Numeric simulations of in situ observations of interacting ejecta near 1 AU

We use a simple numerical model (González-Esparza, J.A., Santillán, A., Ferrer, J. A numerical study of the interaction between two ejecta in the interplanetary medium: one and two dimensional hydrodynamic simulations, Ann. Geophys. 22, 3741–3749, 2004) to study the evolution of three events in the solar wind reported by Wang et al. (Wang, Y.M., Ye, P.Z., Wang, S. Multiple magnetic clouds: several examples during March–April 2001. J. Geophys. Res. 108, 1370, 2003, doi:10.1029/2003JA009850), where two interacting ejecta detected in situ by ACE near 1 AU were related to CMEs observed previously by SOHO-LASCO. The study is based on a 1-D hydrodynamic model using the ZEUS code (Stone, J.M., Norman, M. ZEUS 2-D: A radiation magnetohydrodynamics code for astrophysical flows in two dimensions, I, the hydrodynamics algorithms and tests, Astrophys. J. 80, 753, 1992). Although this model cannot address either the magnetic field dynamics or the complex geometrical effects intrinsic in the three-dimensional nature of the phenomena, it illuminates the transferring of momentum and evolution of interacting large-scale solar wind disturbances in those cases where there is no merging (magnetic reconnection) between the two ejecta. This model can reproduce, in some cases, characteristics of the events such as transit times and flow signatures as inferred from the two-point measurements from spacecraft.     

月球粉尘的研究现状

随着我国探月工程的开展,面临着月球粉尘危害性的问题,急需开展月球粉尘的研究。文章在调研的基础上,阐述了目前国外在月球粉尘方面的研究现状,主要是美国"阿波罗"计划中对月尘的特性、危害性、探测和防护方面的研究。     

A comparative analysis of the role of interplanetary magnetic field (IMF) and sudden impulse (SI) in triggering a substorm

During a typical Akasofu-type of substorm, the southward component of IMF Bz is necessary prior to the onset. However, a sudden compression of solar wind, if intense enough, can also sometimes trigger a substorm, and is independent of the IMF orientation. The Akasofu-type substorm and the Impulse-induced substorm may differ in their occurrence mechanism and ground-based observations. This is shown using the initial four substorm events discussed in this paper having distinctly different IMF and sudden impulse conditions. A question then arises is how will these signatures vary when both sudden impulse and a southward component of IMF Bz are present prior to the onset. To account for the same, we analyze two substorm events of 05th April 2010 and 22nd June 2015. The substorm onsets on these days not just coincided with the sudden impulse but also a southward component of IMF Bz was present prior to the onsets. The present study accounts for the similarities and differences among isolated IMF induced substorms, isolated impulse-induced substorms and when both sudden impulse and a southward component of IMF Bz are present. We examined the relative dominance between the two factors in triggering a substorm using ground-based and satellite-based observations. If IMF Bz is near zero, a strong pressure pulse and/or large IMF By can lead to particle precipitation away from the usual midnight. To further ensure whether a pressure pulse or IMF By predominantly influences the substorm onset location, a statistical analysis of isolated substorms will be needed.     

The global response of terrestrial ionosphere to the December 2015 space weather event

This paper investigates the ionospheric storm of December 19–21, 2015, which was initiated by two successive CME eruptions that caused a G3 space weather event. We used the in situ electron density (N_e) and electron temperature (T_e) and the Total Electron Content (TEC) measurements from SWARM-A satellite, as well as the O/N₂ observations from TIMED/GUVI to study the ionospheric impact. The observations reveal the longitudinal and hemispherical differences in the ionospheric response to the storm event. A positive ionospheric storm was observed over the American, African and Asian regions on 20 December, and the next day showed a negative storm. Both these exhibited hemispheric differences. A positive storm was observed over the East Pacific region on 21 December. It is seen that the net effect of both the disturbance dynamo electric field and composition differences become important in explaining the observed variability in topside ionospheric densities. In addition, we also discuss the T_e variations that occurred as a consequence of the space weather event.     

1-D dusty photo-ionization models of WR planetary nebulae NGC 2452 and IC 2003

We report dusty photo-ionization models for two Planetary Nebulae NGC 2452 and IC 2003, which have [WR] type central stars, using 1D photo-ionization code Cloudy17.02. We used the medium resolution optical spectra and archival IRAS photometry to constrain our models. The physical size of the ionized nebula derived using accurate distance measurements and absolute H$\beta$ flux available in the literature were used as additional constrains. We examine the importance of photo-electric heating and found that models with and without considering photo-electric heating do not make significant difference for both PNe for the MRN grain size distribution considered in this study. We derive the nebular elemental abundances of these PNe by the empirical method as well as by making dusty photo-ionization models. The values of N/O ratios for both PNe obtained from our models are lower than their respective values arrived using empirical methods. The central stars are assumed to be black bodies and the photospheric temperatures derived respectively for NGC 2452 and IC 2003 from their best fit models are 182 kK and 155 kK and their respective luminosities are 630$L_{\odot }$ and 1015$L_{\odot }$. We propose that both the PNe were resulted from low-mass progenitors of mass $?$2.8 M_⊙.