No abstract

Akurasi prakiraan curah hujan harian operasional yang dibuat oleh Badan Meteorologi Klimatologi dan Geofisika (BMKG) dikaji dengan cara diverifikasi berdasarkan kategori hujan dikotomi, lebat dan sangat lebat terhadap data dari 25 titik pengamatan di Jakarta. Prosedur yang sama juga diterapkan pada prakiraan curah hujan model Weather Research and Forecasting (WRF) dengan teknik multi-nesting yang di-downscale dari keluaran global forecast system (GFS). Hasilnya memperlihatkan bahwa kedua metode prediksi tersebut memiliki akurasi yang baik untuk prediksi dikotomi tetapi hampir gagal dalam memprediksi curah hujan lebat dan sangat lebat. Khususnya, kegagalan prediksi operasional dalam mendeteksi tiga kejadian hujan sangat lebat dalam periode kajian. Dalam hal ini, model WRF yang cenderung menghasilkan false alarm memperlihatkan prospek yang bagus untuk pengembangan sistem prediksi cuaca skala lokal/regional yang lebih akurat di Indonesia.

A baroclinic ihrec-dimensional (3D) hydrodynamic model with ihe nonhydroslatic approximalion called Massachusetts Institute of Technology -Global Circulation Model (MlTgcm) has been applied to simulate the generation of internal tidal bores and their disintegration into internal solitary waves in the Strait of Lombok. Numerical simulations have been carried out by incorporating seasonal variations of the stratification of [he water body, which exist during the 1" transitional monsoon, the east monsoon, the 2 M transitional monsoon, and the west monsoon. Our simulation yields the results that the existence of the sill at the southern part of the Lombok Strait, strong tidal flow, and a stratified fluid, play an important role in forming some short of divergence and convergence area as an indication of the birth of internal waves, which are simulated on the both sides of thcsill. The simulated results reproduce reasonably well the basic features of internal waves in the Strait of Lombok as captured by the Synthetic Aperture Radar (SAR) from the European Remote Sensing (ERS) satellites ERS I and ERS 2, such as a north-south asymmetry, propagation speeds, average amplitudes and wavelengths, and soliton packets. Similar to observations made by National Oceanic and Atmospheric Administration (NOAA) satellites, the simulation results also showed the intrusion of warm water from the Pacific Ocean into the Indian Ocean and the existence of well-developed thermal plume at south of the sill. Seasonal variations of interface depth of thermocline and the density difference between the stratified layers influence magnitudes of the amplitudes and wavelengths of the internal waves and solitons, and the distance of thermal plume in the Lombok Strait. It is found that during the monsoon transition periods and the west monson, ihe amplitudes of internal waves and solitons at the southern part of the strait is apparently larger than those at the northern one, whereas during the east monsoon, the wave amplitudes is larger north of the sill than south of it. Meanwhile, the propagation speeds of northward propagating internal solitary waves (0.71 -2.67 m/s) arc stronger than southward propagating ones(0.21-1.53 m/s) throughout the monsoon periods.

Abstract.This study has analyzed a rainfall estimation using a modified convective stratiform technique (CSTm). Unlike the original convective stratiform technique (CST), which only utilizes infrared (IR) data, CSTm applies not only IR data but also passive microwave (PMW) data. Two major modifications contained in CSTm are: (1) the application of a variability index (VI) method that uses PMW data to perform convective and stratiform separation, and (2) the ability to determine the average extensive coverage of the new areas of each pixel point as a result of the utilization of the PMW data. In this study, rainfall estimation was conducted for 23 points spread over four major islands in Indonesia. The estimation was performed based only on IR and PMW data obtained from coincident observations. For verification, the estimation results were compared with real observations. The main verification action conducted in this study used multi-category contingency tables for 4 categories and this action was supported by the root mean square error (RMSE) method. The verification results of the hourly estimation conducted for 4 days in early November 2011 showed that CSTm can effectively improve the performance quality of CST.

Abstract. This paper presents an analytical study on surface wave attenuation in mangrove forest using analytical model developed by Massel et.al. (1999). The energy dissipation in the frequency domain is determined by treating the mangrove forest as a random media with certain characteristics using the geometry of mangrove trunks and their locations. Initial nonlinear governing equations are linearized using the concept of minimalization in the stochastic sense and interactions between mangrove trunks and roots have been introduced through the modification of the drag coefficients. To see the effectiveness of the mangrove forest in attenuating wave energy the analytical model was applied to two types of mangrove forest i.e. Rhizophora and Ceriops forests. The resulting rate of wave energy attenuation depends strongly on the density of the mangrove forest, and on diameter of mangrove roots and trunks. More effective wave energy attenuation is shown by Rhizophora.