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NASA NTRS1982

Solar-stellar astrophysics

Nonthermal physical processes in the solar atmosphere are discussed. The solar atmospheric regions are defined, and solar convection and its phenomena are explained. The relationship of the solar dynamo, magnetic field, and flares is explored. The solar atmospheric velocity fields are discussed, and the unresolved problem of the nature of atmospheric heating is detailed. The solar wind heating and acceleration are discussed and the need for global solar atmospheric models is emphasized. The application of these solar nonthermal processes to the stars in general is then taken up, employing the same categories as were applied to the solar atmosphere.

Jordan, S. D.↗

NASA NTRS1992

The solar cycle; Proceedings of the National Solar Observatory/Sacramento Peak 12th Summer Workshop, Sunspot, NM, Oct. 15-18, 1991

Attention is given to a flux-transport model, the effect of fractal distribution on the evolution of solar surface magnetic fields, active nests on the sun, magnetic flux transport in solar active regions, recent advances in stellar cycle research, magnetic intermittency on the sun, a search for existence of large-scale motions on the sun, and new solar cycle data from the NASA/NSO spectromagnetograph. Attention is also given to the solar cycle variation of coronal temperature during cycle 22, the distribution of the north-south asymmetry for the various activity cycles, solar luminosity variation, a two-parameter model of total solar irradiance variation over the solar cycle, the origin of the solar cycle, nonlinear feedbacks in the solar dynamo, and long-term dynamics of the solar cycle.

Harvey, Karen L.↗

NASA NTRS2018

An Early Prediction of the Amplitude of Solar Cycle 25

A “Solar Dynamo” (SODA) Index prediction of the amplitude of Solar Cycle 25 is described. The SODA Index combines values of the solar polar magnetic field and the solar spectral irradiance at 10.7 cm to create a precursor of future solar activity. The result is an envelope of solar activity that minimizes the 11-year period of the sunspot cycle. We show that the variation in time of the SODA Index is similar to several wavelet transforms of the solar spectral irradiance at 10.7 cm. Polar field predictions for Solar Cycles 21 – 24 are used to show the success of the polar field precursor in previous sunspot cycles. Using the present value of the SODA index, we estimate that the next cycle’s smoothed peak activity will be about 140 ± 30 solar flux units for the 10.7 cm radio flux and a Version 2 sunspot number of 135 ± 25. This suggests that Solar Cycle 25 will be comparable to Solar Cycle 24. The estimated peak is expected to occur near 2025.2 ± 1.5 year. Because the current approach uses data prior to solar minimum, these estimates may improve as the upcoming solar minimum draws closer.

Solar Cycle Predictions↗

NASA NTRS2022

COSMO: The COronal Solar Magnetism Observatory

The COronal Solar Magnetism Observatory (COSMO) will make the first synoptic, simultaneous measurements of magnetic and plasma properties of the global solar atmosphere, filling crucial gaps in our understanding of the drivers of solar eruptions and the evolution of the coronal magnetic field on time scales from minutes to decades. - COSMO uniquely addresses critical Heliophysics science. With an unparalleled combination of large field of view and high magnetic sensitivity, the 1.5m COSMO Large Coronagraph (LC) opens a new window on coronal magnetism on global scales. Along with K-Coronagraph (K-Cor) middle-corona observations and the Chromosphere and Prominence Magnetometer (ChroMag) observations of the photosphere and chromosphere, these capabilities enable researchers to finally answer crucial questions about solar eruptions, coronal heating/solar wind acceleration, and the solar dynamo. - COSMO is mature. K-Cor has been operating at the Mauna Loa Solar Observatory (MLSO) since 2013 and ChroMag is soon to be deployed. Also at MLSO, the 20cm Upgraded Coronal Multichannel Polarimeter (UCoMP) is proving the power of global coronal spectropolarimetry and whetting the community’s appetite for the unprecedented sensitivity of the LC. - COSMO is low risk. A recent development: the NSF-funded COSMO Site and Design Advancement (COSADA) is a three-year effort currently underway that reduces risk through site selection and final design of the LC. - COSMO has broad community support. The fact that COSMO fills a critical gap in our observational capabilities was recognized in the last Solar and Space Physics Decadal Survey. COSMO builds on the legacy and thriving user base of the MLSO, which has provided global synoptic solar observations to the community for over sixty years. - COSMO is complementary to other solar telescopes. The breakthrough observations obtained by COSMO will not be provided by any other current or proposed observatory, and will enhance the value of other ground- and space-based Heliophysics assets.

Steven Tomczyk↗

NASA NTRS1991

The sun and interplanetary magnetic field

The interplanetary magnetic field (IMF) serves as a link between the sun, the response of the earth to solar activity and variations in galactic cosmic radiation. The IMF originates as a solar-coronal magnetic field that is transported into space by the solar wind. The close connection between solar magnetic fields and the origin and structure of the solar wind is described. The solar wind forms the heliosphere, a cavity containing the magnetized solar plasma from which the interstellar plasma and field are excluded. The entry of galactic cosmic rays into the heliosphere and their strong interaction with the IMF are discussed, this topic being of primary importance to the production and temporal variations of radiogenic elements. The profound influence of the IMF on geomagnetic activity and the aurora is discussed within the context of merging or reconnection with the planetary field. The physical connection is thus established between solar magnetic fields, magnetic storms and aurora. The state of the solar wind and IMF during the Maunder minimum is considered and an explanation for the (relative) absence of sunspots and aurora is proposed. The mechanism is an interruption of the oscillatory solar dynamo, a consequent reduction in the heating of the corona, a cessation of the supersonic solar wind and a weakening or absence of southward-directed magnetic fields in the vicinity of the earth.

Smith, Edward J.↗

NASA NTRS2002

Science Prospects from the STEREO Mission

The solar magnetic field is constantly generated beneath the surface of the Sun by the solar dynamo. To balance this flux generation, there is constant dissipation of magnetic flux at and above the solar surface. The largest phenomenon associated with this dissipation is the Coronal Mass Ejection (CME). The Solar and Heliospheric Observatory (SOHO) has provided remarkable views of the corona and CMEs, and served to highlight how these large interplanetary disturbances can have terrestrial consequences. STEREO is the next logical step to study the physics of CME origin, propagation, and terrestrial effects. Two spacecraft with identical instrument complements will be launched on a single launch vehicle in November 2007. One spacecraft will drift ahead and the second behind the Earth at a separation rate of 22 degrees per year. Observation from these two vantage points will for the first time allow the observation of the three-dimensional structure of CMEs and the coronal structures where they originate. Each STEREO spacecraft carries a complement of 10 instruments, which include (for the first time) an extensive set of BOTH remote sensing and in-situ instruments. The remote sensing suite is capable of imaging CMEs from the solar surface out to beyond Earth's orbit (1 AU), and in-situ instruments are able to measure distribution functions for electrons, protons, and ions over a broad energy range, from the normal thermal solar in wind plasma to the most energetic solar particles. It is anticipated that these studies will ultimately lead to an increased understanding, of the CME process and eventually to the ability to predict CME occurrence and thereby 'forecast' the condition of the near-Earth environment.

Davila, Joseph M.↗

NASA NTRS2003

Solar Terrestrial Relations Observatory (STEREO)

The solar magnetic field is constantly generated beneath the surface of the Sun by the solar dynamo. To balance this flux generation, there is constant dissipation of magnetic flux at and above the solar surface. The largest phenomenon associated with this dissipation is the Coronal Mass Ejection (CME). The Solar and Heliospheric Observatory (SOHO) has provided remarkable views of the corona and CMEs, and served to highlight how these large interplanetary disturbances can have terrestrial consequences. STEREO is the next logical step to study the physics of CME origin, propagation, and terrestrial effects. Two spacecraft with identical instrument complements will be launched on a single launch vehicle in November 2007. One spacecraft will drift ahead and the second behind the Earth at a separation rate of 22 degrees per year. Observation from these two vantage points will for the first time allow the observation of the three-dimensional structure of CMEs and the coronal structures where they originate. Each STEREO spacecraft carries a complement of 10 instruments, which include (for the first time) an extensive set of both remote sensing and in-situ instruments. The remote sensing suite is capable of imaging CMEs from the solar surface out to beyond Earth's orbit (1 AU), and in-situ instruments are able to measure distribution functions for electrons, protons, and ions over a broad energy range, from the normal thermal solar wind plasma to the most energetic solar particles. It is anticipated that these studies will ultimately lead to an increased understanding of the CME process and provide unique observations of the flow of energy from the corona to the near-Earth environment. An international research program, the International Heliophysical Year (IHY) will provide a framework for interpreting STEREO data in the context of global processes in the Sun-Earth system.

Davila, Joseph M.↗

NASA NTRS2014

International Space Station Columbus Payload SoLACES Degradation Assessment

SOLAR is a European Space Agency (ESA) payload deployed on the International Space Station (ISS) and located on the Columbus Laboratory. It is located on the Columbus External Payload Facility in a zenith location. The objective of the SOLAR payload is to study the Sun. The SOLAR payload consists of three instruments that allow for measurement of virtually the entire electromagnetic spectrum (17 nm to 100 um). The three payload instruments are SOVIM (SOlar Variable and Irradiance Monitor), SOLSPEC (SOLar SPECctral Irradiance measurements), and SolACES (SOLar Auto‐Calibrating Extreme UV/UV Spectrophotometers). The SolACES payload includes a set of 4 spectrometers that measure the solar EUV flux from 17 nm to 220 nm. One of these 4 spectrometers failed early on (before deployment). EUV data is important in understanding the solar dynamo. Also, EUV flux is the source of most of the ionization that produces the ionosphere plasma. Plasma production is important in understanding the ionosphere environment. The ionosphere conditions affect many subjects including spacecraft charging, dynamo processes, instabilities, and communications. The 3 remaining spectrometers have collected valuable data during the historically low solar cycle 24. Some of this data will be presented. A significant trend in degradation of the remaining SolACES spectrometers was observed towards the end of CY2010 (GMT 310) through mid CY 2011 (GMT 132). The Principle Investigators of SolACES initiated a Mission Evaluation Room (MER) Chit to request an investigation of the degradation in CY 2011 (GMT 230). The Boeing Space Environments team was asked to respond to the ESA initiated MER Chit request to investigate the cause of the degradation. This paper will discuss the findings of that investigation.

Harman, William↗

NASA NTRS2011

Solar Cycle Prediction

Solar cycle predictions are needed to plan long-term space missions; just like weather predictions are needed to plan your next vacation. Fleets of satellites circle the Earth collecting many types of science data, protecting astronauts, and relaying information. All of these satellites are sensitive at some level to solar cycle effects. Predictions of drag on LEO spacecraft are one of the most important. Launching a satellite with less propellant can mean a higher orbit, but unanticipated solar activity and increased drag can make that a Pyrrhic victory. Energetic events at the Sun can produce crippling radiation storms that endanger all assets in space. Testing solar dynamo theories by quantitative predictions of what will happen in 5-20 years is the next arena for solar cycle predictions. I will describe the current state of solar cycle predictions and anticipate how those predictions could be made more accurate in the future.

Pesnell, William Dean↗

NASA NTRS2012

Solar Cycle Predictions

Solar cycle predictions are needed to plan long-term space missions; just like weather predictions are needed to plan the launch. Fleets of satellites circle the Earth collecting many types of science data, protecting astronauts, and relaying information. All of these satellites are sensitive at some level to solar cycle effects. Predictions of drag on LEO spacecraft are one of the most important. Launching a satellite with less propellant can mean a higher orbit, but unanticipated solar activity and increased drag can make that a Pyrrhic victory as you consume the reduced propellant load more rapidly. Energetic events at the Sun can produce crippling radiation storms that endanger all assets in space. Solar cycle predictions also anticipate the shortwave emissions that cause degradation of solar panels. Testing solar dynamo theories by quantitative predictions of what will happen in 5-20 years is the next arena for solar cycle predictions. A summary and analysis of 75 predictions of the amplitude of the upcoming Solar Cycle 24 is presented. The current state of solar cycle predictions and some anticipations how those predictions could be made more accurate in the future will be discussed.

Pesnell, William Dean↗

NASA NTRS2011

The Helioseismic and Magnetic Imager (HMI) Investigation for the Solar Dynamics Observatory (SDO)

The Helioseismic and Magnetic Imager (HMI) instrument and investigation as a part of the NASA Solar Dynamics Observatory (SDO) is designed to study convection-zone dynamics and the solar dynamo, the origin and evolution of sunspots, active regions, and complexes of activity, the sources and drivers of solar magnetic activity and disturbances, links between the internal processes and dynamics of the corona and heliosphere, and precursors of solar disturbances for space-weather forecasts. A brief overview of the instrument, investigation objectives, and standard data products is presented.

Helioseismology↗

NASA NTRS1987

The dynamo dilemma

The recent determination that the angular velocity Omega of the sun declines downward through the convective zone raises serious questions about the nature of the solar dynamo. The principal qualitative features of the sun are the azimuthal fields that migrate toward the equator in association with an oscillating poloidal field which reverses at about the time of maximum appearance of bipolar magnetic regions. If Omega decreases downward, or is negligible, the horizontal gradient in Omega produces a dynamo with some of these essential characteristics. There is reason to think that the dynamo is confined to the lower half of the convective zone, where alpha has the opposite sign from the usual (alpha of greater than 0 in the northern hemisphere) producing equatorward migration but reversing the sign of the associated poloidal field. Meridional circulation may play an essential role in shaping the dynamo. At the present time it is essential to measure Omega accurately and determine the nature of the meridional circulation.

Parker, E. N.↗

NASA NTRS2022

The Puzzling Structure of Solar Convection: Window into the Dynamo

The operation of the solar dynamo, with all of its remarkable spatio-temporal ordering, remains an outstanding problem of modern solar physics. A number of mechanisms that might plausibly contribute to its operation have been proposed, but the relative role played by each remains unclear. This uncertainty stems from continuing questions concerning the speed and structure of deep-seated convective flows. Those flows are in-turn thought to sustain both the Sun’s turbulent EMF and the large-scale flows of differential rotation and meridional circulation suspected of influencing the dynamo’s organization and timing. Ultimately, the convective and large-scale flow structure derive from the Coriolis force. When the Coriolis effect is weak (rapid convective flow), convection exhibits little organization in its spatial structure, and the meridional flow is expected to assume a single-celled profile within each hemisphere. Convection subject to strong Coriolis forces instead organizes into compact, spiraling columnar structures and sustains meridional flows that possess multiple cells in latitude and radius. The implications for the dynamo in these two regimes are substantial, impacting the flux-transport properties of any assumed meridional flow and the convectively-driven EMF. Continued progress in this area is complicated by (i) inconsistencies between helioseismic measurements of convective and meridional flow made with different techniques and instruments, and (ii) a lack of high-latitude data for convection, differential rotation, and meridional flow. We suggest that the path forward to resolving these difficulties is twofold. First, the acquisition of long-term helioseismic and emissivity measurements obtained from a polar vantage point is vital to complete our picture of the Sun’s outer convection zone. Second, sustained and expanded investment in theory-oriented and combined theory/observational research initiatives will be crucial to fully exploit these new observations and to resolve inconsistencies between existing measurements.

SMD↗

NASA NTRS1988

Using geomagnetic indices to forecast the next sunspot maximum

The Babcock (1961) 'solar dynamo' model and known interactions of the interplanetary magnetic field with the earth's magnetosophere are used to explain the relations found between geomagnetic indices at solar minimum and the sunspot number at the following solar maximum. The work of Kane (1987) is augmented by including recent smoothed aa and Ap indices. A smoothed maximum sunspot number of 163 + or - 40 to peak in October 1990 + or - 9 months for solar cycle 22 is predicted. This value is close to the Schatten and Sofia (1987) value of 170 + or - 25, predicted using more direct solar indicators.

Gonzalez, Guillermo↗

NASA NTRS1997

Properties of Nonlinear Dynamo Waves

Dynamo theory offers the most promising explanation of the generation of the sun's magnetic cycle. Mean field electrodynamics has provided the platform for linear and nonlinear models of solar dynamos. However, the nonlinearities included are (necessarily) arbitrarily imposed in these models. This paper conducts a systematic survey of the role of nonlinearities in the dynamo process, by considering the behaviour of dynamo waves in the nonlinear regime. It is demonstrated that only by considering realistic nonlinearities that are non-local in space and time can modulation of the basic dynamo wave he achieved. Moreover, this modulation is greatest when there is a large separation of timescales provided by including a low magnetic Prandtl number in the equation for the velocity perturbations.

Tobias, S. M.↗

NASA NTRS2011

The Sun, Its Extended Corona, the Interplanetary Space, the Earth's Magnetosphere, Ionosphere, Middle and Low Atmosphere, are All Parts of a Complex System - the Heliosphere

Various manifestations of solar activity cause disturbances known as space weather effects in the interplanetary space, near-Earth environment, and all the Earth's "spheres. Longterm variations in the frequency, intensity and relative importance of the manifestations of solar activity are due to the slow changes in the output of the solar dynamo, and they define space climate. Space climate governs long-term variations in geomagnetic activity and is the primary natural driver of terrestrial climate. To understand how the variable solar activity affects the Earth's environment, geomagnetic activity and climate on both short and long time scales, we need to understand the origins of solar activity itself and its different manifestations, as well as the sequence of coupling processes linking various parts of the system. This session provides a forum to discuss the chain of processes and relations from the Sun to the Earth's surface: the origin and long-term and short-term evolution of solar activity, initiation and temporal variations in solar flares, CMEs, coronal holes, the solar wind and its interaction with the terrestrial magnetosphere, the ionosphere and its connection to the neutral dominated regions below and the plasma dominated regions above, the stratosphere, its variations due to the changing solar activity and its interactions with the underlying troposphere, and the mechanisms of solar influences on the lower atmosphere on different time-scales. Particularly welcome are papers highlighting the coupling processes between the different domains in this complex system.

Gopalswamy, Natchimuthuk↗

NASA NTRS1985

Stellar activity cycles

The variety of stellar chromospheric and coronal activity provides a framework for understanding solar and stellar magnetic activity. It is pointed out that the recognition of an 11-yr periodicity within the record of sunspot numbers is a relatively recent discovery of just over a century ago. The solar activity cycle is examined, taking into account the sunspot cycle, and solar dynamo models. Time-averaged stellar chromospheric activity levels are considered along with long-term activity fluctuations of cool stars. Attention is given to the direct measurement of stellar magnetic fields, solar luminosity variations, the RS Canum Venaticorum and BY Draconis variables, continuum variations in lower main sequence stars, chromospheric variations in lower main sequence stars, and chromospheric variations in evolved stars.

Baliunas, S. L.↗

NASA NTRS2003

Invited Talks at Naples and Coimbra

Prior to observations of the solar irradiance from space that began in 1979 there was no hope of obtaining even rough estimates of the solar irradiance variation over a solar cycle, since the space observations made since showed that the magnitude of the variation over a cycle to date is less than 0.1 %, a value too small to measure from the ground. At the same time, it would be useful to know the cycle-dependent variation over more than just the two recent cycles. Lacking a complete theory for the solar dynamo responsible for this variation, the current hope is to determine what proxy might yield the best values. Because there is an excellent database on sunspot umbral and penumbral areas from the Greenwich Observatory for the years 1874-1976 (but not beyond), the possibility exists that these data could be used. This talk will summarize results of a joint study in which satellite measurements of the solar irradiance variation are compared with ground-based measurements from the Coimbra Observatory of sunspot number, umbral area, and total sunspot area to determine which would serve as the best proxy for using the Greenwich observations back to 1874. From the near constancy of sunspot umbral magnetic fields upon which the useful parameter photometric sunspot index is based, we expected that umbral area would yield the beat proxy. To our surprise, after performing a statistical study of the observations over the period 1980-1990, preliminary indications are that sunspot number (a parameter available back into the 18th century) may be just as useful as the umbral area. As expected, both are quite superior as proxies to total sunspot area, which includes the penumbral area. This conclusion is consistent with earlier work of Hop and Schatten, who sought a proxy by studies of the umbral-penumbral area ratio. A second motivation for pursuing this work is the possibility that relatively small variations in the solar irradiance may induce larger responses in Earth's climate than would occur from simply introducing the corresponding heat differential into the terrestrial atmosphere. The talk will conclude with a description of why some climatologists are beginning to explore this possibility, which is suggest by some of the space observations used in the above search for a solar irradiance variation proxy.

Jordan, Stuart↗