IMPACTS OF MJO ON THE ATMOSPHERE-OCEAN VARIABLE AND LINKAGES TO INDONESIAN THROUGHFLOW IN THE INDONESIAN SEAS

• Main Author: Lumban Gaol, Adelina
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/67587
• Institution: Institut Teknologi Bandung

Climate variability at various time scales plays a key role in Earth's climate and global ocean circulation, one of which is the MJO intraseasonal phenomenon. To further understand the linkages of the MJO to the atmospheric-ocean variability affecting ITF transport in the Indonesian seas, MJO events from 1993 to 2019 were classified as MJO-MCC and MJO-MCnC phenomena. The categorization of MJO intra-seasonal phenomena is based on the propagation characteristics and amplitude of the RMM and OMI indices by considering seasonal effects. Furthermore, the composite method of data from the daily 20-90 band pass filter was investigated based on the DJFM and JJAS. MJO-MCC was identified to have a larger index amplitude and a more significant number of events than MJO-MCnC. Atmospheric-ocean variability fluctuations were more significant during MJO-MCC than MJO-MCnC phenomena. The influence of MJO-MCC and MJO-MCnC shows the same pattern, especially in west coast of Sumatra, southern Java coast, to parts of the waters of Nusa Tenggara. Significant differences in sea current and sea level anomalies are also formed in the Natuna and Arafura Seas due to surface wind factors during MJO-MCC and MJO-MCnC. Seasonal effects on atmospheric-ocean variability show that the strongest MJO signal is north of the MC during the JJAS and south of the MC during the DJFM, with the most robust MJO activity being in the DJFM. The weakening of the frequency during the JJAS in both MJO classifications occurred due to the MJO-BSISO interaction effect, which was not well identified by the MJO index. CWT and XWT analyzes were carried out to determine the dominant impact of the relationship between the two-time series of the atmosphere-ocean variables. The results show sea level intraseasonal variations along the west coast of Sumatra, which tend to be in phase with changes in OLR, and alterations in OLR are directly followed by changes in sea level. In contrast, the SST variable during the intraseasonal period tends to have a varied relationship with OLR. SST variability can be caused by changes in OLR and vice versa; SST influences changes in OLR. In addition, SST variability varies with enhancement or reduced OLR. The influence of MJO on Indonesian Seas is identified through the role of coastal Kelvin Wave propagation. Coastal Kelvin waves are more dominant in influencing ocean variability and are identified at the thermocline depth (about 120 m). During the active phase of the MJO, coastal downwelling Kelvin waves formed from the equatorial Indian Ocean and propagated towards the west coast of Sumatra, south Java coast to parts of Nusa Tenggara waters, causing an increase in sea level followed by a weakening of Arlindo transport. On the other hand, during the suppressed MJO phase, coastal Kelvin upwelling causes a decrease in sea level and increases Arlindo transport in Indonesian seas. Evidence of propagation of coastal Kelvin waves can be identified through variations in SST anomalies reaching 0.5oC and intraseasonal sea level anomalies reaching 6.0 cm. In addition, the phase propagation of the variation of sea level anomaly, which propagates eastward can reach ~2.1 m/s during the MJO event. The difference in the MJO propagation effect in the DJFM and JJAS lies in the fluctuation of the maximum MJO signal frequency that occurs during the DJFM compared to the JJAS, as well as lag 1 phase between the DJFM and JJAS. This also causes variations in the frequency of Arlindo's transport from the Lombok Strait to the Makassar Strait during the MJO phase change. Coastal Kelvin waves, as evidence of the MJO effect, significantly affect the Indonesian seas during the DJFM compared to the JJAS.