Kay Shelton Seasonal Tropical Cyclone Prediction with...
Transcript of Kay Shelton Seasonal Tropical Cyclone Prediction with...
Seasonal Tropical Cyclone Prediction with POAMA
Kay Shelton1, Andrew Charles2, Harry Hendon1 and
Yuriy Kuleshov2
1CAWCR, BoM and 2NCC, BoM
What is a tropical cyclone?
• A tropical cyclone (TC) is the generic term for a non-frontal synoptic scale low-pressure system over tropical or sub-tropical waters with organized convection (i.e. thunderstorm activity) and definite cyclonic surface wind circulation (Holland 1993).
• The terms "hurricane" and "typhoon" are regionally specific names for a strong "tropical cyclone".
Schematic structure
of mature TC in SH(Adapted from NOAA NH image)
http://www.aoml.noaa.gov/hrd/tcfaq/tcfaqHED.html
http://www.bom.gov.au/weather/cyclone/faq
How do they form?
• Ingredients for TC formation:
– sufficiently large background vorticity (generally 3° from
the Equator is minimum requirement),
– small vertical wind shear over the disturbance,
– a warm ocean to a sufficient depth (SST>26.5°C),
– conditionally unstable atmospheric column,
– moist mid-levels,
– a pre-existing disturbance.
How do they form?
• Ingredients for TC formation:
– sufficiently large background vorticity (generally 3° from
the Equator is minimum requirement),
– small vertical wind shear over the disturbance,
– a warm ocean to a sufficient depth (SST>26.5°C),
– conditionally unstable atmospheric column,
– moist mid-levels,
– a pre-existing disturbance.Large-scale environment,
strongly modulated by ENSO
How do they form?
• Ingredients for TC formation:
– sufficiently large background vorticity (generally 3° from
the Equator is minimum requirement),
– small vertical wind shear over the disturbance,
– a warm ocean to a sufficient depth (SST>26.5°C),
– conditionally unstable atmospheric column,
– moist mid-levels,
– a pre-existing disturbance.Large-scale environment,
strongly modulated by ENSO
Stochastic component
How do we make a TC prediction?
Use objective TC tracking scheme (Tory et al. 2012):
• Identify disturbances in the model at each time,
• Join these disturbances together to form a track,
• When certain threshold criteria have been met for 3
successive times, the disturbance is declared a “TC”.
t0 t1 t2 t3
How do we make a TC prediction?
Use objective TC tracking scheme (Tory et al. 2012):
• Identify disturbances in the model at each time,
• Join these disturbances together to form a track,
• When certain threshold criteria have been met for 3
successive times, the disturbance is declared a “TC”.
t0 t1 t2 t3
How do we make a TC prediction?
Use objective TC tracking scheme (Tory et al. 2012),:
• Identify disturbances in the model at each time,
• Join these disturbances together to form a track,
• When certain threshold criteria have been met for 3
successive times, the disturbance is declared a “TC”.
t0 t1 t2 t3
How do we make a TC prediction?
• TCs are tracked every day (in the 1 Oct run) for the entire SH
TC season (Nov-Apr) in each member of the POAMA
ensemble.
How do we make a TC prediction?
• TCs are tracked every day (in the 1 Oct run) for the entire SH
TC season (Nov-Apr) in each member of the POAMA
ensemble.
Pre-TC track TC track
How do we make a TC prediction?
• The number of TCs in each region in each member is
determined.
• The proportion of the ensemble above/below the long-term
hindcast average provides the probabilistic prediction.
Aus regions map
Obs. climo. avg.: 7
POAMA climo. avg.: 4
Prob. above: 40%
Obs. climo. avg.: 11
POAMA climo. avg.: 9
Prob. above: 56%
How well does POAMA do?
• The confidence in the TC prediction for each region is
determined by comparing the ensemble hindcast to
observations.
• Interannual variability in POAMA TCs compares well
with observations.
Grey bars are 1 standard deviation from ensemble mean, based on 30 members
How well does POAMA do?
Observations POAMA
ENSO years defined member Niño 3.4 SST anomalyENSO years defined following Kuleshov et al. (2008).
TC prediction products
What can we provide?
• Regional probabilistic TC predictions.
• Spatial distribution of anomalous TC activity.
EXPERIMENTAL
Future directions
• TC intensity predictions – the likelihood of more intense systems; accumulated cyclone energy (ACE) – a measure of the number of cyclone days and aggregated TC intensity.
• Intraseasonal TC predictions – predictions of TC activity for the next one, two or 3 months released more frequently throughout the TC season (POAMA multi-week system).
• Improved TC simulation – with POAMA 3 based on the ACCESS model, expect differences in model physics, dynamics and higher resolution to provide improvements in TC representation, seasonal and interannual variability.
Thank you
For further information
Kay Shelton
Research Scientist
Email: [email protected]
Phone: (03) 8638 8288
Tory, K. J., Dare, R. A., Davidson, N. E., McBride, J. L., and Chand, S. S., 2012a: The importance of low-deformation vorticity in tropical cyclone formation, Atmos. Chem. Phys. Discuss., 12, 17539-17581, doi:10.5194/acpd-12-17539-2012.
Tory, K.J., S. S. Chand, R. A. Dare, and J. L. McBride, 2012b: The development and assessment of a model-, grid- and basin-independent tropical cyclone detection scheme. J Climate, accepted.
Tory, K.J., S. S. Chand, R. A. Dare, and J. L. McBride, 2012c: An assessment of a model-, grid- and basin-independent tropical cyclone detection scheme in selected CMIP3 global climate models. J Climate, accepted.