Micrometetorological measurements of foggy situations in Siójut (November - December, 2018) (original) (raw)
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2012
Fog is a weather phenomenon that produces weather conditions with significant socio-economic impacts, associated with increased hazards and constraints i n road, maritime and air traffic. Air quality is also affected by fog occurrence. While current numerical weather prediction models are able to forecast situ ations that are favourable to fog events, these forecasts re usually unable to determine the exact location and time of formation or dissipation. Fog is influenced by numerous factors, spanning multiple spatial and temporal scales. Its life cycl e is driven by the competing interactions between thermodynamics, dynamics, microphysical and chemical properties of particles, and radiative flu xes, all of which are difficult to model. The ParisFog f ield campaigns (http://sirta.ipsl.polytechnique.fr/paris fog/), aim at documenting the role of aerosols on radiati ve processes and the interactions between turbulence a d aerosol/droplet microphysical properties during the fog life cyc...
Revisiting fog as an important constituent of the atmosphere
Science of The Total Environment, 2018
We examined observation-based fog occurrence at three Czech monitoring sites: Praha 4-Libuš, Košetice and Churáňov, representing different environments-urban, rural and mountain-over a time span of 27 years (1989-2015). We searched for a simple model describing fog occurrence fitting the observed air pollution and meteorological data. For our analysis we used a generalized additive model, GAM, with (penalized) spline components to capture possible nonlinear and a priori unknown functional relationships. In order to cope with the binary nature of the data (indicators of fog presence on individual days), we employed a logistic regression GAM model fitted by a maximizing penalized likelihood (where the penalty coefficients were estimated via cross-validation). After testing several physically motivated models, being guided by AIC and physical interpretation of the components, we arrived at a model which uses the following explanatory variables: relative humidity, ambient SO 2 concentrations, ambient NO x concentrations, air temperature and seasonality. All associations between the response and the analysed explanatory variables were highly significant. According to our results, the most important explanatory variables modelling the fog probability were relative humidity and air pollutants. Interestingly, we observed an increasing trend in fog occurrence at all three sites under review starting around the mid 2000s. Capsule: The most important explanatory variables modelling the fog probability at three Central European sites were humidity, SO 2 and NO x. An increasing trend in fog occurrence has been observed since the mid 2000s.
Fogs: Physical Basis, Characteristic Properties, and Impacts on the Environment and Human Health
Water
This work presents a selective overview of natural fogs in terms of fog types, forms and states of occurrence, physical, micro-physical, chemical and dynamic properties, basic characterizing parameters, etc. In focus are related achievements and contributions reported mainly during the last decade and a half, as a result of both laboratory studies and field observations. Processes of homogeneous and heterogeneous nucleation are analyzed in the aspects of condensation, nuclei diversity and specifics, as related to the activation, growth and deposition of fog droplets. The effect is highlighted of the water vapor's partial pressure on the surface tension of the liquid water-air interface and the freezing point of the water droplets. Some problems and aspects of fog modeling, parameterization, and forecasting are outlined and discussed on the examples of newly developed relevant 1D/3D theoretical models. Important issues of fog impacts on the air quality, ecosystems, water basins, societal life, and human health are also addressed and discussed, particularly in cases of anthropogenically modified (chemical, radioactive, etc.) fogs. In view of reducing the possible negative effects of fogs, conclusions are drawn concerning the new demands and challenges to fog characterization imposed by the changing natural and social environment and the needs for new data on and approaches to more adequate observations of fog-related events.
Development of a mathematical model for the quantification of fog-collection
Resources, Conservation and Recycling, 2011
With the impacts of climate change and impending crisis of potable water, potential sustainable sources of water are under investigations. One of such potential sources is fog water collection. In the past, collection of fog water was considered negligible and non-worthy. However, recent studies suggest that fog-water collection can be a reasonable sustainable source of water depending on favorable topographic and atmospheric conditions. This paper presents development of a mathematical model for fog-formation and eventual quantification of fog-water collection. The National Oceanic and Atmospheric Administration (NOAA) equation for dew point calculation has been modified and extended to incorporate effects of different climatic parameters on fog formation. A new parameter named Fog Potential Index (FPI), which is a function of difference between dew point and air temperature for a particular location has been introduced and defined. NOAA proposed an equation to calculate dew point based on actual water vapor pressure in the air, which can be calculated from dry bulb temperature of the air and relative humidity. Following calculation of average dew point using NOAA equation between a timestep, FPI was calculated for a particular time step. FPI for each timestep was multiplied with the humidity factor, wind velocity factor and area of the fog collector to incorporate the effects of humidity ratio, wind velocity and fog collector area in the quantification of fog water. Effect of wind velocity on fog formation has been discussed. It was found that wind velocity has got twofold impacts on the formation of fog; (i) for a lower wind velocity upto a certain threshold value, fog formation increases with velocity as old condensed moist air is continuously replaced by new moist air, and (ii) for a higher wind velocity (beyond the threshold value), fog formation decreases with velocity due to disturbance in the formation of fog. The developed model was calibrated using fog-water collection experimental data from Asir region of Saudi Arabia.
Environmental Monitoring and Assessment, 2008
Urban areas are facing increasing fog frequencies that may result due to increased air pollution emanating from variety of sources. The increased pollution levels may lead to the atmospheric reactions resulting into the formation of secondary pollutants that may also lead to increased aerosol number concentrations (ANC) in the atmosphere. This could cause enhanced water aerosols in the presence of favourable meteorological conditions and high relative humidity. This study deals with the atmospheric pollution and visibility during winter season of megacity Delhi in order to assess the relationship between the two specifically during fog episodes. Thus, this study analyses the levels of air pollutants, aerosol spectrum and meteorological conditions during one week each in the winter season of the years 2004 and 2006 in order to have an improved understanding of their role in fog formation in mega-city Delhi. More than 300 h of measurements which included episodes of dense, thick and moderate fogs of about 25 h, were studied. The measurements cover most of the accumulation mode and greater size spectrum of aerosols. Thus, the analysis is performed for the entire period, specifically, before the fog sets up, during and afterwards. In general, the relatively small variations in number concentration show larger variations in visibility prior and post dense fog formation than during dense fog episodes. Preliminary analysis of monthly averaged RSPM (Respirable Suspended particulate Matter or PM 10) concentration values for four winter months for a period of 6 years (1996-2001) and visibility did not show a good correlation with total occurrences of fog. However, daily averaged RSPM concentration showed a good correlation with the occurrences of thick fog. Diurnal variation of Sulfur-dioxide and Nitrogen dioxide were found to have inverse relationship with visibility during fog which may be due to formation of secondary pollutants such as sulfate and to a lesser extent nitrates. Amongst, the daily averaged concentrations of all the criteria pollutants, RSPM was found to be best correlated with the fog in comparison to other pollutants.
An analysis of fog events at Belgrade International Airport
Theoretical and Applied Climatology, 2014
A preliminary study of the occurrence of fog at Belgrade "Nikola Tesla" Airport was carried out using a statistical approach. The highest frequency of fog has occurred in the winter months of December and January and far exceeded the number of fog days in the spring and the beginning of autumn. The exceptionally foggy months, those having an extreme number of foggy days, occurred in January 1989 (18 days), December 1998 (18 days), February 2005 (17 days) and October 2001 (15 days). During the winter months (December, January and February) from 1990 to 2005 (16 years), fog occurred most frequently between 0600 and 1000 hours, and in the autumn, between 0500 and 0800 hours. In summer, fog occurred most frequently between 0300 and 0600 hours. During the 11-year period from 1995 to 2005, it was found that there was a 13 % chance for fog to occur on two consecutive days and a 5 % chance that it would occur 3 days in a row. In October 2001, the fog was observed over nine consecutive days. During the winter half year, 52.3 % of fog events observed at 0700 hours were in the presence of stratus clouds and 41.4 % were without the presence of low clouds. The 6-h cooling observed at the surface preceding the occurrence of fog between 0000 and 0700 hours ranged mainly from 1 to 4°C. A new method was applied to assess the probability of fog occurrence based on complex fog criteria. It was found that the highest probability of fog occurrence (51.2 %) takes place in the cases in which the relative humidity is above 97 %, the dew-point depression is 0°C, the cloud base is lower than 50 m and the wind is calm or weak 1 h before the onset of fog.
The Fog Remote Sensing and Modeling (FRAM) field project and preliminary results
12th Conference on Atmospheric Radiation/12th Conference on Cloud Physics (10-14 July 2006), 2006
costs to stranded passengers in terms of money and inconvenience may be impossible to calculate. Previous studies also suggested that human and financial losses were very common due to accidents related to fog episodes. In Canada, approximately 50 people per year die due to fog related accidents (Gultepe et al., 2007). Westcott (2007) stated that approximately 4000 accidents and 30 deaths occur annually in Illinois, USA, exclusive of the city of Chicago. A major European fog project called COST-722 (COoperation in Field of Scientific and Technical Research), was also performed to develop advanced methods for very short-range forecasts of fog and low clouds (Jacobs et al., 2007). An earlier work by Petterssen (1956) suggested that fog types can be divided into three types: 1) liquid fog (T>-10°C), 2) mixed phase fog (-10°C>T>-30°C), and 3) ice fog (T<-30°C). One should recognize that the criteria used in this respect do not always occur in a clear-cut fashion as implied by the classification. For example, ice fog may occur at T=-20°C when excessive vapor is used by ice nuclei within a steady state condition occurring with no mixing processes. Usually, freezing fog occurs when T gradually decreases below 0°C and this is one of the common fog types in the northern latitudes. Previous studies on fog forecasting/nowcasting suggested that a better understanding of fog microphysics and the large/small scale effects on its formation is needed to develop accurate forecasting models (Tardif et al., 2007, Gultepe and Milbrandt, 2007). The current parameterization for fog visibility (Vis) in numerical models is not accurate (Gultepe et al., 2006) because of the incomplete treatment of the physics in the parameterizations. They later showed that droplet number concentration should also be included in the visibility parameterization, otherwise, the uncertainty in Vis can be more than 50%.
What Causes Observed Fog Trends: Air Quality or Climate Change?
Aerosol and Air Quality Research, 2016
Fog is a situation when the visual range, which is the horizontal visibility, is reduced to less than 1000 m near the Earth's surface by the presence of cloud droplets. Fog trend analyses are reported in the literature for hundreds of stations worldwide, the majority of which showing a considerable reduction of fog. Although fog is often associated with conditions at which cloud condensation nuclei had been activated at rH (relative humidity) > 100% and rapid growth had lead to the formation of fog droplets, this study focusses on urban air masses and conditions when rH is just below 100%. Mie scattering analysis shows that fog can form under such conditions and the reduction of the visual range is mainly caused by submicron aerosol particles which grow to diameters around 1 µm through deliquescence. The liquid water content itself is poorly correlated with the visual range. Assuming equilibrium conditions, both an increase of the air temperature and a reduction of the aerosol particle concentration lead to reductions of fog. In our example case, the increment for a temperature increase by 0.1°C had about the same effect as the reduction of aerosol concentrations by 10%. Care must be taken in projecting this result to actual conditions because the system is non-linear. However, physical evidence is presented which confirms that both climate change and an improvement of air quality are mechanisms that can contribute to the reduction of fog.