Fog Conditions Research Articles

Effect of Salt Fog Conditions on Deterioration of Housing Materials for Polymer Insulators in Salt Fog Ageing Test

Salt fog ageing tests are widely conducted for evaluating anti-tracking/anti-erosion performance of housing materials for outdoor polymer insulators. A detailed test method, however, is not yet standardized and round robin tests have been conducted for standardization all over the world. Here we have investigated the effect of fog conditions on the deterioration of silicone rubber under two different salt fog conditions generated by an ultrasonic humidifier and an IEC nozzle. In spite of the same injection rate and the same salinity, comparable results from the viewpoints of leakage/discharge currents and the degree of surface deterioration could not be obtained between the two salt fog conditions generated by the ultrasonic humidifier and the IEC nozzle. Almost comparable test results, however, were obtained under the two salt fog conditions generated by the ultrasonic humidifier and the IEC nozzle after controlling the salt fog particle size distribution.

Seasonal variability of the aerosol parameters over Kanpur, an urban site in Indo-Gangetic basin

With the growing antropogenic activities and urbanization, pollution level is found to be increasing in the Indo-Gangetic (IG) basin. This trend of increasing pollution has direct impact on the climatic conditions, especially the increase of haze, fog and cloudy conditions in the region. A ground-based CIMEL radiometer has been deployed on the campus of the Indian Institute of Technology (IIT) Kanpur, India, as a part of the Aerosol Robotic Network (AERONET) program with an objective to characterize the aerosols in the IG basin. The optical properties of the aerosols over Kanpur, which is one of the largest industrial cities in the IG basin, show strong seasonal and inter-annual variations. The fine mode urban/industrial aerosols contribute more than 75% to the observed aerosol optical depth (AOD) during the post-monsoon and winter seasons, whereas the natural dusts contribute ∼60% to the AOD during the pre-monsoon and monsoon seasons. Effective radius ( R eff) and volume weighted mean radius ( R V), the two best representative parameter of the coarse and fine modes of aerosol size distribution show maximum values during winter season. The increase in the R V is attributed to the hygroscopic growth of fine mode particles in presence of high relative humidity and favorable temperature condition; but the increase in r eff is due to the association of the fine mode absorbing particles to the coarser dusts. This is also reflected in low values (<0.8) of single scattering albedo (SSA) at coarse mode during the season. Higher values of SSA at fine mode indicate dominance of water-soluble aerosols scattering in nature. The linear regression equations between AOD (at 0.67 μm wavelength) and extinction coefficient due to fine and coarse modes also reveal the relative contribution of the fine and coarse mode particles to the observed optical properties during different seasons in Kanpur.

Real-time measurements of visibility and transmission in far-, mid- and near-IR free space optical links

A method for recording real-time measurements of visibility for free space optical links and a careful comparison of different transmission windows in the atmosphere is reported. The results proved that a 10 /spl mu/m window is considerably better than the 1600 and 800 nm ones in dense and thick fog conditions.

High-frequency components of leakage current as diagnostic tool to study aging of polymer insulators under salt fog

The results of using the high-frequency components of the leakage current to study aging of contaminated insulators under salt fog conditions. Experimental results demonstrate that the high-frequency components can be used effectively to study aging of polymer insulators in a salt fog test.

Experimental comparison between far- and near-infrared wavelengths in free-space optical systems

We report an experimental comparison of three atmospheric transparency windows (800 nm, 1600 nm, and 10 μm) upon scattering attenuation from haze and fog. Our results prove that a 10-μm window is considerably better than the 1600 and 800 nm ones in dense and thick upslope fog conditions. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 46: 319–323, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20976

EPDM 고분자 애자에 대한 표면방전 및 누설전류파형의 고조파분석

This paper presents the results of spectrum analysis of leakage current waveforms on contaminated polymer insulators under fog conditions. This is a basic study on development of a monitoring for aging degree and surface pollution state using distortion rate(%) of 3rd and 5th harmonics according fundamental frequency[60Hz] under environment conditions. Arcing on the surface was always associated with distortion in the leakage current ; hence the low frequency components of the leakage current can be used as a means to evaluate the surface degradation. The results indicate that the distortion rate by spectrum analysis is available for the monitoring of contamination condition of EPDM Polymer insulators.

Driver Adjustment to Solar Glare

When the sun is low in the sky, a driver headed directly towards the sun is subject to glare, which impairs target detection. Unobtrusive (video) observations of drivers approaching a setting afternoon sun found only a small decrease in speed compared with a non-glare condition; in addition, speed variability appeared to increase somewhat in the sun condition. These effects, which are similar to what has been reported for driver behavior in fog and other impaired-visibility conditions, increase the risk of accidents. Causes and implications are discussed in the paper.

A Flashover Prediction Method for Contaminated Insulators using a Stochastic Analysis of Leakage Current

In this paper, we present the results of a new stochastic analysis of the leakage current on contaminated insulators under salt fog conditions. The stochastic analysis of the leakage current was conducted using a Hilbert transform and the level crossing rate. The Hilbert transform is used for the leakage current envelope, while the level crossing rate is used to convert the upper envelope into a cdf. Using a new defined weighting factor, the resulting cdfs show a probability that the stages until flashover can be discriminated from each other. Therefore, the proposed method is effective for flashover prediction and for monitoring the contamination conditions of outdoor insulators.

Examination of the Method on Information Supply using Navigation Display in Fog Condition

Examination of the Method on Information Supply using Navigation Display in Fog Condition

Simulation of infrared detection range at fog conditions for Enhanced Vision Systems in civil aviation

The DLR project ADVISE (ADvanced VIsual System for Situation Awareness Enhancement) deals with development, simulations and testing for an Enhanced Vision System (EVS) for visual pilot assistance. Within the frame of the project ADVISE, model calculations in the infrared spectral region have been performed to investigate the influence of low visibility conditions, especially fog, for air traffic during landing approaches. The objectives of this paper are to find out whether the use of IR cameras for an EVS can improve the visibility at defined conditions of ICAO standard visual range categories CAT I, II, IIIa and IIIc for landing approaches. The calculations are carried out with the atmospheric radiative transfer model MODTRAN Version 4.0. The IR detection range is calculated in the atmospheric windows 3–5 μm and 8–12 μm and compared to the visual range defined at 0.55 μm. The sensor properties are simulated with the model TTIM (TACOM Thermal Image Model) for a specific IR camera type Thermovision 570 operating in the spectral band 8–12 μm. The influence of various climatic and seasonal meteorological conditions, aerosol types and target parameters, such as temperature and size, on the IR detection range is taken into account.

Active Nitrogen in Surface Ozone Depletion Events at Alert during Spring 1998

Measurements of NOx,y were made at Alert, Nunavut, Canada (82.5° N, 62.3° W) during surface layer ozone depletion events. In spring 1998, depletion events were rare and occurred under variable actinic flux, ice fog, and snowfall conditions. NOy changed by less than 10% between normal, partially depleted, and nearly completely depleted ozone air masses. The observation of a diurnal variation in NOx under continuous sunlight supports a source from the snowpack but with rapid conversion to nitrogen reservoirs that are primarily deposited to the surface or airborne ice crystals. It was unclear whether NOx was reduced or enhanced in different stages of the ozone depletion chemistry because of variations in solar and ambient conditions. Because ozone was depleted from 15–20 ppbv to less than 1 ppbv in just over a day in one event it is apparent that the surface source of NOx did not grossly inhibit the removal of ozone. In another case ozone was shown to be destroyed to less than the 0.5 ppbv detection limit of the instrument. However, simple model calculations show that the rate of depletion of ozone and its final steady-state abundance depend sensitively on the strength of the surface source of NOx due to competition from ozone production involving NOx and peroxy radicals. The behavior of the NO/NO2 ratio was qualitatively consistent with enhanced BrO during the period of active ozone destruction. The model is also used to emphasize that the diurnal partitioning of BrOx during ozone depletion events is sensitive to even sub ppbv variations in O3.

Universal spectra of electric field pulsations in the atmosphere

Short‐term (f ≃ 10−3–1 Hz) electric field pulsations in the surface atmospheric layer have been measured during 1999–2001 under the fair‐weather and fog conditions. At the frequencies of 10−2–1 Hz these pulsations have a power‐law spectrum with the spectral index varying in the range from −1.23 to −3.36 while the most probable values of the index fall into the range from −2.25 to −3.0, unlike the temperature fluctuation spectra which obey in the inertial subrange the Kolmogorov power law with the spectral index close to −5/3. Under the fog conditions the intensity of electric‐field pulsations increases by about an order of magnitude compared to the fair‐weather conditions. The relation of spectral characteristics to the formation of aero‐electric structures (AESs) is evident; the spectral index distribution during AES flyby has two maxima. Analysis of the mechanisms explains the relationship between electric‐field spectra and the neutral‐gas turbulence and AES formation.

MECHANISMS FOR THE FORMATION OF ELECTRIC-FIELD PULSATION SPECTRA IN THE NEAR-SURFACE ATMOSPHERE

We present the results of detailed measurements of the spectrum of short-term (f≃ 0.001-1 Hz) pulsations of the electric field of the near-surface atmosphere under the fair-weather and fog conditions. It is shown that the electric-field pulsations at frequencies 10-2-10-1 Hz have a power-law spectrum under both fair-weather and fog conditions. The spectral index varies in a range of from -1.23 to -3.36 depending on the experimental conditions, but the most probable values of the index fall in a range of from -2.25 to -3.0. The spectra corresponding to long time intervals of about a few hours are more steep. The relation of the spectral characteristics to the formation of aeroelectric structures (AESs) is studied. The distribution obtained for the structured spectra is bimodal, i.e., it exhibits two maxima in the ranges of spectral indices from -2.75 to -3.0 and from -2.25 to -2.5. The nonstructured-spectrum distribution is asymmetric and has a pronounced maximum corresponding to hard spectra with indices from -2.5 to -3.3. The intensity of the electric-field pulsations under fog conditions increases by about an order of magnitude compared to the case of fair-weather conditions. The mechanisms of spectrum formation of electric-field pulsations and their relations to the pulsation spectra of the electric-charge density with allowance for the neutral-gas turbulence and the presence of AESs are analyzed. We point out the key role of the nonlocal relation between the electric-field intensity and the space-charge density under conditions of spatially inhomogeneous turbulence. Model problems of the spectrum of electric-field fluctuations generated by a homogeneous and “structured” turbulence in the presence of charge-density fluctuations, considered as a passive tracer, are solved.

Frequency agile infrared lidar based on a nontracking KNbO_3 optical parametric oscillator

We present what is to our knowledge the first mid-IR lidar system based on a KNbO(3) optical parametric oscillator pumped by a Ti:sapphire laser. The optical parametric oscillator works in a nontracking configuration and provides high-frequency agility from 1 to 4 mum. This system constitutes an extension to the IR of UV lidars described previously [Europhys. J. D 4, 231 (1998); Appl. Opt. 37, 2231 (1998); Atmos. Environ. 32, 2957 (1998)] for the determination of aerosol concentrations in urban atmospheres. As first field tests, measurements at 3.5 mum were performed in fog conditions. Water droplet size and concentration were determined from Mie calculations. Quantitative temporal mappings and angular profiles are presented.

Avocado and citrus orchards along the coast may use less water

Most citrus and avocado water-use studies have been conducted in inland orchards; however, orchards located in coastal areas are subject to cooler temperatures and foggier atmospheric conditions. To develop coastal area crop coefficients (Kc values) for irrigation management, we measured orchard consumptive water use (ETc) from two different commercial orchards located near Ventura. In addition to coastal climate variability, the ETc measurements were complicated by the wide variability in field soil, slope and elevation. On average, we measured Kc values of 0.46 for young lemons, 0.52 for mature lemons and 0.64 for mature avocados. These values were slightly less than those published, perhaps as a result of greater fog conditions in the orchards as compared to those occurring at the nearest reference ET stations.

An urban climate analysis of Graz and its significance for urban planning in the tributary valleys east of Graz (Austria)

In Graz, the capital of the Austrian province of Styria, located southeast of the main ridge of the Alps, an extensive urban climate analysis was successfully completed in 1995. In the following paper the most important features of the Graz city climate like the different local wind systems, the heat islands as well as the fog and inversion conditions shall be described and illustrated with the help of maps and diagrams. Furthermore, the description of the spreading conditions of air pollutants in selected inversion weather situations will shall play an important role. The results of the study, above all the map of city climatopes are based on the latter a map of planning tips serve as an important basis for urban planning and have already been used for the setting up of a land-use and development plan. Finally the paper will focus its interest on the exceptional quality of the tributary valleys east of Graz, where as a consequence of their highly significance for fresh air supply, a zoning into areas of restricted and banned construction has been carried out. This inclusion of climatological results in urban planning is unique within Austria and is now also being practised in other cities of the province of Styria.

Computer simulation of the transport, formation and dynamics of atmospheric sulfate particles

The present paper investigates the transport, formation and dynamics of atmospheric sulfate particles under different meteorological conditions from point sources. Emissions of SO2 from one and multiple local point sources were modeled. The advection and diffusion of gaseous and particulate matter are described by the atmospheric diffusion equation which is solved numerically using a new developed 3-dimensional model. The evolution of the aerosol size distribution with time was described using the aerosol general dynamic equation. Under fog conditions aqueous phase oxidation is the primary mechanism for sulfate formation. The condensation mechanism from the vapor to liquid phase is the dominant process for sulfate production at moderate relative humidities. The observed mass size distribution of sulfate suggests that the major contribution in the mass size distribution during continental conditions is from long range transport.

Wavelet transform for analyzing fog visibility

The authors present a new technique for estimating the distance of visibility in fog conditions. Based on a psychovisual model and on contrast estimation with wavelet transform, their technique fared well when compared to a direct approach based on local contrast calculation.

Wind Turbine Performance Under Icing Conditions

The effects of rime ice on horizontal axis wind turbine performance were estimated. For typical supercooled fog conditions found in cold northern regions, four rime ice accretions on the S809 wind turbine airfoil were predicted using the NASA LEWICE code. The resulting airfoil/ice profile combinations were wind tunnel tested to obtain the lift, drag, and pitching moment characteristics over the Reynolds number range 1−2 × 106. These data were used in the PROPID wind turbine performance prediction code to predict the effects of rime ice on a 450-kW rated-power, 28.7-m diameter turbine operated under both stall-regulated and variable-speed/variable-pitch modes. Performance losses on the order of 20 percent were observed for the variable-speed/ variable-pitch rotor. For the stall-regulated rotor, however, a relatively small rime ice profile yielded significantly larger performance losses. For a larger 0.08c-long rime ice protrusion, however, the rated peak power was exceeded by 16 percent because at high angles the rime ice shape acted like a leading edge flap, thereby increasing the airfoil Cl,max and delaying stall.

Electrical salt-fog performance of XLPE insulation with different levels of CaCO/sub 3/

This paper presents a study of the electrical performance of crosslinked polyethylene (XLPE) in salt fog conditions. Specimens of XLPE having 0, 15 and 25% calcium carbonate (CaCO/sub 3/) filler, a fixed concentration of 2% carbon black and an additional ultraviolet stabilizer were used. The leakage current and the current pulse counts were monitored as a function of time of exposure to combined electrical stress and salt-fog. Both leakage current and current pulse count were found to increase with increasing test time and with increasing filler concentration. The time to failure of the specimens as a function of the filler concentration was found to increase with increasing filler level. The contact angle decreased, and the surface roughness increased with increasing test time in energized salt fog. A SEM study showed that the surface roughness increased with increasing filler levels, giving an independent confirmation of the results obtained from the surface roughness tester. The EDAX study showed that the intensity count of X-ray of calcium on the surface increased after salt-fog test, indicating that CaCO/sub 3/ was not removed from the surface. Both the SEM and EDAX studies confirmed that the number of CaCO/sub 3/ particles on the surface increased with increasing filler level. It is suggested this was responsible for the observed larger roughness of the surface, higher resistance to arcing erosion and longer lifetime of XLPE polymer with increasing level of CaCO/sub 3/ filler.