The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Michiel R Van Den Broeke - One of the best experts on this subject based on the ideXlab platform.
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a retrospective iterative geometry based rigb tilt correction method for radiation observed by automatic Weather Stations on snow covered surfaces application to greenland
The Cryosphere, 2015Co-Authors: Wensha Wang, Dirk Van As, Charles S Zende, Paul Smeets, Michiel R Van Den BroekeAbstract:Abstract. Surface melt and mass loss of the Greenland Ice Sheet may play crucial roles in global climate change due to their positive feedbacks and large fresh-water storage. With few other regular meteorological observations available in this extreme environment, measurements from automatic Weather Stations (AWS) are the primary data source for studying surface energy budgets, and for validating satellite observations and model simulations. Station tilt, due to irregular surface melt, compaction and glacier dynamics, causes considerable biases in the AWS shortwave radiation measurements. In this study, we identify tilt-induced biases in the climatology of surface shortwave radiative flux and albedo, and retrospectively correct these by iterative application of solar geometric principles. We found, over all the AWS from the Greenland Climate Network (GC-Net), the Kangerlussuaq transect (K-transect) and the Programme for Monitoring of the Greenland Ice Sheet (PROMICE) networks, insolation on fewer than 40 % of clear days peaks within p0.5 h of solar noon time, with the largest shift exceeding 3 h due to tilt. Hourly absolute biases in the magnitude of surface insolation can reach up to 200 W m−2, with respect to the well-understood clear-day insolation. We estimate the tilt angles and their directions based on the solar geometric relationship between the simulated insolation at a horizontal surface and the observed insolation by these tilted AWS under clear-sky conditions. Our adjustment reduces the root mean square error (RMSE) against references from both satellite observation and reanalysis by 16 W m−2 (24 %), and raises the correlation coefficients with them to above 0.95. Averaged over the whole Greenland Ice Sheet in the melt season, the adjustment in insolation to compensate station tilt is ∼ 11 W m−2, enough to melt 0.24 m of snow water equivalent. The adjusted diurnal cycles of albedo are smoother, with consistent semi-smiling patterns. The seasonal cycles and inter-annual variabilities of albedo agree better with previous studies. This tilt-corrected shortwave radiation data set derived using the Retrospective, Iterative, Geometry-Based (RIGB) method provide more accurate observations and validations for surface energy budgets studies on the Greenland Ice Sheet, including albedo variations, surface melt simulations and cloud radiative forcing estimates.
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evaluation of the antarctic surface wind climate from era reanalyses and racmo2 ant simulations based on automatic Weather Stations
Climate Dynamics, 2013Co-Authors: Jeanmarie Uchli, Javier Sanz Rodrigo, Jeroe Van Beeck, Jan T.m. Lenaerts, Michiel R Van Den BroekeAbstract:A continental scale evaluation of Antarctic surface winds is presented from global ERA-40 and ERA-Interim reanalyses and RACMO2/ANT regional climate model at 55 and 27 km horizontal resolution, based on a comparison with observational data from 115 automatic Weather Stations (AWS). The Antarctic surface wind climate can be classified based on the Weibull shape factor k w . Very high values (k w > 3) are found in the interior plateaus, typical of very uniform katabatic-dominated winds with high directional constancy. In the coast and all over the Antarctic Peninsula the shape factors are similar to the ones found in mid-latitudes (k w < 3) typical of synoptically dominated wind climates. The Weibull shape parameter is systematically overpredicted by ERA reanalyses. This is partly corrected by RACMO2/ANT simulations which introduce more wind speed variability in complex terrain areas. A significant improvement is observed in the performance of ERA-Interim over ERA-40, with an overall decrease of 14 % in normalized mean absolute error. In escarpment and coastal areas, where the terrain gets rugged and katabatic winds are further intensified in confluence zones, ERA-Interim bias can be as high as 10 m s−1. These large deviations are partly corrected by the regional climate model. Given that RACMO2/ANT is an independent simulation of the near-surface wind speed climate, as it is not driven by observations, it compares very well to the ERA-Interim and AWS-115 datasets.
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sensible heat exchange at the antarctic snow surface a study with automatic Weather Stations
International Journal of Climatology, 2005Co-Authors: Michiel R Van Den Broeke, C H Reijme, Dirk Van As, Roderik S W Van De WalAbstract:Data of four automatic Weather Stations (AWSs) are used to calculate the turbulent exchange of sensible heat at the Antarctic snow surface for a 4 year period (1998–2001). The AWSs are situated on the ice shelf, in the coastal/inland katabatic wind zone and on the interior plateau in Dronning Maud Land, East Antarctica. Sensible heat flux (SHF) is calculated using the aerodynamic ‘bulk’ method between a single AWS sensor level and the surface, in combination with surface temperature derived from upwelling longwave radiation and surface roughness derived from eddy correlation measurements. Good agreement is found between calculated and directly measured SHF. All AWS sites show a downwarddirected average sensible heat transport, but otherwise the differences between the various zones are large. The surface roughness for momentum differs by an order of magnitude between the interior plateau (0.02 mm) and the katabatic wind zone (0.16 mm). On the ice shelf, frequent clouds limit surface cooling, and annual mean SHF is small (8 W m −2 ). In contrast, clear skies prevail on the interior plateau, but weak winds, an aerodynamically smooth surface and stability effects limit annual mean SHF to an equally low value (8 W m −2 ). The most favourable conditions for sensible heat exchange are found in the katabatic wind zone, where a combination of strong winds, relatively little cloud cover and a rougher surface results in annual mean SHF values of 22 to 24 W m −2 . Copyright 2005 Royal Meteorological Society.
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a study of the surface mass balance in dronning maud land antarctica using automatic Weather Stations
Journal of Glaciology, 2004Co-Authors: Michiel R Van Den Broeke, C H Reijme, Roderik S W Van De WalAbstract:We use data from four automatic Weather Stations (AWSs) in Dronning Maud Land, East Antarctica, to study the surface mass balance and its components. Distinct differences were found between the moisture climates of the high plateau, the katabatic wind zone and the coastal ice shelves: significant undersaturation occurs year-round in the katabatic wind zone, while on the high plateau and on the coastal ice shelf the air is usually close to saturation. In summer, absorption of shortwave radiation at the snow surface enhances surface sublimation at all sites, removing 3-9% of the annual solid precipitation. Significant summer melting is an equally important ablation term near the coast, but vanishes inland. Vertically integrated column drifting-snow sublimation was estimated using two different methods. This process appears to be similar to or greater in magnitude than surface sublimation. Because intervals between significant precipitation events may last as long as several months, sublimation and melt cause extended periods of surface ablation in summer. In summer, all ablation processes together remove 15-56% of the solid precipitation, or 6-27% on an annual basis.
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temporal and spatial variability of the surface mass balance in dronning maud land antarctica as derived from automatic Weather Stations
Journal of Glaciology, 2003Co-Authors: C H Reijmer, Michiel R Van Den BroekeAbstract:Measurements of changes in surface height carried out with sonic altimeters mounted on automatic Weather Stations in Dronning Maud Land (DML) and on Berkner Island, Antarctica, are used to derive the surface mass balance. The surface mass balance is positive at all sites, i.e. accumulation outweighs ablation. The spatial and temporal variability in accumulation is high. Accumulation occurs in numerous small events and a few large events per year. The larger events contribute more to the annual accumulation than the small events; ∼50% of all accumulation is contributed by 10–25% of all events. The accumulation generally decreases with increasing distance from the coast and elevation. Annual averaged values range from ∼375 ± 59 mm w.e. a−1 near the coast to ∼33 ± 25 mm w.e. a−1 on theAntarctic plateau and are in good agreement with long-term averaged annual accumulation rates obtained from snow pits and firn cores. The records show seasonal dependency of the amount of accumulation, with a maximum in winter in the coastal and escarpment region of DML and in summer on Berkner Island and on the plateau. The seasonal cycles are significant on Berkner Island, and in the coastal area and part of the escarpment region.
Roderik S W Van De Wal - One of the best experts on this subject based on the ideXlab platform.
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sensible heat exchange at the antarctic snow surface a study with automatic Weather Stations
International Journal of Climatology, 2005Co-Authors: Michiel R Van Den Broeke, C H Reijme, Dirk Van As, Roderik S W Van De WalAbstract:Data of four automatic Weather Stations (AWSs) are used to calculate the turbulent exchange of sensible heat at the Antarctic snow surface for a 4 year period (1998–2001). The AWSs are situated on the ice shelf, in the coastal/inland katabatic wind zone and on the interior plateau in Dronning Maud Land, East Antarctica. Sensible heat flux (SHF) is calculated using the aerodynamic ‘bulk’ method between a single AWS sensor level and the surface, in combination with surface temperature derived from upwelling longwave radiation and surface roughness derived from eddy correlation measurements. Good agreement is found between calculated and directly measured SHF. All AWS sites show a downwarddirected average sensible heat transport, but otherwise the differences between the various zones are large. The surface roughness for momentum differs by an order of magnitude between the interior plateau (0.02 mm) and the katabatic wind zone (0.16 mm). On the ice shelf, frequent clouds limit surface cooling, and annual mean SHF is small (8 W m −2 ). In contrast, clear skies prevail on the interior plateau, but weak winds, an aerodynamically smooth surface and stability effects limit annual mean SHF to an equally low value (8 W m −2 ). The most favourable conditions for sensible heat exchange are found in the katabatic wind zone, where a combination of strong winds, relatively little cloud cover and a rougher surface results in annual mean SHF values of 22 to 24 W m −2 . Copyright 2005 Royal Meteorological Society.
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a study of the surface mass balance in dronning maud land antarctica using automatic Weather Stations
Journal of Glaciology, 2004Co-Authors: Michiel R Van Den Broeke, C H Reijme, Roderik S W Van De WalAbstract:We use data from four automatic Weather Stations (AWSs) in Dronning Maud Land, East Antarctica, to study the surface mass balance and its components. Distinct differences were found between the moisture climates of the high plateau, the katabatic wind zone and the coastal ice shelves: significant undersaturation occurs year-round in the katabatic wind zone, while on the high plateau and on the coastal ice shelf the air is usually close to saturation. In summer, absorption of shortwave radiation at the snow surface enhances surface sublimation at all sites, removing 3-9% of the annual solid precipitation. Significant summer melting is an equally important ablation term near the coast, but vanishes inland. Vertically integrated column drifting-snow sublimation was estimated using two different methods. This process appears to be similar to or greater in magnitude than surface sublimation. Because intervals between significant precipitation events may last as long as several months, sublimation and melt cause extended periods of surface ablation in summer. In summer, all ablation processes together remove 15-56% of the solid precipitation, or 6-27% on an annual basis.
C H Reijmer - One of the best experts on this subject based on the ideXlab platform.
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surface radiation balance in antarctica as measured with automatic Weather Stations
Journal of Geophysical Research, 2004Co-Authors: Michiel R Van Den Broeke, C H ReijmerAbstract:[1] We present 4 years of near-surface radiation balance observations of four Antarctic automatic Weather Stations (AWS). The AWS are situated along a traverse line in Dronning Maud Land, connecting the coastal ice shelf and the inland plateau via the katabatic wind zone, covering the three major climate regimes of East Antarctica. Important differences in the radiation balance of the three regions are found. Clouds not only limit atmospheric transmissivity for shortwave radiation but also strongly enhance the albedo for the shortwave radiation that reaches the surface. As a result, the snow surface of the coastal ice shelves absorbs up to 65% less shortwave radiation in high summer than at the high plateau, where cloudy episodes and precipitation events are less frequent. In winter, over the slopes, katabatic winds maintain a continuous turbulent transport of sensible heat toward the surface, which enhances outgoing longwave radiation. As a result, the katabatic wind zone shows the largest longwave and all-wave radiation loss in winter and over the year. Clear-sky effective emissivity for incoming longwave radiation shows great spatial variability resulting from differences in vertical temperature and moisture profiles among the various climate zones.
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temporal and spatial variability of the surface mass balance in dronning maud land antarctica as derived from automatic Weather Stations
Journal of Glaciology, 2003Co-Authors: C H Reijmer, Michiel R Van Den BroekeAbstract:Measurements of changes in surface height carried out with sonic altimeters mounted on automatic Weather Stations in Dronning Maud Land (DML) and on Berkner Island, Antarctica, are used to derive the surface mass balance. The surface mass balance is positive at all sites, i.e. accumulation outweighs ablation. The spatial and temporal variability in accumulation is high. Accumulation occurs in numerous small events and a few large events per year. The larger events contribute more to the annual accumulation than the small events; ∼50% of all accumulation is contributed by 10–25% of all events. The accumulation generally decreases with increasing distance from the coast and elevation. Annual averaged values range from ∼375 ± 59 mm w.e. a−1 near the coast to ∼33 ± 25 mm w.e. a−1 on theAntarctic plateau and are in good agreement with long-term averaged annual accumulation rates obtained from snow pits and firn cores. The records show seasonal dependency of the amount of accumulation, with a maximum in winter in the coastal and escarpment region of DML and in summer on Berkner Island and on the plateau. The seasonal cycles are significant on Berkner Island, and in the coastal area and part of the escarpment region.
Lotte De Vos - One of the best experts on this subject based on the ideXlab platform.
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quality control for crowdsourced personal Weather Stations to enable operational rainfall monitoring
Geophysical Research Letters, 2019Co-Authors: Lotte De Vos, H Leijnse, A Overeem, R UijlenhoetAbstract:Automatic personal Weather Stations owned and maintained by Weather enthusiasts provide spatially dense in situ measurements that are often collected and visualized in real time on online Weather platforms. While the spatial and temporal resolution of this data source is high, its rainfall observations are prone to typical errors, currently preventing its large‐scale, real‐time application. This study proposes a quality control methodology consisting of four modules targeting these errors, applicable in real time without requiring auxiliary measurements. The quality control improves the overall accuracy of a year of hourly rainfall depths in Amsterdam to a bias of −11.3% (0.2% when a proxy for overall rainfall underestimation by personal Weather Stations is used), a Pearson correlation coefficient of 0.82, and a coefficient of variation of 2.70, while maintaining 88% of the original data set. Application on a national scale (average 1 station per ∼10 km2) yields high‐resolution nationwide rainfall maps, hence showing the great potential of personal Weather Stations for complementing existing often sparse traditional rain gauge networks
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the potential of urban rainfall monitoring with crowdsourced automatic Weather Stations in amsterdam
Hydrology and Earth System Sciences, 2016Co-Authors: Lotte De Vos, H Leijnse, A Overeem, R UijlenhoeAbstract:Abstract. The high density of built-up areas and resulting imperviousness of the land surface makes urban areas vulnerable to extreme rainfall, which can lead to considerable damage. In order to design and manage cities to be able to deal with the growing number of extreme rainfall events, rainfall data are required at higher temporal and spatial resolutions than those needed for rural catchments. However, the density of operational rainfall monitoring networks managed by local or national authorities is typically low in urban areas. A growing number of automatic personal Weather Stations (PWSs) link rainfall measurements to online platforms. Here, we examine the potential of such crowdsourced datasets for obtaining the desired resolution and quality of rainfall measurements for the capital of the Netherlands. Data from 63 Stations in Amsterdam (∼ 575 km2) that measure rainfall over at least 4 months in a 17-month period are evaluated. In addition, a detailed assessment is made of three Netatmo Stations, the largest contributor to this dataset, in an experimental setup. The sensor performance in the experimental setup and the density of the PWS network are promising. However, features in the online platforms, like rounding and thresholds, cause changes from the original time series, resulting in considerable errors in the datasets obtained. These errors are especially large during low-intensity rainfall, although they can be reduced by accumulating rainfall over longer intervals. Accumulation improves the correlation coefficient with gauge-adjusted radar data from 0.48 at 5 min intervals to 0.60 at hourly intervals. Spatial rainfall correlation functions derived from PWS data show much more small-scale variability than those based on gauge-adjusted radar data and those found in similar research using dedicated rain gauge networks. This can largely be attributed to the noise in the PWS data resulting from both the measurement setup and the processes occurring in the data transfer to the online PWS platform. A double mass comparison with gauge-adjusted radar data shows that the median of the Stations resembles the rainfall reference better than the real-time (unadjusted) radar product. Averaging nearby raw PWS measurements further improves the match with gauge-adjusted radar data in that area. These results confirm that the growing number of internet-connected PWSs could successfully be used for urban rainfall monitoring.
Jens Wend - One of the best experts on this subject based on the ideXlab platform.
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monitoring ice capped active volcan villarrica southern chile using terrestrial photography combined with automatic Weather Stations and global positioning systems
Journal of Glaciology, 2008Co-Authors: Andres Rivera, Javie G Corripio, Enjami Ock, Jorge Clavero, Jens WendAbstract:Volc´an Villarrica (39◦25'12" S, 71◦56'27"W; 2847ma.s.l.) is an active ice-capped volcano located in the Chilean lake district. The surface energy balance and glacier frontal variations have been monitored for several years, using automatic Weather Stations and satellite imagery. In recent field campaigns, surface topography was measured using Javad GPS receivers. Daily changes in snow-, ice and tephra-covered areas were recorded using an automatic digital camera installed on a rock outcrop. In spite of frequently damaging Weather conditions, two series of consecutive images were obtained, in 2006 and 2007. These photographs were georeferenced to a resampled 90m pixel size SRTM digital elevation model and the reflectance values normalized according to several geometric and atmospheric parameters. The resulting daily maps of surface albedo are used as input to a distributed glacier-melt model during a 12 day mid-summer period. The spatial pattern of cumulative melt is complex and controlled by the distribution of airfall and wind-blown tephra, with extremely high melt rates occurring downwind of the crater and exposed ash banks. The camera images are also used to visualize the pattern of glacier crevassing. The results demonstrate the value of terrestrial photography in understanding the energy and mass balance of the glacier, including the generation of meltwater, and the potential value of the technique for monitoring volcanic activity and potential hazards associated with ice–volcano interactions during eruptive activity.
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instruments and methods monitoring ice capped active volc an villarrica southern chile using terrestrial photography combined with automatic Weather Stations and global positioning systems
2008Co-Authors: Javie G Corripio, Enjami Ock, Jorge Clavero, Jens WendAbstract:VolcVillarrica (39 ◦ 25 � 12 �� S, 71 ◦ 56 � 27 �� W; 2847 m a.s.l.) is an active ice-capped volcano located in the Chilean lake district. The surface energy balance and glacier frontal variations have been monitored for several years, using automatic Weather Stations and satellite imagery. In recent field campaigns, surface topography was measured using Javad GPS receivers. Daily changes in snow-, ice- and tephra-covered areas were recorded using an automatic digital camera installed on a rock outcrop. In spite of frequently damaging Weather conditions, two series of consecutive images were obtained, in 2006 and 2007. These photographs were georeferenced to a resampled 90 m pixel size SRTM digital elevation model and the reflectance values normalized according to several geometric and atmospheric parameters. The resulting daily maps of surface albedo are used as input to a distributed glacier-melt model during a 12 day mid-summer period. The spatial pattern of cumulative melt is complex and controlled by the distribution of airfall and wind-blown tephra, with extremely high melt rates occurring downwind of the crater and exposed ash banks. The camera images are also used to visualize the pattern of glacier crevassing. The results demonstrate the value of terrestrial photography in understanding the energy and mass balance of the glacier, including the generation of meltwater, and the potential value of the technique for monitoring volcanic activity and potential hazards associated with ice-volcano interactions during eruptive activity.
