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Abstract: ADCP measurements in the southern Banda Sea, obtained with the bulk carrier “MS First Jupiter” from 1997 until 2000, have been analysed. The observations reveal the presence of an eastward flowing southern boundary current, bringing water from the Indonesian throughflow towards the connections with the Indian Ocean in Ombai Strait and the Timor Sea. The mean transport in the upper 300m is estimated to be about 5Sv, over 50% of the outflow towards the Indian Ocean in this layer through the eastern passages near Timor. The velocity in the boundary current shows a clear annual variation, more or less in phase with the annually varying inflow through Makassar Strait and the outflow near Timor. The phase of the annual variation cannot be explained by the monsoonal variation of the local winds. Therefore this annual variation of the throughflow is probably generated by large-scale forcing. A considerable reduction of the strength of the boundary current was observed in 1998, following the 1997–1998 El Niño with a delay of about half a year. On shorter time scales, Kelvin waves, entering the Banda Sea from the Indian Ocean, cause flow reversals of the boundary current. [Copyright &y& Elsevier]

Abstract: Variations in the diurnal precipitation cycle over equatorial Indonesia was investigated using 1.3-GHz wind profiling radars (WPRs) and rain gauges installed at Pontianak (109.37°E, 0.00°S), Manado (124.92°E, 1.55°N), and Biak (136.10°E, 1.18°S). The horizontal scale of the landmass around Pontianak is more than 100km, while those of Manado and Biak are 10–100km. At all three WPR sites, peak rain rate was detected during 1300–1500 local time (LT) by rain gauges. WPR observations showed that deep convective clouds were predominant during that period. There was a clear difference in the afternoon-to-evening precipitation among the three WPR sites. At Pontianak, the afternoon-to-evening precipitation has the characteristics of a mesoscale convective system (MCS). Stratiform precipitation after the peak deep convective rain rate was predominant, and the transition from convective precipitation to stratiform precipitation was clearly apparent during 1500–2000LT. Black body brightness temperature (T bb) observed by MTSAT-1R satellite also indicated that the precipitation clouds had enough horizontal scale to be well organized as an MCS. At Manado and Biak, the peak rain rate in the early afternoon was characterized by a short period (1–2h), and the precipitation after the convective precipitation was not clear. T bb data showed that the convective precipitation had a horizontal scale of 10–100km. The difference of precipitation features among the three WPR sites is considered to be caused by the difference of horizontal scales of the respective landmasses. The diurnal precipitation cycle was also investigated using 11 years of Tropical Rainfall Measuring Mission (TRMM) data. A 3G68 product with a horizontal resolution of 0.5° could not resolve peak rain rate in the early afternoon at Manado and Biak, where convective clouds developed with the 10–100km horizontal scale. Surface rain data with a horizontal resolution of 0.1° were produced using the TRMM precipitation radar (PR) 2A25 product. This high-horizontal-resolution data set successfully detected the peak convective rain rate in the early afternoon at Manado and Biak. [Copyright &y& Elsevier]

Abstract: Horizontal wind data over Indonesia obtained by global reanalyses were compared with wind-profiling radar (WPR) observations in Indonesia at Kototabang (100.32°E, 0.20°S), Pontianak (109.37°E, 0.00°S), Manado (124.92°E, 1.55°N), and Biak (136.10°E, 1.18°S). The global-reanalysis data were 850- and 700-hPa horizontal winds for 2007 and 2008. These data were obtained from the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) Reanalysis (R1), the NCEP-Department of Energy (DOE) Atmospheric Model Intercomparison Project (AMIP-II) Reanalysis (R2), the Japan Meteorological Agency Climate Data Assimilation System (JCDAS), the European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis-interim (ERA-Interim). All the four reanalyses showed good agreement with the WPR zonal and meridional wind data (correlation coefficient >0.7 in most cases). Of the four reanalyses, ERA-Interim had the highest correlation coefficient with the WPR winds in both zonal (correlation coefficient 0.89) and meridional (0.77) components. It can be explained that ERA-Interim used four-dimensional variational analysis (4D-var) for data assimilation, whereas the other reanalyses used three-dimensional variational analysis (3D-var). The zonal winds of the four reanalyses had smaller (78–87%) amplitudes than did the WPR winds. Further comparison of the zonal winds between the global reanalyses and operational radiosondes indicated that global-reanalysis zonal winds with smaller amplitudes are common in and around Indonesia. [Copyright &y& Elsevier]