mike fiorino michael.fiorino@noaa assimilation and modeling branch global systems division

M. Fiorino :: 63M. Fiorino :: 63rdrd IHC St. Petersburg, FL 20000304 IHC St. Petersburg, FL 20000304

Recent trends in dynamical medium-Recent trends in dynamical medium-range tropical cyclone track range tropical cyclone track

prediction and the role of resolution v prediction and the role of resolution v physics in the ECMWF modelphysics in the ECMWF model

Mike [email protected]

Assimilation and Modeling BranchGlobal Systems Division

Earth System Research LaboratoryBoulder, CO

4 March 2009


Why medium-range (72-h) track?Why medium-range (72-h) track?

Operational – long-range warning is a Operational – long-range warning is a medium-range track problemmedium-range track problem no skill vis-à-vis CLIPER in early 1980s high skill is required for using improved dynamical

intensity guidance – I can’t believe a rapid intensification forecast if the track doesn’t make (physical) sense…

Modeling (& HFIP)Modeling (& HFIP) analysis v model error – 72 h is when model errors become

dominant multi-scale dynamics – synoptic scales dominate, but

vortex scales can have large impacts closely follows tropical wind score

MRT is the 500 mb 5-d Anomaly MRT is the 500 mb 5-d Anomaly Correlation score of the tropicsCorrelation score of the tropics


The importance of modeling…The importance of modeling…

POD of NHEM TC in reanalysis v

operations

improvement in 1989 from physics change,

ditto for degradation in 1994…

TC POD

850 mb tropical wind scoretime when the correlation of forecast and

analysis vector wind drops to 70%


OBS (not) OBS (not) critical to TC analysis?critical to TC analysis?

POD of “TC” in reanalysis v operationsPOD of “TC” in reanalysis v operations ERA-15 uses model physics circa 1994 and

achieves 1994 operational model POD throughout the 1979-1994 period

TC POD TC POD follows follows the tropical wind scorethe tropical wind score… … and the and the tropical wind scoretropical wind score follows the follows the physics…physics… score improves from 1–7 d when score reaches 3-4 d, global models began

showing MRT skill

model of 1model of 1stst order importance in analysing order importance in analysing the 1the 1stst order TC vortex order TC vortex


History of Atlantic MRT (72-h) MFE – Models v CONHistory of Atlantic MRT (72-h) MFE – Models v CON

CLIPER trend? better databaseserror cut in half from ~ 280 130 nm 1990s-> 2008BCON better than modelsOFCL ~ BCON

CLIPER trend? better databaseserror cut in half from ~ 280 130 nm 1990s-> 2008BCON better than modelsOFCL ~ BCON

SKILL– percent improvement over the no-skill baseline aidCLIPER (climatology and persistence)

medium-range track (72-h) mean forecast error – two models UKMO (global) and GFDL (limited-area) with long history v ‘best’ or baseline consensus (BCON) 1992-2008

higher skill in 2008 even though CLIPER error increased UKMO and GFDL models did very well in 2008….higher skill in 2008 even though CLIPER error increased UKMO and GFDL models did very well in 2008….


Atlantic %gain(+)/loss(-) v BCON Atlantic %gain(+)/loss(-) v BCON context for ECMWF context for ECMWF

results:results: 2008 a good year

for the models in the LANT

models typically 20-25% worse than BCON in all basins, but more so in WPAC


ECMWF resolution v physics changesECMWF resolution v physics changes

2005-2008 model changes1) increase in horizontal resolution from T511 T799 (4020 km) 2006022) “significant changes to model physics” on 20071106, including new formulation of “convective entrainment and relaxation time scalesTropical wind scores nearly constant


ALL TCs – % improvement over BCONALL TCs – % improvement over BCON

MRT TC skill difference greater than change in tropical wind scoreincreased resolution (red v orange) improves 72-120 h errorphysics change improves forecast at all timesskill relationship (physics > res) consistent between basins, but stronger signal in WPAC and SHEM, more muted in LANT

MRT TC skill difference greater than change in tropical wind scoreincreased resolution (red v orange) improves 72-120 h errorphysics change improves forecast at all timesskill relationship (physics > res) consistent between basins, but stronger signal in WPAC and SHEM, more muted in LANT

ECMWF is 20% better than BCON when most models are 20% worseat the medium range (72 h)

ECMWF is 20% better than BCON when most models are 20% worseat the medium range (72 h)


SummarySummary

ECMWF has shattered both TC MRT ECMWF has shattered both TC MRT predictability limit predictability limit from the 1990s (~130 from the 1990s (~130 nm); the skill of nm); the skill of consensus;consensus; and the (old) and the (old) PACOM PACOM (50, 100) 150 nm (50, 100) 150 nm requirementrequirement

Updated results as of 20090303 in SHEM Updated results as of 20090303 in SHEM (TC activity ~ 54% below normal) 72-h (TC activity ~ 54% below normal) 72-h MFE: MFE: CONW – 158 nm ECMWF – 108 nm +32% gain over BCON; 61 cases


My personal (biased) takeaways…My personal (biased) takeaways… How ECMWF achieved these results is of How ECMWF achieved these results is of

fundamental importance to HFIP…fundamental importance to HFIP… improved TC v synoptic-scale forecast?

deterministic (hi-res) v ensemblesdeterministic (hi-res) v ensembles can ensembles work until the model(s) achieves

the same skill as ECMWF? no, physics 1st

TC vortex analysisTC vortex analysis 1st order structure (assimilate the “working best

track”) 1st;detailed, hi-res obs 2nd

global v limited-area modelsglobal v limited-area models when do errors the global-scales become

significant? ~ 36 h

mike fiorino michael.fiorino@noaa assimilation and modeling branch global systems division

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