Intraseasonal rainfall variability in North Sumatra and its relationship with Boreal Summer Intraseasonal Oscillation (BSISO)

The Boreal Summer Intraseasonal Oscillation (BSISO) is a mode of climate variability on intraseasonal timescales that dominantly occurs during Northern Hemisphere summer monsoon. Its propagation and activity can be monitored by using indices namely as BSISO1 and BSISO2. The rainfall anomalies and extremes in North Sumatra may be potentially affected by BSISO due to its location within the path of their propagations. This study analyzes the relationship of BSISO with daily rainfall anomalies and extremes during different phases and types of BSISO. The results of spectral analysis show some agreements in the periodicity of BSISO1 and BSISO2 with daily rainfall anomaly. This study also identifies extreme rainfall during different phases of BSISO, showing the increase in the number of extreme rainfall events. High number of extreme rainfall events beyond thresholds at 90th and 95th percentiles are mostly found during phase 1, 2 and 3 of BSISO1 and phase 1 and 2 of BSISO2. Composite analysis conducted separately for spatial standard deviations of daily rainfall anomalies are also performed in this study. Similar results are found, where BSISO influences on rainfall variability especially during phase 1, 2 and 3 of BSISO1, and phase 1 and 2 of BSISO2.