# Presentation: 316953

## Geoeffective Solar Events

- Nat Gopalswamy
- Center For Solar Physics & Space Weather
- The Catholic University of America
- Washington DC
- &
- NASA Goddard Space Flight Center, Greenbelt, Maryland
- Presented at the Huntsville 2000 Meeting, Callaway Gardens, Georgia, Nov 2000

**Notes:**
What Are CMEs ? Basic Properties
Genesis: Closed field regions
Pre-eruption Structures
Pre-eruption Evolution
Emerging Flux, Twist, Shear
Pre-eruption energy release
White light Observations:
OSO-7 White light clouds (Tousey, 1973)
Non-coronagraphic Observations:
X-ray, EUV: Near-surface Manifestations
Microwave: Filament Core, Post-eruption Arcade
Meterwave: Nonthermal Emission, thermal emission
DH: Energetic CMEs
In-situ Observations: ICMEs
IPS: CMEs in the inner heliosphere
Halo CMEs: Geoffective if Earth-Directed
CME interactions: Cannibalism

## Solar Events of Interest

- Flares
- - SEPs, Electromagnetic Radiation
- Coronal Mass Ejections (CMEs)
- - IP shocks & SEPs; ICMEs; Geomagnetic Storms
- Coronal Holes
- Geomagnetic Storms due to high speed streams
- • Flares & CMEs from closed field regions
- • CH in open field regions

## Flares

- Confined flares: Electromagnetic Radiation (X-ray, UV) and Sunward energetic electrons (hard X-rays)
- Eruptive Flares: Mass motion and Impulsive SEPs are involved;  related to  CMEs
- Flare Process: Magnetic Reconnection results in Heating (soft X-rays) and Particle Acceleration (Hard X-rays,  Microwaves, Type III radio bursts, SEPs, H-alpha & white light flares)
- Flares  effects on Earth are prompt: Sudden ionospheric disturbances due to X-rays

## CMEs

- Long-term geoeffects: The severest of geomagnetic storms are due to CMEs (Tsurutani et al., 1990; Gosling et al., 1990)
- Long-lasting SEP events originate from CME-driven shocks (Reames, 1995)
- Energetic Storm Particles (ESPs) are carried by CME-driven IP shocks
-  CMEs are the most important solar events for geoeffectiveness

**Notes:**
Tsurutani, Bruce T.; Goldstein, Bruce E.; Smith, Edward J.;  Gonzalez, Walter D.; Tang, FrancesThe interplanetary and solar causes of geomagnetic activity, Planetary and Space Science, vol. 38, Jan. 1990, p. 109-126.

Coronal mass ejections and large geomagnetic storms, Gosling, J. T.; Bame, S. J.; McComas, D. J.; Phillips, J. L., 1990, GRL, 17, 901
Reames, D., Solar energetic particles: A paradigm shift, Rev. Geophys. 33, 585, 1995

## CMEs: Introduction

- Mass Ejections known for a long time from Radio bursts, H-alpha observations (e.g, Payne-Scott et al., 1947)
- The concept  of plasma ejection known to  solar terrestrial researchers (Lindeman, 1919; Chapman & Bartels, 1940; Morrison, 1954; Gold, 1955)
- CMEs as we know today were discovered in white light pictures obtained by OSO-7  spacecraft (Tousey, 1973)
- Skylab, P78-1, SMM and SOHO missions have accumulated data on thousands of CMEs

## Defining a CME: SOHO/LASCO/C3 Images

- FRONTAL

- CORE

- CAVITY

- Corona before CME                       Corona with CME

**Notes:**
White light CME observed by SOHO/LASCO C3 coronagraph on 2000 February 27 at 07:42 UT.  Left: Pre-event corona. 
The dark circular disk:  Occulter
Small white circle: Optical Sun

## Solar Origin of 1997/02/07 CME

- CME leaving the Sun on the west side: A, B- Frontal structure; C-core

## CME CORE was a Filament

- The brightest core of the
- CME actually originated
- On the disk as seen in the
- He 10830 images (courtesy:
- HAO/NCAR)

- The compact filament at
- 17:54 UT slowly rises and
- Reaches the limb by 00:03 UT
- The next day. The filament
- Was  tracked in microwave
- images

## Filament becomes a Prominenceobserved in Microwaves

- CME core (03:30) can be traced back to a filament observed in microwaves (01:40)

## Arcade Formation in X-rays:1997/02/07 CME

- After the eruption, X-ray arcades form (AF) inside dimming regions (D)

## To summarize the structure of CMEs ...

- Frontal structure
- Cavity
- Prominence Core
- Post-eruption Arcade (Two-ribbon in H-alpha, arcades in X-ray, EUV)
- Note: Not all structures are present in all CMEs!

## CME Properties

- Large-Scale structures carrying plasma and magnetic field
- Typical mass: 1015 g ( 1 billion ton)
- Speed: < 20 to > 2000 km/s
- Typical Kinetic Energy: 1025 J
- Temperature: 8000 K (core) to 2 MK (front)
- Typical width: 70 degrees
- Solar cycle variation: One in two days during minimum; a few per day during maximum.
- Related to Flares, Shocks, Radio bursts, SEPs

## Where do CMEs originate?

- CMEs originate from closed field regions
- Active Regions
- Filament regions
- Combination of AR and Filament regions
- Transequatorial interconnecting regions

## Examples  of Closed Field Regions

- TIL

- Filament

- Active region

- SOHO/EIT image 195 A

- H-alpha picture

## Structure (Sigmoids, Flux Ropes)
Evolution (Flux Emergence, Shear, Twist)
Energy Release (Small-scale Heating & Acceleration)

- Evolution (Flux Emergence, Shear, Twist)
- Energy Release (Small-scale Heating & Acceleration)

- Aspects of Pre-eruption Phase

## Pre-Eruption Structure:Sigmoids

- S- and reverse S-shaped structures in X-ray images of Active Regions (Rust & Kumar 1996).
- Erupt more often than non-sigmoidal regions (Canfield et al. 1999)
- Relation to white light CMEs being studied
- Coronal counterpart of photospheric shear (Ambastha et al., 1993)

**Notes:**
Evolutionary and Flare-Associated Magnetic Shear Variations Observed in a Complex Flare-Productive Active Region, Ambastha, A.; Hagyard, M. J.; West, E. A., 1993,  Solar Phy., 148, 277
Canfield et al., 1999, Sigmoidal morphology and eruptive solar activity,  GRL, 26, 627
Rust, D. and  Kumar, A., 1996, Evidence for Helically Kinked Magnetic Flux Ropes in Solar Eruptions, ApJ, 464, L199. 

## Pre-eruption Structure: Flux ropes

- Naturally support prominences (Linker et al., 2001)
- Often observed as dark cavity in eclipse pictures
- Formed before (Low, 2001) or during (Gosling et al., 1990) eruption?
- Interplanetary Magnetic Clouds are flux ropes (Burlaga et al.,1981)
- MC formed out of filament or cavity of the white light CME? (Bothmer & Schwenn, 1994; Gopalswamy et al., 1998)

## Pre-eruption Structure:Guiding Streamers

- Non-radial motion of filaments
- Obvious during Solar Minimum
- Latitudinal distribution of CMEs peaks near the equator;  associated solar sources peak near the active region belt
-  The solar dipole field has strong influence on CME propagation

## Pre-eruption Evolution

- Substantial Flux emergence near filament before eruption; polarity of new flux  favorable for reconnection (Feynman & Martin, 1995)
- - Confirmed by numerical simulation studies (Chen & Shibata, 2000)
- Significant changes in photospheric flux  in small areas in the eruption region (Lara et al., 2000)
- CMEs without flux emergence also observed (Subramanian & Dere, 2001; Wang & Sheeley, 1999)

## Weak Dimming Before Eruption

- AR-Active Region D-Dimming
- G- GOES X-ray Flux

## Pre-eruption Evolution: Prolonged Dimming

- Weak, prolonged dimming for ~ 1 hr (Gopalswamy et al., 1999)
- Small-scale opening of  field lines resulting in the eruption of underlying structure? (Antiochos et al., 1994)
- Detailed investigation is being carried out (Lara et al. 2001)

## Pre-eruption Energy Release

- Signatures of pre-eruption evolution
- - Small-scale heating near filaments, consistent with reconnection scenario
- - Radio bursts near filaments – nonthermal energy release due to reconnection

## Pre-eruption Heating Near Filament

- F- Filament in Microwaves

- Dark Loops: X-ray structures

## CME Detection

- White light: Thomson scattering of photospheric light; Need occulting disk to block photospheric light (corona is million times dimmer than the photosphere)
- Other wavelengths: Near-surface (X-ray, EUV, Radio) and IP manifestations (Radio, IPS, *In situ*)

## Filament Eruption in EUV

- SOHO/EIT (195 A) images presented as a movie.
- The NW-SE filament in the southern hemisphere erupts and becomes the core of the white light CME
- Arcade formation follows the eruption

## 2000/09/12 CME on the Disk

- SOHO/LASCO C3 movie
- Partial halo event consistent with the southern location on the disk
- The bright core is the filament

## 2000/09/12  CME in LASCO/C3

## Components of a Disk CME

- SOHO/LASCO:
- Leading Edge (LE)
- & Filament (F)

- SOHO/EIT:
- Arcade Forms (AF)After
- Filament (F)Eruption

- Height-Time Plot:
- F lags LE

## Halo CMEs

-  CMEs originating on the disk appear to surround the occulting disk (Howard et al. 1982). These are Earth-directed events.
- Halo events  show that CMEs are three-dimensional structures
- Back side events also would appear as halos

## Halo CMEs Front- or Back-sided?

- EIT diff image shows no activity on the disk

## Halo CMEs

- May be geoeffective if Earth-directed (Gosling, 1993)
- Relation to CMEs at 1 AU is now possible (Gopalswamy et al., 2000; Webb et al., 2000)
- > 70% of ICMEs are followed by at least moderate geomagnetic storms

## Detection in X-rays & EUV

- Coronal Dimming (Hudson and Webb, 1997)
- Coronal Arcade Formation (Post-eruption Arcade)
- EIT Waves (Thompson et al., 1999); Brow waves as shocks (Gopalswamy, 2000)
- Global enhancement (Gopalswamy et al., 1999)

## Global Enhancement

- Observed in X-rays (Gopalswamy et al., 1999) and EUV (Gopalswamy, Lara et al., 2000)
- Maybe the “baby CME”

## Microwave Detection

- Filaments and  Prominences can be observed in microwave images (Gopalswamy et al., 1996)
- Dimming (deficit of free-free emission) can be observed in limb events
- Arcade Formation (enhanced free-free emission) can also be seen (Hanaoka et al., 1994)

## Microwave Prominence

- Complete eruptive prominence can be seen in microwaves
- Only a small portion of it is seen in H-alpha

## Radio: Meterwaves

- Nonthermal Emission:
- - Type II radio bursts due to shocks: Relation to CME is controversial (Gopalswamy et al., 1998; Cliver et al., 1999; Reiner et al., 2001)
- - Type IV bursts: nonthermal electrons trapped in CME cores or substructures (Stewart, 1985; Gopalswamy & Kundu 1990; Maia et al., 1999)
- Thermal emission: Direct imaging using free-free emission from CMEs (Gopalswamy and Kundu, 1992; Sheridan et al., 1978)

## Radio: Decameter-Hectometer (DH: 1-14 MHz)

- Type II

- SA Event (Type III Burst)

## DH Radio Bursts

- All are CME related: Early phase of IP shocks
- Shock-accelerated  (SA) electrons produce complex type III bursts (Reiner & Kaiser, 1998)
- Associated CMEs are faster and wider (Gopalswamy et al. 2000)
- Good indicators of geoeffective CMEs
- CME interaction discovered (Gopalswamy et al. 2001)

## CME Interaction

## A Cannibal CME 

## In situ Observations: ICMEs

- Direct measurement of interplanetary CMEs or ICMEs (magnetic field, density, speed, composition)
- Single point measurement
- Identification of CMEs in in-situ data is an art! There are more than 10 signatures
- Not all signatures are present in all CMEs (Gosling, 1991; Neugebauer 1997)

## CMEs and ICMEs:A tentative correspondence

-     CMEs Near Sun
- Shock                   
- Frontal                 
- Cavity                  
- Prominence Core 
- Arcade Formation

-     ICMEs near Earth
- Shock
- Sheath
- Ejecta/MC
- Pressure Plug
- --------------

## CMEs and ICMEs: Speeds

- Gopalswamy et al., GRL, 27, 145, 2000

- • It is possible to
- Combine Remote
- sensing and
*In situ* observations
- • Fast CMEs decelerate
- • Slow CMEs accelerate

## Summary

- The most important phenomenon relevant to space weather is Coronal Mass Ejections
- CME phenomenon is ultimately related to solar magnetism, but we do not fully understand how CMEs are produced.
- Multiwavelength, multi-instrument data needed to get complete picture of CMEs. The ISTP program has provided this opportunity.
-  Earth-directed CMEs are Geoeffective, but difficult to detect in white light. We need inner coronal imaging in other wavelengths.
- The Decameter-Hectometric radio bursts are indicators of large-scale CMEs  a new tool.