1961-2005年宁夏极端降水事件变化趋势分析   总被引：11，自引：0，他引：11  

陈晓光  Declan Conway  陈晓娟  郑广芬 《气候变化研究进展》2008,4(3):156-160

 利用1961-2005年宁夏逐日降水量资料,将降水量划分为9个级别,分析了宁夏45 a来各级别降水日数的变化趋势。结果表明：年降水量以平均3.6 mm/10 a的速率减少;近15 a来,冬、春季降水量明显减少,夏、秋季10.0 mm以下降水日数明显减少,25.0 mm以上降水日数明显增加。以1986年为界的气候变暖前后25.1～50.0 mm级别的降水日数夏季和年增加的显著性概率分别达到了5%和1%,降水频率分布呈现向高级别降水量增加的变化趋势。  相似文献   

Evolutionary principles applied to mission planning problems     

Bruce A. Conway  Christian M. Chilan  Bradley J. Wall 《Celestial Mechanics and Dynamical Astronomy》2007,97(2):73-86

The space mission planning process is considered as a hybrid optimal control problem. Hybrid optimal control problems are problems that include categorical variables in the problem formulation. For example, an interplanetary trajectory may consist of a sequence of low thrust arcs, impulses and planetary flybys. However, for each choice of the structure of the mission, for example, for a particular choice of the number of planetary flybys to be used, there is a corresponding optimal trajectory. It is not a priori clear which structure will yield the most efficient mission. In this work we present a mathematical framework for describing such problems and solution methods for the hybrid optimal control problem based on evolutionary principles that have the potential for being a robust solver of such problems. As an example, the methods are used to find the optimal choice of three asteroids to visit in sequence, out of a set of eight candidate asteroids, in order to minimize the fuel required.  相似文献   

Long term wind erosion on Mars     

John C. Armstrong  Conway B. Leovy 《Icarus》2005,176(1):57-74

Wind erosion and deposition are powerful agents of surface change on Mars. Erosion is sensitive to the atmospheric density, so feedback between orbit variations and atmospheric density can enhance the sensitivity of erosion rates to orbital parameters. We use statistics derived from a 1 Gyr integration of the spin axis of Mars, coupled with runs of the NASA Ames 3-D general circulation model (GCM) at a variety of orbital conditions and pressures, to explore this feedback. We find that wind erosion in the GCM is associated with two factors: baroclinic zone winds, and strong cross-equator solstice flows. Both of these factors are influenced by topography, producing an asymmetry in the erosion pattern between the north and the south. The erosion model, averaged over 1 Gyr, produces potential erosion rates of in the north and in the south, which increase by an order of magnitude in an early 28 mbar atmosphere. The stability of these potential erosion patterns over geological time indicates that the lowland regions of Mars are continuously eroded, and that wind is capable of revealing ancient sedimentary deposits, or eroding substantial deposits that may have otherwise been preserved.  相似文献   

Land subsidence and earth fissures in south-central and southern Arizona,USA   总被引：1，自引：1，他引：0  

Brian D. Conway 《Hydrogeology Journal》2016,24(3):649-655

Land subsidence due to groundwater overdraft has been an ongoing problem in south-central and southern Arizona (USA) since the 1940s. The first earth fissure attributed to excessive groundwater withdrawal was discovered in the early 1950s near Picacho. In some areas of the state, groundwater-level declines of more than 150 m have resulted in extensive land subsidence and earth fissuring. Land subsidence in excess of 5.7 m has been documented in both western metropolitan Phoenix and Eloy. The Arizona Department of Water Resources (ADWR) has been monitoring land subsidence since 2002 using interferometric synthetic aperture radar (InSAR) and since 1998 using a global navigation satellite system (GNSS). The ADWR InSAR program has identified more than 25 individual land subsidence features that cover an area of more than 7,300 km². Using InSAR data in conjunction with groundwater-level datasets, ADWR is able to monitor land subsidence areas as well as identify areas that may require additional monitoring. One area of particular concern is the Willcox groundwater basin in southeastern Arizona, which is the focus of this paper. The area is experiencing rapid groundwater declines, as much as 32.1 m during 2005–2014 (the largest land subsidence rate in Arizona State—up to 12 cm/year), and a large number of earth fissures. The declining groundwater levels in Arizona are a challenge for both future groundwater availability and mitigating land subsidence associated with these declines. ADWR’s InSAR program will continue to be a critical tool for monitoring land subsidence due to excessive groundwater withdrawal.  相似文献   

The Location of Creativity and U.S. Companies in Germany     

Marlies Kluike  Moira A. Conway 《The Professional geographer》2016,68(4):686-696

This article analyzes how far U.S. companies locate subsidiaries in need of highly skilled staff in state locations in Germany that have a high ranking of creativity. Such locations should provide an especially attractive location for certain “creative” staff, which should be of special interest to U.S. companies in need of highly skilled staff. Analyzing U.S. companies that were established since the year 2000 and with more than fifty staff, we find support for our propositions that nonmanufacturing and organizationally higher rank subsidiaries with a need for urban infrastructure and connectedness are located in creative states in Germany.  相似文献   

A Thin Ring Model for the Oh Megamaser in Iiizw35     

Rodrigo Parra  John Conway  Moshe Elitzur 《Astrophysics and Space Science》2005,295(1-2):325-330

We present a model for the OH megamaser emission in the starburst galaxy IIIZw35. The observed diffuse and compact OH maser components in this source are explained by a single phase of unsaturated clumpy gas distributed in a thin ring structure and amplifying background continuum. We emphasize the importance of clumpiness in the OH masing medium, an effect that has not been fully appreciated previously.The model explains why multiple bright spots are seen only at the ring tangents while smoother emission is found elsewhere. Both the observed velocity gradients and the line to continuum ratios around the ring enquire a geometry where most of the seed photons come from a continuum emission which lies outside the OH ring. To explain both the OH and continuum brightness, free-free absorbing gas is required along the ring axis to partially absorb the far side of the ring. It is proposed that the required geometry arises from an inwardly propagating ring of starburst activity.  相似文献   

Climate change and the water–energy–food nexus: insights from policy and practice in Tanzania     

Joanna Pardoe  Declan Conway  Emilinah Namaganda  Katharine Vincent  Andrew J. Dougill  Japhet J. Kashaigili 《Climate Policy》2018,18(7):863-877

The threat of climate change is emerging at a time of rapid growth for many economies in sub-Saharan Africa (SSA). Dominant narratives comprising ambitious development plans are common and often based around sectors with strong inter-dependencies that are highly exposed to climate variability. Using document analysis and key informant interviews, this article examines how climate change is addressed in policy, how it is being mainstreamed into water, energy and agriculture sector policies and the extent to which cross-sectoral linkages enable coordinated action. These questions are addressed through a case study of Tanzania, highlighting broader lessons for other developing countries, particularly those in SSA facing similar challenges. The article finds that, while the agriculture and water sectors are increasingly integrating climate change into policies and plans in Tanzania, practical coordination on adaptation remains relatively superficial. Publication of the Tanzania National Adaptation Plan of Action (NAPA) in 2007 marked a step change in the integration of climate change in sectoral policies and plans; however, it may have reinforced a sectoral approach to climate change. Examining the policies for coherence highlights overlaps and complementarities which lend themselves to a coordinated approach. Institutional constraints (particularly structures and resources) restrict opportunities for inter-sectoral action and thus collaboration is confined to ad hoc projects with mixed success to date. The results highlight the need for institutional frameworks that recognize and address these constraints to enable development goals to be pursued in a more sustainable and climate-resilient manner.

KEY POLICY INSIGHTS

• The NAPA has been successful at encouraging climate change mainstreaming into sectoral policies in Tanzania; however, the cross-sectoral collaboration crucial to implementing adaptation strategies remains limited due to institutional challenges such as power imbalances, budget constraints and an ingrained sectoral approach.

• Collaboration between nexus sectors in Tanzania is largely through ad hoc projects with limited progress on establishing deeper connections to enable collaboration as a process. Regular cross-sectoral planning meetings and consistent annual budgets could provide a platform to enhance cross-sectoral coordination.

• Plans to develop hydropower and agriculture are prevalent across sub-Saharan Africa. Insights from Tanzania highlight the importance of institutional and policy frameworks that enable cross-sectoral coordination.

  相似文献   

On the history of the lunar orbit     

B.A. Conway 《Icarus》1982,51(3):610-622

A frequency-dependent model of tidal friction is used in the determination of the time rate of change of the lunar orbital elements and the angular velocity of the Earth. The variational equations consider eccentricity, the solar tide on the Earth, Earth oblateness, and higher-order terms in the Earth's tidal potential. A linearized solution of the equations governing the precission of the Earth's rotational angular momentum and the lunar ascending node is found. This allows the analytical averaging of the variational equations over the period of relative precession which, though large, is necessarily small in comparison to the time step of the numerical integrator that yields the system history over geological time. Results for this history are presented and are identified as consistent with origin of the Moon by capture. This model may be applied to any planet-satellite system where evolution under tidal friction is of interest.  相似文献   

The 2dF Galaxy Redshift Survey: the nature of the relative bias between galaxies of different spectral type     

Edward Conway  Steve Maddox  Vivienne Wild  John A. Peacock  Ed Hawkins  Peder Norberg  Darren S. Madgwick  Ivan K. Baldry  Carlton M. Baugh  Joss Bland-Hawthorn  Terry Bridges  Russell Cannon  Shaun Cole  Matthew Colless  Chris Collins  Warrick Couch  Gavin Dalton  Roberto De Propris  Simon P. Driver  George Efstathiou  Richard S. Ellis  Carlos S. Frenk  Karl Glazebrook  Carole Jackson  Bryn Jones  Ofer Lahav  Ian Lewis  Stuart Lumsden  Will Percival  Bruce A. Peterson  Will Sutherland  Keith Taylor 《Monthly notices of the Royal Astronomical Society》2005,356(2):456-474

We present an analysis of the relative bias between early- and late-type galaxies in the Two-degree Field Galaxy Redshift Survey (2dFGRS) – as defined by the η parameter of Madgwick et al., which quantifies the spectral type of galaxies in the survey. We calculate counts in cells for flux-limited samples of early- and late-type galaxies, using approximately cubical cells with sides ranging from 7 to  42 h ⁻¹ Mpc  . We measure the variance of the counts in cells using the method of Efstathiou et al., which we find requires a correction for a finite volume effect equivalent to the integral constraint bias of the autocorrelation function. Using a maximum-likelihood technique we fit lognormal models to the one-point density distribution, and develop methods of dealing with biases in the recovered variances resulting from this technique. We then examine the joint density distribution function,   f (δ_E, δ_L)  , and directly fit deterministic bias models to the joint counts in cells. We measure a linear relative bias of ≈1.3, which does not vary significantly with ℓ. A deterministic linear bias model is, however, a poor approximation to the data, especially on small scales  (ℓ≤ 28  h ⁻¹ Mpc)  where deterministic linear bias is excluded at high significance. A power-law bias model with index   b ₁≈ 0.75  is a significantly better fit to the data on all scales, although linear bias becomes consistent with the data for  ℓ≳ 40  h ⁻¹ Mpc  .  相似文献   

Carbon dioxide and methane in the Arctic atmosphere     

T. J. Conway  L. P. Steele 《Journal of Atmospheric Chemistry》1989,9(1-3):81-99

Fifty flask air samples were taken during April 1986 from a NOAA WP-3D Orion aircraft which flew missions across a broad region of the Arctic as part of the second Arctic Gas and Aerosol Sampling Program (AGASP II). The samples were subsequently analyzed for both carbon dioxide (CO₂) and methane (CH₄). The samples were taken in well-defined layers of Arctic haze, in the background troposphere where no haze was detected, and from near the surface to the lower stratosphere. Vertical profiles were specifically measured in the vicinity of Barrow, Alaska to enable comparisons with routine surface measurements made at the NOAA/GMCC observatory. Elevated levels of both methane and carbon dioxide were found in haze layers. For samples taken in the background troposphere we found negative vertical gradients (lower concentrations aloft) for both gases. For the entire data set (including samples collected in the haze layers) we found a strong positive correlation between the methane and carbon dioxide concentrations, with a linear regression slope of 17.5 ppb CH₄/ppm CO₂, a standard error of 0.6, and a correlation coefficient (r²) of 0.95. This correlation between the two gases seen in the aircraft samples was corroborated by in situ surface measurements of these gases made at the Barrow observatory during March and April 1986. We also find a similar relationship between methane and carbon dioxide measured concurrenty for a short period in the moderately polluted urban atmosphere of Boulder, Colorado. We suggest that the strong correlation between methane and carbon dioxide concentrations reflects a common source region for both, with subsequent long-range transport of the polluted air to the Arctic.  相似文献