Analysis and quantification of contrasts in observed meteorological fields for foggy and non-foggy days

Abstract

The genesis and dynamics of fog take place under certain meteorological conditions. Thus quantification of the differences in different meteorological variables between foggy and non-foggy days can provide insight into the dynamics of fog; such contrasts can also help to identify and quantify precision and the accuracy required in the meteorological forecasts for driving fog prediction models. However, systematic evidence and quantification of differences in meteorological variables for foggy and non-foggy days are missing. Based on analyses of composites of differences between meteorological variables (temperature, relative humidity, wind and dew-depression) for days with no fog, mild fog and dense fog (based on visibility) days over Delhi, a fog-prone metropolis, we show that consistent and appreciable distinctions exist between days with fog and no fog (characterized in terms of hourly visibility) for both December and January. An important finding is that the differences persist not only near the surface, but also at 850 hPa level. Expectedly but consistently, the contrasts were stronger for long-duration (duration C4 h) than those for short duration (duration\2 h) fog; the contrasts were also stronger for dense (visibility \500 m) fog. The average differences between non-foggy and dense fog (duration C4 h) in composite temperature, relative humidity and wind are of the order of 3°C, 10 % and 5 m/s, respectively; these findings can help to assess and validate meteorological forecasts for driving fog prediction. Fog is a high-impact event over many locations world-wide; while the present analysis is for a specific location, the methodology is generic to be applied over any fog-prone location.

Amplification of South Asian haze by water vapour-aerosol interactions

“…One of the main challenges in simulating the AOD over the region is the accurate simulation of relative humidity, which affects hygroscopic growth (Chatani and Sharma, 2018). The mean relative humidity estimated from several re-analysis datasets and measurements in different locations of the IGP varies from 60 to 80% (Chatani and Sharma, 2018;Gautam et al, 2007;165 Ghude et al, 2017;Goswami and Sarkar, 2015). A good agreement is found between measured and simulated (with aerosol feedback) relative humidity over the IGP ( Fig.…”

An analogue dynamical model for forecasting fog‐induced visibility: validation over Delhi

“…There are only a few specific studies (Mitra et al ., ; Mohan and Payra, ; Saraf et al ., ) over India, for fog simulation and prediction. Our earlier study over Delhi (Goswami and Sarkar, ) reveals that the temperature and the relative humidity have 1 °C and 5% contrasts, respectively, near the ground, implying an accuracy of at least 1 °C and 5% to predict fog skilfully with a numerical weather prediction model. Here, the model is presented as an analogue model that represents the key processes of fog; however, the emphasis is on the forecast skill and not on basic physics of fog.…”

Amplification of South Asian haze by water vapour–aerosol interactions

“…Widespread haze and fog over the northern parts of the Indian subcontinent, especially the Indo-Gangetic Plain (IGP), are associated with anthropogenic activities and are noticeable even from space during the winter season (Ali et al, 2019;Gautam and Singh, 2018;Ghude et al, 2017). Poor air quality and visibility persisting throughout the winter period has been a major concern for more than 900 million people living in the IGP (Gautam and Singh, 2018;Gurjar et al, 2008;Lelieveld et al, 2015). Indeed, various studies have shown that the winter concentrations of fine particles (PM 2.5 ) and gaseous pollutants exceed national and international air quality standards over most of the IGP region and are considered extremely hazardous for human health (Ali et al, 2019;Bharali et al, 2019;Ghude et al, 2017;Gurjar et al, 2008;Kumar et al, 2015a;Nair et al, 2007;Rengarajan et al, 2011;Safai et al, 2008).…”

“…Poor air quality and visibility persisting throughout the winter period has been a major concern for more than 900 million people living in the IGP (Gautam and Singh, 2018;Gurjar et al, 2008;Lelieveld et al, 2015). Indeed, various studies have shown that the winter concentrations of fine particles (PM 2.5 ) and gaseous pollutants exceed national and international air quality standards over most of the IGP region and are considered extremely hazardous for human health (Ali et al, 2019;Bharali et al, 2019;Ghude et al, 2017;Gurjar et al, 2008;Kumar et al, 2015a;Nair et al, 2007;Rengarajan et al, 2011;Safai et al, 2008). A recent estimate of premature mortality related to air pollution over India is ∼ 0.65 million per year, mostly found to occur in the IGP due to residential emissions (Lelieveld et al, 2015).…”