Analysis of turbulence in fog episodes

Terradellas, Enric; Ferreres, E.; Soler, M. R.

doi:10.5194/asr-2-31-2008

Cited by 10 publications

(3 citation statements)

References 11 publications

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“…On the one hand, the most common (and probably studied) fog type is radiation fog, formed as a result of the surface radiative cooling during the night (Bergot et al, 2007;Gultepe et al, 2007). Many observational and/or modelling studies have focused on this type of fog (e.g., Terradellas et al, 2008;Van der Velde et al, 2010;Bergot, 2013;Price et al, 2018, among many others), but models still have problems simulating it, especially when its formation is not imposed by the local topography (Müller et al, 2010). The characteristics of radiation fogs are variable, from short-lived, not-mixed and shallow fog events of a few meters to persistent, well-mixed and deep events of several hundreds of meters (Duynkerke, 1999;Román-Cascón et al, 2016b).…”

Section: Introductionmentioning

confidence: 99%

Radiation and cloud-base lowering fog events: Observational analysis and evaluation of WRF and HARMONIE

Román‐Cascón

Yagüe

Steeneveld

et al. 2019

Atmospheric Research

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Most of the effects caused by fog are negative for humans. Yet, numerical weather prediction (NWP) models still have problems to simulate fog properly, especially in operational forecasts. In the case of radiation fog, this is partially caused by the large sensitivity to many aspects that contribute to its formation, evolution and dissipation, such as the synoptic and local conditions, the near-surface turbulence, the aerosol and droplet microphysics, or the surface characteristics, among others. This work focuses on an interesting 8-day period with several alternating radiation and cloud-base lowering (CBL) fog events observed at the Research Centre for the Lower Atmosphere (CIBA) in the Spanish Northern Plateau. The site was appropriately instrumented to characterize fog from the surface up to the height of 100 m. On the one hand, radiation fog events are associated with strong surface cooling leading to high stability close to the surface and low values of turbulence, giving rise to shallow fog. The evolution of this type of fog is markedly sensitive to the dynamical conditions close to the surface (i.e., wind speed and turbulence). On the other hand, CBL fog presents deeper thickness associated with higher values of turbulence and less stability. Subsequently, we evaluated the fog-forecasting skill of two mesoscale models (WRF and HARMONIE) configured as similar as possible. Both models present more difficulties simulating radiation fog events than CBL ones. However, the duration and vertical extension of the CBL fog events is normally overestimated. This extended-fog avoids the surface radiative cooling needed to simulate radiation fog events formed the following nights. Therefore, these periods with alternating CBL and radiation fog are especially challenging for NWP models.

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Section: Introductionmentioning

confidence: 99%

Radiation and cloud-base lowering fog events: Observational analysis and evaluation of WRF and HARMONIE

Román‐Cascón

Yagüe

Steeneveld

et al. 2019

Atmospheric Research

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“…Early studies revealed that the balance between radiative cooling and turbulent mixing was the primary factor in radiation fog development (ROACH et al, 1976;NAKANISHI 2000;TERRADELLAS et al, 2008). Some studies focused on the radiation fogs formed in valleys, and showed that the mountain wind, urban heat island, and water surface were important in the life cycle of valley fogs (PILIE et al, 1979).…”

Section: Introductionmentioning

confidence: 99%

Summary of a 4-Year Fog Field Study in Northern Nanjing, Part 1: Fog Boundary Layer

Liu

Niu

Yang

et al. 2011

Pure Appl. Geophys.

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Comprehensive fog field observations were conducted during the winters of 2006-2009 at the Nanjing University of Information Science and Technology to study the macro and micro-physical structures and the physical-chemical processes of dense fogs in the area. The observations included features of the fog boundary layer, characteristics of fog water, the particle spectrum, the chemical composition of atmospheric aerosols, radiation and heat components, turbulence, meteorological elements (air temperature, pressure, wind speed, wind direction), and environmental monitoring. The fogs observed were divided into four types: radiation fog, advection-radiation fog, advection fog, and precipitation fog, according to the mechanisms and primary factors of the fog processes. Fog boundary-layer structures of different types and their corresponding characteristics were then studied. Fog boundary-layer features, temperature structures, wind fields, and fog maintenance are discussed. The results show that radiation fog had remarkable diurnal variation and formed mostly at sunset or midnight, and lifted after sunrise or at noon, and that advection-radiation fog and advection fog were of very long duration. Extremely dense fogs occurred only in radiation-related cases. Inversion in radiation fog was short-lived, disappearing 1 or 2 hours after sunrise or at noon, faster than that in advectionradiation fog. When wind direction reversed from easterly to westerly or from southerly to northerly, the fog became an extremely dense fog. Low-level jet at times impeded fog development, whereas at other times it encouraged fog continuance. The deep inversion was merely an essential condition for a thick fog layer; sufficient vapor supply was advantageous to the formation and maintenance of a deep fog layer.

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“…Usually, radiation fog is formed through radiative cooling near the surface during the night. Over the past few decades, many observational and numerical studies have shown that turbulence was an essential factor that affected the evolution of radiation fog (e.g., Roach, 1976;Duynkerke, 1991a;Terradellas et al, 2008;Zhou and Ferrier, 2008;Ye et al, 2015; Degefie et al, 2015; Maronga and Bosveld, 2017 [3][4][5][6][7][8][9]). However, discrepancies exist among the arguments for the effects of turbulent mixing on fog formation.…”

Section: Introductionmentioning

confidence: 99%

Influence of Quasi-Periodic Oscillation of Atmospheric Variables on Radiation Fog over A Mountainous Region of Korea

Yum

Gültepe

et al. 2020

Atmosphere

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To enhance our understanding of fog processes over complex terrain, various fog events that occurred during the International Collaborative Experiments for Pyeongchang 2018 Winter Olympics and Paralympics (ICE-POP) campaign were selected. Investigation of thermodynamic, dynamic, and microphysical conditions within fog layers affected by quasi-periodic oscillation of atmospheric variables was conducted using observations from a Fog Monitor-120 (FM-120) and other in-situ meteorological instruments. A total of nine radiation fog cases that occurred in the autumn and winter seasons during the campaign over the mountainous region of Pyeongchang, Korea were selected. The wavelet analysis was used to study quasi-period oscillations of dynamic, microphysical, and thermodynamic variables. By decomposing the time series into the time-frequency space, we can determine both dominant periods and how these dominant periods change in time. Quasi-period oscillations of liquid water content (LWC), pressure, temperature, and horizontal/vertical velocity, which have periods of 15–40 min, were observed during the fog formation stages. We hypothesize that these quasi-periodic oscillations were induced by Kelvin–Helmholtz instability. The results suggest that Kelvin–Helmholtz instability events near the surface can be explained by an increase in the vertical shear of horizontal wind and by a simultaneous increase in wind speed when fog forms. In the mature stages, fluctuations of the variables did not appear near the surface anymore.

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Analysis of turbulence in fog episodes

Cited by 10 publications

References 11 publications

Radiation and cloud-base lowering fog events: Observational analysis and evaluation of WRF and HARMONIE

Radiation and cloud-base lowering fog events: Observational analysis and evaluation of WRF and HARMONIE

Summary of a 4-Year Fog Field Study in Northern Nanjing, Part 1: Fog Boundary Layer

Influence of Quasi-Periodic Oscillation of Atmospheric Variables on Radiation Fog over A Mountainous Region of Korea

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