caa a22 4500 475777794 CHVBK 20180406123636.0 cr unu---uuuuu 170329e20001001xx s 000 0 eng 10.1023/A:1002628924673 doi (NATIONALLICENCE)springer-10.1023/A:1002628924673 Tethered Balloon Observations Of The Nocturnal Stable Boundary Layer In A Valley [Elektronische Daten] [J. Holden, S. Derbyshire, S. Belcher] Detailed measurements of profiles of mean and turbulent variablesthrough the nocturnal stable boundary layer over a valley arepresented. Two nights of data are analysed in detail, one with only aweakly stable boundary layer and one with a strongly stable boundarylayer. The weakly stratified night shows high levels of turbulence inwhich the flow remains attached to the valley and the boundary layeracts as a single coherent layer. On the strongly stratified night, twoflow regimes are identified: attached flow, as on the weaklystratified night, and decoupled flow in which the air in the valleybecomes so dynamically stable that there is no turbulent interactionwith the mean flow aloft. Because the valley is sloping, the decoupledlower stagnant air then forms a drainage current. We find that theFroude number evaluated at the hill height, FH = U(H)/N(H) H,diagnoses the flow regime: when FH = 2, the flow remainsattached and when FH ≲ 2 the flow in the valley becomesdecoupled from the flow aloft. The dynamics of the flow regimes areshown to be understandable in terms of the gradient Richardson number,which indicates the turbulent mixing. We show that the gradientRichardson number is a key parameter in diagnosing each flow regime. Kluwer Academic Publishers, 2000 Boundary layer nationallicence Decoupling nationallicence Flow over hills nationallicence Stable stratification nationallicence Valley flow nationallicence Holden J. Department of Meteorology, University of Reading, U.K. aut Derbyshire S. Department of Meteorology, University of Reading, U.K. aut Belcher S. Department of Meteorology, University of Reading, U.K. aut Boundary-Layer Meteorology Kluwer Academic Publishers 97/1(2000-10-01), 1-24 0006-8314 97:1<1 2000 97 10546 https://doi.org/10.1023/A:1002628924673 text/html Onlinezugriff via DOI 1 research-article jats NATIONALLICENCE 856 40 https://doi.org/10.1023/A:1002628924673 text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Holden J. Department of Meteorology, University of Reading, U.K aut NATIONALLICENCE 700 1- Derbyshire S. Department of Meteorology, University of Reading, U.K aut NATIONALLICENCE 700 1- Belcher S. Department of Meteorology, University of Reading, U.K aut NATIONALLICENCE 773 0- Boundary-Layer Meteorology Kluwer Academic Publishers 97/1(2000-10-01), 1-24 0006-8314 97:1<1 2000 97 10546 Metadata rights reserved Springer special CC-BY-NC licence nationallicence BK010053 XK010053 XK010000 NATIONALLICENCE NATIONALLICENCE NL-springer