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
7
(No Transcript)
8
(No Transcript)
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

10
(No Transcript)
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 resultsSeasonal
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 of output 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

29
(No Transcript)
30
(No Transcript)
31
(No Transcript)
32
(No Transcript)
33
(No Transcript)
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 gt 90 years of data
40
Standard deviation of temperature
Mean over 1 week (26 sections) during summer 1996
Shelfbreak PRIMER cruise
Summer climatology gt 90 years of data
41
Mean salinity
Mean over 1 week (26 sections) during summer 1996
Shelfbreak PRIMER cruise
Summer climatology gt 90 years of data
42
Standard deviation of salinity
Mean over 1 week (26 sections) during summer 1996
Shelfbreak PRIMER cruise
Summer climatology gt 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

46
(No Transcript)
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
51
Planview standard deviation temperature
Winter
Summer
52
Planview standard deviation salinity
Winter
Summer
53
Sample cross-shelf areaEast China Sea NE of
Taiwan
54
Number of points
Winter
Summer
55
Mean temperature
Winter
Summer
56
Mean salinity
Winter
Summer
57
Standard deviation of temperature
Winter
Summer
58
Standard deviation of salinity
Winter
Summer
59
Conclusions and Future Work

• Programs can be run in any data-rich ocean area
• Numerous applications
• Finding variability hotspots
• Initializing numerical models
• Continuing to improve climatology and look at
  different areas near Taiwan
• Comparisons with ODB climatology and synoptic
  fields

60
(No Transcript)
61
Extras
62
Bottom boundary layer investigations Motivation
for improving cross-shelf method
63
Nantucket Shoals Flux Experiment (1979) moored
temperature histograms
Scale of subplots 0-30 C
64
New JerseyCross-shelf temperature mean and
standard deviation
65
New JerseyCross-shelf salinity mean and
standard deviation
66
Potential vorticityWinter
Summer
67
Summer standard deviation of salinity
Mean over 1 week (26 sections) during summer 1996
Shelfbreak PRIMER cruise
Summer climatology gt 90 years of data
68
Other climate analysesNOAA CTD data
(1990-2002)Scatter (gray), monthly mean (line)
and standard deviation (bar)a. 5m temperature
minus 20m temperatureb. Strength of maximum
stratificationc. Location in the water column
of maximum stratification
69
Dominant empirical orthogonal function (EOF)
modes of variability over 1 week from SeaSoar
observations-- another way to location areas of
maximum variability
Subsurface maximum, heart of the frontal zone