Io: Heat flow from dark paterae     

Glenn J. Veeder  David A. Williams  Torrence V. Johnson 《Icarus》2011,212(1):236-261

Dark paterae on the jovian satellite Io are evidence of recent volcanic activity. Some paterae appear to be entirely filled with dark volcanic material, while others have only partially darkened floors. Dark paterae have area and heat flow longitudinal distributions that are bimodal as well as anti-correlated with the longitudinal distribution of mountains on Io at a global scale. As part of our study of Io’s total heat flow, we have examined the darkest paterae and quantified their thermal emission in order to assess their contribution. This is the first time that the areas of the dark material in these paterae have been measured with such precision and correlated with their thermal emission. Dark paterae yield a significantly larger contribution to Io’s heat flow than dark volcanic fields. Dark paterae (including Loki Patera) yield at least ∼4 × 10¹³ W or ∼40% of Io’s total heat flow. In comparison, dark flow fields yield ∼10¹³ W or ∼10% of Io’s total heat flow. Of the total heat loss from dark paterae, Loki Patera alone yields ∼10¹³ W or ∼10% of Io’s total thermal emission.  相似文献   

Comparisons of Supergranule Characteristics During the Solar Minima of Cycles 22/23 and 23/24     

Peter E. Williams  W. Dean Pesnell 《Solar physics》2011,270(1):125-136

Supergranulation is a component of solar convection that manifests itself on the photosphere as a cellular network of around 35 Mm across, with a turnover lifetime of 1 – 2 days. It is strongly linked to the structure of the magnetic field. The horizontal, divergent flows within supergranule cells carry local field lines to the cell boundaries, while the rotational properties of supergranule upflows may contribute to the restoration of the poloidal field as part of the dynamo mechanism, which controls the solar cycle. The solar minimum at the transition from cycle 23 to 24 was notable for its low level of activity and its extended length. It is of interest to study whether the convective phenomena that influence the solar magnetic field during this time differed in character from periods of previous minima. This study investigates three characteristics (velocity components, sizes and lifetimes) of solar supergranulation. Comparisons of these characteristics are made between the minima of cycles 22/23 and 23/24 using MDI Doppler data from 1996 and 2008, respectively. It is found that whereas the lifetimes are equal during both epochs (around 18 h), the sizes are larger in 1996 (35.9 ± 0.3 Mm) than in 2008 (35.0 ± 0.3 Mm), while the dominant horizontal velocity flows are weaker (139 ± 1 m s⁻¹ in 1996; 141 ± 1 m s⁻¹ in 2008). Although numerical differences are seen, they are not conclusive proof of the most recent minimum being inherently unusual.  相似文献   

Restriction of sponges to an atoll lagoon as a result of reduced environmental quality     

Ingrid S.S. Knapp  Gareth J. Williams  José Luis Carballo  José Antonio Cruz-Barraza  Jonathan P.A. Gardner  James J. Bell 《Marine pollution bulletin》2013,66(1-2):209-220

The lagoon at Palmyra Atoll in the central Pacific was subject to major military modifications during WWII and now the dominant fauna on the lagoon’s hard substrate are sponges, not corals. In this study, we quantified the physical and biological factors explaining the variation in sponge distribution patterns across 11 sites to determine the potential for the sponges in the lagoon at Palmyra to invade the surrounding reef systems. Significant differences in sponge assemblages were found among all but three sites. For all the models we examined the strongest environmental relationships were found for variables related to sedimentation/turbidity and food/habitat availability. Our findings suggest that the sponges in Palmyra’s lagoon are likely to be restricted to this habitat type where they are associated with conditions resulting from the earlier heavy disturbance and are unlikely to spread to the outer reef environments unless there is a dramatic decline in environmental quality.  相似文献   

Fast error analysis of continuous GNSS observations with missing data   总被引：3，自引：0，他引：3  

M. S. Bos  R. M. S. Fernandes  S. D. P. Williams  L. Bastos 《Journal of Geodesy》2013,87(4):351-360

One of the most widely used method for the time-series analysis of continuous Global Navigation Satellite System (GNSS) observations is Maximum Likelihood Estimation (MLE) which in most implementations requires $\mathcal{O }(n^3)$ operations for $n$ observations. Previous research by the authors has shown that this amount of operations can be reduced to $\mathcal{O }(n^2)$ for observations without missing data. In the current research we present a reformulation of the equations that preserves this low amount of operations, even in the common situation of having some missing data.Our reformulation assumes that the noise is stationary to ensure a Toeplitz covariance matrix. However, most GNSS time-series exhibit power-law noise which is weakly non-stationary. To overcome this problem, we present a Toeplitz covariance matrix that provides an approximation for power-law noise that is accurate for most GNSS time-series.Numerical results are given for a set of synthetic data and a set of International GNSS Service (IGS) stations, demonstrating a reduction in computation time of a factor of 10–100 compared to the standard MLE method, depending on the length of the time-series and the amount of missing data.  相似文献   

Earth observations during space shuttle mission STS‐34: 18–23 October 1989     

Michael R. Helfert  Kamlesh P. Lulla  Victor S. Whitehead  M. Justin Wilkinson  Donald E. Williams  Michael J.. McCulley 《国际地球制图》2013,28(3):65-79

Abstract

Although high‐resolution microwave synthetic aperture radar (SAR) sensors possess all‐weather capability for mapping soil moisture from spaceborne platforms, continuous temporal and spatial monitoring of this important hydrological parameter has been relatively limited. However, the recent launch of operational SAR sensors aboard various satellites have made possible synoptic soil moisture monitoring a reality. Such systems operate over a wide range of frequencies, look angles, and polarization combinations, and thus show synergistic advantages when combined for estimating soil moisture patterns. Two soil moisture inversion algorithms have been developed using as inputs radar backscattering data at L, S, and C bands in the microwave frequency range. These models have been tested using radar image simulation with speckle added. It is observed that the neural network algorithm yields superior results in mapping actual soil moisture patterns over the linear statistical inversion technique, although both models show comparable errors in soil moisture estimation. We infer that using statistical estimation errors alone for comparison purposes may lead to erroneous conclusions regarding the advantages of one soil moisture inversion algorithm over another.  相似文献   

THE CLIMATOLOGY OF LAKE EFFECT IN MILWAUKEE,WISCONSIN     

Thomas B. Williams 《自然地理学》2013,34(4):333-345

Prevailing onshore winds off Lake Michigan in the warm season (April-October) cause cooling along the adjacent coast during the day. Mesoscale lake breeze formation occurs most frequently in August. Synoptic-aided lake breezes, which combine mesoscale inputs with existing large-scale conditions, are most prevalent in May. Lake breezes are favored by high pressure and airmass weather patterns. Synoptic lake effect dominates in April; large-scale onshore flow is often produced by high pressure, post-cold front, and pre-warm front weather conditions. Overall, lake cooling is experienced 60% of the time during the warmer months. The highest frequency of lake effect is found in May. The cooling impact of Lake Michigan across the Milwaukee area is maximized since spring is the season of greatest contrast in land and lake temperatures. Lake-effect conditions in the cool season (November-March) occur less frequently. Onshore flow off the warmer lake reduces cooling at night along the Milwaukee shoreline. Synoptic lake effect is dominant, with a peak in March. Lake snow and mesoscale land breeze developments are most frequent in midwinter, when large land-lake thermal contrasts exist during outbreaks of cold polar air under high pressure patterns. [Key words: lake effect, climatology, mesoscale, onshore winds.]  相似文献   

LAKE EFFECT OBSERVATIONS IN MILWAUKEE,WISCONSIN     

Thomas B. Williams 《自然地理学》2013,34(1):35-49

Field observations of temperature, humidity, and wind conditions were taken during mesoscale lake breeze, synoptic-aided lake breeze, and synoptic-scale lake effect situations in Milwaukee, Wisconsin. Measurements were made along two east-west transect routes to document Lake Michigan's cooling impact. Lake breezes are characterized by significant changes in weather parameters: a sharp drop in temperature, a rise in dew point, an increase in relative humidity, and a shift from offshore to onshore winds. Temperature contrasts between lakefront and inland envirionments exceed 5°C. Lake cooling is confined to a coastal zone extending 8.0 km inland. Synoptic-aided lake breezes combine mesoscale lake breeze formation with the added influence of developing synoptic onshore winds. These situations are characterized by earlier time of occurrence, greater inland movement, and reduce land-lake thermal contrasts. Synoptic lake effect is produced by steady prevailing onshore winds from the northeast or east under the control of the large-scale pressure pattern. The greatest degree of lake cooling occurs under synoptic lake effect conditions, with widespread impact extending well inland. Maximum temperature differences between nearshore and inland locations exist in spring, the season of greatest land-lake thermal contrast. [Key Words: Lake effect, lake breeze, mesoscale climatology, Lake Michigan.]  相似文献   

The surface energy balance at the Huygens landing site and the moist surface conditions on Titan     

Kaj E. Williams  Christopher P. McKay  Fredrik Persson 《Planetary and Space Science》2012,60(1):376-385

The Huygens Probe provided a wealth of data concerning the atmosphere of Titan. It also provided tantalizing evidence of a small amount of surface liquid. We have developed a detailed surface energy balance for the Probe landing site. We find that the daily averaged non-radiative fluxes at the surface are 0.7 W m^?2, much larger than the global average value predicted by McKay et al. (1991) of 0.037 W m^?2. Considering the moist surface, the methane and ethane detected by the Probe from the surface is consistent with a ternary liquid of ethane, methane, and nitrogen present on the surface with mole fractions of methane, ethane, and nitrogen of 0.44, 0.34, and 0.22, respectively, and a total mass load of ～0.05 kg m^?2. If this liquid is included in the surface energy balance, only a small fraction of the non-radiative energy is due to latent heat release (～10^?3 W m^?2). If the amount of atmospheric ethane is less than 0.6×10^?5, the surface liquid is most likely evaporating over timescales of 5 Titan days, and the moist surface is probably a remnant of a recent precipitation event. If the surface liquid mass loading is increased to 0.5 kg m^?2, then the liquid lifetime increases to ～56 Titan days. Our modeling results indicate a dew cycle is unlikely, given that even when the diurnal variation of liquid is in equilibrium, the diurnal mass variation is only 3% of the total liquid. If we assume a high atmospheric mixing ratio of ethane (>0.6×10^?5), the precipitation of liquid is large (38 cm/Titan year for an ethane mixing ratio of 2×10^?5). Such a flux is many orders of magnitude in excess of the photochemical production rate of ethane.  相似文献   

The politics of defining and alleviating poverty: State strategies and their impacts in rural Kerala     

Glyn Williams  Binitha V. Thampi  D. Narayana  Sailaja Nandigama  Dwaipayan Bhattacharyya 《Geoforum》2012,43(5):991-1001

This paper presents a relational approach to the study of poverty (Mosse, 2010), and uses this to critically evaluate state strategies for identifying and alleviating poverty in Kerala, India. It traces these from national planning documents through to their point of implementation, drawing on qualitative research in two of Kerala’s poorest Districts. Ideas of participatory poverty classification, economic self-reliance and political empowerment are laudable national policy goals, and Kerala has shown innovation in its adaptation of these within the State’s devolved structures of local governance. However, both the framing of policy and its implementation reproduce ideas of individual transitions out of poverty which indicate that the state pays insufficient attention to the highly unequal social and economic relationships reproducing poverty in contemporary Kerala – in short, to poverty’s inherently political nature.  相似文献   

HgO at high pressures: the transition to the NaCl structure (HgO-III) and the equation of state of tetragonal HgO-II     

Jinyuan Yan  Bin Chen  Selva Vennila Raju  Budhiram K. Godwal  Alastair A. MacDowell  Jason Knight  Hongwei Ma  Quentin Williams 《Physics and Chemistry of Minerals》2012,39(4):269-275

The high-pressure behavior of HgO-montroydite was investigated up to 36.5 GPa using angle-dispersive X-ray diffraction. The tetragonal phase of this material (HgO-II), a distortion of the NaCl structure, transforms into the cubic NaCl structure (HgO-III) above ~31.5 GPa. The transformation of mercury oxide from the orthorhombic Pnma (HgO-I) structure to a tetragonal I4/mmm structure (HgO-II) is confirmed to occur at 13.5 ± 1.5 GPa. Neither of the high-pressure phases, HgO-II nor HgO-III, is quenchable in pressure. The derived isothermal bulk modulus of HgO-II and its pressure derivative strongly depend on the assumed zero-pressure volume of this phase, but our elasticity results on HgO-II nevertheless lie significantly closer to theoretical calculations than prior experimental results, and the measured pressure of the phase transformation to the NaCl structure is also in agreement with recent theoretical results. The general accord with theory supports the existence of significant relativistic effects on the high-pressure phase transitions of HgO.  相似文献