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Kikaj, D., T. Kovács, and J. Vaupotič. "ROLE OF METEOROLOGY AND LITHOLOGY IN THE TEMPORAL VARIATION OF THE OUTDOOR RADON LEVEL." Radiation Protection Dosimetry 184, no. 3-4 (May 28, 2019): 474–78. http://dx.doi.org/10.1093/rpd/ncz079.
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Abstract The outdoor radon concentration was monitored together with the meteorological parameters at two contrasting complex topographies: sub-Alpine basin (SA) and sub-Mediterranean valley (SM) in winter (December 2017–February 2018) and summer (June–August 2018). The time series for each site and each season are evaluated in three different ways: (i) clear-sky and cloudy condition together, (ii) clear-sky conditions only (cloud cover <20%) and (iii) cloudy condition only (cloud cover >20%), and compared to the expected atmospheric boundary layer (ABL) ‘mixing volume’ caused by meteorological changes. The results have confirmed the sensitivity of diurnal and seasonal radon concentration to the expected ABL ‘mixing volume’ at the two selected sites. The relationship is more pronounced in calm clear-sky conditions. Cloudy conditions are associated with fast weather changes, when the ABL is well mixed and hourly mean radon concentrations do not follow the typical diurnal trend.
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Tye, Mari R., Sue Ellen Haupt, Eric Gilleland, Christina Kalb, and Tara Jensen. "Assessing Evidence for Weather Regimes Governing Solar Power Generation in Kuwait." Energies 12, no. 23 (November 20, 2019): 4409. http://dx.doi.org/10.3390/en12234409.
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With electricity representing around 20% of the global energy demand, and increasing support for renewable sources of electricity, there is also an escalating need to improve solar forecasts to support power management. While considerable research has been directed to statistical methods to improve solar power forecasting, few have employed finite mixture distributions. A statistically-objective classification of the overall sky condition may lead to improved forecasts. Combining information from the synoptic driving conditions for daily variability with local processes controlling subdaily fluctuations could assist with forecast validation and enhancement where few observations are available. Gaussian mixture models provide a statistical learning approach to automatically identify prevalent sky conditions (clear, semi-cloudy, and cloudy) and explore associated weather patterns. Here a first stage in the development of such a model is presented: examining whether there is sufficient information in the large-scale environment to identify days with clear, semi-cloudy, or cloudy conditions. A three-component Gaussian distribution is developed that reproduces the observed multimodal peaks in sky clearness indices, and their temporal distribution. Posterior probabilities from the fitted mixture distributions are used to identify periods of clear, partially-cloudy, and cloudy skies. Composites of low-level (850 hPa) humidity and winds for each of the mixture components reveal three patterns associated with the typical synoptic conditions governing the sky clarity, and hence, potential solar power.
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Gao, Bo, Huili Gong, Tianxing Wang, and Li Jia. "Reconstruction of MODIS Spectral Reflectance under Cloudy-Sky Condition." Remote Sensing 8, no. 9 (September 9, 2016): 727. http://dx.doi.org/10.3390/rs8090727.
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Li, Danny H. W., and Chris C. S. Lau. "An Analysis of Nonovercast Sky Luminance Models Against Hong Kong Data." Journal of Solar Energy Engineering 129, no. 4 (November 4, 2006): 486–93. http://dx.doi.org/10.1115/1.2770756.
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Daylighting is an important issue in modern architecture that has been characterized by the use of curtain walls in buildings. Nonovercast skies, including clear and partly cloudy days, are essential because they may occur more frequently for places such as in equatorial regions and the tropics. Better understanding of nonovercast sky luminance distribution is vital to estimate the dynamic variation in daylight illuminance as sky condition and solar position change. This paper presents the work on the evaluation of six clear sky and three partly cloudy sky models against three-year (1999–2001) measured Hong Kong sky luminance data. The general features and characteristics for the models were described and assessed. The nonovercast sky conditions were identified using the ratio of zenith luminance (Lz) to diffuse illuminance (Dv) and the ratio of global illuminance (Gv) to the extraterrestrial illuminance (Ev). Subsequent interpretations of the clear skies into high and low turbid types were conducted in conjunction with the cloud cover (CLD) and the luminous turbidity (Tv), and partly cloudy skies were further subdivided into thin and thick cloud modes using sunshine hour (SH) and global irradiance (GSI). A statistical analysis of the models revealed that the Gusev model (i.e., CIE (Internal Commission on Illumination) polluted sky No. 13) and the model by Chen et al. (1999, “Luminance Distribution Model of Intermediate Skies,” Zhaom Ing Gong Chen Xuebao, 10(1), pp. 59–63 (in Chinese)) developed using artificial neural network (ANN) theory with the measured data in Chongqing, China (29.6degN and 106.5degE) showed the best predictions for sky luminance at this location under the clear and partly cloudy sky conditions, respectively.
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Wei, Jiahua, Yang Shi, Yan Ren, Qiong Li, Zhen Qiao, Jiongwei Cao, Olusola O. Ayantobo, Jianguo Yin, and Guangqian Wang. "Application of Ground-Based Microwave Radiometer in Retrieving Meteorological Characteristics of Tibet Plateau." Remote Sensing 13, no. 13 (June 28, 2021): 2527. http://dx.doi.org/10.3390/rs13132527.
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The characteristics of plateau precipitation and atmosphere, once accurately and comprehensively understood, can be used to inform sound air–water resource development practices. In this study, atmospheric exploration of the Tibet Plateau (TP) was conducted using ground-based microwave radiometer (MWR) data collected during the East Asian summer monsoon. Atmospheric temperature, pressure, humidity, and other variables were gathered under clear-sky, cloudy-sky, and rainy-sky conditions. Statistical characteristics of the air parcel height and stability/convection indices such as convective available potential energy (CAPE) and convective inhibition (CIN) were investigated, with a special focus on the rainy-sky condition. Two retrieval applications for characterizing precipitation, namely short-term precipitation forecast and quantitative precipitation estimation were presented. Results showed that CAPE values in the Darlag region reached extremes around 18:00–20:00 (UTC+8) for cloudy-sky and rainy-sky conditions with corresponding peaks of about 1046.56 J/kg and 703.02 J/kg, respectively. When stratiform or convective–mixed precipitation occurs, the precipitable water vapor (PWV) and CAPE values were generally greater than 1.7 cm and 1000 J/kg, respectively. CAPE values are likely to decrease before the occurrence of precipitation due to the release of the latent heat in the atmosphere.
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Wibun, Anuchit, and Pipat Chaiwiwatworakul. "An Estimation of Thailand's Hourly Solar Radiation Using Markov Transition Matrix Method." Applied Mechanics and Materials 839 (June 2016): 29–33. http://dx.doi.org/10.4028/www.scientific.net/amm.839.29.
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To estimate global solar radiation from easy available weather forecast data (sky condition), Markov model is used for this estimation. The five-year (1996-2000) global radiation data that are taken at an hour intervals from Nakhon Pathom station, Thailand (latitude 13.81ºN and longitude 100.04ºE) are used to construct the Markov transition matrices. The global radiation sequences in 2000 will be generated by based on the characteristic probability of moving global radiation values which were observed from the obtained data during 1996-1999. The autocorrelation function is used for checking the order of probability of moving obtained data. In this study, the five first and five second-order Markov transition matrices (MTMs), which are selected from the autocorrelation functions, are constructed, each MTMs will be used for generating global radiation values in each day with different sky conditions (clear, partly cloudy, mostly cloudy, cloudy and overcast). From the results of comparison between the statistical characteristics of observed and two synthetic generated data, global radiation data behavior slightly improved by the second order Markov model.
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Sohn, Byung-Ju, Johannes Schmetz, Rolf Stuhlmann, and Joo-Young Lee. "Dry Bias in Satellite-Derived Clear-Sky Water Vapor and Its Contribution to Longwave Cloud Radiative Forcing." Journal of Climate 19, no. 21 (November 1, 2006): 5570–80. http://dx.doi.org/10.1175/jcli3948.1.
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Abstract In this paper, the amount of satellite-derived longwave cloud radiative forcing (CRF) that is due to an increase in upper-tropospheric water vapor associated with the evolution from clear-sky to the observed all-sky conditions is assessed. This is important because the satellite-derived clear-sky outgoing radiative fluxes needed for the CRF determination are from cloud-free areas away from the cloudy regions in order to avoid cloud contamination of the clear-sky fluxes. However, avoidance of cloud contamination implies a sampling problem as the clear-sky fluxes represent an area drier than the hypothetical clear-sky humidity in cloudy regions. While this issue has been recognized in earlier works this study makes an attempt to quantitatively estimate the bias in the clear-sky longwave CRF. Water vapor amounts in the 200–500-mb layer corresponding to all-sky condition are derived from microwave measurements with the Special Sensor Microwave Temperature-2 Profiler and are used in combination with cloud data for determining the clear-sky water vapor distribution of that layer. The obtained water vapor information is then used to constrain the humidity profiles for calculating clear-sky longwave fluxes at the top of the atmosphere. It is shown that the clear-sky moisture bias in the upper troposphere can be up to 40%–50% drier over convectively active regions. Results indicate that up to 12 W m−2 corresponding to about 15% of the satellite-derived longwave CRF in tropical regions can be attributed to the water vapor changes associated with cloud development.
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Pagès, D., J. Calbó, and J. A. González. "Using routine meteorological data to derive sky conditions." Annales Geophysicae 21, no. 3 (March 31, 2003): 649–54. http://dx.doi.org/10.5194/angeo-21-649-2003.
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Abstract. Sky condition is a matter of interest for public and weather predictors as part of weather analyses. In this study, we apply a method that uses total solar radiation and other meteorological data recorded by an automatic station for deriving an estimation of the sky condition. The impetus of this work is the intention of the Catalan Meteorological Service (SMC) to provide the public with real-time information about the sky condition. The methodology for deriving sky conditions from meteorological records is based on a supervised classification technique called maximum likelihood method. In this technique we first need to define features which are derived from measured variables. Second, we must decide which sky conditions are intended to be distinguished. Some analyses have led us to use four sky conditions: (a) cloudless or almost cloudless sky, (b) scattered clouds, (c) mostly cloudy – high clouds, (d) overcast – low clouds. An additional case, which may be treated separately, corresponds to precipitation (rain or snow). The main features for estimating sky conditions are, as expected, solar radiation and its temporal variability. The accuracy of this method of guessing sky conditions compared with human observations is around 70% when applied to four sites in Catalonia (NE Iberian Peninsula). The agreement increases if we take into account the uncertainty both in the automatic classifier and in visual observations.Key words. Meteorological and atmospheric dynamics (instruments and techniques; radiative processes) – Atmospheric composition and structure (cloud physics and chemistry)
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Molod, A., H. Salmun, and M. Dempsey. "Estimating Planetary Boundary Layer Heights from NOAA Profiler Network Wind Profiler Data." Journal of Atmospheric and Oceanic Technology 32, no. 9 (September 2015): 1545–61. http://dx.doi.org/10.1175/jtech-d-14-00155.1.
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AbstractAn algorithm was developed to estimate planetary boundary layer (PBL) heights from hourly archived wind profiler data from the NOAA Profiler Network (NPN) sites located throughout the central United States. Unlike previous studies, the present algorithm has been applied to a long record of publicly available wind profiler signal backscatter data. Under clear-sky conditions, summertime averaged hourly time series of PBL heights compare well with Richardson number–based estimates at the few NPN stations with hourly temperature measurements. Comparisons with estimates based on clear-sky reanalysis show that the wind profiler (WP) PBL heights are lower by approximately 250–500 m. The geographical distribution of daily maximum PBL heights corresponds well with the expected distribution based on patterns of surface temperature and soil moisture. Wind profiler PBL heights were also estimated under mostly cloudy-sky conditions, and are generally comparable to the Richardson number–based PBL heights and higher than the reanalysis PBL heights. WP PBL heights have a smaller clear–cloudy condition difference than either of the other two. The algorithm presented here is shown to provide a reliable summertime climatology of daytime hourly PBL heights throughout the central United States.
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Yoshimura, M., and M. Yamashita. "A Consideration for the Light Environmental Modeling under Tropical Rainforest Canopies." ISPRS - International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences XL-7 (September 19, 2014): 217–20. http://dx.doi.org/10.5194/isprsarchives-xl-7-217-2014.
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Photosynthetic Active Radiation (PAR) is the most important light source for plant photosynthesis. It is known that most of PAR from solar radiation is well absorbed by the surface. The canopy is the surface in forest region, consists an aboveground portion of plant community and formed by plant crowns. On the other hand, incident solar radiation is fluctuating at all times because of fluctuating sky conditions. Therefore, qualitative light environmental measurements in forest are recommended to execute under stable cloudy condition. In fact, it is quite a few opportunities to do under this sky condition. It means that the diffuse light condition without the direct light is only suitable for this measurement. <br><br> In this study, we challenged the characterization the forest light environment as its representativeness under no consideration of sky conditions through analysis huge quantities of instantaneous data which obtained under the different sky conditions. All examined data were obtained under the different sky conditions at the tropical rainforest canopy as one of the typical fluctuating sky conditions regions. An incident PAR is transmitted and scattered by different forest layers at different heights. Various PAR data were measured with quantum units as Photosynthetic Photon Flux Density (PPFD) at different forest heights by the quantum sensors. By comparing PPFDs at different heights with an incident PPFD, relative PPFDs were calculated, which indicate the degree of PPFD decrease from the canopy top to lower levels. As the results of these considerations, daily averaging is confirmed to be cancelled sky fluctuating influences.
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Conway, J. P., and N. J. Cullen. "Cloud effects on the surface energy and mass balance of Brewster Glacier, New Zealand." Cryosphere Discussions 9, no. 1 (February 18, 2015): 975–1019. http://dx.doi.org/10.5194/tcd-9-975-2015.
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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.
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Hall, Timothy J., Rachel N. Thessin, Greg J. Bloy, and Carl N. Mutchler. "Analog Sky Condition Forecasting Based on a k-nn Algorithm." Weather and Forecasting 25, no. 5 (October 1, 2010): 1463–78. http://dx.doi.org/10.1175/2010waf2222372.1.
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Abstract Very short-range, cloudy–clear sky condition forecasts are important for a variety of military, civil, and commercial activities. In this investigation, an approach based on a k-nearest neighbors (k-nn) algorithm was developed and implemented to query a historical database to identify historical analogs matching the features of a specific instance. This ensemble of analogs was then used to make a probabilistic, clear-sky condition forecast for 1, 2, 3, 4, and 5 h into the future, for local and regional target types in two geographically distinct regions within the continental United States. The analogs were identified in a database comprised of a multiyear, half-hourly time series of atmospheric features that included cloud features identified in weather satellite imagery and meteorological variables extracted or derived from data-assimilation-based model analyses generated by NCEP’s Eta Data Assimilation System. The analog forecast scheme’s performance exceeded persistence at all five forecast intervals for both target types in both regimes based on a group of metrics including the relative operating characteristic (ROC) score, sharpness, accuracy, skill, expected normalized best cost, and reliability.
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Munar, Edwin Andres Villagran, and Carlos Ricardo Bojaca Aldana. "Numerical evaluation of passive strategies for nocturnal climate optimization in a greenhouse designed for rose production (Rosa spp.)." Ornamental Horticulture 25, no. 4 (December 2019): 351–64. http://dx.doi.org/10.1590/2447-536x.v25i4.2087.
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Abstract In passive plastic greenhouses that do not have heating systems, the phenomenon of thermal inversion occurs, which means that the temperature inside the greenhouse is lower than the outdoor environment; therefore, the plants are exposed to thermal conditions that are unsuitable for production. The aim of this work was to evaluate passive air climatization alternatives seeking to optimize the nocturnal microclimate of a multi-tunnel Gothic greenhouse projected for rose production in Bogota savannah. The experimental approach included the use of a CFD-2D simulation model successfully validated by recording and archive of temperature data in a greenhouse. A total of 24 steady-state simulations were developed that included 3 nighttime temperature values, 2 sky conditions and 4 greenhouse configurations. The results showed that under the clear sky condition there was a thermal inversion with a value of −0.53 and −1.11 °C for the standard night-time greenhouse configuration. The installation of a thermal screen and porous mesh in the fixed roof vents allowed to control the presence of thermal inversion under clear sky conditions and optimizing the indoor temperature value in the greenhouse under cloudy sky conditions.
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Conway, J. P., and N. J. Cullen. "Cloud effects on surface energy and mass balance in the ablation area of Brewster Glacier, New Zealand." Cryosphere 10, no. 1 (February 10, 2016): 313–28. http://dx.doi.org/10.5194/tc-10-313-2016.
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Abstract. The effect of clouds on glacier surface energy balance (SEB) has received increased attention in the last decade, but how clouds interact with other meteorological forcing to influence surface mass balance (SMB) is not as well understood. This paper resolves the SEB and SMB at a site in the ablation zone of Brewster Glacier over a 22-month period, 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 a minimal change in air temperature and wind speed. During overcast conditions, positive net long-wave 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 changes in precipitation phase that created a strong albedo feedback. During the spring and autumn seasons, the sensitivity during overcast conditions was strongest. To capture these processes, future attempts to explore glacier–climate interactions should aim to resolve the effects of atmospheric moisture (vapour, cloud, and precipitation) on melt as well as accumulation, through enhanced statistical or physically based methods.
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Apeh, Oliver O., Ochuko K. Overen, and Edson L. Meyer. "Monthly, Seasonal and Yearly Assessments of Global Solar Radiation, Clearness Index and Diffuse Fractions in Alice, South Africa." Sustainability 13, no. 4 (February 17, 2021): 2135. http://dx.doi.org/10.3390/su13042135.
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The constant scheduled load shedding in South Africa has commonly been executed in an attempt to maintain the long aging coal power plants in the country. With the rise in the reduction of fossil fuels, efforts to eradicate environmental hazards of carbon through solar photovoltaic (PV) resources to their complete prospect are in progress. South Africa, and in particular the town Alice, acquires sunshine annually, making it appropriate to harvest solar energy. This work aims to characterize solar radiation, clearness index (Kt), and diffuse fraction (Kd) in Alice, South Africa. Hourly global and diffuse solar irradiance were estimated into monthly, seasonal, and yearly variations of Kt and Kd for the years 2017–2020. The range of values for describing the daily classification of sky condition was centered on earlier studies. The cumulative frequency and frequency distribution of daily Kt was analyzed statistically in an individual month. The analyses show that the average percentage frequency of Kt within the period is 11.72% of the cloudy days, 57% of partially cloudy days, and 31.28% of clear sky days. The findings of this research show that Alice remains a key contender for solar energy conversion location, owing to its reasonably high frequency (Kt > 0.40) of clear and partially cloudy skies. Hence, it is essential to establish energy-efficiency for energy consumption and also for daily performances.
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O’Brien, D. M., Igor Polonsky, Philip Stephens, and Thomas E. Taylor. "Feasibility of Cloud Screening Using Proxy Photon Pathlength Distributions Derived from High-Resolution Spectra in the Near Infrared." Journal of Atmospheric and Oceanic Technology 27, no. 1 (January 1, 2010): 135–46. http://dx.doi.org/10.1175/2009jtecha1340.1.
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Abstract High-resolution spectra of reflected sunlight in the 2-μm absorption band of CO2 are simulated at the top of the atmosphere using cloud profiles and particle sizes from CloudSat analyzed meteorology from ECMWF, surface bidirectional distribution functions over land derived from the Moderate Resolution Imaging Spectroradiometer (MODIS), and a facet model of ocean reflectance. It is argued that in clear sky the photons will follow the direct path from sun to surface to satellite, because Rayleigh scattering is negligible at 2 μm, so the distribution of photon pathlengths will be a δ function. A proxy for the photon pathlength distribution under any sky condition is recovered from the high-resolution spectrum by representing the distribution as a weighted sum of δ functions. Scenes are classified as clear or cloudy according to how closely the distribution approximates the ideal single δ function for the direct path. The algorithm has an efficiency of approximately 75%, meaning that 25% of the clear cases will be rejected as cloudy. For scenes that pass the clear-sky test, the probability that the prediction will be correct is typically 95%. The algorithm appears to be robust, insensitive to instrument noise and to errors in the surface pressure and profiles of temperature and water vapor. The efficiency and confidence level of the algorithm are almost unchanged for bright surfaces such as sun glint.
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Rimasilana, Dea, and Muhammad Irfan Islami. "Seasonal Characteristic of Sky Conditions based on Clearness Index on Aceh Besar." Buletin GAW Bariri 3, no. 2 (December 27, 2022): 32–40. http://dx.doi.org/10.31172/bgb.v3i2.76.
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Knowledge of the sky conditions in particular location is a fundamental to studies about climate and has applications for meteorology, industry, agriculture, architecture, engineering, studies of water resources development and solar energy conversion system. These conditions can be quantified by meteorological parameter such as the clearness index. Clearness index ( is defined as the ratio of global solar irradiance measured at ground level and its counterpart the extra – terrestrial radiation at the top of the atmosphere. In this study, seasonal characteristic of sky condition in Aceh Besar (05.4°S and 95.46°W) has been carried out using . One year (Jan 2020 – Dec 2020) measured data of daily average global radiation has been used to determines the daily and monthly variations of. The result shows that for daily averages, ranges from 0.19 to 0.70 with cloudy days are common days in Aceh Besar with hardly any very clear days. For monthly average, the month of January shows the highest (0.55), while November shows the lowest (0.41). Based on monthly averages of the daily, monthly percentage cumulative frequency, and climatic conditions, the sky condition in Aceh Besar is classified into two seasonal periods. The dry season (January – March and June – September) has values ranging between 0.44 and 0.55, while the wet season (April – May and October – December) has ranging between 0.44 and 0.45.
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Wu, Ting-Chi, Milija Zupanski, Lewis D. Grasso, Christian D. Kummerow, and Sid-Ahmed Boukabara. "All-Sky Radiance Assimilation of ATMS in HWRF: A Demonstration Study." Monthly Weather Review 147, no. 1 (December 13, 2018): 85–106. http://dx.doi.org/10.1175/mwr-d-17-0337.1.
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Abstract Satellite all-sky radiances from the Advanced Technology Microwave Sounder (ATMS) are assimilated into the Hurricane Weather Research and Forecasting (HWRF) Model using the hybrid Gridpoint Statistical Interpolation analysis system (GSI). To extend the all-sky capability recently developed for global applications to HWRF, some modifications in HWRF and GSI are facilitated. In particular, total condensate is added as a control variable, and six distinct hydrometeor habits are added as state variables in hybrid GSI within HWRF. That is, clear-sky together with cloudy and precipitation-affected satellite pixels are assimilated using the Community Radiative Transfer Model (CRTM) as a forward operator that includes hydrometeor information and Jacobians with respect to hydrometeor variables. A single case study with the 2014 Atlantic storm Hurricane Cristobal is used to demonstrate the methodology of extending the global all-sky capability to HWRF due to ATMS data availability. Two data assimilation experiments are carried out. One experiment uses the operational configuration and assimilates ATMS radiances under the clear-sky condition, and the other experiment uses the modified HWRF system and assimilates ATMS radiances under the all-sky condition with the inclusion of total condensate update and cycling. Observed and synthetic Geostationary Operational Environmental Satellite (GOES)-13 data along with Global Precipitation Measurement Mission (GPM) Microwave Imager (GMI) data from the two experiments are used to show that the experiment with all-sky ATMS radiances assimilation has cloud signatures that are supported by observations. In contrast, there is lack of clouds in the initial state that led to a noticeable lag of cloud development in the experiment that assimilates clear-sky radiances.
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İnan Günaydın, Tuğba. "ANALYSIS OF THE ILLUMINANCE LEVEL IN A CLASSROOM FOR DIFFERNT SKY CONDITION." Euroasia Journal of Mathematics, Engineering, Natural & Medical Sciences 9, no. 20 (March 25, 2022): 102–9. http://dx.doi.org/10.38065/euroasiaorg.936.
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Nowadays, due to the decrease in renewable energy sources on a global scale, studies for the effective use of energy and reducing energy consumption gain importance. Buildings have an extremely important role in energy consumption. Educational buildings, which are used for educational purposes, are important in terms of both the duration of use and the comfort level of the user. While the aim in educational institutions is to increase the level of user comfort, the main target is to increase the efficiency in educational activities. In energy consumption, the rate of consumption due to lighting is quite high. For this reason, effective and appropriate design of natural and artificial lighting is important in terms of both user efficiency and minimizing energy consumption. In lighting design, natural and artificial lighting should be considered in an integrated manner. The design should be started by considering daylight as the primary energy source. The homogeneous distribution of light in the space is as important as the average illumination level in the classroom. The light should spread homogeneously in the space in a way that provides equal efficiency to every user. In this study, the illuminance level of a selected classroom in Niğde Ömer Halisdemir University Faculty of Architecture was analyzed. In the selected workshop, measurements were made in the 5 weeks selected in November and December, at different times of the day and in different sky conditions, when the artificial lighting elements were on and off. In the case of the lamp on, generally sufficient average illuminance level can be met in all measurement hours, while it has been observed that sufficient average illuminance level is provided by turning on the lamps in the cloudy sky condition.
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Williamson, Scott N., David S. Hik, John A. Gamon, Jeffrey L. Kavanaugh, and Saewan Koh. "Evaluating Cloud Contamination in Clear-Sky MODIS Terra Daytime Land Surface Temperatures Using Ground-Based Meteorology Station Observations." Journal of Climate 26, no. 5 (February 27, 2013): 1551–60. http://dx.doi.org/10.1175/jcli-d-12-00250.1.
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Abstract Environment Canada meteorological station hourly sampled air temperatures Tair at four stations in the southwest Yukon were used to identify cloud contamination in the Moderate Resolution Imaging Spectroradiometer (MODIS) Terra clear-sky daytime land surface temperature (LST) and emissivity daily level-3 global 1-km grid product (MOD11A1, Collection 5) that is not flagged by the MODIS quality algorithm as contaminated. The additional cloud masking used qualitative ground-based sky condition observations, collected at two of the four stations, and coincident MODIS quality flag information. The results indicate that air temperature observed at a variety of discrete spatial locations having different land cover is highly correlated with MODIS LST collected at 1-km grid spacing. Quadratic relationships between LST and air temperature, constrained by ground observations of “clear” sky conditions, show less variability than relationships found under “mainly clear” and “mostly cloudy” sky conditions, and the more clouds observed in the sky coincides with a decreasing y intercept. Analysis of MODIS LST and its associated quality flags show a cold bias (<0°C) in the assignment of the ≤3-K-average LST error, indicating MODIS LST has a maximum average error of ≤2 K over a warm surface (>0°C). Analysis of two observation stations shows that unidentified clouds in MODIS LST are between 13% and 17%, a result that agrees well with previous studies. Analysis of daytime values is important because many processes are dependent on daylight and maximum temperature. The daytime clear-sky LST–Tair relationship observed for the good-quality confirmed cloud-free-sky MODIS LST quality flag can be used to discriminate cloud-contaminated grid cells beyond the standard MODIS cloud mask.
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Mehta, Sanjay Kumar, Devendra Ojha, Shyam Mehta, Devarajan Anand, Daggumati Narayana Rao, Vanmathi Annamalai, Aravindhavel Ananthavel, and Saleem Ali. "Thermodynamic structure of the convective boundary layer (CBL) over the Indian monsoon region during CAIPEEX campaigns." Annales Geophysicae 35, no. 6 (December 22, 2017): 1361–79. http://dx.doi.org/10.5194/angeo-35-1361-2017.
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Abstract. Spatial and temporal variability in the convective boundary layer (CBL) height for the Cloud Aerosol Interaction and Precipitation Enhancement Experiment (CAIPEEX) study period are examined using the data collected from high-resolution radiosondes during May–September 2009 over the Indian monsoon region. In total, 57 radiosonde launchings were carried out at ∼ 11:00–17:00 IST over six different stations covering a large geographical region, ranging from latitude ∼ 13 to 32° N and longitude 73 to 92° E. Of the total 57 launchings, 17 were made during cloudy conditions during which relative humidity (RH) was found to be greater than 83 % for an ∼ 1.0 km layer at various altitudes below 6 km. Within the layer the difference between saturated equivalent potential temperature and equivalent potential temperature is small, and it satisfies the condition that RH > 83 % for about 1 km is considered as the cloudy layer. There are eight cases when the cloud-topped boundary layer (CTBL) and 19 cases when fair-weather boundary layer (FWBL) is observed. The CBL heights are obtained using thermodynamic profiles, which vary from ∼ 0.4 to 2.5 km a. g. l. The formation of the cloud layers above the boundary layer generally lowers the CBL height and is responsible for its day-to-day variability. The development of the cloud beneath the boundary layer generally elevates the CBL, which is also responsible for the large day-to-day variability in the CBL. The FWBL identified using relative invariance of the thermodynamic profiles varies from ∼ 2.0 to 5.5 km, which is clearly marked by a local minimum in the refractivity gradient. During cloudy days, the CBL is found to be shallow and the surface temperature lower when compared to clear-sky days. The CBL and the lifting condensation level (LCL) heights are randomly related and are found to be at a lower height during cloudy days when compared to clear-sky days. Finally, the typical comparison between the CBL height obtained using thermodynamic profiles and backscattering profiles using Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) is examined.
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Putera, Alexander Kurniawan Sariyanto, Phika Ainnadya Hasan, and Muhammad Rizaldi Trias Jaya Putra Nurdin. "Relationship Between Bird Communities and Environmental Changes in Tandung Village, Tinambung District, Polewali Mandar Regency, West Sulawesi Province." MANILKARA: Journal of Bioscience 1, no. 2 (February 2, 2023): 08–17. http://dx.doi.org/10.33830/manilkara.v1i2.4654.2023.
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Indonesia's coastal region is known for its richness and diverse natural resources. However, the region is experiencing a transformation from mangrove ecosystems to the traditional pond cultures. This was happening in West Sulawesi that could damage the ecosystem in the long term, especially for the bird community. This study aims to inventory bird species in the bird community on the coast of Tandung Village, Tinambung District, Polewali Mandar Regency, West Sulawesi Province. In addition, we also study the bird community structure, find out the correlation among the bird communities, and the environmental condition during the inventory. In this study, we used a fixed-radius point count method to record birds. Field guide titled Burung-burung Pulau Paparan Sunda dan Wallacea di Kepulauan Indonesia was used to identify the species of observed birds. The results showed that of the 27 species recorded, there are 5 species with a high relative abundance, such as Egretta garzetta, Himantopus leucocephalus, Actitis hypoleucos, Ardeola speciosa, and Calidris ruficollis. Only H. leucocephalus is identified as a protected bird by the Indonesian government, while Calidris ruficollis is protected internationally as its conservational status (Near Threatened). The diversity index is moderate level, but it is decreasing day by day of observation, followed by the dominance index, evenness, and species richness. A high correlation between the two bird communities with two adjacent days of observation indicates similarity composition of community structure with different temporal scales and similar spatial scales. The map of environmental conditions shows changing weather in the period of observation sequentially from bright sky to cloudy and heavy rain and back to the normal bright sky at the last period of observation. The response of the bird community to the condition was by flying away when the weather is cloudy and rainy so that may decrease the diversity.
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Putera, Alexander Kurniawan Sariyanto, Phika Ainnadya Hasan, and Muhammad Rizaldi Trias Jaya Putra Nurdin. "Relationship Between Bird Communities and Environmental Changes in Tandung Village, Tinambung District, Polewali Mandar Regency, West Sulawesi Province." MANILKARA: Journal of Bioscience 2, no. 1 (February 2, 2023): 08–17. http://dx.doi.org/10.33830/manilkara.v2i1.4654.2023.
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Indonesia's coastal region is known for its richness and diverse natural resources. However, the region is experiencing a transformation from mangrove ecosystems to the traditional pond cultures. This was happening in West Sulawesi that could damage the ecosystem in the long term, especially for the bird community. This study aims to inventory bird species in the bird community on the coast of Tandung Village, Tinambung District, Polewali Mandar Regency, West Sulawesi Province. In addition, we also study the bird community structure, find out the correlation among the bird communities, and the environmental condition during the inventory. In this study, we used a fixed-radius point count method to record birds. Field guide titled Burung-burung Pulau Paparan Sunda dan Wallacea di Kepulauan Indonesia was used to identify the species of observed birds. The results showed that of the 27 species recorded, there are 5 species with a high relative abundance, such as Egretta garzetta, Himantopus leucocephalus, Actitis hypoleucos, Ardeola speciosa, and Calidris ruficollis. Only H. leucocephalus is identified as a protected bird by the Indonesian government, while Calidris ruficollis is protected internationally as its conservational status (Near Threatened). The diversity index is moderate level, but it is decreasing day by day of observation, followed by the dominance index, evenness, and species richness. A high correlation between the two bird communities with two adjacent days of observation indicates similarity composition of community structure with different temporal scales and similar spatial scales. The map of environmental conditions shows changing weather in the period of observation sequentially from bright sky to cloudy and heavy rain and back to the normal bright sky at the last period of observation. The response of the bird community to the condition was by flying away when the weather is cloudy and rainy so that may decrease the diversity.
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Rayati, Mohammad, Pasquale De Falco, Daniela Proto, Mokhtar Bozorg, and Mauro Carpita. "Generation Data of Synthetic High Frequency Solar Irradiance for Data-Driven Decision-Making in Electrical Distribution Grids." Energies 14, no. 16 (August 4, 2021): 4734. http://dx.doi.org/10.3390/en14164734.
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In this paper, we introduce a model representing the key characteristics of high frequency variations of solar irradiance and photovoltaic (PV) power production based on Clear Sky Index (CSI) data. The model is suitable for data-driven decision-making in electrical distribution grids, e.g., descriptive/predictive analyses, optimization, and numerical simulation. We concentrate on solar irradiance data since the power production of a PV system strongly correlates with solar irradiance at the site location. The solar irradiance is not constant due to the Earth’s orbit and irradiance absorption/scattering from the clouds. To simulate the operation of a PV system with one-minute resolution for a specific coordinate, we have to use a model based on the CSI of the solar irradiance data, capturing the uncertainties caused by cloud movements. The proposed model is based on clustering the days of each year into groups of days, e.g., (i) cloudy, (ii) intermittent cloudy, and (iii) clear sky. The CSI data of each group are divided into bins of magnitudes and the transition probabilities among the bins are identified to deliver a Markov Chain (MC) model to track the intraday weather condition variations. The proposed model is tested on the measurements of two PV systems located at two different climatic regions: (a) Yverdon-les-Bains, Switzerland; and (b) Oahu, Hawaii, USA. The model is compared with a previously published N-state MC model and the performance of the proposed model is elaborated.
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Nielsen, D. G., and M. J. Dunlap. "Efficacy of Insecticides Against Eastern Tent Caterpillar on Common Choke Cherry, Wayne County, Ohio, 1986." Insecticide and Acaricide Tests 13, no. 1 (January 1, 1988): 373. http://dx.doi.org/10.1093/iat/13.1.373a.
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Abstract Choke cherry, growing along roadsides, having at least 1 active nest of eastern tent caterpillar were used to evaluate insect growth regulators (IGRs). A KWH backpack mistblower operating at 0.5 throttle at aperture setting 3 was used to deliver 600 ml of finished spray to the dominant tent and surrounding foliage in each of 3 single-tree replicates/treatment. The sky was cloudy, temperature was 24°C, and there were gusty winds of 24-32 km/h during application on 7 May when larvae were 15-30 mm long. Treatment effectiveness was evaluated 2, 5, 7, and 14 days posttreatment by visually examining each nest for condition of larvae.
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Gao, Zhen, Ying Hou, Benjamin F. Zaitchik, Yongzhe Chen, and Weiping Chen. "A Two-Step Integrated MLP-GTWR Method to Estimate 1 km Land Surface Temperature with Complete Spatial Coverage in Humid, Cloudy Regions." Remote Sensing 13, no. 5 (March 4, 2021): 971. http://dx.doi.org/10.3390/rs13050971.
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There is an increasing demand for a land surface temperature (LST) dataset with both fine spatial and temporal resolutions due to the key role of LST in the Earth’s land–atmosphere system. Currently, the technique most commonly used to meet the demand is thermal infrared (TIR) remote sensing. However, cloud contamination interferes with TIR transmission through the atmosphere, limiting the potential of space-borne TIR sensors to provide the LST with complete spatio-temporal coverage. To solve this problem, we developed a two-step integrated method to: (i) estimate the 10-km LST with a high spatial coverage from passive microwave (PMW) data using the multilayer perceptron (MLP) model; and (ii) downscale the LST to 1 km and fill the gaps based on the geographically and temporally weighted regression (GTWR) model. Finally, the 1-km all-weather LST for cloudy pixels was fused with Aqua MODIS clear-sky LST via bias correction. This method was applied to produce the all-weather LST products for both daytime and nighttime during the years 2013–2018 in South China. The evaluations showed that the accuracy of the reproduced LST on cloudy days was comparable to that of the MODIS LST in terms of mean absolute error (2.29–2.65 K), root mean square error (2.92–3.25 K), and coefficients of determination (0.82–0.92) against the in situ measurements at four flux stations and ten automatic meteorological stations with various land cover types. The spatial and temporal analysis showed that the MLP-GTWR LST were highly consistent with the MODIS, in situ, and ERA5-Land LST, with the satisfactory ability to present the LST pattern under cloudy conditions. In addition, the MLP-GTWR method outperformed a gap-filling method and another TIR-PMW integrated method due to the local strategy in MLP and the consideration of temporal non-stationarity relationship in GTWR. Therefore, the test of the developed method in the frequently cloudy South China indicates the efficient potential for further application to other humid regions to generate the LST under cloudy condition.
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Ghazali, Syafii, and Refdinal Nazir. "Performance and Energy Saving Analysis of Grid Connected Photovoltaic in West Sumatera." International Journal of Power Electronics and Drive Systems (IJPEDS) 7, no. 4 (December 1, 2016): 1348. http://dx.doi.org/10.11591/ijpeds.v7.i4.pp1348-1354.
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<p>The paper presents performance and energy saving analysis of 1.25 kWp grid connected Photovoltaic system under difference weather condition in West Sumatera. The measured data were performed during weather data that often occur in West Sumatra i.e. sunny, overcast, raining and cloudy. The synchronizing process successfully done even bad weather conditions when sunlight was low automatically. Photovoltaic in average start producing power from 7:00 AM to 6:00 PM for normal or clear sky, however under overcast, raining and cloudy weather, the PV power decreased and disconnected earlier before sunset. During intermittent raining, overcast and cloud covered the PV power output show an irregular profile. The PV energy saving performed for three residential connection cases: 1300 VA, 900 VA with subsidized and 900 VA without subsidized. The solar PV installation have more benefits and energy saving for 1300 VA, 900 VA without subsidized with payback period around 8.5 years. However, the 900 VA with subsidized take longer 20.8 years, but still in PV lifespan 25 years. In the future, household subsidies may be reduced or eliminated, the solar energy will be viable alternative of energy resources when it can produce electricity at a cost equivalent to utility grid PLN rate. </p>
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Xu, Shuo, Jie Cheng, and Quan Zhang. "A Random Forest-Based Data Fusion Method for Obtaining All-Weather Land Surface Temperature with High Spatial Resolution." Remote Sensing 13, no. 11 (June 5, 2021): 2211. http://dx.doi.org/10.3390/rs13112211.
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Land surface temperature (LST) is an important parameter for mirroring the water–heat exchange and balance on the Earth’s surface. Passive microwave (PMW) LST can make up for the lack of thermal infrared (TIR) LST caused by cloud contamination, but its resolution is relatively low. In this study, we developed a TIR and PWM LST fusion method on based the random forest (RF) machine learning algorithm to obtain the all-weather LST with high spatial resolution. Since LST is closely related to land cover (LC) types, terrain, vegetation conditions, moisture condition, and solar radiation, these variables were selected as candidate auxiliary variables to establish the best model to obtain the fusion results of mainland China during 2010. In general, the fusion LST had higher spatial integrity than the MODIS LST and higher accuracy than downscaled AMSR-E LST. Additionally, the magnitude of LST data in the fusion results was consistent with the general spatiotemporal variations of LST. Compared with in situ observations, the RMSE of clear-sky fused LST and cloudy-sky fused LST were 2.12–4.50 K and 3.45–4.89 K, respectively. Combining the RF method and the DINEOF method, a complete all-weather LST with a spatial resolution of 0.01° can be obtained.
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Schade, Nils H., Andreas Macke, H. Sandmann, and C. Stick. "Enhanced solar global irradiance during cloudy sky conditions." Meteorologische Zeitschrift 16, no. 3 (June 21, 2007): 295–303. http://dx.doi.org/10.1127/0941-2948/2007/0206.
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Inoue, A., K. Yamamoto, and N. Mizoue. "Comparison of automatic and interactive thresholding of hemispherical photography." Journal of Forest Science 57, No. 2 (February 18, 2011): 78–87. http://dx.doi.org/10.17221/68/2010-jfs.
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This study presents the effects of operator bias and variation in interactive thresholding on the estimation of light environment using hemispherical photography. Twenty-one hemispherical photographs taken beneath a wide range of canopy densities were visually converted to binary images twice by 21 operators, and then the gap fraction was computed from the images. The interactive threshold varied greatly among the different operators and within a single operator, which resulted in a considerable operator bias and variation in the gap fraction. This study also compared three widely used automatic thresholding algorithms, which were installed in freely available software LIA for Win32 for analyzing hemispherical photography, with interactive thresholding using the same photographs. The median of the interactive threshold by repetitive interactive thresholdings from 21 operators was assumed to be correct for the comparison. The results indicated that MINIMUM was considered to be a better algorithm than the other ones installed in LIA32 when the gap fraction was over 10%. However, VARIANCE seemed to be superior to MINIMUM under the low gap fraction and the cloudy sky condition with dark and white clouds. This implied that MINIMUM or VARIANCE should be used for analyzing hemispherical photographs with LIA32. In conclusion, we need to pay attention to the selection of the automatic thresholding algorithm and the sky condition when taking hemispherical photographs.
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Duchon, Claude E., and Kenneth G. Hamm. "Broadband Albedo Observations in the Southern Great Plains." Journal of Applied Meteorology and Climatology 45, no. 1 (January 1, 2006): 210–35. http://dx.doi.org/10.1175/jam2317.1.
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Abstract Time series of daily broadband surface albedo for 1998 and 1999 have been analyzed from six locations in the network of 22 Atmospheric Radiation Measurement Program Solar–Infrared Radiation Stations distributed from central Kansas to central Oklahoma. Two of the stations are in Kansas, and four are in Oklahoma; together they reasonably encompass the variation in geography in the southern Great Plains. Daily precipitation totals locally measured or obtained from nearby Oklahoma Mesonet stations and time series of biweekly maximum normalized difference vegetation index obtained from NOAA’s Advanced Very High Resolution Radiometer were used to determine linkages between surface albedo and amount of precipitation and degree of green vegetation. As part of this determination, daily albedo was categorized according to sky condition, that is, clear, partly cloudy, or overcast, with appropriate boundaries for each category. The more notable results are the following: 1) 2-yr mean annual albedos varied by more than 20% among the six sites, the lowest albedo being 0.18 and the highest albedo being 0.22; 2) the numerical difference was about 4 times the maximum interannual mean difference among the six stations, indicating the importance of geographic location; 3) for sites with a large amount of bare soil, a systematic decrease in albedo in response to rainfall events and a systematic increase in albedo as the soil dried were observed; 4) at the one site with total vegetation cover, that is, no bare soil, albedo response to precipitation events was suppressed; 5) no relation was found between mean annual albedo and annual precipitation; 6) whether days were classified as clear or partly cloudy had little influence on daily albedo, but overcast days typically reduced albedo, sometimes substantially; and 7) the main contributor to low albedos on overcast days with rain was the wet surface; the contribution by the overcast sky was secondary.
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Kumar, Nishant, and Dharamveer Singh. "Study and Analysis of Different Absorber Geometry of Compound Parabolic Solar Collector and its Effect on Thermal Efficiency for Heating Water for Sanitary Use." International Journal for Research in Applied Science and Engineering Technology 10, no. 9 (September 30, 2022): 976–93. http://dx.doi.org/10.22214/ijraset.2022.46775.
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Abstract: This project is focused on carrying out a study of the absorber geometry of the parabolic solar collector compound for heating water for sanitary use, to evaluate the temperature gradient between the inlet and outlet of the water of this concentraDDDtor collector, and the efficiency achieved according to the absorber configuration to later compare it with collectors with a conventional flat absorber surface. The parabola of the reflector of the composite parabolic solar collector was obtained considering the circular absorber, with a concentration ratio of 4 plus 10% of this, to consider a truncation of the reflector, the circular absorber was configured with a small absorber plate of aluminum which has a thermal conductivity of 401 W /mK The values obtained experimentally in the collector were based on the data collected in the field files. It was considered to experience the heating of water on different days with the climatic conditions, cloudy, partially cloudy and sunny, with a totally clear sky. The water heating tests were carried out with two types of geometric configuration of the absorber of the composite parabolic solar collector; circular absorber and configured circular absorber, with which a water outlet temperature of 61 ° C and 76 ° C and a thermal efficiency of 60% respectively were obtained, these results were presented taking into account a climatic condition (sunny day) approximately the same for the two absorber configurations, and with average values of wind speed, ambient temperature and solar radiation.
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Kayombo, Canisius John, Tumaini Kivuyo, Richard A. Giliba, Sefania J. Kyando, Emmanuel Lugumira, and Hussein Said Gwau. "Movement, Feeding Behaviour and Threats of Colobus guereza Ruppellin at Seasonally Dry Riverine Forest of Engare-Olmotonyi and Arboreta of the Forestry Training Institute’s Olmotonyi’s Campus in Northern Highlands of Tanzania." East African Journal of Forestry and Agroforestry 5, no. 1 (February 10, 2022): 22–31. http://dx.doi.org/10.37284/eajfa.5.1.547.
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The observation of feeding and movement behaviour of wild fauna is significant in the process of understanding the ecosystems. The movement and feeding behaviour of An assessment on the movement, feeding behaviour, and threats of Colobus guereza was done in Engare-olmotonyi seasonally dry riverine forest and arboreta at the Forestry Training Institutes-Olmotonyi in northern Tanzania. The movement and feeding behaviour were monitored for 30 days from mid of September to October 2020. Sleeping and waking up times, trees fed by C. guereza, and trees they slept on were recorded and estimated for their height and canopy cover (light or dense). The human threats were also recorded. The findings revealed that C. Guereza members were waking up between 6.30 am and 6.58 am, depending on the condition of the sky (clear or cloudy). When the sky was clear they wake up between 6.30 and 6.45 am, and 6.45 am to 6.58 am on cloudy sky days. They slept on the highest canopy trees and were feeding on tender or mature leaves depending on the type of species. The flowers and fruits of Jacaranda mimosifolia, Albizia gummifera (J.F.Gmel.) C.A.Sm., Cussonia holstii Harms ex Engl and leaves of Lagenaria abyssinica (Hook.fil.) C.Jeffrey were found to be fed by C. guereza. As soon as they wake up, they both of them urinated. Then, young C. guereza were found to be directed to move before adults just after they had urinated. The height of trees the C. guereza were found to jump on and or sleep ranged from 24 ± 10 m, with an average height of 17 m. The tallest trees ranged from a height of 24 ± 20 m; while the medium had a height of ≤ 20 ± ≤15 m. Most of the tallest trees were Albizia gummifera (J.F.Gmel.) C.A.Sm., Jacaranda mimosifolia D.Don; Cussonia holstii Harms ex Engl.; and Eucalptys maidenii F. Muell. The threats to C. guereza were cutting of trees as their food and habitat and illegal routes that disturbed their behaviour of feeding and movement. The direction of C. guereza movements and sleeping depend most on the trees. Further study is needed to evaluate the plant species being fed at different seasons, protect the existing trees, and restore the forest gaps.
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Schröder, Marc, Maarit Lockhoff, Frank Fell, John Forsythe, Tim Trent, Ralf Bennartz, Eva Borbas, et al. "The GEWEX Water Vapor Assessment archive of water vapour products from satellite observations and reanalyses." Earth System Science Data 10, no. 2 (June 15, 2018): 1093–117. http://dx.doi.org/10.5194/essd-10-1093-2018.
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Abstract. The Global Energy and Water cycle Exchanges (GEWEX) Data and Assessments Panel (GDAP) initiated the GEWEX Water Vapor Assessment (G-VAP), which has the main objectives to quantify the current state of the art in water vapour products being constructed for climate applications and to support the selection process of suitable water vapour products by GDAP for its production of globally consistent water and energy cycle products. During the construction of the G-VAP data archive, freely available and mature satellite and reanalysis data records with a minimum temporal coverage of 10 years were considered. The archive contains total column water vapour (TCWV) as well as specific humidity and temperature at four pressure levels (1000, 700, 500, 300 hPa) from 22 different data records. All data records were remapped to a regular longitude–latitude grid of 2∘ × 2∘. The archive consists of four different folders: 22 TCWV data records covering the period 2003–2008, 11 TCWV data records covering the period 1988–2008, as well as 7 specific humidity and 7 temperature data records covering the period 1988–2009. The G-VAP data archive is referenced under the following digital object identifier (doi): https://doi.org/10.5676/EUM_SAF_CM/GVAP/V001. Within G-VAP, the characterization of water vapour products is, among other ways, achieved through intercomparisons of the considered data records, as a whole and grouped into three classes of predominant retrieval condition: clear-sky, cloudy-sky and all-sky. Associated results are shown using the 22 TCWV data records. The standard deviations among the 22 TCWV data records have been analysed and exhibit distinct maxima over central Africa and the tropical warm pool (in absolute terms) as well as over the poles and mountain regions (in relative terms). The variability in TCWV within each class can be large and prohibits conclusions about systematic differences in TCWV between the classes.
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Castellví, Francesc, Noman Ali Buttar, Yongguang Hu, and Kamran Ikram. "Sensible Heat and Latent Heat Flux Estimates in a Tall and Dense Forest Canopy under Unstable Conditions." Atmosphere 13, no. 2 (February 4, 2022): 264. http://dx.doi.org/10.3390/atmos13020264.
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A method to estimate the sensible heat flux (H) for unstable atmospheric condition requiring measurements taken in half-hourly basis as input and involving the land surface temperature (LST), HLST, was tested over a tall and dense aspen stand. The method avoids the need to estimate the zero-plane displacement and the roughness length for momentum. The net radiation (Rn) and the latent heat flux (λE) dominated the surface energy balance (SEB). Therefore, λE was estimated applying the residual method using HLST as input, λER-LST. The sum of H and λE determined with the eddy covariance (EC) method led to a surface energy imbalance of 20% Rn. Thus, the reference taken for the comparisons were determined forcing the SEB using the EC Bowen ratio (BREB method). For clear sky days, HLST performed close to HBREB. Therefore, it showed potential in the framework of remote sensing because the input requirements are similar to current methods widely used. For cloudy days, HLST scattered HBREB and nearly matched the accumulated sensible hear flux. Regardless of the time basis and cloudiness, λER-LST was close to λEBREB. For all the data, both HLST and λER-LST were not biased and showed, respectively, a mean absolute relative error of 24.5% and 12.5% and an index of agreement of 68.5% and 80%.
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Govender, Paulene, and Venkataraman Sivakumar. "Investigating diffuse irradiance variation under different cloud conditions in Durban, using k-means clustering." Journal of Energy in Southern Africa 30, no. 3 (September 18, 2019): 22–32. http://dx.doi.org/10.17159/2413-3051/2019/v30i3a6314.
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Diffuse irradiance is important for the operation of solar-powered devices such as photovoltaics, so it is important to analyse its behaviour under different sky conditions. The primary cause of short-term irradiance variability is clouds. One approach to analyse the diffuse irradiance variation is to use cluster analysis to group together days experiencing similar cloud patterns. A study was carried out to examine the application of k-means clustering to daily cloud data in Durban, South Africa (29.87 °S; 30.98 °E), which revealed four distinct day-time cloud cover (CC) patterns classified as Class I, II, III and IV, corresponding to cloudy, sunny, or a combination of the two. Diffuse irradiance was then correlated with each of the classes to establish corresponding diurnal irradiance patterns and the associated temporal variation. Class I had highest diffuse irradiance variation, followed by Classes III, IV and II. To further investigate the local cloud dynamics, cloud types were also analysed for Classes I−IV. It was found that stratocumulus (low cloud category); altocumulus translucidus, castellanus and altocumulus (middle cloud category); and cirrus fibrates and spissatus (high cloud category), were the most frequently occurring cloud types within the different classes. This study contributes to the understanding of the diurnal diffuse irradiance patterns under the four most frequently occurring CC conditions in Durban. Overall, knowledge of these CC and associated diffuse irradiance patterns is useful for solar plant operators to manage plant output where, depending on the CC condition, the use of back-up devices may be increased or reduced accordingly.
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Ilham, Dirja Nur, Eri Satria, Fera Anugreni, Rudi Arif Candra, and Herma Nugroho Rono Adi Kusumo. "Rain Monitoring System for Nutmeg Drying Based on Internet of Things." Journal of Computer Networks, Architecture, and High-Performance Computing 3, no. 1 (February 26, 2021): 52–57. http://dx.doi.org/10.47709/cnahpc.v3i1.933.
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One of the stages in drying the nutmeg is drying the nutmeg in the afternoon which is directly illuminated by the sun. The nutmeg owners in South Aceh is very difficult to get information about rain falling during the day if they are outside or are not in the nutmeg drying area. The process of monitoring the occurrence of rain during the drying of the nutmeg has been done manually by monitoring or seeing the state of the sky when it is cloudy. The purpose of this research is to create a rain monitoring system based on the “Internet of things” internet to make it easier for nutmeg owners to get information about rain falling from a distance. This research uses nodeMCU which functions as a controller of a rain monitoring system, a raindrop sensor as a rain detection sensor. The working system of the rain monitoring tool is by connecting the nodeMCU to the led light and if the raindrop sensor is exposed to rain then the led light will turn on or light up and the raindrop sensor reads the data point. If the data point is read 1024, it indicates that the condition is not raining, while if the data point value is 700 -1023, it indicates the condition of the drizzle, and the data point value from 0-600 indicates the heavy rain condition. The raindrop sensor sends data points to the ThingsIO.AI website as a condition notification that the nutmeg drying area is drizzling, heavy rain, or no rain. For monitoring of nutmeg drying area, it can be accessed remotely via the “website ThingsIO.AI” using smartphones and computers that are connected by the internet. Based on the results of testing the average data point delivery time is 1 minute and the value of the data point obtained is 488-1009
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A, Usman, Sunday J.A, and Olaore K.O. "Variation Characteristic of Ultraviolet Light and Air Temperature at A Tropical Location in Ilorin, Kwara State, Nigeria." International Journal of Research and Innovation in Applied Science 07, no. 12 (2022): 59–61. http://dx.doi.org/10.51584/ijrias.2022.71203.
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In this study, characteristic variation of ultraviolent light and air temperature were observed, this research work critically analyses some specific days with field data at an experimental site near the Physics/Electronics Unit Laboratory Ilorin, Nigeria between ultraviolet light and air temperature. For the field observations, an instrumented Meteorological Weather Smart System was set up at an experimental site near the Physics/Electronics Unit Laboratory Kwara State Polytechnic, Ilorin for a period of two weeks (18th March-1st April, 2019). The ultraviolet light and air temperature measurement from the Weather Smart System were recorded every 10 seconds and averaged over 2 minutes interval. The sampled data was then stored in the datalogger storage module. After the removal of spurious measurement values, the data stored was further reduced to hourly averages using the Microcal Origin (version 7.0) data analysis software. The results showed that the measured ultraviolent light, UV during the daytime increases until 1200 hrs with maximum value of about 450 Wm-2 and minimum value of about 9 Wm-2 at 800 hrs (DOY 85). The measured air temperature, Ta value of 32.6 0C observed at 1200 hrs (DOY 85), represented the maximum value for the entire period of the study. The value of 193 Wm-2 was observed at1100 hrs (DOY 81), represented the minimum value for the entire period of the study due to the cloudy condition of the sky which reduces the amount of incoming solar radiation reaching the earth surface.
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Wang, Xi, Jian Liu, Hui Liu, and Bingyun Yang. "Characteristics of Arctic Summer Inversion and Its Correlation with Extreme Sea Ice Anomalies." Atmosphere 13, no. 2 (February 14, 2022): 316. http://dx.doi.org/10.3390/atmos13020316.
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Low tropospheric temperature inversion is very common in the Arctic region. Based on the hyperspectral Atmospheric Infrared Sounder (AIRS) profiles from 2002 to 2020, this study provides a comprehensive analysis of the characteristics and anomalies for low tropospheric inversions in the entire Arctic, especially during the summer period. Three types of inversion are classified here, representing the inversions under the clear-sky condition (“clear” inversion), under the cloudy condition with clouds under the inversion layer top (“cloud-I” inversion), and without clouds under the inversion layer top (“cloud-II” inversion). Obvious seasonality is revealed in these three types of inversion, which is stronger in winter than in summer, as per previous studies. We further found that a “summer” peak of inversions occurs in the Arctic, notably in July. Averaged over the study region (60−90° N, 180° W−180° E), the frequencies of “cloud-I” and “cloud-II” inversions peak in July with values of about 22.1% and 34.6%, respectively. Moreover, the three inversion types all display a small “July” peak of inversion strength, ranging from 2.14 to 3.19 K. The result reveals that when the frequency and strength of summer inversions are both with high positive anomalies, there would be a drop in sea ice concentration in September. This implied that the high positive anomalies, both in inversion frequency and strength in summer, might be a predicted signal for the extreme low sea ice event in September. It is also noted that during the extreme low sea ice events in 2007 and 2020, the summer inversion has a strong positive anomaly. However, the summer inversion in 2012, when the sea ice extent also broke the low record, was not extreme as in 2007 and 2020. Further study needs to be supported by follow-up models and observations to evaluate the impact of the inversions on the sea ice.
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Nguyen Thi Khanh Phuong. "Determination of luminance distribution under tropical sky conditions." Vestnik MGSU, no. 9 (September 2019): 1096–105. http://dx.doi.org/10.22227/1997-0935.2019.9.1096-1105.
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Introduction. Natural illumination calculations depend on the sky luminance distribution. The most often used diagram of sky luminance in handbooks and guidelines is the luminance distribution in the cloudy sky proposed by Moon and Spencer. This concept actually includes the tropical areas of Vietnam, where the overcast sky and clear sky does not typically occur. To improve the calculation of natural illumination, it is necessary to determine the luminance distribution in the real sky.
Materials and methods. In solving the research problem, the real sky types for Hanoi were identified using the 15 international standard sky types with their descriptions by lighting climate, which is provided using the method by R. Kittler. The descriptions are derived from the data on diffuse horizontal illumination Dv, extraterrestrial horizontal illumination Ev and light turbidity coefficient Tv. For a specific sky type, the standard parameters were selected for calculating the luminance distribution of the real sky.
Results. The obtained results show that the typical sky type of Hanoi is the partly cloudy sky, no gradation towards zenith, with slight bleaching towards the Sun (type VI). The sky types from October to December are partly cloudy with the obscured Sun (type IX) and partly cloudy with the more luminant circumsolar area (type X). The study shows that the state of cloud coverage has a great influence on the level of diffuse horizontal illumination and luminance distribution under tropical sky conditions.
Conclusions. It is revealed that the typical sky type for Hanoi is neither overcast nor clear sky. A typical sky with statistic dominance of cirrus and stratus clouds under effect of high solar radiation of Vietnamese tropical climate gives a high level of diffuse horizontal illuminance. The results show that the difference in luminance distribution between the CIE standard overcast sky and Kittler’s intermediate sky can be resolved at the angles of sky point elevation above horizon γ is higher than 50° with the relative errors below 10 %. In other words, the luminance distribution β of the considered sky type is significant for a system of side natural illumination.
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Alyosef, Ayham, Domenico Cimini, Lorenzo Luini, Carlo Riva, Frank S. Marzano, Marianna Biscarini, Luca Milani, et al. "Improving atmospheric path attenuation estimates for radio propagation applications by microwave radiometric profiling." Atmospheric Measurement Techniques 14, no. 4 (April 8, 2021): 2737–48. http://dx.doi.org/10.5194/amt-14-2737-2021.
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Abstract. Ground-based microwave radiometer (MWR) observations of downwelling brightness temperature (TB) are commonly used to estimate atmospheric attenuation at relative transparent channels for radio propagation and telecommunication purposes. The atmospheric attenuation is derived from TB by inverting the radiative transfer equation with a priori knowledge of the mean radiating temperature (TMR). TMR is usually estimated by either time-variant site climatology (e.g., monthly average computed from atmospheric thermodynamical profiles) or condition-variant estimation from surface meteorological sensors. However, information on TMR may also be extracted directly from MWR measurements at channels other than those used to estimate atmospheric attenuation. This paper proposes a novel approach to estimate TMR in clear and cloudy sky from independent MWR profiler measurements. A linear regression algorithm is trained with a simulated dataset obtained by processing 1 year of radiosonde observations of atmospheric thermodynamic profiles. The algorithm is trained to estimate TMR at K- and V–W-band frequencies (22–31 and 72–82 GHz, respectively) from independent MWR observations at the V band (54–58 GHz). The retrieval coefficients are then applied to a 1-year dataset of real V-band observations, and the estimated TMR at the K and V–W band is compared with estimates from nearly colocated and simultaneous radiosondes. The proposed method provides TMR estimates in better agreement with radiosondes than a traditional method, with 32 %–38 % improvement depending on frequency. This maps into an expected improvement in atmospheric attenuation of 10 %–20 % for K-band channels and ∼30 % for V–W-band channels.
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Trisolino, Pamela, Alcide di Sarra, Fabrizio Anello, Carlo Bommarito, Tatiana Di Iorio, Daniela Meloni, Francesco Monteleone, Giandomenico Pace, Salvatore Piacentino, and Damiano Sferlazzo. "A long-term time series of global and diffuse photosynthetically active radiation in the Mediterranean: interannual variability and cloud effects." Atmospheric Chemistry and Physics 18, no. 11 (June 7, 2018): 7985–8000. http://dx.doi.org/10.5194/acp-18-7985-2018.
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Abstract. Measurements of global and diffuse photosynthetically active radiation (PAR) have been carried out on the island of Lampedusa, in the central Mediterranean Sea, since 2002. PAR is derived from observations made with multi-filter rotating shadowband radiometers (MFRSRs) by comparison with a freshly calibrated PAR sensor and by relying on the on-site Langley plots. In this way, a long-term calibrated record covering the period 2002–2016 is obtained and is presented in this work. The monthly mean global PAR peaks in June, with about 160 W m−2, while the diffuse PAR reaches 60 W m−2 in spring or summer. The global PAR displays a clear annual cycle with a semi amplitude of about 52 W m−2. The diffuse PAR annual cycle has a semi amplitude of about 12 W m−2. A simple method to retrieve the cloud-free PAR global and diffuse irradiances in days characterized by partly cloudy conditions has been implemented and applied to the dataset. This method allows retrieval of the cloud-free evolution of PAR and calculation of the cloud radiative effect, CRE, for downwelling PAR. The cloud-free monthly mean global PAR reaches 175 W m−2 in summer, while the diffuse PAR peaks at about 40 W m−2. The cloud radiative effect, CRE, on global and diffuse PAR is calculated as the difference between all-sky and cloud-free measurements. The annual average CRE is about −14.7 W m−2 for the global PAR and +8.1 W m−2 for the diffuse PAR. The smallest CRE is observed in July, due to the high cloud-free condition frequency. Maxima (negative for the global, and positive for the diffuse component) occur in March–April and in October, due to the combination of elevated PAR irradiances and high occurrence of cloudy conditions. Summer clouds appear to be characterized by a low frequency of occurrence, low altitude, and low optical thickness, possibly linked to the peculiar marine boundary layer structure. These properties also contribute to produce small radiative effects on PAR in summer. The cloud radiative effect has been deseasonalized to remove the influence of annual irradiance variations. The monthly mean normalized CRE for global PAR can be well represented by a multi-linear regression with respect to monthly cloud fraction, cloud top pressure, and cloud optical thickness, as determined from satellite MODIS observations. The behaviour of the normalized CRE for diffuse PAR can not be satisfactorily described by a simple multi-linear model with respect to the cloud properties, due to its non-linear dependency, in particular on the cloud optical depth. The analysis suggests that about 77 % of the global PAR interannual variability may be ascribed to cloud variability in winter.
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Sianturi, Y., A. Sopaheluwakan, and K. A. Sartika. "Evaluation of ECMWF model to predict daily and monthly solar radiation over Indonesia region." IOP Conference Series: Earth and Environmental Science 893, no. 1 (November 1, 2021): 012074. http://dx.doi.org/10.1088/1755-1315/893/1/012074.
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Abstract Solar radiation forecast is a pivotal information needed in the operational activity of large-scale solar energy production. In this study, the reliability of SSRD (surface solar radiation downward) forecast from the 51 ensemble members in the ECMWF (European Centre for Medium Range Forecast) long-range forecast to predict daily and monthly radiation in 5 climatological stations in Indonesia is evaluated. The global horizontal irradiance (GHI) data from the solar radiation observation network from January 2018 – December 2020 are used in the quantitative evaluation of the SSRD forecast. Post-processing methods are applied to the model output, namely the bilinear interpolation method and the empirical quantile mapping to reduce consistent biases in the model output. The evaluation was carried out for different cloud covers based on the calculation of clearness index (k_t). The cloud condition affects the performance of the model, where the highest correlation value is achieved during sunny days (0.18 – 0.65) and the lowest correlation happens in overcast days (0.05 – 0.35). Models also tend to underestimate radiation when the sky is clear and overestimate it in cloudy days, based on negative MBE values during clear days (-0.47 kWh/m2 – -1.29 kWh/m2). The spatial averaging method did not necessarily improve the accuracy of the forecast, but the empirical quantile mapping method provides better accuracy, which is indicated by a values (mean error ratio) lower than 1 in most stations. Information about the influence of cloud cover on model performance can be used in future application of the model output and the bias correction process carried out in this study can be applied to reduce bias in the model.
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Lei, Siliang, Xijuan Zhu, Yuxiang Ling, Shiwen Teng, and Bin Yao. "Tropical Tropopause Layer Cloud Properties from Spaceborne Active Observations." Remote Sensing 15, no. 5 (February 22, 2023): 1223. http://dx.doi.org/10.3390/rs15051223.
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A significant part of clouds in the tropics appears over the tropopause due to intense convections and in situ condensation activity. These tropical tropopause layer (TTL) clouds not only play an important role in the radiation budget over the tropics, but also in water vapor and other chemical material transport from the troposphere to the stratosphere. This study quantifies and analyzes the properties of TTL clouds based on spaceborne active observations, which provide one of the most reliable sources of information on cloud vertical distributions. We use four years (2007–2010) of observations from the joint Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) and CloudSat and consider all cloudy pixels with top height above the tropopause as TTL clouds. The occurrence frequency of TTL clouds during the nighttime is found to be almost 13% and can reach ~50–60% in areas with frequent convections. The annual averages of tropical tropopause height, tropopause temperature, and cloud top height are 16.2 km, −80.7 °C, and 16.6 km, respectively, and the average cloud top exceeds tropopause by approximately 500 m. More importantly, the presence of TTL clouds causes tropopause temperature to be ~3–4 °C colder than in the all-sky condition. It also lifts the tropopause heights ~160 m during the nighttime and lowers the heights ~84 m during the daytime. From a cloud type aspect, ~91% and ~4% of the TTL clouds are high clouds and altostratus, and only ~5% of them are associated with convections (i.e., nimbostratus and deep convective clouds). Approximately 30% of the TTL clouds are single-layer clouds, and multi-layer clouds are dominated by those with 2–3 separated layers.
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Gallo, Kevin, Robert Hale, Dan Tarpley, and Yunyue Yu. "Evaluation of the Relationship between Air and Land Surface Temperature under Clear- and Cloudy-Sky Conditions." Journal of Applied Meteorology and Climatology 50, no. 3 (March 1, 2011): 767–75. http://dx.doi.org/10.1175/2010jamc2460.1.
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Abstract Clear and cloudy daytime comparisons of land surface temperature (LST) and air temperature (Tair) were made for 14 stations included in the U.S. Climate Reference Network (USCRN) of stations from observations made from 2003 through 2008. Generally, LST was greater than Tair for both the clear and cloudy conditions; however, the differences between LST and Tair were significantly less for the cloudy-sky conditions. In addition, the relationships between LST and Tair displayed less variability under the cloudy-sky conditions than under clear-sky conditions. Wind speed, time of the observation of Tair and LST, season, the occurrence of precipitation at the time of observation, and normalized difference vegetation index values were all considered in the evaluation of the relationship between Tair and LST. Mean differences between LST and Tair of less than 2°C were observed under cloudy conditions for the stations, as compared with a minimum difference of greater than 2°C (and as great as 7+°C) for the clear-sky conditions. Under cloudy conditions, Tair alone explained over 94%—and as great as 98%—of the variance observed in LST for the stations included in this analysis, as compared with a range of 81%–93% for clear-sky conditions. Because of the relatively homogeneous land surface characteristics encouraged in the immediate vicinity of USCRN stations, and potential regional differences in surface features that might influence the observed relationships, additional analyses of the relationships between LST and Tair for additional regions and land surface conditions are recommended.
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Chaudhari, K., N. Nishant, G. Upadhyay, R. More, N. Singh, S. P. Vyas, and B. K. Bhattacharya. "CROP INVENTORY OF ORCHARD CROPS IN INDIA USING REMOTELY SENSED DATA." ISPRS - International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences XLII-3/W6 (July 26, 2019): 269–75. http://dx.doi.org/10.5194/isprs-archives-xlii-3-w6-269-2019.
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<p><strong>Abstract.</strong> The use of satellite remote sensing (RS) technologies for purpose of crop discrimination, mapping, area estimation, condition and yield assessment has been proved to be effective and efficient in terms of time and cost, having better consistency implemented with scientific approaches. However, application of satellite RS technology for horticultural crops in India has certain challenges due to scattered and small field sizes, comparatively short duration such as vegetable crops and mixed cropping. Hence the study was taken for developing research methodology for area assessment of three major fruit crops such as Banana, Mango and Citrus over 20 districts in four states viz. Gujarat, Madhya Pradesh, Uttar Pradesh and Bihar. Appropriate bio-window for analysing different crop types was selected and mapping of crops were done using pixel based hybrid classification i.e. un-supervised ISODATA clustering plus supervised MXL classification as well as object based classification of high resolution remote sensing data (Resourcesat LISS III and/or LISS IV, Cartosat – 1 PAN) followed by their accuracy assessment and their comparison with departmental reported statistics. Overall, the classification accuracy was more than 80% for all the crops. Deviation from statistics were in the range of 3 to 38%. Higher deviations from statistics were mostly due to use of lower resolution satellite data or mixing of crops having similar spectral signatures e.g. mango and sapota in Navsari and Valsad districts of Gujarat. It was very difficult to discriminate the young orchards of 2&ndash;3 years from other field crops due to mixed / inter cropping practices. The maps were checked and certified by respective State Horticulture Departments and were archived in VEADS, SAC and BHUVAN, NRSC geoportals of ISRO. RISAT – 1 (microwave) data were explored for the estimation of banana orchards in order to detect banana plantation at early stage and under cloudy sky conditions. There is huge potential of application in this sector using advanced observations from hyperspectral, thermal infrared sensors and advanced radars or LIDAR’s on-board upcoming satellites.</p>
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Hegedüs, Ramón, Susanne Åkesson, Rüdiger Wehner, and Gábor Horváth. "Could Vikings have navigated under foggy and cloudy conditions by skylight polarization? On the atmospheric optical prerequisites of polarimetric Viking navigation under foggy and cloudy skies." Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 463, no. 2080 (February 6, 2007): 1081–95. http://dx.doi.org/10.1098/rspa.2007.1811.
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In sunshine, the Vikings navigated on the open sea using sundials. According to a widespread hypothesis, when the Sun was occluded by fog or clouds the Vikings might have navigated by skylight polarization detected with an enigmatic birefringent crystal (sunstone). There are two atmospheric optical prerequisites for this alleged polarimetric Viking navigation under foggy/cloudy skies: (1) the degree of linear polarization p of skylight should be high enough and (2) at a given Sun position, the pattern of the angle of polarization α of the foggy/cloudy sky should be similar to that of the clear sky. Until now, these prerequisites have not been investigated. Using full-sky imaging polarimetry, we measured the p - and α -patterns of Arctic foggy and cloudy skies when the Sun was invisible. These patterns were compared with the polarization patterns of clear Arctic skies. We show here that although prerequisite (2) is always fulfilled under both foggy and cloudy conditions, if the fog layer is illuminated by direct sunlight, prerequisite (1) is usually satisfied only for cloudy skies. In sunlit fog, the Vikings could have navigated by polarization only, if p of light from the foggy sky was sufficiently high.
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Kittler, R., and S. Darula. "Parametrization problems of the very bright cloudy sky conditions." Solar Energy 62, no. 2 (February 1998): 93–100. http://dx.doi.org/10.1016/s0038-092x(97)00117-5.
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Liu, Yinghui, Jeffrey R. Key, and Xuanji Wang. "The Influence of Changes in Cloud Cover on Recent Surface Temperature Trends in the Arctic." Journal of Climate 21, no. 4 (February 15, 2008): 705–15. http://dx.doi.org/10.1175/2007jcli1681.1.
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Abstract A method is presented to assess the influence of changes in Arctic cloud cover on the surface temperature trend, allowing for a more robust diagnosis of causes for surface warming or cooling. Seasonal trends in satellite-derived Arctic surface temperature under clear-, cloudy-, and all-sky conditions are examined for the period 1982–2004. The satellite-derived trends are in good agreement with trends in the European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis product and surface-based weather station measurements in the Arctic. Surface temperature trends under clear and cloudy conditions have patterns similar to the all-sky trends, though the magnitude of the trends under cloudy conditions is smaller than those under clear-sky conditions, illustrating the negative feedback of clouds on the surface temperature trends. The all-sky surface temperature trend is divided into two parts: the first part is a linear combination of the surface temperature trends under clear and cloudy conditions; the second part is caused by changes in cloud cover as a function of the clear–cloudy surface temperature difference. The relative importance of these two components is different in the four seasons, with the first part more important in spring, summer, and autumn, but with both parts being equally important in winter. The contribution of biases in satellite retrievals is also evaluated.
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Kent, Wes P., and Scott C. Sheridan. "The Impact of Cloud Cover on Major League Baseball." Weather, Climate, and Society 3, no. 1 (January 1, 2011): 7–15. http://dx.doi.org/10.1175/2011wcas1093.1.
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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.