Interplanetary Coronal Mass Ejections from MESSENGER Orbital Observations at Mercury Reka M. Winslow 1 , Noé Lugaz 1 , Lydia C. Philpott 2 , Nathan A. Schwadron 1 , Charles J. Farrugia 1 , Brian J. Anderson 3 , and Charles W. Smith 1 (1) Institute for the Study of Earth, Oceans, and Space, University of New Hampshire ([email protected]), (2) Earth, Ocean and Atmospheric Sciences, University of British Columbia, (3) John Hopkins University Applied Physics Laboratory. Poster based on: Winslow, R. M. et al. (2015), Interplanetary coronal mass ejections from MESSENGER orbital observations at Mercury, J. Geophys. Res. Space Physics, 120, doi:10.1002/2015JA021200. SH53A-2469 AGU Fall Meeting 2015 1. Summary • Used observations from MESSENGER in orbit around Mercury to study interplanetary coronal mass ejections (ICMEs) near 0.3 AU. • Cataloged over 60 ICMEs at Mercury between 2011 - 2014. • Investigated key ICME property changes from Mercury to 1 AU. Find: • Good agreement with previous studies for magnetic field strength dependence on dis- tance, and evidence that ICME deceleration con- tinues past the orbit of Mercury. • This ICME database useful for multipoint spacecraft studies of recent ICMEs, as well as for model validation of ICME properties. 2. ICME Identification • ICMEs identified using magnetic field measure- ments only, due to lack of solar wind data with MES- SENGER. • Strict selection criteria: a) interplanetary shock observed b) shock followed by sheath and magnetic ejecta c) event lasted for the duration of at least 1 MES- SENGER orbit through Mercury’s magnetosphere d) event caused a visible distortion of the magneto- sphere • Selection criteria biases towards fast ICMEs that are shock-driving and ICMEs with magnetic cloud- like characteristics. • Also determined corresponding CME counter- part at the Sun for each event. Example ICME: 3. ICME Properties at Mercury • ICME speed estimated from CME ejection time at the Sun, arrival time at Mercury, and Mercury’s heliocentric distance. -> This average speed is likely a maximum speed of the ICME at MESSENGER. • Maximum ICME |B| observed is 310 nT. • Fastest transit time from Sun to Mercury was 6 hr, longest transit time 52 hr. • Fastest transit speed 2350 km/s, slowest transit speed 325 km/s. • Large spread in transit times and speeds indicates that due to proximity to Sun, MESSENGER observed a wide range of ICMEs, even ones that may be too slow or small to be detected at 1 AU. 4. Differences in ICME Properties Between Mercury and 1 AU • Used existing databases of ICMEs at 1 AU for the same time period. Main Results: , in good agreement with previous studies. • ICME deceleration continues beyond the orbit of Mercury: (1) Shallow speed decrease with distance, (2) Average transit time from Sun to Mercury 20% faster than expected based on average transit times to 1 AU, (3) Significantly shallower ICME transit time dependence on initial CME speed observed at 1 AU compared to predictions based on MESSENGER ICME catalog. • ICME magnetic shock compression ratio higher at MESSENGER (1.97) than at STEREO (1.64). ICME deceleration may explain the lower mean shock compression at 1 AU compared to that at Mercury. 5. Example ICME: 12 July 2012 Event • Observed by MESSENGER and ACE • Illustrates that this ICME database can be used for both model validation and propagation studies of events observed in conjunction. • Some of the large-scale structure is retained in propagation (B R stongly negative at both distances) • Non-dimensional expansion rate of the cloud con- firmed by two separate methods at Mercury and ACE to be: • Compare to model predictions of Hess & Zhang [2014] for this event, which fit remote-sensing ob- servation a posteriori to the semi-empirical drag model of Vrsnak et al. [2013]. • Model does quite well at estimating sheath size and arrival time at Mercury: 0 50 100 150 200 250 300 0 5 10 15 Max |B| in ME (nT) No. of ICMEs Mean = 86.2±5.0 0 50 100 150 200 250 300 350 0 5 10 15 Max |B| in Sheath (nT) No. of ICMEs Mean = 84.6±5.8 0 10 20 30 40 50 60 0 5 10 15 Shock transit time (hours) No. of ICMEs Mean = 23.0±1.1 0 10 20 30 40 50 60 0 5 10 15 ME transit time (hours) No. of ICMEs Mean = 25.6±1.2 0 500 1000 1500 2000 2500 0 5 10 15 Shock Transit Speed (km/s) No. of ICMEs Mean = 792±45 0 500 1000 1500 2000 2500 0 5 10 15 ME Transit Speed (km/s) No. of ICMEs Mean = 706±41 0 0.2 0.4 0.6 0.8 0 5 10 15 ME radial size (AU) No. of ICMEs Mean = 0.223±0.018 0 0.05 0.1 0.15 0.2 0 5 10 15 Sheath radial size (AU) No. of ICMEs Mean = 0.0434±0.0036 a) b) 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 0 50 100 150 200 250 300 Heliocentric Distance (AU) ME Mean |B (nT) | MESSENGER+ACE data <B> = 10.9 r -1.85 ; Gulisano et al. (2010) <B> = 18.1 r -1.64 ; Leitner et al. (2007) <B> = 8.3 r -1.52 ; Wang et al. (2005) <B> = e (2.01+/-0.15) r (-1.95+/-0.19) 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 0 50 100 150 200 250 300 ME maximum |B| (nT) MESSENGER+STEREO data Bmax = e (2.5+/-0.06) r (-1.89+/-0.14) Bmax = 17.7 r -1.73 ; Farrugia et al. (2005) Heliocentric Distance (AU) 0 500 1000 1500 2000 2500 0 50 100 150 200 250 300 350 Shock transit speed (km/s) Maximum |B| in the ICME (nT) MESSENGER data; |B| = 0.03 v + 59.5 cc = 0.55 0.2 0.4 0.6 0.8 1 0 500 1000 1500 2000 2500 Maximum Shock Speed (km/s) Heliocentric Distance (AU) MESSENGER+ACE data |v| = e (6.14+/-0.05) r (-0.45+/-0.09) 0.2 0.4 0.6 0.8 1 0 500 1000 1500 2000 2500 Maximum ME Speed (km/s) MESSENGER+STEREO data |v| = e (6.18+/-0.04) r (-0.26+/-0.08) a) b) Heliocentric Distance (AU) 0 500 1000 1500 2000 2500 0 25 50 75 100 125 150 Coronal Speed (km/s) ME Transit Time (hrs) Sun to Mercury Predicted Sun to 1 AU TT = e (9.37+/-0.79) v (-0.78+/-0.12) TT = e (7.92+/-1.2) v (-0.71+/-0.17) a) b) 0 500 1000 1500 2000 2500 0 25 50 75 100 125 150 Coronal Speed (km/s) Shock Transit Time (hrs) Sun to Mercury Predicted Sun to 1 AU TT = 441 v -0.29 ; Vrsnak & Zic (2007) TT = e (9.08+/-0.83) v (-0.76+/-0.12) TT = e (7.75+/-1.2) v (-0.704+/-0.17) 0 5 10 15 20 25 30 35 40 45 50 0 25 50 75 100 125 150 175 200 225 Transit time (hours) Radial distance (R Sun ) Shock drag model - Hess & Zhang (2014) Ejecta drag model - Hess & Zhang (2014) MESSENGER shock transit time MESSENGER ejecta transit time 0 5 10 15 20 25 30 35 40 45 50 0 5 10 15 20 25 30 35 40 45 50 Transit time (hours) Standoff distance (R Sun ) Drag model - Hess & Zhang (2014) MESSENGER standoff distance a) b) High ICME |B| -> high ICME speed? B Total (nT) 0 15 30 45 60 75 B R (nT) -75 -50 -25 0 25 50 75 B T (nT) -75 -50 -25 0 25 50 75 UTC 12/30 16:48 12/30 19:12 12/30 21:36 12/31 00:00 12/31 02:24 12/31 04:48 12/31 07:12 12/31 09:36 B N (nT) -75 -50 -25 0 25 50 75 10 12 10 11 10 10 H + (Scan Total)