An assessment by Matthias Tomczak, Professor of Oceanography at Flinders University, Adelaide, South Australia

[18 December 2002]

[cf: Report from Harbour Master at Sunda Kelapa Port, Nth Jakarta re rescue position of SIEVX]

The South Java Current is controlled by the monsoon over the Indian Ocean and Indonesian archipelago. In the climatological mean situation it flows generally towards south-east along the coast during December - April (the Javanese north west monsoon season) and towards north-west along the coast during June - October (the Javanese south east monsoon season) and goes through periods of transition during two weeks in May and November.

Typical current speeds during the two monsoon seasons are about 0.3 - 0.6 m/s (0.6 - 1.2 knots, or nautical miles per hour). Speeds increase to 2 - 3 times these typical values during the transition periods.

During the Javanese south east monsoon season (June - October) the South Java Current is part of a coastal upwelling system. In coastal upwelling situations the surface layer of the ocean is moved offshore by the wind and replaced by water that rises ("upwells") from deeper layers. This movement away from the coast is generally of the order of 0.2 - 0.5 m/s (0.4 - 1.0 knots, or nautical miles per hour). It is important to note that the wind that produces the movement away from the coast blows parallel to the coastline; the difference between the wind direction and the direction of the generated upwelling current is due to the rotation of the earth.

Based on the climatological situation an object or a person drifting in the South Java Current around the 22nd [sic] of October would drift in a general north westward direction parallel to the coastline and gradually increase its distance from the coast as a result of the coastal upwelling. Over a period of 22 hours the resulting displacement would be approximately 13 - 26 nautical miles (24 - 48 kilometers) along the coast, and the distance from the coast would increase by approximately 9 - 21 nautical miles (16 - 40 kilometers).

If the SIEV X survivors were in the water for 22 hours before they were rescued at a location 50 [sic] nautical miles from the Indonesian coast, it can be stated quite categorically that under normal climatological conditions they could not have started their drift from within Indonesian waters (the 12 nautical mile limit).

It has to be noted that the South Java Current displays significant variations from year to year and the climatological mean situation is not necessarily applicable to a particular event. The most significant variation from year to year occurs in the transition periods between the monsoon seasons. The transitions can occur one month earlier or later than May and November, respectively, and the usual November intensification of the South Java Current may thus occur as early as October. But the intensification only occurs in the along-shore current component, not in the upwelling circulation. An object or person drifting with the current would thus be swept along the coast faster than in the climatological mean but would not separate from the island faster. A faster along-shore current would therefore not change the conclusion that the object or person could not cover the distance between the Indonesian waters and the location of rescue of the SIEV X survivors in 22 hours.

A more definite statement would require knowledge of the local wind conditions and of the sea level along the coast of Java for the period under investigation. Such data could put the situation beyond all doubt; they would have to be obtained from the Indonesian authorities. It is my view that they are very unlikely to change my assessment, which is based on the climatological behavior of the current.

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