a climatological perspective

The impact of western North Pacific tropical cyclones on

Rossby Wave Packets: a climatological perspective

Julian F. Quinting1, Sarah C. Jones2

1 Karlsruhe Institute of Technology, 2 Deutscher Wetterdienst

Acknowledgment: DFG research unit Pandowae (896)

20/08/2014 - World Weather Open Science Conference [email protected] 2

MotivationResults of numerical experiments and case studies: TCs impact downstream midlatitude flow (e.g. Riemer et al., 2010; Grams et al., 2013).

Can we see a modification of Rossby wave packets from a climatological point of view?

L H

Rossby wave propagation

Extratropicalcyclogenesis

Extratropical transitionof tropical cyclone(TY Oscar, 1995)

Ridge amplification,Jet streak intensification

adapted from Archambault et al., 2013


Dataset and Methodology● Best track data of western North

Pacific and South Indian Ocean TCs undergoing ET (IBTrACS dataset)

● Period: June to November 1980 – 2010 (280 TCs), December to April 1980 – 2010 (114 TCs)

● ERA-Interim Reanalyses (6-hourly, 1° horizontal resolution)

● Synoptic scale Rossby wave packet identification via Hilbert-Transform of meridional wind at 250 hPa (Zimin et al., 2003; Glatt and Wirth, 2013)

● Monte-Carlo approach to investigate statistical significance (Martius et al., 2006)


Identification of Rossby wave packets

Filtering of meridional wind for zonal wavenumber 5 to 15.

Meridional wind (m/s) @ 250 hPa




Filtered meridional wind (m/s) @ 250 hPa

Envelope of meridional wind for zonal wavenumber 5 to 15.




Filtered meridional wind and envelope (m/s)


Clipping of envelope at certain threshold.




Filtered meridional wind and clipped envelope (m/s)



Averaging between 20 and 80°N for consecutive time steps yields Hovmöller-diagram






Averaging between 20 and 80°N for consecutive time steps yields Hovmöller-diagram

Choi Wan (2009) Sinlaku (2008)

m/s m/s


Results – RWP occurence frequency anomalytim

e

South Indian Ocean (114 ETs)

Statistically significant amplification of synoptic scale Rossby wave packet occurrence frequency...

Western North Pacific (280 ETs)

time

ET ET

-24 0.0 24 % -24 0.0 24 %-12 12 -12 12


Results – RWP amplitude anomaly

time

... and amplitude → RWP associated with ET events are stronger than RWP associated with midlatitude cyclones.

time

ET ET

-2.4 0.0 2.4 m/s -2.4 0.0 2.4 m/s-1.2 1.2 -1.2 1.2

Western North Pacific (280 ETs) South Indian Ocean (114 ETs)


Results – development vs. no development

1. Identification of cases: Computation of area that is filled by Rossbywave-Signal in statistically significant region.

2. Composite analyses for upper/lower quintile (56 TCs) of cases.

time

time

lower quintile – no RWT developmentupper quintile – RWT development

-6.0 0.0 6.0 m/s 0.0 6.0 m/s-6.0

ETET


Results – development vs. no development

Best tracks for upper/lower quintile (56 TCs) of cases.

2 PVU@250 hPa

lower quintile – no RWT development

upper quintile – RWT development


Results – Composite analysis of EKE

Local generation of EKE

(e. g. Orlanski and Sheldon, 1995)

● TC centered composites of eddy-kinetic-energy (EKE) budgets for cases with and without RWT development




9.0 16.0 9.0 16.010**5 J/m210**5 J/m2

+

++

ET-1d

ET-1d

ET-1d

ET-1d

baroclinic conversion


ageostrophic geo.-flux con.


+

-




9.0 16.0 9.0 16.010**5 J/m210**5 J/m2

+

++

ET-0d

ET-0d

ET-0d

ET-0d





+

-


Conclusions

● Western Pacific and South Indian Ocean TCs have a statistically significant impact on downstream midlatitude flow

● increase of synoptic scale Rossby wave packet occurrence frequency in downstream regions

● RWP associated with ET events are stronger than RWP associated with midlatitude cyclones.

Western North Pacific


Conclusions


● increase of synoptic scale Rossby wave packet amplitude and occurrence frequency from Western Pacific to central North America

● distinction between RWT development cases and no-RWT development cases allows to investigate physical processes that favor downstream development:

Precursor Rossby waveBaroclinic generation

and dispersion of EKE

Accumulation of EKE through convergence of ageostrophic

midlatitude flow and TC outflow

ET-2d/ET-1dTY Oscar (1995)

Development of first EKE center


Conclusions


● increase of synoptic scale Rossby wave packet amplitude and occurrence frequency from Western Pacific to central North America

● distinction between RWT development cases and no-RWT development cases allows to investigate physical processes that favor downstream development:

Precursor Rossby wave

Baroclinic generation and dispersion of EKE

Downstream flow amplification through ageostrophic geop. flux convergence

ET-0dTY Oscar (1995)

Development of downstream EKE center


● test sensitivity of Monte-Carlo approach to clipping parameter

● little impact on results of Monte-Carlo approach, but impact on absolute values of amplitude and occurence frequency

Results


Climatology of RWP


Results – composite analysis

recurvature recurvature

ET ET

a climatological perspective

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