We report a study of cloud cover over Indonesia based on meteorological satellite data spanning 15 years (from 1996 to 2010) to aid in the selection of a new astronomical site capable of hosting a multi-wavelength astronomical observatory. High-spatial-resolution meteorological satellite data acquired from Geostationary Meteorological Satellite 5 (GMS 5), Geostationary Operational Environmental Satellite 9 (GOES 9) and Multi-functional Transport Satellite-1R (MTSAT-1R) are used to derive yearly average clear fractions over various regions of Indonesia. This parameter is determined from temperature measurements in the IR3 channel (water vapour, 6.7 µm) for high-altitude clouds (cirrus), and from the IR1 channel (10.7 µm) for lower-altitude clouds. An algorithm is developed to detect the corresponding clouds. The results of this study were used to select the best possible sites in Indonesia, which will be analysed further by performing in situ measurements in the future. The results suggest that regions of East Nusa Tenggara, located in southeastern Indonesia, are the most promising candidates for such an astronomical site. The yearly clear sky fraction of this region may reach better than 70 per cent, with an uncertainty of 10 per cent.

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The proper motions of 276 individual sunspots were observed with a triple-exposures method, and then analyzed. Their linear drifts give the mean motions (degree day−1), which, depending on the heliographic latitude B, are the differential rotation, ω(B) = 14.5 – 2.5sin2B, and the equatorward meridional flow, vB = −0.05sin 2B. The deviations of the linear drift from the mean motions have a small correlation between the longitudinal and latitudinal ones, which correspond to the equatorial acceleration. The deviations in longitude are clearly separated by the sunspot polarities. The average separation velocity between the preceding and following polarities is 52 m s−1. The drifts of individual sunspots corrected for the mean motion are the smallest for the Zürich GHJ class. However, they are fairly large and may influence the determination of the mean motion. Short-term variations appear as positional deviations from the linear-drift curve. These fast drifts are detected in the active Zürich classes, and are one order of magnitude larger than the linear drift.

Solar activities eject high energetic particles, instead of electromagnetic radiation. The well-know solar activity main indicator is the existence of sunspot which has mean variation in 11 years, named by solar cycle. Solar activities are related to the space weather affecting all planets atmospheric variability, moreover to the Earth's climate variability. The big question arises to the relation between solar forcing energy to the Earth's global volcanic activities. We search its connectivity from yearly volcanic activities refer to Volcano Explosive Index (VEI) and sunspot number within year of 1900 to 2013 (113 years) which represent the global warming period and the range of Maunder minimum within year of 1615 to 1751 (136 years) which known as the global cooling period. We found that the declining solar cycle significantly show more volcanic activities (VEI=1 to 5) with more than 40% occurrences for both warming and cooling periods. They have mean occurrences of (50.1±4.5) % and (42.0±10.4) %, respectively. In the rising phase of solar cycle, the average occurrences are (27.1±3.3) % and (28.8±5.3) %, respectively. When we selected the interval time in 3 years around the peak of maximum and minimum of the solar cycle, the global warming period had average of (27.1±5.5) % and (32.1±4.4) %, respectively and the global cooling period showed an average of (32.7±11.1) % and (21.3±5.0) %, respectively. The minimum phase showed higher frequency events of volcanic activity than the maximum phase during the warming period, opposite to the cooling period. Although the physical reason is far for explanation, we argue that solar activities have a clear relation with global volcanic activities.

A satellite placed in space is constantly affected by the space environment, resulting in various impacts from temporary faults to permanent failures depending on factors such as satellite orbit, solar and geomagnetic activities, satellite local time, and satellite construction material. Anomaly events commonly occur during periods of high geomagnetic activity that also trigger plasma variation in the low Earth orbit (LEO) environment. In this study, we diagnosed anomalies in LEO satellites using electron data from the Medium Energy Proton and Electron Detector onboard the National Oceanic and Atmospheric Administration (NOAA)-15 satellite. In addition, we analyzed the fluctuation of electron flux in association with geomagnetic disturbances 3 days before and after the anomaly day. We selected 20 LEO anomaly cases registered in the Satellite News Digest database for the years 2000-2008. Satellite local time, an important parameter for anomaly diagnosis, was determined using propagated two-line element data in the SGP4 simplified general perturbation model to calculate the longitude of the ascending node of the satellite through the position and velocity vectors. The results showed that the majority of LEO satellite anomalies are linked to low-energy electron fluxes of 30-100 keV and magnetic perturbations that had a higher correlation coefficient (~ 90%) on the day of the anomaly. The mean local time calculation for the anomaly day with respect to the nighttime migration of energetic electrons revealed that the majority of anomalies (65%) occurred on the night side of Earth during the duskto-dawn sector of magnetic local time. which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.