Transcript ACRONYM Spell Out Full Name

“Mixed layer” models
We will only consider mixed layer models applied
to the upper part of the ocean, although you can
also have mixed layers near the bottom of the
ocean. As we learned previously, mixed layer
models are 1D models that can help us understand
how currents, temperature and density in the upper
ocean evolve under the influence of wind forcing
and heat exchange with the atmosphere. By
themselves they do not include any effects due to
coastal boundaries, tides, fronts etc.
In this presentation, we’ll consider two systems
used by the Navy:
•TOPS – Thermodynamic Ocean Prediction
System
•WebSAR – the Web-enabled Search And
Rescue system that uses TOPS plus other
information.
TOPS is a mixed layer model, while WebSAR is an
application that uses TOPS.
TOPS
Thermodynamic Ocean Prediction System
Primary contacts: Webb Dewitt (FNMOC)
TOPS was developed by the Navy and has
been running at FNMOC, or its predecessors,
since the 1980s. It is currently used primarily
for estimates of surface drift. Regional TOPS
is scheduled to be phased out in the near
future, but global TOPS will be run until
replaced by another global model.
TOPS
http://www.fnmoc.navy.mil/
TOPS, the upper ocean mixed layer prediction
model currently operational at FNMOC, “is
essentially a synoptic mixed-layer model that
consists of conservation equations for T, S, and
momentum in the upper 400 m of the ocean”
(Clancy and Sadler 1992; Clancy and Pollack
1983).
Physics
• 1D mixed layer model
• 2nd order closure scheme for vertical mixing
• Includes horizontal and vertical advection of
T and S (so it’s not strictly 1D) (Clancy and
Sadler 1992)
• Ekman and inertial currents generated by
TOPS
• Surface geostrophic currents, based on OTIS
dynamic sea surface height field, are
included in the regional, but not the global,
version.
Domain
• Global
• Regional
– West Atlantic
– West Pacific
Spatial Resolution
• 1 for global domain
• 0.2  for regional domains
• Model depths (m) are specified in the
initial configuration of the TOPS model.
•
•
•
•
•
•
•
•
•
0
2.5
7.5
12.5
17.5
25
32.5
40
50
•
•
•
•
•
•
•
•
62.5
75
100
125
150
200
300
400
Temporal resolution
• TOPS uses a 1 hr time step
Forcing
• Wind stress from NOGAPS
• Heat flux from NOGAPS
– total heat flux
– solar radiation flux
– latent heat flux
Initialization
• OTIS provides initial conditions
– T and S fields at all depths at which the forecast is run
• 24-hr forecast currents at all model depths from the
previous day's forecast are saved to local disk files
in order to keep a history of the ocean momentum
and assure continuity of the forecasts. In this
manner, the model "restarts" each day from
previously forecast momentum fields and updated T
and S fields.
• If the forecast velocity is not available, the model
initializes the velocity to zero.
Data Assimilation
• See OTIS description for data assimilated
into T and S fields used for initialization.
• No data is assimilated during the forecast.
Implementation
• Global domain runs daily on the Cray C90.
• Regional forecasts are run daily on an SGI.
Output
• Global: 72-hr forecast of upper ocean (surface –
400 m) V, T, and S.
• Regional: 48-hr forecasts
• Forecasts are in 6-hr time steps
• Surface current and temperature, and MLD, fields
in .dat format thumbnails for viewing in JMV
• For the most part, if thumbnails include TOPS at
all, it is just SST at 12 hr intervals. Only a few
currently include currents.
• TOPS currents are used to drive search and rescue
model.
Indian Ocean TOPS
wind-driven currents
24 hr forecast
Valid 23JUL2002
0000Z
Yellow
OCEAN
3D T
contours
showed on
screen, but
didn’t get
included
in gif file
TOPS SST Analysis
TOPS SST 72-hr forecast
TOPS and OTIS SST may differ
slightly since TOPS starts with
depth = 0 layer from 3D OTIS,
not the 2D OTIS SST, and TOPS
further modifies it with mixed
layer dynamics
Model Surface
In an effort to evaluate the
Current Validation
various
current
fields
or
combination of fields for search
and rescue purposes, FNMOC
A - persistence
has used the model currents to
B - TOPS
try to simulate the week-long
movement
of
free-drifting
95% WOCE buoys. These buoys have
been designed to follow the
C.I.
ocean surface currents and report
their positions by means of the
Global
Telecommunications
System. The following plots
present
the
accumulated
statistical error (starting Apr. 99)
between the simulated buoy
(from FNMOC web site under tracks for various ocean areas
and the actual buoy positions.
Model Performance)
The persistence curve represents
the mean distance between initial
buoy
positions
and
the
subsequent locations.
References
Clancy, R.M., and W.D. Sadler, The Fleet
Numerical Oceanography Center suite of
oceanographic models and products, Weather
and Forecasting, 7, 307-327, 1992.
Clancy, R.M., and K.D. Pollak, A real-time
synoptic ocean thermal analysis/forecast
system, Progress in Oceanography, 12, 383424, 1983.
Documents on FNMOC web site.
WebSAR
http://152.80.49.205/CGI/websar/websar.cgi
"FNMOC's Search And Rescue (SAR) model is an
upgraded version of the Computer Aided Search
Planning (CASP) system used by the Coast Guard.
The model generates probability maps, search
recommendations and reports environmental
conditions from FNMOC environmental model
data.”
All quotes in this section are taken from the FNMOC web site
"The SAR model uses a statistical simulation
method to estimate the position at a certain time of
any object or "target" in the open ocean. This
method takes into account the initial uncertainties
of the target location and inaccuracies in the
environmental data to give a large number of future
possible target locations. A set of up to 2,500
random positions which describe the probabilities
associated with the target initial location are
generated.
Each position is then moved
independently using the best estimate of marine
wind and wind-driven surface current data available
in one-hour steps. At any selected time, the
multiple position locations are assembled into a
distribution or "probability of containment" map."
Forcing
• If the search area falls entirely within the domain
of one of the regional TOPS areas, then the
currents will be a combination of wind-driven and
geostrophic. If the search area does not fall within
the domain of one of the regional TOPS areas,
then the currents will be wind-driven only.
• NOGAPS (or COAMPS, if the search area falls
within one of the regional TOPS areas) winds are
used in WebSAR to estimate the leeway ("leeway
is the movement of the object caused by local
winds blowing against the exposed surface of the
object").
“In all cases 100% of the surface current is applied
to the drift computation. For boats, rafts and other
types of marine craft leeway comes into play.
Leeway is the movement of the target caused by
local winds blowing against the exposed surfaces
(freeboard) of the object. The greater the exposed
surface of the object the more the wind pushes the
object. The direction of the leeway can also vary as
much as 40 off the downwind direction for boats.
Wind effects are handled through a series of leeway
options (or codes). Leeway codes provide two
values to the model. The first digit is the percent of
wind speed at which the object will drift and the
second digit is the angular error, in tens of degrees (1
= 10 degrees), from the downwind course.”
"The position or "area of containment" is
described by a circle with the initial location
at the center and the radius equal to the
uncertainty in the best estimate of the initial
fix.
This specifies a bivariate normal
distribution for the target location, which
means, the target is more likely to be near the
center of the circle than the edge. The tables
below (see web site for most current one) are
provided to assist in defining the uncertainty
(or Navigational Error) to the model. The
model assumes a confidence level of 86% that
the object is contained in the area described
by the circle."
Navigation Fix Errors
Type of Craft
Radius
Ship or Submarine
5.0 nm
Aircraft
10.0 nm
Small Craft
15.0 nm
Note: Type of navigation system should be
taken into account.
SAR is recommended for use only in open ocean
situations, that is, more than 100 nm from any coast
line. Since SAR is driven by the TOPS model, local
coastal effects and tidal effects, among other things,
are not included in the applied current fields. Due to
the coarse grid spacing the effects of islands and
complex coastal topography are also smoothed out.
Web Enabled Search and Rescue (Web-SAR)
Future development plans
Online feedback form
Model details
Pull down menus
Help links
Courtesy of LCDR
Doug Marble
Available to authorized DoD and Government users
30 minute request turn-around-time reduced to less than 60 seconds
Web Enabled Search and Rescue (Web-SAR)
• Text, Image or Combined output.
• Initial point marked, wind and current barbs
• Model used is identified in output.
• Program uses highest resolution ocean and
met model forecast data (COAMPS, NOGAPS
or WW3/TOPS) available in SAR area.
Courtesy of LCDR Doug Marble