NUMERICAL CLIMATE MODEL in Indonesian Region
The Houw Liong
Climate model can be constructed by using the law of physics for the atmosphere i.e.: The Navier-Stokes equation, the conservation of mass, the conservation of energy, the equations of states, including schemes for cloud formations, carbon and sulfur cycle, interactions between atmosphere and land surface, oceans, cryosphere, and biosphere, furthermore we have to include forcing by volcanic eruptions, the solar activity and galactic cosmic rays.
In Indonesia scientists from LAPAN [Ratag, 2002] use Global circulation Model (GCM) with 9 levels vertical resolution and 3.20×5.60 horizontal resolution based on sigma coordinates. Limited local area model (DARLAM) is used to obtain higher resolution 25 km x 25 km. The model also has to include schemes for cloud formations, carbon and sulfur cycle, and interactions between atmosphere and land surface, oceans, cryosphere, and biosphere.
With a scenario that the concentration of CO2 will be doubled in 100 years, the temperature anomaly can be calculated. In 50 years from 1990 most Indonesian regions the temperature very likely will raise by 0.5 to 1.0 degrees Celsius. Some regions the temperature very likely will raise by 1.0 to 1.5 degrees Celsius. This climate model cannot predict the precipitations in Indonesian regions well. However the verification of this forecasting is not convincing because the in Indonesia many good weather stations are located in cities. From these stations the average increase of temperature from 1860 to 2000 is about 10 C, but actually the increase is due to urban warming, not global warming.
The forecasting of rainfall is still poor, for instant using rainfall data from Bandung the best forecasting is obtained using cloud formation according to Arakawa scheme the correlation with the data is 0.46.
It needs some modification before it can be use to predict rainfall well.
Furthermore a realistic model has to include forcing by volcanic eruptions, the solar activity and galactic cosmic rays which is poorly represented in climate model.
Due to the nature of chaotic system [Lorenz, 1960] and the difficulties to formulate complete model, and to get accurate data of boundary conditions and initial conditions are difficult, the accuracy of long term prediction is poor.
The satellite data is regarded even by NOAA administration to be the most reliable but they don’t use it in releases as it is only available for 30 years. It has shown a cooling since 2002.(Figure 6.)
Short range prediction according to WRF (weather research and forecasting), a regional numerical weather model developed by Pennsylvania State University/ National Center for Atmospheric Research (PSU/NCAR), with a horizontal grid resolution of 5 km. (Figure 7.)
By inspecting the model output in the area if interest, it is found that the largest concentration of convective rainfall over Jakarta and other area in the northern coast of West Java occurred particularly during 31 January – 2 February 2007 UTC (Universal Time Coordinated), as shown in Figure 7 & 9. It is important to note that the daily-accumulated rainfall on 1 February 2007 was more concentrated in land and sea area, while almost all of the rainfall on 31 January 2007 was distributed along the coastal area. More interestingly, large convective rainfall occurred in both inland and Jakarta coastal area on 1 February 2007.