Observation at Lombok Geomagnetic Observatory

a b Figure 8. Variation recording of Solar Radiatin at LOK, a during 06.03.2016, 00:00 UTC – 12.03.2016, 23:59 UTC. b during 08.03.2016, 21:00 UTC – 09.03.2016, 05:59 UTC. 3.4. Temperature Measurements Temperatures were measured in the Variation Room, as recorded by the data logger MAGDALOG, with z time sampling and averaged in one‐minute. Results of measurements are depicted in Fig. , which shows that the temperature were mainly stable during the observation days – °C . owever, the temperature were slightly lower on the eclipse time. a b Figure 9. Variation recording of Temperature measured in the Variation Room of LOK, a during 02.03.2016‐ 16.03.2016, and b during 08.03.2016, 21:00 UTC – 09.03.2016, 05:59 UTC.

4. Spectrum of Variation Recording

The variation recordings of total fields F are analyzed to get the spectrum for frequency range , z. The normalized values of power spectral densities are reaching the maximum point of , on th March at f= z, while on other days are , on nd March at f= z, , on th March at f= z, , on th at f= z, , on th at f= z, and , 8 on th at f= , z. Results of spectrum analysis are depicted in Fig. . t can be concluded that the low frequencies are higher on the days before and after the eclipse. t means that the low frequency and contributions of internal sources to the total fields are reaching the minimum value on the solar eclipse day. ‐400 ‐200 200 400 00 800 1000 00 .0 12 .0 00 .0 12 .0 00 .0 12 .0 00 .0 12 .0 00 .0 12 .0 00 .0 12 .0 00 .0 12 .0 So la r Ra di at io n W m Time UTC ‐300.00 ‐200.00 ‐100.00 0.00 100.00 200.00 300.00 400.00 00.00 00.00 700.00 800.00 21 .0 22 .0 23 .0 00 .0 01 .0 02 .0 03 .0 04 .0 .0 So la r Ra di at io n W m Time UTC 1 21 41 61 81 101 121 141 161 181 200 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 20 22 24 26 28 30 32 Minute March 2016 Tem pera ture oC 27.2 27.4 27.6 27.8 28 28.2 28.4 28.6 28.8 29 ‐0.80 ‐0.70 ‐0. 0 ‐0. 0 ‐0.40 ‐0.30 ‐0.20 ‐0.10 0.00 21 .0 22 .0 23 .0 00 .0 01 .0 02 .0 03 .0 04 .0 .0 Variat io n of T °C Time UTC 7 Figure 10. Power spectral density of total fields F for frequency range 0,04Hz

5. Discussions Remarks

Among early study about geomagnetic fluctuation as an effect of the solar eclipse is done by Chapman , who theoritically estimated the effect that should be expected to result from a solar eclipse. Afterward, Chapman and Bartels stated that partial eclipses with more than of the Sun is obscured may be little inferior, in their magnetic effects, to total eclipses. A quite long time after that, Cullington showed that the magnetogram traces recorded at Apia Observatory on the day preceding the eclipse, the day of the eclipse, and the day succeeding the eclipse. At the time of the eclipse there appears to have been a distinct decrease in the horizontal component, with maximum amplitudes of nT in , . in D, and nT in Z. Further studies of solar eclipse has been done by Ates et al. , which resulted a decrease in the intensity of the magnetic field as observed during the total solar eclipse in in Turkey. Low‐pass filtered magnetic data show peculiarity during the eclipse which can be correlated with the fluctuations in the gravity fields. During the previous eclipse on the same region, Korte et al. reported that no eclipse‐related magnetic variations were observed from various parts of Europe. owever, they found a magnetically quiet period with magnetic activity index Kp= around the solar eclipse. On the other hand, during the same previous eclipse, Malin et al. observed changes in the declination angle and a decrease of the intensity of the magnetic field. Babakhanov et al. studied the effect in magnetic field by measuring the geomagnetic variations during a solar eclipse on August 8 in Rusia. They used standard instruments and comparing the results with measurements over the same time span at 8 NTERMAGNET observatories along shadow path from Canada to Japan. Some variations can be noted in the magnetic field in Novosibirsk with amplitude less than nT, which is not reliable for being among geomagnetic variations of non‐eclipse origin. The results for X component show negative anomalies for all mid‐latitude observatories and the times of its extremes coincide with local totality. Finally, Panda et al. studied the impact of January solar eclipse, they refer to Espenak et al. who considered that the effects associated with a solar eclipse is always unique and empasized the necesity to study any individual eclipses. t is because the solar eclipses may occur at various geographic locations during different phases of the solar activity, geomagnetic conditions, seasons, as well as local times of the day. 0.01 0.02 0.03 0.04 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 0.5 1 1.5 2 2.5 Frequency Hz March 2016 N or m al iz ed of P ow er S pe ct ru m D en si ty 0.5 1 1.5 2 2.5 8 Continuous observations at LOK during one month around the day of solar eclipse on th March resulted decrease in total field value of about nT or . from the base value results of absolute measurements during two years interval . This decreases are affected by reductions in the values of X Northing and Y Easting , which are the components related to horizontal component . On the other hand, there was slightly increase in Z vertical component . The frequency spectrum of total field showed decrease in low frequency e.g. internal source contribution. This decrease is about if compared to the maximum specral reached on another day. The absolute measurement results show significant increase in declination and decrease in inclination, and clearly confirm the decreases of fields during eclipse time. These decrease of total fields is more prominent in comparisson with the normal decrease during non‐eclipse days. The fluctuations of declination, inclination, and total magnetic fields are clearly seen since three days before the eclipse. The results of solar eclipse observations in our current study is more touroughly compared to the previous eclipse studies. t is really supported by high quality data, obtained by high resolution of equipment, as well as well done procedures of measurements. Based on the consistency of results which are supported by high quality data, we really confident to use LOK data for the future studies which need sensitive analysis, such as earthquake precursors. Acknowledgements The results presented in this paper rely on the data collected at Kakadu KDU . We thank to Geoscience Australia GA for supporting their operations and NTERMAGNET for promoting high standards of magnetic observatory practice www.intermagnet.org . We also thank to BMKG Stageof Kupang for providing Kupang KPG data. MATLAB ® with license number 8 8 is used for data processing. Funding for this research is provided by ndonesian Ministry of Research, Technology and igher Education under Penelitian Unggulan Perguruan Tinggi PUPT 2016, entitled Observasi Geomagnetik dan Seismologi Terpadu di Pulau Lombok: Kontribusi untuk Pemodelan Global dan Mitigasi Bencana Gempa Bumi Wilayah Indonesia Timur. Contributors of this paper are: Misbahuddin, Rosmaliati, Budi rmawati, Made Sutha Yadnya, Abdullah Zainuddin, L.A.S. rfan Akbar, A. Sjamsjiar Rachman, M. Syamsu qbal, Cipta Ramadhani. The authors would like to thank to the students of Electrical Engineering Dept. of Mataram University, who carried out the absolute measurements at LOK. References Ates, A., Buyuksarac, A., Bekta, O. . Geophysical Variations during the Total Solar Eclipse in in Turkey. Turkish Journal of Earth Sciences, Vol. , pp. – . Babakhanov, .Y., Belinskaya, A.Y., Bizin, M.A., Grekhov, O.M., Khomutov, S.Y., Kuznetsov, V.V., Pavlov, A.F. . The geophysical disturbances during the total solar eclipse of August 8 in Novosibirsk, Russia. Journal of Atmospheric and Solar‐Terrestrial Physics, Vol. , pp. – . Chapman S. . The Effect of a Solar Eclipse on the Earths Magnetic Field. Terr. Magn. Atmos. Elect., Vol. 8, pp. ‐8 . Chapman, S. and Bartel, J. . Geomagnetism, Vols. and , pp. , ‐ 8. 9 Cullington, A.L. . 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