based albedo observations with Landsat and MODIS (Moderate Resolution Imaging Spectroradiometer)-derived albedo showed that both satellite albedo products capture the albedo evolution with root mean square errors of 0.08 and 0.15, respectively, but also illustrate their shortcomings related to temporal resolution and spatial heterogeneity over small mountain glaciers.

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Effects of solar elevation and cloudiness on snow albedo at the South Pole

Cited by 95 publications

References 16 publications

Accounting for the effects of sastrugi in the CERES clear-sky Antarctic shortwave angular distribution models

Accounting for the effects of sastrugi in the CERES clear-sky Antarctic shortwave angular distribution models

Correction of broadband snow albedo measurements affected by unknown slope and sensor tilts

Albedo over rough snow and ice surfaces

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