REAL-TIME USE OF CYCLONE PHASE DIAGRAMS

TO IMPROVE CYCLONE STRUCTURAL DIAGNOSIS & FORECASTING

Robert Hart 1 Jenni Evans 2 1 Florida State University 2 Penn State University

Introduction Provides historical, current (real-time), and forecast diagnostics of cyclone structure using cyclone phase diagrams These diagrams have been used experimentally and operationally since 2001 to diagnose and forecast complex cyclone evolution: (sub)tropical cyclone genesis, extratropical transition, tropical transition, and the development of hybrid structure. Every cyclone is quantified by three physically fundamental measures of thermal & dynamic structure: B:Storm-motion-relative hPa thickness asymmetry -V T L : hPa thermal wind [+/- = warm/cold core] -V T U : hPa thermal wind [+/- = warm/cold core] The various events shown here are examples over the past three years that illustrate their use and insight, while also highlighting the extensive work that remains ahead.

Ensemble approaches to Structural Diagnosis/Forecasting Consensus ensemble phase diagrams provided –Unweighted mean of models having init time within 6hr leading up to analysis time –Shading about consensus mean provides one-standard deviation variability –This one standard deviation range may give measure of model analysis/forecast consensus or variability –May also reflect the number of models or the varying model integration length –Two types of ensembles provided Deterministic model comparison –GFS, CMC, Air Force MM5, NGP, UKMET, GFDL NCEP GFS Perturbed Ensemble Comparison (11 members)

Case: Hurricane Michelle (2001) Case of extratropical transition (ET) of a tropical cyclone Lowest-latitude ET commencement in the period (22°N), perhaps longer. Entire evolution from warm to cold-core (18Z/4 th -12Z/6 th ) took place over SST >= 27°C. Illustrates that you can’t solely rely on climatological aspects or even real-time SST to diagnose potential cyclone structure. Illustrates relationship between track, interaction, and phase forecast NHC Best Track from Beven (2002)

Case: Hurricane Olga (2001) Classic example of tropical development from a cold-core cyclone 2.5-day lead on subtropical transition, 4-5 day lead on tropical transition, while the cyclone was just forming with cold-core structure. The nature of cyclone development in the models is often subtle, or ambiguous when viewed through conventional analyses. The CPS examines the full 3-D thermal & dynamic structure of the cyclone to arrive at an objective diagnosis. NHC Best Track from Avila (2001)

Case: Tropical Storm Ana (2004) Cyclone phase diagrams successfully forecast April (sub)tropical genesis 4-5 days before it formed. Successful forecast of an extremely anomalous structural event CPS diagrams provided the first heads up on the potential historic cyclone development to operational centers. NHC Best Track from Beven (2003)

Case: Brazil Enigma (2004) Operational global model analyses could not agree on the structure of the Brazil cyclone –GFS: Symmetric, shallow warm-core –CMC: Asymmetric, cold-core –NGP: Symmetric,cold-core AMSU-derived cyclone phase diagrams shed light on the true structure of this enigma: Moderately deep, symmetric warm core cyclone 27 March 2004 Imagery: NASA/MODIS

Mixed guidance cases Models generally produce cyclone structural evolution types that are to first order similar Not infrequently, they disagree. Disagreement occurs all months of year, but most frequent in late spring, late autumn Indicates cyclone development is unusually sensitive to: –Analysis structural type or intensity –Model physics –Timing of environmental feature interaction –Everything The example to the right & below is from May 2001, when three models could not agree on the nature of cyclone development, even though the track and intensity of the surface cyclone was quite similar among the three 3-8 May 2001

Cyclone Phase Web Page Overview

Sample multi-model ensemble consensus and variability output from 2003 Hurricane Fabian’s structural forecast envelope based upon seven models

Hurricane Michelle (2001): AVN Phase Verification (black) Vs AVN Forecasts (color)

1800 UTC 22 November1800 UTC 24 November 1800 UTC 25 November 1800 UTC 26 November1800 UTC 27 November 1800 UTC 28 November

1800 UTC 14 April1800 UTC 16 April1800 UTC 17 April 1800 UTC 18 April1800 UTC 19 April1800 UTC 22 April

Full-DiagramZoomed The first full-lifecycle cyclone phase trajectory using AMSU

3 May 2001 Phase Forecasts

Why is the phase of a cyclone important? Predictability is a function of cyclone structure Model interpretation/trust is a function of structure It is often not at first apparent what the model is forecasting, or the nature of cyclone development –Provides insight into the nature of NWP cyclone development that may otherwise be subtle or even ambiguous The envelope of expected intensity (as well as MPI) is a function of cyclone structure

Sample NCEP GFS ensemble consensus and variability output from 2003 Only 7 of 11 perturbed members shown, along with the consensus phase evolution.

00Z 22 November AVN Forecast Phase Evolution

00Z 17 April AVN Forecast Phase Evolution 3-4 day lead on the development of the cyclone and its transition to shallow, then moderately deep warm- core

AMSU-derived Cyclone Structural Verification of Model Analysis

May 2001: 120hr Sfc/500hPa Forecast Comparison Shaded: hPa thickness (dm), Black Contour: 500hPa Height (dm), White Contour: MSLP (hPa)

Caveats Guidance provided by the diagrams are only as good as the source models/analyses Often there is phase dependency on the type of data assimilation or model physics Two highly varying analyses and forecasts for the same cyclone

Sample NCEP GFS ensemble consensus and variability output from 2003

Various post-tropical lifecycles: What determines the trajectory chosen? Explosive cold-core developmentWarm-seclusion Cold-core decay Schizophrenia“ET-interruptus” Merger

Hurricane Olga (2001): 00Z 22 November AVN Forecast Fields

Subtropical Storm Ana (2003): UKMET Phase Verification

AMSU-derived Cyclone Structural Verification of Model Analysis

Summary and Ongoing Research The cyclone phase diagrams provide for a robust multi-dimensional interpretation of cyclone structural evolution, whether historical, analysis, or forecast. Their utility has been proven repeatedly over the past three years for extratropical transition, subtropical development, tropical transition, and more recently for diagnosing the structure of enigmatic cyclones (e.g. Brazil 2004). Current research seeks to utilize further the AMSU-based fields for the development of an observational cyclone phase space to accompany the model analysis/forecast CPS now available. This will enable model verification of cyclone structure and MOS-type post-processing of raw structural forecasts, leading to improved statistical guidance for structural evolution. Additional plans include utilizing ensemble approaches to arrive at quantitative measures of cyclone structural predictability. A third set of CPS ensembles (CMC) may soon be available. Finally, additional future work will utilize the cyclone phase space to augment the Atlantic tropical cyclone reanalysis project (Landsea et al. 2003), allowing for more complete definition of historical tropical cyclones.

NHC/TPC, CHC for continued critical feedback on the CPS Mark DeMaria (CIRA), John Knaff (CIRA) for the AMSU-derived fields Sim Aberson (HRD/AOML) for suggestions on ensemble approaches to cyclone structure. NCDC Historical GOES Browser for archived satellite imagery: Acknowledgments & References Avila, L., 2001: Tropical Cyclone Report: Hurricane Olga: 24 Nov. – 4 Dec Beven, J., 2002: Tropical Cyclone Report: Hurricane Michelle: 29 Oct. – 5 Nov., Beven, J., 2003: Tropical Cyclone Report: Tropical Storm Ana: April Evans, J.L. and R. Hart, 2003: Objective indicators of the extratropical transition lifecycle of Atlantic tropical cyclones. Mon. Wea. Rev.,131, Hart, R.,2003: A cyclone phase space derived from thermal wind and thermal asymmetry. Mon. Wea. Rev., 131, Landsea, C.W., C. Anderson, N. Charles, G. Clark, J. Dunion, J. Partagas, P. Hungerford, C. Neumann, and M. Zimmer, 2003: “The Atlantic hurricane database re-analysis project: Documentation for the alterations and additions to the HURDAT database.” Hurricanes and Typhoons: Past, Present, and Future. R.J. Murnane and K.-B. Liu Editors, Columbia University Press. See also