The Houw Liong* and Plato Martuani Siregar**
*Department of Physics,FMIPA, ITB
**Department of Geophysics and Meteorology,FITB, ITB
The cosmic rays interact in the upper atmosphere and produce secondary particles. Generally the charged particles so produced cannot penetrate to lower layers of the atmosphere, except the neutrons and the muons (below 6 km heights). When the neutrons or the muons interact with the air molecules or water molecules, they become charged and act as condensation nuclei for the formation of clouds. The cosmic ray becomes the source of ions in the air besides radiation coming from earth originated by the radio isotope radon.
During the sunspot minimum, the intensity of the cosmic ray becomes maximum which in turn increase the coverage of clouds. This implies that solar radiation reaching the earth will be minimized. Conversely, during sunspot maximum, the intensity of cosmic ray reaching lower levels of the atmosphere reduces, the cloud cover decreases, furthermore extra energy received from flares during prominent eruptions, maximizes the amount of solar energy received on earth.
The global cloud cover produces global warming (the greenhouse effect) which amounts to 13%, but it also causes a cooling effect as much as 20% due to reflections against direct solar radiation(1). The total energy derived from the sun is thus the solar constant averaging to 6.3 X1020 joules/hour which is equal to the energy of 40 tropical cyclones or 60 times the energy released by a major earthquake in Indonesia.
From the 21st solar cycle the irradiance received on earth shifted between 1367.0 W/m2 and 1368.5 W/m2 – it varies by 0.15 % only5). However, the large quantity of energy derived from the sun together with the forcing of atmosphere and oceans and the variation of the irradiance contribute considerably to the weather and climate.
Landscheidt(4) has shown that between years 1950 to 1975 very strong correlations existed between the events of El Nino and sunspot minimum SMin and its harmonics to SMin/2 or sunspot maximum SMax. The occurrences of La Nina correspond to maximum eruption ME and its harmonics ME/2. Then around the year 1975, a phase reversal occurred, and this continued from year 1976 up to the present, there the ME and its harmonics correlated well to El Nino, while SMax and its harmonics correspond to La Nina. Therefore, in this way, one can predict that the year 2006 will be the year of La Nina.
Starting from year 1950 to 1976, during the occurrences of El Nino, the sea temperature in the eastern region of the archipelago was low, and conversely during La Nina, the sea temperature was high, which means that low sea temperature in the archipelago correlates positively to sunspot minimum SMin and its harmonics, while the high sea temperature correlates positively to maximum eruptions ME and its harmonics. In 1976 phase reversal occurred, SM and SM/2 or sunspot maximum SMax correlate positively with high sea surface temperature in eastern Indonesia and as a result precipitations increased.
The Correlation of Sunspot to Rainfall in the Indonesian Archipelago
With the equator crossing Indonesia, the sensible heat flux plays an important role in global circulations. The latent heat which originates mainly from the release of latent heat when water vapour condenses into clouds droplets(a number of large clouds form through convections in the Inter Tropical Convergence Zone (ITCZ) which is above Indonesia). The cold monsoon season in northern hemisphere (Asian monsoon) and in the southern hemisphere (Australian monsoon) are influenced by the heat source distribution or the release of latent heat above Asia and in the neighbourhood regions(13). At present it seems that the Indonesian zone holds the key to southern oscillation system which determines the forcing of El Nino-Southern Oscillation (ENSO)14). Therefore, Indonesia, through which the equator crosses has the maximum sensible heat flux, high rainfall, and monsoon circulations. Consequently, it is one of the most primal zones for convection processes, an equatorial-tropical zone where Coriolis effects are practically nullified, where atmospheric circulations are very different compared to the extra-tropical zones15).
The observations and studies on Indonesian climate are limited, and the mathematical formulations of tropical dynamics are far more complex relative to those in the extra-tropical zones. For decades the awareness of the importance of climates in Indonesia have been neglected by international research community(16). The distinct daily convection variability induced by land-sea wind circulations over some islands in Indonesia characterizes the aspect of rainfall throughout the Indonesian Archipelago which are very different from other regions on the earth(17). The studies mentioned above, show that rainfall is an important quantity in the Indonesian Archipelago and sunspot is believed to be the major predictor.
Although there is an indirect physical link between sunspot and rainfall, the correlations which existed in general are weak. In other words, these signify that the dynamics of the atmosphere is being viewed as the cause of the small correlations. However, in the case of static model atmosphere, determination of correlations based on data-averaging of anomalies of sunspot on a monthly basis against the average anomaly of rainfall for various stations in Indonesia, one comes to time series as shown in Figures 1a, 1b, and 1c at various regions for the period 1948-2003.
From Figure 1 and Figure 2 we can conclude that eastern Indonesia (Jayapura region) which represent Eastern Indonesian Maritime Continent is strongly influenced by ENSO. After 1976 sunspot maximum SMax and sunspot minimum SMin correspond to precipitations above normal also to La Nina and maximum eruptions ME corresponding to precipitations below normal and also to El Nino. In Pontianak region which represent western Indonesian Maritime Continent, the yearly precipitation is mainly determined by sunspot cycles. Precipitations above normal occur at sunspot maximum SMax, and precipitations below normal at sunspot minimum SMin. Precipitations in middle and east Java which represent North Australia Indonesian Monsoon are influenced by ENSO similar to those observed in Jayapura region. Precipitations in Jakarta region are weakly influenced by ENSO.
The fuzzy c-means clustering shows that the west Indonesian regions are influenced by IOD, the east Indonesian regions are influenced by ENSO and the middle region is mainly influenced by sunspot numbers.