Best Track Development

Outline

Current PracticeHistory – the Australian Region Critical changes to TC tracking over

decadesHistory – the Southern HemisphereConclusions

Current Practice

Mostly by Severe Weather SectionsReanalysis from ‘scratch’ (usually!)Modified Knaff-Zehr WPR usedFocus on TC threshold and peak intensityComprehensive set of parametersSix-hourly (00, 06, 12, 18UTC) time fixes

plus additional (3 to 1-hourly) near coastReport produced in addition to BT data

Current Issues Resource constraints: oceanic weak TCs

get less than optimum BT approach Varying analyst skill levels, eg.

scatterometer interpretationAssigning gale radii in asymmetric

systems with temporal variations in structure

Consistency of application of definition of TC

Monsoon low vs extra-tropical vs hybrid …Determining size parameters &

environmental pressure

History Best track procedures have changed over

time due toChanges in priority placed on TC analysisChanges in staffing arrangementsImproved technologyHistorical database limitationsChanging TC interpretations Different WPRs used

Before 1908

Knowledge limited to historical records of significant impacts on coastal communities.

1908-1950

Bureau of Meteorology formed in 1908 Cyclone tracks recorded – but only few

detected; (good coverage of Queensland coast south of Cairns, very limited elsewhere)

Post-event reanalysis not practiced (but some basic reanalysis in a 1981 study)

More technology introduced to support WWII operations - acts as springboard to future developments

1950-1965

Tropical Cyclone Warning Centres introduced in the mid 1950s (no specialist staffing). More detailed recording of cyclone

tracks (although many non cyclone events recorded)

1965-1978

Evolution of polar satellite imagery Raw analysis and observational data

from cyclone events archived Introduction of satellite intensity

techniques 1969; 1973 Dvorak TC Tracy (1974) focuses national

attention on TCs

1978-1987

Introduction of regular geostationary satellite data: April 1978

Progressive changes in DVORAK analysis techniques

Introduction of CYCARD centralised database in 1983 (collation of disparate data sources)

1987-1995

Implementation of dedicated severe weather sections More focused study of Tropical Cyclones Specialised skills at the best track analysis stage Closer focus on Cold cored “Monsoon Lows” &

extra-tropical transitions has lead to better analysis

Introduction of McIDAS Better radar analysis & display tools Large increase in numbers of Automatic

Weather Stations (some offshore)

1995-2009

Improvement in the understanding of some of the limitations of the original DVORAK techniques – particularly rapidly developing systems

Evolution of new satellite tools has assisted in the analysis of tropical cyclones esp. microwave and QScat (real-time and post-event)

Improved understanding of wind structure and intensity changes (global work)

Single WPR (modifeid Knaff-Zehr) introduced 2008/09

2009 New database structure allows for

more parameters to be stored Old database was based on 132 character

formatted text fields (based on old card technology)

New data to be stored on file includesDVORAK dataQuadrant wind data (34, 48, 63 kn)Comments field Uncertainty fields

Critical changes over time

Mid-1950s: founding of TC warning centres, introduction of radar coverage

1957: improved marine data collection through introduction of Port Meteorological Agents

Critical changes over time Late 1960s/early 1970s: progressive

improvement in satellite data availability 1969: Satellite intensity technique

(Oliver) 1973-1983: Dvorak technique introduced 1980-83: Dvorak used in close to its

current form 1978: change in definition for ‘hybrid’

systems – only small impact on total numbers but big local impact on high-latitude systems

1984: maximum wind introduced in BT

Net impact of changes (relative to current DB)

Cyclone numbers: slightly too high 1955-1978 (but problem

largely addressed by work already done); too low pre-1955, especially outside

Queensland Intensity: generally too weak pre-1985

and especially pre-1970

Database improvement Review of best track archive commenced.

Phase one removal of obvious errors• Obvious typographical errors fixed• Duplications and omissions fixed• Obvious non-TC events removed

Phase two (2009/10)• Digitisation and checking of satellite data back to

1978• Collation of other data

Phase three (2010/12)• Reanalysis of the geostationary satellite

era ?????

Summary - AR

1 2 3 4 5

Poor Adequate Fair Good Very Good

N Numbers

I Intensity

1995 onwards New satellite data (microwave and QScat), improved understanding of Dvorak, wind structure etc

N 5 I 5

1987 – 1995 Dedicated severe weather sections established. Improved data availability and analysis (AWSs, radar analysis etc)

N 5 I 4-5

1978 – 1987 Geo-stationary era (April 1978). Progressive changes in the Dvorak Technique.

N 5 I 4

1965 – 1978 Polar satellite imagery available. The Dvorak technique introduced in 1973.

N 4 I 2

Prior to 1965 Historical records of significant impacts on coastal

communities N 1-3 I 1

Summary - WSIO

1 2 3 4 5

Poor Adequate Fair Good Very Good

1998 onwards Geo-stationary era (and microwave era 5

1993 – 1997 RSMC La Reunion started operations in 1993 4

1982 – 1992 the Dvorak Technique applied from 1982 3

1967 – 1981 Beginning of the satellite era in the western SIO in 1967

2

Prior to 1967 Historical TC Records start in 1848 1

Summary - ESPO

1 2 3 4 5

Poor Adequate Fair Good Very Good

2006 onwards

Built on the gains of late 1990s and early 2000s. Greater sharing of information between centres.

4

1998 – 2005

Greater use of Dvorak; better quality satellite imagery with better coverage. Microwave and QScat (late 1990s). More cooperation through RA V TCC. Individual intensities specified.

3

1979 – 1997

Geo-stationary imagery. Dvorak technique was only starting in early 1990s (mainly due to the absence of high resolution satellite data). Maximum intensity estimated but intensities depicted in bands in database.

2

1969 – 1979

Beginning of satellite era. Maximum intensity estimated but intensities depicted in bands in database.

1

Prior to 1969

No record of track data

Conclusions

Consolidation of historical data from various regions is currently limited by the inhomogeneity of TC observation and analysis practice

There is evidently a considerable need for re-analysis of the historical TC data in order to obtain globally homogeneous records, something required to address the important question of how TC activity is changing and its possible relationship to global climate change more generally.

Acknowledgements

Australian Government Department of Climate Change and NOAA’s National Climatic Data Center for financial support of the project “Climate change and the Southern Hemisphere tropical cyclones”

Météo-France (La Réunion), the Meteorological Services of Fiji and New Zealand for providing regional TC data

Philippe Caroff, Jim Davidson, Steve Ready, Alipate Waqaicelua and Howard Diamond for discussions on quality of regional TC data