Analysis Systems
What is the purpose of analysis systems?
- To combine available observations,
climatological data, and other analyses into one
consistent picture, and to derive non-observed
fields such as sound velocity from observed fields
such as temperature and salinity.
Analysis systems do not make predictions or
forecasts.
Analysis Systems
What are the Navy’s Ocean Analysis Systems?
• MODAS – Modular Ocean Data Assimilation
System
• OTIS – Optimum Thermal Interpolation System
• MVOI – Multivariate Optimum Interpolation
MODAS
Modular Ocean Data Assimilation System
Primary contacts: Dan Fox (NRLSSC),
Martin Booda (NAVO)
MODAS was developed at the Naval
Research Lab at Stennis Space Center in the
1990’s (Fox et al., 2002). It is currently used
in a stand-alone mode and also to initialize a
relocatable version of the Princeton Ocean
Model. A subset of the full capabilities is
available for use on submarines.
MODAS
http://www7320.nrlssc.navy.mil/modas/
Analysis system that uses optimal interpolation
to incorporate MC-SSTs, SSH from satellite
altimetry, T and S data from profilers (XBTs
and CTDs) and fixed or drifting buoys, with
climatological data to produce 3D T and S
fields. 3D sound velocity fields, and associated
acoustic parameters, and geostrophic velocity
fields, are derived from the temperature and
salinity fields.
Physics
•Geostrophic.
In water depths greater than the reference level,
geostrophic velocities are referenced to the reference
level. In water depths less than the reference level,
geostrophic velocities are referenced to the bottom,
i.e. it is assumed that there is no horizontal pressure
gradient at the bottom, which can produce a velocity
field that is locally divergent. Strictly speaking, the
geostrophic velocity field should be non-divergent.
The reference level is user-selectable. The default is
1000 m.
Domain
•Determined by user
The EOF scheme used to compress the 3D
temperature and salinity output has a limit of 360
grid points in the east-west direction and 181 grid
points in the north-south direction. The spatial
resolution, in combination with the maximum
number of grid points, sets the maximum allowable
domain, if the EOF-compressed output is needed.
As of 28 Feb. 2002
Spatial Resolution
•Determined by user as a result of specifying
the domain size, and the number of grid points
or the spatial resolution:
xmin: longitude at the left edge of the grid (+E, -W)
xmax: longitude at the right edge of the grid
ymin: latitude at the bottom edge of the grid (+N, -S)
ymax: latitude at the top edge of the grid
nx: number of grid points in the east-west
direction (max = 360)
ny: number of grid points in the north-south
direction (max = 181)
E-W grid spacing: dx = (xmax - xmin) / (nx - 1)
N-S grid spacing: dy = (ymax - ymin) / (ny - 1)
# grid pts E-W dir. nx = 1 + (xmax-xmin)/dx
# grid pts N-S dir. ny = 1 + (ymax-ymin)/dy
If specifying, dx and dy, program will calculate nx and
ny, and GUI will alert user if nx, ny aren’t integers.
From the MODAS 2.1 User's Manual, applies to the GUI-based version.
Try out the Interactive MODAS Grid Calculator
Temporal resolution
•None
This is not a time-stepping predictive model.
The analysis can be updated at whatever interval the
user chooses, but should be based on the availability
of new data to assimilate. NAVO’s update cycle is
generally once per day.
Initialization
• The user has the option of using a previous
MODAS run as the first guess or using climatology.
MODAS2.1 has its own climatology. The MODAS
climatology is based on a blend of MOODS T and S
data in the upper 1500 m of the ocean with the
Levitus climatology in the deeper ocean. The
MODAS climatology is stored as bimonthly T and
S at 37 depth levels from 0 to 6500 m, on a grid
with horizontal resolution ranging from 1/2 in the
open ocean to 1/4 in coastal seas and 1/8 near the
coasts. The MODAS climatology extends into
water depths as shallow as 5 m.
Data Assimilation
• Assimilates SSH, SST, XBTs, fixed buoys, and
PALACE floats at this time (May 2002).
• There is a time window over which data is
assimilated – in other words how far back in time
should data be included and with what weighting.
This time window is not easily changed, or
viewable, by the user, but can be accessed and
modified.
• 1/8° resolution global field of SSH is supplied by
the altimetry data fusion center (ADFC). Does not
improve solution in all regions (due to seiching,
among other things), so is not used everywhere.
Altimetry Processing Upgrade: “CLAM II”
* Implements “moving covariance” function in MODAS OI
(more continuity of features between tracks)
Original Results
Updated Results
Note particularly significant improvement in these areas
Note sampling impact: Red would be green but for this area
Courtesy
of John
Harding,
NRL-SSC
Clam Shallow Water Evaluation
Most Accurate Modas First-Guess Field (Bottom Depth < 200 m)
MODAS Seasonal Climatology
MODAS Climatology - MCSST’s
Latitude
Longitude
NAVO MODAS areas not using SSH
(as of 7/3/02)
• Adriatic
• Arabian Sea
• Gulf of Alaska/Eastern
Aleutians
• Gulf of Cadiz
• Central Med
• Central North Atlantic
• Eastern Med
• Greenland/Iceland/
Norwegian Sea
• Kamchatka
• Mediterranean
regional
• Bay of Biscay/NE
Atlantic
• Northeast Pacific
• Gulf of
Oman/Arabian Gulf
• SOCAL
• Straits of Sicily
• Western Med
Data Assimilation (con’t.)
• 8.8 km resolution MC-SST, derived from 2x2 blocks of
4.4 km Global Area Coverage (GAC) data
• Relationships between SSH and subsurface T, and SST and
subsurface T, based on historical data, are used together
with climatology to produce synthetic vertical profiles of
T, down to a depth of 1500 m.
• After SSH and SST have been used to create the “dynamic
climatology”, in-situ data from XBTs, CTDs, buoys and
floats is assimilated through an optimal interpolation (OI)
scheme. The 3D grid of T is then modified near the
surface by using an analysis of mixed layer depths. T/S
relationships are then used to produce a 3D S field as well.
If S observations are available, they are then used to
modify the first guess salinity field.
MODULAR OCEAN DATA ASSIMILATION SYSTEM
MOODS Profiles
MODAS Climatology
Satellite
Measured
SSH and SST
Green line represents
profile derived only
using satellite measured
height and temperature
Decades of edited MOODS
profiles are used to derive
statistical relationships
between surface height and
temperature and subsurface
temperature and salinity
Relationships are stored on
an irregular mesh, varying
from 1 to 1/8 degree in
resolution to permit high
resolution analyses in shallow
water regions
Climatology
MODAS Synthetic
Final Analysis
In Situ BT
Courtesy of Dan Fox, NRL-SSC
MODAS Validation Example: AXBT Survey
Climatological Temp
AXBT Temp
MODAS results
SSH + SST + Clim
Cold core eddy
MODAS
Temperature
at 200m
Courtesy of Dan Fox, NRL-SSC
Temperature (C)
T/S plot from central California
1997-2002
Equatorial
Intermediate
Water
El Nino
affect
North Pacific
Intermediate Water
31
33
31 Salinity 34
35
Implementation
• Set of Fortran programs and UNIX scripts run
under the UNIX operating system. Different
versions of MODAS have different subsets of the
full suite of modules installed.
• MODAS modules have been "wired together" to
produce several analysis and forecast systems
presently running at various Navy facilities.
Versions designed for shipboard and submarinebased users are under development now.
• PC-IMAT now includes MODAS-Lite, basically
the same version as is run at the METOC centers,
but with different GUI and Perl scripts.
MODULAR OCEAN DATA ASSIMILATION SYSTEM
Versions: Central Site, METOC Center, On Scene
MODAS2.1 “Heavy”
Run at NAVOCEANO on SGI Origin, Power Challenge Array, and ONYX systems
Satellite altimetry and MCSSTs plus in situ data
Includes reloctable Princeton Ocean Model
Approx 6 GB of disk space required
MODAS2.1 : NITES-I ASHORE
METOC Center version
All capabilities of above except would normally receive first guess field from NAVO
via TEDS METCAST.
Variable disk space (max 6 GB) depending on desired area of coverage
UNIX systems (HP TAC4, Sun, SGI, PC LINUX, …)
MODAS2.1 : NITES-I AFLOAT (“MODAS/Lite”)
No direct altimetry use. Requires first guess field from MODAS run at Center.
Input/output via TEDS database
Minimal disk space required ( less than 1 GB for global coverage )
UNIX systems (as above)
MODAS 2.1 OUTPUT PRODUCTS
ZNR UUUUU
O 281742Z OCT 98
MSGID/NAVO/GRIDFLD/1504/OCT
PROD/OCEANMET/281742Z4/OCT/000/1OF1
GRID/3100N4/04700E1/0M/133/97/34/0.068DEG/0.083DEG/VAR/03
NARR/UNCL prgars MODAS2 TEMPERATURE 98301 981028
8
5 133
1
97
97
-2.027655125
1.865198374
:I8:U98:D9.875420ZYXVUTSSRR.Q.POMMKJIHG.E.DCC.B:JA:DB:DC.DEE
LMMRW027CHJQW2556795ZUTMEBLYGQ5CTXJL0JLX1JO7WQ0CVE82O9ZCQZG7WPXY5OD0
20.210847855
:KB:YA.B.CDDEGGHHIIJJKLMMOOPQRSTTUUVVWXX.YZ01223344.5:D677668:M9:E8:
JJXX
JJXX
JJXX
JJXX
JJXX
JJXX
JJXX
JJXX
JJXX
28108
28108
28108
28108
28108
28108
28108
28108
28108
0000/
0000/
0000/
0000/
0000/
0000/
0000/
0000/
0000/
12930
13000
12830
12900
12930
12800
12830
12900
12930
04800
04800
04830
04830
04830
04900
04900
04900
04900
88888
88888
88888
88888
88888
88888
88888
88888
88888
00275
00276
00292
00283
00279
00294
00293
00291
00286
MODAS
MODAS
03291 08290 MODAS
03282 08281 13280 MODAS
03279 08279 MODAS
03293 MODAS
03292 08292 13290 18286 MODAS
03291 08290 13289 18288 MODAS
03285 08285 13286 18285 MODAS
Text/Binary/Message Files:
•Byte-Encoded & EOF-Compacted
Temperature/SV (also pushed to
centers, facilities & ships at sea)
• JJXX/JJYY/KKXX Synthetic BTs
• OVLY2 of Physical/Acoustic
parameters
• NetCDF of Temperature/SV/Salinity
• ARCVIEW Format (for REACTs)
Physical/Acoustic Graphics:
• Temperature Contours
at Depth
• Currents over Temperature
at Depth
• DSCA, SSCA, MLD, SLD, ZX
• Observations Chart (Secret)
Wavelet-compressed fields became available in May 2001
MODAS
Note that velocity
scale is different
for every picture
The arrows are parallel to the streamlines everywhere and their length
indicates the speed, as referenced to the velocity scale vector. The
length of the curved arrow is a function of the velocity all along it's
short path - not just at the beginning.
Typical Satellite SSTs of
Kuroshio Current (2/19/1996)
Estimated surface current conditions in
Kuroshio area during time period of the
MODAS data analysis. Data are from
weekly survey reports produced by
Japanese researchers. These reports are
independent of MODAS calculations,
though the same data may be used.
Adapted from Johnson and Broome 1999
References
Fox, D. N., W. J. Teague, C. N. Barron, M. R. Carnes,
and C. M. Lee, 2002: The Modular Ocean Data
Assimilation System (MODAS). Journal of
Atmospheric and Oceanic Technology, 19, 240-252.
Fox, D.N., C.N. Barron, M.R. Carnes, M. Booda, G.
Peggion, and J. Gurley, The Modular Ocean Data
Assimilation System, Oceanography, 15 (1), 22-28,
2002a.
Johnson, A. and R. Broome, 1999: Validation Test
Report for the Modular Ocean Data Assimilation
System (MODAS 2.1), 42 pp.
Naval Research Laboratory, P. S. I., 1999: User's Manual
for the Modular Ocean Data Assimilation System
(MODAS) Version 2.1. PSI Technical Report S-285.
OTIS
Optimum Thermal Interpolation
System
Primary contact: Webb DeWitt (FNMOC)
OTIS predates MODAS. It was developed at
FNMOC in the 1980’s. While it is still being
run by FNMOC, it is scheduled to be phased
out.
OTIS
http://www.fnmoc.navy.mil/
• OTIS is an optimum
objective analysis
produce analysis
temperatures in the
ocean.
interpolation (OI) based
scheme designed to
or "nowcasts" of
upper 5000 m of the
• OTIS does not provide currents as output, but
feeds into TOPS (see below), which does.
Domain
OTIS has been implemented at FNMOC on a
variety of regional (eddy resolving) and global
(non-eddy resolving) grids.
Temporal and Spatial
Resolution
• This is not a time-stepping predictive model.
• Presently, SST-only runs are done for the
global domain twice a day at 1 by 1
horizontal resolution, and once a day at 0.25
by 0.25. There is also a global 3D OTIS with
1 resolution run twice a day. Regional 3D
runs are done once per day for the Atlantic and
Pacific oceans using 0.2 by 0.2 resolution.
• 34 levels are used in the vertical, with 5 m
spacing near the surface, expanding to 100 m
at 400 m depth and 200 m at 2000 m depth.
Initialization
• The 3D implementation uses GDEM climatology as a
starting point and then uses a real-time "ocean bogus"
database. This is a significant difference from the way
MODAS works. The "ocean bogus" is the fronts and eddies,
or Oceanographic Features Analysis product, from NAVO. It
gives positions of ocean features determined from satellite
data, and each grid point in OTIS is assigned a water mass
classification based on its position relative to these features.
"The water mass classification determines the appropriate
water mass climatology model to apply at the grid point"
(Cummings et al. 1997). The water mass climatology model
uses date, location, and remote and in-situ measurements, to
determine the temperature and salinity versus depth for that
grid point.
• The OTIS SST-only runs use the previous analysis as the
first guess field.
Oceanographic Features Analysis
(Fronts and Eddies Bogus)
Data Assimilation
• OTIS makes full use of the global real-time
observations received at FNMOC. This
includes, ships, fixed and drifting buoys, and
satellite-derived sea surface temperatures,
and bathythermograph and buoy subsurface
temperatures. All observations are qualitycontrolled prior to being assimilated by
OTIS.
• The 2D and 3D versions may use different
time windows over which they accept
observations.
Output
• Global OTIS SST may be viewed on the
FNMOC web site (www.fnmoc.navy.mil).
• Other OTIS fields are available as JMV
thumbnails, or could be requested via
Metcast, and viewed with JMV.
References
Cummings, J. A., C. Szczechowski, and M.
Carnes, 1997: Global and regional ocean
thermal analysis systems. Marine Technology
Society Journal, 31, 63-75.
Documents on FNMOC web site.
3D-MVOI
3-Dimensional Multivariate
Optimum Interpolation
Primary contact: Jim Cummings (FNMOC)
3D-MVOI was developed at NRL Monterey in
the late 1990’s.
3D-MVOI
• Currently being used in a 2D mode to provide
SST to the operational COAMPSTM, the
Coupled
Ocean-Atmosphere
Model
Prediction System, and its regional versions
DAMPS (Distributed Atmospheric Model
Prediction System) or TAMS/RT.
• Ultimately, 3D-MVOI will serve as the ocean
data assimilation scheme feeding the
predictive ocean models (NCOM regionally
and POP globally) that will be coupled to the
atmospheric models (COAMPSTM regionally
and NOGAPS globally).
Domain
Must match domain of atmospheric or ocean
model that it’s being used with.
Ocean Forecast Component
Sequential Incremental Update Cycle
Analysis-Forecast-Analysis
Ocean Obs
MCSST
GOES SST
Ship SST
Buoy SST
XBT, CTD
PALACE Float
Fixed Buoy
Drift Buoy
Altim SSHA
SSM/I Sea Ice
Ocean QC
Forecast Fields
Prediction Errors
Innovations
3D MVOI
First Guess
Increments
Ocean Model
MVOI - simultaneous analysis 5 ocean variables
temperature, salinity, geopotential, velocity (u,v)
Courtesy of Jim Cummings, NRL-Monterey
Initialization
• A nowcast of the observed state is obtained
by combining new observations with a
background field. The background field can
be from a short-term model forecast or a
previous analysis (warm start), or
climatology (cold start). The use of a
previous analysis as the background field
implies a persistence forecast from the last
time the analysis was executed.
Operational Observation Data Sources
NRL Coupled Systems
•
•
•
•
•
•
Satellite SST
~330,000 obs/day
– satellite SST retrievals (NOAA 16)
In Situ SST/SSS
~15,000 obs/day
– surface ship, fixed and drifting buoys, CMAN, TRACKOB
Subsurface Temperature and Salinity Profiles
~500 obs/day
– XBTs, CTDs (TESACS), PALACE floats
– fixed buoys (TAO, PIRATA), thermistor chain drifting buoys
Sea Surface Height Anomaly (SSHA)
~100,000 obs/day
– altimeter (TOPEX, ERS2, GFO), in situ observations (PALACE floats)
Sea Ice Concentration
~1,2000,000 obs/day
– SSM/I (DMSP F13, F14, F15)
Synthetic Salinity-Temperature-Depth Profiles (STDs)
– temperature profiles computed from SST and SSHA, salinity
computed from temperature (using MODAS databases)
– synthetic profiles are generated in a sampling pattern to capture
analyzed changes in SSHA that exceed ~2 cm
Note that the type and amount of data is subject to change depending on
what is available. (Slide is courtesy of Jim Cummings, NRL-Monterey)
Data Assimilation
• In addition to numerous satellite and in-situ
observations,
MVOI
uses
synthetic
temperature and salinity profiles calculated
using the same databases and algorithms as
MODAS, to project satellite sea surface
height and temperature data down to the
subsurface ocean.
• A sophisticated interpolation scheme, which
varies the weighting of the observations as a
function of variable type, time, depth and
horizontal distance is used.
Horizontal Correlation Length Scales
NRL Coupled Systems
Rossby radius of deformation (from Chelton et al. (1998), JPO 28: 433-460).
Used as default for horizontal correlation length scales in the 3D-MVOI.
Scales range from ~10 km at the poles to ~240 km in the tropics.
Courtesy of Jim Cummings, NRL-Monterey
Data Assimilation (cont.)
• Another method that is used to
incorporate the SSH into the analysis is
to adjust the model T and S fields to
improve the agreement between the
observed and modeled SSH field. This
has the advantage of not always trying
to restore the modeled field towards
climatology.
References
Cummings, J., 2002. Powerpoint brief.