Light Winds Research Articles

Energy Efficiency of Small Wind Turbines in an Urbanized Area—Case Studies

This study aimed to determine whether the wind zone that characterizes a given area of the country in open area is reflected in the built-up area lying within the zone. Analysis included four Polish cities located in different wind zones. The two-parameter Weibull density distribution function was used to present the wind conditions at each location. Two 3 kW VAWT devices were selected to evaluate the productivity of wind turbines at the locations analyzed. It was shown that the wind zones characterizing the wind potential of a region in an open area have no significant influence on the wind conditions in the built-up area located in that area. It was determined that the study location’s did not exhibit wind potential that could be economically justified by a wind turbine. WTs in the city do not reach their nominal productivity. A decisive advantage of very light winds was observed (up to 2 m/s) and a large proportion of so-called atmospheric calms. It was shown that the installation of small wind turbines in an urbanized area requires a minimum of annual wind measurements at the exact location and height of each future turbine planned.

Effects of natural surfactants on the spatial variability of surface water temperature under intermittent light winds on Lake Geneva

The spatial variability of lake surface water temperature (LSWT) between smooth and rough surface areas and its potential association with the natural surfactant distribution in the surface microlayer were investigated for the first time in a lake. In spring 2019, two different field campaigns were carried out in Lake Geneva to measure: i) the enrichment factor of fluorescent dissolved organic matter (FDOM) as a proxy for biogenic surfactants, and ii) LSWT and near-surface water temperature profiles while simultaneously monitoring water surface roughness in both cases. Results indicate that, under intense incoming short-wave radiation and intermittent light wind conditions, the atmospheric boundary layer (ABL) was stable and the accumulation of heat due to short-wave radiation in near-surface waters was greater than heat losses by surface cooling, thus creating a diurnal warm layer with strong thermal stratification in the water near-surface layer. A threshold wind speed of 1.5 m s-1 was determined as a transition between different dynamic regimes. For winds just above 1.5 m s-1, the lake surface became patchy, and smooth surface areas (slicks) were more enriched with FDOM than rough areas (non-slick) covered with gravity-capillary waves (GCW). Sharp thermal boundaries appeared between smooth and rough areas. LSWT in smooth slicks was found to be more than 1.5°C warmer than in rough non-slick areas, which differs from previous observations in oceans that reported a slight temperature reduction inside slicks. Upon the formation of GCW in non-slick areas, the near-surface stratification was destroyed and the surface temperature was reduced. Furthermore, winds above 1.5 m s-1 continuously fragmented slicks causing a rapid spatial redistribution of LSWT patterns mainly aligned with the wind. For wind speeds below 1.5 m s‑1 the surface was smooth, no well-developed GCW were observed, LSWT differences were small, and strong near-surface stratification was established. These results contribute to the understanding and the quantification of air-water exchange processes, which are presently lacking for stable Atmospheric Boundary Layer conditions in lakes.

Soybean performance under moisture limitation in a temperate tree-based intercropping system

CONTEXTTree-based intercropping (TBI) systems show promise in reducing the vulnerability of field crops to increasing water stress. TBI can generate several above- and belowground interactions between trees and crops. These interactions remain poorly documented, especially in the context of moisture limitation. OBJECTIVEThe objective of this study was to determine the performance of soybean within a TBI system under moisture limitation. We hypothesized that TBI generates both positive (near the alleyway centre) and negative (near the trees) effects on soybean performance and that these effects are accentuated when moisture availability decreases. METHODSA partial rainfall interception treatment (50% of the soil surface) in a soybean crop (stages R1 to R7) was installed for two years (2018 and 2019) in a TBI (50 trees/ha planted in 2012) in southern Quebec. TBI was composed of hybrid poplars (Populus deltoides × P. nigra) and different high-value hardwood species that were planted alternately within rows. A tree root-pruning treatment was also applied to understand belowground effects of tree roots on soybean growth under moisture limitation. Various microclimatic (light availability, wind speed and soil moisture) and soybean performance variables (leaf traits, 100-grain weight and yield) were measured at four distances from the tree row (4, 12 and 20 m, and control). RESULTS AND CONCLUSIONSRainfall exclusion decreased soil moisture and had a negative effect on soybean yield (−14%). The effect of the rain exclusion treatment on soybean performance was similar across all tree row distances and in both root-pruning treatments, which is contrary to our prediction. In 2018, an abnormally dry and warm season, yield near the alley centres was higher than near the tree row and tended to outperform the control. In 2019, a season with normal rainfall and temperature, soybean yield within the alleys was consistent among the different measured distances and did not differ from that in the control. Moderate shading at 4 m (−26% of PAR) was not associated with a change in soybean yield or leaf traits compared to other distances where shading was negligible or absent. Root pruning negatively affected soybean yield in 2018 (−14%) and 2019 (−22%), which is contrary to our prediction. SIGNIFICANCEThis case study adds to our knowledge regarding interactions between crops and trees in widely spaced TBI systems. TBI effects on spatial patterns of crop yield may vary substantially depending upon inter-annual variation in climatic conditions. This study suggests that more facilitative effects would prevail in dryer and warmer years, in contrast to near neutral effects in normal years.

Hot Spot Detection of Photovoltaic Module Based on Distributed Fiber Bragg Grating Sensor

The hot spot effect is an important factor that affects the power generation performance and service life in the power generation process. To solve the problems of low detection efficiency, low accuracy, and difficulty of distributed hot spot detection, a hot spot detection method using a photovoltaic module based on the distributed fiber Bragg grating (FBG) sensor is proposed. The FBG sensor array was pasted on the surface of the photovoltaic panel, and the drift of the FBG reflected wavelength was demodulated by the tunable laser method, wavelength division multiplexing technology, and peak seeking algorithm. The experimental results show that the proposed method can detect the temperature of the photovoltaic panel in real time and can identify and locate the hot spot effect of the photovoltaic cell. Under the condition of no wind or light wind, the wave number and variation rule of photovoltaic module temperature value, environmental temperature value, and solar radiation power value were basically consistent. When the solar radiation power fluctuated, the fluctuation of hot spot cell temperature was greater than that of the normal photovoltaic cell. As the solar radiation power decreased to a certain value, the temperatures of all photovoltaic cells tended to be similar.

Influence of view factors on intra-urban air temperature and thermal comfort variability in a temperate city

Urban geometry is known to be one of the major factors in explaining the intra-urban temperature variations. A commonly used indicator to describe the urban geometry is the sky view factor. However, the existing studies have shown that the relationship between SVF and urban temperature is quite contradictory. This suggests that a single SVF cannot accurately quantify the urban geometry. For comparison, we here propose to use view factors, including sky, building and tree view factors (SVF, BVF, and TVF, respectively), to accurately quantify the three-dimensional urban geometry. Based on microclimate measurements conducted in Beijing Olympic Park and its surrounding urban environment in Beijing, China, the impact of view factors on intra-urban air temperature and thermal comfort was evaluated. Measurements were conducted along a selected path during hot summer days with clear skies and light winds by mobile traverses. The obtained results showed that SVF was positively correlated with air temperature during the day but negatively correlated with air temperature at night. BVF mainly played a warming role in both daytime and nighttime. Especially at night, BVF was the main geometric warming factor. TVF had a significant cooling effect during the day but did not have a negative effect at night due to reduced SVF. There was a strong point-to-point correlation between SVF and outdoor thermal comfort in the daytime. The mean differences in Mean Radiant Temperature and Physiologically Equivalent Temperature between shaded and unshaded sites were 12.0 °C and 6.8 °C, respectively, which suggested that providing effective shading is extremely important for improving outdoor daytime thermal comfort.

A New combined MPPT-Pitch Angle control of a Large Variable Speed Wind Turbine in Different Operating Areas based on Synergetic control

The aim of this paper is to create a novel combination between two controls, maximum power point tracking (MPPT) and Pitch angle control system of a variable-speed wind turbine. The main objective sought is to achieve the maximization of the power produced by the fixed pitch angle turbine through the MPPT control in the zone 02 of operation. Then, limit the power to its nominal value by using the Pitch control with variable pitch angle in zone 03 of operation. Our contribution will be to propose strategies based on two types of controllers. The first is the control by the MPPT control, it is applied in light winds to extract the maximum power. The second is Variable Pitch Control, which is applied in strong winds to keep power constant at its nominal value, as well as protecting the wind turbine from high winds. For this, linear and non-linear control laws (PI, SC) respectively are implemented to achieve the defined objective. The simulation results show the feasibility and effectiveness of the techniques used.

Characteristics of the Marine Atmospheric Boundary Layer under the Influence of Ocean Surface Waves

Abstract The deviation of the mean wind profile from Monin–Obukhov similarity theory (MOST) within the wave boundary layer (WBL) is investigated by combining four levels of turbulence data measured on a fixed platform with wave measurements. The data suggest that the mean wind profile follows MOST under wind-sea conditions because the turbulence statistics and structure are consistent with the attached eddy model. However, pronounced swell-related peaks appeared in the velocity spectra and uw cospectra under swell conditions. The upward wave-induced stress resulted in a large wind gradient within the WBL when light winds traveled with the swell, while the opposite result was found for the wind-opposite swell. These phenomena were analyzed based on the velocity spectra and turbulence variances. We found that the deviation of the wind profile was due to the longer or shorter length of the f −1 scaling region appearing in the velocity spectra. Significance Statement The interactions between ocean waves and adjacent airflow affect the functioning of Earth’s climate and weather systems. However, our physical understanding of air–wave interactions remains incomplete, for example, the deviation of the mean wind profile from Monin–Obukhov similarity theory within the wave boundary layer. In this study, we aim to provide new insights by analyzing four-level turbulence data and wave measurements. We found that when the local wind travels faster than the wave, the airflow over the wavy surface is similar to that over land because the effects of waves do not reach the measurement heights. In conditions with wind-following or -opposing fast-propagating waves, the overlying airflow is greatly modified as the turbulence is affected by wave-induced perturbations.

Variability of Sea Breezes Over the Cameroonian Coast and Their Interaction With the West African Monsoon

The sea breeze characteristics of over two coastal areas of Cameroon were studied. The study used 3-hourly wind (speed and direction), rainfall, and atmospheric pressure data of 4 years (2006–2009) at Tiko and 5 years (2011–2015) at Ebodje to examine various characteristics of sea breezes. Statistics are presented that describe the occurrence, onset and cessation, and strength of the sea breezes. The frequency of occurrence clearly shows two regimes by two maxima (November and March) at Tiko and (January and July) at Ebodje. The results show that a sea breeze usually starts few hours (about 3–4 h) after the sunrise as a light onshore surface wind, has a mean duration of about 9 h at Tiko, and occurs during all seasons at both coastal areas. The sea breeze occurrence is found to be strongly influenced by the West African monsoon winds, and its onset and cessation times show a pronounced seasonal variation. The sea breeze strength is greater at Tiko than that at Ebodje during the West African monsoon season. Average daily hodographs for Tiko reveals that the sea breeze circulation is in both clockwise and anticlockwise rotation. There would be a significant seasonal effect of large-scale flows on sea breeze hodograph patterns. A wind roses analysis at Ebodje shows a high temporal variability of sea breeze frequencies at 09:00 (Local Standard Time: LST) in the south direction (36%), then at 15:00 LST in the west direction (26%), because of the preponderance of calm atmospheric situations conducive to its onset. Therefore, the circulation of the sea breeze is influenced by local factors (topography and vegetation). This phenomenon in the coastal regions of Cameroon can be the main factor controlling the transport of accidental near shore oil slicks and air pollutants.

Optimal scheduling strategy of electricity‐heat‐hydrogen integrated energy system under different operating modes

With the increasing penetration level of renewable energy in the integrated energy system (IES), water electrolysis for hydrogen production (WEHP) technology has become an effective solution to increase the capacity of renewable energy utilization. Therefore, this paper proposes to take WEHP and hydrogen fuel cell (HFC) as flexible resources to participate in the optimal scheduling of IES under grid-connected/off-grid operation mode. Firstly, focusing on the production, storage and utilization of hydrogen energy, a unified operation model of WEHP module is built by analyzing the differences of the three WEHP technologies. And then, “co-generation” model of HFC, the residual capacity and transportation cost model of hydrogen storage device (HSD) are built. Second, by analyzing the uncertainty of light intensity and wind speed, a prediction error correction method is proposed to improve the prediction data accuracy of renewable energy power generation. Third, taking the lowest daily operation cost as the objective function, the optimal scheduling model of electricity-heat-hydrogen integrated energy system under grid-connected/off-grid operation mode is constructed. On this basis, the operation scheduling model of electricity-heat-hydrogen integrated energy system is transformed into a mixed integer linear model by piecewise linearization method, and the model is solved by CPLEX solver. Finally, an example is given to verify the rationality of the proposed scheduling model in the grid-connected/off-grid operation mode. On one hand, reasonable optimal scheduling of multiple WEHP combination is helpful to reduce the daily operation cost of IES. On the other hand, by correcting the prediction data deviation of renewable energy power generation, the equipment output of electricity-heat-hydrogen integrated energy system can be more reasonable, which is helpful to reduce the daily operation cost and improve the operation reliability. The effects of sensitive factors such as the penetration level of renewable energy, the relative fluctuation of electricity price and hydrogen price on the operation cost of optimal scheduling scheme are further analyzed, which provides a theoretical reference for the optimal scheduling of IES.

Optimal Scheduling of Regional Combined Heat and Power System Based on Improved MFO Algorithm

Due to the inflexibility of cogeneration power plants and the uncertainty of wind power production, the excess power of the distribution network brings challenges to the power grid operation. This paper introduced an improved moth-flame optimization algorithm to meet the challenge of energy complementary dispatching. The proposed algorithm adopts three effective strategies, namely inertia weight, unified initialization, and the spiral position update strategy, which maintains a strong global search ability and a potent compromise between global and local search. The effectiveness of the proposed method was evaluated by benchmark functions. Furthermore, the proposed method was applied to combine heat and power system operation problems and economic dispatch in light load and wind power unpredictability. In order to verify the robustness of the algorithm and solve the complex constraints of power systems under extreme conditions, three different cases had been discussed. The experimental findings indicate that the proposed algorithm shows better performances in terms of convergence speed, ability to escape from a local optimum solution, and population diversity maintenance under different complexity conditions of engineering problems.

Innovative aerodynamic rotor concept for demand-oriented power feed-in of offshore wind turbines

We introduce an aerodynamic rotor concept for a 15 MW offshore wind turbine which is tailored for an increased power feed-in at low wind speeds. The main objective of the conceptual design is to limit the stationary loads (blade flapwise root bending moment (RBM) and thrust) to the maximum value of the IEA 15 MW offshore reference turbine, while greatly increasing the swept rotor aera. The outer part of the blade (e.g. outer 30% of the rotor) is designed for a higher design tip speed ratio (TSR) and a lower axial induction than the inner part. By operating at the high TSR in light winds, the slender outer part fully contributes to the increased power capture. In stronger winds the TSR is reduced and the torque generation is shifted to the inner section of the rotor. Moreover, the blade is designed in a way that makes the limitation of the flapwise RBM through peak shaving aerodynamically more efficient. With static blade element momentum simulations the characteristics of the rotor are investigated and the economic revenue of the turbine is estimated, considering a wind speed dependent feed-in price. Our results show that the revenue can be increased by 30% compared to the reference turbine with an increase of rotor diameter by 36%.

Uji Efektifitas Sistem Smart Green House Bertenaga Surya Untuk Budidaya Tanaman

A greenhouse is one form of optimal environmental controlled monitoring for plant growth. Light intensity, air temperature, humidity, wind speed, and heat transfer, and mass transfer are microclimate parameters that are generally observed. Greenhouses can be integrated with the Internet of Things (IoT) to facilitate monitoring called smart greenhouses in real-time. Previously, a solar-powered IoT integrated plant monitoring system has been designed but its effectiveness is not yet known. The purpose of this study was to test the smart greenhouse system for plant cultivation including watering and providing light by utilizing solar panels as a source of electrical energy for the system. The research was carried out in several stages, namely system design, timer testing, pump testing, and watering and lighting. The effectiveness of the greenhouse system has been successfully tested. The test results show good accuracy. There is a slight difference between the test results and the comparison. However, the difference is still tolerable. The smart greenhouse systems can be used for plant cultivation.

Development of Artificial Intelligence Model to Forecast Photovoltaic Power Generation Including Airborne Particulate Matter

Purpose : This study aims to suggest an optimal model for predicting photovoltaic (PV) power generation by comparing single and hybrid models that include particulate matter in the atmosphere as input parameters.Methods : From December 2016 to December 2019, 1 MW-class PV power generation data in Jindo-gun, Jeollanam-do and meteorological data and particulate matter data from Mokpo were used. Radiation, sunshine time, pressure, temperature, humidity, wind speed, wind direction, snow load, precipitation, PM10, and PM2.5 were used as input parameters. We used single models such as random forest (RF), artificial neural network (ANN), long short-term memory (LSTM), and gate recurrent unit (GRU) and hybrid model such as LSTM-ANN and GRU-ANN. Coefficient of determination (R2), root mean square error (RMSE), and mean absolute error (MAE) were used to compare and evaluate the prediction performance of the models.Results and Discussion : The variable importance through RF was as follows: radiation (77.66%), day light hours (4.85%), pressure (4.16%), temperature (3.98%), humidity (2.25%), wind speed (2.21%), PM10 (2.72%), PM2.5 (1.65%), wind direction (1.44%), snow cover (0.05%), and precipitation (0.02%). GRU-ANN showed the highest R2 (0.838) among the models and lower epoch (8) than GRU using the early stop.Conclusion : The GRU-ANN model was the most suitable for forecasting PV power generation including particulate matter.

Performance analysis based on GPS data of Olympic class windsurfing

ABSTRACT This study examined the technical and tactical variables that determine performance before departure and during a race in all wind conditions. Data were collected from 44 Olympic-class windsurfers who participated in the World Cup and Allianz Regatta. Distance to the start line and speed 5 s before departure, distance to start line and speed when starting, and distance travelled and time at each leg were recorded via GPS (5 Hz). Average speed was calculated through distance travelled and time. Results indicated that the high-performance group had significantly (p < 0.05) less distance from the starting line and faster speed when starting than the low-performance group in heavy wind conditions. During the first or third legs with light and medium winds, the high-performance group demonstrated a significantly (p < 0.05) faster average speed in heavy wind and significantly less distance travelled, and faster average speed was observed in all legs. The first half of the high-performance group had significantly (p < 0.05) longer distance travelled than the second half. Significantly faster average speed was observed in light wind. These results may assist in preparing for the tactical and technical requirements during a race and enhance performance in every situation.

Curating the TD6405 database of 1-min interval wind observations across the USA for use in Wind Engineering studies

The TD6405 online database of wind observations at 1-min intervals from 2000 onwards at almost 1000 stations across the USA is a highly valuable on-demand resource for Wind Engineering studies, but it contains numerous defects. Many defects are common to other observational databases, for which detection and repair methods already exist. Others are unique to TD6405 for various operational reasons, including the requirement for real time quality control and the adoption of sonic anemometers. Having no moving parts, sonic anemometers provide ideal perches for birds which interrupt the observations and create spurious large gusts on landing and take-off. The real time quality control test added in 2013 to excise bird-generated gusts is shown to miss many of them and to generate four false positives for each one it does find. Each false positive also removes the following 5-min period of valid observations. Consequently, after 2013, the incidence of calms is suppressed, and thunderstorm downbursts are disproportionally censored in light winds. An efficient retrospective test is proposed and validated using observations prior to 2013, but the data missing after 2013 is permanently lost and cannot be recovered. Urgent action is required to correct this ongoing situation.

Modal identification of a light and flexible wind turbine blade under wind excitation

Modal identification of a light and flexible wind turbine blade under wind excitation

Spatial analysis of outdoor wet bulb globe temperature under RCP4.5 and RCP8.5 scenarios for 2041–2080 across a range of temperate to hot climates

Wet bulb globe temperature (WBGT) is commonly used to assess human physical activity limits and risk exposure to heat-related injury. Using Australia as a case study location, rates of change in WBGT across a range of temperate to hot and dry to humid climates in response to selected projected climate scenarios were investigated. An established physics-based method for estimating WBGT using standard meteorological data was incorporated into a spatial modelling framework to map WBGT for a baseline period (1986–2005) for mid-summer daytime, mid-summer early morning and mid-winter daytime scenarios, under clear sky conditions and both light (0.5 ms−1) and moderate (3.0 ms−1) wind speeds at a nominal resolution of 0.05 decimal degrees. The resulting maps of WBGT revealed significant spatial variability in the range and pattern of increased WBGT across the three baseline scenarios in response to projected change under RCP4.5 and RCP8.5 for 2041–2060 and 2061–2080 generated by the ACCESS1.0 climate model. Moderate wind speed scenarios produced significantly cooler WBGTs than the equivalent low wind speed scenarios, reducing mean modelled summer daytime WBGT by 3.2 °C, summer morning WBGT by 0.8 °C, and winter daytime WBGT by 3.0 °C. Projected future summer daytime WBGT under unshaded clear atmospheric conditions with light wind speeds can be expected to exceed the range of the commonly used heat categorisation system used to inform recommended restrictions on physical activity and regularly exceed 35 °C in northern Australia's equatorial and tropical climates by mid-century under RCP4.5 and RCP8.5. Summer early morning WBGT and winter daytime WBGT were projected to reach heat categories that would result in recommended restrictions in physical activity continuously (across consecutive 24-h periods) in summer and intermittently (for at least part of the day) year-round by 2050 with more severe conditions by 2070 and/or under RCP8.5 scenarios. Investigations into physical activity limits beyond the current highest heat category and the efficacy of the employed methodology to estimate WBGT above 35 °C using standard meteorological data are required to prepare for the projected warmer climate.

The Expression to Fanny About

The Oxford English Dictionary (OED) records the expression to ‘fanny around (or about): to mess around, waste time; to act in an unproductive or dithering manner’ only from 1969.1 The etymology is given as ‘< fanny, n.1, “female genitals”’, and we are asked to compare the vulgarisms to fuck about, and to arse around. There is, however, an earlier use of the term which, if not the direct origin, may have contributed to the history of this expression. The Suffolk writer Edward Fitzgerald published a collection of what he called ‘sea words and phrases along the Suffolk coast’ in 1869,2 and amongst these is given ‘FANNY ABOUT. A light variable wind fannies about’. This is formally identical to the modern expression, and from the notion of ‘variable wind’, the current sense could easily have developed via the ‘dithering manner’ mentioned in the OED entry. Fitzgerald’s text was noted by James Joyce circa 1920, though he made no comment upon it.3 There are apparently no other records of intermediate date to support the slight, but conjectural, extension of meaning suggested here.

Land use and anthropogenic heat modulate ozone by meteorology: a perspective from the Yangtze River Delta region

Abstract. With the rapid advance in urbanization, land use and anthropogenic heat (AH) dictated by human activities significantly modify the urban climate and in turn the air quality. Focusing on the Yangtze River Delta (YRD) region, a highly urbanized coastal area with severe ozone (O3) pollution, we estimate the impacts of land use and AH on meteorology and O3 using the Weather Research and Forecasting model coupled to Chemistry (WRF-Chem). These results enhance our understanding of the formation of O3 pollution in rapidly developing city clusters with place-specific topography, as most of our results can be supported by previous studies conducted in other regions around the world. Regional O3 pollution episodes occurred frequently (∼ 26 times per year) in the YRD from 2015 to 2019. These O3 pollution episodes are usually in calm conditions characterized by high temperature (over 20 ∘C), low relative humidity (less than 80 %), light wind (less than 3 m s−1) and shallow cloud cover (less than 5 okta). In this case, O3 pollution belts tend to appear in the converging airflows associated with the sea and the lake breezes. On the other hand, rapid urbanization has significantly changed land use and AH in this region, which subsequently affects meteorology and O3 concentration. The largest change in land use comes from urban expansion, which causes an increase in 2 m temperature (T2) by a maximum of 3 ∘C, an increase in planetary boundary layer height (PBLH) by a maximum of 500 m, a decrease in 10 m wind speed (WS10) by a maximum of 1.5 m s−1 and an increase in surface O3 by a maximum of 20 µg m−3. With regard to the sea and lake breezes, the expansion of coastal cities, like Shanghai, can enhance the sea breeze circulation by ∼ 1 m s−1. During the advance of the sea breeze front inland, the updraft induced by the front causes strong vertical mixing of O3. However, once the sea breeze is fully developed in the afternoon (∼ 17:00 LT), further progression inland will stall. Then O3 removal by the low sea breeze will be weakened, and surface O3 can be 10 µg m−3 higher in the case with cities than in the case with no cities. The expansion of lakeside cities, such as Wuxi and Suzhou, can extend the lifetime of lake breezes from noon to afternoon. Since the offshore flow of the lake breeze transports high O3 from the land to the lake, the onshore flow brings high O3 back to the land. Surface O3 in lakeside cities can increase by as much as 30 µg m−3. Compared to land use, the effects of AH are relatively small. The changes mainly appear in and around cities where AH fluxes are large. There are increases in T2, PBLH, WS10 and surface O3 when AH fluxes are taken into account, with increments of approximately 0.2 ∘C, 75 m, 0.3 m s−1 and 4 µg m−3, respectively. AH contributes largely to the urban environment, altering meteorological factors, O3 concentration and urban breeze circulation, but its effect on the sea and the lake breezes seems to be limited.

FAKTOR-FAKTOR YANG MEMPENGARUHI PRODUKTIVITAS KELAPA SAWIT (Elaeis guineensis jacq) PADA BERBAGAI AFDELING DI KEBUN BAH JAMBI PT. PERKEBUNAN NUSANTARA IV

North Sumatra Province, where the second-highest oil palm productivity in Indonesia, has successfully reached fresh fruit bunches (FFB) production of 5,775,631.82 tons in 2016. However, the level of oil palm productivity tends to be unstable and low. The purpose of this study was to identify and analyze factors influencing the level of oil palm productivity at the Bah Jambi Plantation PTPN IV, Simalungun Regency, North Sumatra Province. The method used in this study was the qualitative descriptive analysis method by collecting secondary data at research locations at 4 Afdeling Kebun Bah Jambi PT. Nusantara IV Plantation. The results of correlation and regression analysis showed that soil factor such as organic C, soil pH, cation exchange capacity and the availability of soil N, P, K and Mg is the most dominant factors in influencing the amount of oil palm productivity which have determination coefficient (R2) more than 90%. Meanwhile, climate factors such as evapotranspiration, duration of light exposure, wind speed and rainfall have the most role in influencing oil palm productivity which has a coefficient of determination (R2) of 95%, 94%, 88% and 33%.