The interannual and interdecadal variability of the Borneo vortex during boreal winter monsoon.

摘要

The boreal winter monsoon over the Malaysian region has long been associated with heavy rainfall activity and flood disaster. One of the main features that characterize this monsoon is the presence of Borneo vortices. The main purpose of this study is to identify these vortices and determine their long-term climatological behavior over 41 winter monsoon seasons that ran between November and February of the following year from 1970 to 2010. Once congregated, the vortices are divided into five different seasonal aspects, which include the frequency, position, lifespan, intensity, and onset and retreat dates of the first and last vortex of the season.;2,278 of Borneo vortices were identified throughout the study period. Out of this number, about 77% were considered as the weak type of vortex, 17% moderate and 5% strong. More than 60% of the vortices were discovered on a water body and the vortex long-term mean position was located at 2.4°N and 110.6°E, which is just off coast of the Borneo Island. In addition, the vortex systems have a mean lifespan of 3.6 days, which suggests that they are a synoptic type of weather event. The first vortex of the season tended to appear in early November while the last one generally left the region by end of February.;All of the polynomial long-term trends of the vortex aspects show a pattern that emulates the (Pacific Decadal Oscillation) PDO interdecadal variability except in the case of the vortex system lifespan. Besides the PDO, the vortex aspects also demonstrate strong signals of emulating the (El Nino Southern Oscillation) ENSO, (Tropospheric Oscillation Oscillation) TBO and/or (Quasi Biennial Oscillation) QBO interannual variability when their time-series data are transformed into a function of oscillation through the Fourier power spectra analysis.;The data from each aspect of the Borneo vortices were then compared with all these interdecadal and interannual variabilities using the compositing analysis technique. The outcomes reveal that the majority of the vortex aspects show strong feedback with regard to different phases of the ENSO, TBO and PDO events, but not the QBO. Furthermore, the EN signal is found to be strong in PDO1 period while the LN signal is strong in PDO2. Also, it was discovered that the EN tends to weaken the TBO event, while the impact was reversed during the LN years. Even though most of the relationships identified here show strong confidence levels, however, some were not strong enough to be considered as statistically significant. In addition, this study also examined two selected events in order to find the differences among the Borneo vortices of different intensities based on their convective parameters.