Studies Of The Interplanetary Structure And Its Geoeffectiveness

Interplanetary Coronal Mass Ejections(ICMEs)and Streaming Interaction Re-gions(SIRs)are the two major large-scale interplanetary sources of disastrous space weather of Earth,whose magnetic field and solar wind plasma properties are different from solar wind.The study of ICME and SIR's properties and their geoeffectiveness are an important area in space physics.The study is also helping us understand the space weather research and forecasting.Using the in-situ observations from the Wind and ACE spacecraft and the criteria for ICME and SIR,we established long duration ICME and SIR lists.First,we established an ICME catalog for a long duration from 1995 to 2015 using the in-situ observations from the Wind and ACE spacecraft.Based on this catalog,we confirm previous results that the yearly occurrence frequencies of ICMEs and shocks,the ratios of ICMEs driving shocks are correlated with the sunspot numbers.For the including magnetic cloud ICME(short for,MC),we confirm that the yearly occurrence frequencies of MCs do not show any correlation with sunspot numbers.The highest MC ratio of ICME occurred near the solar minimum.In addition,we analyzed the yearly variation of the ICME parameters.We found that the ICME velocities,the magnetic-field strength,and their related parameters varied in pace with solar-cycle variation.At the solar maximum,ICMEs move faster and carry a stronger magnetic field.By comparing the parameters between MCs and non-MC ejecta,we confirm the result that the magnetic-field intensities of MC are higher than those in non-MC ejecta.Further-more,we also discuss the forward shocks driven by ICMEs.We find that one half of the ICMEs have upstream shocks and ICMEs with shocks have faster speed and higher magnetic-field strength than the ICMEs without shocks.The magnetic-field parameters and solar-wind plasma parameters in the shock sheath regions are higher than those in the ejecta regions of ICMEs from a statistical point of view.Based on the ICME catalog and the Dst indices from the World Data Center,we study and compare the geoeffectiveness of ICMEs of different in-situ signatures and different solar phases from 1995 to 2014.According to the different in-situ signatures,all ICMEs are divided into three types:isolated ICMEs(I-ICMEs),multiple ICMEs(M-ICMEs),and shock-embedded ICMEs(S-ICMEs),resulting in a total of 363 group events.Fifty-eight percent of ICMEs caused geomagnetic storms with Dstmin?-30 nT.Furthermore,a large fraction(87%)of intense geomagnetic storms are caused by ICME groups and their sheath regions.Numbers of ICME groups and the probabili-ties of ICME groups in causing geomagnetic storms varied in pace with the solar cycle.Meanwhile,the ICME groups and the probabilities of them in causing geomagnetic storms in Solar Cycle 24 are much lower than those in Solar Cycle 23.The maximum value of the intensity of the magnetic field(B),south component of the magnetic field(Bs),and dawn-dusk electric field vBs are well correlated with the intensity of the mag-netic storms.Shock-embedded ICMEs have a high probability of causing geomagnetic storms,especially intense geomagnetic storms.The compression of shock on the south component of magnetic field is an important factor to enhance the geoeffectiveness of S-ICMEs structures.Stream interaction regions(SIRs)are important sources of the geomagnetic storms.In this work,we first extend the end time of the widely used SIRs catalogue developed by Jian,et al.(2010),which covered the period from 1995 to 2009,to the end of 2016.Thus,the number of the SIRs is expanded from 576 to 866.Based on this extended SIRs catalogue,the geoeffectiveness of SIRs is discussed in detail.It is found that 52%of the SIRs caused geomagnetic storms with Dstmin?-30 nT and only 3%of the SIRs caused intense geomagnetic storms with Dstmin?-100 nT.Furthermore,we found that 10 of the intense geomagnetic storms caused by SIRs were associated with a complex structure due to the interaction between SIRs and interplanetary coronal mass ejections(ICMEs).In such a structure,an ICME is embedded in the SIR and located between the slow solar and fast solar wind stream.In addition,we found that the SIRs interacted with ICMEs could enhance their geoeffectiveness.The possibility of the SIR-ICME interaction structures in causing geomagnetic storms is obviously higher than that of isolated SIRs or isolated ICMEs.Especially,the geoeffectiveness of SIR-ICME interactions structures is similar to that of the Shock-ICME interaction structures which have been proven as main causes of geomagnetic storms.In addition,we prove the previous results that SIRs are more likely to cause geomagnetic storms near the equinoctial months,during which about 60%of the SIRs caused geomagnetic storms.An Earth-affecting ICME is generally considered as the counterpart of an Earth-directed CME originated from the Sun.An Earth-directed CME,or a CME propagating along the Sun-Earth line,usually appears as a full halo CME in SOHO/LASCO coro-nagraphs field of view.However,it is also known that ICMEs identified by in-situ observations do not show one-to-one correspondence with front side halo CMEs.This study presents the first detailed analysis of a geoeffective stealth ICME on 2011 May 28.whose progenitor CMEs are difficult to be identified in LASCO images,but for-tunately captured by SECCHI onboard STEREO spacecraft in the quadrature configu-ration.There are two progenitor CMEs launching from the Sun in succession of eight hours.We apply the Graduated Cylindrical Shell(GCS)model to reconstruct the 3D geometry,propagating direction,velocity,and brightness of the two CMEs.The main cause of the first CME(CME-1)invisible in SOHO/LASCO is due to its low mass,that is,when the CME emerges above the occulter its brightness is as faint as the noise.The second CME(CME-2)is small-size,including narrow angular width and small cross section of the magnetic flux rope.Although propagating toward the Earth,CME-2 ap-peared as a narrow CME,instead of halo or partial halo CME in the LASCO field of view.We also show that CME-2 propagates faster than CME-1,and they might have interacted in the interplanetary space.