scholarly journals On the use of incoming longwave radiation parameterizations in a glacier environment

2008 ◽  
Vol 2 (4) ◽  
pp. 487-511 ◽  
Author(s):  
J. Sedlar ◽  
R. Hock
Keyword(s):  
Meteorological Data ◽  
Global Radiation ◽  
Correlation Coefficients ◽  
Longwave Radiation ◽  
Near Surface ◽  
Clear Sky ◽  
Radiation Parameterizations ◽  
Cloud Parameterization ◽  
Sky Conditions ◽  
Parameter Values

Abstract. Energy balance based glacier melt models require accurate estimates of incoming longwave radiation since it is generally the largest source of energy input. Multi-year near-surface meteorological data from Storglaciären, northern Sweden, were used to evaluate commonly used longwave radiation parameterizations in a glacier environment under clear-sky, overcast-sky and all-sky conditions. The tested parameterization depending solely on air temperature performed worse than those including also air humidity. Adopting parameter values from the literature instead of fitting them to the data resulted in similar correlation coefficients between modeled and measured radiation, but generated larger biases, emphasizing the need to derive site-specific coefficients. Nearly all models including those fitted to the data tended to overestimate longwave radiation during periods of low longwave radiation, and vice versa when radiation input was high. An attempt was made to parameterize cloud cover using top of atmosphere and measured global radiation. Both hourly and daily calculations of incoming longwave radiation using the cloud parameterization provided similar, or even stronger, correlations to the measurements compared to using observed cloud fraction as input. Using the global radiation cloud parameterization is promising for use in high-latitude regions where global radiation measurements exist but cloud observations do not.

scholarly journals Testing longwave radiation parameterizations under clear and overcast skies at Storglaciären, Sweden

2009 ◽  
Vol 3 (1) ◽  
pp. 75-84 ◽  
Author(s):  
J. Sedlar ◽  
R. Hock
Keyword(s):  
Meteorological Data ◽  
Water Vapor Pressure ◽  
Longwave Radiation ◽  
Cloud Fraction ◽  
Shortwave Radiation ◽  
Mean Bias Error ◽  
Bias Error ◽  
Near Surface ◽  
Radiation Parameterizations ◽  
Sky Conditions

Abstract. Energy balance based glacier melt models require accurate estimates of incoming longwave radiation but direct measurements are often not available. Multi-year near-surface meteorological data from Storglaciären, Northern Sweden, were used to evaluate commonly used longwave radiation parameterizations in a glacier environment under clear-sky and all-sky conditions. Parameterizations depending solely on air temperature performed worse than those which include water vapor pressure. All models tended to overestimate incoming longwave radiation during periods of low longwave radiation, while incoming longwave was underestimated when radiation was high. Under all-sky conditions root mean square error (RMSE) and mean bias error (MBE) were 17 to 20 W m−2 and −5 to 1 W m−2, respectively. Two attempts were made to circumvent the need of cloud cover data. First cloud fraction was parameterized as a function of the ratio, τ, of measured incoming shortwave radiation and calculated top of atmosphere radiation. Second, τ was related directly to the cloud factor (i.e. the increase in sky emissivity due to clouds). Despite large scatter between τ and both cloud fraction and the cloud factor, resulting calculations of hourly incoming longwave radiation for both approaches were only slightly more variable with RMSE roughly 3 W m−2 larger compared to using cloud observations as input. This is promising for longwave radiation modeling in areas where shortwave radiation data are available but cloud observations are not.

scholarly journals Solar radiation, cloudiness and longwave radiation over low-latitude glaciers: implications for mass-balance modelling

2009 ◽  
Vol 55 (190) ◽  
pp. 292-302 ◽  
Author(s):  
Thomas Mölg ◽  
Nicolas J. Cullen ◽  
Georg Kaser
Keyword(s):  
Mass Balance ◽  
Global Radiation ◽  
Longwave Radiation ◽  
Balance Model ◽  
Glacier Mass Balance ◽  
Peruvian Andes ◽  
Tropical Glaciers ◽  
Clear Sky ◽  
Physically Based ◽  
Radiation Parameterizations

AbstractBroadband radiation schemes (parameterizations) are commonly used tools in glacier mass-balance modelling, but their performance at high altitude in the tropics has not been evaluated in detail. Here we take advantage of a high-quality 2 year record of global radiation (G ) and incoming longwave radiation (L ↓) measured on Kersten Glacier, Kilimanjaro, East Africa, at 5873 m a.s.l., to optimize parameterizations of G and L ↓. We show that the two radiation terms can be related by an effective cloud-cover fraction neff , so G or L ↓ can be modelled based on neff derived from measured L ↓ or G, respectively. At neff = 1, G is reduced to 35% of clear-sky G, and L ↓ increases by 45–65% (depending on altitude) relative to clear-sky L ↓. Validation for a 1 year dataset of G and L ↓ obtained at 4850 m on Glaciar Artesonraju, Peruvian Andes, yields a satisfactory performance of the radiation scheme. Whether this performance is acceptable for mass-balance studies of tropical glaciers is explored by applying the data from Glaciar Artesonraju to a physically based mass-balance model, which requires, among others, G and L ↓ as forcing variables. Uncertainties in modelled mass balance introduced by the radiation parameterizations do not exceed those that can be caused by errors in the radiation measurements. Hence, this paper provides a tool for inclusion in spatially distributed mass-balance modelling of tropical glaciers and/or extension of radiation data when only G or L ↓ is measured.

scholarly journals Cloud effects on the surface energy and mass balance of Brewster Glacier, New Zealand

2015 ◽  
Vol 9 (1) ◽  
pp. 975-1019 ◽  
Author(s):  
J. P. Conway ◽  
N. J. Cullen
Keyword(s):  
Surface Energy ◽  
Mass Balance ◽  
Air Temperature ◽  
Longwave Radiation ◽  
Heat Fluxes ◽  
Glacier Surface ◽  
Surface Mass ◽  
Clear Sky ◽  
Climate Interactions ◽  
Sky Conditions

Abstract. A thorough understanding of the influence of clouds on glacier surface energy balance (SEB) and surface mass balance (SMB) is critical for forward and backward modelling of glacier–climate interactions. A validated 22 month time series of SEB/SMB was constructed for the ablation zone of the Brewster Glacier, using high quality radiation data to carefully evaluate SEB terms and define clear-sky and overcast conditions. A fundamental change in glacier SEB in cloudy conditions was driven by increased effective sky emissivity and surface vapour pressure, rather than the minimal change in air temperature and wind speed. During overcast conditions, positive net longwave radiation and latent heat fluxes allowed melt to be maintained through a much greater length of time compared to clear-sky conditions, and led to similar melt in each sky condition. The sensitivity of SMB to changes in air temperature was greatly enhanced in overcast compared to clear-sky conditions due to more frequent melt and the occurrence of precipitation, which enabled a strong accumulation–albedo feedback. During the spring and autumn seasons, the sensitivity during overcast conditions was strongest. There is a need to include the effects of atmospheric moisture (vapour, cloud and precipitation) on melt processes when modelling glacier–climate interactions.

scholarly journals Cloud Influence on ERA5 and AMPS Surface Downwelling Longwave Radiation Biases in West Antarctica

2019 ◽  
Vol 32 (22) ◽  
pp. 7935-7949 ◽  
Author(s):  
Israel Silber ◽  
Johannes Verlinde ◽  
Sheng-Hung Wang ◽  
David H. Bromwich ◽  
Ann M. Fridlind ◽  
...  
Keyword(s):  
Longwave Radiation ◽  
Surface Energy Budget ◽  
Polar Regions ◽  
Model Errors ◽  
Microphysics Scheme ◽  
Clear Sky ◽  
Radiation Component ◽  
West Antarctic ◽  
Downwelling Longwave Radiation ◽  
Sky Conditions

Abstract The surface downwelling longwave radiation component (LW↓) is crucial for the determination of the surface energy budget and has significant implications for the resilience of ice surfaces in the polar regions. Accurate model evaluation of this radiation component requires knowledge about the phase, vertical distribution, and associated temperature of water in the atmosphere, all of which control the LW↓ signal measured at the surface. In this study, we examine the LW↓ model errors found in the Antarctic Mesoscale Prediction System (AMPS) operational forecast model and the ERA5 model relative to observations from the ARM West Antarctic Radiation Experiment (AWARE) campaign at McMurdo Station and the West Antarctic Ice Sheet (WAIS) Divide. The errors are calculated separately for observed clear-sky conditions, ice-cloud occurrences, and liquid-bearing cloud-layer (LBCL) occurrences. The analysis results show a tendency in both models at each site to underestimate the LW↓ during clear-sky conditions, high error variability (standard deviations > 20 W m−2) during any type of cloud occurrence, and negative LW↓ biases when LBCLs are observed (bias magnitudes >15 W m−2 in tenuous LBCL cases and >43 W m−2 in optically thick/opaque LBCLs instances). We suggest that a generally dry and liquid-deficient atmosphere responsible for the identified LW↓ biases in both models is the result of excessive ice formation and growth, which could stem from the model initial and lateral boundary conditions, microphysics scheme, aerosol representation, and/or limited vertical resolution.

scholarly journals Temporal heterogeneity in aerosol characteristics and the resulting radiative impacts at a tropical coastal station – Part 2: Direct short wave radiative forcing

2007 ◽  
Vol 25 (11) ◽  
pp. 2309-2320 ◽  
Author(s):  
S. Suresh Babu ◽  
K. Krishna Moorthy ◽  
S. K. Satheesh
Keyword(s):  
Radiative Forcing ◽  
Monsoon Season ◽  
Short Wave ◽  
Coastal Station ◽  
Near Surface ◽  
Aerosol Radiative Forcing ◽  
Clear Sky ◽  
Synoptic Conditions ◽  
Post Monsoon Season ◽  
Sky Conditions

Abstract. Seasonal distinctiveness in the microphysical and optical properties of columnar and near-surface (in the well mixed region) aerosols, associated with changes in the prevailing synoptic conditions, were delineated based on extensive (spread over 4 years) and collocated measurements at the tropical coastal location, Trivandrum (8.55° N; 76.97° E, 3 m a.m.s.l.), and the results were summarized in Part 1 of this two-part paper. In Part 2, we use these properties to develop empirical seasonal aerosol models, which represent the observed features fairly accurately, separately for winter monsoon season (WMS, December through March), inter-monsoon season (IMS, April and May), summer monsoon season (SMS, June through September) and post monsoon season (PMS, October and November). The models indicate a significant transformation in the aerosol environment from an anthropogenic-dominance in WMS to a natural-dominance in SMS. The modeled aerosol properties are used for estimating the direct, short wave aerosol radiative forcing, under clear-sky conditions. Our estimates show large seasonal changes. Under clear sky conditions, the daily averaged short-wave TOA forcing changes from its highest values during WMS, to the lowest values in SMS; this seasonal change being brought-in mainly by the reduction in the abundance and the mass fraction (to the composite) of black carbon aerosols and of accumulation mode aerosols. The resulting atmospheric forcing varies from the highest, (47 to 53 W m−2) in WMS to the lowest (22 to 26 W m−2) in SMS.

Estimation of All-weather Downward Longwave Radiation over the Tibetan Plateau

2021 ◽  
Author(s):  
Lirong Ding ◽  
Zhiyong Long ◽  
Ji Zhou ◽  
Shaofei Wang ◽  
Xiaodong Zhang
Keyword(s):  
Climate Change ◽  
Tibetan Plateau ◽  
Energy Budget ◽  
Water Cycle ◽  
Longwave Radiation ◽  
Radiation Balance ◽  
The Tibetan Plateau ◽  
Clear Sky ◽  
Downward Longwave Radiation ◽  
Sky Conditions

<p>The downward longwave radiation (DLR) is a critical parameter for radiation balance, energy budget, and water cycle studies at regional and global scales. The accurate estimation of the all-weather DLR with a high temporal resolution is important for the estimation of the surface net radiation and evapotranspiration. However, the most DLR products involve instantaneous DLR estimates based on polar orbiting satellite data under clear-sky conditions. To obtain an in-depth understanding of the performances of different models in the estimation of the DLR over the Tibetan Plateau, which is a focus area of climate change study, this study tested eight methods under clear-sky conditions and six methods under cloudy conditions based on ground-measured data. The results show that the Dilley and O’Brien model and the Lhomme model are most suitable under clear-sky conditions and cloudy conditions, respectively. For the Dilley and O’Brien model, the average root mean square error (RMSE) of the DLR under clear-sky conditions is approximately 22.5 W/m<sup>2</sup> at nine ground sites; for the Lhomme model, the average RMSE is approximately 23.2 W/m<sup>2</sup>. Based on the estimated cloud fraction and meteorological data provided by the China land surface data assimilation system (CLDAS), the hourly all-weather daytime DLR with 0.0625° over the Tibetan Plateau was estimated. The results show that the average RMSE of the estimated hourly all-weather DLR was approximately 26.4 W/m<sup>2</sup>. With the combined all-weather DLR model, the hourly all-weather daytime DLR dataset with a 0.0625° resolution from 2008 to 2016 over the Tibetan Plateau was generated. This dataset can better contribute to studies associated with the radiation balance and energy budget, water cycle, and climate change over the Tibetan Plateau.</p>

scholarly journals Downward longwave radiation estimates for clear-sky conditions over northeast Brazil

2011 ◽  
Vol 26 (3) ◽  
pp. 443-450 ◽  
Author(s):  
Carlos Antonio Costa dos Santos ◽  
Bernardo Barbosa da Silva ◽  
Tantravahi Venkata Ramana Rao ◽  
Prakki Satyamurty ◽  
Antonio Ocimar Manzi
Keyword(s):  
Arid Regions ◽  
Longwave Radiation ◽  
Radiation Budget ◽  
Semiarid Region ◽  
Northeast Brazil ◽  
Hydrological Models ◽  
Experimental Site ◽  
Clear Sky ◽  
Downward Longwave Radiation ◽  
Sky Conditions

The main objective of this paper is to assess the performance of nine downward longwave radiation equations for clear-sky condition and develop a locally adjusted equation using the observed vapor pressure and air temperature data. The radiation and atmospheric parameters were measured during the months of October 2005 to June 2006 at a micrometeorological tower installed at the experimental site in a banana orchard in the semiarid region of Northeast Brazil. The comparative statistics for the performance of the downward longwave radiation calculation models during daytime and nighttime compared to measured data have shown that the parameterizations with more physical foundations have the best results. The locally adjusted equation and Sugita and Brutsaert model developed in 1993 showed errors less than 1.0% in comparison with measured values. Downward longwave radiation is one of the most expensive and difficult component of the radiation budget to be monitored in micrometeorological studies. Hence, the locally adjusted equation can be used to estimate downward longwave energy, needed as input to some agricultural and hydrological models, in semi-arid regions of the Northeast Brazil, where this component is not monitored.

scholarly journals Skill of Direct Solar Radiation Predicted by the ECMWF Global Atmospheric Model over Australia

2014 ◽  
Vol 53 (11) ◽  
pp. 2571-2588 ◽  
Author(s):  
Alberto Troccoli ◽  
Jean-Jacques Morcrette
Keyword(s):  
Solar Radiation ◽  
Power Plants ◽  
Solar Power ◽  
Weather Prediction ◽  
Global Radiation ◽  
Atmospheric Model ◽  
Direct Solar Radiation ◽  
Efficient Production ◽  
Clear Sky ◽  
Sky Conditions

AbstractPrediction of direct solar radiation is key in sectors such as solar power and agriculture; for instance, it can enable more efficient production of energy from concentrating solar power plants. An assessment of the quality of the direct solar radiation forecast by two versions of the European Centre for Medium-Range Weather Forecasts (ECMWF) global numerical weather prediction model up to 5 days ahead is carried out here. The performance of the model is measured against observations from four solar monitoring stations over Australia, characterized by diverse geographic and climatic features, for the year 2006. As a reference, the performance of global radiation forecast is carried out as well. In terms of direct solar radiation, while the skill of the two model versions is very similar, and with relative mean absolute errors (rMAEs) ranging from 18% to 45% and correlations between 0.85 and 0.25 at around midday, their performance is substantially enhanced via a simple postprocessing bias-correction procedure. There is a marked dependency on cloudy conditions, with rMAEs 2–4 times as large for very cloudy-to-overcast conditions relative to clear-sky conditions. There is also a distinct dependency on the background climatic clear-sky conditions of the location considered. Tests made on a simulated operational setup targeting three quantiles show that direct radiation forecasts achieve potentially high scores. Overall, these analyses provide an indication of the potential practical use of direct irradiance forecast for applications such as solar power operations.

scholarly journals A Simple Method for the Assessment of the Cloud Cover State in High-Latitude Regions by a Ground-Based Digital Camera

2006 ◽  
Vol 23 (3) ◽  
pp. 437-447 ◽  
Author(s):  
M. P. Souza-Echer ◽  
E. B. Pereira ◽  
L. S. Bins ◽  
M. A. R. Andrade
Keyword(s):  
A Priori ◽  
Digital Camera ◽  
Correlation Coefficients ◽  
Visible Range ◽  
Direct Sunlight ◽  
Simple Method ◽  
Charge Coupled Device ◽  
Clear Sky ◽  
Sky Conditions ◽  
Overcast Sky

Abstract This work describes the development of a simple method of field estimating the sky cloud coverage percentage for several applications at the Brazilian Antarctic Station, Ferraz (62°05′S, 58°23.5′W). The database of this method was acquired by a digital color camera in the visible range of the spectrum. A new algorithm was developed to classify each pixel according to a criteria decision process. The information on the pixel contamination by clouds was obtained from the saturation component of the intensity, hue, and saturation space (IHS). For simplicity, the images were acquired with a limited field of view of 36° pointing to the camera’s zenith to prevent direct sunlight from reaching the internal charge-coupled device (CCD) on the camera. For a priori–classified clear-sky images, the accuracy of the method was superior to 94%. For overcast-sky conditions, the corresponding accuracy was larger than 99%. A comparison test was performed with two human observers and our method. The results for the 29 images collected for several time of days during 50 days in 1999 summer were compared to visual observations of these same digital images by two trained field meteorologists. Correlation coefficients between human observers and the automatic method ranged from 0.84 for clear-sky conditions, and the lowest was 0.09 for undefined-sky conditions.

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