Successful operation of a cooperative SLR station of China and Argentina in San Juan

We introduced the observations and researches using a Satellite Laser Ranging (SLR) system with high precision, which was designed and made in China and installed in the Observatory of San Juan Uni- versity, Argentina, the capability of the system and the achievement of the cooperative procedure be- tween China and Argentina. The SLR station in San Juan, set up by China and Argentina, is quite sig- nificant for improving the distribution of SLR stations and enhancing the orbital coverage of the whole earth. Since the SLR system started to work in the Observatory of San Juan University in the beginning of 2006, the operation is rather good, and rich data with high precision have been obtained. Further plan of the cooperation for the near future is also presented.     

Seasonal and inter-annual variations of length of day and polar motion observed by SLR in 1993―2006

A time series of length of the day (LOD) and polar motion (PM) were estimated from the range data measured by the satellite laser ranging technique (SLR) to LAGEOS 1/2 through 1993 to 2006. Compared with EOPC04 released by the International Earth Rotation and Reference Systems Service (IERS), the root mean squares errors for LOD, X and Y of PM are 0.0067 milliseconds (ms), 0.18 milli-arc-sec- onds (mas) and 0.20 mas, respectively. Then the time series are analyzed with the wavelet transformation and least squares method. Wavelet analysis shows that there are the obvious seasonal and inter- annual variations of LOD and PM, but the annual variation cannot be distinguished from the Chandler variation because these two frequencies are very close. The trends and periodic variations of LOD and PM are given in the least squares sense. LOD changes with the annual and semiannual periods. The annual and Chandler variations for PM are also detected, but the semiannual motion for PM is not found. The trend rate of the LOD change in 1993―2006 is ?0.18 ms per year, and the difference from the well- known 1.7 ms per century showed that the trend rate is diverse in different periods possibly. The trend rates of PM in the X and Y directions are 2.25 and 1.67 mas per year respectively, and the North Pole moves to 36.5°E relative to the crust, which is different from the direction of Greenland.     

Lons-term variations of solar activity

Using the Lomb-Scargle periodogram we analyzed two sunspot series： the one over the past 11000 years at the 10-year interval based upon the survey data of ^14C concentration in tree-rings, reconstructed by Solanki et al.; and the sunspot number over the past 7000 years, derived from geomagnetic variations by Usoskin et al. We found the periods and quasi-periods in solar activity, such as about 225, 352, 441,522 and 561 a, and near 1000 and 2000 a. An approach of wavelet transform was applied to check the two sunspot time series, with emphasis on investigating time-varying characteristics in the long-term fluctuations of solar activity. The results show that the lengths and amplitudes of the periods have changed with time, and large variations have taken place during some periods.     

Progress of research on anomalies of astronomical time and latitude observations before earthquake

This paper introduces the discovery of the phenomenon that short-term anomalous fluctuations appeared in residuals of astronomical time and latitude observations before earthquakes and the progress of related researches carried out for many years.The relations between the anomalous variations of time and latitude residuals of astronomical time and latitude instruments in different regions and the earthquakes around these instruments as well as the characteristics of residuals’ anomalous variations are analyzed.The significance of the anomalous fluctuations in residuals of astronomical time and latitude caused by the anomalous variations of the local plumb line before earthquake and detecting the vertical variation with astronomical time and latitude observations as well as the importance of carrying out further researches are discoursed.The possibility that the phenomenon will become an effective short-term earthquakes precursor,the current situations and the problems to be solved,are discussed.Also we offer the proposals to develop new roboticized astrometric instruments with high-precision and set up test observation networks in earthquake-prone areas in order to do research in-depth,optimize methods of observing and extracting anomalous information for short-term earthquake prediction,and so on.     

South American SLR stations monitoring ground displacement caused by the M8.8 Chilean earthquake of 2010

The M8.8 Chilean earthquake of February 27, 2010 caused a large surface displacement near its epicenter. Satellite Laser Ranging (SLR) station 7405, cooperatively operated by Germany and Chile about 130 km from the epicenter was affected by the earthquake. Another SLR station, No. 7406, operated jointly by the National Astronomical Observatories of the Chinese Academy of Sciences and San Juan University of Argentina, was about 600 km from the epicenter. Combining the observations of these two SLR stations with global SLR station observations, we calculate the geocentric coordinates of the two stations based on ITRF2000. The results show that the coordinates of the two stations have changed by varying degrees. SLR-7405 moved substantially towards the southwest with displacements of about 3.11, 0.52 and 0.49 m in X, Y, Z directions; the corresponding displacements for SLR-7406 are about 0.02, 0.03 and 0.02 m. This solution, as an independent result derived from SLR observations, could provide an essential external check for other positioning techniques such as GPS.     

Solar release time of solar energetic particles and associated acceleration source in corona

Solar energetic particles （SEPs） are accelerated in corona at an early phase of solar energetic particle events （SEPE）. The acceleration mechanism of SEPs in corona can only be inferred from an analysis of multi-band observational data, as the observation of SEPs is usually made around 1AU. In this context, people have investigated spectrums, charge state, solar release time （SRT）, and multi-band data of SEPEs, in an attempt to judge the acceleration mechanism of SEPs. The SRT computation of SEPs is an important and commonly used approach to study the acceleration mechanism of SEPs in corona. This paper reviews some important findings concerning the SRT computation of SEPs, and analyzes different merits of each approach for such calculation, based on a range of SEPE case studies. This paper also analyzes and discusses both possible and actual acceleration mechanisms of a number of SEPEs, by calculating the SRT of the SEPEs. Finally, the paper summarizes the possible problems in studying an acceleration mechanism of SEPEs inferred from the SRT of SEP.