Observations of horizontal transport effects on high latitude metastable O(¹D), N(²D) auroral emissions     

M.L. Duboin  K. Lassen  G.G. Shepherd 《Planetary and Space Science》1984,32(11):1407-1421

An analysis is presented of photometric measurements of the NI (λ = 520nm),OI(λ = 630nm)and other emissions made at Nord, where the invariant latitude is Λ = 80°4. The time variations of the intensities are interpreted in the following way by comparison with simultaneous ground based or satellite measurements.The N(²D) atoms formed in the dayside cleft are carried by the neutral wind in a plume across the polar cap, so that the ratio of λ(630 nm) to λ(520 nm) intensities decreases along the plume with increasing distance from the source region.In the polar cap, but outside the plume region, 630 nm emission is produced by electron impact of polar rain and by substorms that reach high latitudes. Ionization produced at the same time, especially by the substorms, will produce further 630 nm emission through dissociative recombination. In any case, the region outside the plume may be regarded as a source region, with a high value of the ratio $\text{I(630)}\text{I(520)}$. This explains in part the diurnal variations, since this ratio is depressed as Nord crosses the dayside plume.The electron energy along the oval increases progressively from the dayside to the nightside. The intensity ratio increases with increasing electron energy because N(²D) is quenched more rapidly than O(¹D). Thus the ratio rises progressively from noon to midnight.An effect of the interplanetary magnetic field is superimposed on this pattern : as its North-South component B_z increases, the oval contracts so that Nord becomes nearer from the cleft source and the intensity ratio increases on the dayside. The inverse effect is also observed. On the nightside, negative B_z is associated with substorms that produce poleward expansions of the poleward oval boundary, that brings more energetic precipitation to Nord. This causes the intensity ratio to increase with decreasing B_z in a way that is opposite to that for the dayside.  相似文献   

Photometric observations of the dayside cleft emissions from Cambridge Bay,December 1976     

R.N. Peterson  R.A. Koehler  G.J. Gotshalks  J.F. Pieau  G.G. Shepherd 《Planetary and Space Science》1980,28(2):149-158

Dayside cleft emissions were observed from Cambridge Bay, N.W.T. during quiet, very quiet and disturbed periods from 10–17 December 1976. Good agreement is found in comparisons of the ground based photometric data with ISIS satellite data for the cleft region. A marked asymmetry around noon was found. Dynamical changes, observed especially in the poleward emission boundary, appear to have no counterpart in the nightside magnetometer data.  相似文献   

Multiplicative modelling of catch-at-age data, and its application to catch forecasts     

Shepherd  J. G.; Nicholson  M. D. 《ICES Journal of Marine Science》1991,47(3):284-294

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A mechanism for density-dependent survival of larval fish as the basis of a stock-recruitment relationship   总被引：4，自引：2，他引：2  

Shepherd  J. G.; Cushing  D. H. 《ICES Journal of Marine Science》1980,39(2):160-167

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Inter-hemispheric mesospheric coupling in a comprehensive middle atmosphere model     

Bodil Karlsson  Charles McLandress  Theodore G. Shepherd 《Journal of Atmospheric and Solar》2009,71(3-4):518-530

Observations of noctilucent clouds have revealed a surprising coupling between the winter stratosphere and the summer polar mesopause region. In spite of the great distance involved, this inter-hemispheric link has been suggested to be the principal reason for both the year-to-year variability and the hemispheric differences in the frequency of occurrence of these high-altitude clouds. In this study, we investigate the dynamical influence of the winter stratosphere on the summer mesosphere using simulations from the vertically extended version of the Canadian Middle Atmosphere Model (CMAM). We find that for both Northern and Southern Hemispheres, variability in the summer polar mesopause region from one year to another can be traced back to the planetary-wave flux entering the winter stratosphere. The teleconnection pattern is the same for both positive and negative wave-flux anomalies. Using a composite analysis to isolate the events, it is argued that the mechanism for inter-hemispheric coupling is a feedback between summer mesosphere gravity-wave drag (GWD) and zonal wind, which is induced by an anomaly in mesospheric cross-equatorial flow, the latter arising from the anomaly in winter hemisphere GWD induced by the anomaly in stratospheric conditions.  相似文献   

Validation of a region-wide model of landslide susceptibility in the Manawatu–Wanganui region of New Zealand     

John R. Dymond  Anne-Gaelle Ausseil  James D. Shepherd  Lars Buettner 《Geomorphology》2006,74(1-4):70-79

Since European settlement 160 years ago, much of the indigenous forest in New Zealand hill country has been cleared for pastoral agriculture, resulting in increased erosion and sedimentation. To prioritise soil conservation work in the Manawatu–Wanganui region, we developed a model of landslide susceptibility. It assigns high susceptibility to steep land not protected by woody vegetation and low susceptibility everywhere else, following the commonly used approach for identifying inappropriate land use. A major storm on 15–16 February 2004 that produced many landslides was used to validate the model. The model predicted hills at risk to landsliding with moderate accuracy: 58% of erosion scars in the February storm occurred on hillsides considered to be susceptible. The model concept of slope thresholds, above which the probability of landsliding is high and below which the probability is low, is not adequate because below 30° the probability of landsliding is approximately linearly related to slope. Thus, reforestation of steep slopes will need to be combined with improved vegetation management for soil conservation on moderate slopes to significantly reduce future landsliding.  相似文献   

Observations of trace gases and aerosols over the Indian Ocean during the monsoon transition period     

T. K. Manual  Ateef Khan  Y. Nazeer Ahammed  R. S. Tanwar  R. S. Parmar  K. S. Zalpuri  Prabhat K. Gupta  S. L. Jain  Risal Singh  A. P. Mitra  S. C. Garg  A. Suryanarayana  V. S. N. Murty  M. Dileep Kumar  Andrew J. Shepherd 《Journal of Earth System Science》2006,115(4):473-484

Characteristics of trace gases (O₃, CO, CO₂, CH₄ and N₂O) and aerosols (particle size of 2.5 micron) were studied over the Arabian Sea, equatorial Indian Ocean and southwest part of the Bay of Bengal during the monsoon transition period (October–November, 2004). Flow of pollutants is expected from south and southeast Asia during the monsoonal transition period due to the patterns of wind flow which are different from the monsoon period. This is the first detailed report on aerosols and trace gases during the sampled period as the earlier Bay of Bengal Experiment (BOBMEX), Arabian Sea Monsoon Experiment (ARMEX) and Indian Ocean Experiments (INDOEX) were during monsoon seasons. The significant observations during the transition period include: (i) low ozone concentration of the order of 5 ppbv around the equator, (ii) high concentrations of CO₂, CH₄ and N₂O and (iii) variations in PM2.5 of 5–20μg/m³.  相似文献   

Upper atmospheric temperatures from Doppler line widths—I. Some preliminary measurements on OI 5577 Å in aurora     

J. A. Nilson  G. G. Shepherd 《Planetary and Space Science》1961,5(4):299-306

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Characteristics of optical emissions and particle precipitation in polar cap arcs     

J.S. Murphree  S. Ismail  L.L. Cogger  D.D. Wallis  G.G. Shepherd  R. Link  D.M. Klumpar 《Planetary and Space Science》1983,31(2):161-172

Simultaneous optical and particle data from the ISIS-2 satellite are used to characterize polar cap arcs. Polar cap arcs are identified from two-dimensional geomagnetic transforms of the optical data along with precipitating electron data for the time at which the satellite is on the field line intersecting the arc. No precipitating protons were detected for any of the arc crossings. The pitch angle. distribution of the precipitating electrons is generally isotropic and the differential electron spectra show enhancements in the flux in the 300–750 eV energy range. The average energy of the precipitating electrons for the different arcs ranges from about 300 to 600 eV. A possible explanation of the observed precipitating particle characteristics is that parallel electric fields are accelerating polar rain type spectra at an altitude of several thousand km. For the arc crossings reported here the equivalent 4278 Å emission rate per unit energy deposition rate has a mean value of 162 R/(erg cm^?2 s^?1). Average 3914 Å intensities are about 0.8 kR while 6300 Å intensities range from 0.5 to 3 kR. Model calculations indicate that direct impact excitation is a minor source for the 5577 Å emission rate, but supplies approx. 40% of the 6300 Å emission.  相似文献   

A comparison of the performance of various methods for tuning VPAs using effort data   总被引：2，自引：1，他引：1  

Pope  J. G.; Shepherd  J. G. 《ICES Journal of Marine Science》1985,42(2):129-151

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