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The Indonesian seas located in the tropical area between the Pacific and the Indian Oceans, comprise shelf and deep sea areas with their spatial characteristics. Moreover, it lies between Asia and Australia continent and it compasses the equator region in Southeast Asia. This region is also known as the 'Maritime Continent' (Ramage 1968; Qu et.al. 2005). Moreover, Ffield and Gordon (1996) describe that the regions are not a passive channel linking the two oceans (Pacific and Indian Ocean) that within the seas the thermal and salinity stratification and the sea surface temperature (SST) are significantly modified by tidal and wind-induced mixing and by sea-air fluxes.
The region experiences some of the most variable climate condition. The specific geographical position of Indonesia influences the characteristics of climate and ocean dynamics. The inter-tropical convergence zone (ITCZ) shifts from northern hemisphere in July to the southern hemisphere in January crossing the equatorial line. Therefore, the difference of air pressure between Asia and Australia continents that's changes every 6 months causes the monsoonal winds over Indonesia and drives not only the sea surface current (SSC) patterns but also the influences of sea surface temperature (SST) and sea surface salinity (SSS). During the boreal summer, Indonesia indicates a dry season and during the boreal winter indicates a rainy season. The difference of the sea surface level between the Pacific and the Indian Oceans causes the currents to flow from the Pacific to the Indian Ocean through Indonesian waters, which is known as the Indonesian Throughflow (ITF) (Gordon 2005, Susanto 2006, Susanto et.al, 2001; Meyers et.al., 1999; Potemra 1999).
In the ensuing study, the ocean has a function to stabilise the surface temperature of the Earth due to its ability to organise latent heat and to perform as the dominant source of atmospheric moisture (Duxbury et.al., 2002; Tomczak and Godfrey 2003). In addition, Tomczak and Godfrey (2003) explain that the magnitude and the spatial distribution of the moisture flux to the atmosphere are controlled largely by the SST. Hence, the SST is the principal oceanic parameter for the atmosphere. A proper understanding of how the SST variability in Indonesian region during monsoon period is important especially in the Makassar Strait as the main pathway of ITF.
1.2 Outline of Thesis Proposal
This thesis proposal is divided into three chapters. Chapter 1 summarises the background and relevant literature review of sea surface temperature in Indonesian Seas from previous studies. The research objectives of this study are listed at the end of this section. Chapter 2 explains the data set that will be utilised in this study. Chapter 3 explains the methods will be used to achieve these objectives.
1.3. The Indonesian climate
The climate of Indonesian seas is influenced dominantly by the monsoon, and by high rainfall (Tomczak and Godfrey 2001). Furthermore, the region is located at the action centres of north-south (meridional) circulation, known as Hadley Circulation, and the west-east (zonal) circulation, known as the Walker Circulation. Hence, the following section will describe the climate factors in Indonesian region.
The term monsoon itself is traced back to an Arabic root meaning 'season' (Das, 1968). The monsoon refers to a seasonally reversing circulation with a period of one year. The main driving force for the monsoon circulation is the contrast in thermal properties of land and sea. The Earth's surface has different response to the solar radiation from the Sun. Since land has smaller heat conduction than the sea, the absorption of solar radiation increases the surface temperature over land much more rapidly than over the sea. The monsoon changes direction twice a year and the winds are practically reversed at the time of their strongest development, and affects the oceanic circulation (Wyrtki 1961; Das 1968; Duxbury et.al. 2002). Moreover, Roy (1996) explains that monsoon wind system is a tropical phenomenon that resulted by the interaction between a high atmospheric pressure cell centred over the continent in the winter hemisphere as a low atmospheric pressure cell that develops in the summer hemisphere over the continent.
The monsoon is a macro-scale phenomenon in character and its exciting features of the climate fascinate scientist. Moreover, there is enormously importance for being able to forecast the monsoon due to its great impact on socio-economical and regional (Webster et.al., 1998; Webster and Yang 1992). Furthermore, according to Webster and Yang (1992), the variability of the Asian monsoon is related with the El-Nino Southern Oscillation (ENSO). Weak monsoon period is linked with El-Nino and strong monsoon period is associated with La-Nina. Meanwhile, during normal period, the warm pool (SST>27 oC) expands from eastern Indian Ocean toward western Pacific Ocean and is linked with a broad precipitation maximum. In Indonesia, the monsoonal activity is mainly related to the meridional movement of the ITCZ.
Ramage (1971) in Hastenrath (1985) proposes four criteria to outline the monsoon regions:
1. the prevailing wind directions shifts by at least 120 degrees in January and July.
2. the average frequency of prevailing wind directions in January and July exceeds 40%.
3. the mean resultant wind in at least one of the months exceeds 3 m/s.
4. fewer than one cyclone-anticyclone alternation occurs every two years in either month in a 5 degree latitude-longitude rectangle.
Figure 1. Description of the world's monsoon region (from Ramage 1971 in Hastenrath 1985). Hatched areas meet simultaneously the wind criteria (1) to (3), meanwhile heavy lines mark the northern limit of the region within the northern hemisphere where the cyclone/anticyclone criterion (4) is satisfied. Rectangle encloses the monsoon region. Indonesia is in the monsoon region with criteria (1) to (3).
During normal condition (December - March), the air pressure in Asia is higher than Australia. The northeasterly wind blows north of the equator; it is known as northeast monsoon and turns southeastward in the south of equator. Thus, in Indonesia this monsoon is known as the northwest monsoon (NWM) from December to March, or boreal winter. Normally, during the NWM known as a rainy season and the peak occurs in January. The wind blows southeastward and eastward near the equator. Meanwhile, in the southern hemisphere from 10 oS the wind blows to the north and then turns to the east (Wyrtki, 1961). In addition, Wyrtki (1961) described that the equatorial trough lies over the Indian Ocean around 10 oS, in the southern part of which the southeast trades are found.
The transition period occurs from April to May. In May, the system of the northeast wind over the South China Sea and the Philippines decreases and the south monsoon predominates over the Indonesian region. In the south of the equator, the southeast wind blows and enters to the Indian Ocean as the southeast trades. At the equator, south wind prevails, whereas in the north of the equator southwest wind dominates. Meanwhile, during southeast monsoon (SEM) or boreal summer (June-September), the wind blows from Australia, which has a higher air pressure than Asia continent. In July to August, the SEM reaches its peak (fully developed). October and November is the transition period from SEM to NWM (Wyrtki, 1961).
The rainfall climate of the maritime continent is very unique as it is situated in the most active convective area of the world (Aldrian, 2003). Maximum rainfall over most location in this region occurs during the boreal winter (Chang et al., 2005). This wet season is often related to the Australian summer monsoon due to the nearness of the two regions (McBride, 1987; Chang et al., 2005).
In order to give a broad description about the climate of the region based on the rainfall variability, Aldrian and Susanto (2003) found the three climate regions by using double correlation method (DCM). The result is three regions as shown in Figure 2. Region A (solid line) covers south and central Indonesia from south Sumatra to Timor Island, parts of Kalimantan, parts of Sulawesi and parts of Papua Island. Region B (short dashed line) is located in northwest Indonesia (close to the Asian continent) and Region C in Maluku and parts of Sulawesi (close to the western Pacific region).
Region A, which covers the largest area, is the dominant pattern over Indonesia. This region experiences strong influence of two monsoons; there are the northwest monsoon from November to March (NDJFM) with the wettest in December and the southeast monsoon from May to September (MJJAS) with the driest in JAS. The minimum rainfall reaches a mean below 3.3 mm/day and the maximum is about 10.7 mm/day. On the other hand, region B has rainfall maximum about 10.3 mm/day in October-November (ON) and in March to May (MAM). The region C has maximum rainfall about 10 mm/day in June-July and reaches minimum in November-February (Aldrian and Susanto 2003).
Figure 2. the three regions according to the mean annual patterns using the DCM method. Indonesia is divided into region A in solid line, region B in short dashed line and region C in long dashed line (Aldrian and Sutanto 2003).
1.4. El-Nino Southern Oscillation (ENSO)
The air-sea interaction and the ocean dynamics in the Pacific and the Indian Ocean influence the conditions in the Indonesian seas. According to Tomczak and Godfrey (1994), ENSO is irregular climate phenomenon which relates to fluctuation of rainfall, winds, ocean currents and SST of the tropical oceans and Pacific Ocean. In addition, Suppiah (2004) defined ENSO as El-Nino phenomena and the southern oscillation together comprises a mode of climate fluctuations (Suppiah 2004).
The southern oscillation index (SOI) is a measure of the variability in ENSO. Troup (1965) defines the SOI with the differences in surface atmospheric pressure between Tahiti and Darwin. In addition, the SOI is observed as a planetary scale phenomenon which involves variations in the atmospheric pressure difference at the surface between the Indonesian-Austalian region and the southeast Pacific (Drosdowsky and Williams 1991).
The monsoon, ENSO and the complex bathymetry interplay affect the air-exchange and the inter-ocean throughflow within Indonesian Seas (Potemra 1999; Webster et.al., 1998). During SEM, the south-easterly wind from Australia generates upwelling along the Java-Sumatra south coast. The upwelling is mainly forced both locally by alongshore winds associated with the SEM and remotely by atmosphere-ocean circulation related with ENSO (Susanto et.al.,2001)
Hamada et.al (2002) attributed ENSO-Indonesian rainfall relationship to the different monsoon onset dates during ENSO. They reported that the onsets are earlier in La Nina years and later in El Nino years. During the wet season of northern winter, the negative correlation between Indonesian rainfall and eastern equatorial Pacific sea surface temperature is the lowest in the annual cycle. The correlation is low even though in northern winter the anomalous Walker circulation associated with ENSO events exhibits large-scale upper-level convergence over the Maritime Continent during warm events and divergence during cold events.
In order to understand the weakening of the Indonesian rainfall - ENSO relationship from dry season to the wet season, Hendon (2003) examined the relationships between Indonesian rainfall, SSTs and atmospheric circulation over the entire tropical Indian Ocean and Pacific Ocean. He suggested that the weakening of the relationship results from seasonally varying feedback of ENSO on the local SST surrounding Indonesia.
Across the eastern equatorial Pacific, El-Nino events are characterised by anomalously high SST and weaker trade winds. The latter have a tendency to reverse direction in extreme El-Nino events (Suppiah 2004). Warmer waters in the eastern Pacific lead the region to lower atmospheric pressure there, while in the western Pacific, pressure increases as a result of reduced transport of warm waters under the influence of the southeast trade winds.
The rainfall in the maritime continent region has considerable interannual variation (e.g. Webster et.al. 1998; McBride 1998). Many investigators (McBride and Nicholls 1983; Nichols 1985; Nichols 1981) noted the significant relationship between rainfall in the Indonesia-northern Australia area and the ENSO. This relationship is sometimes manifested in the rampant forest fires and the resulting haze in Indonesia during El-Nino condition (Nichol 1998). However, the ENSO-Indonesian rainfall relationship is strongest during the northern summer and fall, which are the dry and transitional seasons respectively (Aldrian et.al., 2003)
Chang et.al (2004) suggested that the low correlation between all-Indonesian rainfall during the wet monsoon season and ENSO reported by previous studies may be in part due to the averaging of rainfall across the eastern (east of 112oE) and western (west of 112oE) regions that have opposite characteristics. In addition, Indonesia region has a strong seasonal reversal of winds that is often coupled with annual variation of rainfall, particularly near the equator where the prevailing wind is westerly during the wet season of boreal winter, which reach the maximum rainfall and easterly during the dry season of boreal summer (McBride 1998; Hamada et.al. 2002, Ramage 1971 in Chang et.al. 2004).
1.5. Indonesian Sea Surface Temperature
The greatest variability of SST in the eastern Indonesian seas occurs in the eastern Banda and the Arafura Sea. The SST averaged over the Banda Sea from 1982 to 2000 displays an annual cycle from 29 oC - 30 oC from late November to May period to 26.5 oC in August. Moreover, the SST variability is related to thermocline depth changes, which vary with the monsoon and with the ENSO (Gordon and Susanto, 2001).
A mechanism controlling the spatial and temporal scales of SST in this region has been studied by Susanto et.al (2006), which follows the Wyrtki's (1961) role using the Ekman theory. They found that the monsoon cycle has affected to the climatological monthly SST. Colder temperatures are found in the boreal winter months (December to March) in the South China Sea due to the northwest monsoon and in June to August in the south of the equator due to the southeast monsoon. Meanwhile, during the peaks of southeast monsoon, from June-September, colder temperatures are observed in the Arafuru Sea, Banda Sea and off the southern part of the Jawa-Nusa Tenggara Island chain. Strong south easterly winds induce divergence along the coasts of the Jawa-Nusa Tenggara Island chain and within the Banda Sea, and generate upwelling, reducing the SST. In addition, strong winds enhance vertical mixing, also reducing the SST.
Furthermore, Susanto et al. (2006) investigated the patterns of ocean color variability and how physical processes affect those patterns in the Indonesian seas by using 6 years (1998-2003) of satellite-derived ocean color (SeaWiFS) and 7 years of sea surface temperature (AVHRR) and sea surface wind (ERS1/2, NSCAT, and QuikSCAT). During the southeast monsoon, easterly winds turn and become southwesterly to the north of the equator. Similarly, during the northwest monsoon, winds to the north of the equator are northeasterly and become northwesterly in the southern hemisphere.
For short term global climate prediction, the SST anomalies associated with ENSO are recognised as the most dominant forcing factor (Trenberth 1998; Annamalai and Liu 2005). However, Godfrey (1996) explained the correlation of Indonesian SST with ENSO is not principle. Nicholls (1989) found a pattern of SST anomaly that was orthogonal to the Southern Oscillation Index, which correlated closely with anomalies of southern Australian rainfall. This pattern had a dipole shape, with one pole in the middle of the Indian Ocean and the other in Indonesian seas. Godfrey (1996) suggested that climatically this pattern provides additional empirical indication that the small Indonesian SST anomalies are quite significant. Godfrey (1996) based on Allan and Haylock (1993) investigation explains that SST changes in Indian Ocean were affected by Indonesian Throughflow (ITF).
1.6. The Makassar Strait
Many researchers observed the Makassar Strait since it is the main waterway of water through the Indonesian Seas that known as ITF (Ffield and Gordon 1992; Illahude and Gordon 1996; Gordon and Susanto 1999; Waworuntu et al., 1999). Bathymetrically, the Makassar Strait is shallow in the west but over 2000 m deep in the east where it is connected directly to the Sulawesi Sea in the north. Still, the Makassar Strait is a transition between eastern region and western region, which has a sill at about 550 m in the southern end the strait (Tomczak and Godfrey, 2003; Gordon et.al 1994; Wyrtki 1961).
Concerning SST and its relation to monsoon, Illahude and Gordon (1996) describe that during SEM the SST in the Makassar Strait is mostly between 28,2 oC and 28,7 oC, which indicates as a part of warm pool of the tropical Pacific Ocean. Meanwhile during NWM the SST reaching values around 29,4 oC. Moreover, the SST in the northern Makassar Strait is higher than the south for both monsoon periods. Meanwhile, vertically the main Makassar Strait thermocline layer is discovered between 60 and 300 dbar with the temperature declining from 27 oC to 10 oC and a gradient of 0,7 oC/m.
The Makassar Strait surface currents tend to southward and its speed is slow during the NWM period; however, the wind is northerly wind. Gordon et.al. (2003) suggested that the reduction of the current speed is possibly caused by the strong Java Sea eastward current that inhibits the southward Makassar Strait during the NWM. Moreover, the southward Makassar Strait current speed is faster during the SEM. The strong southward Makassar Strait current push back the low salinity and low temperature of surface water back to the Java Sea.
Other oceanographic parameters are water mass, tides and intraseasonal variability that are investigated by researcher. Water mass analysis confirms that the Makassar Strait is the major path for the ITF from the equatorial Pacific route to the various export passages of the Nusa Tenggara Islands arc (Lombok, Ombai and Timor) to the eastern Indian Ocean (Gordon and Fine 1996; Susanto and Gordon 2005). On the other hand, Susanto et.al (2000 and 2001) investigated intraseasonal variability and tides along the Makassar Strait using spectral and time frequency analysis. They found that intraseasonal variability probably is a response to remotely Kelvin waves from Indian Ocean through Lombok Strait and to Rossby waves from the Sulawesi Sea. Furthermore, semidiurnal and diurnal tides are dominant features, with higher semidiurnal and lower diurnal in the north compared to the south.
1.7. Objectives and Aims:
Although the monsoon has such a strong effect on the sea, not many studies on the monsoonal properties and its effect to the SST of Indonesian waters in comparison to other atmospheric studies. This study also developed from the knowledge that climate variability is related to the dynamics of the ocean and the atmosphere, both regionally and globally. Knowledge of the influence that these processes have is important for the survival of agricultural viability, population and economy. Hence the aim of this study is to:
Improve understanding the ocean-atmosphere processes within Indonesian Seas, especially within the Makassar Strait.
Examine the dynamical and statistical significance of SST variability during monsoon periods (NEM and SEM).
Provide links between the large-scale modes of SST variability and climate events over Indonesia.
Chapter 2 Data
In order to support the research, the following data sets will be used.
2.1. Sea Surface Temperature
The SST data will be obtained from the International Comprehensive Ocean-Atmosphere Data Set (ICOADS). The ICOADS data is provided by National Oceanic and Atmospheric Administration (NOAA) Earth System Research Laboratory/Physical Sciecne Division (ICOADS, 2007). The SST data is a reconstructed monthly mean SST data set from the collection of surface marine data for the world ocean with a resolution of 1o latitude x 1o longitude (ICOADS 2007). Moreover, the monthly mean SST data set will span the period 1960 to 2002. The SST will be averaged in 10 degree latitude-longitude boxes (e.g. 5oS - 5oN, 110oE - 120oE). Meanwhile, the in situ data will be acquired from International Nusantara Stratification and Transport (INSTANT) project in particular location, which provides mooring and CTD data in the Makassar Strait.
Figure 3. Indonesia map and study area in this research (blue box).
To identify the advection of moisture across the region during monsoon periods, seasonal composites of wind anomalies at the 850hPa level are producing for the relevant periods. The wind data will be achieved from 40 year European Centre for Medium range Weather Forecast (ECMWF) reanalysis (ERA-40) data sets (ECMWF 2007). ERA-40 is a reanalysis of meteorological observations in period of time 1957 to 2002 produced by the ECMWF and other institution, which is 45-year second generation re-analysis data set. The main goal of this data set is producing the best possible set of analyses, given the changing observing system and the available computational resources. The ERA-40 850hPa winds come as separate meridional (v) and zonal (u) components on a 2.5o latitude x 2.5o longitude grid (Uppala et.al, 2005).
2.3. Precipitation and Rainfall
The precipitation and rainfall data will be derived from Indonesia Meteorology and Geophysics Agency (BMG). This data set contains Indonesian monthly total rainfall.
Moreover, to support this local data set we use the data set that provided by Global Historical Climate Network (GHCN) ver.2. (Peterson and Vose 1997). Another data set is the 1950-1997 Indonesian rainfall reports, which was made available by J. McBride of the Australian Bureau of Meteorology Research Centre. The reports more accurately represent the rainfall at each local station than the GHCN data within Indonesia region.
2.2. Calculated indices
A monthly value of the Dipole Mode Index (DMI) is computed by taking the difference between the climatological mean and monthly mean SST averaged over the spatial extent of the region.
Chapter 3 Methodology
The following research methods will be used to investigate the variability of SST during monsoon period in the Makassar Strait.
3.1. Principal Component Analysis (PCA)
Principal component analysis is a tool and a technique for compressing the variability in the time series data of physical field (Preisendorfer, 1988; Emery and Thomson 1997). In climatology field, which has spatial complexity and interpretation difficulty, PCA represents these complex variations such that interpretation is made easier (Preisendorfer 1988). In addition, PCA gives the most efficient description of the observed variability by reducing large data sets to a few dominant modes. This is multivariate statistical analysis method in weather prediction that introduced by Lorenz (1956) and became popular in the atmospheric analysis then by term Empirical Orthogonal Function (EOF). This method has broad application not only in oceanography but also in meteorology (Wilks 2006; Emery and Thomson 1997).
This method is chosen due to its ability to provide a compact description of the spatial and temporal variability of data series. According to Emery and Thomson (1997), there are two primary methods for computing the PCAs/EOFs for a grid of time series of observations. First, the scatter matrix method that uses a 'brute force' that is decomposed into eigenvalues and eigenvectors using standard computer algorithms (Preisendorfer, 1988). Second, the computationally efficient singular value decomposition (SVD) method which derives all the components of the EOF analysis (eigenvectors, eigenvalues and time-varying amplitudes) without computation of the covariance matrix (Kelly 1988 in Emery and Thomson 1997).
In this present research we are going to choose the second method since it required computational speed and stability through SVD approach.
Given a data vector x, that contains observation of a variable at a number of different locations, PCA finds
Study on ocean climate variability (1960-2002) in the Makassar Strait during monsoon periods.
The Maritime Continent consists of 17.508 islands (Indonesian Hydro-Oceanographic Office 2003), with five main islands with an area bigger than 132.000 km2. These main islands are Kalimantan, Sumatra, Sulawesi, Irian Jaya and Java. Moreover, the population in this country is about 206 million (population census 2000).
Aldrian and Susanto (2003) have introduced a regionalisation method, 'double
correlation method (DCM)', based on the annual rainfall cycle or the annual mean
variability. The result of the DCM is three climate regions as shown in Figure 1-3a.
The mean annual rainfall cycles of each region and their interannual standard
deviations are described in Figure 1-3b. Region A (solid line) covers south Indonesia
from Sumatra to Timor Island, parts of Kalimantan, parts of Sulawesi, parts of Irian
Jaya. Region B (short dashed line) is located in northwest Indonesia (close to the
Asian continent) and Region C in Maluku and parts of Sulawesi (close to the western
The region 'maritime continent' was defined by Ramage (1968) to consist of Malaysia, Indonesia and the surrounding land and oceanic areas of the equatorial western Pacific between 10oS - 10oN.
Review of previous researchers:
Gordon (2006) suggested that the surface current within the Java sea, the Makassar strait, the Flores sea and the Banda sea are modulated by the monsoonal wind.
Although the monsoon has such a strong effect on the sea as well, studies on the monsoonal properties of Indonesian waters have been very rare in comparison to similar atmospheric studies.
This explains that the SST is the principal oceanic parameter for the atmosphere that provides the link between two components of a tightly coupled system (Tomczak and Godfrey, 2003).
In order to give broad description about the climate of the region based on the rainfall variability, Aldrian and Susanto (2003) found the three climate regions according to the mean annual precipitation patterns using the double correlation method (DCM). This method based on the annual rainfall cycle or the annual mean variability. The result of DCM is three regions as shown in Figure 1.1. Region A (solid line) covers south and central Indonesia from south Sumatra to Timor Island, parts of Kalimantan, parts of Sulawesi and parts of Papua Island. Region B (short dashed line) is located in northwest Indonesia (close to the Asian continent) and Region C in Maluku and parts of Sulawesi (close to the western Pacific region).
Region A, which covers the largest area, is the dominant pattern over Indonesia. This region has one peak and one minimum and experiences strong influences of two monsoons. Those are the wet northwest monsoon from November to March (NDJFM) and the dry southeast monsoon from May to September (MJJAS). Region B has two peaks, in October-November (ON) and in March to May (MAM). Those two peaks are associated with the southward and northward movement of the Inter Tropical Convergence Zone (ITCZ). There is no clear reason why the peak in ON is much higher than that of MAM. There is a possible influence of a cool surface current from the north out of the South China Sea during January-March (JFM) that suppresses the rainfall amount. Otherwise the annual cycle of Region B would be similar to that of Region A (Aldrian and Susanto 2003).
Moreover, Aldrian and Susanto 2003 explained that the region C has one peak in June to July one minimum (NDJF). The JJ peak in Region C is about 10 mm/day, while the peaks in Region A and B are 10.7 and 10.3 mm/day respectively. The minimum in region A is the lowest and reaches a mean below 3.3 mm/day. Thus, region A is the driest region during the dry season in JAS and the wettest region in December. Region C, in com-parison to the other two, has a unique annual cycle. The other two regions have its peaks near in the end of the year, while the Region C's peak is in the middle. There is a strong evidence of the possibility of ocean influence in Region C. Region C, or Maluku, is along the eastern route of the Indonesian Throughflow (ITF; a water passage from the Pacific to the Indian Ocean via Indonesian Seas).
The ITF flows mainly through the Makassar Strait with a small part flowing through the Maluku Sea (Gordon et al., 1999). The ITF in Maluku brings sea surface current from the warm pool area, which is located northeast of Irian Jaya Island (New Guinea).
Rainfall variability in this region is very complex and is considered as the 'chaotic part' of the monsoon variability (Ferranti 1997).
In addition, the interannual variability of monsoon rainfall over India and the Indonesian-Australian region shows the biennial variability.
The monsoon regime creates such a strong seasonality of the characteristics of the environment that the alternation of the north and south winds completely reorganises the surface circulation this can be expected to have a strong ecological impact interannual variability exits (webster et.al, 1998).
at each latitudes, the annual temperature changes are controlled by changes in available solar radiation and heat loss that merged with the heat capacity of the surface material (Duxbury et.al 2002).
Where evaporation at the sea surface is high, at tropic and sub tropic latitudes, there is a high rate of removal of heat energy and large quantities of water vapour enter the atmosphere. Moreover, the oceans play a significant role in stabilising the surface temperature of the earth. They can store and release large quantities of heat without large changes in temperature moderates surface temperature both seasonally and over the day and night cycles (Duxbury et.al 2002).
characterised by monsoonal winds and high rainfall. Winds blow from the south, curving across the equator with a westward component in the south and an eastward component in the north, during May to September and in nearly exactly the opposite direction during November to March (Tomczak and Godfrey 2001). During the southeast monsoon from May to September, the easterly and southerly wind blows in the Java Sea and the Makassar Strait, respectively. Moreover, during the northwest monsoon from November to March, the Java Sea and the Makassar Strait wind directions are changed from easterly and southerly to westerly and northerly, respectively.
Annual rainfall in excess of 1000 mm occurs in many of the Indonesia areas and annual minimum temperatures are usually more than 20°C other than in the highlands. Rainfall in the region is highest on the upland areas, notably of central Kalimantan (Borneo), central Sumatra, Java and Papua. Some places receive more than 3000 mm of rain annually. By contrast, parts of the lowlands, coastal areas and other areas in rain-shadows receive far less rain (less than 1000 mm/year), and may experience severe water shortages and droughts.
According to Lau et.al, (1997), the rainfall amount is increases with SST although the increase is not linear below 29 oC. Meanwhile, they showed that the above 29.6 oC the increase of local SST causes a decrease in the maximum rainfall amount.
The local SSTA during ENSO tend to be of opposite sign to those in eastern Pacific and western Indian Oceans during the dry season but of the same sign during the wet season (Rasmusson and Carpenter 1982).
There is enhancement of the equatorial Pacific SST gradient and Walker circulation from the dry season to the transition season and a rapid reduction in the correlation between SSTs and rainfall during the wet season and reduction in spatial coherence of rainfall across Indonesia in going from dry season to the wet season (Chang, et.al. 2004)
Meanwhile, during normal conditions, ascending air creates lower surface pressure and high rainfall over the western Pacific arising from the Walker Circulation and the development of El-Nino conditions (Colls and Whitaker 2001).
The maritime continent is often considered to be a part of the Asian monsoon regime because maximum rainfall over most of the region occurs during boreal winter (Ramage 1971 in Chang et.al. 2004)
In addition, Susanto et.al (2006) shows that the lowest overall wind speeds or wind stress appear in April, which clearly represents the month of transition between the northwest and southeast monsoons. The southeast monsoon begins in May, with winds in the Arafuru Sea and the eastern Indian Ocean indicating first. The zone of maximum wind moves northwest in the Indian Ocean along the Nusa Tenggara Island chain from Jawa to Sumatra. Easterly winds spread and intensify through June reaching their maximum in July and August, and then they begin to subside. A band of very low wind speed brackets a zone slightly north of the equator. Meanwhile, during the northwest monsoon (rainy season), the precipitation is higher than the evaporation, so that the sea surface salinity and sea surface temperature become lower. On the other hand, during southeast monsoon (dry season), the evaporation is higher than the precipitation. Hence, sea surface salinity and sea surface temperature are increased (Sutanto et al., 2006).
However, according to Roy (1996), sea surface temperature variability in the western Indonesian region doesn't to be closely associated with ENSO events.
On the other hand, Godfrey (1996) believed that SST change by tidal mixing in the Indonesian seas probably quite essential component of the ENSO unsteadiness system.
Wyrtki (1961) gives detail description of the region's complex bathymetry. The Indonesian seas can be sub-divided into the following two major regions; the shallow (<75 m) western region over the Sunda shelf, primarily the Java sea and the South China sea, and the eastern region consisting of a series of deep (>1000 m) basins connected by shallower sills.
In the ensuing study, the ocean has a function to stabilise the surface temperature of the Earth due to its ability to keep and discharge heat without large changes in average temperature (Duxbury et.al., 2002). The ocean, moreover, is the dominant source of atmospheric moisture and the latent heat released when this moisture condenses into rain or snow in the primary driving force for the atmospheric circulation. The winds in turn affect the SST in several different ways and the SST largely controls the magnitude and the spatial distribution of the moisture flux to the atmosphere. This explains that the SST is the principal oceanic parameter for the atmosphere (Tomczak and Godfrey, 2003). Therefore a discussion of the ocean and the world's climate has to begin with a detailed understanding of the SST distribution and Indonesian region is one of the important positions that need to be investigated.
Susanto et.al (2000 and 2001) investigated intraseasonal variability and tides along the Makassar Strait using spectral and time frequency analysis. and Atmospheric Dataset) during 1950-1990 periods. He found the minimum temperature (27.5°C) observed in January and February in the Natuna sea High sea surface temperature (>25 oC) and small seasonal amplitude (< 3 oC) are the dominant characteristics of Southeast Asian waters; moreover, their spatial distribution is quite uniform, with small gradient over the entire region.
The Java Sea lies on the Sunda Shelf with an average depth of about 40 m and is a semi-closed sea located between Sumatra in the west, Kalimantan in the north, and Java in the south (Figure 1-6).
On the other hand, water mass analysis confirms that the Makassar Strait is the major path for the ITF from the equatorial Pacific route to the various export passages of the Nusa Tenggara Islands arc (Lombok, Ombai and Timor) to the eastern Indian Ocean (Gordon and Fine 1996; Susanto and Gordon 2005).
A part of this water also exits to the Indian Ocean through the Lombok Strait (Murray and Arief 1988). Prior to entering the Banda Sea, water which takes the eastern route (east of Sulawesi Island) is mostly from the South Pacific (Van Aken et.al., 1988; Gordon 1995; Ilahude and Gordon, 1996; Gordon and Fine 1996; Hautala et.al, 1996). It flows via the Halmahera and the Seram Sea to the Banda Sea and the Timor Sea. Most studies abandon the ITF from the western Pacific through the South Cina Sea, the Karimata Strait and the Java Sea due to the shallowness of the shelf (mean depth of Java Sea is around 40 m) (Waworuntu et.al 2000; Putri 2005).
Eastern Indonesian Seas
Oceanographic studies ;
In this region, there are many oceanographic studies, most of them are the Indonesian Throughflow (ITF) issue. The ITF transfer warm, low salinity waters from the western Pacific into the Indian Ocean (Gordon and Fine 1996; Sprintal et al 2004). There are two main ITF pathways in the Indonesian Seas; the western route and eastern route. The water that flows through the western route is mostly from the North Pacific. It flows through the Makassar Strait, the Flores Sea and the Banda Sea before exiting to the Indian Ocean via the Timor Sea and the Ombai Strait (Fine, 1985; Ffield and Gordon 1992; Fieux et.al, 1994, 1996; Gordon et.al., 1994; Bingham and Lukas 1995; Ilahude and Gordon 1996; Gordon and Fine 1996).
Meteorological condition :
1.6.1. Oceanographic condition
1.6.2. Meteorology condition
Modes of climate variability
Sea Level variations and Indonesian throughflow during ENSO years
El Nino Southern Oscillation (ENSO) is the most famous interannual climate variability in the world climate. It is well known that ENSO is associated with devastating dhroughts over western tropical Pacific, torrential floods around the eastern tropical Pacific and unusual weather pattern over the world (Nkendirim 2000). El-Nino events occur irregularly at intervals of 2 to 7 years, although the average is about once every 3 to 4 years (McPhaden 1993). Throughout the strong 1997 to 1998 ENSO years particularly during the northwest monsoon, Indonesian region had severe drought (Kumar et.al. 1999).
The main problem of the ENSO is the evolution of near-equator sea surface temperature (Harrison 1990).
In the western Pacific warm pool is migrated eastward with the fall down of the trade winds (McPhaden 1999). Based on the higher correlation between SST and sea level and between SOI and sea level, Nerem and Mitchum (2001) developed simulated long-term series of global mean sea level variations. A large increase in global mean SST was observed since 1982 and the largest changing occurred during the ENSO event from 1997 to 1998; moreover, SST has changed about 0,35 oC (Nerem 1999; Nerem and Mitchum 2001).
The characteristic of Indonesian throughflow was affected by ENSO. Ffield et.al. (2000) found the high correlation between the thermocline and the southward Makassar transport; moreover, Ffield (2000) also found that SOI has highly correlated with thermocline. From these relationships, during the El Nino period the total of the southward transport (0 m - 200 m) is high during the El-Nino period and low during the La Nina (Sofian et.al., 2006). On the other hand, Waworuntu et.al (2000) explains that the reinforcement of the pressure gradient in the lower thermocline between the Pacific Ocean and the Indonesian Seas during the La-nina period could increase the flow in the deeper thermocline from the Banda Sea to the Makassar Strait. In the eastern Indian Ocean, the significant interannual variability of the upwelling along the southern coast of Java and Sumatra Island is linked to the ENSO by way of the Indonesian throughflow and by irregular easterly wind (Susanto et al 2001).
Southward transport within the Makassar Strait shows high correlation with the thermocline. During high (low) temperature, the volume transport is also high (low) (Ffield et al. 2000). Gordon et.al (2003) shows that the result from the measurement using MAK-1 and MAK-2 moorings that the largest volume transport was occurred during the La-Nina period and getting smaller during the El-nino period. The direct measurements from MAK-1 and MAK-2 moorings were 12,5 Sv during the La-nina months of December 1996 through February 1997, and 5,1 Sv during El Nino months of December 1997 through February 1998 (Gordon et.al, 1999)
1.2.4. Indian Ocean Dipole
1.3. Oceanography of the Indonesian seas
We will review the oceanographic researches conducted in the internal Indonesian seas. Figure 1-5 illustrates the distribution of reviewed papers collected from many sources. Inferring from those papers, there are two main regions that intensively have been studied, first, western Indonesian seas (western of 112oE) and second, eastern Indonesian seas (Eastern 112o E) (Chang et.al. 2004). The western Indonesian seas region covers the Java Sea which is the largest sea in this region, Karimata Strait, Natuna Sea, Sunda Strait, and Malaka Strait. Meanwhile, the eastern Indonesian Seas covers the Banda Sea, Flores Sea, Maluku Sea, Seram Sea, Halmahera Sea, Savu Sea, and Arafura Sea. Correspondingly, the reviews on oceanographic condition and fisheries/marine biodiversity for western and eastern Indonesian Seas are given in the next couple sub-chapters.
Western Indonesian seas
i. Oceanographic Condition
In this region, Gordon (2005) explains that the monsoonal winds shift the lowest surface salinity into the Java Sea and the southern Makassar Strait from January to March, and into the South China Sea from July to September.
Concerning the largest sea in this area, which is the Java Sea, Putri (2005) explains that the exchange of water mass to/from the sea is through the Karimata Strait that is the passage in the western part. Meanwhile, in the eastern part of the Java Sea, there is a passage between the Java Sea and the eastern part of the Indonesian Seas. In addition, Sunda Strait is a passage between the Java Sea and the Indian Ocean in the southern part of the Java Sea.
Hydrographically, the vertical temperature in the Java Sea, which has an average depth of about 40 m, is well mixed as typical for shallow waters.
With a population of about 206 million, Indonesia mainly depends on rain-fed agriculture for food grains. Seventy percent of the annual rainfall over Indonesia comes from the monsoon rain.
when this moisture condenses into rain or snow in the primary driving force for the atmospheric circulation. The winds in turn affect the SST in several different ways and the SST largely controls the magnitude and the spatial distribution of the moisture flux to the atmosphere. This explains that the SST is the principal oceanic parameter for the atmosphere (Tomczak and Godfrey, 2003). Therefore a discussion of the ocean and the world's climate has to begin with a detailed understanding of the SST distribution and Indonesian region is one of the important positions that need to be investigated.
Principal component analysis is a tool and a technique for compressing the variability in the types of time series data the analysis of the spatial or temporal variability of physical field (Preisendorfer, 1988). In climatology field, which has spatial complexity and interpretation difficulty, PCA can represent these complex variations such that interpretation is made easier (Preisendorfer 1988). In addition, PCA gives the most efficient description of the observed variability by reducing large data sets to a few dominant modes. This is multivariate statistical analysis method in weather prediction that introduced by Lorenz (1956) and became popular in the atmospheric analysis then by term Empirical Orthogonal Function (EOF) (Wilks 2006; Emery and Thomson 1997).
With an improved understanding of the ocean processes within the Indonesian seas and of the variability of the SST, we can anticipate enhanced understanding of the importance of the ocean's role in this region in governing ENSO and the Asian Monsoon.
MJO forces surface current that drive SST variations at the eastern edge of the warm pool (Kessler et.al 1995)