Climatology Software for Matlab Test region: Middle Atlantic Bight

1. Climatology Software for MatlabTest region: Middle Atlantic Bight Chris Linder and Glen Gawarkiewicz Woods Hole Oceanographic Institution

2. Climatology Software for MatlabTest region: Middle Atlantic Bight ...and preliminary results from Taiwan! Chris Linder and Glen Gawarkiewicz Woods Hole Oceanographic Institution Jen Hua Tai National Taiwan University

3. Outline • Overview of the Middle Atlantic Bight test region • Previous climatology research and motivation for new software • Matlab planview climatology program • Seasonal mean and standard deviation results for Middle Atlantic Bight • Matlab cross-shelf climatology program • Seasonal mean and standard deviation results for Nantucket Shoals subregion • Comparison of output fields to observations • Preview of application of climatology to SCS/ECS

4. Large-scale North Atlantic circulation • Southward-flowing Labrador current • Northeastward-flowing Gulf Stream

5. Middle Atlantic Bight Shelfbreak front • Separates cold, fresh shelf water from warm, salty slope water • Slope of front leads to strong baroclinic jet • Gulf Stream rings • Filaments, meanders

6. Typical cross-shelf temperature, salinity, and density plots for winter and summer time periods • Winter (left-hand side): steeply sloping isopycnals, clear division between shelf and slope water masses • Summer (right-hand side): “cold pool” over shelf, isopycnal slope flattened by seasonal thermocline Figure courtesy C. Flagg and T. Hopkins, from Houghton et al., 1988

9. Initial climatology of the shelfbreak front 1994-1996 • Goal: determine seasonal differences in the position, strength, and cross-shelf gradients of the shelfbreak front at three locations • Challenge: How do we synthesize 100 years of hydrographic data into three cross-shelf sections? • Assumption: across-shelf gradients are much stronger than along-shelf – CTD data can be sorted into bins based on cast depth to preserve water mass characteristics

11. Winter and summer shelfbreak jet(Blue = West-flowing current) Max 18 cm/s west Max 25 cm/s west

12. Motivation for climatology tools • Multiple projects • Correlation with bottlenose dolphin sightings • Bottom boundary layer detachment (publications: Pickart 2002, Linder et al., 2004) • Characterizing uncertainty initiative: desire to identify regions of high variability, and thus high error in acoustic propagation calculations • How could we map out these areas of high variability? • Given a set of CTD observations, compute planview and cross-shelf maps of the mean and standard deviation of temperature and salinity • Can tools be created to analyze these problems globally? • Standard ASCII input file format • Program as a Matlab function • Industry-standard platform-independent plotting and analysis program • Allows for easily changed user-defined input parameters

13. Bottlenose dolphin sightingsMotivation for planview maps of MAB T/S

14. Bottom boundary layer results:Seasonal differences in upwelling Winter Summer From Linder et al., 2004

15. Improvements over 1998 climatology • 40% more data available • Four 3-month seasons instead of bi-monthly improves statistics • Fixed horizontal bin size of 10km doubles the resolution in low bottom slope areas such as the continental shelf • Addition of planview analysis feature

16. Data sources for MAB planview climatologyTotal 41345 CTD casts • Hydrobase2 (Curry, 2002) 21835 casts • Raw profiles from World Ocean Database 1998, WOCE, ICES, BarKode • Quality controlled data from other sources • NMFS dataset (M. Taylor) 19200 casts • Shelf-Edge Exchange Processes project (C. Flagg) 310 casts

17. Seasonal definition and data distribution • Spring = April 1 to June 30 30% • Summer = July 1 to Sept 30 24% • Fall = Oct 1 to Dec 31 20% • Winter = Jan 1 to March 31 26% • Majority of data from 1990-2002

18. Methods – Planview • Assumptions • No cross-shelf or along-shelf flow assumptions required • Averaging scheme • Season and depth range selected by user • Resolution (degrees), search range (km), minimum to comprise mean selected by user • T/S averaged for each node using a Hamming window spatial weighting function

19. Planview climatology program inputs • Input data specifications • Data file, in ASCII text format: location, date, T, S • Season: a listing of all months to include in average • Domain boundaries: define box in degrees lat/lon • Cutoffhighdepth and cutofflowdepth: only CTD casts taken at depths in between these bounds will be included • Slice depth limits: data points must be in between these depth bounds • Averaging and output grid specifications: • Gridspacing: spacing in decimal degrees of output grid • Search radius: casts must be closer than this distance from the output grid node to be included in the mean; larger radius means more overlap and smoother results • Minnumpts : minimum number of points to comprise a good average (NaN is assigned to output otherwise)

20. Resolution (degrees) Search radius (km)

21. Winter mid-depth Middle Atlantic Bight example Output grid example Cutoffhighdepth Cutofflowdepth

22. Sample planview output – MAB mid-depth (40-55m)Number of casts per grid node

23. Sample planview output – MAB mid-depth (40-55m)Mean temperature

24. Sample planview output – MAB mid-depth (40-55m)Standard deviation of temperature

25. Sample planview output – MAB mid-depth (40-55m)Mean salinity

26. Sample planview output – MAB mid-depth (40-55m)Standard deviation of salinity

27. Methods – Cross-shelf • Assumptions • Cross-shelf gradients are much higher than along-shelf • Currents and water properties align with local bathymetry • Averaging scheme • Season (specific months) and vertical and horizontal bin sizes specified by user • User selects baseline isobath • Program sorts each cast into proper “bin” based on its perpendicular distance to the baseline; once T/S data is binned, mean and standard deviation are computed for each bin

28. Cross-shelf climatology program inputs • Input data specifications • Data file: in ASCII text format: location, date, T, S • Season: a listing of all months to include in average • Baseline isobath: midpoint of the x-axis for the analysis and figures • Domain boundaries: define box in degrees lat/lon • Averaging and output grid specifications: • Maximum depth: data points deeper than this will be excluded • Extent ofoutput grid onshore and offshore: measured in km from the baseline isobath - the horizontal extent of the climatology • Horizontal bin size: in kilometers - horizontal resolution • Vertical bin size: in meters - vertical resolution • Minnumpts: minimum number of points to comprise a good average (NaN is assigned to output otherwise) • Smoothing: amount of smoothing (can be zero) applied by PlotPlus ppzgrid routine adapted for Matlab

34. Nantucket ShoalsCross-shelf temperature – mean and standard deviation

35. Nantucket ShoalsCross-shelf salinity – mean and standard deviation

36. Nantucket Shoals Geostrophic velocityWinter Summer

37. Relative vorticityWinter Summer

38. Comparison with observations • Climatology sections vs. summer Shelfbreak PRIMER 1996 experiment SeaSoar mean section • Mean T/S • Standard deviation T/S • Comparison with individual high-resolution SeaSoar sections from winter and summer • Cross-shelf T/S gradient comparison • Stratification (N2) comparison

39. Mean temperature Mean over 1 week (26 sections) during summer 1996 Shelfbreak PRIMER cruise Summer climatology > 90 years of data

40. Standard deviation of temperature Mean over 1 week (26 sections) during summer 1996 Shelfbreak PRIMER cruise Summer climatology > 90 years of data

41. Mean salinity Mean over 1 week (26 sections) during summer 1996 Shelfbreak PRIMER cruise Summer climatology > 90 years of data

42. Standard deviation of salinity Mean over 1 week (26 sections) during summer 1996 Shelfbreak PRIMER cruise Summer climatology > 90 years of data

43. Cross-shelf gradient comparison with SINGLE SeaSoar section

44. Stratification comparison with SINGLE SeaSoar section

45. Preliminary figures of Taiwan area • Planview maps: mean & standard deviation temperature and salinity, summer and winter, 40km search radius for near-surface (0-15m) • Cross-shelf sample area for East China Sea northeast of Taiwan: mean & standard deviation temperature and salinity, summer and winter

47. Grid setup for planview case - 0.25 degree grid spacing, 40km search radius, 0-15m depth

48. Planview number of points Winter Summer

49. Planview mean temperature Winter Summer

50. Planview mean salinity Winter Summer