A5010350957- Solar and Space Plasma Dynamics
- Ionosphere and magnetosphere dynamics
- Stellar, planetary, and galactic studies
- Geomagnetism and Paleomagnetism Studies
- Astro and Planetary Science
- Geophysics and Gravity Measurements
- Solar Radiation and Photovoltaics
- Geological and Geophysical Studies
- Magnetic confinement fusion research
- Remote Sensing and LiDAR Applications
- Earthquake Detection and Analysis
- Oil, Gas, and Environmental Issues
- Fluid Dynamics and Turbulent Flows
- Satellite Image Processing and Photogrammetry
- Geophysical and Geoelectrical Methods
- Gamma-ray bursts and supernovae
- Global Energy and Sustainability Research
- Spacecraft and Cryogenic Technologies
- Infrared Target Detection Methodologies
- Planetary Science and Exploration
- 3D Surveying and Cultural Heritage
- Advanced Thermodynamics and Statistical Mechanics
- Magnetic Field Sensors Techniques
- Inertial Sensor and Navigation
- Calibration and Measurement Techniques
National Solar Observatory
2015-2024
West Chester University
2010-2012
High Altitude Observatory
2005-2006
NSF National Center for Atmospheric Research
2005
National and Kapodistrian University of Athens
2003-2005
University of Crete
2002-2003
Foundation for Research and Technology Hellas
2002-2003
University of St Andrews
1999-2000
This review describes observations of the polar magnetic fields, models for cyclical formation and decay these evidence their great influence in solar atmosphere. The field distribution dominates global structure corona over most cycle, supplies bulk interplanetary via coronal holes, is believed to provide seed creation activity cycle that follows. A broad observational knowledge theoretical understanding fields therefore an essential step towards a view heliospheric fields. Analyses both...
Coronal magnetic field models use photospheric measurements as boundary condition to model the solar corona. We review in this paper most common assumptions, starting from MHD-models, magnetohydrostatics, force-free and finally potential models. Each list is somewhat less complex than previous one makes more restrictive assumptions by neglecting physical effects. The magnetohydrostatic approach neglects time-dependent phenomena plasma flows, additionally gradient of pressure gravity force....
The Daniel K. Inouye Solar Telescope (DKIST) will revolutionize our ability to measure, understand and model the basic physical processes that control structure dynamics of Sun its atmosphere. first-light DKIST images, released publicly on 29 January 2020, only hint at extraordinary capabilities which accompany full commissioning five facility instruments. With this Critical Science Plan (CSP) we attempt anticipate some what those enable, providing a snapshot scientific pursuits hopes engage...
We analyze the spatial and temporal variations of abrupt photospheric magnetic changes associated with six major flares using 12-minute, 0.5-arcsec vector magnetograms from NASA's Helioseismic Magnetic Imager instrument (HMI) on Solar Dynamics Observatory satellite. The occurred near main neutral lines four active regions, NOAA 11158, 11166, 11283 11429. During all line field vectors became stronger more horizontal, in each case almost entirely due to strengthening horizontal components...
We characterize the changes in longitudinal photospheric magnetic field during 38 X-class and 39 M-class flares within $65^{\circ}$ of disk-center using 1-minute GONG magnetograms. In all 77 cases we identify at least one site flaring active region where clear, permanent, stepwise occurred. The median duration was about 15 minutes approximately equal for flares. absolute values ranged from detection limit $\sim\!\!10$~G to as high $\sim\!\!450$~G two exceptional cases. value 69~G. Field were...
It has been realized for some time that the slow solar wind with its embedded heliospheric current sheet often exhibits complex features suggesting at least partially transient origin. In this paper we investigate structure of using observations by Wind and STEREO spacecraft during two Carrington rotations (2054 2055). These occur minimum activity when interplanetary medium is dominated recurrent high-speed streams large-scale coronal mass ejections (ICMEs) are rare. However, signatures...
The declining phases of solar cycles are known for their high speed wind streams that dominate the geomagnetic responses during this period. Outstanding questions about these streams, which can provide fastest winds cycle, concern origins, persistence, and predictability. phase cycle 23 has lasted significantly longer than corresponding previous two cycles. Solar magnetograph observations suggest polar magnetic field is also ∼ 2 – 3 times weaker. launch STEREO in late 2006 provided...
We study the evolution of observed photospheric magnetic field and modeled global coronal during past 3 1/2 solar activity cycles since mid-1970s. use synoptic magnetograms extrapolated potential-field models based on longitudinal full-disk from National Solar Observatory's three magnetographs at Kitt Peak, Synoptic Optical Long-term Investigations Sun vector spectro-magnetograph, spectro-magnetograph 512-channel magnetograph instruments, Stanford University's Wilcox Observatory. The...
Abstract Global coronal models seek to produce an accurate physical representation of the Sun’s atmosphere that can be used, for example, drive space-weather models. Assessing their accuracy is a complex task, and there are multiple observational pathways provide constraints tune model parameters. Here, we combine several such independent constraints, defining model-agnostic framework standardized comparison. We require predict distribution holes at photosphere, neutral line topology model’s...
Observations from the Hinode/XRT telescope and STEREO/SECCHI/EUVI are utilized to study polar coronal jets plumes. The focuses on temporal evolution of both structures their relationship. data sample, spanning 2007 April 7-8, shows that over 90% 28 observed jet events associated with EUV images (STEREO/SECCHI) show plume haze rising location approximately 70% X-ray (Hinode/XRT) jets, appearing minutes hours after was observed. remaining occurred in areas where material previously existed,...
We analyzed ground- and space-based observations of the eruptive flare (3B/X6.5) associated Moreton wave (∼850 km s−1; ∼270° azimuthal span) 2006 December 6 to determine driver—either pressure pulse (blast) or coronal mass ejection (CME). Kinematic analysis favors a CME driver wave, despite key gaps in data. The scenario has less constrained/smoother velocity versus time profile than is case for hypothesis requires an acceleration rate more accord with observations. picture based, part, on...
Abstract As solar activity steadily declined toward the cycle 24 minimum in early months of 2017, expectation for major energetic particle (SEP) events diminished with sunspot number. It was thus surprising (though not unprecedented) when a new, potentially significant active region rotated around East limb July that by midmonth producing series coronal eruptions, reaching crescendo 23 July. This series, apparently associated birth growing pseudostreamer, produced largest SEP event(s) seen...
Regular remote sensing of the magnetic field embedded within million-degree solar corona is severely lacking. This reality impedes fundamental investigations nature coronal heating, generation and stellar winds, impulsive release energy into system via flares other eruptive phenomena. Resulting from advancements in large aperture coronagraphy, we report unprecedented maps polarized spectra emitted at 1074 nm by Fe +12 atoms active corona. We detect clear signatures Zeeman effect that are...
We investigate the role of coronal mass ejections (CMEs) in global magnetic field reconfiguration, a debate that has lasted for about two decades. Key evidence restructuring during 2007 December 31 CME is provided by combining imaging observations from widely separated spacecraft with potential-field source-surface (PFSS) model, thanks to extraordinarily quiet Sun at present solar minimum. The helmet streamer, previously disrupted CME, re-forms but displaced southward permanently;...
Accurate prediction of solar activity calls for precise calibration cycle models. Consequently we aim to find optimal parameters models which describe the physical processes on surface, in turn act as proxies what occurs interior and provide source terms coronal We use a genetic algorithm optimize surface flux transport using National Solar Observatory (NSO) magnetogram data Cycle 23. This is applied both 1D model that inserts new magnetic form idealized bipolar regions, also 2D assimilates...
We present generalized Kippenhahn-Schlüter (KS) equilibrium and steady-flow solutions of the magnetohydrodynamic (MHD) equations. These are constructed arrays laminated isothermal KS prominence sheets whose temperatures, sag angles, dip positions may vary arbitrarily from sheet to sheet. Moreover, can move at arbitrary constant uniform velocities relative each other within their planes. This great versatility allows us model filamentary structure prominences illustrate why observed...
Besides their own intrinsic interest, correct interpretation of solar surface magnetic field observations is crucial to our ability describe the global structure atmosphere. Photospheric magnetograms are often used as lower boundary conditions in models corona, but not data from nearly force-free chromosphere. National Solar Observatory's (NSO) Synoptic Optical Long-term Investigations Sun VSM (Vector Spectromagnetograph) produces full-disk line-of-sight flux images deriving both...
Compared to cycle 23, coronal mass ejections (CMEs) with angular widths >30° have been observed occur at a higher rate during solar 24, per sunspot number. This result is supported by data from three independent databases constructed using Large Angle and Spectrometric Coronagraph Experiment coronagraph images, two employing automated detection techniques one compiled manually human observers. According the that cover larger field of view, enhanced CME actually began shortly after 23 polar...
We present an overview of the data and models collected for Whole Heliosphere Interval, international campaign to study three-dimensional solar–heliospheric–planetary connected system near solar minimum. The correspond Carrington Rotation 2068 (20 March – 16 April 2008) extending from below photosphere, through interplanetary space, down Earth's mesosphere. Nearly 200 people participated in aspects WHI studies, analyzing interpreting nearly 100 instruments order elucidate physics fundamental...