On the source of the slowly varying component at centimeter and millimeter wavelenghts     

Fred I. Shimabukuro  Gary A. Chapman  Earle B. Mayfield  Sidney Edelson 《Solar physics》1973,30(1):163-173

The general features of the slowly varying component at centimeter and millimeter wavelengths are explained by magneto-ionic thermal emission. A model of an active region is constructed in which the electron temperature and density profile is based on recent EUV measurements, and the current-free magnetic field configuration is derived from a longitudinal magnetogram and scalar potential theory. In the model, the contributions of the reflected component of the inward extraordinary wave is important in determining the characteristic features of the radio flux and polarization. Emission by the mechanism of resonance absorption does not appear to be a significant factor in this model.  相似文献   

J, H, K photometry of 433 Eros and other asteroids     

Clark R. Chapman  David Morrison 《Icarus》1976,28(1):91-94

We report photometry for nine asteroids at wavelengths of 1.25, 1.65, and 2.22 μm. Three C-type objects (88, 129, and 511) seem slightly redder in H?K and J?H color indices than four S-type objects (5, 6, 7, and 116) and an E-type object (64). Eros has an unusually red J?H color index; its infrared spectral reflectance is consistent with an appreciable quantity of metallic iron plus some pyroxene and olivine on its surface. JHK photometry is less diagnostic of composition than either higher resolution spectrophotometry in the infrared or spectrophotometry at shorter wavelengths.  相似文献   

Detailed 1×1° gravimetric Indian Ocean geoid and comparison with GEOS-3 radar altimeter geoid profiles     

Hans-Gert Kahle  Michael Chapman  Manik Talwani 《Geophysical Journal International》1978,55(3):703-720

Summary. A new set of 1×1° mean free-air anomalies in the Indian Ocean is determined on the basis of previously published free-air anomaly maps (Talwani & Kahle) and the most recent Lamont surface ship gravity measurements. The data are then used to compute a (total) 1×1° gravimetric Indian Ocean geoid. The computation is carried out by combining the Goddard Space Flight Center (GSFC) GEM-6 geoid and a difference geoid that corresponds to the differences between the set of 1×1° surface gravity values and the GEM-6 gravity anomalies. The difference geoid is highest over the Madagascar Ridge (+ 20 m) and lowest over the Timor Trough (-30 m). The total geoid is compared with GEOS-3 radar altimeter derived geoid profiles and geophysical implications are discussed.  相似文献   

Geoid anomalies over deep sea trenches     

Michael E. Chapman  Manik Talwani 《Geophysical Journal International》1982,68(2):349-369

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Imaging Spectropolarimetry of Ti  I 2231 nm in a Sunspot     

M.J. Penn  W.D. Cao  S.R. Walton  G.A. Chapman  W. Livingston 《Solar physics》2003,215(1):87-97

Spectro-polarimetric observations at 2231 nm were made of NOAA 10008 near the west solar limb on 29 June 2002 using the National Solar Observatory McMath–Pierce Telescope at Kitt Peak and the California State University Northridge – National Solar Observatory infrared camera. Scans of spectra in both Stokes I and Stokes V were collected; the intensity spectra were processed to remove strong telluric absorption lines, and the Stokes V umbral spectra were corrected for instrumental polarization. The sunspot temperature is computed using the continuum contrast and umbral temperatures down to about 3700 K are observed. A strong Tii line at 2231.0 nm is used to probe the magnetic and velocity fields in the spot umbra and penumbra. Measurements of the Tii equivalent width versus plasma temperature in the sunspot agree with model predictions. Zeeman splitting measurements of the Stokes I and Stokes V profiles show magnetic fields up to 3300 G in the umbra, and a dependence of the magnetic field on the plasma temperature similar to that which was seen using Fei 1565 nm observations of the same spot two days earlier. The umbral Doppler velocity measurements are averaged in 16 azimuthal bins, and no radial flows are revealed to a limit of ±200 m s^–1. A Stokes V magnetogram shows a reversal of the line-of-sight magnetic component between the limb and disk center sides of the penumbra. Because the Tii line is weak in the penumbra, individual spectra are averaged in azimuthal bins over the entire penumbral radial extent. The averaged Stokes V spectra show a magnetic reversal as a function of sunspot azimuthal angle. The mean penumbral magnetic field as measured with the Stokes V Zeeman component splitting is 1400 G. Several weak spectral lines are observed in the sunspot and the variation of the equivalent width versus temperature for four lines is examined. If these lines are from molecules, it is possible that lines at 2230.67, 2230.77, and 2231.70 nm originate from OH, while the line at 2232.21 nm may originate from CN.  相似文献   

Hypoxia in the northern Gulf of Mexico: Does the science support the Plan to Reduce,Mitigate, and Control Hypoxia?     

N. N. Rabalais  R. E. Turner  B. K Sen Gupta  D. F. Boesch  P. Chapman  M. C. Murrell 《Estuaries and Coasts》2007,30(5):753-772

We update and reevaluate the scientific information on the distribution, history, and causes of continental shelf hypoxia that supports the 2001 Action Plan for Reducing, Mitigating, and Controlling Hypoxia in the Northern Gulf of Mexico (Mississippi River/Gulf of Mexico Watershed Nutrient Task Force 2001), incorporating data, publications, and research results produced since the 1999 integrated assessment. The metric of mid-summer hypoxic area on the LouisianaTexas shelf is an adequate and suitable measure for continued efforts to reduce nutrients loads from the Mississippi River and hypoxia in the northern Gulf of Mexico as outlined in the Action Plan. More frequent measurements of simple metrics (e.g., area and volume) from late spring through late summer would ensure that the metric is representative of the system in any given year and useful in a public discourse of conditions and causes. The long-term data on hypoxia, sources of nutrients, associated biological parameters, and paleoindicators continue to verify and strengthen the relationship between the nitratenitrogen load of the Mississippi River, the extent of hypoxia, and changes in the coastal ecosystem (eutrophication and worsening hypoxia). Multiple lines of evidence, some of them representing independent data sources, are consistent with the big picture pattern of increased eutrophication as a result of long-term nutrient increases that result in excess carbon production and accumulation and, ultimately, bottom water hypoxia. The additional findings arising since 1999 strengthen the science supporting the Action Plan that focuses on reducing nutrient loads, primarily nitrogen, through multiple actions to reduce the size of the hypoxic zone in the northern Gulf of Mexico.  相似文献   

Doppler Patterns Associated with Emerging Flux Regions     

G.A. Chapman 《Solar physics》1998,183(1):15-28

We have observed several emerging flux regions (EFRs) using the Video Spectra-Spectro-Heliograph (VSSHG) at the San Fernando Observatory (SFO). The best studied region, NOAA 7968, was near disk center when it was observed on 5–8 June 1996. This EFR showed no organized upflow between the leader and follower spots over the 4-day period covered by our observations. The main concentrations of magnetic flux in the region (leader and follower) showed a slow separation as flux emerged, but little or no upflow was seen. Two other EFRs were observed for part of a single day each and one region was observed for only one sequence. For all regions observed, no discrete features were seen between the leader and follower polarity sunpots that had upflowing material as the regions grew. In all cases, the downward velocities were smaller in area than the magnetic parts of the regions. At times there were several localized areas of greater-amplitude downflows near sunspots.  相似文献   

Seasonal changes in the depth distributions of interstitial salinities in the Fraser River estuary,British Columbia     

Peter M. Chapman 《Estuaries and Coasts》1981,4(3):226-228

The vertical distribution of interstitial salinities to a depth of 6 cm in subtidal estuarine sediments was measured monthly from June 1977 to August 1978 in mud substrates in the Fraser River estuary, British Columbia. Measurements were made at six stations ranging from oligohaline to polyhaline. The results of this study demonstrated that vertical salinity gradients were present, particularly in the mesohaline zone of the estuary, in the sediments and that the magnitude of these gradients changes seasonally.  相似文献   

Exploration geochemistry—Distribution of elements and recognition of anomalies     

G. J. S. Govett  W. D. Goodfellow  R. P. Chapman  C. Y. Chork 《Mathematical Geosciences》1975,7(5-6):415-446

The exploration geochemist faces a serious problem in reconciling theoretical statistics with the empirical distribution of elements in materials in the earth's crust. The results of computer-simulation experiments being conducted by the Exploration Geochemistry Group at the University of New Brunswick illustrate some of the problems of the relation between frequency distributions and spatial distributions of elements and raise some interesting questions about sampling patterns and physical size of samples. Most importantly, the simulation experiments and empirical examples support the contention that attempts to make an assumption of normality more efficient by performing log transformations on positively skewed data may defeat the purpose of statistical analysis for exploration work. New developments in computer-data presentation and interpretation, including population sorting and classification, illustrate the increasing use of the computer in exploration geochemistry.  相似文献   

Convective Heat Transfer in Selected Geologic Situations     

Kevin Kilty  David S. Chapman 《Ground water》1980,18(4):386-394

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