DETERMINING THE ACTIVE MONSOON PERIODS IN INDONESIA BASED ON LOCAL RAINFALL AND REGIONAL MOISTURE SOURCES

• Main Author: Yolanda, Selvy
• Format: Theses
• Language: Indonesia
• Subjects: Geologi, hidrologi & meteorologi
• Online Access: https://digilib.itb.ac.id/gdl/view/78264
• Institution: Institut Teknologi Bandung

Active monsoon period is one of the crucial phases in the monsoon life cycle but has not been determined operationally by the Indonesian Agency for Meteorological, Climatological, and Geophysics (BMKG). In this regard, the date of commencement of rainy season is an existing operational product of BMKG, which is locally determined using a criteria based on ten-day accumated rainfall. In this study, a method to determine active monsoon periods is developed, incorporating criteria of local rainfall and regional moisture sources. Regional moisture sources are first climatologically analyzed by applying harmonic analysis and selecting the month of maximum rainfall from the annual cycle. The sources of mositure transport are then examined from the results of backward trajectory analysis using Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model. The dominant sources of moisture are than used for the criteria of active monsoon; additional criterion of local rainfall rainfall is determined as five-day area-averaged rainfall exceeding a threshold, whose values depend on data being used. The method is applied to determine active active monsoon periods over an area of Java Island with monthly rainfall maxima around January-February (known as Region A). It is found that active monsoon periods in this area are characterized by dominant moisture sources from the Indian Ocean (IO) (29.4%) and the northern maritime continent (NM) (25.4%), whereas area-averaged local rainfall threshold is 7 mm (from global reanalysis data). The results also show that active monsoon periods can be identified as contiguous pentads. However, there pentads where only one type of criteria are satisfied. Composite analyses suggest that these cases might occurr due to conditions associated with intraseasonal variations such as monsoon break, the passage of Madden-Julian Oscillation, etc. Application of the method to other regions in Indonesia is still limted to examination of moisture sources. It is found that, in general, NM contributes significant portion of moisture sources during active monsoon periods in Indonesia but there are differences in the complimentary sources. Nevertheless, the method developed in this study is promising as a new way to monitor monsoon onset, at least in the Region A.