Journal of the Meteorological Society of Japan, Vol. 89A, pp. 49--59, 2011.

DOI:10.2151/jmsj.2011-A03

E¤ects of Large-scale Moisture Transport and Mesoscale Processes
on Precipitation Isotope Ratios Observed at Sumatera, Indonesia

Hironori FUDEYASU
Yokohama National University, Yokohama, Japan

Kimpei ICHIYANAGI
Kumamoto University, Kumamoto, JapanKei YOSHIMURA
University of Tokyo, Kashiwa, Japan

Shuichi MORI, HAMADA Jun-Ichi
Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Yokosuka, Japan

Namiko SAKURAI
National Research Institute for Earth Science and Disaster Prevention (NIED), Tsukuba, Japan

Manabu D. YAMANAKA
Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Yokosuka, Japan
Kobe University, Kobe, Japan

Jun MATSUMOTO
Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Yokosuka, JapanTokyo Metropolitan University, Hachioji, Japan

and
Fadli SYAMSUDIN
Agency for the Assessment and Application of Technology (BPPT), Jakaruta, Indonesia(Manuscript received 30 April 2010, in ﬁnal form 9 September 2010)

Corresponding author: Hironori Fudeyasu, Department of Science Education, Yokohama National
University, 79-1 Tokiwadai, Hodogaya-ku, Yokohama
240-8501, Japan.
E-mail: fude@ynu.ac.jp
6 2011, Meteorological Society of Japan49

Journal of the Meteorological Society of Japan

50

Vol. 89A

Abstract
Isotopic and meteorological observations in November 2006 on the west coast of Sumatera, Indonesia during
the intense observation period of the Hydrometeorological ARray for Intraseasonal Variation-Monsoon AUtomonitoring (HARIMAU2006), revealed the impacts of large-scale moisture transport and mesoscale processes
on precipitation isotope ratios. Intraseasonal changes in the precipitation d 2 H in November had large variability
ranging from þ10 to 65 per mil, as a result of the changes in the large-scale moisture transport associated with
the intraseasonal oscillation with a time-scale of 10–15 day over Sumatera. The isotopic composition of precipitation was independent from di¤erence in precipitation type (convective or stratiform precipitation). An isotope
circulation model reproduced the observed isotopic changes, supporting that the isotopic e¤ect of large-scalemoisture transport was the main contributor to intraseasonal isotopic changes.
In high-frequency samples taken over a shorter time scale, isotopic variability was related to event type classiﬁed by the analysis of radar observations, although the isotopic e¤ects of mesoscale processes on the isotopic
averages of each precipitation event were almost masked by the isotopic e¤ect of large-scale moisture transport.
The precipitation d 2 H accompanying the well-organized convection type decreased signiﬁcantly by about 20 per
mil. Drastic changes in isotope ratios could be described by the Rayleigh distillation process. Isotope ratiosof precipitation gently decreased and subsequently increased in the unorganized convection type since the water
vapor in surrounding convectively rising air isotopically enriched the remaining low-isotope water vapor advectedfrom the precedent clouds. Isotope ratios in the stratiform precipitation remained steady, possibly attributable tothe homogeneous moisture of stratiform clouds.

1. Introduction
Stable hydrogen and oxygen isotope ratios (d 2 H
and d 18 O) of precipitation undergo temporalchanges at various time scales. Many isotopic
studies have observed long-term isotopic changes
in precipitation in time periods of more than a day
or several hours (e.g., Ichiyanagi et al. 2005). Suchlong-term isotopic changes in precipitation may becontrolled by large-scale moisture transport, i.e.,
the water source and transport route. However, thebehavior of precipitation isotope ratios is also intimately linked to precipitation growth mechanisms,
namely precipitation/cloud processes (mesoscale
processes). Isotopic fractionation in clouds occurs
during evaporation and condensation of water
vapor and precipitating particles, with the exception of the sublimation and melting of compact ice(e.g., Dansgaard 1953). Mesoscale processes may
cause short-term isotopic changes with time scalesof less than few hours.
Drastic decreases in precipitation isotope ratios
have often been observed during individual precipitation events at various sites (e.g., Sugimoto and
Higuchi 1988; Lawrence et al. 1998; Gedzelman
et al. 2003). Sugimoto and Higuchi (1988) reported
large (small) decreases in precipitation isotope
ratios when the precipitation intensity was high(low). Fudeyasu et al. (2008) found increases in theisotope ratios of precipitation accompanying a
tropical cyclone eyewall. Dansgaard (1953) ob-

served that isotopic ratios in precipitation did notvary with time throughout a rain shower. Morerecently, Risi et al. (2009) also reported on an isotopic observational campaign and analyzed theisotope ratios of precipitation accompanying four
squall lines over the Sahel in August 2006. Their
high-frequency sampling (5–10 minutes) of the precipitation showed a systematic evolution of precipitation isotope ratios in di¤erent phases of the squalllines.
The various mesoscale processes, characterized
by di¤erent precipitation types (convective andstratiform precipitation) and cloud structures, could
contribute to the variability in short-term isotopic
changes in precipitation. Although previous isotopic observations have provided much information
on individual precipitation events, few studies havedemonstrated how the isotopic e¤ects of large-scalemoisture transport and mesoscale processes simultaneously contribute to the isotope composition
in precipitation. This may reﬂect the lack of longterm precipitation sampling at high temporal resolutions or the di‰culty of simultaneously capturing
cloud processes, or both. Therefore, we conducted
a 1-month intensive isotopic observation of precipitation samples taken at 1-mm amount intervals and6-hourly intervals on the west coast of Sumatera,
Indonesia (Fig. 1), in November 2006 during the intense observation period of the Hydrometeorological ARray for Intraseasonal Variation-Monsoon
AUtomonitoring (HARIMAU2006). The compre-

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H. FUDEYASU et al.

51

2. Isotopic and meteorological observations andisotope circulation modelFig. 1. Terrain map of Sumatera Island andlocation of observation sites. Altitudes of
500–1,000 m are lightly shaded, while
those above 1,000 m are heavily shaded.
The dot indicates the isotopic and meteorological observation site at Tabing. Crosses
indicate the XDR observation sites at
MIA and Tiku. The open circles show the
MIA-XDR and Tiku-XDR observationarea.

hensive meteorological and radar observations conducted during the HARIMAU2006 were aimed atbetter understanding cloud structures. The purposeof present study is to investigate how large-scalemoisture transport and mesoscale processes inﬂuence the variability of precipitation isotope ratios.
Notably, this is the ﬁrst report to describe thehigh-resolution measurement of isotope ratios in
tropical precipitation together with comprehensive
meteorological observations and an isotope circulation model that not only captured the large-scalemoisture transport but also mesoscale processes
over the tropics.
The rest of the paper is organized as follows. The
next section brieﬂy describes the isotopic and meteorological observations and the isotope circulation
model. Section 3 presents the observed intraseasonal isotopic changes controlled by large-scalemoisture transport. Section 4 discusses the variability of precipitation isotope ratios in several precipitation events. The main ﬁndings are summarized in
the last section.

The HARIMAU2006 (Yamanaka et al. 2008),
conducted on the west coast of Sumatera (Fig. 1)
from 26 October to 27 November 2006, consistedof intensive rawinsonde and surface observationsat Tabing (100.4 E, 0.8 S) and dual X-band Doppler radar (XDR) observations at Tiku (TikuXDR) and Minangkabau International Airport(MIA-XDR). Surface observations provided 1minute averages of temperature, relative humidity,
winds, pressure, radiation, and accumulated precipitation. Two XDRs collected three-dimensional reﬂectivity and Doppler velocity data every 6 minutes
in observation ranges 83 km in radius. Reﬂectivity
was interpolated on a Cartesian coordinate systemwith 500-m grid spacing in the horizontal andthe vertical. Dual Doppler analysis, using Doppler
velocity data and a continuity equation (Ray et al.
1980), provided three components of wind. Additionally, the MIA-XDR results were used in algorithms (Steiner et al. 1995) to objectively classify
the precipitation as convective or stratiform (Moriet al. 2011; Kawashima et al. 2011). We also usedthe equivalent black body temperature (TBB ) of satellite images from the geostationary meteorologicalsatellite (MTSAT), to describe the large-scale
cloud features. These data were deﬁned on a 0.2horizontal grid.
Intense isotopic observation was conducted atTabing from 1 to 27 November 2006. Precipitation
samples were automatically collected for every
1-mm amount, with an auto-precipitation sampler
to describe short-term isotopic changes. Here, wedeﬁne ‘‘short term’’ as a period within 6 hours, inwhich the isotopic variability is a¤ected by mesoscale processes. We stored precipitation samples
in sealed bottles promptly after the cessation of a
precipitation event to prevent evaporation. In total,
103 complete samples were collected during the
HARIMAU2006. We also collected 25 samples at
6-hour intervals to describe intraseasonal isotopic
changes. The isotopic composition of samples wasanalyzed by a MAT-252 analyzer with a water
equilibrium device at the laboratory of the Instituteof Observational Research for Global Change, Japan Agency for Marine-Earth Science and Technology (JAMSTEC). Analytical errors were lessthan G1 per mil for d 2 H and G0.1 per mil for d 18 O.
We used isotopic compositions of precipitation
simulated by the Rayleigh-type Isotope Circulation

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Journal of the Meteorological Society of Japan

Model (ICM) to detect the e¤ect of large-scalemoisture transport (Yoshimura et al. 2003a, b;
Yoshimura et al. 2004). The ICM is a type of atmospheric transport model for water isotopes with ahorizontal resolution of 1.0 and one vertical layer.
The model is driven by global atmospheric analysis
ﬁelds from the operational weather forecast system of the Japan Meteorological Agency, and themodel estimates global distributions of vapor andprecipitation isotope ratios at 6-hour intervals.
Note that the ICM only focuses on large-scalemoisture transport and does not include cloud/precipitation processes.
3. Intraseasonal changes in precipitation isotope
ratiosFigure 2a shows the time series of 6-hourly precipitation observed at Tabing from 1 to 27 November 2006. The active period of precipitation started
in late November, which is consistent with the previously reported climatological change from the dry
to the rainy season (Hamada et al. 2002). Precipitation in late November was also characterized bydeveloped convective precipitation with diurnal
variation that peaked in the afternoon, which wasconsistent with previous studies (Murakami 1983;
Nitta and Sekine 1994; Wu et al. 2003; Mori et al.
2004).
Figure 2b shows the time series of precipitationd 2 H observed at Tabing. Values of precipitationd 2 H ranged from þ10 to 65 per mil with an aver-Vol. 89A

age of 24 per mil. Using the classiﬁcations forconvective and stratiform precipitation (Steiner etal. 1995) derived from the analysis of MIA-XDR
observations, 42 precipitation samples collected for
1-mm amount were taken during stratiform precipitation, while 61 samples were taken during convective precipitation. The di¤erence in average isotope
ratios between stratiform (22 per mil) and convective (27 per mil) precipitation was not statisticallysigniﬁcant. It means that the isotopic compositionof precipitation was independent from di¤erence inprecipitation type.
The precipitation d 2 H ranged from þ5 to 0 per
mil in early November, whereas low precipitationd 2 H of around 40 per mil was observed on 13
November (Fig. 2b). In the following several days,
the precipitation d 2 H remained relatively low ataround 15 per mil. The precipitation d 2 H from21 through 25 November decreased day by day,with a large variability ranging from 0 to 65 permil. Intraseasonal changes in the precipitation d 2 H
featured decreases in middle and late November.
Figure 3 shows the time-height section of winds
and relative humidity derived from upper air
sounding and surface observations at Tabing. At
the surface, throughout the entire observation period, south or southwest winds dominated during
the day at Tabing. On 13 November, easterlies
with high relative humidity of more than 80%
started to appear in the mid-troposphere. Afterseveral days of inactive precipitation in middle No-

Fig. 2. Time series of observed (a) 6-hourly precipitation and (b) 6-hourly precipitation d 2 H (dashed line),
1-mm precipitation d 2 H (circle), and simulated 6-hourly precipitation d 2 H (solid line). Numerals in (a)indicate the event number shown in Table 1.

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H. FUDEYASU et al.

53

Fig. 3. Time-height section of winds (arrows, scale at bottom) and relative humidity (shaded). Regions with greater than 80
and 90% relative humidity are lightly andheavily shaded, respectively. Surface windis added at the bottom.

vember, strong easterlies were dominant in the midlower troposphere above 2-km height. Figure 4
shows the time-longitude cross-section of MTSATTBB zonally averaged for 0.5–1.5 S. There were organized cloud clusters at 100 E longitude whichcorresponded to the precipitation observed at Tabing. In early November, cloud clusters with timescales shorter than a day intermittently appeared
around 100 E. In middle and late November, cloudclusters developed around 105–115 E and moved
westward to 100 E with time scales exceeding a few
days, typical features in the westward-propagating
mesoscale cloud clusters associated with the intraseasonal oscillation (Shibagaki et al. 2006a, b).
Therefore, the intraseasonal changes in the precipitation isotope ratios can be considered as a resultof the changes in the large-scale environment associated with the intraseasonal oscillation with atime-scale of 10–15 day over Sumatera.
Figure 2b also shows the ICM-simulated precipitation d 2 H at the grid point (100.5 E, 0.5 S) near
Tabing. Although there is systematic model underestimation in the simulation values due to the lower
isotope ratio of evaporation from the sea surface(Yoshimura et al. 2004), the model reproduced theintraseasonal changes with a time-scale of 10–15
day in the observed precipitation d 2 H well. The
biases between observed and ICM-simulated precipitation d 2 H in late November decreased when
the amount of observed precipitation increased(Fig. 2a) but the modeled precipitation did not increase so much (not shown). The ICM using under-

Fig. 4. Time-longitude section of equivalent
black body temperature (TBB ) zonally averaged in 0.5–1.5 S. Regions with TBB of
220–260 K are lightly shaded, while thosewith TBB smaller than 220 K are heavily
shaded. The broken line indicates the longitude of 100 E.

estimated modeled precipitation simulated gentle
decreases in precipitation d 2 H in late November
due to the lack of amount e¤ect on precipitation
isotopes (Lee and Fung 2008). The isotopic changes
simulated by the ICM were only a¤ected by largescale moisture transport, suggesting that the isotopic e¤ect of mesoscale processes on the isotopic
averages of each precipitation event was almost
masked and only the isotopic e¤ect of large-scalemoisture transport became apparent in this timescale.
4. Short-term isotopic variability in precipitation
eventsTen precipitation events exceeding 3 mm wereobserved at Tabing (Table 1 and Fig. 2a). From
precipitation types and cloud structures derived

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Journal of the Meteorological Society of Japan

Vol. 89A

Fig. 5. Horizontal pattern of objective precipitation classiﬁcation derived from MIAXDR observations at (a) 2142 LT (localtime) on 19 November 2006, Event 3;(b) 1554 LT on 23 November, Event 6;
and (c) 0212 LT on 24 November, Event
7. The regions with convective and stratiform precipitation are heavily and lightly
shaded, respectively. The cross indicatesthe isotope observation site at Tabing.
Dots indicate the XDR observation sites
at MIA and Tiku. The open circle shows
the MIA-XDR observation area.

from the analysis of XDR observations, these ten
precipitation events were divided into three types:
the well-organized convection type, unorganized
convection type, and stratiform type. In Event 3,
on 19 November, the cloud structure was characterized by an organized convective line developedin the front side of the system with a trailing broad
stratiform area (Fig. 5a), referred to as the wellorganized convection type. Several convective
clouds developed around the region during Event 6
on 23 November (Fig. 5b). These convective clouds
were not organized and intermittently passed overTabing. We refer to this event as the unorganized
convection type. In Event 7, on 24 November,widespread stratiform clouds covered the areaaround Tabing (Fig. 5c), representing the stratiform type.
The average precipitation d 2 H values in each precipitation event were related to the intraseasonal
isotopic changes as described in Section 3 andTable 1. It means that the mesoscale isotopic e¤ectof event types on the averaged precipitation d 2 H
was masked. However, the di¤erences in the precipitation d 2 H between the ﬁrst and last samples ineach event were related to event types (Table 1).
The di¤erence was larger in the well-organized convection type and smaller in the stratiform type.
Figure 6 shows the time tendency of precipitationd 2 H from the ﬁrst samples in each event. The duration of precipitation in the well-organized convection type had short period about 30 minutes, while
those in the stratiform and unorganized convection
types were relatively long. The precipitation d 2 H
in the well-organized convection type decreased signiﬁcantly by about 20 per mil within ﬁrst 20 minutes, whereas that in the stratiform type remained
steady. The precipitation d 2 H in the unorganized
convection type decreased at the beginning, followed by increases and ﬁnally decreases. The rates
were here deﬁned as the changes in precipitation

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H. FUDEYASU et al.

55

Table 1. Summary of the features of ten precipitation events. These events were divided into three types of precipitation processes. O: well-organized convection type; U: unorganized convection type; and S: stratiform type. Di¤erence represents the changes in precipitation d 2 H between the ﬁrst and last samples in each event.
Event
1
2
3
4
5
6
7
8
9
10

Date in
Nov.

Event
type

Duration(min)

Total numberof samples

Average ofd 2 H (per mil)Di¤erence(per mil)

13
19
19
22
23
23
24
25
26
27

O
S
O
U
U
U
S
U
U
S

40
30
25
73
50
103
81
15
29
85

13
3
8
24
5
14
5
6
5
4

40.5
3.9
21.5
6.9
4.9
28.3
43.1
46.5
45.4
51.1

12.3
0.6
15.6
10.3
5.8
12.2
3.2
5.6
13.3
1.7

Fig. 6. Time tendency of changes in precipitation d 2 H from the ﬁrst sample for (a) well-organized convection
and stratiform types and (b) unorganized convection type.

d 2 H divided by the duration of precipitation. The
averaged rate in the well-organized convection
type was the largest (0.47 per mil minute1 ),whereas that in the stratiform type was the smallest(0.03 per mil minute1 ).
In Event 3, the organized convective clouds
quickly moved westward at about 30 km hour1(Fig. 5a), causing heavy precipitation for 30 minutes and subsequently weak stratiform precipitation at Tabing (Fig. 7). The precipitation d 2 Hquickly decreased from 11 to 30 per mil. Figure
8 shows a scatter plot of d 18 O and d 2 H values. Samples from Event 3 were plotted above the meteoric
water line (MWL; Craig 1961) and decreased overa wide range parallel to the MWL. At the cloudscale, previous isotopic models using Rayleigh’s
equation (e.g., Taylor 1972) have attempted to clarify the relationship between d 18 O and d 2 H. Taylor(1972) showed that the isotopic composition ofsubsequent precipitation decreases parallel to the
MWL, assuming that the isotopic equilibrium fractionation described by Rayleigh’s equation prevails
in atmospheric condensation processes, and thatthe condensed phase is immediately removed fromthe cloud system without causing isotope exchange
between the falling droplets and ambient water
vapor, i.e., the kinetic isotopic e¤ect. Therefore,
the drastic changes in precipitation isotopic ratios
in the well-organized convection type can be interpreted by Rayleigh’s distillation process.

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Vol. 89A

Fig. 7. Time (local time) series of observational results for Events 3, 6, and 7. (a) Reﬂectivity and systemrelative wind (scale at lower right in Event 3), (b) 6-minutes precipitation, and (c) precipitation d 2 H overTabing. Regions of 10–20 dBZ reﬂectivity are lightly shaded, while those more than 20 dBZ are heavily
shaded.

Fig. 8. Scatterplot showing d 18 O and d 2 H
for Events 3, 6, and 7. The dashed line denotes the meteoric water line.

Figure 7a shows the reﬂectivity over Tabing derived from MIA-XDR and system-relative winds
derived from dual Doppler analysis. Unfortunately,
wind data over Tabing were not complete becauseof deﬁciencies in the Doppler velocity observed
by Tiku-XDR due to precipitation attenuation. At

2148 local time (LT), system-relative winds in convective cloud showed an upward-motion trend
beginning in the lower troposphere and then extending into the trailing stratiform region in the
mid-troposphere after 2200 LT. Therefore, the continuous depletion of water vapor isotopes in saturated rising air decreased isotope ratios in the convective precipitation. Stratiform precipitation thenformed from the remaining water vapor with lower
isotope ratios, leading to the lowest precipitation
isotope ratios. The three-dimensional wind ﬁeld
over Tabing derived from dual Doppler analysis revealed the isotopic e¤ect of quasi two-dimensional
processes. The quick propagation of the squall line
over the observation site also caused quick decreases in the precipitation isotope ratios. The
same situation appeared in Event 1 (not shown).
On the other hand, in the unorganized convection type in Event 6, the precipitation d 2 H gently
decreased and subsequently increased around 25
per mil until 1718 LT (Fig. 7). The unorganized
convection type should be three-dimensional systemand the water vapor was entrained to the subsequent clouds over Tabing from various directions.
Since water vapor from the lower troposphere has
relatively high isotope ratios (e.g., Dansgaard
1953), surrounding convectively rising air originating from the lower troposphere isotopically en-

February 2011

H. FUDEYASU et al.

riched the remaining low-isotope water vapor
advected from the precedent cloud, slowing the decrease in isotope ratios in subsequent precipitation(Fig. 7c). After convective clouds passed, the precipitation d 2 H in the subsequent stratiform precipitation after 1730 LT signiﬁcantly decreased from
27 to 36 per mil, as described by Rayleigh’s distillation process, because of the isotopic changes
parallel to the MWL (Fig. 8).
In event 7, the widespread stratiform clouds
slowly moved westward (Fig. 5c), causing precipitation for 2 hours at Tabing (Fig. 7). The precipitation d 2 H also remained steady at around 43
per mil. Dual Doppler observations revealed weakwinds in the stratiform clouds and the absenceof convective updrafts. Therefore, the steadiness of
the isotope ratios in the stratiform precipitation
may be attributable to the homogeneous moistureof stratiform clouds.
There were no remarkable changes in deuterium excess (d-excess, d-excess ¼ d 2 H  8d 18 O)
during each precipitation event (not shown). The
main physical process causing changes in d-excess
is the kinetic isotopic e¤ect, while the productionof precipitation from water vapor essentially conserves the d-excess (e.g., Craig 1961). From our observation, the kinetic isotopic e¤ect on the shortterm isotopic changes in precipitation was insigniﬁcant, compared with the isotopic e¤ects of precipitation/cloud processes. Due to limitations of theobservational data, quantitative understanding ofthese isotopic e¤ects on short-term changes in precipitation isotope ratios remains unclear. Examination of these isotopic e¤ects should be considered
for future study.
5. Summary
This study has described the isotopic variability
in response to isotopic e¤ects of large-scale moisture transport and mesoscale processes, observedon the west coast of Sumatera, Indonesia, from 1
to 27 November 2006. The precipitation d 2 H hadlarge variability, ranging from þ10 per mil to 65
per mil. Intraseasonal changes in the precipitationd 2 H in November were resulted from the changes
in the large-scale environment associated with theintraseasonal oscillation with a time-scale of 10–15
day over Sumatera, namely the large-scale moisturetransport. Isotopic composition of precipitation
was independent from di¤erence in precipitation
type. The ICM-simulated precipitation d 2 H at the
point near Tabing reproduced the observed intra-

57

seasonal isotopic changes, supporting the premisethat the isotopic e¤ect of large-scale moisture transport was the main contributory factor of the intraseasonal isotopic changes.
High-frequency sampling of precipitation and radar observations revealed the short-term isotopic
variability in precipitation in several precipitation
events. Isotopic ratios of precipitation accompanying the well-organized convection type decreased
signiﬁcantly by about 20 per mil, resulting fromthe continuous depletion of water vapor isotopes
in the convectively rising air. Isotope ratios in organized convective precipitation underwent drasticchanges which could be described by Rayleigh’s
distillation process. In the unorganized convection
type, the precipitation d 2 H gently decreased andthen increased since the water vapor in surrounding
convectively rising air isotopically enriched the remaining low-isotope water vapor advected fromthe precedent clouds. Isotope ratios in the stratiform precipitation remained steady, which could
be attributable to the homogeneous moisture ofstratiform clouds.
The ﬁndings suggest that the isotopic e¤ect of
mesoscale processes on the isotopic average ofeach precipitation event was almost masked by theisotopic e¤ect of large-scale moisture transport.
However, the short-term isotopic variability, withthe exception of intraseasonal isotopic changes,
was related to event type classiﬁed by the analysisof radar observations. The study results are very
encouraging since the short-term isotopic frequency
can capture the features of mesoscale processes.
Therefore, high-frequency isotopic observation canbe applied as a diagnostic tool to understand theprecipitation type and cloud structure in individual
precipitation events.
Acknowledgments
The authors would like to thank Drs. Naoyuki
Kurita and Shingo Shimizu for their helpful comments and supports of data analysis. The authors
are also grateful for the assistance of sta¤ membersof the Agency for the Assessment and Applicationof Technology (BPPT) and the Indonesian Meteorological and Geophysical Agency (BMG; now
the Indonesian Meteorological Climatological andGeophysical Agency, BMKG) on the Indonesianside and of JAMSTEC, Hokkaido University, andKyoto University on the Japanese side. This work
was supported by the Japan Earth Observation System Promotion Program (JEPP) of the Ministry ofJournal of the Meteorological Society of Japan

58

Education, Culture, Sports, Science and Technology, (MEXT), Japan.
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