Impacts of afternoon and evening sea‐breeze fronts on local turbulence, and on CO₂ and radon‐222 transport

Abstract

We investigated sharp disruptions of local turbulence and scalar transport due to the arrival of sea-breeze fronts (SBFs). To this end, we employed a comprehensive 10-year observational database from the Cabauw Experimental Site for Atmospheric Research (CESAR, the Netherlands). Sea-breeze (SB) days were selected using a five-filter algorithm, which accounts for large-scale conditions and a clear mesoscale-frontal signal associated with the land-sea contrast. Among those days (102 in all, 8.3%), based on the value of the sensible-heat flux at the onset of SB, we identified three atmospheric boundary-layer (ABL) regimes: convective, transition and stable. In the convective regime, the thermally driven convective boundary layer is only slightly altered by a small enhancement of the shear when the SBF arrives. Regarding the transition regime, we found that the ABL afternoon transition is accelerated. This was quantified by estimating the contributions of shear and buoyancy to the turbulent kinetic energy. Other relevant disruptions are the sharp reduction in ABL depth (∼250 m/hr) and the sudden increase in average wind speed (> 2 m/s). In the stable regime, the arrival of the SB leads to disturbances in the wind profile at the surface layer. We observed a deviation of more than 1 m/s in the observed surface-layer wind profile compared with the profile calculated using Monin-Obukhov Similarity Theory (MOST). Our findings furthermore reveal the determinant role of the SB direction in the transport of water vapour, CO 2 and 222 Rn. The return of continental air masses driven by the SB circulation generates sharp CO 2 increases (up to 14 ppm in half an hour) in a few SB events. We suggest that the variability in 222 Rn evolution may also be influenced by other non-local processes such as the large-scale footprint from more remote sources.

Weak and intense katabatic winds: impacts on turbulent characteristics in the stable boundary layer and CO<sub>2</sub> transport

“…The algorithm consists of four different filters, which are shown in Table 2. The first three are coincident with the algorithm defined in Arrillaga et al (2018), just modifying the precipitation-amount threshold for Filter 3: 0.5 instead of 0.1 mm/day, since weak and scattered showers (< 0.5 mm) do not alter the onset and development of katabatic winds. From detailed individual analysis we found that the large-scale conditions favourable for the formation of katabatic flows are those that apply for sea breezes, i.e.…”

“…The research strategy from Arrillaga et al (2018), in which they applied an objective and systematic algorithm to the observational data in order to select sea-breeze events, is followed. In this work, we adjust the algorithm for selecting events that fulfil predefined katabatic criteria.…”

“…More or less directly continuous turbulence in the SBL has been linked with a stronger background wind (e.g. > 5-7 m s -1 in Van de Wiel et al (2012b)) and low-level jets (Sun et al, 2012), or even with occasional irruption of sea-breeze fronts (Arrillaga et al, 2018).…”

Analyzing the Synoptic‐, Meso‐ and Local‐ Scale Involved in Sea Breeze Formation and Frontal Characteristics

“…Finally, given the importance of the SB‐turbulence interaction during the AET, as was proved in Arrillaga et al (), the coincident SB events have been classified into different ABL regimes. These, are defined according to the local turbulence at the moment of the onset.…”

Dutch fog: On the observed spatio‐temporal variability of fog in the Netherlands

“…Similarly, the presence of the North Sea and the IJsselmeer (the large freshwater lake in the north of the country) have a significant impact on local weather conditions, through such effects as sea‐breeze circulation, which can alter aerosol concentration (Arrillaga et al . ) and local temperatures, as well as the modulation of diurnal and seasonal temperature cycles through the increased heat capacity of the water. At the same time, the North Sea also brings with it a thermal memory in the form of the Gulf Stream circulation, making the coastal waters warmer than they would otherwise be without the transatlantic transport of heat from the tropical and Equatorial regions (Palter, ).…”