the modulation of tropopause- level wave breaking by the madden julian oscillation richard moore 1,...
TRANSCRIPT
The Modulation of Tropopause-level Wave Breaking by the Madden Julian Oscillation
Richard Moore1, Olivia Martius2, Thomas Spengler2 & Huw Davies2
Motivation
Average MJO Phase Shading: anomaly from DJF average
250 hPa Wind Velocity 500 hPa Height
Quantitatively assess the behavior of wave breaking that accompanies the observed flow anomalies
Roadmap
• Ingredients of analysis
• Briefly outline the climatological response of WB to MJO forcing
• Combine climatological and case study viewpoints to gain further insight
• Simplify and summarize via a ‘Cartoon’ interpretation of observed evolution
Data & Methodology
• ERA-40 Re-Analysis Data for NH Winter from 1979-2002:
• Wave breaking (Wernli & Sprenger 2007; Martius et al. 2007)
• Surface cyclone frequency (Wernli et al. 2006)
• Atmospheric blocking frequency (Croci-Maspoli et al. 2007)
• 10 MJO Indices (Climate Prediction Center)Combine a climatological and case-study
analysis of the response to MJO forcing
“The basic criterion for saying whether a wave of any kind is breaking is whether material contours and surfaces are being irreversibly deformed rather than simply undulating back and
forth as is assumed in linear wave theory”
McIntyre and Palmer 83
Extratropical Wave Breaking
PV on 325K January 2007 troposphere, low PVtroposphere, low PV
stratosphere, high PV
Synoptic Scale Rossby Wave Breaking
‘Lifecycle’ Separation of Wave Breaking (WB) Events
cyclonic life-cycle in cyclonicshear
anticyclonic life-cycle in anti-cyclonic shear
Thorncroft et al. 93
jet
jet
Dynamical Tropopause
LC1, AC
LC2, CLC1/LC2 wave breaking in ERA-40: Martius et al. 2007
Wave Breaking Frequency: 1979-2002 DJF
Cyclonic (LC2) on 310 K Anticyclonic (LC1) on 330 K
PV on 320KSLP
strong convective activityalong eastern flank
formation of low pressure systems
L
Floods in Algeria November 2001
cyclonic windfield which can reach the surface
wind on 850hPa
precipitation
IR meteosat
Links to Severe Weather
Massacand et al. 98, 01
Alps
PV-streamer
wind field sea
sea
tropopause
Links to Severe Weather
Gondo October 2000
A disruption in the midlatitude westerlies due to the presence of a quasi-stationary high pressure system
TP
Z
Atmospheric Blocking
- PV Anomaly
Cyclonic WB
Anomalies
Average for MJO Phase Shading: anomaly from DJF average
MJO INDEX 3 (120E) MJO INDEX 7 (40W)
Cyclonic WB on 310 K
WB Anomalies: Overview
• Statistically significant anomalies are prevalent
• Dynamical distinction between baroclinic lifecycles is instructive
• Strong anti-correlation, fairly rapid transition between anomalies of opposite sign
Cyclonic WB on 310 K
Anticyclonic WB on 340 K
Outstanding Questions
What is the relationship between the tropical convection and the observed jet – wave breaking anomalies?
Might wave breaking be integral to the observed evolution?
Direct Impact of MJO Convection
Shading: Daily Mean OLR
Streamfunction Anomaly
POS NEG
January 16, 1993
upper-level anticyclone: shifts jet to the north;
local jet intensification
Jet / WB Structure
• Predisposition to anticyclonic lifecycle
• Weak waveguide in central Pacific coincides with anticyclonic WB
• WB locally shifts jet north
+-
+-+
250 hPa Velocity
Anticyclonic WB
12Z January 16, 1993
2 PVU on 310 K2 PVU on 330 K2 PVU on 350 K
Shading: instantaneous 250 hPa velocity
Jet / WB Structure
• Cyclonic WB in west-central Pacific on northside of locally-enhanced jet
• baroclinic instability?
250 hPa Velocity
Cyclonic WB
+-
12Z January 28, 1993
Jet / WB Structure: Index 7 (40W)
• Eastward extended, zonal jet – strong waveguide
• Southward shift over Asia – cyclonic lifecyle
• WB shifts jet southward
+-
12Z February 5, 1993
-+
-
3 (120E)4 (140E)5 (160E)6 (120W)
WB and PNA-like signal
Average MJO Phase Shading: anomaly from DJF average
500 hPa Height Cyclonic WB on 310 K
MJO Index: 7 (40W)
Anticyclonic WB
Anomalies
Average for MJO Phase Shading: anomaly from DJF average
MJO INDEX 3 (120E) MJO INDEX 7 (40W)
modulation of sub & extratropics
Northward shifted jet over Asia
Anticyclonic WB in central Pacific
Double jet structure Enhanced blocking
frequency in central Pacific
modulation of sub & extratropics
Pattern shifts east Cyclonic WB ensues
on northside of zonally, locally-strong jet
Surface cyclone often co-located in time and space with cyclonic wave breaking event
LC2 wave breaking leads to quick transition of PNA
modulation of sub & extratropics
Single jet extended to the east, southward shift over Asia
Cyclonic WB (surface cyclones) eastern Pacific in jet exit region
Subsequent to this time, in absence of MJO convection the jet breaks down and retreats westward
Questions?
http://www.met.reading.ac.uk/~pete/
MJO Indices
http://www.cpc.noaa.gov/products/precip/CWlink/daily_mjo_index/mjo_index.html
based on 200 hPa velocity potential
Anticyclonic WB
Anomalies
Average for MJO Phase Shading: anomaly from DJF average
MJO INDEX 3 (120E) MJO INDEX 7 (40W)
LC1,AC
instantaneous field
Shading: anomaly from DJF average
LC2,C
instantaneous field
Shading: anomaly from DJF average
Jet Structure
MJO forcing changes jet
strength, meridional & longitudinal
location
+ anomaly
- anomaly
250 hPa Jet:
Surface Cyclone FrequencyMJO Index 3 MJO Index 7
@
@
- anomaly+ anomaly
What is the MJO?
• Dominant source of tropical intraseasonal variability
• Large-scale coupled patterns in deep convection & atmospheric circulation
• Characteristics: – Zonal scale ~ 12-20K km
– Eastward propagation ~ 5 m/s
– Lifecycle ~ 48 days
http://www.met.reading.ac.uk/~pete/
Wave Breaking Frequency: 1979-2002 DJF
Cyclonic (LC2) on 310 K Anticyclonic (LC1) on 330 K