Subjects: Geosciences >> Space Physics submitted time 2016-05-04
Abstract： The inherent shortcoming of most regional models is the lack of altitude information. In order to overcome this, the objective of this study is to establish the three-dimensional (3D) model of element X, Y, Z, and F over Chinese and its adjacent regions in 2010.0 at the height of about 300 km. Based on the vector and scalar geomagnetic measuring data of CHAMP satellite, associated with 3D Taylor polynomial method, we try to create the 3D model over China and calculate the spatial distribution of geomagnetic field region. 3D model not only has the advantages like simple calculation and convenient to use, but also takes into account the height. In addition, the selection of truncation level of 3D model was also discussed. In order to verify the constructed 3D model, a comparison between 3D and Taylor polynomial (2D) model was taken, we analyzed the Root-mean-square error (RMSE) and the residual distributions between 3D and 2D models in different truncation level. Results showed RMSE and the mean absolute residuals of each level of the 3D model are about 45% smaller than that of 2D model. The 3D model of degree 5 basically has the same precision as that of 2D model of degree 8 in this study. Geomagnetic distributions and residuals of 3D and 2D models have high consistency. After comparing with 2D model, the 3D model considers the altitude information, so the precision is really improved; the coefficients show that 3D model of low degree can reflect more information and has the similar precision when compared to 2D model of high degree. � 2015, Science Press. All right reserved.
Peer Review Status:
Awaiting Review
Subjects: Geosciences >> Space Physics submitted time 2016-05-04
Abstract： Coronal mass ejections (CMEs) and corotating interaction regions (CIRs) are two significant contributors to interplanetary disturbances and geomagnetic disturbances, which also play as major drivers of geomagnetic storms to modulate the geo-space environment. In order to comprehensively investigate the characteristic temporal features of the solar wind activity and associated geomagnetic activity, a large amount of solar wind data and geomagnetic activity indices are analyzed in detail. Firstly, using the public data of solar wind parameters and geomagnetic activity indices provided by the NASA OMNIWeb, the MATLAB codes are developed to deal with a number of key parameters including IMF B-z solar wind velocity, solar wind proton density, solar wind dynamic pressure, Dst, AE, and Kp for the entire Solar Cycle 23 from 1996 to 2008. The complete database with a full list of 269 CME events and 456 CIR events is identified. Case event studies and superposed epoch analyses are implemented to carefully investigate the statistical features of four important solar wind parameters (IMF 13,, solar wind speed, solar wind proton density, and solar wind dynamic pressure) and three major geomagnetic indices (Dst, AE, and Kp) associated with the two types of solar disturbances. Secondly, the minimum of Dst index is utilized to differentiate 355 isolated geomagnetic storms occurring during the Solar Cycle 23. These storms are further categorized according to the magnitude of Dst minimum into 145 weak storms, 123 moderate storms, 70 strong storms, 12 severe storms, and 5 extreme storms. Finally, superposed epoch analysis is applied to evaluate the statistics of solar wind parameters and geomagnetic indices corresponding to magnetic storms with different intensities. It is found that in general the linearly fitted slope of N-sw/P-dyn (where N-sw is the solar wind proton density and P-dyn the dynamic pressure) with respect to epoch time remains positive for CME events but negative for CIR events, which can act as a feasible means to distinguish CME and CIR events. On average, compared to CIR events, CME events have larger magnitudes of southward IMF B solar wind dynamic pressure, AE and Kp indices but smaller Dst(min). In principle, CMEs bear higher possibility to drive extremely intense (i. e., super) geomagnetic storms. The overall variations of Dst tend to be similar to some extent for different levels of geomagnetic storms, however, Dst decreases faster for stronger storms. There are a large number of differences between CME and CIR events and their driven geomagnetic storms as well. Therefore, CME-driven storms and CIR-driven storms should be studied separately. The established database of CME and CIR events and geomagnetic storms and the quantitative statistical information in combination can provide a useful aid for better understanding the responses of Earth's plasma sheet, radiation belts, and ring current to various solar activities.
Peer Review Status:Awaiting Review
Subjects: Geosciences >> Space Physics submitted time 2016-05-04
Abstract： Based on the long-term observations from Beijing sodium lidar of Chinese Meridian Project, 162 monochromatic gravity waves was distinguished in the sodium layer during the 2208 hours' observation in 253 nights (from 2010 April to 2011 September). The vertical wavelength, wave period, wave amplitude and its growth factor of every monochromatic gravity wave were precisely extracted with the method derived by Yang et al. (2008). Statistical results reveal that there are systematic relationships between those wave parameters, and they respectively are λz=0.226Tob0.530, KE=6.66×10-10 kZ-3.091 and KE=8.97×10-6 fob-1.696 Those results partially agree well with the results predicted by Gardner's (1994) diffusive filtering theory. However, it is found incorrect to regard the wave-induced eddy diffusivity as the only main damping processes of gravity waves. It is suggested that the damping processes caused by other possible factors also play important roles in the saturation and dissipation mechanisms of gravity waves. ©, 2015, Chinese Society of Astronautics. All right reserved.
Peer Review Status:Awaiting Review
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