Aspects of Dynamical Processes and Aspects of Dynamical Processes and Predictability in Medium Range Forecasts Predictability in Medium Range Forecasts

of High Impact Weatherof High Impact Weather

Edmund K.M. ChangEdmund K.M. ChangSchool of Marine and Atmospheric SciencesSchool of Marine and Atmospheric Sciences

Stony Brook UniversityStony Brook UniversityStony Brook, New York, USAStony Brook, New York, USA

WWRP/THROPEX HIW WorkshopKarlsruhe, Germany

March 18, 2013

Alternative TitleAlternative Title

Some thoughts on predictability and Some thoughts on predictability and dynamical processes dynamical processes – Using Rossby Wave Trains (RWTs, or Using Rossby Wave Trains (RWTs, or

baroclinic wave packets) as an illustrative baroclinic wave packets) as an illustrative exampleexample

From THORPEX International Science Plan(Shapiro and Thorpe, 2004)

Cyclogenesis near Japan

Flooding over Europe

Dundee Satellite Station: 1241 UTC 11 Aug. 2002Dundee Satellite Station: 1241 UTC 11 Aug. 2002

France

Italy

The StormThe Storm

Courtesy of Mel Shapiro

Dresden GermanyDresden Germany

Courtesy of Mel Shapiro

THORPEX Research Objectives:THORPEX Research Objectives:

Investigate the evolution of dynamical and Investigate the evolution of dynamical and physical processes and their influence on physical processes and their influence on forecast skillforecast skill– The skill of forecast systems in predicting Rossby The skill of forecast systems in predicting Rossby

wave properties (amplitudes, ray paths, group wave properties (amplitudes, ray paths, group velocities …)velocities …)

– The initiation of Rossby wave trains by various The initiation of Rossby wave trains by various processes (tropical convection, extratropical cyclones, processes (tropical convection, extratropical cyclones, large-scale topography …)large-scale topography …)

– The initiation of tropical convection by Rossby wave-The initiation of tropical convection by Rossby wave-trains propagating into the tropicstrains propagating into the tropics

From Shapiro and Thorpe (2004)

Examples of progress since 2004Examples of progress since 2004

New techniques developed to highlight New techniques developed to highlight RWTsRWTs

Zimin et al. (2006): Extracting envelopes of nonzonally propagating Rossby Wave Packets

Martius et al (2006): A refined Hovmoller diagram:- Hovmoller diagram constructed following the 2 PVU PV contour instead of along a fixed latitude band

Linkage between RWTs and high impact Linkage between RWTs and high impact weather events strengthenedweather events strengthened

Martius et al (2008)- Wave packet signal precedes Alpine heavy precipitation events, especially in SON and DJF

0

Chang (2005): RWT signal traced back to Asia at least 3 days prior to strong cyclone events over NW Pacific

Eichorn and Wirth (2013):- RWT signal traced back to Northeastern Pacific at least 6 days prior to strong cyclone events over central Europe- Presence of RWT over NE Pacific significantly enhance probability of strong cyclone over Europe 6 days later

Eichorn and Wirth (2013)

Characteristics of RWTs examinedCharacteristics of RWTs examined

Glatt et al. (2011): Used Hovmoller diagrams to examine multiple processes associated with RWTs

ET vs. Winter Rossby Waves (Torn and Hakim 2013)ET vs. Winter Rossby Waves (Torn and Hakim 2013)- composites based on 112 ET and 281 winter cyclones- composites based on 112 ET and 281 winter cyclones

Amplitude

Linkage suggested between RWTs and Linkage suggested between RWTs and growth of uncertainties in medium range growth of uncertainties in medium range EPSEPS

From Zheng et al. (2013)

Majumdar et al. (2010):- “… distinctive targets could be traced upstream near Japan at lead time of 4-7 days. In these cases, the flow was predominantly zonal and a coherent Rossby wave packet was present over the northern Pacific Ocean.”

Zheng et al. (2013):- Used ensemble sensitivity analysis to study U.S. east coast snowstorm on 26-28 December 2010- Sensitivity signal developed and propagated across the Pacific accompanying the development and propagation of a RWT

Analysis of V300

Sensitivity signal

Many issues still remain:Many issues still remain:Process Studies:Process Studies:– Initiation? Dissipation?Initiation? Dissipation?– What physical processes control propagation, duration, What physical processes control propagation, duration,

coherence, amplitude, frequency?coherence, amplitude, frequency?– How do atmospheric low frequency variability impact How do atmospheric low frequency variability impact

RWTs?RWTs?– How do RWTs impact low frequency variability?How do RWTs impact low frequency variability?

Forecast Science:Forecast Science:– How well do our forecast models predict RWTs?How well do our forecast models predict RWTs?– Do (How do) more accurate forecasts of RWTs transfer Do (How do) more accurate forecasts of RWTs transfer

to better forecasts of high impact weather events?to better forecasts of high impact weather events?– Does the growth of a significant RWT imply increased or Does the growth of a significant RWT imply increased or

decreased predictability downstream?decreased predictability downstream?– Are RWTs initiated by ET less predictable?Are RWTs initiated by ET less predictable?

SERA:SERA:– Can we quantify the socio-economical impacts of RWTs?Can we quantify the socio-economical impacts of RWTs?

Challenges:Challenges:– It is difficult to define RWTs exactly (Glatt et It is difficult to define RWTs exactly (Glatt et

al. 2011)al. 2011)– An objective climatology of RWTs is still An objective climatology of RWTs is still

lackinglackingNeed objective identification and trackingNeed objective identification and tracking

Glatt et al. (2011):RWT object identification based on Hovmoller diagram

Example of objective tracking results (Courtesy Matt Souders)Jan 29 – Feb 12, 2009: Focus on packet number 107

An objective tracking algorithm has been developed at SBU

Ongoing research at SBU:Ongoing research at SBU:

– Process studies:Process studies:Climatology and variabilityClimatology and variability

Links to low frequency variabilityLinks to low frequency variability

Dynamics of growth and decayDynamics of growth and decay

……

– Forecast Science:Forecast Science:Verify and calibrate ensemble forecasts of RWTsVerify and calibrate ensemble forecasts of RWTs

Links to forecast uncertainty and error growthLinks to forecast uncertainty and error growth

……

Challenges (continued)Challenges (continued)

Multiple scales in space and timeMultiple scales in space and time

Time/Longitude: 250-mb Meridional Wind (m s-1); 55-40N.

Oct. 12

Oct. 18

Oct. 24

Nov. 3

Cal.Japan W. Africa

Courtesy Mel Shapiro

Synoptic-scale phase velocity

Time-mean planetary-waves

Wave-train group velocity

Courtesy Mel Shapiro

Short-range

Medium-range

Sub-seasonalto

Seasonal

Rodwell et al (2013)

- ECMWF large error forecasts over Europe associated with errors in convective heating over central U.S. which acts to slow the progression of the RWT

Multiple scales (continued)

Forecast verificationForecast verification– Object (process) oriented forecast verification?Object (process) oriented forecast verification?

Cyclones (Froude et al. 2007, 2009, 2010)Cyclones (Froude et al. 2007, 2009, 2010)

RWTs (or any other object or process)RWTs (or any other object or process)– Need to identify model errors and biases in forecasting Need to identify model errors and biases in forecasting

dynamical processesdynamical processes

– HIW? How (and what) to verify?HIW? How (and what) to verify?Especially in the medium rangeEspecially in the medium range

Verification of impact?Verification of impact?

Challenges (continued)

Opportunities (THORPEX and legacy)Opportunities (THORPEX and legacy)International field campaigns (e.g. International field campaigns (e.g. TNAWDEX)TNAWDEX)

Availability of high quality data for PDP Availability of high quality data for PDP researchresearch– State of the art reanalysisState of the art reanalysis– TIGGETIGGE– Reforecast – multi-model multi-ensemble?Reforecast – multi-model multi-ensemble?– Develop effort parallel to CMIP?Develop effort parallel to CMIP?

Basically free and unrestricted availability of data Basically free and unrestricted availability of data for broad research communityfor broad research community

Broad participation by international community Broad participation by international community (including data providers and data users)(including data providers and data users)