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Register a new userCoronal dimmings associated with coronal mass ejections on the solar limb
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We present a statistical analysis of 43 coronal dimming events, associated with Earth-directed CMEs that occurred during the period of quasi-quadrature of the SDO and STEREO satellites. We studied coronal dimmings that were observed above the limb by STEREO/EUVI and compared their properties with the mass and speed of the associated CMEs. The unique position of satellites allowed us to compare our findings with the results from Dissauer et al. (2018b, 2019), who studied the same events observed against the solar disk by SDO/AIA. Such statistics is done for the first time and confirms the relation of coronal dimmings and CME parameters for the off-limb viewpoint. The observations of dimming regions from different lines-of-sight reveal a similar decrease in the total EUV intensity ($c=0.60pm0.14$). We find that the (projected) dimming areas are typically larger for off-limb observations (mean value of $1.24pm1.23times10^{11}$ km$^2$ against $3.51pm0.71times10^{10}$ km$^2$ for on-disk), with a correlation of $c=0.63pm0.10$. This systematic difference can be explained by the (weaker) contributions to the dimming regions higher up in the corona, that cannot be detected in the on-disk observations. The off-limb dimming areas and brightnesses show very strong correlations with the CME mass ($c=0.82pm0.06$ and $c=0.75pm0.08$), whereas the dimming area and brightness change rate correlate with the CME speed ($csim0.6$). Our findings suggest that coronal dimmings have the potential to provide early estimates of mass and speed of Earth-directed CMEs, relevant for space weather forecasts, for satellite locations both at L1 and L5.
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Solar cycle 23 witnessed the observation of hundreds of halo coronal mass ejections (CMEs), thanks to the high dynamic range and extended field of view of the Large Angle and Spectrometric Coronagraph (LASCO) on board the Solar and Heliospheric Observatory (SOHO) mission. More than two thirds of halo CMEs originating on the front side of the Sun have been found to be geoeffective (Dst =< -50 nT). The delay time between the onset of halo CMEs and the peak of ensuing geomagnetic storms has been found to depend on the solar source location (Gopalswamy et al., 2007). In particular, limb halo CMEs (source longitude > 45deg) have a 20% shorter delay time on the average. It was suggested that the geomagnetic storms due to limb halos must be due to the sheath portion of the interplanetary CMEs (ICMEs) so that the shorter delay time can be accounted for. We confirm this suggestion by examining the sheath and ejecta portions of ICMEs from Wind and ACE data that correspond to the limb halos. Detailed examination showed that three pairs of limb halos were interacting events. Geomagnetic storms following five limb halos were actually produced by other disk halos. The storms followed by four isolated limb halos and the ones associated with interacting limb halos, were all due to the sheath portions of ICMEs.
The scenario of twin coronal mass ejections (CMEs), i.e., a fast and wide primary CME (priCME) preceded by previous CMEs (preCMEs), has been found to be favorable to a more efficient particle acceleration in large solar energetic particle (SEP) events. Here, we study 19 events during 2007--2014 associated with twin-CME eruptions but without large SEP observations at L1 point. We combine remote-sensing and in situ observations from multiple spacecraft to investigate the role of magnetic connectivity in SEP detection and the CME information in 3-dimensional (3D) space. We study one-on-one correlations of the priCME 3D speed, flare intensity, suprathermal backgrounds, and height of CME-CME interaction with the SEP intensity. Among these, the priCME speed is found to correlate with the SEP peak intensity at the highest level. We use the projection correlation method to analyze the correlations between combinations of these multiple independent factors and the SEP peak intensity. We find that the only combination of two or more parameters that has higher correlation with the SEP peak intensity than the CME speed is the CME speed combined with the propagation direction. This further supports the dominant role of the priCME in controlling the SEP enhancements, and emphasizes the consideration of the latitudinal effect. Overall, the magnetic connectivity in longitude as well as latitude and the relatively lower priCME speed may explain the existence of the twin-CME SEP-poor events. The role of the barrier effect of preCME(s) is discussed for an event on 2013 October 28.
In order to discuss the potential impact of solar superflares on space weather, we investigated statistical relations among energetic proton peak flux with energy higher than $ 10 rm MeV$ ($F_p$), CME speed near the Sun ($V_{CME}$) obtained by {it SOHO}/LASCO coronagraph and flare soft X-ray peak flux in 1-8AA band ($F_{SXR}$) during 110 major solar proton events (SPEs) recorded from 1996 to 2014. The linear regression fit results in the scaling relations $V_{CME} propto F_{SXR}^alpha$, $F_ppropto F_{SXR}^beta$ and $F_ppropto V_{CME}^gamma$ with $alpha = 0.30pm 0.04$, $beta = 1.19 pm 0.08$ and $gamma = 4.35 pm 0.50$, respectively. On the basis of simple physical assumptions, on the other hand, we derive scaling relations expressing CME mass ($M_{CME}$), CME speed and energetic proton flux in terms of total flare energy ($E_{flare}$) as, $M_{CME}propto E_{flare}^{2/3}$, $V_{CME}propto E_{flare}^{1/6}$ and $F_{p}propto E_{flare}^{5/6}propto V_{CME}^5$, respectively. We then combine the derived scaling relations with observation, and estimated the upper limit of $V_{CME}$ and $F_p$ to be associated with possible solar superflares.
The Coronal Multichannel Polarimeter (CoMP) measures not only the polarization of coronal emission, but also the full radiance profiles of coronal emission lines. For the first time, CoMP observations provide high-cadence image sequences of the coronal line intensity, Doppler shift and line width simultaneously in a large field of view. By studying the Doppler shift and line width we may explore more of the physical processes of CME initiation and propagation. Here we identify a list of CMEs observed by CoMP and present the first results of these observations. Our preliminary analysis shows that CMEs are usually associated with greatly increased Doppler shift and enhanced line width. These new observations provide not only valuable information to constrain CME models and probe various processes during the initial propagation of CMEs in the low corona, but also offer a possible cost-effective and low-risk means of space weather monitoring.
Coronal Mass Ejections (CMEs) may have major importance for planetary and stellar evolution. Stellar CME parameters, such as mass and velocity, have yet not been determined statistically. So far only a handful of stellar CMEs has been detected mainly on dMe stars using spectroscopic observations. We therefore aim for a statistical determination of CMEs of solar-like stars by using spectroscopic data from the ESO phase 3 and Polarbase archives. To identify stellar CMEs we use the Doppler signal in optical spectral lines being a signature of erupting filaments which are closely correlated to CMEs. We investigate more than 3700 hours of on-source time of in total 425 dF-dK stars. We find no signatures of CMEs and only few flares. To explain this low level of activity we derive upper limits for the non detections of CMEs and compare those with empirically modelled CME rates. To explain the low number of detected flares we adapt a flare power law derived from EUV data to the H{alpha} regime, yielding more realistic results for H{alpha} observations. In addition we examine the detectability of flares from the stars by extracting Sun-as-a-star H{alpha} light curves. The extrapolated maximum numbers of observable CMEs are below the observationally determined upper limits, which indicates that the on-source times were mostly too short to detect stellar CMEs in H{alpha}. We conclude that these non detections are related to observational biases in conjunction with a low level of activity of the investigated dF-dK stars.
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