Fog Liquid Water Content Research Articles

Role of thermodynamic and turbulence processes on the fog life cycle during SOFOG3D experiment

Abstract. In this study, we use a synergy of in situ and remote sensing measurements collected during the SOuthwest FOGs 3D experiment for processes study (SOFOG3D) field campaign in autumn and winter 2019–2020 to analyse the thermodynamic and turbulent processes related to fog formation, evolution, and dissipation across southwestern France. Based on a unique measurement dataset (synergy of cloud radar, microwave radiometer, wind lidar, and weather station data) combined with a fog conceptual model, an analysis of the four deepest fog episodes (two radiation fogs and two advection–radiation fogs) is conducted. The results show that radiation and advection–radiation fogs form under deep and thin temperature inversions, respectively. For both fog categories, the transition period from stable to adiabatic fog and the fog adiabatic phase are driven by vertical mixing associated with an increase in turbulence in the fog layer due to mechanical production (turbulence kinetic energy (TKE) up to 0.4 m2 s−2 and vertical velocity variance (σw2) up to 0.04 m2 s−2) generated by increasing wind and wind shear. Our study reveals that fog liquid water path, fog top height, temperature, radar reflectivity profiles, and fog adiabaticity derived from the conceptual model evolve in a consistent manner to clearly characterise this transition. The dissipation time is observed at night for the advection–radiation fog case studies and after sunrise for the radiation fog case studies. Night-time dissipation is driven by horizontal advection generating mechanical turbulence (TKE at least 0.3 m2 s−2 and σw2 larger than 0.04 m2 s−2). Daytime dissipation is linked to the combination of thermal and mechanical turbulence related to solar heating (near-surface sensible heat flux larger than 10 W m−2) and wind shear, respectively. This study demonstrates the added value of monitoring fog liquid water content and depth (combined with wind, turbulence, and temperature profiles) and diagnostics such as fog liquid water reservoir and adiabaticity to better explain the drivers of the fog life cycle.

Microphysics and Optical Attenuation in Fog: Observations from Two Coastal Sites

A total of 15 fog events from two field campaigns are investigated: the High Energy Laser in Fog (HELFOG) project (central California) and the Toward Improving Coastal Fog Prediction (C-FOG) project (Ferryland Newfoundland). Nearly identical sensors were used in both projects to sample fog droplet-size spectra, wind, turbulence, and thermodynamic properties near the surface. Concurrent measurements of visibility were made by the present weather detector in both experiments, with the addition of a two-ended transmissometer in the HELFOG campaign. The analyses focused first on contrasting the observed fog microphysics and the associated thermodynamics from fog events in the two locations. The optical attenuation by fog was investigated using three methods: (1) derived from Mie theory using the measured droplet-size distribution, (2) parametrized as a function of fog liquid water content, and (3) parametrized in terms of total fog droplet number concentration. The consistency of these methods was investigated. The HELFOG data result in an empirical relationship between the meteorological range and liquid water content. Validation of such relationship is problematic using the C-FOG data due to the presence of rain and other factors. The parametrization with droplet number concentration only does not provide a robust visibility calculation since it cannot represent the effects of droplet size on visibility. Finally, a preliminary analysis of the mixed fog/rain case is presented to illustrate the nature of the problem to promote future research.

Characterizing and Predicting Marine Fog Offshore Newfoundland and Labrador

Abstract As several review papers have concluded, marine fog is imperfectly characterized, and quantitative visibility forecasts are difficult to produce accurately. Some unique measurements have been made offshore Newfoundland and Labrador of the climatology of occurrence and the microphysical characteristics of marine, or open-ocean, fog. Based on measurements made at an offshore installation over 21 years, the percent of time with visibilities less than 0.5 n mi or approximately 1 km (1 n mi ≈ 1.85 km) reaches 45% in July, with a low of about 5% during the winter. The occurrence of fog is mainly due to warm air advection, with the highest frequency occurring with wind directions from over the warm Gulf Stream, and with air temperatures about 2°C warmer than the sea surface temperature. There is no diurnal variation in the frequency of occurrence of fog. The microphysical properties of the fog have been documented in the summer time frame, with over 550 h of in situ measurements made offshore with fog liquid water content greater than 0.005 g m−3. The fog droplet number concentration spectra peaks near 6 μm, with a secondary peak near 25–40 μm, which typically contains most of the liquid water content. The median droplet concentration is approximately 70–100 cm−3. The microphysical spectra have been used to develop a new NWP visibility parameterization scheme, and this scheme is compared with other parameterizations currently in use.

Observation and Simulation Studies of Three Types of Wire Icing

Research on three types of wire icing evolution mechanism is of great significance for ice disaster recognition and prediction. Comprehensive field observations of wire icing were conducted in the winters of 2015/2016 and 2016/2017 at the Lushan Mountain Meteorological Bureau Observatory (elevation 1164.5 m), Jiangxi Province, China, and the ice thickness, weather phenomena, meteorological elements, and fog spectrum were measured. Four icing cases were recorded, in which high ice-producing conditions, such as freezing rain, snow and supercooled fog, occurred. The icing growth and shedding mechanisms in three types of weather (freezing rain, snow, and supercooled fog) were analyzed and compared. Considering mixed ice-producing conditions, the ice thickness was simulated by integrating freezing rain, snow, and supercooled fog icing models, with inputs such as the precipitation rate and wind speed. The average measured icing growth rates in freezing rain, snow, and supercooled fog were 0.4, 0.3, and 0.2 mm h−1, respectively. The correlations between the icing growth rate and both the temperature and the wind speed were stronger in the snow and supercooled fog than in freezing rain. With the decreasing temperature, the icing growth rate increased faster with snow, while that in supercooled fog increased faster as the wind speed increased. In freezing rain, snow, and supercooled fog, the icing growth rates were all positively correlated with the ice thickness, with correlation coefficients of 0.55, 0.67, and 0.79, respectively. Ice was shed when the temperature remained below 0 °C, the wind speed fell to 2.7 m s−1, and the fog liquid water content fell to 0.036 g m−3 in supercooled fog, and when the solar radiation increased and the temperature exceeded 0 °C in freezing rain. The average sticking efficiency of the wire to snow was 0.03; its variation range was 0.01–0.10. The integrated model can simulate the changes in actual ice thickness well.

The hourly characteristics of aerosol chemical compositions under fog and high particle pollution events in Kinmen

The hourly measurement of inorganic soluble ions in PM10 aerosols was conducted with new in situ air composition measuring equipment (ACME) from March 15 to April 15, 2016, on Kinmen Island. The purposes of this study are to understand the influences of fog on secondary aerosol formation and to determine the impacts of air pollutants on haze formation under different relative humidity conditions.The hourly measurements showed that the mass fraction of sulfate in PM10 increased with increases in the liquid water content of fog and decreases in the gaseous concentrations of SO2. The value of the SO42−/PM10 ratio is also affected by the concentration of SO2 before the fog occurs and the level of the fog. This finding indicates that a humid environment is important for enhancing the heterogeneous reaction of sulfate formation. The nitrate concentrations were related to the ratio of NH4+ to SO42− during fog episodes. The formation of particulate NO3− was associated with ammonium formation under ammonium-rich conditions (NH4+/SO42− > 1.5). The gas-phase nitrate was usually observed under ammonium-poor conditions. During periods of high particle pollution, the air mass was from near the ground surface in the mainland coastal areas and transported more pollution to Kinmen. The concentrations of NO2− were higher during periods of high particle pollution, which means that the secondary aerosol formation in the nearby areas also strongly affected the air quality degradation. The short-term and rapid change in the north-south wind system not only brings water vapor from the south but also delivers accumulated pollutants via the transport of northern pollution at low wind speeds.

Advances in fog microphysics research in China

Fog microphysical research in China based on field experiments obtained many important results in recent 50 years. With the fast development of China’s economy, urbanization in the last 30 years, special features of fog microphysical structure also appeared, which did not appear in other countries. This article reviews the fog microphysical research around China, and introduces the effect of urbanization on fog microphysical structure and the microphysical processes as well as macroscopic conditions of radiation fog droplet spectral broadening. Urbanization led to an increase in fog droplet number concentration but decreases in fog liquid water content (LWC) and fog droplet size, as well as a decrease in visibility in large cities. Observations show that the radiation fog could be divided into wide-spectrum one, which is all extremely dense fog with the spectral width more than 40 μm, and narrow-spectrum one, most of which is dense fog with the spectral width less than 22 μm, according to droplet spectral distribution. During developing from dense fog to extremely dense fog, the widespectrum radiation fog is characterized by explosive deepening, that is, within a very short time (about 30 min), the droplet concentration increase by about one order of magnitude, droplet spectral broadening across 20 μm, generally up to 30-40 μm, or even 50 μm. As a result, water content increased obviously, visibility decreased to less than 50 m, when dense fog became extremely dense fog.

Long-term observation of fog chemistry and estimation of fog water and nitrogen input via fog water deposition at a mountainous site in Hokkaido, Japan

To evaluate water and nitrogen input via fog deposition, the fog water chemistry and deposition around a crater lake (Lake Mashu) in northern Japan were investigated in the growing seasons of trees (summer to autumn) in 2006–2012. The fog samples were collected using an active fog collector and droplet size distribution was measured with a droplet size spectrometer (FM-100). The visibility (VIS)–liquid water content of fog (LWC) relationship differed between summer and autumn. Large fog droplets decreased in autumn and the calculated LWC from FM-100 measurements (LWCobs) were lower than those in summer at the same VIS. Two empirical curves between LWCobs and VIS were obtained and used for better estimation of fog deposition. Fog deposition was calculated from LWC empirically derived from past VIS data and deposition velocity (Vd) estimated using wind speed and vegetation parameters. The mean pH of fog water was 4.6 and the percentage of samples of pH4.0 or more was 93%. Compared to previous literature of exposure experiments of acid mist on plants, fog acidity in this study did not seem to injure plant leaves. The water input via fog deposition accumulated for each growing season was estimated at 107–140mm, corresponding to 18–23% of the precipitation in the same period. Nitrogen deposition via fog deposition in a plant growing season was estimated at 26–30meqm−2 (3.6–4.2kg Nha−1). As a long-term trend, NO3− concentration in fog water decreased significantly. However, the long-term trends of fog and nitrogen depositions were not clear.

Aerosol Deposition and Behavior on Leaves in Cool-temperate Deciduous Forests. Part 3: Estimation of Fog Deposition onto Cool-temperate Deciduous Forest by the Inferential Method

Fog deposition onto the cool-temperate deciduous forest around Lake Mashu in northern Japan was estimated by the inferential method using the parameterizations of deposition velocity and liquid water content of fog (LWC). Two parameterizations of fog deposition velocity derived from field experiments in Europe and numerical simulations using a detailed multi-layer atmosphere-vegetation-soil model were tested. The empirical function between horizontal visibility (VIS) and LWC was applied to produce hourly LWC as an input data for the inferential method. Weekly mean LWC computed from VIS had a good correlation with LWC sampled by an active string-fog collector. By considering the enhancement of fog deposition due to the edge effect, fog deposition calculated by the inferential method using two parameterizations of deposition velocity agreed with that computed from throughfall data. The results indicated that the inferential method using the current parameterizations of deposition velocity and LWC can provide a rough estimation of water input due to fog deposition onto cool-temperature deciduous forests. Limitations of current parameterizations of deposition velocity related to wind speed, evaporation loss of rain and fog droplets intercepted by tree canopies, and leaf area index were discussed.

A method for simple and accurate estimation of fog deposition in a mountain forest using a meteorological model

[1] To apply a meteorological model to investigate fog occurrence, acidification and deposition in mountain forests, the meteorological model WRF was modified to calculate fog deposition accurately by the simple linear function of fog deposition onto vegetation derived from numerical experiments using the detailed multilayer atmosphere-vegetation-soil model (SOLVEG). The modified version of WRF that includes fog deposition (fog-WRF) was tested in a mountain forest on Mt. Rokko in Japan. fog-WRF provided a distinctly better prediction of liquid water content of fog (LWC) than the original version of WRF. It also successfully simulated throughfall observations due to fog deposition inside the forest during the summer season that excluded the effect of forest edges. Using the linear relationship between fog deposition and altitude given by the fog-WRF calculations and the data from throughfall observations at a given altitude, the vertical distribution of fog deposition can be roughly estimated in mountain forests. A meteorological model that includes fog deposition will be useful in mapping fog deposition in mountain cloud forests.

Environmental Role of Rime Chemistry at Selected Mountain Sites in Poland

The results of field experiments on fog pollutant deposition enhanced by local mountain climate, completed by the dendrochronological analysis of the forest response, are presented in this paper. In spite of their low absolute altitude (1,000–1,600 m a.s.l), the Sudetes and the Silesian Beskid form a noticeable orographic barrier for the airflow of the humid Atlantic air masses. This results in the increase of cloudiness and fog frequency as well as both atmospheric precipitation and horizontal precipitation volume. Between January and December 2009 the daily samples of atmospheric precipitation and rime were collected on three selected mountain tops of similar height. The selected measurement sites were situated along a 300 km WNW-ESE profile parallel to the direction of the prevailing atmospheric circulation. High day-to-day variability of rime water volume, the total ionic content and chemical composition of the individual samples were typical of each measurement site and depended on the emission patterns, synoptic situation and the local climatic conditions influenced chiefly by terrain relief. Significantly larger rime efficiency and pollution deposition via fog were observed at the westernmost Szrenica Mt site rather than more to the southeast at Śnieznik Mt and Skrzyczne Mt. This difference should be explained by more intense orographic deformation of predominant airflow from the western sector as well as the higher liquid water content of fog in the vicinity of Szrenica. Both temporal and spatial variability of fog deposition correlates closely with the health status of the drilled trees of Norway Spruce (Picea Abies) in the Śnieznik Massif. The averaged annual tree rings width near the local tree line (1,350 m a.s.l.) on the summit dome of Śnieznik decreased by 71% between 1950 and the early 1980s. This is also the area of the highest rate of atmospheric pollutant deposition due to particularly important role of fog. At an altitude of 1,200 m a.s.l. The relevant changes of ring width were different depending on slope aspect: 60% on western slopes well exposed for orographic fog formation and 42% on eastern slopes where fog deposition is less intense. The results of the dendrochronological analysis provide the evidence for the upward trend of tree rings width since 1981–1984 break through up to date, which should be attributed to the progressive reduction of pollutant emission in Central Europe.

A comparison of the performance of three types of passive fog gauges under conditions of wind‐driven fog and precipitation

AbstractUnderstanding of the ‘typical’ amounts of fog intercepted by different types of cloud forests is hampered by a lack of comparative information on local fog climatology. Usually some kind of ‘fog gauge’ is used to characterize fog occurrence and amounts. Moreover, wind‐driven fog and precipitation are difficult to measure separately and reported measurements of ‘fog’ often represent a combination of the two. In this paper, the term ‘occult precipitation’ (HP) is used to represent fog in combination with the horizontal component of wind‐driven precipitation (WDR). Collection efficiencies of three widely used types of passive fog gauges, viz. a wire harp (WH) screen, a modified cylindrical gauge (MJU, Juvik‐type) and a tunnel gauge (TTG, Daube‐type), were derived by comparing the volumes of water collected by the respective gauges with horizontal cloud water fluxes (CWFs) derived from wind speed (u) and the fog liquid water content (LWC) as measured by a cloud particle spectrometer during conditions of fog at a windward cloud forest site in northern Costa Rica. Under conditions of fog‐only, the collection efficiencies of the three gauges were linearly related to the horizontal CWF as measured by the gauges themselves. Therefore, additional information on wind speed, droplet size and fog LWC was not needed. During conditions of HP, relative collection efficiencies were derived by comparing the volumes collected by the respective gauge types. The modified Juvik gauge had an efficiency close to 100%, independently of the wind speed and direction, whereas the efficiency of the WH depended critically on the wind speed. The tunnel gauge had an efficiency comparable to that of the Juvik gauge, with some additional catch occurring under conditions of low precipitation angles due to the reclined frontal surface of the gauge. Copyright © 2010 John Wiley & Sons, Ltd.

Analysis of the microphysical structure of heavy fog using a droplet spectrometer: A case study

The microphysical properties of a long-lasting heavy fog event are examined based on the results from a comprehensive field campaign conducted during the winter of 2006 at Pancheng (32.2 ◦ N, 118.7 ◦ E), Jiangsu Province, China. It is demonstrated that the key microphysical properties (liquid water content, fog droplet concentration, mean radius and standard deviation) exhibited positive correlations with one another in general, and that the 5-min-average maximum value of fog liquid water content was sometimes greater than 0.5 g m −3 . Further analysis shows that the unique combination of positive correlations likely arose from the simultaneous supply of moist air and fog condensation nuclei associated with the advection of warm air, which further led to high liquid water content. High values of liquid water content and droplet concentration conspired to cause low visibility (<50 m) for a prolonged period of about 40 h. Examination of the microphysical relationships conditioned by the corresponding autoconversion threshold functions shows that the collision-coalescence process was sometimes likely to occur, weakening the positive correlations induced by droplet activation and condensational growth. Statistical analysis shows that the observed droplet size distribution can be described well by the Gamma distribution.

Three‐dimensional fog forecasting in complex terrain

AbstractFog in complex terrain shows large temporal and spatial variations that can only be simulated with a three‐dimensional model, but more modifications than simply increasing the resolution are needed. For a better representation of fog, we present a second‐moment cloud water scheme with a parametrization of the Köhler theory which is combined with the mixed‐phase Ferrier microphysics scheme. The more detailed PAFOG microphysics produce many differences to the first‐moment Ferrier scheme and are responsible for the typically low liquid water content of fog. The inclusion of droplet sedimentation in the Ferrier scheme cannot reproduce the results obtained with PAFOG, as there is a large sensitivity to the sedimentation velocity. With explicitly predicted droplet number concentrations, sedimentation of cloud water can be modelled with variable fall speeds, which mainly affects the vertical distribution of cloud water and the end of the fog's life cycle. The complex topography of the Swiss Alps and their surroundings are used for model testing. As the focus is on the model's ability to forecast the spatial distribution of fog, cloud patterns derived from high‐resolution MSG satellite data, rather than few point observations from ground stations, are used. In a five‐day period of anticyclonic conditions, the satellite‐observed fog patterns showed large day‐to‐day variations from almost no fog to large areas of fog. This variability was very well predicted in the three‐dimensional fog forecast. Furthermore, the second‐moment cloud water scheme shows a better agreement with the satellite observations than its first‐moment counterpart. For model initialization, the complex topography is actually a simplifying factor, as cold air flow and pooling dominate the more uncertain processes of evapotranspiration or errors in the soil moisture field. Copyright © 2010 Royal Meteorological Society

A Collector for Fog Water and Interstitial Aerosol

Abstract An active heatable cloud water collector for ground sampling is presented. The collector can be operated unattended for approximately one week, even in harsh winter conditions. The collection strands are Teflon tubes. A preset cycle of 15-min sampling followed by 250 s of mild heating using wires inserted into the tubes is used. The lower cutoff diameter for fog droplets is 7.3 μm, and its overall collection efficiency is 79% for the liquid water content of fogs at the experimental site in central Europe. It performed reliably during a 2-yr experiment. The collected fog water interacts exclusively with inert materials such as Teflon and Perspex so the collector is well suited for trace analyses of fog water. The collector can be upgraded with an interstitial aerosol collection unit, at the expense of unattended operation. The lower cutoff diameter of the fog water collection strands is 8.1 μm when the interstitial aerosol module is installed. The module efficiently collects particles with diameters &amp;lt;3.5 μm. For these particles, size-segregated samples in four size classes at diameters down to 0.06 μm are collected with a Berner-type impactor. The collector was successfully employed in a mountainous region of central Europe. Over 400 samples were collected within 2 yr. With the collection unit for interstitial aerosol added, 31 samples were collected in a 2-month period.

An automated fog water collector suitable for deposition networks: Design, operation and field tests

The study of fog water chemical composition and the contribution of fog droplets to total chemical deposition has become a relevant environmental subject over the past few years. This paper describes a fog water collector suitable for deposition network operation, due to its complete automation and to the facility of remote acquisition of sampling information. Sampling of fog droplets on teflon strings is activated by an optical fog detector according to a particular protocol operated by a microprocessor controller. Multiple sample collection, also microprocessor controlled, is possible with this instrument. The problem of fog droplet sampling in sub-freezing conditions is overcome using a sampling schedule implemented by the microprocessor controller which alternates between sampling periods and stand-by periods during which melting of the rime collected on the strings is allowed. Field tests on the reliability and reproducibility of the sampling operations are presented in the paper. Side by side operation of the fog collector with a PVM-100 fog liquid water content meter shows that the amount of water per unit volume of air collected by the sampling instrument is proportional to the fog liquid water content averaged over the period of an entire fog event.

Modeling the atmospheric chemistry of mercury

A model describing the aqueous chemistry and mass transfer processes of atmospheric mercury (Hg) has been used for analyzing the influence of various chemical and physical parameters on aqueous Hg concentrations. The model involves 39 gas phase species in 79 reactions and 32 aqueous species in 93 reactions. Modeled concentrations are in the range 2 to 5 and 5 to 10 ng L -1 for dissolved and total Hg respectively. Accurate descriptions of gas phase as well as aqueous phase chemistry of oxidants, acidifying substances and chlorine chemistry are necessary since there is a complex relationship between a number of species and the aqueous Hg concentrations. Of the physical parameters studied the influence of the assumed fog liquid water content was also found to be of great importance.

A case study on the determination of fog optical depth and liquid water path using AVHRR data and relations to fog liquid water content and horizontal visibility

An improved direct method is presented for the calculation of fog optical depth and liquid water path from fog top albedo using AVHRR channel 1. Fog top albedo is determined by means of a simple ra...

Comparison of techniques for measurements of fog liquid water content

Comparison of techniques for measurements of fog liquid water content

Meteorological characteristics of the Po Valley fog

The meteorological situation during the first joint field campaign from 10-17 November 1989 of the EUROTRAC subproject GCE is discussed. The synoptic situation is illustrated by weather charts and satellite pictures. Backtrajectories were calculated in order to identify the origins of airmasses reaching the observation point. Model calculations were performed to explain the observed counter current channelling in the Po Valley. For the 5 different fog episodes observed, fog liquid water content, temperature, humidity, and wind speed are displayed as a function of height. Possible reasons for formation, evolution, and dissipation are discussed. It was found that the radiation effects only played a minor role. Most of the time, the fog at the observation site was either advected or formed due to the advection of cold or moist air. DOI: 10.1034/j.1600-0889.1992.t01-4-00003.x

The collection of fog droplets by a jet impaction stage

Jet impaction stages are not commonly used for collecting wet aerosol particles from nearly saturated or slightly supersaturated atmospheres, and yet, with an adequate design, the advantages of jet impaction stages, i.e. a sharp effeciency curve and well determined volumetric flow rate, can be made available to fog collection techniques. The condensation of water from supersaturated vapours is unlikely to play an important role in jet impaction stages if the transit times of the supersaturated fluid are sufficiently short. Initial experiments performed at a field site near Bologna, Italy, in 1986 to determine the liquid water content of fogs, demonstrated that the temporal resolution is better than 0.5h and low liquid water contents of ∼ 0.01 g m −3 can be determined with confidence.