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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)
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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
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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)
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Identification of Rossby wave packets
Filtering of meridional wind for zonal wavenumber 5 to 15.
Meridional wind (m/s) @ 250 hPa
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Identification of Rossby wave packets
Filtering of meridional wind for zonal wavenumber 5 to 15.
Filtered meridional wind (m/s) @ 250 hPa
Envelope of meridional wind for zonal wavenumber 5 to 15.
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Identification of Rossby wave packets
Filtering of meridional wind for zonal wavenumber 5 to 15.
Filtered meridional wind and envelope (m/s)
Envelope of meridional wind for zonal wavenumber 5 to 15.
Clipping of envelope at certain threshold.
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Identification of Rossby wave packets
Filtering of meridional wind for zonal wavenumber 5 to 15.
Filtered meridional wind and clipped envelope (m/s)
Envelope of meridional wind for zonal wavenumber 5 to 15.
Clipping of envelope at certain threshold.
Averaging between 20 and 80°N for consecutive time steps yields Hovmöller-diagram
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Identification of Rossby wave packets
Filtering of meridional wind for zonal wavenumber 5 to 15.
Envelope of meridional wind for zonal wavenumber 5 to 15.
Clipping of envelope at certain threshold.
Averaging between 20 and 80°N for consecutive time steps yields Hovmöller-diagram
Choi Wan (2009) Sinlaku (2008)
m/s m/s
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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
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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)
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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
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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
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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
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Results – Composite analysis of EKE
lower quintile – no RWT developmentupper quintile – 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
baroclinic conversion
ageostrophic geo.-flux con.
ageostrophic geo.-flux con.
+
-
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Results – Composite analysis of EKE
lower quintile – no RWT developmentupper quintile – RWT development
9.0 16.0 9.0 16.010**5 J/m210**5 J/m2
+
++
ET-0d
ET-0d
ET-0d
ET-0d
baroclinic conversion
baroclinic conversion
ageostrophic geo.-flux con.
ageostrophic geo.-flux con.
+
-
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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
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Conclusions
● Western Pacific and South Indian Ocean TCs have a statistically significant impact on downstream midlatitude flow
● 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
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Conclusions
● Western Pacific and South Indian Ocean TCs have a statistically significant impact on downstream midlatitude flow
● 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
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● 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
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Climatology of RWP
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Results – composite analysis
recurvature recurvature
ET ET