Longitudinal conjunction between MESSENGER and STEREO A: Development of ICME complexity through stream interactions

We use data on an interplanetary coronal mass ejection (ICME) seen by MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) and STEREO A starting on 29 December 2011 in a near‐perfect longitudinal conjunction (within 3°) to illustrate changes in its structure via interaction with the solar wind in less than 0.6 AU. From force‐free field modeling we infer that the orientation of the underlying flux rope has undergone a rotation of ∼80° in latitude and ∼65° in longitude. Based on both spacecraft measurements as well as ENLIL model simulations of the steady state solar wind, we find that interaction involving magnetic reconnection with corotating structures in the solar wind dramatically alters the ICME magnetic field. In particular, we observed a highly turbulent region with distinct properties within the flux rope at STEREO A, not observed at MESSENGER, which we attribute to interaction between the ICME and a heliospheric plasma sheet/current sheet during propagation. Our case study is a concrete example of a sequence of events that can increase the complexity of ICMEs with heliocentric distance even in the inner heliosphere. The results highlight the need for large‐scale statistical studies of ICME events observed in conjunction at different heliocentric distances to determine how frequently significant changes in flux rope orientation occur during propagation. These results also have significant implications for space weather forecasting and should serve as a caution on using very distant observations to predict the geoeffectiveness of large interplanetary transients.Key PointsICME complexity increases due to interaction with corotating structures in the solar windMagnetic reconnection between ICME and HPS/HCS alters the magnetic topology of the ICME flux ropeCaution on using distant observations to predict the geoeffectiveness of interplanetary transientsPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/134123/1/jgra52739.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/134123/2/jgra52739_am.pd

Critical role of risk management in ground engineering and opportunities for improvement

Green mining is concerned with mining in a sustainable manner, such that the needs of the present are met without compromising future generations. The achievement of this objective depends on balancing social, environmental and economic objectives and has to have regard to both active mining operations and legacy issues associated with mine closure. Ground engineering has a critical role in achieving green mining objectives but its contribution is characterised by pervasive uncertainty. Uncertainty equates to risk. This means that ground engineering should be practiced within a risk management framework that aims to both prevent unwanted outcomes and to mitigate their consequences to an acceptable level. This keynote address presents the fundamentals of risk management and demonstrates its effectiveness by reference to improvements in the safety performance of the NSW coal sector over the past three decades. Nevertheless, ground control remains a mix of art and science, relying heavily on judgements which should be premised on knowledge, skill and experience (that is, competence). Risk management has now been enshrined in mining legislation and operating practice in Australia for over two decades. Notwithstanding this, near-hit and accident and incident investigations, commissions of inquiry and legal proceedings almost invariably identify deficiencies and opportunities for improvements necessary to achieve the objectives of sustainable mining. Three of the more important opportunities which have global application in relation to ground engineering are discussed. These relate to the vexing issue of defining competency in ground engineering; the criteria for undertaking rigorous risk assessment; and the need for ground engineers to become involved in mine rehabilitation and closure planning over the full life cycle of a mine, commencing at the prefeasibility stage. Keywords: Bow tie analysis, Mine safety, Mine closure, Risk assessment, Risk management, Sustainable mining, Uncertaint