%0 Journal Article %1 De1999 %A Silva, I. P. D. De %A Brandt, A. %A Montenegro, L. J. %A Fernando, H. J. S. %D 1999 %J DYNAMICS OF ATMOSPHERES AND OCEANS %K imported %N 1 %P 47--63 %T Gradient Richardson number measurements in a stratified shear layer %V 30 %X This paper presents instantaneous local gradient Richardson number Ri(g)(t) measurements in a stratified shear layer using a novel laser-Doppler anemometer and conductivity probe assembly with a resolution of Delta z = 0.27 cm, The aim was to study the dependence of Ri(g)(t) on the bulk Richardson number Ri(o). The shear layer was established between two co-flowing streams of different densities and velocities, and the motion field within the shear layer allowed the development of Kelvin-Helmholtz (K-H) instabilities, internal waves and turbulence. Ri(g)(t) was also measured at lesser resolutions (Delta z > 1.8 cm) using conventional measurement techniques. Although the mean background flow was quasi-steady, Ri(g)(t) was highly time dependent due to the variable internal strain field induced by the combined effect of instabilities, waves and turbulence. When K-H instabilities were present, the time-averaged gradient Richardson number <(Ri(g))over bar> (Delta z = 0.27 cm) was approximately a constant 0.06 +/- 0.02, irrespective of Ri(o). When K-H instabilities were absent, <(Ri(g))over bar> (Delta z = 0.27 cm) assumed larger values that are dependent on Ri(o). <(Ri(g))over bar> (Delta z > 1.8 cm) was always found to be dependent on Delta z and <(Ri(o))over bar>. It is argued that <(Ri(g))over bar> should be measured with a resolution better than the scale of density overturns to properly account for vertical small-scale processes of the stratified shear layer. The measurements are consistent with the notion that when Ri(o) < 10 or so the energy supplied to a sheer layer at large scales can be dissipated at smaller scales by the turbulence associated with the breakdown of K-H instabilities.

@article{De1999, abstract = {This paper presents instantaneous local gradient Richardson number Ri(g)(t) measurements in a stratified shear layer using a novel laser-Doppler anemometer and conductivity probe assembly with a resolution of Delta z = 0.27 cm, The aim was to study the dependence of Ri(g)(t) on the bulk Richardson number Ri(o). The shear layer was established between two co-flowing streams of different densities and velocities, and the motion field within the shear layer allowed the development of Kelvin-Helmholtz (K-H) instabilities, internal waves and turbulence. Ri(g)(t) was also measured at lesser resolutions (Delta z > 1.8 cm) using conventional measurement techniques. Although the mean background flow was quasi-steady, Ri(g)(t) was highly time dependent due to the variable internal strain field induced by the combined effect of instabilities, waves and turbulence. When K-H instabilities were present, the time-averaged gradient Richardson number <(Ri(g))over bar> (Delta z = 0.27 cm) was approximately a constant 0.06 +/- 0.02, irrespective of Ri(o). When K-H instabilities were absent, <(Ri(g))over bar> (Delta z = 0.27 cm) assumed larger values that are dependent on Ri(o). <(Ri(g))over bar> (Delta z > 1.8 cm) was always found to be dependent on Delta z and <(Ri(o))over bar>. It is argued that <(Ri(g))over bar> should be measured with a resolution better than the scale of density overturns to properly account for vertical small-scale processes of the stratified shear layer. The measurements are consistent with the notion that when Ri(o) < 10 or so the energy supplied to a sheer layer at large scales can be dissipated at smaller scales by the turbulence associated with the breakdown of K-H instabilities.}, added-at = {2009-11-03T20:21:25.000+0100}, author = {Silva, I. P. D. De and Brandt, A. and Montenegro, L. J. and Fernando, H. J. S.}, biburl = {https://www.bibsonomy.org/bibtex/277dc1dd13402c6a48672777d2f677803/svance}, citedreferences = {BROWNING KA, 1971, Q J ROY METEOR SOC, V97, P283 ; CHERESKIN TK, 1986, J GEOPHYS RES, V91, P12887 ; DESAUBIES Y, 1981, J PHYS OCEANOGR, V11, P541 ; DESILVA IPD, 1992, J FLUID MECH, V240, P601 ; DESILVA IPD, 1996, EARTH PLANET SC LETT, V143, P217 ; DILLON TM, 1984, J PHYS OCEANOGR, V14, P541 ; ERIKSEN CC, 1978, J GEOPHYS RES, V83, P2989 ; FERNANDO HJS, 1991, ANNU REV FLUID MECH, V23, P455 ; GEYER WR, 1985, THESIS U WASHINGTON ; GEYER WR, 1987, J PHYS OCEANOGR, V17, P1668 ; GIBSON CH, 1987, PHYSICOCHEM HYDRODYN, V8, P1 ; GIBSON CH, 1993, DYNAM ATMOS OCEANS, V19, P175 ; GIBSON CH, 1998, 44 ANN M DIV FLUID D ; GREGG MC, 1987, J GEOPHYS RES-OCEANS, V92, P5249 ; HALPERN D, 1976, DEEP-SEA RES, V23, P495 ; HERBERT D, 1992, J PHYS OCEANOGR, V22, P1346 ; HINES CO, 1988, J ATMOS SCI, V45, P1269 ; IERKIC HM, 1990, RADIO SCI, V25, P941 ; KOOP CG, 1981, J FLUID MECH, V113, P347 ; KUNDU PK, 1991, J GEOPHYS RES-OCEANS, V96, P4855 ; LAWRENCE GA, 1991, PHYS FLUIDS A-FLUID, V3, P2360 ; MOUM JN, 1992, J PHYS OCEANOGR, V22, P1330 ; NAPPO CJ, 1991, BOUND-LAY METEOROL, V54, P69 ; ODELL GM, 1971, J FLUID MECH, V50, P535 ; PERERA MJAM, 1994, J FLUID MECH, V267, P275 ; PETERS H, 1988, J GEOPHYS RES, V93, P1199 ; SHERMAN FS, 1978, ANNU REV FLUID MECH, V10, P267 ; STRANG EJ, 1998, UNPUB J FLUID MECH ; THORPE SA, 1973, BOUND-LAY METEOROL, V5, P95 ; THORPE SA, 1977, PHILOS T ROY SOC A, V286, P125 ; TOOLE JM, 1987, J PHYS OCEANOGR, V17, P1397 ; WESSON JC, 1994, J GEOPHYS RES-OCEANS, V99, P9847 ; WOODS JD, 1968, J FLUID MECH, V32, P791}, interhash = {06c872ba89b06c7817b8835c414ccd89}, intrahash = {77dc1dd13402c6a48672777d2f677803}, journal = {DYNAMICS OF ATMOSPHERES AND OCEANS}, keywords = {imported}, number = 1, owner = {svance}, pages = {47--63}, timestamp = {2009-11-03T20:21:44.000+0100}, title = {Gradient Richardson number measurements in a stratified shear layer}, volume = 30, year = 1999 }