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
3-1. Time variations of the indices
• 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
Wheeler and Hendon (2004)
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
3-2. daily composite analysis
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
3-1. Time variations of the indices
★: 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
3-2. daily composite analysis
• 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
Wheeler and Hendon (2004)
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
3-2. daily composite analysis
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
3-2. daily composite analysis
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
• Upwelling with positive
humidity anomaly
predominates in E-QBO
5≦t≦15
• Upwelling with positive
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