Propagating and Non-Propagating MJO Events
over Maritime Continent
Tim Li and Jing Feng
University of Hawaii
Feng, J., T. Li, and W. Zhu, 2015: Propagating and Non-Propagating MJO Events
over Maritime Continent, J. Climate, in press.
WMO: Seamless weather-climate prediction (S2S project)
Courtesy of Duane Waliser
ACC
PDO
ENSO
ISV
50%
Weather
100%
Normalized Useful Predictability (%)
A gap between weather (< 1 week) and climate (monthly, seasonal) prediction
 Extended-Range (10-30天) Forecast (ERF)
Major Predictability Sources of ERF:
 Madden-Julian Oscillation (MJO) or
Atmospheric Intraseasonal Oscillation (ISO)
in general
International Field Campaign: DYNAMO/CINDY (Oct 2011 - Jan 2012)
Objective: Understand MJO convection initiation mechanism
Left: Time-longitude section of
unfiltered rainfall field along the equator
(averaged at 10S-10N)
Top: 3-hourly intensive observational
sites (two ships, island stations)
Role of PBL moisture asymmetry in MJO eastward propagation
MJO equivalent potential temperature
From Benedict and Randall (2007)
unstable
stratification
Stable stratification
MJO convection
Convective instability index:
e1000~850hPa  e500~ 400hPa
 PBL moistening causes convectively unstable
stratification ahead of MJO convection
Hsu, P.-C., and T. Li, 2012: Role of the boundary layer moisture
asymmetry in causing the eastward propagation of the MaddenJulian Oscillation. J. Climate, 25 (14), 4914-4931
Issues on MJO propagation:
• column integrated MSE (moisture
mode theory)
• role of horizontal advection
• role of eddy moisture transport
• effect of PBL convergence
5
Moisture and MSE profiles
A vertically integrated MSE tendency equation
was often used to study MJO propagation
mechanism. Note that the column-integrated
MSE is approximately in phase with midtropospheric specific humidity anomaly and MJO
convection center.
• Why a symmetric MSE (relative to convection)
favor eastward propagation?
For given an eastward-propagating system, any variables (say, Y) have an eastward
tendency. Thus, an eastward tendency does not necessarily mean that this
variable would play a critical role in propagation.
Y(t0)
Y(t1)
X
Y=Y(t1 )-Y(t 0 )
X
Vertical Profile of Specific Humidity
What causes maximum mid-tropospheric moisture anomaly ?  due to
vertical advection by MJO convection. Imagine if no moisture tilting in PBL,
vertical integrated SH or MSE would be exactly in phase with MJO
convection. In this case, SH or MSE would be symmetric about the convection
(no east-west asymmetry); why does the system move eastward?
The observed slight phase leading of column integrated MSE is attributed
to PBL moisture leading. Therefore, essential physics that cause the
eastward propagation is attributed to zonal asymmetry of PBL SH or MSE.
What causes the zonal asymmetry of PBL SH?
q'/ t  (V q)'  (q / p)'  Q2 '/ L sum
Hsu and Li, 2012,
J. Climate
MJO convection
Issues on Role of Horizontal Advection and Eddy Moisture Transport
Maloney (2009) analyzed moisture budget at 155oE in NCAR CAM3
 Horizontal advection dominates the MJO moisture budget
 Eddy has a large (~50%) contribution to the advection term
Hsu and Li, 2012, JC
Low-level easterly flow to east of
convection  suppressed eddy
activity  suppressed dry air mixing
from extratropics  moistening
(V q)'
(V  q' )' (V '  q)' (V ' q' )' (V*  q* )'
WIO
-6.5
27.8
-2.5
-2.2
EIO
MC
3.5
-1.2
3.8
13.4
2
5.0
-1
0.9
WP
-6.0
8.0
-0.6
-5.4
Hsu, Li et al. 2014, JC
q'/ t  (V q)'  (q / p)'  Q2 '/ L sum
Motivation: MJO Variability over Maritime Continent
Propagating and Non-Propagating MJO Events over Maritime Continent
20-90-day filtered OLR composites along the equator during 1979- 2008
Propagating MJO Events across Maritime Continent
Hovmöller diagrams of 20-90 day filtered OLR anomaly averaged over 10S-10N for
two groups (with and without positive OLR anomaly to the east of MJO convection)
What is the role of小结
positive OLR anomaly
to east of MJO convection center?
Kim et al. (2013): moistening lower-mid troposphere in
front of the MJO convection via anomalous meridional
advection
Science Questions:
 Why some MJO convective events can propagate eastward across the
maritime continent (MC) but others cannot. What is the critical
difference between the eastward propagating (EP) and non-propagating
(NP) MJO events ?
 For the eastward propagating (EP) events, some are accompanied
with a strong positive OLR anomaly to east of the MJO convection but
others are not. What is the difference in moisture profile ahead of MJO
convection? What are fundamental factors regulating MJO propagation
across the MC?
Data
 q, u, v, ω from ERA-interim Reanalysis
 Daily OLR from NOAA with 2.5x2.5 spatial resolution
We focus on northern winter period (Nov. ~ Apr.) for 1979-2008
Method
 Lanczos filtering
 Moisture budget analysis
 EOF analysis, Composite analysis
Moisture equation
Q
q
q
 V  q  
 2
t
p
Lv
(1)
To investigate the intraseasonal moisture tendency, a 20-90-day band-pass filter operator may
be applied to equation (1) (Hsu and Li, 2012) as following
(
Q
q
q
) '  (V  q) ' (
) ' ( 2 ) '
t
p
Lv
(2)
To examine specific advective processes responsible for the intraseasonal moisture change,
the dependent variables such as q, u ,v, ω were decomposed into three components, the
longer than 90-day low-frequency background mean state, the 20-90-day MJO component,
and the less than 20-day higher-frequency component:
A  A  A'  A*
(3)
The three components of all the variables can be substituted into equation (2) so that each
advection term can be separated into 9 terms. By comparing each of the nine terms, one
can reveal major processes that cause the intraseasonal moisture change.
(4)
Question 1:
Why some MJO convective events can propagate eastward
across the maritime continent (MC) but others cannot. What is
the critical difference between the eastward propagating (EP)
and non-propagating (NP) MJO events ?
MJO Case Selection
Because 20-90-day filtered OLR field has a maximum variance center over
equatorial Indian Ocean (75E-100E,10S-5N), we select this box as a reference
region.
Step 1: Selected MJO cases based on the 20-90-day filtered OLR at the reference
box. The criterion is that the OLR anomaly is stronger than -1.0 STD. The time of
minimum OLR anomaly was defined as Day 0.
Step 2: Plot the Hovmöller diagrams of the filtered OLR anomaly from day -20 to
day 25 days averaged over 10S-10N.
Step 3: Eastward Propagating NJO case was defined when the OLR contour of -10
W/m2 continuously passed over 120E without any interruption or gap. NonPropagating case was defined when the contour of -10 W/m2 shows continuous
eastward propagation within the equatorial IO but stops before approaching
120E.
Propagating and Non-Propagating MJO Events over Maritime Continent
Fig. 20-90day filtered OLR and V850
Specific Humidity Vertical Profiles and Evolution for EP and NP
The vertical-longitude
cross sections of 20-90day filtered specific
humidity from day -10
to day 20 for a) EP and
b) NP composite.
Black box denotes the
position of convective
center on the day 0.
Red solid line denotes
120E.
Westward-propagating dry signal in non-propagating composite
A
A
A
A
A
A
The evolution of composite 20-90-day
filtered specific humidity (shaded, unit:
0.001 g·kg-1) averaged from 700 to 850
hPa and filtered 850hPa wind field (unit:
m·s-1) from day 0 to day 15 derived from
11 NP case composite .
A further analysis shows that the
westward propagating signal is equatorial
Rossby wave at time period of 10-30 days
and zonal wave number 3-10.
Symbol “A” denotes anomalous anticyclonic circulation. Red color denotes
dry signal.
A
A
Vertically-integrated Moisture and MSE Budget Analysis (Day 5-10 average)
(TOP) 20-90-day filtered
OLR and 850hPa wind
fields
(Bottom) Column (1000250hPa) integrated (a)
specific humidity
tendency and (b)
anomalous vertical
advection terms
averaged in the region
of 130E-170E, 10S-10N
at day 5-10 for EP (red
bar) and NP (blue bar)
composite
Moisture budget analysis (cont.)
Column (1000250hPa) integrated
(top) moisture
budget terms,
(middle) horizontal
advection terms, and
(bottom) zonal
component of
horizontal advection
term averaged in the
region of 130E - 170E,
10S-10N at day 5-10
Propagating and Non-Propagating MJO Events over Maritime Continent
(Top) Column (1000250hPa) integrated ucomponent of horizontal
advection term averaged
in the region of 130E 170E, 10S-10N at day 5-10
for NP composite
(Bottom) (a) The background mean wind (unit: m·s-1) and 20-90-day filtered specific humidity (unit: kg·kg-1·104) at
600-750 hPa and (b) 20-90-day filtered wind (unit: m·s-1) and the background mean specific humidity (unit: kg·kg1·104) at 600-750 hPa averaged at day 5-10 for NP composite.
Significance Tests between EP and NP Group
Table 1 Monte Carlo Test for 20-90-day anomalies of OLR, qtend and q Index
averaged during the 5-10th day in 10S-10N,130-170E
OLR’
qtend’
q’
Samples Number
Samples Number
Samples Number
14-46
14-46
14-46
Confidenc
e Interval
[-4.1,4.1]
DIFF
Confidence
Interval
DIFF
Confidence
Interval
DIFF
6.3
[-14.9,14.8]
-29.1
[-77.4,73.7]
-167.7
95% confidence Interval of difference between two samples for 105 times roundly
sampling. The red bold number denotes that the difference is statistically significant.
Conclusion: What causes the difference in propagating and non-propagating cases?
The observed OLR and ERA-I data during 1979-2008 were analyzed to reveal
fundamental differences between eastward-propagating (EP) and nonpropagating (NP) MJO events across the maritime continent (MC).
When the maximum MJO convection arrives near 120E, a positive
moisture tendency lies in a longitudinal zone (130E-170E, 10S-10N) for the
EP cases, whereas a negative tendency appears for the NP cases. In the latter
cases there are clearly detectable westward-propagating Rossby-wave dry
signals over the equatorial central-western Pacific. The dry Rossby Wave
signal hindered the development of new convection to the east of MJO
convection center, preventing the MJO across MC.
A moisture budget analysis shows that the positive tendency of specific
humidity in the EP composite is mainly attributed to anomalous vertical
advection (i.e., advection of mean moisture by intraseasonal ascending
anomaly), whereas the negative tendency in the NP composite arises from
anomalous horizontal advection associated with westward-propagating dry
signal.
Question 2:
For the eastward propagating (EP) events, some are
accompanied with a strong positive OLR anomaly to east of
the MJO convection but others are not. What is the
difference in moisture profile between the two cases? Do
the same processes contribute to MJO propagation in the
two groups?
An index representing the strength of OLR anomaly to the east of MJO convection
The scatter plot of the MJO
convection index and the
suppressed index for all 46
EP cases. The upper (lower)
red line denotes the
suppressed OLR index
greater (less) than a half
(negative a half) standard
division (unit: W·m-2).
They are called the EPStrongly Suppressed cases
and the EP Weakly
Suppressed cases.
EP Strongly Suppressed (EP-SS) and EP Weakly Suppressed (EP-WS) Case Composite
Hovmöller diagrams of 20-90 day filtered OLR anomaly averaged over
10° S-10° N from day -20 to day 25 for a) EP-WS and b) EP-SS
composite. (unit: W·m-2)
Evolution of 2D 20-90-day filtered OLR (unit: W·m-2) and 850hPa wind (unit:
m·s-1) from day -10 to day 10 for a) EP-WS and b) EP-SS composite.
Moisture and Moisture Tendency in EP-WS (left) and EP-SS (right) Cases
(Top) The vertical-longitude
cross sections of 20-90-day
filtered q tendency (unit: kg·kg1·s-1·1/3·1010) averaged over
10 ͦS-10 ͦN at day 0 for a) EPWS and b) EP-SS composite.
(Middle) Longitudinal
distribution of 20-90-day
filtered OLR (unit: W·m-2, blue
line), column (1000-250hPa)
integrated intraseasonal q
tendency (unit: s-1·kg·m-2·108,
red line) and column integrated
specific humidity anomaly (unit:
kg·m-2·102, black line) averaged
over 10S-10N at day 0 for c) EPWS and d) EP-SS composite.
(Bottom) The vertical-longitude
sections of 20-90-day filtered pvertical velocity (ω) averaged
over 10S-10N (unit: kg·m·s-3·102)
at day 0 for e) EP-WS and f) EPSS composite.
Propagating and Non-Propagating MJO Events over Maritime Continent
Fig. Column (1000-250hP
integrated
(top) a) specific humidity
tendency,
b) vertical advection;
(bottom) a) 3 components of
horizontal advection,
b) 9 terms of ucomponent horizontal
advection
at day 0 averaged over
10° S-10° N, 120° E-170° E.
Blue bar is for EP-WS and red
bar is for EP-SS composite.
(unit: kg·m-2·105).
Anomalous Meridional Moisture Advection in EP-WS and EP-SS
Column (1000-250hP
integrated meridional
advection terms at day
0 averaged over 10S10N, 120E-170E.
Blue bar is for EP-WS
and red bar is for EP-SS
composite.
Horizontal patterns of 20-90-day
filtered wind (unit: m·s-1) and
mean specific humidity (unit:
0.1g·kg-1) fields at 800 hPa on
day 0 for a) EP-WS and b) EP-SS
composite.
The Effect of Eddy Moisture Transport
Column (1000-250hP
integrated meridional
moisture advection
at day 0 averaged over 10S10N, 120E-170E.
Blue bar is for EP-WS and red
bar is for EP-SS composite.
The dominant EOF pattern of
eddy specific humidity
meridional gradient (shading,
unit: kg·kg-1·m-1·1010) and
regressed eddy wind field (unit:
m·s-1) at 800 hPa. The EOF
analysis was done for the highfrequency fields during day -5
to day 5 for all EP-SS cases. The
eddy wind field is regressed to
the principle component of the
dominant EOF mode.
Statistical Significant Tests for EP-SS and EP-WS Cases
Table 2 Monte Carlo Test for anomaly of OLR’, qtend’, q’ Index on the 0th day
averaged in 10S-10N,120-170E for EP-weak~EP-strong group
OLR’
qtend’
q’
Samples Number
Samples Number
Samples Number
12-13
12-13
12-13
Confidence
Interval
DIFF
Confidence
Interval
DIFF
Confidence
Interval
DIFF
[-5.0,5.0]
-20.0
[-15.8,16.0]
-12.0
[-100.0,97.8]
299.3
95% confidence Interval of difference between two samples for 105
times roundly sampling. The bold red number denotes that the
difference between the two groups is statistically significant.
Summary for EP-WS and EP-SS composite study
 46 EP cases were separated into two groups, a group with large positive
OLR anomaly east of the MJO convection and another group without such
OLR signal. In the former (latter) group, column integrated moisture
anomaly is negative (positive) to the east of the convection. Nevertheless,
MJOs move across the maritime continent in both the groups. The
common feature is positive moisture tendency to the east of the MJO
convection.
 Processes that cause the positive SH tendencies are different. The
former is attributed to anomalous horizontal advections associated with
eddy moisture transport and mean moisture advection by intraseasonal
meridional wind. The latter it is attributed to anomalous vertical
advection (advection of mean moisture by anomalous vertical velocity).
Thanks!
Planetary scale selection
0day
Li and Zhou (2009) suggested that it arises from
nonlinear heating and PBL – free atmosphere
coupling.
5day
Why eastward propagation?
11day
Hsu and Li (2012) indicated that it is attributed to
the zonal asymmetry of PBL moisture.
What initiates MJO convection in WIO？
16day
Zhao, Li, et al. (2013) suggested that it is caused by
moisture advection due to downstream Rossby
wave forcing/mid-latitude wave activity flux
22day
MJO multi-scale feature？
Liu and Wang (2012) suggested that CCKW and Wpropagating IGW are important for MJO
amplification.
Zhou and Li (2010) and Hsu and Li (2011) showed
that there are two-way interaction between MJO
and synoptic-scale variability.
Eastward
28day
34day
40day
From Madden and Julian (1972)
38