A multipoint study of a substorm occurring on 7 December, 1992, and its theoretical implications   总被引：1，自引：0，他引：1  

N. J. Fox  S. W. H. Cowley  V. N. Davda  G. Enno  E. Friis-Christensen  R. A. Greenwald  M. R. Hairston  M. Lester  M. Lockwood  H. Lühr  D. K. Milling  J. S. Murphree  M. Pinnock  G. D. Reeves 《Annales Geophysicae》1999,17(11):1369-1384

On 7 December 1992, a moderate substorm was observed by a variety of satellites and ground-based instruments. Ionospheric flows were monitored near dusk by the Goose Bay HF radar and near midnight by the EISCAT radar. The observed flows are compared here with magnetometer observations by the IMAGE array in Scandinavia and the two Greenland chains, the auroral distribution observed by Freja and the substorm cycle observations by the SABRE radar, the SAMNET magnetometer array and LANL geosynchronous satellites. Data from Galileo Earth-encounter II are used to estimate the IMF B_z component. The data presented show that the substorm onset electrojet at midnight was confined to closed field lines equatorward of the pre-existing convection reversal boundaries observed in the dusk and midnight regions. No evidence of substantial closure of open flux was detected following this substorm onset. Indeed the convection reversal boundary on the duskside continued to expand equatorward after onset due to the continued presence of strong southward IMF, such that growth and expansion phase features were simultaneously present. Clear indications of closure of open flux were not observed until a subsequent substorm intensification 25 min after the initial onset. After this time, the substorm auroral bulge in the nightside hours propagated well poleward of the pre-existing convection reversal boundary, and strong flow perturbations were observed by the Goose Bay radar, indicative of flows driven by reconnection in the tail.  相似文献   

Seasonal photometric variability of Titan, 1972–2006     

G.W. Lockwood  D.T. Thompson 《Icarus》2009,(2):616-626

Measurements at Lowell Observatory of Titan in the b (472 nm) and y (551 nm) filters of the Strömgren photometric system at thirty four consecutive apparitions (282 nights) from 1971/72 to 2006 show a 10% sinusoidal variation that lags seasonal extremes by about 1/8 of a Titan year. The seasonal variations are asymmetric: the autumn lightcurve maxima of the northern and southern hemispheres differ significantly as do the spring lightcurve minima. Changes also occur from one Titan year to the next: Titan was ∼3% fainter in b and ∼1% fainter in y following the 2002 southern summer solstice than it was one Titan year earlier in 1973. These changes appear to be intrinsic to Titan's atmosphere and cannot be explained by instrumental effects and changing geometries. Orbital variations visible in recent Hubble Space Telescope images at 673 nm and Voyager orange images (590–640 nm) may have a small (0.002±0.001 mag) counterpart in the b, y photometric record (eastern elongation brighter, consistent with the Cassini near-infrared albedo map).  相似文献   

Galactic Cosmic Ray Modulation near the Heliospheric Current Sheet     

S. R. Thomas  M. J. Owens  M. Lockwood  C. J. Scott 《Solar physics》2014,289(7):2653-2668

Galactic cosmic rays (GCRs) are modulated by the heliospheric magnetic field (HMF) both over decadal time scales (due to long-term, global HMF variations), and over time scales of a few hours (associated with solar wind structures such as coronal mass ejections or the heliospheric current sheet, HCS). Due to the close association between the HCS, the streamer belt, and the band of slow solar wind, HCS crossings are often associated with corotating interaction regions where fast solar wind catches up and compresses slow solar wind ahead of it. However, not all HCS crossings are associated with strong compressions. In this study we categorize HCS crossings in two ways: Firstly, using the change in magnetic polarity, as either away-to-toward (AT) or toward-to-away (TA) magnetic field directions relative to the Sun and, secondly, using the strength of the associated solar wind compression, determined from the observed plasma density enhancement. For each category, we use superposed epoch analyses to show differences in both solar wind parameters and GCR flux inferred from neutron monitors. For strong-compression HCS crossings, we observe a peak in neutron counts preceding the HCS crossing, followed by a large drop after the crossing, attributable to the so-called ‘snow-plough’ effect. For weak-compression HCS crossings, where magnetic field polarity effects are more readily observable, we instead observe that the neutron counts have a tendency to peak in the away magnetic field sector. By splitting the data by the dominant polarity at each solar polar region, we find that the increase in GCR flux prior to the HCS crossing is primarily from strong compressions in cycles with negative north polar fields due to GCR drift effects. Finally, we report on unexpected differences in GCR behavior between TA weak compressions during opposing polarity cycles.  相似文献   

The 22-Year Hale Cycle in Cosmic Ray Flux – Evidence for Direct Heliospheric Modulation     

S. R. Thomas  M. J. Owens  M. Lockwood 《Solar physics》2014,289(1):407-421

The ability to predict times of greater galactic cosmic ray (GCR) fluxes is important for reducing the hazards caused by these particles to satellite communications, aviation, or astronauts. The 11-year solar-cycle variation in cosmic rays is highly correlated with the strength of the heliospheric magnetic field. Differences in GCR flux during alternate solar cycles yield a 22-year cycle, known as the Hale Cycle, which is thought to be due to different particle drift patterns when the northern solar pole has predominantly positive (denoted as qA>0 cycle) or negative (qA<0) polarities. This results in the onset of the peak cosmic-ray flux at Earth occurring earlier during qA>0 cycles than for qA<0 cycles, which in turn causes the peak to be more dome-shaped for qA>0 and more sharply peaked for qA<0. In this study, we demonstrate that properties of the large-scale heliospheric magnetic field are different during the declining phase of the qA<0 and qA>0 solar cycles, when the difference in GCR flux is most apparent. This suggests that particle drifts may not be the sole mechanism responsible for the Hale Cycle in GCR flux at Earth. However, we also demonstrate that these polarity-dependent heliospheric differences are evident during the space-age but are much less clear in earlier data: using geomagnetic reconstructions, we show that for the period of 1905?–?1965, alternate polarities do not give as significant a difference during the declining phase of the solar cycle. Thus we suggest that the 22-year cycle in cosmic-ray flux is at least partly the result of direct modulation by the heliospheric magnetic field and that this effect may be primarily limited to the grand solar maximum of the space-age.  相似文献   

The political sustainability of climate policy: The case of the UK Climate Change Act     

Matthew Lockwood 《Global Environmental Change》2013,23(5):1339-1348

This paper assesses the forces working for and against the political sustainability of the UK 2008 Climate Change Act. The adoption of the Act is seen as a landmark commitment to action on climate change, but its implementation has not been studied in any depth. Recent events, including disagreements over the fourth carbon budget and the decarbonisation of the electricity sector, shows that while the Act might appear to lock in a commitment to reducing emissions through legal means, this does not guarantee political lock-in. The assumption, made by some proponents of the Act, that accountability of political leaders to a public concerned about climate change, via Parliament, would provide the main political underpinning to the Act is criticised. An analysis of alternative sources of political durability is presented, drawing on a framework for understanding the sustainability of reform developed by Patashnik. It is argued that the Act has helped create major institutional transformations, although the degree to which new institutions have displaced the power of existing ones is limited. The Act has produced some policy feedback effects, especially in the business community, and some limited investment effects, but both have been insufficient to withstand destabilisation by recent party political conflicts. The Climate Change Act remains at risk.  相似文献   

The Latitudinal Effect of Corotating Interaction Regions on Galactic Cosmic Rays     

A. P. Rouillard  M. Lockwood 《Solar physics》2007,245(1):191-206

The response of galactic cosmic rays (GCRs) to an isolated enhancement of the non-axisymmetric component of the solar open magnetic field between June and November 1996 is investigated by using a combination of solar observations and numerical modelling of the interplanetary medium. The most obvious coronal hole visible from Earth at the time had little shielding effect on the flux of GCRs, as measured at Earth by neutron monitors. It is found that the evolution of the corotating interaction regions generated by a less obvious coronal hole was the principal controlling factor. Moreover, we demonstrate the imprint of the latitudinal and longitudinal evolution of that coronal hole on the variation of GCRs. The latitudinal extent of this solar minimum corotating interaction region had a determining, but local, shielding effect on GCRs, confirming previous modelling results.  相似文献   

1989 Exclusive economic zone symposium: Summary and recommendations     

Millington Lockwood  Gary W. Hill 《Marine Geodesy》2013,36(4):347-350

Abstract

The fourth in a series of biennial national Exclusive Economic Zone symposia was held on November 14–16, 1989. The purpose of the meeting was to examine ongoing and planned mapping and research activities in the ocean waters of the United States. Approximately 220 individuals attended the meeting. Issues discussed related to digital seafloor mapping projects, cooperative federal‐state programs, and requirements for additional data and information. Symposium recommendations included the need for increased surveying in coastal waters, development of standards for digital data dissemination, increased coordination with coastal states and federal agencies, and additional geophysical measurement systems abroad all mapping ships.  相似文献   

Uranus in 2003: Zonal winds, banded structure, and discrete features     

H.B. Hammel  I. de Pater  G.W. Lockwood 《Icarus》2005,175(2):534-545

Imaging of Uranus in 2003 with the Keck 10-m telescope reveals banded zonal structure and dozens of discrete cloud features at J and H bands; several features in the northern hemisphere are also detectable at K′. By tracking features over four days, we extend the zonal wind profile well into the northern hemisphere. We report the first measurements of wind velocities at latitudes −13°, +19°, and northward of +43°, the first direct wind measurements near the equator, and the highest wind velocity seen yet on Uranus (+218 m/s). At northern mid-latitudes (+20° to +40°), the winds appear to have accelerated when compared to earlier HST and Keck observations; southern wind speeds (−20° to −43°) have not changed since Voyager measurements in 1986. The equator of Uranus exhibits a subtle wave structure, indicated by diffuse patches roughly every 30° in longitude. The largest discrete cloud features on Uranus show complex structure extending over tens of degrees, reminiscent of activity seen around Neptune's Great Dark Spot during the Voyager encounter with that planet. There is no sign of a northern “polar collar” as is seen in the south, but a number of discrete features seen at the “expected” latitudes may signal the early stages of development of a northern collar.  相似文献   

The use of a modified Gulf V plankton sampler from a small open boat     

Lockwood  Stephen J. 《ICES Journal of Marine Science》1974,35(2):171-174

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The daily food intake of 0-group plaice (Pleuronectes platessa L.) under natural conditions   总被引：1，自引：0，他引：1  

Lockwood  Stephen J. 《ICES Journal of Marine Science》1980,39(2):154-159

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