Open magnetic fields in active regions     

Zdeněk Švestka  Craig V. Solodyna  Robert Howard  Randolph H. Levine 《Solar physics》1977,55(2):359-369

Soft X-ray observations confirm that some of the dark gaps seen between interconnecting loops and inner cores of active regions may be loci of open fields, as it has been predicted by global potential extrapolation of photospheric magnetic fields. It seems that the field lines may open only in a later state of the active region development.Skylab Solar Workshop Post-Doctoral Appointee, 1975–1977. The Skylab Solar Workshops are sponsored by NASA and NSF and managed by the High Altitude Observatory, National Center for Atmospheric Research.  相似文献   

High resolution mapping of the magnetic field of the solar corona     

Martin D. Altschuler  Randolph H. Levine  Michael Stix  John Harvey 《Solar physics》1977,51(2):345-375

High resolution KPNO magnetograph measurements of the line-of-sight component of the photospheric magnetic field over the entire dynamic range from 0 to 4000 gauss are used as the basic data for a new analysis of the photospheric and coronal magnetic field distributions. The daily magnetograph measurements collected over a solar rotation are averaged onto a 180 × 360 synoptic grid of equal-area elements. With the assumption that there are no electric currents above the photospheric level of measurement, a unique solution is determined for the global solar magnetic field. Because the solution is in terms of an expansion in spherical harmonics to principal index n = 90, the global photospheric magnetic energy distribution can be analyzed in terms of contributions of different scale-size and geometric pattern. This latter procedure is of value (1) in guiding solar dynamo theories, (2) in monitoring the persistence of the photospheric field pattern and its components, (3) in comparing synoptic magnetic data of different observatories, and (4) in estimating data quality. Different types of maps for the coronal magnetic field are constructed (1) to show the strong field at different resolutions, (2) to trace the field lines which open into interplanetary space and to locate their photospheric origins, and (3) to map in detail coronal regions above (specified) limited photospheric areas.The National Center for Atmospheric Research is sponsored by the National Science foundation.Kitt Peak National Observatory is operated by the Association of Universities for Research in Astronomy, Inc. Under contract with the National Science Foundation.  相似文献   

Photospheric subrotation,differential rotation and zonal wind bands: A reverse pirouette     

K. H. Schatten  H. G. Mayr  Randolph H. Levine 《Solar physics》1981,71(1):169-173

Recently Mayr et al. (1980) have suggested that the superrotation of planetary atmospheres could, in principle, be understood as a pirouette. Equatorial heating is pumping atmospheric material toward the poles, and with a concomitant reduction in moment of inertia, the atmosphere has the tendency of spinning up. On the Sun, the core is assumed to be rotating with a period of about 12 days (Dicke, 1976; Knight et al., 1979) while the overlaying mantle convection zone has a solid body component of about 27 days. We propose here that this phenomenon could simply be understood as a reverse pirouette. Our model is similar to the models put forth by Kippenhahn (1963), Weiss (1965), Durney (1968), Busse (1970), Yoshimura (1972), Gilman (1974), and Gierasch (1974). Whereas the models listed provided solutions of valid equations and computer analyses, they lack a simple physical picture to explain the phenomenon. In our case, we have the solar oblateness conventionally providing added heat input at the poles. The result is the large scale transport of material toward the equator giving rise to subrotation. The model thus facilitates an understanding of the formation of a slowly rotating convection zone above the more rapidly rotating core. The latitudinal photospheric differential rotation is interpreted as a second order effect associated with horizontal momentum transport. The recent observations of zonal winds drifting equatorward with a 22-year period (Howard and LaBonte, 1980) may be related by this model as a third order effect from a similar periodicity in differential solar heating (pole to equator).  相似文献   

Simulation of the magnetic structure of the inner heliosphere by means of a non-spherical source surface     

Randolph H. Levine  Michael Schulz  E. N. Frazier 《Solar physics》1982,77(1-2):363-392

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The coronal and transition region temperature structure of a solar active region     

Randolph H. Levine  J. P. Pye 《Solar physics》1980,66(1):39-60

Using measurements of EUV and X-ray spectral lines we derive the differential emission measure vs electron temperature T from the transition region to the corona of an active region (10⁵ T <5 × 10⁶ K). The total emission measure and radiative losses are of order 3 × 10⁴⁸ cm^–3 and 4 × 10²⁶ ergss^–1 respectively. The emission measure at T > 10⁶ K (i.e. that mainly responsible for the X-ray emission) is about 75% of the total. We also examine the use of Mg x 625 Å as an indicator of coronal electron density. A set of theoretical energy balance models of coronal loops in which the loop divergence is a variable parameter is presented and compared with the observations. Particular attention is given to the limitations inherent in any such comparison.  相似文献   

Recent tectonics of the Blanco Ridge,eastern blanco transform fault zone     

Dziak  Robert P.  Fox  Christopher G.  Embley  Robert W.  Nabelek  John L.  Braunmiller  Jochen  Koski  Randolph A. 《Marine Geophysical Researches》2000,21(5):423-450

Bathymetric, hydro-acoustic, seismic, submersible, and gravity data are used to investigate the active tectonics of the eastern Blanco Transform Fault Zone (BTFZ). The eastern BTFZ is dominated by the 150 km long transform-parallel Blanco Ridge (BR) which is a right-lateral strike-slip fault bordered to the east and west by the Gorda and Cascadia Depressions. Acoustic locations, fault-parameter information, and slip vector estimates of 43 earthquakes (M _w3.8) that occurred along the eastern BTFZ over the last 5 years reveal that the Blanco Ridge is a high-angle right-lateral strike-slip fault, with a small component of dip-slip motion, where the Juan de Fuca plate is the hanging wall relative to the Pacific plate. Furthermore, the Cascadia and Gorda basins are undergoing normal faulting with extension predominantly oblique to the transform trend. Seafloor submersible observations agree with previous hypotheses that the active transform fault trace is the elongate basin that runs the length of the BR summit. Brecciated and undeformed basalt, diabase, and gabbro samples were collected at the four submersible survey sites along the Blanco Ridge. These petrologic samples indicate the Blanco Ridge is composed of an ocean crustal sequence that has been uplifted and highly fractured. The petrologic samples also appear to show an increase in elevation of the crustal section from east to west along the Blanco Ridge, with gabbros exposed at a shallower depth farther west along the southern (Pacific plate side) BR ridge flank. Further supporting evidence for BR uplift exists in the seismic reflection profiles across the BR showing uplift of turbidite sequences along the north and south ridge base, and gravity and magnetics profiles that indicate possible basement uplift and a low-density zone centered on the ridge's Pacific plate side. The BR formation mechanism preferred here is first, uplift achieved partially through strike-slip motion (with a small dip-slip component). Second, seawater penetration along the fault into the lower crust upper mantle, which then enhanced formation and intrusion of a mantle-derived serpentinized-peridotite diapir into the shallow ocean crust, causing further uplift along the fault.  相似文献   

Domestic water supply impacts by underground coal mining in Virginia, USA   总被引：2，自引：0，他引：2  

C. Zipper  W. Balfour  R. Roth  J. Randolph 《Environmental Geology》1997,29(1-2):84-93

 Underground coal mining can affect wells and springs used as water supplies. In Virginia, concerns over such impacts are felt by both surface owners and coal-mining firms. Virginia's geologic history has caused faults and fractures to be common in its coalfield region, relative to other Appalachian coal-mining areas. The results of 73 investigations of alleged domestic water supply impacts by underground mining were analyzed; the investigations were conducted by the Virginia Division of Mined Land Reclamation (VDMLR). This analysis was conducted with reference to guidelines that define a primary zone of underground mining influence where dewatering of aquifers is to be expected. The VDMLR data set included 27 investigations of alleged water supply impacts by partial-extraction room-and-pillar mines, 41 investigations of high-extraction room-and-pillar mines, and 4 investigations of longwall mines. VDMLR investigators found that 14 of 16 water supplies within the primary zone of influence were likely to have been affected by pillar-retreat mining, but no water supplies within the primary zone of influence for longwall and room-and-pillar mines were represented in the data base. VDMLR investigators found 42 of 56 water supplies outside of the primary zones were likely to have been affected by mining; these cases represented room-and-pillar, pillar-retreat, and longwall mining. Geologic circumstances not directly related to subsidence were found to be responsible for 31 of these 42 impacts. These geologic circumstances included subsurface fractures and other geologic features acting as aquifers that were drained by underground mining operations. VDMLR investigators also found some of the investigated water losses to have been caused by factors other than mining. These results demonstrate the inherent difficulties of any attempt to rigidly define a "zone of underground mining impact" based solely on mine subsidence effects, especially in regions where geologic faults and fractures are common such as the southwest Virginia coalfield. Received: 4 August 1995 · Accepted: 23 October 1995  相似文献   

Decadal Current Variations in the Southwestern Japan/East Sea     

William?J.?TeagueEmail author  Gregg?A.?Jacobs  Douglas?A.?Mitchell  Mark?Wimbush  D.?Randolph?Watts 《Journal of Oceanography》2004,60(6):1023-1033

Absolute geostrophic velocities were calculated along TOPEX/Poseidon (T/P) groundtracks located in the Ulleung Basin of the southwestern Japan/East Sea (JES) from a combined analysis of nearly a decade of T/P data and two years of pressure-gauge-equipped inverted echo sounder (PIES) data obtained during the United States Office of Naval Research’s JES Program. Geostrophic velocities have been calculated daily for the Ulleung Basin from June 1999 to July 2001 from a three-dimensional mapping of temperature and salinity produced by PIES data interpreted via the Gravest Empirical Mode (GEM) technique combined with the Navy’s Modular Ocean Data Assimilation System (MODAS). These velocities were then used to convert T/P velocity anomalies to absolute velocities for the T/P time period of 1993 to 2002. Current intensities and variabilities associated with the East Korean Warm Current, Ulleung Warm Eddy, and Offshore Branch are examined. Spatial and temporal variations of the sea surface circulation are strong. Intensification of the currents generally occurred during the fall season. The flow pattern in individual years differed greatly from year to year and differed from climatology in important qualitative ways.  相似文献   

Deposition of talc — kerolite–smectite — smectite at seafloor hydrothermal vent fields: Evidence from mineralogical,geochemical and oxygen isotope studies     

Vesselin M. Dekov  Javier Cuadros  Wayne C. Shanks  Randolph A. Koski 《Chemical Geology》2008,247(1-2):171-194

Talc, kerolite–smectite, smectite, chlorite–smectite and chlorite samples from sediments, chimneys and massive sulfides from six seafloor hydrothermal areas have been analyzed for mineralogy, chemistry and oxygen isotopes. Samples are from both peridotite- and basalt-hosted hydrothermal systems, and basaltic systems include sediment-free and sediment-covered sites. Mg-phyllosilicates at seafloor hydrothermal sites have previously been described as talc, stevensite or saponite. In contrast, new data show tri-octahedral Mg-phyllosilicates ranging from pure talc and Fe-rich talc, through kerolite-rich kerolite–smectite to smectite-rich kerolite–smectite and tri-octahedral smectite. The most common occurrence is mixed-layer kerolite–smectite, which shows an almost complete interstratification series with 5 to 85% smectitic layers. The smectite interstratified with kerolite is mostly tri-octahedral. The degree of crystal perfection of the clay sequence decreases generally from talc to kerolite–smectite with lower crystalline perfection as the proportion of smectite layers in kerolite–smectite increases.Our studies do not support any dependence of the precipitated minerals on the type/subtype of hydrothermal system. Oxygen isotope geothermometry demonstrates that talc and kerolite–smectite precipitated in chimneys, massive sulfide mounds, at the sediment surface and in open cracks in the sediment near seafloor are high-temperature (> 250 °C) phases that are most probably the result of focused fluid discharge. The other end-member of this tri-octahedral Mg-phyllosilicate sequence, smectite, is a moderate-temperature (200–250 °C) phase forming deep within the sediment (～ 0.8 m). Chlorite and chlorite–smectite, which constitute the alteration sediment matrix around the hydrothermal mounds, are lower-temperature (150–200 °C) phases produced by diffuse fluid discharge through the sediment around the hydrothermal conduits. In addition to temperature, other two controls on the precipitation of this sequence are the silica activity and Mg/Al ratio (i.e. the degree of mixing of seawater with hydrothermal fluid). Higher silica activity favors the formation of talc relative to tri-octahedral smectite. Vent structures and sedimentary cover preclude complete mixing of hydrothermal fluid and ambient seawater, resulting in lower Mg/Al ratios in the interior parts of the chimneys and deeper in the sediment which leads to the precipitation of phyllosilicates with lower Mg contents. Talc and kerolite–smectite have very low trace- and rare earth element contents. Some exhibit a negative or flat Eu anomaly, which suggests Eu depletion in the original hydrothermal fluid. Such Eu depletion could be caused by precipitation of anhydrite or barite (sinks for Eu²⁺) deeper in the system. REE abundances and distribution patterns indicate that chlorite and chlorite–smectite are hydrothermal alteration products of the background turbiditic sediment.  相似文献   

Temporal variation and the effect of rainfall on metals flux from the historic Beatson mine,Prince William Sound,Alaska, USA     

Lisa L. Stillings  Andrea L. Foster  Randolph A. Koski  LeeAnn Munk  Wayne C. Shanks III 《Applied Geochemistry》2008

Several abandoned Cu mines are located along the shore of Prince William Sound, AK, where the effect of mining-related discharge upon shoreline ecosystems is unknown. To determine the magnitude of this effect at the former Beatson mine, the largest Cu mine in the region and a Besshi-type massive sulfide ore deposit, trace metal concentration and flux were measured in surface run-off from remnant, mineralized workings and waste. Samples were collected from seepage waters; a remnant glory hole which is now a pit lake; a braided stream draining an area of mineralized rock, underground mine workings, and waste piles; and a background location upstream of the mine workings and mineralized rock. In the background stream pH averaged ∼7.3, specific conductivity (SC) was ∼40 μS/cm, and the aqueous components indicative of sulfide mineral weathering, SO₄ and trace metals, were at detection limits or lower. In the braided stream below the mine workings and waste piles, pH usually varied from 6.7 to 7.1, SC varied from 40 to 120 μS/cm, SO₄ had maximum concentrations of 32 mg/L, and the trace metals Cu, Ni, Pb, and Zn showed maximum total acid extractable concentrations of 186, 5.9, 6.2 and 343 μg/L, respectively.  相似文献