Transcript Climatology tools for Matlab

Climatology Software for Matlab
Test region: Middle Atlantic Bight
Chris Linder and Glen Gawarkiewicz
Woods Hole Oceanographic Institution
Climatology Software for Matlab
Test region: Middle Atlantic Bight
...and preliminary results from Taiwan!
Chris Linder and Glen Gawarkiewicz
Woods Hole Oceanographic Institution
Jen Hua Tai
National Taiwan University
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
Large-scale North
Atlantic circulation
• Southward-flowing
Labrador current
• Northeastwardflowing Gulf
Stream
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
• 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
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
Winter and summer shelfbreak jet
(Blue = West-flowing current)
Max 18 cm/s west
Max 25 cm/s west
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
Bottlenose dolphin sightings
Motivation for planview maps of MAB T/S
Bottom boundary layer results:
Seasonal differences in upwelling
Winter
Summer
From Linder et al., 2004
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
Data sources for MAB planview climatology
Total 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
Seasonal definition and data distribution
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•
•
•
•
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
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
Planview climatology program inputs
– Input data specifications
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•
•
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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)
Resolution (degrees)
Search
radius
(km)
Winter mid-depth Middle Atlantic Bight example
Output
grid
example
Cutoffhighdepth
Cutofflowdepth
Sample planview output – MAB mid-depth (40-55m)
Number of casts per grid node
Sample planview output – MAB mid-depth (40-55m)
Mean temperature
Sample planview output – MAB mid-depth (40-55m)
Standard deviation of temperature
Sample planview output – MAB mid-depth (40-55m)
Mean salinity
Sample planview output – MAB mid-depth (40-55m)
Standard deviation of salinity
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
Cross-shelf climatology program inputs
– Input data specifications
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•
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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
Nantucket Shoals
Cross-shelf temperature – mean and standard deviation
Nantucket Shoals
Cross-shelf salinity – mean and standard deviation
Nantucket Shoals Geostrophic velocity
Winter
Summer
Relative vorticity
Winter
Summer
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
Mean temperature
Summer climatology
> 90 years of data
Mean over 1 week (26 sections)
during summer 1996 Shelfbreak
PRIMER cruise
Standard deviation of temperature
Summer climatology
> 90 years of data
Mean over 1 week (26 sections)
during summer 1996 Shelfbreak
PRIMER cruise
Mean salinity
Summer climatology
> 90 years of data
Mean over 1 week (26 sections)
during summer 1996 Shelfbreak
PRIMER cruise
Standard deviation of salinity
Summer climatology
> 90 years of data
Mean over 1 week (26 sections)
during summer 1996 Shelfbreak
PRIMER cruise
Cross-shelf gradient comparison with SINGLE SeaSoar section
Stratification comparison with SINGLE SeaSoar section
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
Grid setup for planview case - 0.25 degree grid
spacing, 40km search radius, 0-15m depth
Planview number of points
Winter
Summer
Planview mean temperature
Winter
Summer
Planview mean salinity
Winter
Summer
Planview standard deviation temperature
Winter
Summer
Planview standard deviation salinity
Winter
Summer
Sample cross-shelf area
East China Sea NE of Taiwan
Number of points
Winter
Summer
Mean temperature
Winter
Summer
Mean salinity
Winter
Summer
Standard deviation of temperature
Winter
Summer
Standard deviation of salinity
Winter
Summer
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
Extras
Bottom boundary layer investigations
Motivation for improving cross-shelf method
Nantucket Shoals Flux Experiment (1979) moored temperature histograms
Scale of subplots: 0-30 C
New Jersey
Cross-shelf temperature – mean and standard deviation
New Jersey
Cross-shelf salinity – mean and standard deviation
Potential vorticity
Winter
Summer
Summer standard deviation of salinity
Summer climatology
> 90 years of data
Mean over 1 week (26 sections)
during summer 1996 Shelfbreak
PRIMER cruise
Other climate analyses:
NOAA CTD data (1990-2002)
Scatter (gray), monthly mean (line)
and standard deviation (bar)
a. 5m temperature minus 20m
temperature
b. Strength of maximum
stratification
c. Location in the water column of
maximum stratification
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”