This document summarizes the effects of an active phase of the Madden-Julian Oscillation (MJO) on an extreme precipitation event over western Java Island in January 2013. It finds that an active phase of the MJO was propagating eastward in late December 2012 through mid-January 2013, coinciding with a persistent northwesterly monsoonal flow. This provided favorable conditions for the formation of heavy rain over western Java Island from January 15-18, 2013, as convection regularly initiated over the sea northwest of the island each night and propagated southeastward with the upper winds. The coincidence of the active MJO phase and monsoonal flow produced significantly more rainfall compared to occurrences of the monsoonal flow alone

1. 79SOLA, 2013, Vol. 9, 79−83, doi:10.2151/sola.2013-018
Abstract
An extreme precipitation/flood event that occurred in the Indo­
nesian capital of Jakarta on Java Island in the middle of January
2013 coincided with an active phase of the Madden-Julian Oscil­
lation (MJO) with the enhanced convective phase centered on the
western Pacific. Analysis of upper-air sounding data showed that
strong to moderate upper westerly to northwesterly winds persist­
ed over the island prior to and during the heavy rain event, which
were caused by the active phase of the MJO, while northwesterly
winds occurred near the surface. Meteorological radar observa­
tions indicated regular genesis of convection at night over the sea
to the northwest of the island, and southeastward propagation over
the island from the nighttime to early morning. The movement
of the precipitation systems was dominated by the upper north­
westerly winds. The results suggest that the eastward propagation
of an active phase of the MJO exerted a strong influence on the
formation of extreme heavy rain over western Java Island.
(Citation: Wu, P., A. A. Arbain, S. Mori, J.-I. Hamada, M.
Hattori, F. Syamsudin, and M. D. Yamanaka, 2013: The effects of
an active phase of the Madden-Julian Oscillation on the extreme
precipitation event over western Java Island in January 2013.
SOLA, 9, 79−83, doi:10.2151/sola.2013-018.)
1. Introduction
In the middle of January 2013, Jakarta, the capital of Indonesia
(Fig. 1) experienced an extraordinary heavy precipitation/flood
event. Heavy rainfall repeatedly occurred in a local area over
western Java Island for the 4 days 15 to 18 January. Daily rainfalls
of 193.0 and 118.0 mm were observed at Cengkareng and Tanjung
Priok Meteorological Observatory in Jakarta on 17 January 2013.
Most observation points in Jakarta recorded accumulated rainfall
of more than 300 mm over the 4 days, resulting in the most disas­
trous flood since 2007. The entire central part of Jakarta city was
inundated during 17−18 January 2013. At least 20 people lost their
lives, and thousands of houses were flooded. The event ranked
with the 1996, 2002, and 2007 flood events in Jakarta as one of
the worst floods in recorded history.
Wu et al. (2007) reported, for the first time, an unusually long
duration of heavy precipitation that occurred in Jakarta during late
January into early February 2007. Later the case was investigated
in detail with a numerical non-hydrostatic model (Trilaksono et al.
2011; Trilaksono et al. 2012). Their results showed that strong
trans-equatorial Asian winter monsoonal flow from the Northern
Hemisphere plays an important role in the formation of heavy rain
over western Java Island. The persistent northwesterly wind near
the surface over the Java Sea created an intensive low-level wind
convergence and a strong low-level vertical shear of wind over the
island. The thermally and convectively induced local circulation
repeatedly initiated convection over the northern plains near the
foot of the mountain in the evening, causing a long spell of heavy
rain and widespread flooding over Jakarta and surrounding areas.
The El Niño/Southern Oscillation (ENSO) is the most im­
portant coupled ocean-atmosphere phenomenon causing global
climate variability on interannual time scales. The oceanic and at­
mospheric features in December 2012 into January 2013 indicated
ENSO-neutral conditions. Hamada et al. (2012) studied the annual
variability of rainfall in western Java Island. Their results showed
that heavy rain in the region can occur in both the cold, neutral
and the warm ENSO phases. The Madden-Julian Oscillation (MJO)
(Madden and Julian 1994), or intraseasonal oscillation, is the
largest element of 30-day to 90-day intraseasonal variability in the
tropical atmosphere. It is characterized by an eastward progression
of large regions of both enhanced and suppressed tropical rainfall
that mainly occurs over the Indian Ocean and Pacific Ocean. The
MJO significantly affects tropical weather, especially in the Indian
Ocean, the Maritime Continent and western Pacific Ocean regions.
An active MJO can cause widespread, enhanced convection over
the Maritime Continent region for an extended period of time.
However, as the heavy rain/flood event of 2007 in Jakarta was in
an inactive phase of the MJO, exactly how the MJO influences
extreme rain events on Java Island is not well understood.
In this study, we examined the atmospheric circulations
leading to the local, extreme precipitation event that occurred in
Jakarta during 15−18 January 2013, focusing on the effects of an
active phase of the MJO on the extreme precipitation using Wind­
Sat ocean surface winds, GMS infrared images, meteorological
radar observations and balloon sounding data for January 2013.
2. Occurrence of a trans-equatorial monsoonal flow
from the Northern Hemisphere in mid-January
2013
Every year in the middle of the boreal winter season during
December to February, strong northerly Asian winter monsoonal
flow from the Northern Hemisphere mid-latitudes can blow
The Effects of an Active Phase of the Madden-Julian Oscillation
on the Extreme Precipitation Event over Western Java Island in January 2013
Peiming Wu1
, Ardhi Adhary Arbain2
, Shuichi Mori1
, Jun-ichi Hamada1, *
, Miki Hattori1
,
Fadli Syamsudin2
and Manabu D. Yamanaka1
1
Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Yokosuka, Japan
2
Agency for the Assessment and Application of Technology (BPPT), Jakarta, Indonesia
Corresponding author: Peiming Wu, Japan Agency for Marine-Earth Sci­
ence and Technology, Natsushima-cho 2-15, Yokosuka-City, Kanagawa
237-0061, Japan. E-mail: pmwu@jamstec.go.jp.
* Present affiliation: Graduate School of Urban Environmental Sciences,
Tokyo Metropolitan University, Japan
©2013, the Meteorological Society of Japan.
Fig. 1. The topography of Java Island and location of Jakarta (red
circle). The shades denote terrain elevation.

2. 80 Wu et al., The Effects of an Active Phase of the MJO on Extreme Precipitation Event
The ocean surface winds derived from the WindSat satellite
measurements showed strong northeasterly winter monsoon flow
with a wind speed greater than 10 m s−1
over the central South
China Sea from 11 to 12 January 2013. Thereafter, strong north­
erly winds were observed over the Karimata Strait and northwest­
erly winds over the Java Sea in the Southern Hemisphere during
13 to 18 January 2013 (Fig. 2). The areas of strong wind were
consistent with the presence of a large pressure gradient at sea
level, as mentioned.
Balloon soundings were performed twice a day at Soekarno-
Hatta International Airport, Jakarta, on Java Island. Profiles of
horizontal wind vs. time for the period 1−20 January 2013 are
shown in Fig. 3. Above the 300-hPa level, easterly winds pre­
vailed throughout the period. The sounding data indicated north­
westerly winds below the 800-hPa level over western Java Island
during 13−18 January. These northwesterly winds resulted from
the strong trans-equatorial monsoonal flow from the Northern
Hemisphere, as described previously by reference to the surface
pressure distributions and ocean surface winds from satellite mea­
surements.
To summarize, a persistent trans-equatorial monsoonal flow
from the Northern Hemisphere occurred in mid-January prior to
and during the extreme precipitation event of 2013 in Jakarta,
similar to that reported by Wu et al. (2007) as the main cause of
the long duration of heavy precipitation that occurred in Jakarta
during late January into early February 2007.
3. Eastward propagation of an active phase of the
MJO in late December 2012 into January 2013
As mentioned, the MJO is characterized by an eastward pro­
gression of large regions of both enhanced and suppressed tropical
rainfall. During late December 2012, convection was well-orga­
nized over the Indian Ocean and western Maritime Continent,
consistent with MJO activity. In early January 2013, the enhanced
convection associated with the MJO further developed over the
Maritime Continent and shifted east across the Maritime Conti­
nent toward the western Pacific, while convection was suppressed
over the western Indian Ocean. Subsequently, by mid-January
the enhanced convection shifted eastward to the western Pacific,
followed by suppressed convection in the Indian Ocean.
To assess the relative position and strength of the MJO, an
all-season, real-time multivariate MJO index was used (see http://
cawcr.gov.au/staff/mwheeler/maproom/RMM/). The index is
based on the first two empirical orthogonal functions (EOFs) of
the combined fields for the near-equatorially-averaged 850-hPa
and 200-hPa zonal winds, and satellite observations of outgoing
longwave radiation (OLR) (Wheeler and Hendon 2004). The
results showed that the MJO index had amplitude greater than 1.3
with current phase 3 (the enhanced convective phase was centered
on the eastern Indian Ocean) continuing in late December 2012
(Fig. 4). The MJO strengthened considerably in early January
2013, with rapid propagation across the Indian Ocean and the
Maritime Continent toward the western Pacific. The MJO ampli­
tude increased from 1.7 to 2.9 in the 3 days from 3 to 6 January.
The amplitude of the MJO index greater than 2.5 with current
phase 4 (the enhanced convective phase was centered on the west­
ern Maritime Continent) continued for 4 days during 5 to 8 Janu­
ary. Thereafter, in mid-January 2013, the MJO index continued to
show a relatively strong amplitude (1.4−2.0), although eastward
propagation had slowed. In late January, the MJO remained active
with a moderate amplitude and propagated across the western and
central Pacific, although the large-scale enhanced and suppressed
convection pattern had become less coherent.
Profiles of horizontal winds at Jakarta (Fig. 3) showed that
during 4−13 January, strong westerly winds > 10 m s−1
were
observed from near the surface up to 400 hPa (~8 km), with
maximum wind speed being at the 900-600-hPa layer, consistent
with the passage of the strong active phase of the MJO over the
Maritime Continent and the western Pacific regions. It is note­
worthy that the upper westerly winds continued over Java Island
to a lower latitude and can even penetrate into the Southern
Hemisphere (Wu et al. 2007; Hattori et al. 2011). A strong and
persistent trans-equatorial monsoonal flow is a crucial factor in
extremely heavy rain over western Java Island. It was reported
that a strong trans-equatorial monsoonal flow that causes extreme
rain over Java Island is estimated to occur once every 5−10 years
(Wu et al. 2007). In this section, we examine the occurrence of the
trans-equatorial monsoonal flow in January 2013.
Daily sea-level pressure distributions indicated a stationary
surface high-pressure area situated over northern China during
11−18 January 2013, a typical pattern of surface pressure in this
boreal mid-winter season. The high-pressure area extended south­
eastwards to the southern China coast. A large pressure gradient
existed across the East China Sea, northern parts of the Philip­
pines and most parts of the South China Sea, as the isobars are
closely spaced there (not shown). There was little change in this
surface-pressure pattern in the mid-latitudes for the whole period
of the heavy rain event.
Fig. 2. Sea surface wind vectors measured by WindSat satellite for
17 January 2013. The shades denote wind speed.
Fig. 3. Profile of horizontal winds obtained from up-air soundings
at Jakarta as a function of time for January 2013. The shades in
the upper and lower panels denote meridional wind component
and zonal wind component, respectively. The tick marks in the
abscissa indicate 00 UTC or 07 LT of the days.

3. 81SOLA, 2013, Vol. 9, 79−83, doi:10.2151/sola.2013-018
subsequently in mid-January when the MJO-enhanced convective
phase had shifted to the western Pacific (phases 6), although the
upper westerly winds weakened to a moderate speed.
Summarizing the results of this section, strong and coherent
MJO activity took place in late December 2012 into January 2013.
During 15−18 January, the time of the heavy rain/flood event of
2013 in Jakarta, the enhanced convective phase was centered on
the western Pacific. With the eastward propagation of the active
phase of the MJO, moderate westerly winds occurred over Java
Island during the heavy rain event.
4. The effects of the active phase of the MJO on the
extreme precipitation event
Hattori et al. (2011) investigated the occurrence of cross-
equatorial northerly surge and its relation to precipitation over
the Maritime Continent during the regional wet season from
December to March for the 11 years from 1998 to 2009. Their
results showed that during cross-equatorial northerly surge events,
enhanced precipitation is evident over the northern coast of Java
Island and the Java Sea in both active and inactive MJO phases.
It is notable that simultaneous occurrences of a cross-equatorial
northerly surge with an active phase of the MJO produce much
more precipitation with striking positive anomalies in northwest­
ern Java than in only occurrence of a northerly surge. Therefore,
the coincidence of the active phase of the MJO with the persistent
trans-equatorial monsoonal wind in January 2013 provided favor­
able conditions for precipitation in the region.
Since 2009, we have performed meteorological radar obser­
vations continuously at Serpong in the suburbs of Jakarta using
a C-band Doppler radar (CDR). Reflectivity CAPPI at 2.0 km
altitude obtained from the CDR radar for 15−17 January 2013 is
shown in Fig. 5. The CAPPI, or Constant Altitude Plan Position
Indicator, is a radar display that gives a horizontal cross-section of
data at constant altitude. The results indicated regular occurrences
of rain over western Java Island during the nighttime to early
morning during the heavy rain event.
In the infrared (IR) images from the Geostationary Mete­
orological Satellite (GMS) MTSAT-2 (Fig. 6), convection was
regularly initiated in the night during 1900 to 2200 LT in the 4
days from 14 to 17 January over the sea to the northwest of Java
Island, just beyond the scope of our radar observations. Then,
after a short time of 1−2 h, in the radar images the convection
solidified into a line orientated north-south or northeast-southwest,
extending for about 100 km. Subsequently, the line of storms mi­
grated southeastward over western Java Island from the nighttime
to early morning. It took 4−5 h for the rain systems to move from
the northwestern edge of the island to the mountainous areas to
the south of Jakarta. The propagation speed of the precipitation
system was estimated to be close to ~8 m s−1
. The initiation and
propagation of convection were markedly different from those
during the heavy rain event of late January to early February 2007
reported by Wu et al. (2007).
During the daytime, air along a mountain slope is heated more
intensely than air at the same elevation over the valley. The warm
air rises, creating an upslope wind. The heavy rain event of 2007
was in an inactive period of the MJO, during which the upper
prevailing winds over Java Island were weak, providing favorable
conditions for development of thermally-induced valley-mountain
circulation. Consequently, convection developed frequently over
the island’s mountainous areas in the afternoon. In the evening,
convection was triggered over the northern plains near the foot
of the mountain by the outflow from convection that developed
earlier over the mountainous areas. Precipitation continued for
4−5 hours during the convection moved northward over the
northern plains of the island, stopped falling in the early morning.
Subsequently, rainfall occurred again in the morning and contin­
ued until around noon on 1 and 2 February 2007 (Wu et al. 2007).
Numerical simulations for the extreme rain event by Trilaksono
et al. (2012) reproduced two types of initiation and propagation
of convection, that is, convection that initiated in the evening near
the foot of the mountain propagate northward over the northern
plains, and convection that initiated in the early morning over the
Java Sea propagate southward to western Java Island.
In contrast to the weak upper prevailing winds in late January
and early February 2007, the eastward propagation of an active
phase of the MJO caused strong to moderate northwesterly winds
from near the surface up to 400 hPa over Java Island in early to
mid-January 2013 (Fig. 2). The diurnal variation of winds over
western Java Island in the rainy season was unclear when the pre­
vailing northwesterly to westerly was strong (Araki et al. 2006).
Radar observations and cloud images from the GMS satellite
showed that strong convection did not develop in the afternoon
over the mountainous areas of Java Island (Fig. 6, upper panels).
This is because the comparatively strong winds prevented accu­
mulation of heated air on the mountain slope, inhibiting upslope
winds and suppressing afternoon convection over the mountains.
However, in the statistical analysis of Hattori et al. (2011), sup­
pression of convection over the mountainous areas of Java Island
is indistinct in the cross-equatorial northerly surge events with an
active phase of the MJO (their Fig. 16). This is probably due to
insufficient spatial resolution of the TRMM 3B42 rain data that
they used in their study.
Meanwhile, relatively strong northerly wind persisted over
the Karimata Strait, and northwesterly wind over the Java Sea in
mid-January 2013. Tangang et al. (2008) suggested that strong
westerly winds over and north of Java Island caused by an active
phase of the MJO lead to a counter-clockwise turning of the
northeasterly winds over the southern South China Sea and help to
form the Borneo vortex and strong cross-equatorial flow. Accord­
ingly, the eastward propagation of the active phase of the MJO
over the Maritime Continent in January 2013 may have produced
an effect to strengthen the cross-equatorial monsoonal flow. Even
so, the penetration of the northwesterly wind into the Southern
Hemisphere was not as far south as it was in late January into
early February 2007. The northwesterly wind from the trans-equa­
torial monsoon, in conjunction with the westerly wind from the
active phase of the MJO, created an intensive wind convergence
at the low levels along its leading edge near western Java Island.
As convection is initiated over the sea to the northwest of
the island, the movement of mesoscale convective systems is a
determining factor in the occurrence of heavy rain over western
Fig. 4. Phase diagrams of the Madden-Julian Oscillation (MJO)
during late December 2012 into January 2013. The axes (RMM1
and RMM2) represent daily values of the principal components
from the two leading modes. Dots are for each day. Distance from
the origin is proportional to MJO strength.

4. 82 Wu et al., The Effects of an Active Phase of the MJO on Extreme Precipitation Event
Fig. 6. GMS satellite infrared (IR) images over Java Island for 16 to 18 January 2013. These images
were made using the infrared channel of MTSAT-2 image, which has a spatial resolution of 5 km.
Fig. 5. Reflectivity CAPPI (Constant Altitude Plan Position Indicator) at 2.0 km altitude from the Serpong C-band Doppler radar (CDR)
for the 3 days from 15 to 17 January 2013. The CAPPI is a radar display that gives a horizontal cross-section of data at constant altitude.

5. 83SOLA, 2013, Vol. 9, 79−83, doi:10.2151/sola.2013-018
Java Island. It has been reported that the propagation of mesoscale
convective complexes (MCSs) is basically determined by the
mean flow of the cloud-layer (850−300 hPa) and development
of new convective cells (Corfidi et al. 1996). In the mid-latitude
MCSs, new cell formation is usually opposite in direction to that
in the low-level (850 hPa) jet but equal in magnitude. During
15−18 January 2013, when the extreme rain occurred on western
Java Island, northwesterly winds with speeds of 5−10 m s−1
were
observed at the levels from 850 up to 400 hPa (~8 km) (Fig. 3).
Unlike typical mid-latitude MCSs, in the present case there was
no low-level jet. The results from radar observations indicated a
southeastward propagation of the precipitation systems (Fig. 5).
Its speed was close to ~8 m s−1
, almost equivalent to the mean
wind vector of the 850−300-hPa layer winds. These results sug­
gest that the movement of the mesoscale convective systems was
dominated by the upper northwesterly winds in the cases being
studied. The precipitation systems propagated southeastward
during nighttime and early morning, bringing heavy rainfall over
western Java Island.
The reason why there is regular initiation of convection over
the coastal sea at night is unclear. A reasonable explanation is the
thermally-induced diurnal changes in the land-sea boundary-layer
flow. Owing to differential heating of land/ocean surfaces, during
the day, air temperature over land increases much more quickly
than it does over water. At night, rapid radiation loss creates
cooler air over land. Therefore, diurnal changes in the sea/land-
breeze component in the boundary-layer flow were expected in the
coastal areas of Java Island. The interaction of the trans-equatorial
monsoonal flow with the boundary-layer flow strengthens the
low-level wind convergence at night, initiating convection over
the coastal sea to the northwest of the island, as observed by the
meteorological satellite. To understand the details of the initiation
and propagation mechanisms of convection in these low-latitude
regions, further study with observational data and employment of
numerical experiments with the aid of regional circulation models
is necessary.
5. Summary
The present study investigated the effects of an active phase
of the MJO on the extreme precipitation event that occurred on
western Java Island during 15−18 January 2013, using WindSat
ocean surface winds, GMS infrared images, meteorological radar
observations and balloon sounding data. A persistent, trans-
equatorial, northerly wind took place in mid-January 2−3 days
prior to and during the heavy precipitation event, similar to that
which occurred during the extreme precipitation event in Jakarta
during late January into early February 2007. A strong, persistent,
trans-equatorial Asian-winter monsoonal flow from the Northern
Hemisphere was a main factor in the formation of extreme rain
over western Java Island.
In contrast to the extreme rain event of 2007, which was in
an inactive MJO phase, the extreme precipitation/flood event
of 2013 coincided with strong and coherent MJO activity with
the enhanced convective phase centered on the western Pacific.
The active phase of the MJO caused strong to moderate westerly
to northwesterly winds at the levels from near the surface up to
400 hPa (~8 km) over Java Island in early to mid-January 2013.
The westerly winds, in conjunction with the trans-equatorial mon­
soonal flow, produced an intensive wind convergence at the low
levels near western Java Island, providing favorable conditions
for precipitation. Satellite and radar observations indicated regular
genesis of convection over the sea to the northwest of the island
at night, and southeastward propagation over Java Island during
nighttime and early morning in the 4 days of the heavy rain event.
The movement of the precipitation systems was dominated by the
upper northwesterly winds. The results of the present study sug­
gest that the eastward propagation of an active phase of the MJO
produced a great effect on the formation of extreme heavy rain
over western Java Island.
Acknowledgements
The authors are grateful to two anonymous reviewers for their
constructive comments. We are deeply grateful to Drs. Kentaro
Ando and Jun Matsumoto of Japan Agency for Marine-Earth
Science and Technology, and Mr. Yunus S. Swarinoto of Indo­
nesian Meteorological, Climatological and Geophysical Agency
(BMKG), for their encouragements and helpful suggestions. The
present work was supported by the Climate Variability Study and
Societal Application through Indonesia-Japan “Maritime Conti­
nent COE”-Radar-Buoy Network Optimization for Rainfall Pre­
diction Project of Science and Technology Research Partnership
for Sustainable Development (SATREPS) of Japan Science and
Technology Agency (JST) and Japan International Cooperation
Agency (JICA).
References
Araki, R., M. D. Yamanaka, F. Murata, H. Hashiguchi, Y. Oku, T.
Sribimawati, M. Kudsy, and F. Renggono, 2006: Seasonal
and interannual variations of diurnal cycles of local circu­
lation and cloud activity observed at Serpong, West Jawa,
Indonesia. J. Meteor. Soc. Japan, 84A, 171−194.
Corfidi, S. F., J. H. Merritt, and J. M. Fritsch, 1996: Predicting the
movement of mesoscale convective complexes. Wea. Fore-
casting, 11, 41−46.
Hamada, J.-I., S. Mori, H. Kubota, M. D. Yamanaka, U. Haryoko,
S. Lestari, R. Sristyowati, and F. Syamsudin, 2012: Inter­
annual rainfall variability over northwestern Jawa and its
relation to the Indian Ocean Dipole and El Niño-Southern
Oscillation events. SOLA, 8, 69−72.
Hattori, M., S. Mori, and J. Matsumoto, 2011: The cross-equa­
torial northerly surge over the maritime continent and its
relationship to precipitation patterns. J. Meteor. Soc. Japan,
89A, 27−47.
Madden, R. A, and P. R. Julian, 1994: Observations of the 40−50-
Day tropical oscillation ‒ A review. Mon. Wea. Rev., 122,
814−837.
Tangang, F. T., L. Juneng, E. Salimun, P. N. Vinayachandran, Y. K.
Seng, C. J. C. Reason, S. K. Behera, and T. Yasunari, 2008:
On the roles of the northeast cold surge, the Borneo vortex,
the Madden-Julian Oscillation, and the Indian Ocean Dipole
during the extreme 2006/2007 flood in southern Peninsular
Malaysia. Geophys. Res. Lett., 35, L14S07, doi:10.1029/
2008GL033429.
Trilaksono, N. J., S. Otsuka, and S. Yoden, 2011: Dependence of
model-simulated heavy rainfall on the horizontal resolution
during the Jakarta flood event in January‒February 2007.
SOLA, 7, 193−196.
Trilaksono, N. J., S. Otsuka, and S. Yoden, 2012: A time-lagged
ensemble simulation on the modulation of precipitation over
west Java in January‒February 2007. Mon. Wea. Rev., 140,
601−616.
Wheeler, M., and H. Hendon, 2004: An All-Season Real-Time
Multivariate MJO Index: Development of an Index for Mon­
itoring and Prediction. Mon. Wea. Rev., 132, 1917−1932.
Wu, P., M. Hara, H. Fudeyasu, M. D. Yamanaka, J. Matsumoto, F.
Syamsudin, R. Sulistyowati, and Y. S. Djajadihardja, 2007:
The impact of trans-equatorial monsoon flow on the forma­
tion of repeated torrential rains over Java Island. SOLA, 3,
93−96.
Manuscript received 23 February 2013, accepted 1 May 2013
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