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Impacts of afternoon and evening sea‐breeze fronts on local turbulence, and on CO 2 and radon‐222 transport
Author(s) -
Arrillaga Jon A.,
de Arellano Jordi VilàGuerau,
Bosveld Fred,
Baltink Henk Klein,
Yagüe Carlos,
Sastre Mariano,
RománCascón Carlos
Publication year - 2018
Publication title -
quarterly journal of the royal meteorological society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.744
H-Index - 143
eISSN - 1477-870X
pISSN - 0035-9009
DOI - 10.1002/qj.3252
Subject(s) - sea breeze , wind shear , mesoscale meteorology , planetary boundary layer , convective boundary layer , convection , turbulence , boundary layer , atmospheric sciences , environmental science , meteorology , troposphere , atmospheric instability , turbulence kinetic energy , potential temperature , wind speed , geology , climatology , mechanics , physics
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.