SAMS Gliders: Research Activities

Transcription

1 SAMS Gliders: Research Activities Mark Inall, Toby Sherwin, Stuart Cunningham Estelle Dumont, Marie Porter, Dmitry Aleynik Scottish Association for Marine Science Scottish Marine Institute Oban PA37 1QA

2 Extended Ellett Line The Extended Ellett Line : Majorgateway for water exchange between the Atlantic and the Nordic seas important area for the moderation of Western Europe s climate Sub polar gyre key component 25 on AMOC Studied by research cruises since Annual summer occupations continue 2 Glider missions since 2009, continuing annually (winter) from o N Norwegian Basin 62 o N 60 o N 58 o N 56 o N Iceland Basin ED DIE S Rockall Bank Rockall Trough Warm surface Atlantic water Deep cold overflow water Traditional Ellett Line Seaglider Ellett Line o W 20 o W 15 o W 10 o W 5 o W 0 o

3 Dive average currents (DACs) from selected transects

4 N T G a T track to target G track taken by glider a apparent drift current

5 Dive Average Currents (to ~ 1000 m) in cm s -1 computed from binned averages Dive North North East East range (W to E) (E to W) (W to E) (E to W) No of dives 304: : * 532: : : * 708: : mean std dev ±2.8 ±0.25 ±0.06 ±0.32 * some dive sequences ignored Approx width of Rockall Trough = 250 km; Implied surface transport from = 11 Sv to the south!!!!

6 Fluxes Across Sloping Topography of the North EastAtlantic NERC Directed Consortium on Ocean Shelf Exchange: SAMS (lead), NOC, U. Bangor, U. Liverpool, U. Plymouth and PML October 2011 September 2015 Scientific Aim: To construct a new paradigm of Ocean/Shelf exchange using novel observations and model techniques to resolve the key seasonal, interannual and regional variation absent from existing knowledge URL:

7 June 2003

8 Glider Deployments overview Glider Deployment Recovery date date Coprolite 25/06/12 23/07/12 25/08/12 01/10/12 Bellamite 27/06/12 23/08/12 Unit_194 27/06/12 23/08/12 Talisker 15/09/12 Jan 2013 Coprolite Bellamite Unit_194 Talisker June July August September October January

9 Planned Analysis IT sampling: profiles per M2 period 2 day moving window, M2 bestfit to isopycnal displacements: baroclinically de tided data set spatial and temporal variation of IT Problems with alternating direction of transects systematic? Flying a virtual Glider through MITgcm simulations Range of isopycnal depths as a function of distance offshore stats of variance of properties on opposing transects Long term evolution of basic T/S structure compared with ADCP currents S U & T U

10 VE = VN t 12 = t t= 1 t 12 = = = t 1 VE ( t max ), VN max Sum of VE for tidal period ( t) Δx = Δ y = m Sum of VN for tidal period th (m) Dept ST Depth (m) ST Longitude Latitude 0.05

11 Future plans for NE Atlantic: FASTNEt phases 2, UK OSNAP (S. Bacon et al) & FSC (with Marine Scotland Science) 64 o N 62 o N 60 o N 58 o N 56 o N 25 o W 20 o W 15 o W 10 o W 5 o W 0 o

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13 FASTNET glider data Cross shelf exchange Internal tides DACs and Geostrophic currents

14 Cross shelf exchange

15 Salinity on isopycnal 27.1 all gliders

16 Salinity on isopycnal 27.1 glider 194

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18 Internal tides tides

19 Glider Bellamite salinity (color) and density (contours) 27.1 Long gitude Depth (m) Time (hours) Lati itude

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21 Colour is time (hrs)

22 Latitude

23 Along slope flow DACs (dive averaged currents)

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25 a) 5 cm/s Pseudo glider tracks track direction a) No compass error; the mean current ( 5 cm/s) is correctly measured b) Simple compass offset; errors in the measured current cancel c) Variable compass offset; errors in mean current do not cancel b) c) V = +3.5 cm/s V = cm/s V = 2 cm/s V = 55 cm/s

26 Impact of eddy motion on mean transport estimates Max eddy speed = 0.30 m s 1, mean drift = +3.7 cm s 1 or ~ 7.4 Sv (no difference between traverses)

27 What do the Mission 1 observations tell us? The standard deviations, σ, for all drift currents are: σ u = 12.3 cm s 1 (E W), σ v = 13.8 cm s 1 (N S) Say 45 drift estimates are independent, the error in the mean N S velocity is: v ε = 13.8/ 45 = 2.0 cm s 1 i.e the error in the section transport is: T ε = ±4 Sv (assuming the Rockall Trough is 200 km wide)