Warm Fog Research Articles

WiFEX: Walk into the Warm Fog over Indo-Gangetic Plain Region

Abstract The presence of persistent heavy fog in northern India during winter creates hazardous situations for transportation systems and disrupts the lives of about 400 million people. The meteorological factors responsible for its genesis and predictability are not yet completely understood in this region. Given its high potential for socioeconomic impact, there is a pressing need for extensive research that understands the inherently complex nature of the phenomena through field observations and modeling exercises. WiFEX is a first-of-its-kind multi-institutional initiative dealing with intensive ground-based measurement campaigns for developing a suitable fog forecasting capability under the aegis of the smart cities mission of India. Measuring campaigns were conducted during the 2015–20 winters at the Indira Gandhi International Airport, New Delhi, covering more than 90 dense fog events. The field experiments involved extensive suites of in situ instruments and gathered simultaneous observations of micrometeorological conditions, radiative fluxes, turbulence, droplet/aerosol microphysics, aerosol optical properties, fog water chemistry, and vertical thermodynamical structure to describe the environmental stability in which fog develops. An operational modeling framework, the WRF Model, was set up to provide fog predictions during the measurement campaign. These field observations helped to interpret the strengths and deficiencies in the numerical modeling framework. Four scientific objectives were pursued: (i) the life cycle of optically thin and thick fog, (ii) microphysical properties in the polluted boundary layer, (iii) fog water chemistry, gas–aerosol partitioning during the fog life cycle, and (iv) numerical prediction of fog. This paper presents an overview of WiFEX and a synthesis of selected observational and modeling analyses/findings related to the abovementioned scientific topics.

Seasonal and Microphysical Characteristics of Fog at a Northern Airport in Alberta, Canada

Reduction in visibility (Vis) due to fog is one of the deadliest severe weather hazards affecting aviation and public transportation. Nowcasting/forecasting of Vis reduction due to fog using current models is still problematic, with most using some type of empirical parameterization. To improve the models, further observational studies to better understand fog microphysics and seasonal variability are required. To help achieve these goals, the seasonal and microphysical characteristics of different fog types at Cold Lake airport (CYOD), Alberta, Canada were analyzed using hourly and sub-hourly METAR data. Microphysical and meteorological measurements obtained using the DMT Fog Monitor FM-120 and the Vaisala PWD22 were examined. The results showed that radiation fog (RF) dominates at CYOD in summer while precipitation, advection and cloud-base-lowering fogs mostly occur in fall and winter. All fog types usually form at night or early morning and dissipate after sunrise. The observed dense fog events (Vis < 400 m) were mainly caused by RF. The observed mean fog particle spectra (n(D)) for different fog types and temperatures showed bimodal n(D) (with two modes near 4 μm and 17–25 μm; the maximum total number concentration (Nd) was 100 cm−3 and 20 cm−3, respectively, corresponding to each mode). Parameterizations of Vis as a function of liquid water content (LWC) and Nd were developed using both the observed Vis and calculated Vis based on n(D). It was found that the observed Vis was higher than the calculated Vis for warm fog with LWC > 0.1 gm−3 and most of the mass was contributed by the large drops. Based on the observed Vis, the relative error of the visibility parameterization as a function of both LWC and Nd (32%) was slightly lower than that (34%) using LWC alone for warm fogs.

ЛАБОРАТОРНЫЙ ЭКСПЕРИМЕНТ ПО ИССЛЕДОВАНИЮ ВОЗДЕЙСТВИЯ ИОННОГО ВЕТРА КОРОННОГО РАЗРЯДА НА ТЕПЛЫЙ ТУМАН В ЗАМКНУТОМ ОБЪЕМЕ

The ion wind ability to initiate motions in the originally motionless warm fog inside an enclosed volume is studied. The objective of the study is the experimental check of the possibility to exploit corona discharges for the warm fog modification. The experiment was carried out in a specialized laboratory unit in the Fedorov Institute of Applied Geophysics. The possibility of using the unit to explore the effect of corona discharges on warm fogs is clearly demonstrated.

A Laboratory Experiment to Study Ion Wind Effects on the Warm Fog in an Enclosed Volume

A Laboratory Experiment to Study Ion Wind Effects on the Warm Fog in an Enclosed Volume

Physical Processes in Sea Fog Formation and Characteristics of Turbulent Air-Sea Fluxes at Socheongcho Ocean Research Station in the Yellow Sea

The Yellow Sea is the most fog-prone region of the East Asian marginal seas. Since sea fog is caused due to complex interactions between atmospheric and oceanic environments, direct observations can help understand the physical processes involved in fogging over the oceans. Completed in 2014, the Socheongcho Ocean Research Station (S-ORS) plays a critical role in monitoring air-sea interactions over the Yellow Sea. This study aimed to evaluate the conditions favorable for fog generation and the physical processes underlying it using a suite of observations and turbulent heat flux data from S-ORS. First, we used the visibility data from S-ORS to quantify the frequency of sea fog over the Yellow Sea. From April to June 2016, sea-fog occurred 61 times, with a maximum duration of 135 h (approximately 5.6 days). Next, to understand the origin and characteristics of air mass associated with fog events, we classified the primary airflow paths in the region using a Hybrid Single-Particle Lagrangian Integrated Trajectory model. Among the four clusters identified from the cluster analysis, the third and fourth had distinct physical properties characteristic of cold and warm fog, respectively. The third cluster was characterized by relatively weak or negative heat advection and weak vertical mixing, while the fourth one featured strong positive heat transport and moisture convergence over the Yellow Sea. Finally, based on cluster analysis, we choose the representative cases related to these two clusters observed at S-ORS and compared the characteristics of turbulent air-sea fluxes associated with fog formations.

Warm Fog Elimination by Seeding with Salty Drops: Experiments and Theory

Warm Fog Elimination by Seeding with Salty Drops: Experiments and Theory

Scattering of fogs and clouds of the lower tier

The paper presents the results of numerical modeling of active effects on warm fogs and clouds of the lower tier, as well as the results of field experiments on the creation of illumination zones in these fogs and clouds (increasing the meteorological visibility range (MVR)). A cylindrical volume filled with a combustible composition of high calorific value with a highly dispersed powder of calcium carbide was used as a heat source (exposure model). When the heat source is triggered, 104 kcal kg-1 of the fuel composition is released. Numerical modeling has shown that after 5–6 seconds after the thermal source is triggered, the MVR increases to 2 km (from the initial 50 m). Field experiments have shown an increase in the MVR by 5–50 or more times at different values of the meteorological parameters of fogs and clouds of the lower tier.

Possible impacts of climate change on fog in the Arctic and subpolar North Atlantic

Abstract. A conventional parameterization of midlatitude warm fog occurrence, based on in situ observations, is employed to estimate marine surface visibility in the Arctic and North Atlantic from three datasets: an ensemble member of the Hadley Earth System (HadGEM2) model and a nested regional WRF simulation that follow historical and future emissions scenarios for 1979–2100, and the ERA-Interim reanalysis for 1979–2004. Over large scales (of an entire year and region), all three gridded datasets agree well in terms of variables like surface air temperature, whose systematic differences seem small by comparison with its predicted change over the course of this century. On the other hand, systematic differences are more apparent in large-scale estimates of relative humidity and visibility. Large differences are attributed to a sensitivity to representation bias that is inherent in the formulation of each individual model and analysis. Two simple linear calibrations are examined, both of which assume that an in situ based parameterization is broadly consistent with the use of marine (ICOADS) observations of air and dew point temperature as an error-free reference. A single-step calibration is considered that takes the mean and variance of ICOADS frequency distributions as a reference. A two-step calibration is also performed in which ICOADS collocations are taken as a reference for the ERA reanalysis, which in turn is taken as a large-scale reference for the 1979–2004 HadGEM2 and WRF simulations. Both linear calibrations are applied (locally in time and space to air and dew point temperature) to the future climate scenarios of HadGEM2 and WRF. Although ICOADS observations are not error-free and parameterized visibility estimates are unlikely to capture much more than half the variance found in observations, attempts are made to present consistent regional changes in the frequency of high relative humidity, as a proxy for warm fog occurrence. The large-scale decrease in visibility over the 21st century is in the range of 8 %–12 % in the Arctic and 0 %–5 % in the North Atlantic.

Numerical Simulation Of Fog Occurrences Over A Southern Part Of Nigeria West Africa

Numerical prediction of fog evolution remains difficult due to its complex processes that require adequate representation of the local perturbations in weather models despite the progress made in advance weather prediction models. The performance and sensitivity of the Weather Research and Forecasting (WRF) model in reproducing fog episodes over Akwa Ibom international airport (AKIA) Nigeria for the first time in West Africa was studied. Some real cases of radiation fog over AKIA were simulated using a set of parameterization schemes to simulate warm fog and visibility limits. Seven fog events were selected for model validation and sensitivity studies in this research work. The use of Kunkel (1984) empirical relationship result showed good agreement between simulated horizontal visibility limits using Liquid Water Content (LWC) when compared with observation. The modeled diurnal patterns of temperature, relative humidity and wind speed were also evaluated with the observed. It was found out that the model also captures the diurnal pattern and the value with very slight biases. These slight biases however, do not affect model results except where overestimation of wind speed and temperature could give rise to an earlier dissipation of fog. Fog estimation through temperature and relative humidity profile is as a result of the turbulent mixing within fog that causes the homogenization of the layers where the fog is present. The result showed evolution of fog through quasi-saturated state between temperature and relative humidity defining fog characteristic onset pronounced by surface inversion.

The Measurement and Analysis of Microphysical Capabilities of the Condensation Nucleus of Artificial Warm Fog

In this paper, the microcosmic capabilities of the condensation nucleus and fog droplets of artificial fog were observed and sampled by ELPI, SEM, XRD and LPSA. The chemical composition, number concentration, volume concentration and nucleation efficiency of the artificial condensation nucleus were gained. The condensation nucleus was mainly made up of chloride. The size distribution scope was about 0.291 ∼ 1.59μm and the peak particle size was 0.609∼0.942μm. The number concentration of the condensation nuclei was 3.98×105∼4.82×105/cm3, the volume concentration was 2.02×105∼2.30×105μm3/cm3, and the maximum nucleation efficiency was 3.07×1012/g. Actually, most condensation nuclei did not participate in the actual fog performing process, and the nucleation activation proportion was 13.57%. The condensation nucleus played an important role in the microphysical performance of fog droplets. However, the growing velocity of fog droplets was not identical as the catalytic performance difference of nuclei and the uneven distribution of watervapor in air. That was the reason why the fog droplets size distribution behaved the characteristic of bi-spectrum converting into uni-spectrum gradually.

Modeling of the Denebulization of Warm Fogs by Hygroscopic Seeding: Effect of Various Operating Conditions and of the Turbulence Intensity

AbstractThis study addresses the modeling of the denebulization (i.e., the removal of droplets) of warm fogs (T ≥ 0°C) by hygroscopic salt microparticles from the initial seeding at the top of the fog layer to the fall of the rain droplets on the ground. Two main phenomena can occur: condensation of water vapor on salted droplets and the concomitant evaporation of fog droplets, and coalescence between the salted droplets and the fog droplets. Three salts have been investigated: NaCl, CaCl2, and KCl. Based on the conservation equations, the modeling approach (1D) considers the hygroscopicity of the salts through the water activity in the aqueous solution and the coalescence induced by gravity and turbulence. From this study, NaCl is the most efficient salt in the tested operating conditions. Actually, this result can be explained by the strong hygroscopicity of this salt in very dilute solutions. From the calculations, 15 kg of NaCl particles of 6.7-μm diameter can dissipate a typical fog layer of 40 m in height within less than 17 min over 0.25 km2. According to the calculations, a fog layer of 100 m in height can be denebulized within 45 min. The contribution of the coalescence induced by gravity and by turbulence seems to have a negligible effect on the final horizontal visibility, the condensation/evaporation phenomena being preponderant for these operating conditions.

Mesoscale numerical simulation study of warm fog dissipation by salt particles seeding

Based on the dynamic framework of WRF and Morrison 2-moment explicit cloud scheme, a salt-seeding scheme was developed and used to simulate the dissipation of a warm fog event during 6–7 November 2009 in the Beijing and Tianjin area. The seeding effect and its physical mechanism were studied. The results indicate that when seeding fog with salt particles sized 80 µm and at a quantity of 6 g m-2 at the fog top, the seeding effect near the ground surface layer is negative in the beginning period, and then a positive seeding effect begins to appear at 18 min, with the best effect appearing at 21 min after seeding operation. The positive effect can last about 35 min. The microphysical mechanism of the warm fog dissipation is because of the evaporation due to the water vapor condensation on the salt particles and coalescence with salt particles. The process of fog water coalescence with salt particles contributed mostly to this warm fog dissipation. Furthermore, two series of sensitivity experiments were performed to study the seeding effect under different seeding amounts and salt particles sizes. The results show that seeding fog with salt particles sized of 80 µm can have the best seeding effect, and the seeding effect is negative when the salt particle size is less than 10 µm. For salt particles sized 80 µm, the best seeding effect, with corresponding visibility of 380 m, can be achieved when the seeding amount is 30 g m-2.

Study of Sodium Chloride’s Effect on Warm Fog Dissipation and its Mechanism Research

Sodium chloride (NaCl) is often used for warm mist elimination because of its easy deliquescence performance. In this paper, how dosages of NaCl with two sizes affect warm fog was investigated. The changes of light transmittance (T) and fog drops inside the fog chamber were monitored. Results indicate that NaCl particles smaller than 40μm work better than that of 40-100μm, shortening time of the light transmittance recovering to 60%(t60%) by 83.3% with 25g. Reasons for this are they can decrease the percentages of small droplets, increase that of large droplets and the average sizes of fog drops, which are results from the condensation growth and coalescence growth.

The Challenge of Forecasting the Onset and Development of Radiation Fog Using Mesoscale Atmospheric Models

The numerical weather prediction of radiation fog is challenging, as many models typically show large biases for the timing of the onset and dispersal of the fog, as well as for its depth and liquid water content. To understand the role of physical processes, i.e. turbulence, radiation, land-surface coupling, and microphysics, we evaluate the HARMONIE and Weather Research and Forecasting (WRF) mesoscale models for two contrasting warm fog episodes at the relatively flat terrain around the Cabauw tower facility in the Netherlands. One case involves a radiation fog that arose in calm anticyclonic conditions, and the second is a radiation fog that developed just after a cold front passage. The WRF model represents the radiation fog well, while the HARMONIE model forecasts a stratus lowering fog layer in the first case and hardly any fog in the second case. Permutations of parametrization schemes for boundary-layer mixing, radiation and microphysics, each for two levels of complexity, have been evaluated within the WRF model. It appears that the boundary-layer formulation is critical for forecasting the fog onset, while for fog dispersal the choice of the microphysical scheme is a key element, where a double-moment scheme outperforms any of the single-moment schemes. Finally, the WRF model results appear to be relatively insensitive to horizontal grid spacing, but nesting deteriorates the modelled fog formation. Increasing the domain size leads to a more scattered character of the simulated fog. Model results with one-way or two-way nesting show approximately comparable results.

Study on the Effect of Sodium Polyacrylate and its Compounds on Artificial Warm Fog Dissipation

Sodium polyacrylate as a kind of high absorbent resin, has an excellent water absorption performance, is low in price and isn’t corrosive. Compounds of different particle sizes and components were prepared using sodium polyacrylate and sodium chloride. They were used in the fog chamber to disperse warm fog respectively then. Experiments were carried out to investigate how particle size and composition affect the warm fog dissipation. Results as follows are obtained: the time light transmittance recovers to 60% (t60%) is 85min when the fog dissipates naturally; 30g sodium polyacrylate whose average size is 30μm has a good effect on warm fog dissipation, t60% being 14min; when the sodium polyacrylate and sodium chloride are mixed by 1:2 in mass ratio, the fog elimination effect is the best, with t60% 6min. The reasons are analyzed at the same time.

Examination of microphysical relationships and corresponding microphysical processes in warm fogs

In this paper, the microphysical relationships of 8 dense fog events collected from a comprehensive fog observation campaign carried out at Pancheng (32.2°N, 118.7°E) in the Nanjing area, China in the winter of 2007 are investigated. Positive correlations are found among key microphysical properties (cloud droplet number concentration, droplet size, spectral standard deviation, and liquid water content) in each case, suggesting that the dominant processes in these fog events are likely droplet nucleation with subsequent condensational growth and/or droplet deactivation via complete evaporation of some droplets. The abrupt broadening of the fog droplet spectra indicates the occurrence of the collision-coalescence processes as well, although not dominating. The combined effects of the dominant processes and collision-coalescence on microphysical relationships are further analyzed by dividing the dataset according to visibility or autoconversion threshold in each case. The result shows that the specific relationships of number concentration to volume-mean radius and spectral standard deviation depend on the competition between the compensation of small droplets due to nucleation-condensation and the loss of small droplets due to collision-coalescence. Generally, positive correlations are found for different visibility or autoconversion threshold ranges in most cases, although negative correlations sometimes appear with lower visibility or larger autoconversion threshold. Therefore, the compensation of small droplets is generally stronger than the loss, which is likely related to the sufficient fog condensation nuclei in this polluted area.

The characteristics of sea fog with different airflow over the Huanghai Sea in boreal spring

Using the observations from ICOADS datasets and contemporaneous NCEP/NCAR reanalysis datasets during 1960–2002, the study classifies the airflows in favor of sea fog over the Huanghai (Yellow) Sea in boreal spring (April–May) with the method of trajectory analysis, and analyzes the changes of proportions of warm and cold sea fogs along different paths of airflow. According to the heat balance equation, we investigate the relationships between the marine meteorological conditions and the proportion of warm and cold sea fog along different airflow paths. The major results are summarized as follows. (1) Sea fogs over the Huanghai Sea in spring are not only warm fog but also cold fog. The proportion of warm fog only accounts for 44% in April, while increases as high as 57% in May. (2) Four primary airflow paths leading to spring sea fog are identified. They are originated from the northwest, east, southeast and southwest of the Huanghai Sea, respectively. The occurrence ratios of the warm sea fog along the east and southeast airflow paths are high of 55% and 70%, while these along the southwest and northwest airflow paths are merely 17.9% and 50%. (3) The key physical processes governing the warm/cold sea fog are heat advection transport, longwave radiation cooling at fog top, solar shortwave warming and latent heat flux between airsea interfaces. (4) The characteristics of sea fog along the four airflow paths relate closely to the conditions of water vapor advection, and the vertical distribution of relative humidity.

Leadership in These Challenging Times

It is not the clear-sighted who rule the world; great achievements are accomplished in a blessed, warm fog. - Joseph Conrad IN AN INDUSTRY undergoing seismic change, today's healthcare executive is entitled to feel a little shell shocked. Technologies are evolving at light speed, yielding an expectation for enhanced mobility, collaboration, and access to information. Breakthroughs in treatment modalities, therapeutic options, and patient care seem to be reported every week. Consumer expectations continue to rise as the healthcare debate is played out in the national media, and the political football game that is reform shows no sign of resolving neatly. On top of this, the global economic crisis adds one more level of complexity, ambiguity, and stress. This is the environment in which McCutcheon and Sukin position their lead articles and, in turn, demonstrate that they clearly get what is required to navigate these confusing times. Both have kept their balance and perspective, and each has worked to position her organization to thrive rather than simply survive - a rare accomplishment these days. As consulting psychologists, we've spent the better part of the last three decades readying leadership talent across a wide range of industries to handle whatever is thrown in their path. Yet, it's clear to us that nothing has fully prepared today's executives for the demands of this remarkable period. Once confident and poised, senior leaders are being knocked off their feet, and their organizations are feeling the brunt of increasingly ineffective strategies. Most leaders feel enormous responsibility to step up and deliver, yet few actually know what to do. Much of the wisdom McCutcheon and Sukin offer is applicable to any leader. Obviously, each has approached the challenges facing her system differently, but both offer distinct and relevant leadership insights. Our intention is to highlight the most salient of these, add some color commentary, and close with a few additional opinions of our own. LEADERSHIP AND CHANCE Let's start with the common ground between their stories. Fundamentally, McCutcheon and Sukin recognize that leaders cast very long shadows, and both make a compelling argument for visible and proactive behavior during these uncertain times. It is easy to spot their forward-facing orientations. They see opportunity where others might see peril, offering their managers and staff confidence and purpose. Both executives provide excellent examples of how important clear vision and an underlying set of core operating principles can be in leading a dynamic enterprise through turbulence. In addition, they place enormous value on fully engaging their organizations in practical work around the real demands and issues facing their businesses rather than dictating abstract strategy from above. Finally, each readily agrees that the journey is just beginning and that hope for a return to normal is folly. To take this analysis a step further, let's dive deeper into the actual leadership lessons the articles reflect. In McCutcheon's feature, three key themes for management emerge: preparing people for current (and future) realities, engaging stakeholders in thinking through the process, and focusing on tangible and consistent business results. Sukiris approach is a bit more personal, but it yields a similar payoff. She stresses the importance of leading with passion, establishing a clear and compelling vision, and insisting on continuous learning. When blended together, their leadership principles frame a cogent and practical approach to management. Defining the Imperative for Change The importance of conducting an honest assessment of the situation and then pinpointing key change drivers cannot be overstated, and each author takes on this task directly. McCutcheon identifies a set of forces that define the current context, establish urgency, and align energy. …

Microphysical Observations and Mesoscale Model Simulation of a Warm Fog Case during FRAM Project

The objective of this work is to apply a new microphysical parameterization for fog visibility for potential use in numerical weather forecast simulations, and to compare the results with ground-based observations. The observations from the Fog Remote Sensing And Modeling (FRAM) field which took place during the winter of 2005 – 2006 over southern Ontario, Canada (Phase I) were used in the analysis. The liquid water content (LWC), droplet number concentration (Nd), and temperature (T) were obtained from the fog measuring device (FMD) spectra and Rosemount probe, correspondingly. The visibility (Vis) from a visibility meter, liquid water path from microwave radiometers (MWR), and inferred fog properties such as mean volume diameter, LWC, and Nd were also used in the analysis. The results showed that Vis is nonlinearly related to both LWC and Nd. Comparisons between newly derived parameterizations and the ones already in use as a function of LWC suggested that if models can predict the total Nd and LWC at each time step using a detailed microphysics parameterization, Vis can then be calculated for warm fog conditions. Using outputs from the Canadian Mesoscale Compressible Community (MC2) model, being tested with a new multi-moment bulk microphysical scheme, the new Vis parameterization resulted in more accurate Vis values where the correction reached up to 20 –50%.

A Satellite-Based Fog Detection Scheme Using Screen Air Temperature

Abstract A warm fog detection (air temperature > −5°C) algorithm using a combination of Geostationary Operational Environmental Satellite-12 (GOES-12) observations and screen temperature data based on an operational numerical model has been developed. This algorithm was tested on a large number of daytime cases during the spring and summer of 2004. Results from the scheme were compared with surface observations from four manned Canadian weather stations in Ontario, including Ottawa, Windsor, Sudbury, and Toronto. Initially, when all cases were included, fog detection (hit rate) by the satellite scheme ranged between 0.26 and 0.32. It is suggested that mid- or high-level clouds within the satellite imagery during the observed foggy periods affected the scheme’s performance in detecting surface-level fog for the majority of the cases. When cases with mid- and high-level clouds were removed using model-based screen temperatures, the hit rate ranged between 0.55 and 1.0. With an average false alarm rate of 0.10, the inclusion of model-based sounding values can be seen to improve results from the satellite-based algorithms by an average of 0.42. Average differences between the screen temperature and the surface-observed air temperature were found to be up to 2°C and this can likely account for some discrepancies in detecting fog. Finally, averaging GOES and model data to scales representing single data-point observations likely resulted in some of the failure of the fog algorithm.