# Changes between Version 3 and Version 4 of WikiStart

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Sep 8, 2017, 1:13:03 PM (3 years ago)
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 v3 [[PageOutline]] = '''SLOCET''' = ||Infrastructure||CNRS_Coriolis|| ||Project (long title)||Shelf sLOpe impact on Coastal Eddy Turbulence|| ||Campaign Title (name data folder)||17SLOCET|| ||Lead Author||Alex Stegner|| ||Contributors||Remi Laxenaire, Ted Johnson, Chunxin Yuan,  Joel Sommeria, Samuel Viboud|| ||Date Campaign Start||13/02/2017|| ||Date Campaign End||10/03/2017|| = '''ICESHELF''' = ||Infrastructure||CNRS_Coriolis Topographic Barriers and warm Ocean currents controlling Antarctic ice shelf melt|| ||Project (long title)||Topographic Barriers and warm Ocean currents controlling Antarctic ice shelf melt|| ||Campaign Title (name data folder)||17ICESHELF|| ||Lead Author||Elin Darelius (part I) and Anna Wåhlin (part II)|| ||Contributors||Nadine Steiger,  Joel Sommeria, Samuel Viboud|| ||Date Campaign Start||04/09/2017|| ||Date Campaign End||27/09/2017|| = 0 - Publications, reports from the project = = 1 - Objectives = New theoretical analyses and numerical computations have shown that regions of the continental shelf where the offshore shelf profile changes significantly can be sources of coastal eddies and thus regions of coastal turbulence. The size and intensity of the eddies is determined by the rapidity of the change in the profile and also by the stratification of the flow on the shelf. Eddies can be excited both by coastal currents (Pennel et al. 2012; Cimoli et al. 2017) passing along the shelf over the profile change and, in the correct parameter regime, by incident Topographic Rossby Waves (Rodney & Johnson 2014). A series of experiments will be carried out using PIV in both layers to demonstrate this mechanism for coastal eddy generation in two­ layer flow. The results will be compared with existing and new theory and with new numerical simulations run with the MITgcm. The warm water threatening to melt the Antarctic ice shelves originates from the deep ocean north of the continental shelf. In order for the warm water to reach the ice shelf cavities it has to pass to topographic barriers: the shelf break and the ice shelf front. In a series of experiments we will explore the role of topography in controlling the onshelf flow of warm water. = 2 - Experimental setup: = == 2.1 General description == In order to mimic the oceanic stratification a two ­layer salt stratification with a thin upper layer ( H1= 8cm) above a deep layer ( H2=72cm) is set up on the rotating platform.The ration period is fixed at To=50s (i.e. a Coriolis parameter f=4*pi/T0=0.25s-1) and adjusting the density difference rho2-rho1=10 g/l between the two layers give baroclinic deformation radius Rd around 32cm. This deformation radius will be large in comparison with the upper layer thickness ( Rd>H1) but remain small in comparison with the tank diameter D=13m. Hence, for eddies in the upper layer, we will satisfy the shallow­ water aspect ratio (H1/Reddy<<1) at meso­scale when the typical radius is of the same size or larger than Rd. == 2.2 Wave maker == == 2.3 Jet forcing == == 2.4 References axis along the wall (horizontal and vertical) == By definition we will use Ox and Oy axis to define the along shore and the cross shore axis. The central reference point (0,0) along the wall is chosen to be the closest point to the center of the tank (also labeled '''M0'''). Positive direction corresponds to the mean wave or the mean flow direction. We use seven references points along the wall to quantify the impact of the free surface deformation and the possible vertical deviation of the laser sheet. The two Barriers - the shelf break and the ice shelf front - will be studied in two separate sets of Experiments. Part I: Divergent isobaths at the shelf break An idealized topography representing a widening continental shelf and a trough crosscutting the Continental shelf break is used and the effect of changing 1) water depth 2) radius of curvature and 3) flow speed will be explored. The experiments will be repeated with a) a barotropic and b) a baroclinic current. Part II: Flow across an ice shelf front == 2.2 Topography == === 2.2.1 Topography for the shelf break experiments (Nadine) === * Check and add the location of the wall/sink! === 2.2.2 Topography for the ice shelf experiments === == 2.3 Reference axis == === 2.3.1 Reference axis for shelf break experiments (Nadine) === By definition we will use Ox and Oy axis to define the along slope and the cross slope axis. The central reference point (0,0) along the slope is chosen to be the first "land" corner downstream of the source. Positive u - direction corresponds to the along slope flow direction, while positive  v - direction is directed onshelf. 2.3.2 Reference axis for ice front experiments 2.4 References axis along the wall (horizontal and vertical) By definition we will use Ox and Oy axis to define the along shore and the cross shore axis. The central reference point (0,0) along the wall is chosen to be the closest point to the center of the tank (also labeled '''M0'''). Positive direction corresponds to the mean wave or the mean flow direction. __We use seven references points along the wall to quantify the impact of the free surface deformation and the possible vertical deviation of the laser sheet???__ [[Image(DSC_0811_00001.jpg)]] All these points will be measured every day before starting the experiment. __All these points will be measured every day before starting the Experiment??__ ||Position||M2||M1||M0||M-1||M-2|| == 2.5 Fixed Parameters == ||'''Notation'''||'''Definition'''||'''Values'''||'''Remarks'''|| ||$T_0$||Rotation period||$50 \ s^-^1$|||| ||$\Delta\rho$||Density difference||$10 \ kg \ m^-^3$||The vertical stratification evolves in time, here we consider the maximum and minimum densities|| ||$W$||Upstream shelf width||$1 \ m$|||| ||$S$||Upstream shelf slope||$60%$|||| ||$T_0$||Rotation period||$60 \ s^-^1$|||| ||||Shelf height||$0.5\ m$|||| ||||Trough height||$0.42\ m$|||| ||$s$||slope||!1:2|||| ||$\nu$||Viscosity||$10^-^6m^2s^-^1$ ^|||| ||$L$||Total length of the wall||$11 \ m$|||| ||$L$||Total length of the wall||$\ m$|||| == 2.5 Variable Parameters == ||'''Notation'''||'''Definition'''||'''Unit'''||'''Initial Estimated Values'''||'''Remarks'''|| ||$Htot$||Total water depth||$cm$||80||estimated at the center of the wall|| ||$Hcoast$||Water depth at coast (at M0)||$cm$||20||estimated at the center of the wall|| ||$W_1$||Downstream shelf width||$m$||0-1-4|||| ||$S_1$||Downstream shelf slope||$%$||0-15-60|||| ||$T_{flap}$||Flap period||$s$||40-200|||| ||$A_{flap}$||Amplitude of carriage motion||$cm$||10-60||peak to peak amplitude|| ||$V_{flap}$||Max speed of oscillating carriage||$cm/s$||1-4|||| ||$Q_{jet}$||Flow rate of the jet||$l/min$||0.5-4|||| ||$Htot$||Total water depth||$cm$||60 - 70||estimated where?|| ||$Hcoast$||Depth on shelf||$cm$||10 - 20||estimated where?|| ||$R_c$||Radius of curvature||$m$||0 - 0.5|||| ||$Q$||Flux||$L min-1$||20 - ??- ?? - 135|||| ||$\Delta \rho$||Density difference (ambient - inflow)||$kg$||0 - 3 - 10|||| == 2.6 Additional Parameters == ||'''Notation'''||'''Definition'''||'''Unit'''||'''Initial Estimated Values'''|| ||$g'$||Reduced gravity||$cm/s2$||9.81|| ||$Rd$||Baroclinic deformation radius||$cm$||32.4|| ||$RD$||Barotropic deformation radius||$cm$||1050|| ||$H2$||Mean lower layer depth over shelf||$cm$||46|| ||$g'$||Reduced gravity||$cm/s2$|||| ||$Rd$||Baroclinic deformation radius||$cm$|||| == 2.7 Definition of the relevant non-dimensional numbers == Vertical aspect ratio (gamma), $\ gamma = H1/H2$. Rossby number, $Ro =$. Froud number (equivalent Fd), $Fd = Umax/fRd = Umax/C$. Batch processed camera data in to .png files for those experiments from 18-43 that have PIV data, so that images are in a non-proprietary format. PIV analysis of the flow field through multiple horizontal slices in different Z-positions, for the non-rotating case, and for the rotating cases (experiments 18-43 as above), dependent on the quality of the captured PIV images. Average velocity vectors for the channel slices. Potentially information on vorticity would enable the smaller-scale vortical structures that are obvious in some of the videos, to be identified. = 4 - Methods of calibration and data processing = = 4 - Methods of calibration and data Processing (NADINE) = The MSCTI conductivity probe is calibrated after each set of experiments when the tank is drained (see Section 3.1 for full details). The ADVs have 4 heads and as such this enables some internal verification of the instrument. The ADV and UVP datasets are processed using a series of bespoke Matlab scripts. The PIV data will be processed using a bespoke script. Access to commercial PIV processing packages is also available.