| dc.description.abstract | This study explores the contrasting characteristics of large-scale circulation that led to the precipitation anomalies over the northern parts of Sumatra Island and investigates the schematic mechanism of teleconnection between the Asian-Australian Monsoon (AAM) and other circulations. The moisture budget analysis was applied to quantify the most dominant component that induces precipitation variability during the JJA (June, July, and August) period. Then, the composite analysis and statistical approach were applied to confirm the result of the moisture budget. The linear regression analysis was applied to compare the climate indices in both spatial and temporal scales, such as Dipole Mode Index (DMI), the Oceanic Niño Index (ONI), and the Western North Pacific Subtropical High (WNPSH) index. Using the European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis Interim (ERA-Interim) from 1981 to 2016, we identified 9 (nine) dry and 6 (six) wet years based on precipitation anomalies, respectively. The dry years (wet years) anomalies over the study area were supported mainly by downward (upward) vertical velocity anomaly instead of other variables such as specific humidity, horizontal velocity, and evaporation. Instead of El Niño-Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD), WNPSH has a stronger relationship with the study area′s precipitation anomalies. However, the WNPSH index is inconsistent with the precipitation variability because it cannot be found in all wet/dry year cases. By contrast, most cases (especially the wet events) were associated with the fluctuation of zonal winds in the tropical western North Pacific. This fluctuation explains why the WNPSH index has a stronger correlation with the precipitation in the study area. Then, a new climate index was proposed to identify the precipitation anomalies over the north of Sumatra Island, called the Easterly Wind Index (EWI). A strong positive (negative) phase of EWI is related to the magnitude of easterly (westerly) wind anomaly, which induces the positive (negative) precipitation anomaly over the northern part of Sumatra Island. The westerly and easterly wind anomaly is possibly related to the PWC modulation (Pacific Walker Circulation). Further, the AAM variability proven has a significant role in the precipitation variability over the study area. A teleconnection between the AAM and other global circulations implies that the precipitation variability over the northern part of Sumatra Island is not a regional phenomenon related to the large-scale tropical circulation over the Philippine Sea and the Maritime Continent/eastern Indian Ocean region. In conclusion, the easterly anomaly is the main feature resulting in precipitation anomaly over the northern Sumatra Island. When the monsoon westerly that creates subsidence in northern Sumatra is weaker (easterly anomaly), there tends to be more precipitation and conversely. | en_US |