Judul: Karakteristik Gelombang Kelvin Ekuatorial Atmosferik pada Kondisi Normal (1990), La Nina (1988–1989), dan El Nino (1997–1998)
Abstrak: The purpose of this research is to analyze the characteristics of atmospheric equatorial Kelvin waves using spectral technique of upper winds in the level of 100 mb (tropopause) and 50 mb (lower-stratosphere) in Normal (1990), La Nina (1988–1989) and El Nino (1997–1998) condition. In tropopause, Kelvin waves are predominantly excited by deep tropical convections. Generally, behavior of Kelvin waves in the Normal condition is similar to those observed during the La Nina condition, namely the energy of waves is substantially strong over the maritime continent (Indonesia), but during the La Nina condition the energy of waves is also strong over Pasific ocean. Whereas the energy of waves over Indonesia is low during the El Nino condition because strong energy of the waves moves to western Pasific ocean following deep tropical convections. Kelvin waves have an upward energy propagation. The observed energy of the waves over Indonesia in the level of 100 mb is strong, thus, Indonesian region becomes a favorable region to induce the equatorial stratosphere circulation, especially on the quasi-biennial oscillation (QBO). In the lower-stratospher, we indetify the QBO during the period of 24 and 28 months. In the level of 50 mb the energy of Kelvin waves is strong when phase of QBO changes from easterly to westerly and westerly momentum increases. This is caused by easterly QBO phase dominates layer under the level of 50 mb, so the energy of Kelvin waves can penetrate to the level of 50 mb. The energy of Kelvin waves in tropopause is stronger than in lower-stratosphere due to distance from the forcing (tropical convection centre).
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Judul: Analisis Gelombang Atmosfer Ekuatorial Planeter (EPW) di Lapisan Tropopause dan Stratosfer Bawah Indonesia dengan Menggunakan Data NCEP/NCAR Reanalysis I.
Abstrak: Equatorial Atmospheric Planetary Waves (EPW) in the Tropopause and Lower Stratosphere of Indonesia are discussed. This research is motivated by complete unsolved problems relating to evidence of existence, behavior, propagation (horizontal and vertical structure), and periodicity of EPW as well as interconnected to other equatorial atmospheric oscillations in Indonesia. Based on linearized equations of EPW in β-plane, EPW n=0 mode has greatest meridional wind amplitude in Equator and decays exponentially when away from the Equator (Gaussian Decay). EPW n=1 mode has greatest amplitude of meridional wind pertubation (v’) at latitude y= ± 1 (dimensionless) and v’ equal to zero in Equator. For EPW n=2 mode, amplitude of v’ equal to zero at latitude y = ±1/2√2 and greatest amplitudes outside the Tropics. Simulation of mixed Rossby Gravity wave results that either zonal wind or geopotential field has greatest pertubation amplitudes at latitudinal domain y= ±1 (u’=0 in Equator). Pertubation of zonal wind (u’) and geopotential field (Ф’) be in geostrophic balance at latitude y>1 and y<-1 (dimensionless) or -(β-1√gH)1/2 < y < (β-1√gH)1/2 (length dimension unit). Simulation of Kelvin wave results that either zonal wind or geopotential field has symmetric amplitude and symmetric pertubation relative to Earth latitude. Based on spectral and kinetic energy (KE) analysis, Kelvin waves in the tropopause of Western Indonesia are found in the 15 days in wet season and 18 days in dry season. Energy of Kelvin wave in this region is stronger than others. In the Middle of Indonesia, these waves are found in a period of about 12.9-18 days in wet season and do not appear in dry season. While in Eastern Indonesia, this wave appears in period of 10-12.9 days (wet season) and 11.3-18 days (dry season). Their presence in transition season is not clearly found. KE response for Kelvin waves oscillations in 10- 18 days will exhibit when monsoon strengthened in the tropopause of Southeast Asia. In the Stratosphere of Indonesia Kelvin wave appears only in wet season. Presumably, existence of Kelvin wave in the lower stratosphere is produced by vertically propagation of Kelvin wave in the tropopause.
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Judul: Hydroxyapatite-Chitosan Composite Coating on Stainless Steel 316 to Improve Corrosion Resistance
Abstrak: Metals that were used in bone implantation should have good corrosion resistance that were not easily corroded when implanted into the body. Metal corrosion resistance of stainless steel 316 can be enhanced through the metal coating by hydroxyapatite-chitosan composite with composition ratio of hydroxyapatite (gram) and chitosan 3% (mL) 0.2:0, 0.2:0.1, 0.2:0.5, 0.2:1.0, and 0.2:1.5. Besides improving the corrosion resistance of metal, the presence of chitosan also maintain the position of hydroxyapatite on metal surfaces. Corrosion resistance increases with increasing amount of chitosan added and the best composition of hydroxyapatite-chitosan composite was 0.2:1.0.
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