Impact Of Cloud Cover Research Articles

Impact of cloud cover on local remote sensing – Piaśnica River case study

New satellite-based techniques open up new horizons to researchers and local communities. Concurrently, however, requirements and expectations with regard to satel-lite-based remote sensing products are increasingly higher. By relying on satellite-derived information, environmental observations can cover areas of a few to several metres resolution. Here we are dealing with freeof-charge and generally available sources of satellite-based information. The Piaśnica River mouth area was selected as an observation site representing a highly dynamic morphological transect. The paper compares products of cloud cover detection, supplied with data and available in the Copernicus database for a local area in the coastal zone of the Baltic Sea. The absolute difference did not exceed 5%, which confirms a high efficiency of the solutions offered. More than 96% of the clouded area determined for the Sentinel-2/MSI (Multispectral Instrument) was correctly identified when compared with supervised observations. The rate was lower (92%) for the Sentinel-3/OLCI (Ocean and Land Colour Instrument). It was eventually concluded that, at the local level, successful observations can be conducted using the cloud cover map supplied with the satellite data. At the same time, the analyses presented do not rule out further efforts to, e.g., increase the accuracy and speed of the analyses.

Assessment of the impact of current weather forecasts in the task of space survey planning

The article is devoted to the actual task of planning the work of a group of different types of spacecraft for remote sensing of the Earth. An enlarged algorithm for solving the planning problem for different types of spacecraft is described. The result of the enlarged algorithm is sought in the form of a set of reference plans for groups of similar spacecraft, thinned out by removing some of the conflicting operations of resetting the sensing data. The characteristics of the developed plans largely depend on the methodology used to account for the impact of cloud cover. The possibility of implementing a methodology based on the use of files of current weather forecasts of hydrometeorological centers downloaded from the Internet in the form of a special application is investigated. The created application is being tested on the real data of the hydrometeorological center downloaded from the American server, which covers a large region, including the European part of Eurasia and part of Africa. An application that simulates the distribution of points within a region estimates the number of points covered by weak cloud cover (20% or less). Based on the results of the simulation, it was found that the proportion of points available for shooting lies in the range from about a quarter to a third. Based on the obtained quantitative estimates, it is concluded that taking into account the influence of cloud cover radically changes the reference plans calculated taking into account only illumination, and affects the structure of the enlarged planning algorithm.

Quantifying the observational requirements of a space-borne LiDAR snow mission

This study quantifies the level of observational accuracy required from a spaceborne light detection and ranging (LiDAR) snow depth retrieval mission for enabling beneficial impacts for snow estimation. The study is conducted over a region in Western Colorado using a suite of observing system simulation experiments (OSSEs). The Joint UK Land Environment Simulator, version 5.0 (JULES v5.0) is employed to simulate a suite of idealized LiDAR observations, considering a range of LiDAR snow depth retrieval errors, different hypothetical sensor swath widths, and the impact of cloud cover on observability. These simulated observations are then assimilated into the Noah land surface model with multi-parameterization options, version 3.6 (Noah-MP v3.6) model. This data assimilation setup is used to systematically evaluate the potential utility of LiDAR observations for improving modeled snow water equivalent (SWE) estimates and water budget variables such as runoff. Results from the OSSE runs show that, in general, assimilation of synthetic LiDAR observations provide beneficial impacts when the LiDAR snow depth retrieval error standard deviation (σerror) is below 60 cm. Based on comparisons between the realistic (i.e., swath-limited and cloud-attenuated) case and the idealized (i.e., infinite swath width in the absence of cloud cover) case, this study concludes that observations with a conservative error standard deviation threshold of 40 cm (i.e., upper limit of the snow depth retrieval error that adds value to the SWE estimates via assimilation) are needed for improving modeled snow estimates. More than a 33% reduction in SWE root mean square errors and more than a 15% increase in correlation coefficients are achieved when σerror ≤ 40 cm using a 170-km sensor swath width in the presence of cloud attenuation effects. Further, the integrated hydrologic response, as represented by total (surface and subsurface) runoff estimates during the snow ablation season, are also enhanced when assimilating synthetic LiDAR snow depth retrievals with errors below this level.

Review of the PV Electricity Production Estimate under the Effect of Climatic Disturbances and Sunspots by Using Deep-Learning Tools

The mathematical models used in the estimation of GHI on the Earth's surface are inconvenient because they always assume that the sky clarity index is constant. Hence, these models are often confronted with long-period empirical ground measurements that may exceeds 11 years. The impact of cloud cover on an electric power generation site is a very critical parameter for installing a solar power plant and evaluating its productivity. The state of knowledge about the sun influence, the greenhouse effect on climate change, and cloud occurrence can’t be described in a mathematical or numerical model.Therefore, in this paper, we propose the use of Deep-Learning techniques to predict any site’s productivity by analyzing its potential insolation. We also suggest the analysis of the ground and satellite- based measurements collected over 30 years. We propose the estimation of future climate change affecting cloud cover.

Simulation Modeling of Cloud Cover Projection Movement over the Plane of Solar Power Station

In the presented article results of imitation modeling of the solar power station element in the MATLAB® Simulink® software environment are presented. The modeling was provided taking in account the motion of the projection of the cloud cover over the plane of the element. Maximum level of energy that can be obtained from solar power station is determined by the intensity of the solar radiation, the total area of solar panels and their coefficient of efficiency. Regardless of the ratio of the size of the solar power station and cloud, it is necessary to develop a solar cell model, the analysis of the results of which would allow estimating the dependence of power at the output of the power station on the magnitude of the intensity of the solar radiation and the vector of clouds the projections movement. Given the limited computing power of an existing computer, the simulation is carried out on an example of individual photocells as components of the solar panel. The model of the solar power station element is developed using the main elements of the Simulink graphical environment, SimElectronics and Simscape libraries, as well as programming elements. In the model, the fundamental element is the Solar Cell, simulating the work of the solar panel, which consists of 16 photocells. The scheme of solar panel model with possible directions of cloud cover projection movement is given. The impact of cloud cover on the solar panel output power is determined by change in the intensity of solar radiation at certain intervals for each photocell. To simplify the simulation, it is assumed that the cloud boundaries are clearly defined. The shadowing of the solar panel by the projection of the cloud is presented by discrete change in the magnitude of the intensity of solar radiation on individual photocells with the help of Repeating Sequence Stairs block. The imitation model for the movement vector of cloud projection and its setting parameters are given. The model of the solar power station element with the change the vector of cloud cover projection movement, in which the stabilization of the load voltage at the level of 10 V is presented. Maintenance of the necessary load voltage level on time intervals when the power of the solar power station is insufficient, is ensured by the inclusion of the storage battery into the system. In the case when the speed of cloud cover projection movement reaches several m/s, the photocell in the proposed model corresponds to a block of 16 solar panels, and a solar panel rack corresponds to 64 solar panels. Time dependencies of the voltage at the output of the individual racks of the solar panel, the load voltage and the battery current are given. Re. 9, fig. 4

Extreme temperature differences in the city of Lahti, southern Finland: Intensity, seasonality and environmental drivers

Abstract The extremes of month-specific spatial temperature differences were studied for a first time in the high-latitude city of Lahti and its surroundings in southern Finland. During the 2-year observation period (6/14–5/16), the largest momentary temperature difference, 11.1 °C, was detected in February, and the smallest, 6.2 °C, in April. The impacts of various environmental factors during the extreme situations were estimated by site-specific analysis of the warmest and coldest observation sites and a stepwise multiple linear regression model including all the 8 observation sites. The extreme temperature differences were characterised by inversions especially in winter and spring, the warmest site being the hill-top location in Kivistonmaki. In summer the role of urban heating was more apparent, and the temperature was the highest in the relatively low-lying city centre. In autumn the heating impact of the relatively warm Lake Vesijarvi caused the largest temperature differences with harbour as the warmest site. The weather during all of the momentary extreme situations was calm and in the majority of the situations also clear. The impact of cloud cover was less critical than that of wind speed in reducing spatial temperature differences. The momentary extreme situations existed at night or at dawn, with one exception: only in January, during the cold weather period dominated by high pressure, the delayed break of inversion in the vicinity of Lake Vesijarvi caused the extreme temperature difference to exist in the afternoon, reflecting for its part the substantial stabilising impact of seasonal ice cover on Lake Vesijarvi.

Quantifying the impact of cloud cover on ground radiation flux measurements using hemispherical images

Linking observed or estimated ground incoming solar radiation with cloud coverage is difficult since the latter is usually poorly described in standard meteorological observation protocols. To investigate the benefits of detailed observation and characterization of cloud coverage and distribution, a fieldwork campaign has been set up in order to collect data about cloud cover conditions and daily evolution to directly analyse their impacts on solar radiation fluxes. To do so, daytime hemispherical images have been collected at a very high frequency, simultaneously to ground measurements of solar radiation fluxes in a scientific station close to Lake NamCo, China. After calibration, one of the main tasks was the classification of those hemispherical images and the extraction of meaningful indices to describe the cloud cover, such as cloud fraction or cloud cover distribution. The classification is based on automatic detection of threshold on the red channel histogram. The results show that several cloud indices could be successfully derived from the hemispherical images, even if very thin clouds can be difficult to detect. The indices are then correlated to the measured solar radiation values and the impact of cloud cover on surface radiation fluxes were analysed. This analysis highlights that, more than the cloud fraction, the cloud distribution in the hemisphere is of importance when modelling radiation fluxes in the solar domain.

Topographic controls on spatio-temporal snow cover distribution in Northwest Himalaya

The present study deals with spatio-temporal snow cover distribution in Northwest Himalaya (NWH) in a discourse on regional topography and prevalent climatology. Snow cover variation during 2001–2012 in NWH and eight major river basins was examined using MODIS data on board the Terra satellite. Slope match topographic correction was applied to eliminate the differential illumination effect on satellite imagery. The impact of cloud cover was removed by generating a 10-day maximum snow cover product. Annual and seasonal analysis shows a decreasing trend in snow cover area (SCA) over the entire NWH. Maximal SCA was observed in the windward river basins of the Lower and the Middle Himalayan zones and in the highly glaciated Shyok river basin of the Upper Himalaya. Monthly snow cover duration (SCD) maps revealed the effect of longitudinal variation as well as the strong influence of regional climatology and topography. The relationship of SCA with altitude and aspect was studied in all the river basins of NWH. The study shows a linear increment of SCA/D with increasing respect to elevation in all river basins. The maximum rate of SCA/D change with elevation was observed in the Jhelum river basin. In the Middle Himalayan Zone, an effect of basin orientation in regard to elevation was observed. Mean annual SCA at altitudes of up to 4500 m shows a decreasing trend. Seasonal analysis of aspect-wise snow cover shows that southern slopes have lower SCA during winter months. The difference in SCA between northern and southern slopes is even higher in summer and the monsoon period.

Evaluation of Algorithms to estimate Daily Evapotranspiration from Instantaneous Measurements under All-sky Conditions

Instantaneous EvapoTranspiration (ET) can be estimated using a single set of instantaneous observations by polar orbiting satellites during the day. Daily, weekly or monthly total ET is required for hydrological studies and water resources assessment. This requires daily total ET regardless of cloud cover. The daily total ET is usually determined assuming that the evaporative fraction (EF) remains constant during at least the central hours of the day and that the product of EF times the daily total net radiation gives a satisfactory estimate of daily total ET. The impact of cloud cover is rarely discussed. In this paper, we used data collected at two experimental sites in the Heihe River basin in northwestern China: Arou with grassland in an alpine region and Yingke with agricultural crops in a semi-arid region. Two methods were evaluated to determine daily total ET with instantaneous observations: a) self-conservation of evaporative fraction (EF_const); b) assuming the diurnal course of ET is the same sinusoidal function of the time of the instantaneous observation as the solar irradiance (Rs) (ET-Rs). Daily ET calculated with the two methods were evaluated against observed daily values. The results showed that these assumptions did not hold and the accuracy of ET estimates obtained with either method was reduced by: a) diurnal variation of ET and b) the time lag between ET and net radiation under clear skies. Larger errors occurred when applying both methods under cloudy conditions during the growing season, while in the remaining part of the year the impact of cloud cover was lower.

Impact of Cloud Cover on Global UV Irradiance over Baghdad, Iraq

Six months of continuous of hourly records of Ultraviolet irradiance recorded at Baghdad, (33.34 o N, 44.45 o E, 34 m a.m.s.l.), Iraq, were combined with concurrent synoptic cloud observations to investigate the relative influence of clouds on UV irradiance. The ratio of UV irradiance to the total solar irradiance increases with cloud cover, especially for cloud cover greater than 4 octas, In order to determine the effect of cloud on UV irradiance, a cloud modification factor was considered, it is defined as the ratio between the UV measurements and the corresponding clear sky UV irradiance that would be expected for the same time period and atmospheric conditions. It was shown that the effect of cloud with 4 octas increases demonstrating the spectral dependence of the cloud radiative extinction, while the impact of cloud cover less than 4 octas is relatively constant and ranged between (3.6 - 4.3%). Broadband solar irradiance (0.3-3 µm), global, ultraviolet global irradiance, photo synthetically active irradiance (0.4-0.7 µm) and other meteorological variables were continuously recorded for the period between first of October 1994 and 30 March 1995 in the Radiometric Station of the Center of Energy and Environment Researches (33.34 0 N, 44.45 0 E, 34 m a.m.s.l.), in Baghdad, Iraq. The measurements were taken every 10 minutes. Solar global irradiance was measured using Eppely pyranometer, An Eppley TUVR radiometer was used to measure the ultraviolet irradiance (0.29-0.385 µm) on a horizontal surface. Air temperature and relative humidity were also recorded for the same period. From this database, hourly values have been generated for the mentioned period to guarantee that a wide range of seasonal conditions and solar elevation angles are covered. It is important to point out that there are significant differences in temporal and cosine response between the radiometers used for the measurements of UV and broadband solar irradiance. Consequently hourly values have been computed, in order to reduce the temporal effects that could be introduced in obtaining the ratio of UV radiation to broadband solar radiation. These undesirable effects can reach quite a significant level, especially under highly changing conditions, which are usually associated with broken cloud fields. III. RESULTS AND DISCUSSION

Persistent solar signatures in cloud cover: spatial and temporal analysis

A consensus regarding the impact of solar variability on cloud cover is far from being reached. Moreover, the impact of cloud cover on climate is among the least understood of all climate components. This motivated us to analyze the persistence of solar signals in cloud cover for the time interval 1984–2009, covering two full solar cycles. A spatial and temporal investigation of the response of low, middle and high cloud data to cosmic ray induced ionization (CRII) and UV irradiance (UVI) is performed in terms of coherence analysis of the two signals. For some key geographical regions the response of clouds to UVI and CRII is persistent over the entire time interval indicating a real link. In other regions, however, the relation is not consistent, being intermittent or out of phase, suggesting that some correlations are spurious. The constant in phase or anti-phase relationship between clouds and solar proxies over some regions, especially for low clouds with UVI and CRII, middle clouds with UVI and high clouds with CRII, definitely requires more study. Our results show that solar signatures in cloud cover persist in some key climate-defining regions for the entire time period and supports the idea that, if existing, solar effects are not visible at the global level and any analysis of solar effects on cloud cover (and, consequently, on climate) should be done at the regional level.

Tracking seasonal changes in vegetation phenology with a SunScan canopy analyzer in northwestern England

This paper explores the changes in the phenological trends of vegetation through measurement of biophysical properties of leaf area index/plant area index (LAI/PAI) over time in two contrasting vegetation canopies of broadleaf woodland and coniferous forests in the northwest of England for a period of 13 months in the year 2005/06. These biophysical variables were measured at 2 m intervals along 60 m cross-transects at both study sites and a validation site was chosen to test the impact of cloud cover on the measurements. Measurement errors were determined at the three sites and these data were used to ensure the reliability of the biophysical measurements throughout the study period. The results show that the SunScan canopy analyzer actually measures plant area index (PAI) but “effective” leaf area index (LAI) can be estimated for broadleaf canopy by subtracting measurement when there are no leaves from the other measurements when there are leaves. The seasonal variations of biophysical estimates derived can describe the phenological trends of LAI in a broadleaf canopy, but the results of “effective” PAI in both broadleaf and coniferous canopies were subject to larger measurement errors due to the inability of the SunScan canopy analyzer to distinguish between photosynthetic and non-photosynthetic tissues. It is concluded that the SunScan canopy analyzer can estimate “effective” LAI that will be appropriate in providing datasets for environmentally driven processes.

Using SunScan Canopy Analyzer to Assess Seasonal Changes in Vegetation Biophysical Parameters in the Northwestern England

This study investigates the variations of leaf area index (LAI) and plant area index (PAI) over time in broadleaf woodland and coniferous forest study sites in the northwest of England. Field measurements were carried out with a sunscan canopy analyzer for a period of thirteen months in the year 2005/06. This biophysical parameter was measured at 2m interval along 60m cross transects in both study sites and a validation site was chosen to test the impact of cloud cover on the measurements. Measurement errors were determined at the three sites and these data were used to ensure consistency of the biophysical measurements throughout the study period. The results show that this instrument actually measures plant area index (PAI) but leaf area index (LAI) can be estimated for broadleaf canopy by subtracting measurement taken when there were no leaves from measurements taken when there were leaves. The seasonal variations of biophysical parameters derived can describe the phenological trends of LAI in a broadleaf canopy, but the results of PAI in both broadleaf and coniferous canopies were subject to larger measurement errors. Using optical instruments and physical principles of spectral reflectance of vegetation, it is concluded that, based on the theory of groundbased measurement methods SunScan canopy analyzer can estimate LAI that will be appropriate in providing datasets for monitoring vegetation change at a high temporally dynamic scale. The result can also be used as an important input in climate change and global warming models. Keywords-Variation; SunScan; Canopoly Analyzer; Vegetation; Biophisical

The Impact of Cloud Cover on Major League Baseball

Abstract Although it is often suggested that direct sunlight may affect a player’s vision, no published studies have analyzed this interaction. In this research, a variety of statistical tests were utilized to study how baseball variables respond to different cloud cover conditions. Data from more than 35 000 Major League Baseball games, spanning the seasons from 1987 through 2002, were studied. Eleven baseball variables covering batting, pitching, and fielding performance were included. Overall responses were analyzed, as well as individual responses at 21 different stadiums. Home and away team performances were evaluated separately. This study then synthesized the synergistic differences in offensive production, pitching performance, and fielding performance into changes in the “home field advantage.” Offensive production generally declines during clearer-sky daytime games compared to cloudy-sky daytime games, while pitching performance increases as conditions become clearer. Strikeouts show the strongest response in the study, increasing from 5.95 per game during cloudy-sky conditions to 6.40 per game during clear-sky conditions. The number of errors per game increases during clear-sky daytime games compared to cloudy-sky daytime games, while fly outs increase and ground outs decrease between daytime and nighttime games, regardless of the amount of cloud cover. Results at individual stadiums vary, with some stadiums displaying a very strong association between baseball performance and changes in cloud cover, while others display a weak association. All of these impacts affect the home field advantage, with the home team winning 56% of the games played under clear skies compared to 52.3% of the games played under cloudy skies.

The Impact of Canyon Geometry on Intra Urban and Urban: Suburban Night Temperature Differences Under Warm Weather Conditions

The present paper investigates the impact of canyon geometry on the temperature regime and nocturnal heat island development in the very dense urban area of Athens, Greece. Detailed measurements of air temperature have been carried out within three deep urban canyons of different aspect ratios (H/W = 3, 2.1 and 1.7) during the night period of the summer and autumn of 2007. An analysis was carried out to investigate the relative impact of the canyon geometry, the undisturbed wind velocity, ambient temperature, and cloud cover on the development of a nocturnal heat island. A clear increase of the median, maximum and minimum values of the cooling rates has been observed for decreasing aspect ratios. Under low ambient temperatures, high wind speeds correspond to a substantial rise of the cooling rate in the urban canyons mainly because of the increased convective losses. On the contrary, cooling rates decrease substantially under high-undisturbed wind speeds and ambient temperatures because of the important convective gains. The impact of cloud cover was found to be important as cloudy skies cause a substantial decrease of the cooling rates in the urban canyons. Comparisons were performed between the temperature data collected in the three studied urban canyons and temperatures recorded in an urban as well as a suburban open space station.

On the simulation of regional scale sublimation over boreal and agricultural landscapes in a climate model

In this study, a detailed evaluation of regional scale sublimation over two contrasting surface types is performed, based on observations and simulations from a regional climate model. New observed estimates of regional scale evaporative fractions (sublimation/precipitation) based on remotely sensed and gridded surface climate data suggest values of 0.16 and 0.09 respectively for boreal forest and agricultural regions during midwinter. While not dominating the water balance, this does indicate that sublimation is a significant component at the regional scale. On the other hand, simulated results were substantially less: 0.02 and ‐0.02 (i.e., net vapour deposition) respectively. Further analysis revealed that in both cases a net vapour deposition onto the ground snowpack was found, though in the forested case this was offset by a positive vapour flux off the canopy yielding a small net positive flux overall. Even over the agricultural region, sublimation was simulated during daytime in January, but this was overwhelmed by night‐time frost, resulting in a net daily vapour deposition. The source of the surface vapour flux bias was further investigated. An attempt was made to enhance sublimation by increasing the sensible heat flux based on the “windless exchange” concept, which has been found helpful in studies of stand‐alone snowpack models. However, in the coupled atmosphere‐land surface model used here, increases in sensible heat flux into the snow were largely offset by increases in upward surface longwave flux: the net impact on sublimation and surface temperature bias was small. A proposed cold snow‐vapour deposition feedback mechanism, under clear sky conditions, was determined to be unlikely for the simulation under consideration. The impact of cloud cover appears to be much more relevant to our simulation of the surface energy balance over snow. Satellite and limited surface radiation observations suggest that insufficient cloud radiative forcing simulated in the model was responsible for the excessive night‐time frost.

Impact of Cloud Cover on Solar Radiative Biases in Deep Convective Regimes

Abstract Conflicting claims have been made concerning the magnitude of the bias in solar radiative transfer calculations when horizontal photon transport is neglected for deep convective scenarios. The difficulty of obtaining a realistic set of cloud scenes for situations of complex cloud geometry, while certain characteristics such as total cloud cover are systematically controlled, has hindered the attempt to reach a consensus. Here, a simple alternative approach is adopted. An ensemble of cloud scenes generated by a cloud resolving model are modified by an idealized function that progressively alters the cirrus anvil coverage without affecting the realism of the scene produced. Comparing three-dimensional radiative calculations with the independent column approximation for all cloud scenes, it is found that the bias in scene albedo can reach as much as 22% when the sun is overhead and 46% at low sun angles. The bias is an asymmetrical function of cloud cover with a maximum attained at cirrus anvil cloud cover of approximately 30%–40%. With a cloud cover of 15%, the bias is half its maximum value, while it is limited for coverage exceeding 80%. The position of the peak occurs at the cloud cover coinciding with the maximum number of independent clouds present in the scene. Increasing the cloud cover past this point produces a decrease in the number of isolated clouds because of cloud merging, with a consequential bias reduction. With this systematic documentation of the biases as a function of total cloud cover, it is possible to identify two contributions to the total error: the geometrical consequences of the effective cloud cover increase at low sun angles and the true 3D scattering effect of photons deviating from the original path direction. An attempt to account for the former geometrical contribution to the 1D bias is made by performing a simple correction technique, whereby the field is sheared by the tangent of the solar zenith angle. It is found that this greatly reduces the 1D biases at low sun angles. Because of the small aspect ratio of the cirrus cloud deck, the remaining bias contribution is small in magnitude and almost independent of solar zenith angle.

The impact of cloud cover on the net radiation budget of the Greenland ice sheet

AbstractEnergy-balancemodels driven by radiation and turbulent heat fluxes have been widely applied to predicting the response of the Greenland ice sheet to climate change. However, a lack of knowledge of the temporal and spatial distribution of cloud amount and type has necessitated the use of parameterizations or statistical models of cloud cover. This deficiency results in large uncertainties in both shortwave and longwave radiation fluxes. Stereo-matching of nadir and forward view AlongTrack Scanning Radiometer-2 (ATSR-2) image pairs has been shown to be a reliable method of retrieving cloud top height, and further cloud properties can be derived from thermal imagery allowing classification into cloud type. A 1 year cloud record for a transect across southern Greenland derived from stereo-matching is presented here, and comparisons are made with climate re-analysis data and ground observations. The cloud-cover data were used in a simple radiative transfer model, and the impact of clouds on the net radiation fluxes was found to be considerable. Different cloud scenarios produced up to 40 Wm–2 difference in net radiation balance. In the ablation zone, where the albedo is lower and most variable, the sensitivity to cloud-cover fraction was less marked, but the higher spatial resolution of the ATSR-2 cloud record was reflected by a much more varied trend in radiation balance. Whether the net radiation balance increases or decreases with increased cloud cover was found to be a function of the cloud amount and type and also the surface albedo. The sensitivity of the model to a ±5% change in cloud amount was found to be comparable to a 1 K change in temperature. This clearly demonstrates the importance of reliable, quantitative cloud data in mass-balance and other glaciological studies.