Rossby waves and high impact weather

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Rossby waves and high impact weather Arwen
Twitchett and Conny Schwierz Institute of
Atmospheric Science, University of Leeds, UK
Background and motivation

• Motivation
• Wave breaking and PV Streamers have been linked
  to high impact weather such as heavy
  precipitation events (Martius et al, 2007).
• The motivation behind this research into Rossby
  waves is to understand their impact on severe
  weather, as well as to aid in the future
  predictability of the waves.
• Main Goal
• This study focuses on building a climatology of
  tracked PV streamers to analyse the triggers
  leading to the propagation of Rossby waves in
  order to improve the predictability of the waves.
  It also investigates triggers of streamer
  related heavy precipitation cases.

Streamer climatology
Streamer Tracking

• Further Work
• Assess the climatology with Hovmoeller diagrams
  to track the precursor waves back to their
  trigger point.
• Analyse triggers leading to Rossby waves for
  patterns and significance.

• Persistence of streamers
• is analysed by
• checking for vertically coherent structures
• identification and tracking of central grid point
  position of the streamer in previous and
  subsequent time steps (on 315K-330K levels)

• Data
• ECMWF ERA40 reanalysis data set from 1958 to
  2002
• Streamer climatology along 2PVU contour from
  Martius et al, 2006
• Area enclosed by 2pvu contour (with distance
  across contour of lt800km and total length of
  gt1500km) is identified as a streamer

PV _at_ 320K 09-Feb-2002 Sat 06h
Streamers and central streamer points
Heavy precipitation case studies
13 November 1996 Alps
9-15 November 2001 Mediterranean and Alps
Key
Diabatic heating, low level synoptic systems and
upper level cut offs/streamers trigger waves
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PV _at_ 320K 09-Nov-1996 Sat 00 h
PV _at_ 320K 07-Nov-2001 Wed 00 h
PV _at_ 320K 08-Nov-2001 Thu18 h
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• Heavy precipitation (fig 1) caused by streamer
  28 (fig 1, 5)
• Trigger point of wave caused by High and Low
  pressure (fig 2) intensifying at the jet
  entrance (and moving from land to ocean)

• Persistent streamer (17) (fig 1, 5) caused heavy
  precipitation
• Trigger related to Low pressure associated with
  previous streamer (9) (fig 2, 3) and upstream
  diabatic heating

PV _at_ 320K 13-Nov-1996 Wed 06 h
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Acknowledgements Olivia Martius for providing the
streamer climatology, and Heini Wernli for the
streamer identification routine.
References Martius O. Schwierz, C. Davies H.C.,
Breaking waves at the Tropopause Climatological
analyses of the orientation and
theoretical LC1/2 classification Journal of the
Atmospheric Sciences, 64, pp.2576-2592, 2007
Martius, O., E. Zenklusen, C. Schwierz, and H.
C. Davies 2006, Episodes of alpine heavy
precipitation with an overlying
elongated stratospheric intrusion A climatology.
International Journal of Climatology, 1149-1164.