international symposium on the whole atmosphere (iswa...

Influence of the stratospheric Quasi-Biennial Oscillation on the Madden-Julian Oscillation

during austral summer

Eriko Nishimoto and Shigeo Yoden

Kyoto University, Japan

International Symposium on the Whole Atmosphere (ISWA) @Tokyo

Day 2, Session 6: Stratosphere-troposphere coupling II

15 September, 2016

1

The Quasi Biannual Oscillation (QBO)1. Introduction

Equatorial zonal wind in the lower stratosphere (deseasoned monthly means)

Baldwin et al.

(2001)

• The QBO is a dominant interannual variation in the lower

stratosphere with the period of years.

• The QBO modulates the conditions in the UT/LS.• dU/dz

• w

• T

• Static stability (N2)

• Tropopause height

→ This can affect the tropical deep convection

Collimore et al. (2003)

W-QBO E-QBO

Tropopaus

e

2

DJF-mean OMI

E-QBO = 1.9

W-QBO = 1.3

Modulation of the austral summertime MJOby the stratospheric QBO

• Yoo and Son (2016, Geophys. Res. Lett. )

• Relationship between the MJO and the QBO was examined for each season.

• The MJO amplitude during austral summer is generally stronger

in the E-QBO phase at 50hPa than in the W-QBO phase.

1. Introduction

Correlation coefficients betweem

OMI amplitude and [U] at various p-levels.

Bold: 95% statistically significant 3

Aim of this study

• A further data analysis on the influence of the stratospheric QBO on the MJO during austral summer (DJF) for 35 years during 1979—2013.

• Two different types of composite analyses are performed in three QBO phases (E-QBO, Neutral, and W-QBO):

1. Daily composite analyses to examine the MJO evolutionby focusing on the MJO events at Phase 4

2. Conditional sampling analysesby focusing on the most active convective region of each day to examine the UT/LS conditions there

1. Introduction

Nishimoto and Yoden (2016; submitted to JAS )

“Influence of the stratospheric QBO on the MJO during austral summer”4

3-1. Time variations of the indices

marks only for DJF

W-QBO

Zonal Mean Zonal Wind at 50 hPa

N-QBO

E-QBO

Nino 3.4 Sea Surface Temperature Anomaly

Time-variations of QBO, ENSO, and MJO indices for 1979-2013

OLR-based MJO index (OMI)

Neutral-ENSO

La Nina

El Nino

marks only for DJF in the Neutral ENSO

marks only for DJF

5

Wheeler and Hendon (2004)

OMI Phase diagram


• During the E-QBO phase,

OMI amp tends to be

large in all OMI phases.

W-QBON-QBOE-QBO All-QBO

Neutral

ENSO

La Nina

El Nino

All

6

• Time evolution of the MJO is

divided into 8 phases, according

to the relationship between

PC1 and PC2 of the OMI.

Composites of the MJO time evolution in different QBO phases

3-2. daily composite analysis

• The day that satisfies � � ≥ 1 in Phase 4 is

referred as the key day.

• The composites are made for each QBO phase

for the 51-days period centered on the key day.

7

W-QBON-QBOE-QBO

Phase 4


Phase 4

key-day(★)

±25days

W-QBON-QBOE-QBO

Longitude-time sections of the composite OLR anomaly of MJO events

averaged

over 10S-10N

key-day


E-W composite difference

key-day

8

• OLR in E-QBO compared

with OLR in N-/W-QBO

• larger negative value

• prolonged period

• slower propagation

Longitude-time sections of

other variables (anomalies)ERA-interim

averaged over 10S-10N

Significant E-W

differences also exist

in other variables with

dynamical consistency.

3-2. daily composite analysis div V @UT w @MT div V @LT q @MT TRMM pr.

W-

QBO

E-

QBO

E-W

90%

Stat. sig.9

Conditional sampling analysis focusing on the most active convective region

1. Find the location of minimum OLR, �� , at each day

on the 10S-10N mean daily data in DJF during the neutral ENSO.

2. Use samples that satisfy the following conditions:

(1) �� and (2) OMI amp.

W-QBO

E-QBO

3-3. Conditional

Sampling

10

• The E-W difference of

the mean value of ��

is significant with 95%

confidence level.

Effective

sample size

E-QBO: 84

W-QBO:92

Composites of the conditional samples at ��3-3. Conditional

Sampling

statisticalsignificance

● 99%

○ 95%

・ 90%

E-W

T and N2 in UT are lower in E-QBO than in W-QBO,

i.e., favorable to develop intensive deep convection

W-QBO

E-QBO

11

conditional

samples

Unconditional

samples

Lon-height sections of the T composite of conditional samples relative to ��

3-3. Conditional Sampling

12

E-QBO

W-QBO

Kiladis et al., 2005

Zonal and vertical T

structure of the MJO

• The large-scale convective system associated

with the MJO, including a packet of equatorial

Kelvin waves

• Significant E-W differences are seen

• on the whole longitudes above 70hPa

• at �� in UT/LS

• at the east and west of �� in LT/MT

E-W

90% sig.

Summary

• Reconfirmation of Yoo and Son (2016, GRL):

• Basically larger OMI amp. in DJF in the E-QBO phase than in the W-QBO phase

• Daily composite analyses to examine the MJO evolution

• The composites made for the period centered on the key day in Phase 4

• Prolonged period, slower propagation, and more activity in the E-QBO

• Significant E-W differences in OLR, 3-D wind, moisture, and TRMM precip.

• Conditional sampling analyses over the most active convective region ��

• Daily samples satisfying the conditions: (1) � � ≥ 1 and (2) 40°E ≤ ��(�) ≤ 220°E

• More favorable condition of T, N2, and w in the UT/LS at ��

to develop deep convection in the E-QBO phase than in the W-QBO phase

• Significant E-W differences in the east and west of �� in the LT/MT,

but NOT significant around ��

4. Summary

13

14

Conditional sampling analysis focusing on the most active convective region

1. Find the location of minimum OLR, �� , for each day in DJF during the neutral ENSO.

2. Then, use samples that satisfy the following conditions:

• ��

• OMI amp.

3-3. Conditional

Sampling

10S-10N averaged OLR

20° running mean in lon.

OLR

HRC

tropopause pressure

zonal wind shear

W

E

Observational evidence of the QBO influence on tropical deep convections (1/2)

• Data analyses (Seasonal to interannual time scale)

Pacific region

• Collimore, et al. (1998, Geophys. Res. Lett.)

• Collimore, et al. (2003, J. Clim.�)

• On the relationship between the QBO and tropical deep convection for 1958–2001

• OLR in the chronically convective regions (W m-2)• highly reflective cloud (HRC) index• tropopause pressure (hPa)• 50–200hPa zonal wind shear(ms-1)

• Huang et al. (2012, Clim.Dyn.)

• Connection of stratospheric QBO with global atmospheric general circulation and tropical SST.

• Liess and Geller (2012, J. Geophys. Res.)

• Careful separation of QBO signal from ENSO and other signals.

Indian summer monsoon

• Claud and Terray (2007, J. Clim.)

• Precipitation fields

1. Introduction

15

Data and Methodology

� Indices: Jan. 1979-Dec. 2013

• QBO index: [U] at 50hPa over 10S-10N (U50), obtained from ERA-Interim

• ENSO index: SSTA at Nino 3.4 region (5S-5N, 190E-240E), obtained from HadISST v1.1.

• MJO index: OLR-based MJO index (OMI), obtained from the NOAA ESRL

� Other Datasets

• NOAA/OLR: Jan. 1979-Dec.2013

• Meteorological variables from reanalysis data: Jan. 1979-Dec.2013

• ERA-Interim: U, W, Divergence, and Specific humidity

• NCEP1: Temperature at the cold point tropopause

• TRMM precipitation: Jan. 1998-Dec.2013

2. Data

16

★: Month when a key day of MJO event is

selected (details are shown in later)

◇: Other months

3-1. Time variations of the indicesE-QBO N-QBO W-QBO

El Nino

La Nina

ENSONeutral

Scatter plot of U50 versus Nino3.4 SSTA during DJF

17

OLR-based MJO index (OMI) amplitude

Only for ENSO neutral years

divided into E-, Neutral-, and W-QBO

Colors for OMI amp≧1


★: key day of MJO event

• During DJF, OMI amp tends to be

large during E-QBO phase.

• During the other seasons, the

difference is not large.

18

Composites of the MJO time evolution in different QBO phases


• An MJO event is defined at the middle of each OMI phase for a period

with large OMI amplitude (amp≧1) in DJF during the neutral ENSO

period

key-day(★)

±25days

19

W-QBON-QBOE-QBO


Phase 4 in real space:• The active convective system is

located over the eastern Indian

ocean and the western Pacific

• Peak of the wet phase of the MJOPhase 4


20

Phase 4

20

W-QBON-QBOE-QBO

Longitude-time sections of the composite OLR anomaly of MJO events

averaged

over 10S-10N

key-day


E-W composite difference

key-day

21

• OLR in E-QBO compared

with OLR in N-/W-QBO

• larger negative value

• prolonged period

• slower propagation

Time evolution of lon-lat sections of OLR anomaly3-2. MJO composite

E-QBO

W-QBO

E-W

Climatology

22

Time evolution of lon-height sections of

specific humidity anomaly

3-2. MJO composite

-15≦t≦-5

• Upwelling with positive

humidity anomaly follows

downwelling with negative

humidity anomaly

-5≦t≦5


humidity anomaly

predominates in E-QBO

5≦t≦15


humidity anomaly preceeds

downwelling with negative

humidity anomaly 23

Time evolution of lon-lat sections of T anomaly3-2. MJO composite

at the lapse rate tropopause

24

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