- 1Sorbonne Université, Institut Pierre Simon Laplace (IPSL), Ecole Polytechnique, 91128 Palaiseau, France
- 2Institut Pierre-Simon Laplace, École Polytechnique, UVSQ, Université Paris-Saclay, 91128 Palaiseau, France
- 3Institut Pierre Simon Laplace, CNRS, Ecole Polytechnique de Paris, Institut Polytechnique de Paris, Paris, France
Based on an instrumental synergy of in-situ and remote sensing measurements collected at SIRTA observatory, a peri-urban site located near Paris, and a fog conceptual model (CM), this study presents a statistical analyses of the local and synoptic processes driving the different phases (formation, evolution and dissipation) of radiation fogs (RADs) and stratus lowering fogs (STLs). The very high resolution of the co-localised BASTA cloud Radar, Ceilometer and visibilimeter, allows to estimate the occurrence of fog during the 2013-2023 period. A microwave radiometer (MWR Hatpro) and the equivalent adiabaticity by closure from the CM are used to estimate the lowest layer atmospheric stability. 191 fogs (82 RADs and 99 STLs) are well documented and divided into several categories depending on their geometry (radiation fogs), their type of dissipation (lifting or lowering cloud base height), and their time of dissipation (nocturnal or diurnal).
By associating fog types with large-scale atmospheric circulations, the result show the role of synoptic regimes on the fog evolution at SIRTA. Longer RADs and STLs are associated with strong temperature inversions driven by the Atlantic Ridge and positive North Atlantic Oscillation (NAO+) regimes. These two regimes promote the advection of warm air to the West of Europe and contribute to the diurnal variability of temperatures in the region.
The analysis of the local processes driving the different phases of fogs is conducted using the turbulent kinetic energy (TKE), the sensible heat flux (SHF) and the fog reservoir of liquid water path (RLWP) estimated by a sonic anemometer and at 30 m a.g.l, the Licor analyzers at 2 m a.g.l, and the CM, respectively. For RAD fogs, mechanical turbulence is the factor favoring the vertical development of fog making it adiabatic. Therefore, fine and very fine RADs remain in their stable phase when the TKE is less than 0.2 m2 s-2. RADs begin their transition as soon as the TKE exceeds this threshold and remains less than 0.4 m2 s-2 and the RLWP > 0 g m-2. The dissipation of thick RADs is observed when the TKE exceeds 0.4 m2 s-2 and the RLWP < 0 g m-2. This strong turbulence can be of mechanical origin associated with an advection across the site or thermal with a diurnal increase in the SHF (50 W m-2). Less SHF (25 W m-2) is needed to dissipate very thin RADs. The amount of heat required for the diurnal dissipation of RADs is proportional to their geometric and microphysical characteristics. STLs persist for a stable TKE around 0.4 m2 s-2 and dissipate by elevation of the CBH when the SHF is low (25 W m-2). Their dissipation by evaporation needs more SHF (75 w m-2). The results indicates that the instrumental synergy and the metrics used in this study allows to produce an early warning tools for the nowcasting of RAD and STL formation, evolution and dissipation.
How to cite: Dione, C., Dupont, J.-C., Haeffelin, M., and Ribaud, J.-F.: Statistical analysis of the influence of local and synoptic processes on radiation and stratus lowering fogs at SIRTA Observatory, Paris, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19911, https://doi.org/10.5194/egusphere-egu25-19911, 2025.