Jon A. Arrillaga (UCM, SP) Sea-breeze occurrences in cabauw: implications for the scalar-transport and dynamics of the boundary layer Jon A. Arrillaga (UCM, SP) Jordi Vilà-Guerau de Arellano (WUR, NL) Fred Bosveld (KNMI, NL) Henk Klein Baltink (KNMI, NL) Carlos Yagüe (UCM, SP) Arjan Hensen (ECN, NL) Danielle van Dinther (ECN, NL) Arnoud Frumau (ECN, NL) Mariano Sastre (UCM, SP) Carlos Román-Cascón (CNRS, FR) BBOS Barcelona - 14 October 2016

De Haij et al., 2007 Sunrise Sunset BBOS Barcelona - 14 October 2016

De Haij et al., 2007 BBOS Barcelona - 14 October 2016

Sudden breakdown of the convective boundary layer: MOTIVATION DATA METHODOLOGY SB EVENTS IN CABAUW DYNAMICS TRANSPORT FINAL REMARKS Sudden breakdown of the convective boundary layer: Interaction between the mesoscale (SB) and microscale? How does it affect the afternoon-evening transition of the ABL? BBOS Barcelona - 14 October 2016

Time period: 01/01/2001 - 31/12/2010. (10 YEARS) MOTIVATION DATA METHODOLOGY SB EVENTS IN CABAUW DYNAMICS TRANSPORT FINAL REMARKS Observational site AREA OF STUDY Ideal site: CESAR (Cabauw). Time period: 01/01/2001 - 31/12/2010. (10 YEARS) ≈ 50 km from the sea. Two main SB directions. EUMETSAT/OSI SAF, full resolution METOP data (SST 28/06/09-02/07/09). BBOS Barcelona - 14 October 2016

Cabauw Experimental Site for Atmospheric Research (CESAR) MOTIVATION DATA METHODOLOGY SB EVENTS IN CABAUW DYNAMICS TRANSPORT FINAL REMARKS Cabauw Experimental Site for Atmospheric Research (CESAR) Validated data: Temperature Specific humidity Wind speed and direction Surface turbulent fluxes Turbulent fluxes at different levels (2007-2008) CO2 concentration (several gaps) 222Rn concentration (2006-2010). * Mixing layer height from LD40 AND CT75 ceilometers and LAP3000 wind profiler 200 m 140 m 80 m 40 m 20 m 10 m 2 m BBOS Barcelona - 14 October 2016

1) We select only the warm period from the 10 years: MJJA MOTIVATION DATA METHODOLOGY SB EVENTS IN CABAUW DYNAMICS TRANSPORT FINAL REMARKS 1) We select only the warm period from the 10 years: MJJA 2) SB filtering SB algorithm (Arrillaga et al., 2016) Weak synoptic forcing and fair-weather conditions Clear SBF (sea-breeze front) passage Steele et al., 2013 45º ONSHORE 𝜶 OFFSHORE 225º BBOS Barcelona - 14 October 2016

SB ALGORITHM 18 UTC – FILTER 3 (21.8 %) 18 UTC – FILTER 4 (17.1%) MOTIVATION DATA METHODOLOGY SB EVENTS IN CABAUW DYNAMICS TRANSPORT FINAL REMARKS SB ALGORITHM Wind speed (m s-1) 18 UTC – FILTER 3 (21.8 %) 18 UTC – FILTER 4 (17.1%) 18 UTC – FILTER 1 (31.2 %) 18 UTC – FILTER 2 (26.6 %) 18 UTC – FILTER 5 (8.4 %). 18 UTC – NO FILTER BBOS Barcelona - 14 October 2016

102/1220 (8.4%) well-defined Sea-Breeze (SB) days MOTIVATION DATA METHODOLOGY SB EVENTS IN CABAUW DYNAMICS TRANSPORT FINAL REMARKS 102/1220 (8.4%) well-defined Sea-Breeze (SB) days NW [290º-350º]: 44% N-NE [350º-45º]: 47% Rest [225º-290º]: 9% July: 26% June: 35% August: 16% May: 23% BBOS Barcelona - 14 October 2016

Impact of the SBF on the ABL? MOTIVATION DATA METHODOLOGY SB EVENTS IN CABAUW DYNAMICS TRANSPORT FINAL REMARKS Impact of the SBF on the ABL? ARRIVAL -2h +2h t = 0 RQ1: Impact of different SB directions, scalar transport? RQ2: Interaction with turbulence under different ABL regimes? 3 different ABL regimes: Convective: S 𝐻 𝑎𝑟𝑟𝑖𝑣𝑎𝑙 ≥0.5 𝑆𝐻 𝑚𝑎𝑥 (14 events) Transition: 0.5 𝑆𝐻 𝑚𝑎𝑥 > 𝑆𝐻 𝑎𝑟𝑟𝑖𝑣𝑎𝑙 ≥0 (66 events) Stable: 𝑆𝐻 𝑎𝑟𝑟𝑖𝑣𝑎𝑙 <0 (22 events) BBOS Barcelona - 14 October 2016

RQ1: Impact of different SB directions? MOTIVATION DATA METHODOLOGY SB EVENTS IN CABAUW DYNAMICS TRANSPORT FINAL REMARKS RQ1: Impact of different SB directions? ∆𝜑= 𝜑( 𝑡 𝑎𝑟𝑟𝑖𝑣𝑎𝑙 )−𝜑( 𝑡 𝑎𝑟𝑟𝑖𝑣𝑎𝑙 −1) Specific humidity (10’) Δq (g·kg-1) CO2 (30’) ΔCO2 (ppm) Cabauw Main cities in the area of Cabauw. SB events from the N-NE trigger the largest q jumps. Sharp CO2 increment in some W-NW events. BBOS Barcelona - 14 October 2016

RQ2: Interaction with turbulence under different ABL regimes? MOTIVATION DATA METHODOLOGY SB EVENTS IN CABAUW DYNAMICS TRANSPORT FINAL REMARKS RQ2: Interaction with turbulence under different ABL regimes? Surface heat fluxes (W m-2) Time from SB onset The local surface fluxes remain virtually unchanged by the SBF. BBOS Barcelona - 14 October 2016

RQ2: Interaction with turbulence under different ABL regimes? MOTIVATION DATA METHODOLOGY SB EVENTS IN CABAUW DYNAMICS TRANSPORT FINAL REMARKS RQ2: Interaction with turbulence under different ABL regimes? Wind speed (m s-1) Time from SB arrival Clear SB frontal passage Transition and stable regimes: significant increase of wind shear! BBOS Barcelona - 14 October 2016

RQ2: Interaction with turbulence under different ABL regimes? MOTIVATION DATA METHODOLOGY SB EVENTS IN CABAUW DYNAMICS TRANSPORT FINAL REMARKS RQ2: Interaction with turbulence under different ABL regimes? Potential temperature (K) Substantial differences between the regimes. Abrupt transition in the transition regime. Time from SB onset BBOS Barcelona - 14 October 2016

RQ2: Interaction with turbulence under different ABL regimes? MOTIVATION DATA METHODOLOGY SB EVENTS IN CABAUW DYNAMICS TRANSPORT FINAL REMARKS RQ2: Interaction with turbulence under different ABL regimes? ABLH from wind profiler (m) The arrival of the SB accelerates the afternoon transition of the ABL. We explore how the shear (S) and buoyancy (B) are affected by the SB. Time from SB onset BBOS Barcelona - 14 October 2016

RQ2: Interaction with turbulence under different ABL regimes? MOTIVATION DATA METHODOLOGY SB EVENTS IN CABAUW DYNAMICS TRANSPORT FINAL REMARKS RQ2: Interaction with turbulence under different ABL regimes? 𝑑𝑆 𝑑𝑡 = 𝑑 𝑑𝑡 𝜕𝑢 𝜕𝑧 2 + 𝜕𝑣 𝜕𝑧 2 𝑑𝐵 𝑑𝑡 = 𝑑 𝑑𝑡 𝑔 𝜃 𝑣 𝜕 𝜃 𝑣 𝜕𝑧 𝑑 2 𝐵 𝑑𝑡 2 <0 𝑑 2 𝐵 𝑑𝑡 2 >0 Both dB/dt and dS/dt indicate an acceleration of the afternoon ABL transition (SH>0). 𝑑 2 S 𝑑𝑡 2 (30)>0 𝑑 2 S 𝑑𝑡 2 (30)=0 Time from SB onset BBOS Barcelona - 14 October 2016

CHALLENGING INTERACTION WITH LOCAL TURBULENCE (30 m, 110 m, 170 m) MOTIVATION DATA METHODOLOGY SB EVENTS IN CABAUW DYNAMICS TRANSPORT FINAL REMARKS CHALLENGING INTERACTION WITH LOCAL TURBULENCE (30 m, 110 m, 170 m) Acceleration of the afternoon ABL transition TRANSITION REGIME dB/dt and dS/dt increase at all levels Thermally-buoyant conditions are maintained CONVECTIVE REGIME σw/w* constant w*/u* very slight decrease Tendency towards a weakly-stable state in the evening transition STABLE REGIME SC increases BBOS Barcelona - 14 October 2016

take-home ideas future work MOTIVATION DATA METHODOLOGY SB EVENTS IN CABAUW DYNAMICS TRANSPORT FINAL REMARKS take-home ideas The transport of scalars is occasionally affected by the SB direction. The impact of the SB on the ABL is different depending on the ABL regime. Surface fluxes remain unaltered by the SBF: the observed features are only due to the mesoscale. The arrival of the SB accelerates the ABL afternoon transition but shifts the NBL towards a weakly stable/continuously turbulent state during the evening transition. future work Theoretical studies for the different ABL regimes (CLASS). 10-year WRF simulations. BBOS Barcelona - 14 October 2016

THANK YOU FOR YOUR ATTENTION! ACKNOWLEDGEMENTS: Basque Government (PRE_2016_2_0160, EP_2016_1_0048), Spanish Government (CGL2015-65627-C3-3-R), Royal Netherlands Meteorological Institute (KNMI), OSI SAF. BBOS Barcelona - 14 October 2016