MET Tool: TC-Pairs

TC-Pairs Tool: General

TC-Pairs Functionality

The TC-Pairs tool provides position and intensity information for tropical cyclone forecasts in Automated Tropical Cyclone Forecast System (ATCF) format. Much like the Point-Stat tool, TC-Pairs produces matched pairs of forecast model output and an observation dataset. In the case of TC-Pairs, both the model output and observational dataset (or reference forecast) must be in ATCF format. TC-Pairs produces matched pairs for position errors, as well as wind, sea level pressure, and distance to land values for each input dataset.

TC-Pairs Usage

View the usage statement for TC-Pairs by simply typing the following:

tc_pairs

Usage: tc_pairs
	-adeck source	Input ATCF format track files
	-edeck source	Input ATCF format ensemble probability files
	-bdeck source	Input ATCF format observation (or reference forecast) file path/name
	-config file	Configuration file
	[-out_base]	path of output file base
	[-log_file]	name of log associated with tc_pairs output
	[-v level]	Level of logging (optional)

At a minimum, the input ATCF format -adeck (or -edeck) source, the input ATCF format -bdeck source, and the configuration -config file must be passed in on the command line.

The -adeck, -edeck, and -edeck options can be set to either a specific file name or a top-level directory which will be searched for files ending in ".dat".

cindyhg Mon, 06/24/2019 - 11:18

Input format

TC-Pairs input data format

As mentioned previously, the input to TC-Pairs is two ATCF format files, in addition to the distance_to_land.nc file generated with the TC-Dland tool. The ATCF file format is a comma-separated ASCII file containing the following fields:

	Basin	basin
	CY	annual cyclone number (1-99)
	YYYYMMDDHH	Date - Time - Group
	TECHNUM/MIN	Objective sorting technique number, minutes in Best Track
	TECH	acronym for each objective technique
	TAU	forecast period
	LatN/S	Latitude for the date time group
	LonE/W	Longitude for date time group
	VMAX	Maximum sustained wind speed
	MSLP	Minimum sea level pressure
	TY	Highest level of tropical cyclone development
	RAD	wind intensity for the radii at 34, 50, 64 kts
	WINDCODE	radius code
	RAD1	full circle radius of wind intensity, 1st quadrant wind intensity
	RAD2	radius of 2nd quadrant wind intensity
	RAD3	radius of 3rd quadrant wind intensity
	RAD4	radius of 4th quadrant wind intensity
	...

These are the first 17 columns in the ATCF file format. MET-TC requires the input file has all 17 comma-separated columns present (although valid data is not required). For a full list of the columns as well as greater detail on the file format, see: http://www.nrlmry.navy.mil/atcf_web/docs/database/new/abdeck.txt

Model data must be run through a vortex tracking algorithm prior to becoming input for MET-TC. Running a vortex tracker is outside the scope of this tutorial, however a freely available and supported vortex tracking software is available at:https://dtcenter.org/community-code/gfdl-vortex-tracker/download

If users choose to use operational model data for input to MET-TC, all U.S. operational model output in ATCF format can be found at: ftp://ftp.nhc.noaa.gov/atcf/archive. Finally, the most common use of MET-TC is to use the best track analysis (used as observations) to generate pairs between the model forecast and the observations. Best track analyses can be found at the same link as the operational model output.

Open files aal112017.dat (model data) and bal112017.dat (BEST track). Take a look at the columns and gain familiarity with ATCF format. These files are input ATCF files for TC-Pairs.

vi ${METPLUS_DATA}/met_test/atcf_data/aal182012.dat

vi ${METPLUS_DATA}/met_test/atcf_data/bal182012.dat

In addition to the files above, data from five total storms over hurricane seasons 2011-2012 in the AL basin will be used to run TC-Pairs. Rather than running a single storm, these storms were chosen to provide a larger sample size to provide more robust statistics.

aal092011: Irene
aal182011: Rina
aal052012: Ernesto
aal092012: Isaac
aal182012: Sandy

cindyhg Mon, 06/24/2019 - 11:56

Configure

TC-Pairs Tool: Configure

Start by making an output directory for TC-Pairs and changing directories:

mkdir -p ${METPLUS_TUTORIAL_DIR}/output/met_output/tc_pairs

cd ${METPLUS_TUTORIAL_DIR}/output/met_output/tc_pairs

Like the Point-Stat tool, the TC-Pairs tool is controlled by the contents of the configuration file passed to it on the command line. The default TC-Pairs configuration file may be found in the data/config/TCPairsConfig_default file.

The configurable items for TC-Pairs are used to specify which data are ingested and how the input data are filtered. The configurable items include specifications for the following:

All model names to include in matched pairs
Storms to include in verification: parsed by storm_id, basin, storm_name, cyclone
Date/Time/Space restrictions: initialization time, valid time, lead time, masking
User defined consensus forecasts
Thresholds over watch/warning status of storm

The first step is to set-up the configuration file. Keep in mind, TC-Pairs should be run with the largest desired sample in mind to minimize re-running this tool! First, make a copy of the default:

cp ${MET_BUILD_BASE}/share/met/config/TCPairsConfig_default TCPairsConfig_tutorial_run

Next, open up the TCPairsConfig_tutorial_run file for editing and modify it as follows:

vi TCPairsConfig_tutorial_run

Set the model and basin entries:

model = [ "HWRF", "AVNO", "GFDL" ];
basin = [ "AL" ];

To identify the models that we want to verify, as well as the basin. The three models identified are all U.S. operational models: HWRF, GFS (AVNO), and GFDL. Any field left blank will assume no restrictions.

Set the following in the consensus library:

consensus = [
{
name = "CONS";
members = [ "HWRF", "AVNO", "GFDL" ];
required = [ false, false, false ];
min_req = 2;
}
];

To compute a user defined consensus named "CONS". The membership of the consensus are the three listed models, none are required, but 2 must be present to calculate the consensus.

Update the match_points entry to:

match_points = TRUE;

To only keep pairs that are the intersection of the model forecast and observation.

Next, save the TCPairsConfig_tutorial_run file and exit the text editor.

This run uses the default distance to land output file. Run ncview to see it:

ncview ${MET_BUILD_BASE}/share/met/tc_data/dland_global_tenth_degree.nc &

Water points have distance to land values greater than 0 while land points have distances <= 0.

cindyhg Mon, 06/24/2019 - 11:57

Run

TC-Pairs Tool: Run

Next, run TC-Pairs to compare all three ATCF forecast models specified in configuration file to the ATCF format best track analysis. Run the following command line:

tc_pairs \

-adeck ${METPLUS_DATA}/met_test/atcf_data/aal*dat \

-bdeck ${METPLUS_DATA}/met_test/atcf_data/bal*dat \

-config TCPairsConfig_tutorial_run \

-out tc_pairs \

-v 2

TC-Pairs is now grabbing the model data we requested in the configuration file, generating the consensus, and performing the additional filtering criteria. It should take approximate 20 seconds to run. You should see several status messages printed to the screen to indicate progress.

There should be an output file "tc_pairs.tcst" in the directory, where .tcst stands for TC statistics. The next page will describe what is in the file.

If you are running many models over many storms/seasons, it is best to run TC-Pairs using a script to call TC-Pairs for each storm. This avoids potential memory issues when parsing very large datasets.

cindyhg Mon, 06/24/2019 - 11:58

Output

TC-Pairs Tool: Output

The output of TC-Pairs is an ASCII file containing matched pairs for each of the models requested. In this example, the output is written to the tc_pairs.tcst file as we requested on the command line. This output file is in TCST format, which is similar to the STAT output from the Point-Stat and Grid-Stat tools. For more header information on the TCST format, see the tc_pairs output section of the MET User's Guide.

Remember to configure your text editor to NOT use dynamic word wrapping. The files will be much easier to read that way:

In the kwrite editor, select Settings->Configure Editor, de-select Dynamic Word Wrap and click OK.
In the vi editor, type the command :set nowrap. To set this as the default behavior, run the following command:

echo "set nowrap" >> ~/.exrc

Open tc_pairs.tcst

vi tc_pairs.tcst

Notice this is a simple ASCII file with rows for each matched pair for a single valid time and similar to the MPR line type written by other tools.
Any field that has A in the column name (such as AMAX_WIND, ALAT) indicate the model forecast.
Any field that has B in the column name (such as BMAX_WIND, BLAT) indicate the observation field (Best Track).
The TK_ERR, X_ERR, Y_ERR, ALTK_ERR, CRTK_ERR columns are calculated track error, X component position error, Y component postion error, along track error, and cross track error, respectively.
Columns 34-63 are the 34-, 50-, and 64-kt wind radii for each quadrant.

cindyhg Mon, 06/24/2019 - 11:59