Space Weather Science from the Sun-Earth L5. Nat Gopalswamy Solar Physics Laboratory, NASA/GSFC, Greenbelt, MD 20771, USA. Expert Meeting on Improving Space Weather Forecasting in the Next Decade Feb 10-11, 2014. 10,000. 0.1. CMEs & Space Weather. Dst (nT). 0. CIR. - 100. CMEs.
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Space Weather Science from the Sun-Earth L5 Nat GopalswamySolar Physics Laboratory, NASA/GSFC, Greenbelt, MD 20771, USA Expert Meeting on Improving Space Weather Forecasting in the Next Decade Feb 10-11, 2014
10,000 0.1 CMEs & Space Weather Dst (nT) 0 CIR - 100 CMEs - 200 - 300 - 400 - 500 UT (h) Magnetic storms SEPs On the way and upon arrival Upon arrival at Earth CME’s Magnetic Structure Is Crucial (Bz <0) Shock-driving Capability is Crucial VCME -VSW > VMS Space systems Airplanes atmosphere Space systems Magnetosphere Ionosphere Atmosphere Ground
Corotating Interaction Regions (CIRs) • CIRs are identified using plasma signatures such as proton density (peaks at the stream interface) • Proton thermal pressure (peaks at the interface), solar wind speed (peaks about half a day after the interface),and the flow direction, which changes from west to east at the interface • Magnetic measurements: CIR magnetic content and structure decide the strength of the geomagnetic storm 25 Streams E SIR W Superposed epoch analysis of 25 CIRs Gosling 1996
Comparing CMEs and CIRs CIRs Dst>-150 Dst>-1500 CMEs
SUN Why Go to L5? CIRs can be observed in situ ~4 days ahead of earth arrival Earthward CMEs can be measured without projection effects SUN CIR Earth View Halo CME L5 View Limb CME 2009 October
A CME in Three Views: True Speed from STEREO STEREO A STEREO B Halo CME ~600 km/s 1000 km/s 1000 km/s Limb CME Limb CME S Earthward CMEs W/O projection effects Quadrature observations 2010-2012 Gopalswamy et al. 2013 STEREO-A STEREO-B E
CMEs that Matter for Space Weather Earth View Difficult to measure the true speed from the Sun-Earth line (e.g. L1) L5 View The storm CMEs come from close to the disk center (15W) while the SEP ones comes from the western hemisphere, typically 45W Most of the storm and SEP CMEs will appear as limb CMEs from L5. SEP CMEs will appear as halos from L4. Storm CMEs will be only 45 east of Sun-L4 line, so the measurements will be subject to projection effects.
Remote-sensing andin-situ instruments observe different parts of the CME Earth-impacting part of the CME not imaged from Sun-Earth line • Sun-Earth line is not well-suited to observe earth-affecting CMEs and CIRs • Need a different vantage point: Sun-Earth L5 May 2005
Coronagraph Observations Cannot say whether a CME is frontsided or Backsided EUV image superposed on the LASCO image identifies the solar source (Earth-directed CME) Sometimes the surface signatures may be too weak making it difficult to tell the CME origin
From Off the Sun-Earth line • Front-back ambiguity is resolved if Earthward CMEs viewed from L5 • The section outside of the red lines is visible from L1 (as halo CME) • An imager from off the Sun-Earth line can view the CME in broadside • and also its direction (towards Earth or behind the Sun).
CME Propagation Affected by Preceding CMEs • In addition to the aerodynamic drag, the propagation of CMEs is significantly affected by • large-scale structures such as CMEs and coronal holes • Preceding CMEs were observed only in the broadside view (by STEREO), not by SOHO (L1). • Arrival time predictions by both ESA and ENLIL models were much earlier than • actual CME arrival because they did not account for these preceding CMEs Gopalswamy et al. 2013
CME- Solar Wind Interactiona = - α (uCME - usw) • The background solar wind model is critical in understanding CME propagation • This model is generally derived from the photospheric synoptic magnetograms, which contain information taken over a Carrington rotation (WSA-ENLIL) • An L5 magnetograph can update the older half of the synoptic map, making the background model more realistic
Synoptic Maps used for Solar Wind Models L5 data can update this
Arrival of Solar Sources (Active Regions & Coronal holes) to Earth View Known Days Ahead from L5
Shock & Flux Rope CME SHOCK Shock feature can be viewed best from broadside Useful measurement can be made on spatial dimensions (e.g., standoff distance, flux rope size) For Bz prediction we still needs near-surface observations from the Sun-Earth line
From SOHO & STEREO to Earth Affecting Solar Causes Observatory (EASCO) • EASCO concept was studied at GSFC and reported to the Decadal survey committee • SOHO lacked radio instrument and magnetometer • STEREO did not have a magnetograph • The EASCO mission to overcome these deficits and expand with a Hard X-ray Imager (HXI) and UV Off-limb Spectrograph (UVOS)
MDL Study: Spacecraft Assembly & Launch Configuration For Space Weather Total payload mass 138 kg
Summary • The L5 is the next logical location for observing Earth-affecting solar disturbances such as coronal mass ejections (CMEs) and corotating interaction regions (CIRs) • The arrival of both CIRs and CMEs affecting Earth can be predicted with long lead time • Kinematics of Earth-affecting CMEs can be obtained with minimal projection effects • Proof of concept the transit of STEREO B through L5 • Best way to obtain input data (CME, magnetogram) needed by models such as ENLIL • Details: http://adsabs.harvard.edu/abs/2011SPIE.8148E..30G http://adsabs.harvard.edu/abs/2011JASTP..73..658G
Deflection by Coronal Hole S15W11 2014 Jan 07 19:00 UT • CME Speed: 2100 km/s • CME moves mostly to the south and west • even though the source is near the disk center • Prediction errors range from -19 h to -31 h • because earthward speed overestimated • many such events in cycle 23: Gopalswamy et al. 2009 S15W11