noel davidson

The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology

Initialization, Prediction and Diagnosis of some Rapid Change Phenomena in Tropical Cyclones

Noel Davidson, Yi Xiao, Yimin Ma, Harry Weber, Jeff Kepert, Kevin Tory, Richard Dare, Hongyan Zhu, Xingbao Wang, Ying Jun Chen,

Michael Reeder and Mai Nguyen

Acknowledgments: Kamal Puri, John McBride, Gary Dietachmayer and Peter Steinle

ACCSP and NOPP/ONR

Special thanks to WEP and ESM Programs at CAWCR, and UKMO

Weather and Environmental Prediction and Environmental System Modelling Groups

CAWCR, Centre for Australian Weather and Climate Research A Partnership between CSIRO and the Bureau of Meteorology

TC behaviour and forecast issues:

• Track,

• Genesis,

• Intensification/RI/Decay,

• Structure Change (size, etc),

• ET

• Landfall!!!

Points of Origin

Points of Final Decay

Points with Min. CP

Tropical Cyclone Characteristics in the Australian Region

(Dare and Davidson, 2004, MWR)


Scope of Talk

• Operational ACCESSTC Verification

• ACCESSTC System Configuration

• Vortex Specification

• Initialization with 4DVAR

• Objective Verification

• Structure Diagnostics

• Forecasts for TCs undergoing rapid changes in track, intensity, structure

• Related Projects (Genesis, HBL, SEF/ERC, DD (RI, ET, XR), VS, TC Rain)

• Summary, Conclusion and Future Plans

Verification statistics for operational ACCESSTC. Left panels: 20112012 Australian Region (00– 350S, 800–1800E), 6TCs. Right panels: 2012 northwest Pacific, 16 TCs up until early October 2012. Vertical panels are: (top) number of forecasts, (center) mean track error, and (lower) mean absolute central pressure error, every 6 hours to 72 hours. The dashed green curves on the center panels are approximate longterm mean (last 5 years) track errors and on the lower panel, mean absolute central pressure error using persistence as the forecast. For the northwest Pacific, forecast central pressures have been biascorrected using the initialized minus observed value at t = 0.

Verification Statistics for Operational ACCESSTC.

Obsvd and Forecast Tracks and Central Pressures for TC Lua from Operational ACCESSTC


Animation of Synthetic and Actual IR Imagery (Sun and Rikus, 2004) ACCESSTC Operational Forecast of TC Lua, Base Time 12UTC, 15 March 2012 Courtesy Lawrie Rikus, ESM Program, CAWCR Sun, Z. and L.J. Rikus, 2004: Validating model clouds and their optical properties using Geostationary satellite imagery.Mon. Wea. Rev., 132, 20062020


ACCESSTC runs on named TCs over the approximate domain 40 0 S 40 0 N, 70 0 E – 180 0 E

Some examples:

Not All Good News …

More recently some poor forecasts for KaiTak, Talim and Doksuri,

particularly when they were weak storms

Location and structures are uncertain,

Enviroment sometimes not well defined => can be difficult to forecast.


ACCESSTC for Operations and Research

1. Resolution:

0.11 0 X50L, relocatable grid, with TC near centre of domain, option for higherresolution forecasts.

2. Vortex Specification:

(a) Structure based on observed location, central pressure and size (tuned and validated using ~6000 dropsonde observations from the Atlantic)

(b) Only synthetic MSLP obs used in the 4DVAR to (a) relocate the storm to observed location, (b) define the innercore circulation, and (c) impose steering flow asymmetries consistent with the past motion.

3. Initialization using 4DVAR Assimilation:

5 cycles of 4DVAR over 24 hours. Uses all standard obs data, plus synthetic MSLP obs (no upper air synthetic obs).

4DVAR then: (a) Defines the horizontal structure of the innercore at the observed location, (CP, VMAX, RMW, R34) (b) Builds the vertical structure from MSLP obs, (c) Constructs the secondary circulation, (d) Creates a balanced TC circulation at the observed location, with correct (?) structure and intensity. (e) Creates a structure which is responsive to environmental wind shear without imposing constraints

on the verticalstacking or tilt of the circulation. (important for vortex dynamics and cloud asymmetries)

4. Forecast Model:

UKMO Unified Model from ACCESS.


Verification of large scale global forecasts

MSLP RMSE at 72 hours over the Australian Region

Red curve is ACCESSG, Cyan curve is ECMWF

⇒ Prediction of the LSE of storms competitive with the best guidance

Verification of Forecasts of the Large Scale Environment over the Australian Region

Vortex Specification (Weber, 2011)

Figure 2: Tangential wind v(r) in m s1 as a function of radius in km of Hurricane Fran on September 29, 1996 (top) and Hurricane Floyd on September 19, 1999 (bottom). Thick lines represent the average v(r) of all flight passes and the AVSM output v(r) (smoother curve). The thin lines define an envelope given by the minimum and maximum v(r) of all flight passes at each radial grid point. The input parameters of AVSM are rm and vm of the average v(r) of all flight passes in (a), (b), the operational estimates of roci and vm in (c), (d) and the operational estimates of roci and vm – c in (e), (f).

Validation of Vortex Structure: Use EXBT data sets for the NA and NP to validate TC structures obtained from the Vortex Specification (RMW, R34). (CLOK: Charlie Lok)

Type 1 Type 3

Count MAE (nm) Count MAE

(nm)

TS 2400 40.1 2261 38.3

Cat 12 1728 42.6 1726 40.0

Cat 35 653 36.3 653 40.2

TOTAL 4781 40.5 4640 39.2

Type 1 Type 3

Count MAE (nm) Count MAE (nm)

TS 3945 19.2 3945 19.0

Cat 12 1686 11.4 1686 12.1

Cat 35 653 6.9 653 10.5

TOTAL 6284 15.8 6284 16.3

MAEs for R34 and RMW: EXBT data sets and ACCESSTC Vortex Specification from CP and Objective ROCI Limitations of EXBT: Subjective, difficult, no dynamical constraints (Gradient wind balance, Inertial Stability, Finite AM)

Validation of Initial Vortex Structure:

I: Comparison of Subjective and Objective Estimates (from vortex specification) of R34 and RMW

OBS Network

Without Vortex Specification (VS) : Initial Position/Intensity Errors for TC Anthony were ~ 230km and 5hPa

With VS: Initial Position/Intensity Errors reduced to 40km and 0hPa VS: blue MSLP obs in upper left panel:

Obs distribution: Dense enough to define Vmax at RMW, extensive enough to merge vortex with LSE.

For Anthony at Landfall:

Obsvd and fcast track and intensity without and with VS

500 hPa Initial Condition without and with VS (synthetic MSLP obs only)

4DVAR builds primary and secondary circulations, as well as depth and tilt of vortex,

Important for evolution of vortex

Top panels: Observed and 72hour forecast tracks and central pressures for TC Yasi from base time 00UTC 31 January 2011. Lower panels: Southnorth crosssections of zonal wind, meridional wind and vertical motion through the initialized center of TC Yasi at 00UTC, 31 January 20111. Units are m/s and hPa/sec.

Initialization of the Primary and Secondary Circulations by ACCESSTC


Validation of Vortex Structure. I: Cloud Fields (Rikus and Sun, 20XX)

Actual and Synthetic Cloud Imagery

Yasi at t = 0 and t = 46 hours from base time, 12Z, 20110131

• 4DVAR initializes the ascent and moisture fields.

• Model maintains cloud fields during the forecast.


Validation of Vortex Structure.

II: Cloud Bands and Convective Asymmetries

85GHz Imagery (left panels) and ACCESSTC 500 hPa vertical motion field at t = 6 (initialized with 4DVAR) and t = 55 hours for Yasi from base time 00Z, 20110131

• Note regions of observed active inner rainbands and eyewall convection, and corresponding forecast regions of strong and weak ascent.

• Based on use of synthetic MSLP obs and 4DVAR, structures are consistent from even the early hours of the forecast.

• Rainfall in TCs (Ying Jun Chen)

Preliminary Validation of Vortex Structure. III: Intensity and Windfields

(Y. Ma)

Critical for Storm Surge and Rainfall

For Yasi from base time 00Z, 20110131:

Time series of forecast

(a) Central Pressure,

(b) Maximum Wind,

(c) Radius of Maximum Wind,

(d) Radius of 64, 50 and 34 knot winds.

Symbols indicate estimated values, where available

Encouraging preliminary verification

***** What defines size and the RMW? <<<<<

Illustrative Examples of Rapid Change:

Landfall


Rapid Changes in Track ?

Observed (red ‘O’s) and forecast (Green ‘F’s) tracks and central pressures for TCs Mawar, Saola, Haikui (examples of moderate intensifiers), from the base times indicated. The table in the track panels shows valid time of forecast, forecast hours, observed central pressure, forecast central pressure (hPa) and track error (TERR) in kms. The dashed curve on the intensity panels show forecast maximum wind in knots.

Can forecast moderate intensification reasonably well, while retaining good track forecasts

Moderate Changes in Intensity ?

Moderate Intensifiers

Observed (red ‘O’s) and forecast (Green ‘F’s) tracks and central pressures for TCs Bolaven, Sanba, Jelawat (examples of rapid intensifiers) from the base times indicated. The table in the track panels shows valid time of forecast, forecast hours, observed central pressure, forecast central pressure (hPa) and track error (TERR) in kms. The dashed curve on the intensity panels show forecast maximum wind in knots.

Still cannot forecast RI, but track forecasts are good:

Need for increased resolution, improved VSs, improved physical parameterizations, improved representation of physical processes (limiting drag coeff, sea spray?)

Rapid Changes in Intensity ?

Rapid Intensifiers

Model Evaluation and Diagnostics

• ACCESSTC has been operational for one year.

• Verification has been rather encouraging => useful for operations and research.

• The forecast archive now contains many examples of vortex structure change, intensification, rapid track changes, ET, landfall, rainfall.

• Valuable data sets for investigating rapid change phenomena and internal dynamics. (Genesis, RI, Internal Structure Change, SEF/ERC, LF, ET)

• Basis for much higher resolution forecasts and diagnosis of rapid change phenomena and possibly SEF/ERC? (4km, 1.5km, 0.5km stretched grids)


Improving Parameterisation of AirSea Exchange Processes in ACCESSTC

Yimin Ma, Yi Xiao, Jeff Kepert and Noel Davidson

Realistic physical representation of airsea exchange in high wind conditions.

Limiting drag coefficient at high wind speeds

Parameterisation sea spray effects

Preliminary Results (so far): • Small changes in track forecast • Large improvements in intensity forecast • Small changes in outer structure • More development and testing • future collab NOAA Boulder (JW Bao, Chris Fairall)

Structure prediction from ACCESSTC for YASI. Base time 20110131/00Z

OWZ Diagnostics for Genesis (verticallyaligned, moist regions with curvature vorticity in low shear)

Kevin Tory and Colleagues

Rapid Changes in Innercore Structure: Genesis ?

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Downstream Development during the Rapid Intensification of Hurricanes Opal and Katrina: the Distant TroughInteraction Problem

Rapid Changes in the LSE and Impact on Intensity and Structure ?

Dynamics of Secondary Eyewall Formation and Eyewall Replacement Cycles

Xingbao Wang, Yimin Ma, Noel Davidson

Tangential Wind Radar Reflectivity(dBZ)

Eastwest Diametertime Hovmoller diagram of Radar Reflectivity and Tangential Wind

Conceptual Model of SEF/ERC,

Based on Advanced Diagnostics of (a) the evolving secondary circulation, (b) broadening of the swirling flow (Huang et al. 2012), (c) AM conservation, and (d) Unbalanced Forces in the Boundary Layer.

Wang, X., Y. Ma and N.E. Davidson, 2012: Secondary Eyewall Formation and Eyewall Replacement Cycles in a Simulated Hurricane: Effect of the Net Radial Force in the Hurricane Boundary Layer. J.Atmos Sci., 69, (accepted) Future collab: CC Wu, Wes Terwey, MTM??)

example

US14111; 7.45 151.83; atoll site

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atoll rain TRMM 3B42

correl=0.906

US14585; 9.57 138.12; coastal with orographic influence

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correl=0.74 9

US14111 Gauge:749mm TRMM: 563mm

US14419 Gauge: 256mm TRMM: 423mm

US14590 Gauge:223mm TRMM: 204mm

Rainfall in TCs : Ying Jun Chen, Kevin Walsh, Beth Ebert, Noel Davidson

Analyse (TRMM),

Verify,

Predict

TC Rainfall

example

Rainfall in TCs : Richard Dare, Ying Jun Chen,

Kevin Walsh, Beth Ebert, Noel Davidson

Figure 10: Mean and standard deviation of interannual percentage of all rain that is due to TCs within 50 km of the coast and within 5° longitude bands.

Figure 11: Radial distribution of mean rain within 500 km from TC center. Black line for all TCs rain, red line for rain from CAT12 TCs, blue line for rain from CAT35 TCs.

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pa)

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Mai NGUYEN: Rapid Intensification: InnerCore Processes:

Internal Structure Change during RI (Vacillation Cycles, QJRMS, 2011)

Left panel: Analysis of 24hour rainfall accumulations for 29 January 1990. Centre and right panels: 500 hPa wind valid 24 and 29 January 1990, respectively. X marks the approximate location of Tropical Cyclone Tina at the analysis times, as it moves to the southeast and is captured and transitions into a midlatitude system.

Figure 1: (a) Number of extreme rain events by month, and (b) percentage of events occurring within each latitude zone, by month.

Amplifying Planetary Rossby Waves and Extreme Rain Events

in Current and Future Climates

Future Plans

• Upgrades to APS1(more satellite data, higher resolution, improved physics, ….)

• Realtime forecasts from pregenesis over the north Atlantic (assim of innercore recon data with 4DVAR)

• Specification, Prediction and Validation of TC Structure (CP, Vmax, RMW, R34, ROCI): Critical for prediction of track, intensity, structure, storm surge and rainfall

• Experiments with High Resolution Initialization and Prediction; Experiments with Ensemble Prediction; “Hybrid Assimilation” UKMO : E4DVAR Experiments with Revised and New Physics;

Diagnostics for TC boundary layer and moist processes

• Enhancements with 4DVAR (inner and outer loops) Impact of extra observation types

• NWP and basic research applications from special experimental data sets: TPARC/TCS08, PREDICT: Genesis and Rapid Intensification

• Diagnosis of Rapid Change Phenomena from ACCESSTC archive.

• Rainfall in TCs

• Influence of Amplifying Rossby Waves on TC structure and intensity

• Innercore Dynamics (eg, What defines RMW and R34?)

• Challenge: Initialize CAT 3 5 storms without the use of reconnaissance data or vortex specification?

noel davidson

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