NCEP Operational Global Cyclone Tracking and Verification System. Guang Ping Lou, Geoff DiMego, Tim Marchok, Binbin Zhou, Mike Charles NCEP/EMC/MMB EMC seminar Nov. 4, 2008. 1. The Ideas. What are needed:
Guang Ping Lou, Geoff DiMego, Tim Marchok,
Binbin Zhou, Mike Charles
EMC seminar Nov. 4, 2008
What are needed:
1. The system is objective;
2. It is a completely automated system and no human intervention is needed from identifying both analysis and forecast tracks to verification, plotting and web displaying;
3. Provide a quick look at how well the forecasts are against the analysis tracks;
4. It can be used to generate retro-run tracks and verification easily.
1. The analysis tracks are often short lived due to weakening and observation data ingest in each synoptic time;
2. The tracks can only be verified against model self analysis because matching difficulties against another model analysis.
Where dn is the distance from a data point n to the grid point g, and re is the e-folding radius. Typically an re value of 75 km for models with a grid resolution finer than 1.25 degree and 150 km for those with coarser resolution.
Cyclone thermal symmetry parameter B:
Where h = 1 for northern hemisphere and h = -1 for southern hemisphere.
Lower-tropospheric thermal wind:
Upper-troposheric thermal wind:
d: the distance between the geopotential extrema
Old regional tracker: System
Include only CONUS, Atlantic basin, West Pacific basin, East Pacific basin, and Alaska, mainly north America-centric;
Single CPU does all processing. Regional search needs as much as 3.5 hrs wall clock.
Storm ID has no continuity.
New global tracker:
From -90~90, 0~360, lat & lon, truly global coverage;
Multitasking schemes to have as many tasks as number of ensemble members. Global search finishes within 20 minutes wall clock. Users have much earlier access to tracks.
New storm ID is named with initial date, lead-time in forecast and lat/lon position where storm was first identified.3. Differences Between Old Regional and New Global Trackers
4. In addition to regular output, added phase parameters: Positions for the 3 diagnostics from Bob Hart's cyclone phase space. Mean & max values of relative vorticity near the storm at 850 & 700. Direction of model storm motion, Translation speed of model storm, The pressure of the last closed isobar and the radius of that closed isobar.
5. TIGGE web format output. (THORPEX Interactive Grand Global Ensemble)3. Old Regional And New Global (Cont.)
Operational tracker is invoked whenever model forecast data
arrive at NCO. The forecast models include GFS, NAM, CMC,
UKMO, ECMWF, NOGAPS, and ensemble forecasts such as
NCEP ensemble GEFS and SREF, CMC and ECMWF. Cyclone
tracks are plotted and graphics are pushed to a web server.
They are also archived in ATCF, MySQL format and TIGGE
http://www.emc.ncep.noaa.gov/mmb/gplou/emchurr/verify/4. The Steps
b) Getting the analysis tracks:
c) Matching forecasts with analysis tracks:
4 times daily: GFS, NAM, GEFS, SREF
2 times daily: ECMWF, CMC, NOGAPS,
UKMET, CENS (00Z, 12Z)
1 time daily: EENS (12Z)
21 CPU for GEFS, SREF
17 CPU for CENS
50 CPU for EENS
Single CPU for GFS, NAM, ECMWF, CMC, UKMET, NOGAPS
Output forecast tracks (ATCF, TIGGE)
Climate pairs each month (ATCF, MySQL)
Climate verification month, season, year
X-Y biases, etc
F vs A
Position error and bias:
OB1-3: Observed positions
FC: Forecast position
DX: Error in the East-West direction
DY: Error in the North-South direction
AT: Error in the Along Track direction
CT: Error in the Cross Track direction
DX=Xo-Xf : DX errors are positive if the forecast position lies westward of obs
DY=-(Yo-Yf) : DY errors are positive if the forecast position lies poleward of obs
PE=SQT(DX*DX+DY*DY): Position error
Following conventional tropical storm verification procedure, cyclone tracks are arranged in two separate decks:
In the examples shown previous slides, track errors are
calculated as displayed next.
1. Tracking forecast cyclone tracks
2. Seeking out analysis tracks
3. Matching forecast with analysis tracks
5. Plotting and pushing plots to server