Changes In Solar Radiation Research Articles

Analysis of ENSO influence on the solar and wind potential of the department of La Guajira

ABSTRACT This study explores how solar radiation and wind speed in La Guajira vary in response to El Niño/Southern Oscillation (ENSO) events. Climatic data were collected and analysed at three iconic locations: Upper Guajira, Middle Guajira, and Lower Guajira, over a span of three decades. The data were obtained from reliable sources such as IDEAM and NASA stations. To identify El Niño and La Niña periods, Southern Oscillation Index (ONI) data were utilised. Subsequently, the data underwent detailed statistical analyses, including hypothesis testing. During El Niño, solar radiation is altered solely in Lower Guajira; for La Niña, no significant changes in solar radiation across the region are observed. Wind speed, for the most part, remains unaffected by the studied climatic phenomena in these areas, with an exception in Middle Guajira during La Niña, where it is notably influenced.

Alleviation of Power Quality Issues in MVF-DEANF-PLL Based Solar PV Systems under Polluted Grid Conditions

Solar energy is a sustainable and environmentally safe power source due to its widespread availability and cleanliness. Nowadays, the grid-integrated solar photovoltaic system (SPVS) has to work with a polluted grid, an imbalanced load, and changing solar irradiation. When the grid is polluted, it is also crucial to enhance power quality (PQ) at a common coupling point (CCP) while supplying significantly distorted and unreliable loads. For effective synchronization and the production of unit templates, it is necessary to retrieve positive sequence components (PSCs) from distorted/imbalanced grid voltages. In this study, a control algorithm for a grid-integrated SPVS is developed using a multi-variable filter dual-enhanced adaptive notch filter phase-locked loop (MVF-DEANF-PLL) which offers seamless grid synchronization and PQ issue alleviation. In a polluted grid environment, the proposed control approach aids in the reduction in current/voltage harmonics, DC offset, unity power factor (UPF) operation, and rapid estimation of sequence components. Even in unbalanced grid conditions, the proposed control approach efficiently extracts PSCs of both unbalanced load current and polluted CCP grid voltages. These PSCs are utilized to generate unit templates and reference source currents. By using a flexible step-size incremental conductance (FSSINC) maximum power point tracking (MPPT) technique, the highest available power of SPVS is gathered. MATLAB/Simulink is utilized for modelling a 7.22 kW SPV system, and results from simulations which depict that the proposed algorithm efficiently resolves PQ concerns in distribution networks with a polluted grid. Test observations of a 1 kW laboratory-developed SPVS prototype were recorded in compliance with the IEEE-519 standard. The suggested control technique complies with the aforementioned standards by providing a sinusoidal balanced source current that has a THD of 2.5%. Comparisons between the proposed control’s performance and that of a conventional SRF-PLL-based control technique were also performed.

Global distribution and evolutionary transitions of floral symmetry in angiosperms.

Floral symmetry plays an important role in plant-pollinator interactions and may have remarkable impacts on angiosperm diversification. However, spatiotemporal patterns in floral symmetry and drivers of these patterns remain unknown. Here, using newly compiled floral symmetry (actinomorphy versus zygomorphy) data of 279,877 angiosperm species and their distributions and phylogenies, we estimated global geographic patterns and macroevolutionary dynamics of floral symmetry. We found that frequency of actinomorphic species increased with latitude, while that of zygomorphic species decreased. Solar radiation, present-day temperature, and Quaternary temperature change correlated with geographic variation in floral symmetry frequency. Evolutionary transitions from actinomorphy to zygomorphy dominated floral symmetry evolution, although the transition rate decreased with decreasing paleotemperature throughout the Cenozoic. Notably, we found that zygomorphy may not favor diversification of angiosperms as previously observed in some clades. Our study demonstrates the influence of (paleo)climate on spatiotemporal patterns in floral symmetry and challenges previous views about role of flower symmetry in angiosperm diversification.

Long-term changes in solar activity and irradiance

The Sun is the main energy source to Earth, and understanding its variability is of direct relevance to climate studies. Measurements of total solar irradiance (TSI) exist since 1978, but this is too short compared to climate-relevant time scales. Coming from a number of different instruments, these measurements require a cross-calibration, which is not straightforward, and thus several composite records have been created. All of them suggest a marginally decreasing secular trend in solar minima levels since 1996. Most composites actually feature a weak decrease over the entire period of observations, which is also seen in observations of the solar surface magnetic field and is further supported by Caii Kdata. Some inconsistencies, however, remain and overall the magnitude and even the presence of the secular change over the satellite era remain uncertain. Different models have been developed, which are used to understand the irradiance variability over the satellite period and to extend the records of solar irradiance back in time. Differing in their methodologies, all models require proxies of solar magnetic activity as input. The most widely used proxies are sunspot records and cosmogenic isotope data on centennial and millennial time scale, respectively. None of this, however, offers a sufficiently good, independent description of the long-term evolution of faculae and network responsible for solar brightening. This leads to significant uncertainties in the amplitude of the changes in solar irradiance on time scales longer than the solar cycle. Here we review recent efforts and advances aiming at improving long-term irradiance reconstructions and to reduce the existing uncertainty in the magnitude of the long-term variability. In particular, by employing state-of-the-art 3D magnetohydrodynamical simulations, an upper limit of 2±0.7 Wm−2 was set on the possible increase of TSI since the end of the Maunder minimum as compared to the 2019 minimum level. Besides, significant progress has been made in collecting and processing historical solar observation in Caii Kspectral line, which provide direct information on bright magnetic features on the Sun and can be used to improve the accuracy of past irradiance reconstructions, pending some remaining issues with the data.

Carbon budget response to climate change varies with grassland type in Qilian Mountains, China

Carbon budget estimation is crucial for scientifically assessing the ecosystem’s carbon sequestration capacity. Grasslands in the Qilian Mountains are widely recognized as vulnerable and sensitive to ongoing climate change. However, it is still unclear how the carbon budget of different grassland types responds to climate change in this area. Here, we evaluated the net primary productivity (NPP), soil heterotrophic respiration (RH), and net ecosystem productivity (NEP) of grassland ecosystems in the Qilian Mountains. Correlation analysis, linear regression, and standardized coefficient methodologies were employed to explore the response of NPP, RH, and NEP in various grassland types to changes in temperature, precipitation, and solar radiation over the past two decades. The results showed that the alpine meadow has the highest NPP and NEP while the temperate typical steppe has the highest RH. Grassland NPP, RH, and NEP increased significantly from 2001 to 2020, with a distinct spatial pattern of being low in the northwest and high in the southeast of the Qilian Mountains. NPP and NEP correlated with precipitation and solar radiation more closely than with temperature. Precipitation and solar radiation, respectively, explained 43.7% and 52.9% of grassland NEP alterations, and there was a threshold effect on the response of NEP and NPP to climate factors. Specifically, the NPP and NEP increased at first and then decreased as the precipitation, temperature, and solar radiation increased. The highest NEP and NPP occurred when precipitation ranged from 415 to 455 mm, along with temperatures between − 0.1–1.5 ℃ and solar radiation reaching 7685–7905MJ/m2. The warming and humidification of climate is conducive to the increase of NPP and NEP in alpine meadows and alpine steppes, but when the precipitation exceeds 415 mm and the temperature is greater than 1.5 ℃, the NPP and NEP begin to decrease. Solar radiation dominated changes in NPP and NEP of alpine meadows, alpine steppes, and temperate desert steppes. With the increase of solar radiation, NPP and NEP of these three grasslands first increased and then decreased. However, the changes in NPP and NEP of the temperate typical steppe were most affected by precipitation, and NPP and NEP first increase and then decrease with the increase of precipitation The higher the temperature, the higher the NPP, RH, and NEP of the temperate typical steppe. This study helps better understand how climate change impacts the carbon budget components of different grassland types in the Qilian Mountains and provides more theoretical thoughts on managing local grasslands sustainably.

Study of Vertically Oriented Solar Battery by Exposure of Concentrated Solar Radiation

Solar power is one of the largest sectors of the global electric and heat power industry. In search of new energy sources, scientists and engineers around the world are increasingly turning their attention to solar batteries, which can be a suitable replacement for non-renewable energy sources. Vertically oriented solar batteries will generate electricity throughout the daylight hours, which eliminates use of additional equipment. The paper proposes a 3D model of a solar battery with a vertical orientation of its modules, as well as the calculation and evaluation of temperature characteristics and the range of efficiency variations obtained under conditions of both the diurnal and seasonal changes in ambient temperature, and the power density changes of concentrated solar radiation, the maximum values of which were chosen equal to 1; 5 and 10 kW/m2. The dependences of the maximum values of the solar battery temperature and the temperature gradient inside it, as well as the dependences of the minimum, average and maximum values of the radiative heat flux to the solar battery surface in the presence and absence of temperature stabilization of the heat sink backside versus the time of day in the middle of January and July have been plotted. As calculations have shown, at the solar radiation concentration of 10 kW/m2, the efficiency in July is increased by more than 2 times due to the use of thermoelectric converters in the battery. Moreover, according to the obtained results, when the solar modules are oriented vertically, temperature gradients and, consequently, the total efficiency of the solar battery and power generation time will be greater compared to the horizontal position of the solar modules, which will reduce operational costs.

Development of pore water pressure during freeze-thaw cycles in weather conditions

To assess the risk of frost damage to building materials, the mechanisms of pressure development in a material due to freezing under weather conditions should be adequately understood. In this study, we have demonstrated the evolution of pore water pressure in a brick wall during cyclic freezing and thawing caused by changes in air temperature and solar radiation. We developed a coupled hygrothermal and mechanical model of brick walls based on the theory of poromechanics. The calculation results showed that the water pressure in a south facing wall increases significantly during the night in a cold region. For a south facing wall, the surface thaws during the day due to solar radiation and freezes again at night, while the interior remains frozen throughout the day. We conclude that such incomplete freeze-thaw cycles in the weather conditions are much more damaging to building materials than a monotonous repetition of complete freezing and thawing.

Salinity and total suspended solids control mercury speciation in a tidal river: Comparisons with a photochemical mercury model

Daytime volatilization of gaseous elemental mercury (Hg(0)aq) is a significant mechanism for mercury removal from aquatic systems and potentially limits the production and bioaccumulation of methylmercury. Changes in incoming solar radiation (in the ultraviolet range), dissolved organic matter, salinity, and total suspended particles were investigated concurrently with several mercury species (Hg(0)aq, dissolved total mercury (THg), easily reducible mercury (ERM), and mercury associated with total suspended solids (THgTSS)) during daylight hours near the mouth of a hypertidal river. There were no predictable temporal changes observed for Hg(0)aq in unfiltered surface water. Hg(0)aq ranged from 0 to 12 pg L−1, THg ranged from 0 to 492 pg L−1, ERM ranged from 13 to 381 pg L−1, and THgTSS ranged from <1.58 ng g−1 to 261.32 ng g−1. The range of Hg(0)aq predicted by the empirical model was similar to measured ERM concentrations, but it was shown that ERM did not significantly predict in-situ photoreducible Hg(II) (Hg(II)RED). Production of Hg(0)aq appears to largely be suppressed by suspended solids, which limits ultraviolet radiation transmission through surface water. Comparison of these results to an empirical model developed for this site to predict Hg(0)aq indicates that significantly more mercury is available for photoreduction near the mouth of the tidal river, and that Hg(II) will likely photoreduce quickly when TSS levels decrease with ocean mixing.

Global Sensitivity of Penman–Monteith Reference Evapotranspiration to Climatic Variables in Mato Grosso, Brazil

Understanding how climatic variables impact the reference evapotranspiration (ETo) is essential for water resource management, especially considering potential fluctuations due to climate change. Therefore, we used the Sobol’ method to analyze the spatiotemporal variations of Penman–Monteith ETo sensitivity to the climatic variables: downward solar radiation, relative humidity, maximum and minimum air temperature, and wind speed. The Sobol’ indices variances were estimated by Monte Carlo integration, with sample limits set to the 2.5th and 97.5th percentiles of the daily data of 33 automatic weather stations located in the state of Mato Grosso, Brazil. The results of the Sobol’ analysis indicate considerable spatiotemporal variations in the sensitivity of ETo to climatic variables and their interactions. The dominant climatic variable responsible for ETo fluctuations in Mato Grosso is incident solar radiation (53% to 93% of annual total sensitivity—Stot), which has a more significant impact in humid environments (70% to 90% of Stot), as observed in the areas of the Amazon biome in the state. Air relative humidity and wind speed have higher sensitivity indices during the dry season in the Cerrado biome (savanna) areas in Mato Grosso (20% and 30% of the Stot, respectively). Our findings show that changes in solar radiation, relative humidity, and wind speed are the main driving forces that impact the reference evapotranspiration.

Performance enhancement of photovoltaic solar collector using fins and bi-fluid: Thermal efficiency study

This work exhibits a three-dimensional numerical investigation of a solar collector Photovoltaic Thermal (PV/T) bi-fluid based on the use of dual exchangers cooling with both water and air simultaneously. The effect of the absorber plate design and water mass flow rate (mf) of water and natural airflow has been studied according to the fins added to the system, which mainly includes a flat plate of aluminum attached to the tubes of aluminum. The objective is to analyze the effects of water mf fluctuating between 0.01 and 0.02 kg/s, fins location and number (from 20 to 40 fins), and changing solar irradiation values (100 to 1050 W/m2) on the flow structure and thermal efficiency of photovoltaic solar cells. The hybrid collectors studied are made of monocrystalline photovoltaic cells and an absorber plate of aluminum in the lower of the PV module. An evaluation was made between three configurations of bi-fluid (air and water) PV/T manifolds according to the number of fins. The first configuration is a hybrid PV/T system containing tubes without fins. The second configuration is a hybrid PV/T system containing tubes attached with 20 fins. The third configuration is a hybrid PV/T system containing tubes attached with 40 fins. The results confirm that the thermal efficiency of the PV/T system using (water and air) as a working fluid increase with increasing the number of fins (from 20 to 40 fins) and with increasing solar radiation (100 to 1050 W/m2), but it decreases a little with increasing mf of water (0.01 to 0.02 kg/s) by about 1.1%. For the mf of water equal to 0.01 kg/s, the thermal efficiency of the PVT system configurations 1, 2, and 3 are equal to 50.54%, 52.33%, and 54.25%, respectively. The optimal design for good cooling of the photovoltaic cells and higher yields of the hybrid collector is the third configuration with a water mf of 0.01 kg/s.

Modelling and simulation of an on grid 100-kW photovoltaic system

&lt;span lang="EN-US"&gt;This work proposes a design of a solar radiation generator system to extract a maximum power of 100 kilowatts for the uses of 400 volts, 50 Hertz electrical network, under standard conditions (1000 Watts/m&lt;sup&gt;2&lt;/sup&gt; and 25 °C). The main goal is to inject and control active and reactive power to the grid by a three-phase, one-stage solar grid-connected 100-kW photovoltaic (PV) plant, to keep the current's total harmonic distortion (THD) within the international requirements, and maintain a constant voltage regardless of solar radiation changes. This design consists of three control loops those are: the maximum power point tracking (MPPT), the DC-link voltage, and the current controller. The proposed system was simulated in MATLAB/Simulink environment and was applied on part of the Baghdad electrical network. The obtained results showed the efficiency of the proposed design and modelling.&lt;/span&gt;

The Global Variation of Low Ionosphere Under Action of Energetic Electron Precipitation

AbstractThe density in the D region is hard to observe on a large scale, because the density in this region is too low. In addition to solar radiation changes with a sinusoidal period of 24 hr, the energetic electron precipitation (EEP) is the major source for the ionospheric D region. In this study, we utilized observations from NOAA/MetOp satellites to derive the electron density profile from 60 to 150 km under the influence of EEP. It seems that the derived electron profile is roughly consistent with the observed one. Additionally, using above derived method of low ionospheric (D and E regions) electron profile based on the observations of NOAA/MetOp satellites, the actions of EEP on global ionosphere under different level of geomagnetic activity are analyzed. We find that EEP has a significant impact on the electron density in the altitude range from 60 to 90 km in the L ∼ 4.5–8 and MLT ∼ 9–14 regions, particularly during strong geomagnetic activity. A peak in Total Electron Content (TEC) was observed at MLT ∼ 11–12 and L ∼ 5.5–6, exhibiting an enhancement approximately 19.96 times higher than that observed during quiet periods. However, the effects of EEP decrease as altitude increases. The TEC enhancement at altitudes from 90 to 120 km during strong geomagnetic activity is like that at 60–90 km, but only about 2.08 times higher than that during quiet periods. In addition, only a weak increase is detected around midnight at altitudes from 120 to 150 km.

Different photovoltaic power potential variations in East and West China

Photovoltaic (PV) technology can help reduce carbon emissions significantly, but its benefits may be affected by climate change. Few studies have reported on the impact of climate change on the spatial and temporal distribution of solar energy in China based on the latest Coupled Model Intercomparison Project Phase 6 (CMIP6) models, and few have explored the rooftop PV potential. In this study, 16 CMIP6 models are used for evaluation of the inter-annual and seasonal changes of solar irradiance and PV capacity factor under low (SSP1–2.6), medium (SSP2–4.5) and high (SSP5–8.5) greenhouse gas emission scenarios. The effects on the variation of solar irradiance of three factors are examined: clouds, aerosol optical thickness (AOT) and specific humidity. Furthermore, the future power generation potential of rooftop PV is investigated. It is found that the solar irradiance exhibits an upward trend on national level under all the future scenarios, especially for the SSP1–2.6 scenario, with an increasing rate of 1.4 W m−2 decade−1, mainly due to a reduction in AOT. Solar irradiance increases notably in southeast China while increases little in west China, and the level for 2051–2060 remains lower than that for 1960–2014. The PV capacity factor increases in southeast China with increasing solar irradiance, with a maximum increase of about 4% compared to the average PV CF for 1960–2014 and the highest increasing rate being 0.37% decade−1. In addition, to achieve the projected national distributed PV power generation level, >70% of the effective rooftop area needs to be utilized in 2050. This study hopes to enhance understanding of the impact of climate change on solar energy and provide recommendations for future PV planning to better achieve the long-term planetary temperature goal set by the Paris Agreement.

Power Quality Improvement of a Hybrid Renewable Energy Sources Based Standalone System Using Neuro-Fuzzy Controllers

Wind and Photovoltaic (PV) based hybrid standalone systems for supplying electricity to remote consumers are becoming increasingly popular around the world. In general, power generation from both PV and wind is always variable due to irradiance and speed fluctuations. Furthermore, the load is unpredictably variable and changes at random. As a result, one of the main challenges in such standalone micro grids is maintaining power quality. To maintain power quality in such standalone systems, a novel controller should be developed. Furthermore, due to the unpredictable random changes in wind speed, solar irradiance, and load, a battery bank must be integrated into the standalone system via a bidirectional converter. Furthermore, the interconnection of multiple wind turbines and PV panels can create a powerful hybrid system. This paper examines a 1 MW stand-alone power generation system using numerous PV and wind systems. Maximum power points tracking devices with perturbed and observe algorithms are used to optimize the utilization of individual PV modules and wind turbines. Because of its superior priority over conventional PI controllers, a Neuro-Fuzzy integrated controller-based novel control scheme for both inverter and bidirectional converter is proposed to achieve precise response while maintaining power quality. This paper discusses extensive results obtained by establishing hardware-in-the-loop on the OPAL-RT platform to evaluate the responses of proposed controllers. The experimental results also included to provide strength to the paper.

Improving the power quality and hydrogen production from renewable energy sources based microgrid

The world is looking for utilization of renewable energy sources to reduce global warming as well as the consumption of fossil fuels. In this scenario, solar and wind energy are widely used at many places worldwide. However, both solar irradiance and wind speed are depending on nature. Hence, an energy storage device must be required to operate at their best utilization level by converting them to electricity. One of the best energy storage devices for medium power range is the battery. However, batteries require high maintenance and suffering from self-discharge as well as storage capacity will be decreased day by day. Hence, storing hydrogen can be an economically feasible solution instead of using batteries for high power range. Usually an aqua electrolyzer can easily convert water to hydrogen and oxygen through electricity. However, due to slow dynamics of heat transfer from electricity, the generation of hydrogen cannot meet the fast response like electrical devices. Therefore, a novel controlling technique is required to increase the production quality of hydrogen during random changes in both solar irradiance and wind speed. In order to achieve the best utilization, both photovoltaic panels and wind turbines are operated at their maximum power point levels. In this research boost converters are used to operate as maximum power point tracking devices. The whale optimization technique is integrated to respective controllers of all the converters to achieve stable production of hydrogen during rapid changes in irradiance and wind speed. The Whale Optimization Algorithm (WOA) technique is compared with Genetic Algorithm (GA), Particle Swarm Optimization (PSO) and Grey Wolf Optimization (GWO) to show the benefits of tracking response of the system on improving production of hydrogen from hybrid renewable energy sources based Microgrid. Hardware—in the—Loop (HIL) is developed to analyze the results with the help of OPAL-RT modules. Along with HIL results, a Real Time Digital Simulator (RTDS) based results are also presented to evaluate the performance of the proposed method.

Uncovering the primary drivers of regional variability in the impact of climate change on wheat yields in China

Responses of wheat yield in different regions to separate and joint changes in mean temperature (Tmean), precipitation (Prec), and solar radiation (Rad) are the foundation for sustainable development under climate change; however, these remain uncertain. Here, we quantified the response of wheat yield variation to changes in Tmean, Prec, and Rad by building multiple regression models, de-trending analysis, and MK trend tests. Multi-site meteorological data was obtained from different wheat growing areas and corresponding wheat yield data from provinces. Our findings showed that the effects of different climatic elements on wheat yield are spatially heterogeneous by region, and the combined effects of climatic elements are higher than those of single elements. Climate change caused an increase of 1% and 4.52% in winter and winter-spring wheat areas, respectively, and a loss of 3.72% in spring wheat areas. In addition, the effect of single meteorological factors on wheat yield varied depending on their rate of change. Rad and Prec are the main drivers of wheat yield variability; in winter, spring and winter-spring wheat areas, Rad significantly impacted wheat yield by 0.89%, −1.18%, and 2.46%, respectively, and Prec caused changes of −0.18%, −1.54%, and 1.33%, respectively. Considering normal and extreme climate fluctuations, we found that the contribution of climate change to wheat yield changes in different wheat-growing regions reached 26.1%, 18.6%, and 16.7%, respectively. Our results indicate that the overall climatic conditions in the spring wheat region are moving in an unfavourable direction, while Prec variability has become the main limiting factor for wheat production in the current winter and winter-spring wheat regions. These comprehensive and detailed findings provide a reference for the development of more accurate adaptation strategies and management measures in different regions. Going forward, the results of this study can be better applied to the development of region-specific climate-smart agricultural practices and extended to other crops and regions to better understand the broader impacts of climate change on global food security.

Climate change impact on photovoltaic power potential in South America

Abstract This paper presents the first study of the long-term impact of climate change on photovoltaic potential in South America. This region has great potential for implementing renewable energy, mainly solar energy solutions, due to its high solar irradiance levels. Based on the Coordinated Regional Downscaling Experiment (CORDEX) for the South American region, we estimate how climate change could affect photovoltaic power potential by the end of the century. The evidence suggests that photovoltaic potential could have a maximum decrease of around 15%, and a maximum increase of approximately 7%, primarily due to changes in solar irradiance of different zones. Furthermore, it is observed that regions with increased temperature also show increased solar irradiance levels, which could, to some extent, compensate for the losses caused by the rise in temperature. Therefore, photovoltaic production in most of the territory will not be negatively affected.

Field measurement of environmental parameters in solar greenhouses and analysis of the application of passive ventilation

Solar greenhouses are passive agricultural facilities that can realize off-season production. The growth of crops in greenhouses is affected by various environmental parameters. Therefore, it is necessary to understand the variations of environmental parameters in solar greenhouses through field testing to improve their internal environment. Through field tests, it was found that the temperature variation in solar greenhouses was positively correlated with the change in solar radiation. When the top vent was opened, the minimum temperature in the greenhouse remained higher than 30 °C. The temperature gradient in the tall-plant greenhouse was twice that in the short-plant greenhouse. The relative humidity at the bottom of the tall-plant greenhouse remained greater than 65%. Top-vent opening for greenhouse ventilation is not conducive to the cooling and dehumidification of these relatively large sized greenhouses tested in this study. Passive ventilation via an integrated solar chimney and earth-air heat exchanger was applied in an experimental solar greenhouse. The results showed that when the passive ventilation was turned on, the indoor air temperature in the horizontal and vertical direction could be maintained in the range of 25 ∼ 28 °C and 25 ∼ 30 °C, respectively. The air temperature in the vertical direction had been decreased by approximately 3.5 to 6.5 °C. The passive ventilation effectively prevented continuous increases in indoor temperature, improved indoor air distribution and was conducive to the normal growth of crops.

Differential responses of CO2 and latent heat fluxes to climatic anomalies on two alpine grasslands on the northeastern Qinghai–Tibetan Plateau

Discrete extreme heat events, deluges, and droughts will become more frequent and disproportionately affect the processes and functions of grassland ecosystems. Here, we compared the responses of CO2 and heat fluxes to natural extreme events in 2016 in a lower alpine meadow and neighboring upper shrubland on the northeastern Qinghai–Tibetan Plateau. Unlike insensitive sensible heat flux, latent heat flux (LE) increased by 21.8 % in the meadow and by 56.4 % in the shrubland during a dry period and subsequent compound hot-dry period in August. Changes (Δ, data for 2016 minus the corresponding means from other years) in the heat flux at both sites were determined by changes in solar radiation (ΔSwin), as sufficient soil moisture was available. ΔLE was more sensitive to ΔSwin in the open-canopy shrubland, reflecting its greater capacity for evaporative cooling to buffer climate anomalies. CO2 fluxes responded weakly to extreme wet or dry events but strongly when those events were accompanied by exceptional heat. During single or compound hot events, the mean changes in total ecosystem respiration (ΔTER) increased by about 30 % in both grasslands, although ΔTER was more sensitive to changes in the topsoil temperature in the more productive meadow than in the shrubland. The mean changes in gross primary productivity (ΔGPP) fluctuated by <10 % in the warmer meadow but increased by 29.3 % in the cooler shrubland relative to the respective baseline, probably because of the differences in canopy structure and root depth and the consequent high-temperature stress on vegetation photosynthesis. The changes in net ecosystem CO2 exchange (ΔNEE) were significantly related to ΔTER in the meadow and increased by 55.8 %, whereas ΔNEE was controlled mainly by ΔGPP in the shrubland and decreased by 22.4 %. Overall, both alpine grasslands were resistant to rainfall anomalies but susceptible to exceptional warmth, with the differential responses being ascribed to canopy structure and root depth. Our results provide helpful insights based on which the carbon sequestration and water-holding functions of alpine grasslands during future climate change can be predicted.

Prediction of Direct and Diffuse Solar Radiation on Pokhara, Nepal

The measurement of direct and diffuse solar radiation is not easily possible because instruments are quite expensive. The main objective of this study was to predict direct solar radiation (IB) and diffuse solar radiation (ID) on Pokhara (28.186643o N, 83.97518o E, 800 m asl) for a period of one year (2017). Daily data of spectral Aerosol optical depth (AOD) and total ozone column are obtained from NASA website. The maximum value of direct solar radiation and diffuse solar radiation values were found 932.9 ± 65.9 W/m2 in January and 363.0 ± 87.9 W/m2 in February respectively. The minimum value of direct solar radiation and diffuse solar radiation values were found 692.8 ±142.0 W/m2 in April and 107.7 ± 20.4 W/m2 in July respectively. The diffuse solar radiation changes with season. The annual average of direct solar radiation and diffuse solar radiation are found 808.1± 133.7 W/m2 and 220.8 ± 102.8 W/m2 and respectively. The results of this research work will help further identification, impact and analysis of solar radiation in different locations in Nepal with the same geographic conditions.