School of Earth Sciences - Research Publications
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ItemNo Preview AvailableThe Australian Northwest Cloudband: Climatology, Mechanisms, and Association with Precipitation(AMER METEOROLOGICAL SOC, 2019-10-01)Australian northwest cloudbands (NWCBs) are continental-scale bands of continuous cloud that stretch from northwest to southeast Australia. In earlier studies, where the characteristics of NWCBs and their relationship with precipitation were identified from satellite imagery, there was considerable uncertainty in the results due to limited quality and availability of data. The present study identifies NWCBs from 31 years of satellite data using a pattern-matching algorithm. This new climatology is the longest record based entirely on observations. Our findings include a strong annual cycle in NWCB frequency, with a summer maximum and winter minimum, and a statistically significant increase in annual NWCB days over the period 1984–2014. Physical mechanisms responsible for NWCB occurrences are explored to determine whether there is a fundamental difference between summer and winter NWCBs as hypothesized in earlier studies. Composite analyses are used to reveal that a key difference between these is their genesis mechanisms. Whereas summer NWCBs are triggered by cyclonic disturbances, winter NWCBs tend to form when meridional sea surface temperature gradients trigger baroclinic instability. It was also found that while precipitation is enhanced over parts of Australia during a cloudband day, it is reduced in other regions. During a cloudband day, precipitation extremes are more likely over northwest, central, and southeast Australia, while the probability of extreme precipitation decreases in northeast and southwest Australia. Additionally, cold fronts and NWCBs can interact, leading to enhanced rainfall over Australia.
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ItemSeasonal dependence of rainfall extremes in and around Jakarta, Indonesia(Elsevier, 2019)This study investigates the interannual, seasonal, and intraseasonal variation in rainfall extremes (REs) in Jakarta and surroundings. We used datasets of daily rainfall at three sites at coastal, inland and mountainous environments during 1974–2016 (42 years), Sea Surface Temperature, 850-hPa zonal and meridional winds, and Outgoing Longwave Radiation during 1979–2016 (37 years). The results show that intensity and frequency of REs, and their relative contribution to the total rainfall, have strong relationships with the Indian Ocean Dipole and El Niño Southern Oscillation in the dry season (Jun–Nov) but weak relationships in the wet season (Dec–May) at all sites. During active Madden-Julian Oscillation (MJO) period, the daily average rainfall and the number of RE days relative to all days show strong variation between MJO phases at all sites and the MJO signature differs between the three stations. At the coastal and inland sites, there is a less marked variation of the number of RE events relative to all days with MJO phases. Compared to lower altitudes, the high-altitude station has a greater number of RE events relative to all days in the wet season and a lower intensity of REs relative to total rainfall amount in the dry season. The results of the study suggest that the REs vary in each station due to highly localised differences in responses to large-scale conditions.
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ItemUsing Global and Regional Model Simulations to Understand Maritime Continent Wet-Season Rainfall Variability(American Geophysical Union, 2018)The Maritime Continent is a densely populated area of complex topography located between the Pacific and Indian Oceans. It is an area where model skill is particularly important but also difficult to obtain. In this study we examine interannual austral summer rainfall variability in the region and the teleconnection to the El Niño–Southern Oscillation (ENSO) in observation‐based data, reanalyses, and global and regional atmosphere‐only model simulations. We show that model ability to capture interannual rainfall variability is strongly related to model skill in reproducing the ENSO teleconnection to the region, despite strong spatial variability in the ENSO‐rainfall response in coastal areas. Model ability in capturing the spatial pattern of both the midtropospheric moisture and circulation response to ENSO is a strong predictor for model performance in capturing the ENSO‐Maritime Continent rainfall teleconnection. High‐resolution regional simulations and better performing models have opposing ENSO‐rainfall teleconnections between land and sea areas.