Figure 4.3. Sea level pattern at ebb tide When surface current pattern near land area between spring tide and neap tide
is different, the surface current in open sea shows similar direction, moving from west to east. In December-February, timescale of model generating tides, the
periods has been known as west monsoon periods with it northwest wind propagation. Wind blowing from northwest passing Java Sea to the east,
causing current moves following wind direction. Wind propagation affecting surface current so that it direction was almost similar in open sea. This result
also supported by Sofian 2007 and Widyastuti 2010.
4.1.2. Regional Sea Level Change
As technology advances, the use of technology to record sea level data had been increasing. In some area where tide gauges data relatively rare andor
difficult to obtain, data record from satellite measurement can be a solution. Regional sea level data derived from TOPEXPoseidon has shown the variation
of sea level change during 2004-2010 Figure 4.4.
Figure 4.4. Trend of regional mean sea level around Indonesia data from University of Colorado
The result shows that in 2004, mean sea level was 22.986 mm above zero and in 2005 has reach 36.713 mm above zero. In 2006, sea level has increase around
1.7 times from it level in 2005 and in 2007 sea level was reach 64.569 mm above zero. In 2008, sea level has been increase significantly from it values in 2007 and
reach 137.356 mm above zero while in 2009 and 2010 mean sea level reach 105.164 mm and 124.159 mm above zero. The result also shows that average of
sea level rise from 2004 to 2010 was 2.535 cmyear. The complete data of yearly regional sea level change can be seen in table 4.1.
Table 4.1. Result of regional sea level change data processing
Year Mean Sea Level mm
Rising Level
2004 22.98621622
2005 36.71316216
13.72694595 2006
63.38036111 26.66719895
2007 64.56962162
1.189260511 2008
137.3559722 72.7863506
2009 105.5638649
-31.79210736 2010
124.1595676 18.5957027
4.1.3. Global Sea Level Change
Based on result of tide gauge data processing data from CSIRO, eustatic sea level change shows the increasing of sea level linearly since 1880-2009 follows
equation Y=1.54X – 3060.07 with 0.97 of coefficient determinates R
2
. This equation is not constant as it is and might be changed along the time because
input of sea level height is not linearly constant either it decreasing or increasing. Figure 4.5 shows the pattern of global sea level change during 1880 to 2009.
Assumption from those CSIRO data, time when level of seawater firstly equal to the land has been occurred on December 1982 indicate in figure 4.5 by red
color of dot. Before that time, sea level constantly rose from -181.4 mm in January 1980 to -0.5 mm in November 1982 or rising rate is 0.1465 mmyear.
After 1982, sea level still raised with rising rate around 0.2108 mmyear or 1.5 times it rising before seawater equal to the land. Figure 4.5 below shows the
relation of sea level value and year where the average of sea level increasing from 1880-2009 is 22.2859 mmmonth complete data is in Appendix 2.
Figure 4.5. Monthly average of global mean sea level pattern based on tide gauge recorded andor reconstructed data data from CSIRO
As technology advances, the use of technology to record sea level data had been increasing and global sea level data as data comparison of tide gauge data
has been recorded. High quality measurements of global sea level have been made since late 1992 by satellite altimeters. In particular, TOPEXPoseidon launched
August, 1992, Jason-1 launched December, 2001 and Jason-2 launched June, 2008 had been recording sea level data globally. Data sets as a combination of
data from TOPEXPoseidon, Jason-1 and Jason-2OSTM has shown a steady increase in global mean sea level. The illustration of sea level increasing in 1993-
2010 can be seen in Figure 4.6.
Figure 4.6. Monthly average of global mean sea level pattern based on data of tide
gauge and altimetry satellite
The average level of rising between over from 1993-2010 based of satellite- derived data was 0.28 mmyear. If this rising is compared with rising level from
tide gauge data in 1903-1920 and 1953-1970 100 and 50 years ago, the rising average nowadays is 4.8 times higher than the value in 100 years ago and 3.9
times higher than the value in 50 years ago. Even if we compared global mean sea level from tide gauge data in the same previous periods 100 and 50 years ago
with the tide gauge data in this period 1993-2010, the rising average nowadays is 5.2 times higher than the value in 100 years ago and 4.2 times higher than the
value in 50 years ago. The value of the change is not the same between tide gauge and satellite, but the pattern of chart Figure 4.6 represent the same meaning, the
linear increasing of sea level with uncertain value. The data of sea level rise in from tide gauge and satellite in specific time can be seen in table 4.2.
