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Search Results: 1 - 10 of 378518 matches for " P. R. Goode "
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Umbral Dynamics in the Near Infrared Continuum
A. Andic,W. Cao,P. R. Goode
Physics , 2011, DOI: 10.1088/0004-637X/736/2/79
Abstract: We detected peaks of oscillatory power at 3 and ~6.5 minutes in the umbra of the central sunspot of the active region NOAA AR 10707 in data obtained in the near infrared (NIR) continuum at 1565.7 nm. The NIR dataset captured umbral dynamics around 50 km below the photospheric level. The umbra does not oscillate as a whole, but rather in distinct parts that are distributed over the umbral surface. The most powerful oscillations, close to a period of ~ 6.5, do not propagate upward. We noted a plethora of large umbral dots that persisted for more than 30 minutes and stayed in the same locations. The peaks of oscillatory power above the detected umbral dots are located at 3 and 5 minutes oscillations, but are very weak in comparison with the oscillations of ~ 6.5 minutes.
Does the Sun Shrink with Increasing Magnetic Activity?
W. A. Dziembowski,P. R. Goode,J. Schou
Physics , 2001, DOI: 10.1086/320976
Abstract: We have analyzed the full set of SOHO/MDI f- and p-mode oscillation frequencies from 1996 to date in a search for evidence of solar radius evolution during the rising phase of the current activity cycle. Like Antia et al. (2000), we find that a significant fraction of the f-mode frequency changes scale with frequency; and that if these are interpreted in terms of a radius change, it implies a shrinking sun. Our inferred rate of shrinkage is about 1.5 km/y, which is somewhat smaller than found by Antia et al. We argue that this rate does not refer to the surface, but rather to a layer extending roughly from 4 to 8 Mm beneath the visible surface. The rate of shrinking may be accounted for by an increasing radial component of the rms random magnetic field at a rate that depends on its radial distribution. If it were uniform, the required field would be ~7 kG. However, if it were inwardly increasing, then a 1 kG field at 8 Mm would suffice. To assess contribution to the solar radius change arising above 4Mm, we analyzed the p-mode data. The evolution of the p-mode frequencies may be explained by a magnetic^M field growing with activity. The implications of the near-surface magnetic field changes depend on the anisotropy of the random magnetic field. If the field change is predominantly radial, then we infer an additional shrinking at a rate between 1.1-1.3 km/y at the photosphere. If on the other hand the increase is isotropic, we find a competing expansion at a rate of 2.3 km/y. In any case, variations in the sun's radius in the activity cycle are at the level of 10^{-5} or less, hence have a negligible contribution to the irradiance variations.
Magnetic and Kinetic Power Spectra as a Tool to Probe the Turbulent Dynamo
V. I. Abramenko,V. B. Yurchyshyn,P. R. Goode
Physics , 2011,
Abstract: Generation and diffusion of the magnetic field on the Sun is a key mechanism responsible for solar activity on all spatial and temporal scales - from the solar cycle down to the evolution of small-scale magnetic elements in the quiet Sun. The solar dynamo operates as a non-linear dynamical process and is thought to be manifest in two types: as a global dynamo responsible for the solar cycle periodicity, and as a small-scale turbulent dynamo responsible for the formation of magnetic carpet in the quiet Sun. Numerous MHD simulations of the solar turbulence did not yet reach a consensus as to the existence of a turbulent dynamo on the Sun. At the same time, high-resolution observations of the quiet Sun from Hinode instruments suggest possibilities for the turbulent dynamo. Analysis of characteristics of turbulence derived from observations would be beneficial in tackling the problem. We analyse magnetic and velocity energy spectra as derived from Hinode/SOT, SOHO/MDI, SDO/HMI and the New Solar Telescope (NST) of Big Bear Solar Observatory (BBSO) to explore the possibilities for the small-scale turbulent dynamo in the quiet Sun.
Automated Observations of the Earthshine
P. R. Goode,S. Shoumko,E. Pallé,P. Monta?és-Rodríguez
Advances in Astronomy , 2010, DOI: 10.1155/2010/963650
Abstract: The overall reflectance of sunlight from Earth is a fundamental parameter for climate studies. We have designed and implemented small aperture, remote control telescopes in Big Bear Solar Observatory in California and in Tenerife in the Canary Islands. These telescopes observe the earthshine to obtain a global mean terrestrial reflectance utilizing a coronagraph-like design for long exposures of the dark of the Moon and have internal moving parts in the optical train, which presented some design and control problems. 1. Introduction For a decade, we have been measuring the Earth's reflectance by observing the earthshine, which is sunlight reflected from the Earth to the Moon and retroflected to the nighttime Earth. These observations provide an absolutely calibrated measure of the terrestrial albedo—a fundamental climate parameter. For our observations, we have utilized a terrestrial determination of the Earth's global albedo from an old, and largely forgotten method. That is, an absolutely calibrated, large-scale albedo can be determined by measuring the amount of sunlight reflected from the Earth and in turn, back to the Earth from the dark portion of the face of the Moon (earthshine) and taking the ratio of that to the brightside (moonshine) signal; see Figure 1 [1, 2]. In Figure 1, the fiducial points used in the measurements are shown in a single image in which the brightside is heavily filtered. The most important historical program of earthshine measurements was carried out by Danjon [3, 4] from a number of sites in France. Danjon estimated his uncertainty at roughly 5% (ignoring his appreciable systematic error from an incorrect determination of the Moon's reflectivity). Our measurements are about an order of magnitude more precise than his estimates, in large part because we have better measurement technologies. We have also eliminated his systematic error by correctly measuring the scattering from the Moon as a function of the phase of the Moon [1]. At about 1% precision on individual nights, our terrestrial estimates of the Earth's albedo have a precision comparable to that from satellites like ERBE with around the same value [5], and to those of the CERES instrumentation, of around 1% [6] making our method sufficiently precise to usefully complement satellite measurements. Figure 1: The moon showing the brightside and the earthshine. The Grimaldi side is in the moonshine (brightside) and the Crisium side is in the earthshine. Our ten highlands fiducial patches used in the observations made from BBSO are indicated. The crosses give the
On the origin of solar oscillations
P. L. Goode,L. H. Strous,T. R. Rimmele,R. T. Stebbins
Physics , 1998, DOI: 10.1086/311203
Abstract: We have made high resolution observations of the Sun in which we identify individual sunquakes and see power from these seismic events being pumped into the resonant modes of vibration of the Sun. A typical event lasts about five minutes. We report the physical properties of the events and relate them to theories of the excitation of solar oscillations. We also discuss the local seismic potential of these events.
On the origin of intergranular jets
V. B. Yurchyshyn,P. R. Goode,V. I. Abramenko,O. Steiner
Physics , 2011, DOI: 10.1088/2041-8205/736/2/L35
Abstract: We observe that intergranular jets, originating in the intergranular space surrounding individual granules, tend to be associated with granular fragmentation, in particular, with the formation and evolution of a bright granular lane (BGL) within individual granules. The BGLs have recently been identified as vortex tubes by Steiner et al. We further discover the development of a well-defined bright grain located between the BGL and the dark intergranular lane to which it is connected. Signatures of a BGL may reach the lower chromosphere and can be detected in off-band \ha images. Simulations also indicate that vortex tubes are frequently associated with small-scale magnetic fields. We speculate that the intergranular jets detected in the NST data may result from the interaction between the turbulent small-scale fields associated with the vortex tube and the larger-scale fields existing in the intergranular lanes. The intergranular jets are much smaller and weaker than all previously known jet-like events. At the same time, they appear much more numerous than the larger events, leading us to the speculation that the total energy release and mass transport by these tiny events may not be negligible in the energy and mass-flux balance near the temperature minimum atop the photosphere. The study is based on the photospheric TiO broadband (1.0 nm) filter data acquired with the 1.6 m New Solar Telescope (NST) operating at the Big Bear Solar Observatory. The data set also includes NST off-band \ha images collected through a Zeiss Lyot filter with a passband of 0.025 nm.
Response of Granulation to Small Scale Bright Features in the Quiet Sun
Aleksandra Andic,J. Chae,K. Ahn,P. R. Goode,W. Cao,V. Yurchyshyn,V. Abramenko
Physics , 2011, DOI: 10.1088/0004-637X/731/1/29
Abstract: We detected 2.8 bright points (BPs) per Mm$^2$ in the Quiet Sun (QS) with the New Solar Telescope (NST) at Big Bear Solar Observatory; using the TiO 705.68 nm spectral line, at an angular resolution ~ 0.1'' to obtain 30 min data sequence. Some BPs formed knots that were stable in time and influenced the properties of the granulation pattern around them. The observed granulation pattern within ~ 3'' of knots presents smaller granules than those observed in a normal granulation pattern; i.e., around the knots a suppressed convection is detected. Observed BPs covered ~ 5% of the solar surface and were not homogeneously distributed. BPs had an average size of 0.22'', they were detectable for 4.28 min in average, and had an averaged contrast of 0.1% in the deep red TiO spectral line.
Oscillatory behavior in the quiet Sun observed with the New Solar Telescope
A. ~Andic,P. R. Goode,J. Chae,W. Cao,K. Ahn,V. Yurchyshyn,V. Abramenko
Physics , 2010, DOI: 10.1088/2041-8205/717/2/L79
Abstract: Surface photometry of the quiet Sun has achieved an angular resolution of $0".1$ with the New Solar Telescope at Big Bear Solar Observatory revealing that a disproportionate fraction of the oscillatory events appear above observed bright point-like structures. During the tracking of these structures, we noted that the more powerful oscillatory events are cospatial with them, indicating that observed flux tubes may be the source of many observed oscillatory events.
Maximum Coronal Mass Ejection Speed as an Indicator of Solar and Geomagnetic Activities
A. Kilcik,V. B. Yurchyshyn,V. Abramenko,P. R. Goode,N. Gopalswamy,A. Ozguc,J. P. Rozelot
Physics , 2011, DOI: 10.1088/0004-637X/727/1/44
Abstract: We investigate the relationship between the monthly averaged maximal speeds of coronal mass ejections (CMEs), international sunspot number (ISSN), and the geomagnetic Dst and Ap indices covering the 1996-2008 time interval (solar cycle 23). Our new findings are as follows. (1) There is a noteworthy relationship between monthly averaged maximum CME speeds and sunspot numbers, Ap and Dst indices. Various peculiarities in the monthly Dst index are correlated better with the fine structures in the CME speed profile than that in the ISSN data. (2) Unlike the sunspot numbers, the CME speed index does not exhibit a double peak maximum. Instead, the CME speed profile peaks during the declining phase of solar cycle 23. Similar to the Ap index, both CME speed and the Dst indices lag behind the sunspot numbers by several months. (3) The CME number shows a double peak similar to that seen in the sunspot numbers. The CME occurrence rate remained very high even near the minimum of the solar cycle 23, when both the sunspot number and the CME average maximum speed were reaching their minimum values. (4) A well-defined peak of the Ap index between 2002 May and 2004 August was co-temporal with the excess of the mid-latitude coronal holes during solar cycle 23. The above findings suggest that the CME speed index may be a useful indicator of both solar and geomagnetic activities. It may have advantages over the sunspot numbers, because it better reflects the intensity of Earth-directed solar eruptions.
Time Distributions of Large and Small Sunspot Groups Over Four Solar Cycles
A. Kilcik,V. B. Yurchyshyn,V. Abramenko,P. R. Goode,A. Ozguc,J. P. Rozelot,W. Cao
Physics , 2011, DOI: 10.1088/0004-637X/731/1/30
Abstract: Here we analyze solar activity by focusing on time variations of the number of sunspot groups (SGs) as a function of their modified Zurich class. We analyzed data for solar cycles 2023 by using Rome (cycles 2021) and Learmonth Solar Observatory (cycles 2223) SG numbers. All SGs recorded during these time intervals were separated into two groups. The first group includes small SGs (A, B, C, H, and J classes by Zurich classification) and the second group consists of large SGs (D, E, F, and G classes). We then calculated small and large SG numbers from their daily mean numbers as observed on the solar disk during a given month. We report that the time variations of small and large SG numbers are asymmetric except for the solar cycle 22. In general large SG numbers appear to reach their maximum in the middle of the solar cycle (phase 0.450.5), while the international sunspot numbers and the small SG numbers generally peak much earlier (solar cycle phase 0.290.35). Moreover, the 10.7 cm solar radio flux, the facular area, and the maximum CME speed show better agreement with the large SG numbers than they do with the small SG numbers. Our results suggest that the large SG numbers are more likely to shed light on solar activity and its geophysical implications. Our findings may also influence our understanding of long term variations of the total solar irradiance, which is thought to be an important factor in the Sun - Earth climate relationship.
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