Janet C. Johnston

On the Evolution of Coronal Mass Ejections in the Interplanetary Medium

Two coronal mass ejections (CMEs) are presented which were tracked through the LASCO field of view (FOV) within 30 R? and later as interplanetary CMEs (ICMEs) through the SMEI FOV from 80 to 150 R?. They were also associated with erupting filaments observed by EIT, providing information on trajectory of propagation. This allowed three-dimensional reconstructions of CME/ICME geometry, along with corrected (not sky plane projected) measurements of distance-time (DT) plots for each event to ~0.5 AU. An investigation of morphology was conducted. The results suggest that fine structures of the CMEs are eroded by the solar wind, and curvature becomes more sharply convex outward, suggesting that ICME footpoints remain fixed to the Sun even at 0.5 AU. We also present two models describing the evolution of CMEs/ICMEs at large distances from the Sun (far from the launch mechanism and effects of gravity and solar pressure) and consider two drag models: aerodynamic drag and snowplow. There was little difference between these, and their DT profiles matched well with the SMEI data for event 1. Event 2 showed a net acceleration between the LASCO and SMEI FOVs and we could match the data for this event well by introducing a driving Lorentz force. ICME mass almost doubled as a result of swept-up solar wind material from the snowplow model. Finally, we compared the geometry and kinematics of the ICME with that produced by the HAFv2 model and found that the model reasonably matched the geometry, but overestimated the ICME speed.

Tracking a major interplanetary disturbance with SMEI

[1] We present the first clear observations of an Earth-directed interplanetary disturbance tracked by the Solar Mass Ejection Imager (SMEI). We find that this event can be related to two halo CMEs seen at the Sun about 2 days earlier, and which merged in transit to 1 AU. The disturbance was seen about 16 hours before it reached Earth, and caused a severe geomagnetic storm at the time which would have been predicted had SMEI been operating as a real-time monitor. It is concluded that SMEI is capable of giving many hours advance warning of the possible arrival of interplanetary disturbances.

The Solar Mass Ejection Imager (SMEI): A new tool for space weather

Later this year, the U.S.Air Force will launch the Solar Mass Ejection Imager (SMEI). SMEI is an instrument that will detect and measure coronal mass ejections (CMEs) which can cause large geomagnetic storms, a major component of space weather. CMEs are very large structures containing plasma and magnetic fields that are expelled from the Sun into the heliosphere at speeds of several hundred to over 1000 km s−1. CMEs often drive interplanetary shock waves which, upon arrival at Earth, can cause geomagnetic disturbances. There is currently no reliable way to accurately predict arrival of these disturbances at Earth or to study them in the inner heliosphere. SMEI is designed to fill this gap by detecting and tracking CMEs in interplanetary space before they reach Earth. SMEI data will be complementary to many other satellite missions and national programs, such as the current National Space Weather and International Solar Terrestrial Programs.

Earth-Affecting Solar Causes Observatory (EASCO): A mission at the Sun-Earth L5

Coronal mass ejections (CMEs) and corotating interaction regions (CIRs) as well as their source regions are important because of their space weather consequences. The current understanding of CMEs primarily comes from the Solar and Heliospheric Observatory (SOHO) and the Solar Terrestrial Relations Observatory (STEREO) missions, but these missions lacked some key measurements: STEREO did not have a magnetograph; SOHO did not have in-situ magnetometer. SOHO and other imagers such as the Solar Mass Ejection Imager (SMEI) located on the Sun-Earth line are also not well-suited to measure Earth-directed CMEs. The Earth-Affecting Solar Causes Observatory (EASCO) is a proposed mission to be located at the Sun-Earth L5 that overcomes these deficiencies. The mission concept was recently studied at the Mission Design Laboratory (MDL), NASA Goddard Space Flight Center, to see how the mission can be implemented. The study found that the scientific payload (seven remote-sensing and three in-situ instruments) can be readily accommodated and can be launched using an intermediate size vehicle; a hybrid propulsion system consisting of a Xenon ion thruster and hydrazine has been found to be adequate to place the payload at L5. Following a 2-year transfer time, a 4-year operation is considered around the next solar maximum in 2025.

Imaging coronal mass ejections and other heliospheric phenomena: six years of observations and implications for future capabilities

January 2009 marked the 6th anniversary of the launch of the Air Force Research Laboratory Solar Mass Ejection Imager (SMEI) instrument on the Coriolis spacecraft. Originally planned as a three year mission, SMEI has amassed an unprecedented dataset of ~25,000 full-sky images since 2003 with a 102-minute cadence, 1° spatial resolution, and better than 8th magnitude sensitivity. SMEI, with its Sun/Earth line views, has been joined by the twin STEREO spacecraft, launched in October 2006, whose heliospheric Imagers (HIs) image along the ecliptic with opposing, off-axis views, 70° in diameter. These two data sets are complementary and several events observed by both SMEI and STEREO are being analyzed. But SMEI is nearing its end of life and the STEREO spacecraft continue to drift apart by 45°/year with decreasing telemetry coverage. What would be the characteristics of the next generation instrument in heliospheric imaging? What would the differences be for an operational instrument vs. a research instrument? What are the advantages of staring vs. composite imaging, views from the Sun/Earth line vs. other views, L1 position vs. low Earth orbit, etc? What are the engineering lessons learned from SMEI and STEREO and the environment through which such an instrument operates? In this presentation we discuss these issues and some possible future mission concepts.

Observations of Coronal Mass Ejections from the Solar Mass Ejection Imager and Space Weather Implications

The Solar Mass Ejection Imager (SMEI) was launched into a Sun-synchronous orbit in January 2003. Its mission objective is to detect and track coronal mass ejections (CMEs) from the Sun in order to improve space weather forecasts. In the three years since launch, over 200 CMEs, about 30 of which were Earth-directed, have been observed by SMEI. We have been able to track several of these CMEs from the SOHO LASCO coronagraphs ( 20◦) out to 0.5 AU and beyond, and to observe the morphology and evolution of distinctive features over this wide distance range. We report on comparisons of measurements of CME parameters made in the inner heliosphere with the more typical measurements made nearer the Sun with coronagraphs. We illustrate SMEI’s capabilities and present key statistical results on basic CME parameters and the use of SMEI-type data in space weather forecasting models. For example, timely observations by SMEI of CMEs en route to Earth could be input to DoD’s operational Hakamada-Akasofu-Fry solar wind model to correct or refine its real-time forecasts of approaching disturbances.