Solar Drivers of Space Weather Steven Hill NOAA/SEC June 14, 2007 Research Experience for Undergraduates

Energy and Power in Context

Outline Overview of the Sun –Interior –Surface –Corona Solar Drivers of Space Weather –Coronal Holes –Flares –Coronal Mass Ejections (CMEs) Summary

Interior Courtesy UC Berkeley

Sunspots and Subsurface Structure Courtesy S. Kosovichev, Stanford University ( Convection and magnetic fields below the solar surface drive the appearance and physical conditions in sunspots

Surface and Corona The ‘average’ surface and corona are shown Heating of the corona is a major unsolved problem in solar physics Note comparisons of temperature and density to terrestrial standards

Sun at Different Wavelengths Because of the temperature differences at different heights in the corona, different wavelengths highlight features and phenomena occurring at different heights

Magnetic Fields Magnetic fields dominate the corona and are responsible for much of its structure, from coronal holes to active regions

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Solar Wind I The mass that the Sun continuously loses through the corona is called the solar wind It is highly variable spatially and temporally Major eruptions of mass are called Coronal Mass Ejections (CMEs) SOHO coronagraph movie showing solar wind, CMEs, and radiation storm

Solar Wind II Courtesy C. Russell Ulysses near polar passes show the latitudinal structure of the solar wind speed. Open field at high latitudes leads to predominantly high speed winds A depiction of the process leading to the Parker spiral (Parker, 1958).

year Variability Courtesy Yohkoh SXT While the total solar irradiance – the solar constant – is nearly constant over an 11-year cycle, the X-ray irradiance changes by a factor of 100. If flares are included, then this factor is

Outline Overview of the Sun –Interior –Surface –Corona Solar Drivers of Space Weather –Coronal Holes –Flares –Coronal Mass Ejections (CMEs) Summary

Coronal Holes Regions of open magnetic field related to high speed solar wind. Changes in solar wind speed at the boundaries of coronal holes compresses Earth’s magnetic field. Since coronal holes ‘live’ for more than a solar rotation, these storms recur. One solar rotation shows the persistance of active regions and coronal holes.

CIRs and Recurring Geomagnetic Storms Co-rotating Interacting Regions (CIRs) are regions of compressed, even shocked, solar wind caused by high speed streams from coronal holes CIRs lead to the majority of recurring geomagnetic storms as they sweep past Earth Courtesy C. Russell Coronal Hole

Solar Wind Effects Stars, comet Encke, and the solar wind STEREO spacecraft provides a visual look at solar wind effects near 0.5AU Tail disconnections occur at discontinuities in the solar wind Courtesy D. Biesecker & STEREO

Flares Sudden conversions of magnetic energy into thermal and kinetic energy. Closely associated with coronal mass ejections CMEs. Rapid changes in solar EUV and X-ray emissions affect thermosphere and ionosphere. Large flares can have an extreme effect. In addition, flares are related to energetic particle events that result in Solar Radiation Storms.

Stressed Magnetic Fields Active region complexity –Active region magnetic fields become stressed by convective motions in the photosphere –As energy builds up it can be released catastrophically –Particular morphologies, illuminated by emitting plasmas, are more susceptible to eruption –Region below resulted in flare and CME Non-Potential: Twist Simple + - Non-Potential: Shear Non-potential region (twist / sigmoid) prior to flaring as seen by several instruments (Nitta et al., 2004 – unpublished)

Solar Eruption Process One concept of the relationship between flares and CMEs Process of magnetic reconnection is key Conceptual models abound Computational modeling is more experimental than predictive Lin & Forbes, 2002

Forecasting Flare Effects Flares are a source of ‘directly connected’ energetic particles (Reames, 1999) Radiation storm arrival time correlates with flare longitude (Balch, 2000) //// 0533 LEA C RSP III/ GO8 5 XRA 1-8A M E LEA G RBR LEA G RBR LEA G RBR B0618 U LEA 2 FLA S05W04 SF 9718 Earliest Possible Location of flares Impulsive Flare Phase on 2 deg grid Weighted Centroid Location :36: SEC ground system, using both XRS and SXI data, provides flare locations within two minutes of initial XRS flare detection (‘XFL’ product)

Record X28 Flare in False Color Combined EIT and SXI data.

Coronal Mass Ejections Coronal Mass Ejections (CMEs) are massive expulsions of matter from the Sun’s outer atmosphere. – km/sec speed –10 14 to g –1-4 days to reach Earth –Shock generated radiation storms can reach Earth much sooner –Location of the source region on the solar disk is key to estimating the trajectory of the CME and its likelihood of hitting Earth CME generated shock creates energetic particle radiation storm (Reames, 1999) Ejected material associated with a CME seen by GOES 12 SXI in 2001 (Hill et al., 2001)

Coronal Mass Ejection SOHO Cornograph Observations of a CME.

IPS Tomography Tomographic reconstruction of CMEs in interplanetary space Radio sources distant from the solar system are monitored Signal scintillation occurs when the CME crosses the line-of-sight

Interplanetary Medium Not quite ‘empty’ Contains ions, elections, currents and magnetic fields Solar disturbances propagating toward Earth can be strongly affected by the state of the IPM and the passage of previous disturbances

Interplanetary Medium Contains ions, elections, currents and magnetic fields Solar disturbances propagating toward Earth can be strongly affected by the state of the IPM and the passage of previous disturbances

Summary Important, Recurring Themes –Solar activity evolves from the interior, through many layers and phases until we see it manifested on the surface and in the corona –Magnetic fields thread through every phenomena and dominate many –Truly predictive physics-based numerical models of solar phenomena are not yet available –Forecasting relies heavily on observations and empirical models Resources: –MSFC - –UCB - –Flare cartoons -