7_3_Gopalswamy

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

CMEs & Space Weather 10,000

Dst (nT)

CMEs CIR 0.1 UT (h)

On the way and upon arrival

Shock-driving Capability is Crucial VCME -VSW > VMS

SEPs

Magnetic storms

Space systems Airplanes atmosphere

Space systems Magnetosphere Ionosphere Atmosphere Ground

0 - 100 - 200 - 300 - 400 - 500

Upon arrival at Earth

CME’s Magnetic Structure Is Crucial (Bz -150

CMEs

Dst>-1500

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

SUN

CIR

2009 October

Earth View Halo CME

L5 View Limb CME

A CME in Three Views: True Speed from STEREO STEREO A

1000 km/s

1000 km/s

Limb CME Quadrature observations 2010-2012 Gopalswamy et al. 2013

STEREO B

Halo CME ~600 km/s

Limb CME

S

Earthward CMEs W/O projection effects STEREO-B

E

STEREO-A

Earth View

CMEs that Matter for Space Weather 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 and in-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 wellsuited to observe earthaffecting 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 Interaction a = - 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 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

CME

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 S15W11 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