On the roles of circulation and aerosols in the decline of mist and dense fog in Europe over the last 30 years

Abstract

Abstract. Fog and mist are meteorological phenomena that have significant contributions to temperature variations. Understanding and predicting them is also crucial for transportation risk management. It has been shown that low visibility phenomena over Europe have been declining over the past three decades. The trends in mist and haze have been correlated to atmospheric aerosol trends. However, dense fog has not received yet such focus. The goal of this paper is to examine the roles of synoptic atmospheric circulation and aerosol content on the trends of dense fog. We show that sulphur emission trends are spatially correlated with visibility trends, with a maximum correlation when visibility is between 1 km and 10 km. We find that atmospheric dynamics overall contributes up to 40% of the variability of the frequency of fog occurrences. This contribution is spatially variable and highly depends on the topography and the season, with higher values in the winter. The observed long-term circulation changes do not contribute much to the trends in low visibility found in the data. This process is illustrated on three stations (De Bilt, Zürich Airport and Potsdam) for which a long-term visibility data and a thorough meteorological description are available. We conclude that to properly represent fog in future climate simulations, it is necessary to include realistic representations of aerosol emissions and chemistry, land surface properties and atmospheric dynamics.

UCLALES–SALSA v1.0: a large-eddy model with interactive sectional microphysics for aerosol, clouds and precipitation

“…Moreover, the intensity of the cooling increases with increasing aerosol concentration, owing to the higher optical depth; in A800 the peak cooling rate is approximately 7 K h −1 and in A200 4 K h −1 . This is in agreement with the range of values reported in Nakanishi (2000). The peak water vapour supersaturation is found at the same altitudes as the strongest radiative cooling.…”

“…Similar to the observation-based reports by Price (2011) and LES studies (Nakanishi, 2000;Porson et al, 2011), the fog layer investigated here undergoes distinct thermodynamical transitions during its evolution. Initially, the fog forms near the surface in a very stable layer due to the long-wave cooling effect.…”

“…During the last decades, a clear decrease has been observed in fog occurrence throughout central Europe (Vautard et al, 2009;Giulianelli et al, 2014). This has occurred together with improved air quality due to a decreasing trend in sulfur emissions, especially in the case of dense fog, but thus far a quantitative connection has not been established (van Oldenborgh et al, 2010). Although in many ways driven by the same principles as clouds, fog also feature many unique aspects considering their evolution (Nakanishi, 2000;Gultepe et al, 2007).…”

“…This has occurred together with improved air quality due to a decreasing trend in sulfur emissions, especially in the case of dense fog, but thus far a quantitative connection has not been established (van Oldenborgh et al, 2010). Although in many ways driven by the same principles as clouds, fog also feature many unique aspects considering their evolution (Nakanishi, 2000;Gultepe et al, 2007). For example, while cloud droplets are mainly formed at the height of the peak saturation ratio at cloud base, in radiation fog, one of the most common fog types, the droplet formation is primarily driven by radiative cooling at the top of the developing fog layer or by high supersaturation inside the fog induced by turbulence.…”

Synoptic climatology of fog in selected locations of southern Poland (1966–2015)

“…Klemm and Lin (2016) found that a change of ten percent in aerosol concentration had about the same effect on fog occurence as a change of 0.1°C in air temperature. Reduction in fog frequency over the last 30 years has been reported for more than 300 stations in Europe (Vautard et al 2009) and other localities (Gomez and Smith 1984;Koepke 1995, 1997;Kokkola et al 2003;Shi et al 2008;Witi and La Dochy 2008;van Oldenborgh et al 2010;Sugimoto et al 2013;Fu et al 2014). An increase in the frequency of fog events due to growing industrial activity and rising atmospheric pollution concentration is observed in India (Singh and Dey 2012;Shrivastava et al 2016) and other parts of South Asia (Syed et al 2012).…”