Volcan ceboruco: A major composite volcano of the mexican volcanic belt     

R. S. Thorpe  P. W. Francis 《Bulletin of Volcanology》1975,39(2):201-213

Ceboruco is a major composite volcano at the western end of the Mexican Volcanic Belt, near the junction between the North American and Pacific plates. The volcano is built from successive eruptions of andesite lavas and pyroclastic rocks, and major eruptions during its history have resulted in the formation of two concentric calderas. The youngest volcanic activity has included the extrusion of dacites within the inner caldera and a voluminous flank eruption of andesite during 1870–72. Fumarolic activity persists to the present day. Chemical analyses show that the lavas are of cale-alkaline type and rangs from andesite (SiO₂=58–61%) to acid dacite (SiO₂=68%) in composition. The rate of increase of K₂O relative to SiO is greater than that in volcanic rocks from the Mexican Volcanic Belt as a whole. This indicates that simple models based on the application of such relationships may not be adequate to explain the petrogenesis of calc-alkaline lavas.  相似文献   

Seasonal variation of the diurnal cycle of rainfall in the eastern equatorial Indian Ocean     

M. R. Ramesh Kumar  S. M. Pednekar  M. Katsumata  M. K. Antony  Y. Kuroda  A. S. Unnikrishnan 《Theoretical and Applied Climatology》2006,85(1-2):117-122

Summary The diurnal cycle of rainfall over the eastern equatorial Indian Ocean was studied for the period 23^rd October 2001 to 31^st October 2003 using hourly data from the Triton buoy positioned at 1.5° S and 90° E. An analysis of the active and weak spells of rainfall for different seasons revealed peaks in the late evening hours in Winter, Summer and Fall and in early morning hours (in Spring) in 2002. The active spell of rainfall peaked in the afternoon hours, during Winter, Spring and Summer in 2003, which agrees with the previous results of Janowiak et al. (1994). An analysis of rainfall events showed that Fall 2002 had a maximum number of rainfall events (90) and minimum (60) were observed in Spring 2003. Further it was found that the majority of rain events (>60%) were less than 3 hours in duration throughout the study period. The longer duration rainfall events (i.e. rain events greater than 6 hour duration) contributed significantly to Spring 2002 (20% of the total rainfall) and Winter 2003 (21% of the total rainfall). Harmonic analysis of the hourly rainfall data for different seasons revealed that diurnal harmonic explains more than 80% of the variance for all seasons. Furthermore, the diurnal harmonic has a maximum amplitude for all seasons except summer, where the semidiurnal and six hourly harmonics are significant.  相似文献   

Viking orbiter observations of the Mars opposition effect     

Thomas E. Thorpe 《Icarus》1978,36(2):204-215

The Viking Extended Mission has experienced two major dust storms that have changed the global photometric properties of Mars. Large quantities of atmospheric dust arising from the June 5, 1977, storm have been observed at very low phase angles to measure the opposition effect. These particles yield only a small increase in brightness at 0° phase angle with the least enhancement seen in violet light. The phase function is well modeled by nonspherical particles with a spectrally dependent single scattering albedo. It is doubtful, therefore, that atmospheric dust plays a significant role in the reported blue light brightness surge. Such particles as surface structure combined with a lunar photometric function could, however, produce the wavelength-dependent backscattering observed during the 1967 and 1969 oppositions under clearer conditions.  相似文献   

Multiproxy late Holocene peat records from Ireland: towards a regional palaeoclimate curve     

Antony Blundell  Dan J. Charman  Keith Barber 《第四纪科学杂志》2008,23(1):59-71

Two new peat‐based climate records from Ireland covering the late Holocene are presented. The sequences are dated by a strong chronological framework formed by AMS radiocarbon dates and SCPs. Three proxy indicators (testate amoebae, macrofossils and humification) have been determined allowing the limitations and strengths of each to be identified and utilised to provide a bog surface wetness (BSW) record for both sites. Age–depth models take into account the potential for accumulation rates to vary with bog vegetation. The records from each site have been used to derive a combined BSW record that displays changes to a wetter/cooler climate from ca. AD 30 (1920 BP), ca. AD 310 (1640 BP), ca. AD 805 (1145 BP), ca. AD 1040 (910 BP) and ca. AD 1300 (650 BP). Changes follow closely those identified in a northern Britain composite BSW record and largely correspond with lake‐level data in central France suggesting the main changes in water balance were coherent over a large region. Correspondence with increases in IRD and slower Iceland‐Scotland Overflow Water (ISOW) suggests that these changes were related to oceanic forcing influencing the track of dominant westerly air flow over Ireland. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

SiO maser emission and the intrinsic properties of Mira variables     

Nimesh A. Patel  Antony Joseph  R. Ganesan 《Journal of Astrophysics and Astronomy》1992,13(3):241-265

This paper presents observations of SiO maser emission from 161 Mira variables distributed over a wide range of intrinsic parameters like spectral type, bolometric magnitude and amplitude of pulsation. The observations were made at 86.243 GHz, using the 10-4 m millimeter-wave telescope of the Raman Research Institute at Bangalore, India. These are the first observations made using this telescope. From these observations, we have established that the maser emission is restricted to Miras having mean spectral types between M6 and M10. The infrared period-luminosity relation for Mira variables is used to calculate their distances and hence estimate their maser luminosities from the observed fluxes. The maser luminosity is found to be correlated with the bolometric magnitude of the Mira variable. On an H-R diagram, the masing Mira variables are shown to lie in a region distinct from that for the non-masing ones.  相似文献   

Single epoch estimation of the Galileo integrity chain sensor station clock offsets     

Marek Ziebart  Paul Cross  Antony Sibthorpe  Peter Arrowsmith  Washington Ochieng  Shaojun Feng  Umar Bhatti  Peter Niemann 《GPS Solutions》2007,11(4):227-237

The Galileo integrity chain depends on a number of key factors, one of which is contamination of the signal-in-space errors with residual errors other than imperfect modelling of satellite orbits and clocks. A potential consequence of this is that the user protection limit is driven not by the errors associated with the imperfect orbit and clock modelling, but by the distortions induced by noise and bias in the integrity chain. These distortions increase the minimum bias the integrity chain can guarantee to detect, which is reflected in the user protection limit. A contributor to this distortion is the inaccuracy associated with the estimation of the offset between the Galileo sensor station (GSS) receiver clocks and the Galileo system time (GST). This offset is termed the receiver clock synchronization error (CSE). This paper describes the research carried out to determine both the CSE and its associated error using GPS data as captured with the Galileo System Test Bed Version 1 (GSTB-V1). In the study we simulate open access to a time datum using IGS data. Two methods are compared for determining CSE and the corresponding uncertainty (noise) across a global network of tracking stations. The single-epoch single-station method is an ‘averaging’ technique that uses a single epoch of data, and is carried out at individual sensor stations, without recourse to the data from other stations. The global network solution method is also single epoch based, but uses the inversion of a linearised model of the global system to solve for the CSE simultaneously at all GSS along with a number of other parameters that would otherwise be absorbed into the CSE estimate in the averaging technique. To test the effectiveness of various configurations in the two methods the estimated synchronisation errors across the GSS network (comprising 25 stations) are compared to the same values as estimated by the International GPS Service (IGS) using a global tracking network of around 150 stations, as well as precise orbit and satellite clock models determined by a combination of global analysis centres. The results show that the averaging technique is vulnerable to unmodelled errors in the satellite clock offsets from system time, leading to receiver CSE errors in the region of 12 ns (3.7 m), this value being largely driven by the satellite CSE errors. The global network approach is capable of delivering CSE errors at the level of 1.5 ns (46 cm) depending on the number of parameters in the linearised model. The International GNSS Service (IGS) receiver clock estimates were used as a truth model for comparative assessment.  相似文献   

The Viking Orbiter cameras' potential for photometric measurement     

Thomas E. Thorpe 《Icarus》1976,27(2):229-239

Although photometry of Mars is not listed as a major mission objective, the Viking Project has provided the Orbiter Imaging Team with cameras exhibiting significant improvement in photometric measurement as compared with past Mariners. Sample calibration data are described, together with predicted performance capabilities.  相似文献   

Application of discriminant analysis to evaluate compositional controls of stratiform massive sulfide deposits in Canada     

S. R. Divi  R. I. Thorpe  J. M. Franklin 《Mathematical Geology》1979,11(4):391-406

Multiple discriminant analysis is used to identify systematic variations of Cu, Pb, Zn, Ag, and Au grade values in the Canadian massive sulfide deposits with the three geological parameters of age, environment, and composition of volcanic lithology. The deposits have been separated into three groups on each of the three parameter scales and discriminant functions that separated the three groups on the basis of metal grades were then obtained. The results of the analysis indicated that Pb and Cu are the most significant in indicating specific trends along the three geological parameter scales. Pb grade increases in younger deposits with an increase in the sedimentary character of their environments, or with a more felsic nature to their volcanic rocks. On the other hand, Cu grade increases in deposits that occur in volcanic environments and with a more mafic nature to the volcanic host rocks. The results could have useful applications in mineral exploration.  相似文献   

Effects Of Changing Surface Heat Flux On Atmospheric Boundary-Layer Flow Over Flat Terrain     

Antony?Z.?OwinohEmail author  Julian?C.?R.?Hunt  Andrew?Orr  Peter?Clark  Rupert?Klein  H.?J.?S.?Fernando  Frans?T.?M.?Nieuwstadt 《Boundary-Layer Meteorology》2005,116(2):331-361

We examine the unsteady response of a neutral atmospheric boundary layer (ABL) of depth h and friction velocity u _* when a uniform surface heat flux is applied abruptly or decreased rapidly over a time scale t<inf>θ</inf> less than about h /(10u _*). Standard Monin–Obukhov (MO) relationships are used for the perturbed eddy viscosity profile in terms of the changes to the heat flux and mean shear. Analytical solutions for changes in temperature, mean wind and shear stress profile are obtained for the surface layer, when there are small changes in h /|L_MO| over the time scale t_MO~|L _MO|/(10u_*) (where L _MO and t _MO are the length and time scales, respectively). They show that a maximum in the wind speed profile occurs at the top of the thermal boundary layer for weak surface cooling, i.e. a wind jet, whereas there is a flattening of the profile and no marked maximum for weak surface heating. The modelled profiles are approximately the same as those obtained from the U.K. Met Office Unified Model when operating as a mesoscale model at 12-km horizontal resolution. The theoretical model is modified when strong surface heating is suddenly applied, resulting in a large change in h /|L _MO| (>>1), over the time scale t _MO. The eddy structure is predicted to change significantly and the addition of convective turbulence increases the shear turbulence at the ground. A low-level wind jet can form, with convective turbulence adding to the mean momentum of the flow. This was verified by our laboratory experiment and direct numerical simulations. Additionally, it is shown that the effects of Coriolis acceleration diminish (rather than as suggested in the literature, amplify) the formation of the wind jets in the situations considered here. Hence, only when the surface heat flux changes over time scales greater than 1/f (where f is the Coriolis parameter) does the ABL adjust monotonically between its equilibrium states. These results are also applicable to the ABL passing over spatially varying surface heat fluxes.  相似文献   

Systematic optimisation and climate simulation of FAMOUS, a fast version of HadCM3     

Chris Jones  Jonathan Gregory  Robert Thorpe  Peter Cox  James Murphy  David Sexton  Paul Valdes 《Climate Dynamics》2005,25(2-3):189-204

FAMOUS is an unfluxadjusted coupled atmosphere-ocean general circulation model (AOGCM) based on the Met Office Hadley Centre AOGCM HadCM3. Its parametrisations of physical and dynamical processes are almost identical to those of HadCM3, but by virtue of reduced horizontal and vertical resolution and increased timestep it runs about ten times faster. The speed of FAMOUS means that parameter sensitivities can be investigated more thoroughly than in slower higher-resolution models, with the result that it can be tuned closer to its target climatology. We demonstrate a simple method for systematic tuning of parameters, resulting in a configuration of FAMOUS whose climatology is significantly more realistic than would be expected for a model of its resolution and speed. FAMOUS has been tuned to reproduce the behaviour of HadCM3 as nearly as possible, in order that experiments with each model are of maximum relevance to the physical interpretation of the other. Analysis of the control climate and climate change simulation of FAMOUS show that it possesses sufficient skill for its intended purposes in Earth system science as a tool for long-timescale integrations and for large ensembles of integrations, when HadCM3 cannot be afforded. Thus, it can help to bridge the gap between models of intermediate complexity and the higher-resolution AOGCMs used for policy-relevant climate prediction.  相似文献