the modulation of tropopause- level wave breaking by the madden julian oscillation richard moore 1,...

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