An EventBased JetStream Climatology

1
An Event-Based Jet-Stream Climatology

• Patrick Koch1, Heini Wernli2 and Huw C. Davies1
• 1 Institute for Atmospheric and Climate Science,
  ETH Zürich, Switzerland
• 2 Institute for Atmospheric Physics, University
  of Mainz, Germany
• pkoch_at_env.ethz.ch

2
Motivations
Potential vorticity, potential temperature and
zonal wind
5W
J1
J1
J2
J3
Pressure hPa
Latitude
Winter Mean ERA15
3
Plan

• Data set
• Methodology
• Deep and shallow layer baroclinicity
• Single and double jets
• Conclusions and further applications

4
1. Data Set

• ERA15 re-analysis data set
• 6-hourly available from Jan. 1979 to Dec. 1993
• Interpolated on a regular lat/long grid with 1
  resolution

5
2a. Methodology
avel

• Horizontal wind speed vertically averaged in the
  100-400 hPa layer (avel)
• Search for gridpoints having an avel larger than
  30 m/s.
• Time and position recorded.

00 UTC, 3 January 1979
6
2b. Methodology
Jet Events Winter Climatology


180E
0
NH
SH
0
180E
Northern Hemisphere
Southern Hemisphere
See also Plate D in Barry and Chorley (2003)
7
3a. Jets and storm tracks?
Winter jet event climatology
Surface cyclone frequency


180E
180E
NH
0
0
Wernli and Schwierz (2004)
8
3b. Deep and shallow layer baroclinicity

• Calculate the ratio R(V200-V500)/V200
• For a linear vertical profile, R0.375
• Here, threshold value for R 0.4

9
3b. Deep and shallow layer baroclinicity


0
180E
NH
SH
Deep layer baroclinicity (Rlt0.4)
0
180E


0
180E
NH
SH
Shallow layer baroclinicity (Rgt0.4)
subtropical jet??
0
180E
10
3c. Deep and shallow layer baroclinicity


0
180E
NH
SH
Deep layer baroclinicity (Rlt0.4)
polar-front jets??
0
180E


0
180E
NH
SH
Surface Cyclone Frequency
180E
0
11
4a. Single and Double Jets
Identification
JT J1 J2 JREST
12
4b. Single and Double Jets


0
180E
NH
SH
Single Jet
180E
0


180E
0
NH
SH
Double Jet
0
180E
13
4c. Single and Double Jets
Vertically Averaged Potential Vorticity (150-500
hPa)composites
pvu
pvu
0
180E
NH
SH
Single Jet
180E
0
pvu
pvu
180E
0
NH
SH
Double Jet
0
180E
14
4d. Single and Double Jets
Potential vorticity, potential temperature and
zonal wind composites
NH, 0
SH, 180E
pvu
pvu
Single Jet
Pressure hPa
Latitude
Latitude
NH, 0
SH, 180E
pvu
pvu
Double Jet
Pressure hPa
Latitude
Latitude
15
5. Conclusions and Further Applications

• 15-year jet-stream climatology based on events
• Identification of deep and shallow layer
  baroclinicity
• Identification of single- and double-jet events

• Study of jet event patterns relative to NAO,
  PNA, etc
• Case studies of single- or double-jet events
• Study of the transition single/double jet
• Use of the 40-year ERA40 data set

16
Thank You !
17
4e. Single and Double Jets
m/s
m/s
0
180E
180E
0
m/s
m/s
180E
0
0
180E