Characteristics of Local Flow in Jakarta, Indonesia and Its Implication in Air Pollution Transport

Jakarta, Indonesia has experienced serious air pollution problems associated with the use of energy in the transport, domestic, and industrial sectors. Meteorological conditions in a region often play a dominant role in building up severe air pollution. Yet the local flow system in this large tropical coastal city is not well understood. Thus our primary concern in this study was to investigate characteristics of meteorology over western Java area, especially Jakarta city and its implication for air pollution transport. Climate in west Java area is classified roughly into two types, “rainy” from December to March, and “dry” from May to October. Thus as a first step we focused on the local flow system under the typical “rainy” weather by using PSU-NCAR MM5. We performed five days long simulation on 8-13 February 2001 to see how local flows develop over the area in this season. Obtained results can be summarized as follows: (1) Under synoptic scale WSW wind as background, which is typical in the “rainy” season, significant sea breeze developed on 9 and 10 February. In particular, on February 10, the sea breeze could penetrate to around 20 km inland from the coast of Jakarta. (2) In almost any time when sea breeze develops, convergence line due to synoptic WSW and local NW (sea breeze) was formed over Jakarta area; the convergence line typically runs from the west of the coastal Jakarta to the south-east of the city, indicating that the synoptic WSW wind tends to prohibit inland-ward penetration of the sea breeze from Java sea. (3) Subsidence behind the convergence line lowered the depth of the sea breeze with time, by warming upper part of the wind layer, such as 0.5, 0.8, 0.4, and 0.2 km at 1200, 1300, 1400, and 1500 LST on 10 February, respectively. (4) By this convergence line and the subsidence, stable thin-layer was formed over the Jakarta area, indicating possible trap of the air pollutants in the layer and increased air pollution potential. (5) In the mountainous area to the south of Jakarta, another local flow of northerly valley wind independently developed; that is, the synoptic WSW wind zone always existed and separated the sea breeze from the valley wind. This disconnection of the two local flows again may increase air pollution in Jakarta by prohibiting ventilation of the polluted air mass over the Jakarta. In our presentation, we will also discuss the difference of the local flow between “rainy” and “dry” seasons.