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Information from a variety of sources, including an airborne field expedition in November 1985, is used to produce estimates of the annual emissions of some hydrocarbons from bushfires, and isoprene from trees, in tropical Australia. For the continent north of 23° S the annual bushfires (biomass burning) input was estimated, in units of Tg carbon, to be 2 TgC (uncertainty range 0.8–5 TgC), emitted predominantly during the May to October dryseason. Isoprene emissions during this period were estimated also to be 2 TgC (uncertainty range 0.5–8 TgC), but were estimated to be an order of magnitude higher during the November to April wet season, at a level of 23 TgC (uncertainty range 6–100 TgC).The large annual emission of isoprene over the tropical part of the Australian continent yields ppbv levels of isoprene measured at the surface in summertime. Isoprene reactivity with hydroxyl radical is such that at these concentrations isoprene must be a dominant factor in controlling the concentration of OH radical in the convective boundary layer. Simple arguments based on the convective velocity scale suggest that the shape of the isoprene vertical profile in November 1985 would be consistent with available data on the OH-isoprene reaction rate if OH concentration in the boundary layer averaged about 2.5×106 cm-3 over the middle part of the day.Temporarily at the International Meteorological Institute, Stockholm University, S-106 91, Stockholm, Sweden. 相似文献
3.
Global trends and patterns of drought from space 总被引：1，自引：0，他引：1
This paper analyzes changes in areas under droughts over the past three decades and alters our understanding of how amplitude and frequency of droughts differ in the Southern Hemisphere (SH) and Northern Hemisphere (NH). Unlike most previous global-scale studies that have been based on climate models, this study is based on satellite gauge-adjusted precipitation observations. Here, we show that droughts in terms of both amplitude and frequency are more variable over land in the SH than in the NH. The results reveal no significant trend in the areas under drought over land in the past three decades. However, after investigating land in the NH and the SH separately, the results exhibit a significant positive trend in the area under drought over land in the SH, while no significant trend is observed over land in the NH. We investigate the spatial patterns of the wetness and dryness over the past three decades, and we show that several regions, such as the southwestern United States, Texas, parts of the Amazon, the Horn of Africa, northern India, and parts of the Mediterranean region, exhibit a significant drying trend. The global trend maps indicate that central Africa, parts of southwest Asia (e.g., Thailand, Taiwan), Central America, northern Australia, and parts of eastern Europe show a wetting trend during the same time span. The results of this satellite-based study disagree with several model-based studies which indicate that droughts have been increasing over land. On the other hand, our findings concur with some of the observation-based studies. 相似文献
4.
The energy balance of an upland heath dominated by heather (Calluna vulgaris) was measured in dry and wet weather. Median values of both transpiration and evaporation rates were ca. 2 mm hr-1. The median Bowen ratio for the dry canopy was 2.0 and for the wet canopy 0.6. On dry days the median value of the saturation deficit was only 3.8 mb and that of the climatological resistance was 30 s m-1. The bulk stomatal resistance increased from ca. 50 s m -2 in the morning to over 290 s m-1 in the afternoon with an overall median value of 110 s m-1. Transpiration from the dry canopy was controlled by a combination of small saturation deficits and large stomatal resistances. The median value of the boundary-layer resistance of the canopy was 22 s m-1 and was low partly because of a large low-level drag coefficient. Saturation deficits on wet days were close to zero and evaporation of intercepted water proceeded at close to the equilibrium rate, being largely limited by the low fluxes of available energy. The water loss from heather was compared with simulated losses from coniferous forest, herbaceous crops and grassland in the same conditions to evaluate the effects of vegetation on water loss from catchments.Laboratorio de Ecologia, Dept. de Biologia Vegetal, Universidade de Brasilia, 70 910 — Brasila — DF, Brazil. 相似文献
5.
潘涛 《高原山地气象研究》2001,21(4)
利用振筒式气压仪串行输出接口,在Win98操作平台下,使用DELPHI5.0编写应用程序,实现振筒式气压仪数据的自动采集,处理和显示,并显示AWOS气压值和其他数据;程序自动读取两设备的数据并进行比较,当出现误差值大于规定值时,出现一个告警提示信息. 相似文献
6.
Two new indicators of rainfall seasonality based on information entropy, the relative entropy (RE) and the dimensionless seasonality index (DSI), together with the mean annual rainfall, are evaluated on a global scale for recently updated precipitation gridded datasets and for historical simulations from coupled atmosphere–ocean general circulation models. The RE provides a measure of the number of wet months and, for precipitation regimes featuring a distinct wet and dry season, it is directly related to the duration of the wet season. The DSI combines the rainfall intensity with its degree of seasonality and it is an indicator of the extent of the global monsoon region. We show that the RE and the DSI are fairly independent of the time resolution of the precipitation data, thereby allowing objective metrics for model intercomparison and ranking. Regions with different precipitation regimes are classified and characterized in terms of RE and DSI. Comparison of different land observational datasets reveals substantial difference in their local representation of seasonality. It is shown that two-dimensional maps of RE provide an easy way to compare rainfall seasonality from various datasets and to determine areas of interest. Models participating to the Coupled Model Intercomparison Project platform, Phase 5, consistently overestimate the RE over tropical Latin America and underestimate it in West Africa, western Mexico and East Asia. It is demonstrated that positive RE biases in a general circulation model are associated with excessively peaked monthly precipitation fractions, too large during the wet months and too small in the months preceding and following the wet season; negative biases are instead due, in most cases, to an excess of rainfall during the premonsoonal months. 相似文献
7.
自动气象站缺测数据分析及处理 总被引：3，自引：3，他引：3
地面自动观测系统正逐步替代传统的人工气象观测,自动气象站容易受到直接雷击及雷电电磁脉冲的侵害、仪器性能下降、电磁干扰和人为操作失误等因素影响,导致自动站采集器等设备损坏,造成业务中断,数据缺测,影响了气象数据的及时性、完整性、连续性。因此,台站观测人员需要在自动站设备故障,资料不正常时及时采取有效措施,对数据进行补测、挽救,保证气象数据完整、按时上传。对自动气象站资料缺测的原因进行初步分析,并着重对自动站定时观测、每小时上传文件及日、月数据极值、统计缺测等方面的处理进行探讨。 相似文献
8.
Abstract An experiment using turbulence probes and an array of side‐scan and vertically pointing pencil beam sonars mounted on the U.S. submarine Dolphin was carried out to measure turbulence in near‐surface regions of acoustic scattering, in particular, those caused by subsurface bubbles produced by breaking wind waves. The dataset collected during winds of 5–9 m s?1 reveals the banded patterns of bubbles associated with Langmuir circulation, even though no surface manifestations were visible. A forward‐pointing side‐scan sonar determined the “age” of bubble clouds after their generation by breaking waves. There is enhanced turbulent dissipation in the bubble clouds, and the dissipation rate close to the surface exceeds that predicted using conventional calculations based on the law of the wall and buoyancy flux. The correspondence between bubbles and turbulence implies a horizontally patchy turbulent structure near the surface. Below the base of the bubble clouds the distance between turbulent patches increases and is much greater than that of the bubble clouds. The submarine provides an excellent platform for multi‐sonar near‐surface studies. 相似文献
9.
利用振筒式气压仪串行输出接口，在Win98操作平台下，使用DELPHI5．0编写应用程序，实现振筒式气压仪数据的自动采集，处理和显示，并显示A－WOS气压值和其他数据，程序自动读取两设备的数据并进行比较，当出现误差值大于规定值时，出现一个告警提示信息。 相似文献
10.
Pierre Welander 《Dynamics of Atmospheres and Oceans》1977,1(3):215-223
A theoretical discussion is given of the thermal transients and self-sustained oscillations in a fluid, heated at a constant rate below the surface, and cooled from the top strongly enough to allow freezing. Assuming that the fluid is well mixed and that the thickness of the ice is small compared to the fluid depth, it is shown that the system can have zero, one, or two steady states. The ice-covered steady state is stable for small perturbations; however, the ice-free steady state may be unstable with the impulsive addition of a thin ice sheet. Transient developments may include both ice-covered and ice-free states. In the case where no steady state exists the system exhibits periodic self-sustained oscillations. Application of the theory to a laboratory experiment is considered. 相似文献
11.
利用ASTER数据估算2002年4月阿克苏地表特征和植被参数 总被引：1，自引：1，他引：0
利用ASTER卫星可见光和短波红外波段数据,估算了2002年4月12日阿克苏地区地表特征参数(地表温度T、地表反射率α)和植被参数(归一化植被指数NDVI、修正的土壤调整植被指数MSA-VI、植被覆盖度Pv和叶面积指数LAI等)。结果表明,各种植被参数在沙漠地区较小,而在绿洲中的值较大。同时本文认为ASTER遥感数据有较高的地面分辨率,利用它可以更好地反映地表的植被参数及地表特征参数状况;还指出了ASTER卫星数据在沙漠绿洲中的适用性。 相似文献
12.
K. Kürbis M. Mudelsee G. Tetzlaff R. Brázdil 《Theoretical and Applied Climatology》2009,98(1-2):187-195
For the analysis of trends in weather extremes, we introduce a diagnostic index variable, the exceedance product, which combines intensity and frequency of extremes. We separate trends in higher moments from trends in mean or standard deviation and use bootstrap resampling to evaluate statistical significances. The application of the concept of the exceedance product to daily meteorological time series from Potsdam (1893 to 2005) and Prague–Klementinum (1775 to 2004) reveals that extremely cold winters occurred only until the mid-20th century, whereas warm winters show upward trends. These changes were significant in higher moments of the temperature distribution. In contrast, trends in summer temperature extremes (e.g., the 2003 European heatwave) can be explained by linear changes in mean or standard deviation. While precipitation at Potsdam does not show pronounced trends, dew point does exhibit a change from maximum extremes during the 1960s to minimum extremes during the 1970s. 相似文献
13.
Methane flux from northern wetlands and tundra 总被引：2，自引：0，他引：2
T. R. CHRISTENSEN I. C. PRENTICE J. KAPLAN A. HAXELTINE S. SITCH 《Tellus. Series B, Chemical and physical meteorology》1996,48(5):652-661
14.
R. A. Brown 《Boundary-Layer Meteorology》1978,14(3):381-396
A two-layer, first-order closure model for the Planetary Boundary Layer (PBL) is developed with the objective of parameterizing the surface stress with respect to the synoptic scale. The model includes stability effects by considering stratification-dependent secondary flow in the outer layer and empirical corrections to the surface layer flow. It shows the compatibility of simple eddy viscosity closure solutions with similarity theory by producing the now well-known Rossby similarity equations. It allows further insight into the Rossby similarity parameters by relating them to a single similarity parameter which is the ratio of the characteristic scales of the PBL and the surface layer.The measured and derived values of the similarity parameters A and B are compared with AIDJEX data and other published values. The variation in these values in stably stratified conditions is predicted and two alternate similarity parameters are calculated, one a constant and the other with a small variation and decreasing influence on the drag coefficient in stable stratification. The result is an empirical resistance law for a geostrophic drag coefficient variation which parameterizes an observed order-of-magnitude change in surface stress with changes in roughness or PBL stratification. This variation is related to similarity parameters characteristic of the region and to measurable changes in the geostrophic departure angle. 相似文献
15.
Edward R Cook 《Climate Dynamics》1995,11(4):211-222
Recent temperature trends in long tree-ring and coral proxy temperature histories are evaluated and compared in an effort to objectively determine how anomalous twentieth century temperature changes have been. These histories mostly reflect regional variations in summer warmth from the tree rings and annual warmth from the corals. In the Northern Hemisphere, the North American tree-ring temperature histories and those from the north Polar Urals, covering the past 1000 or more years, indicate that the twentieth century has been anomalously warm relative to the past. In contrast, the tree-ring history from northern Fennoscandia indicates that summer temperatures during the Medieval Warm Period were probably warmer on average than those than during this century. In the Southern Hemisphere, the tree-ring temperature histories from South America show no indication of recent warming, which is in accordance with local instrumental records. In contrast, the tree-ring records from Tasmania and New Zealand indicate that the twentieth century has been unusually warm particularly since 1960. The coral temperature histories from the Galapagos Islands and the Great Barrier Reef are in broad agreement with the tree-ring temperature histories in those sectors, with the former showing recent cooling and the latter showing recent warming that may be unprecedented. Overall, the regional temperature histories evaluated here broadly support the larger-scale evidence for anomalous twentieth century warming based on instrumental records. However, this warming cannot be confirmed as an unprecedented event in all regions. 相似文献
16.
采用有关方法,分析了我市的光热水和土壤肥力等自然资源与冬小麦生产的关系,估算了气候土壤资源对作物具有的生产潜力,并阐明了影响潜在产量的主要自然因素,同时提出了相应的对策建议。 相似文献
17.
Boundary-layer heat and moisture budgets from fife 总被引：1，自引：0，他引：1
A. K. Betts R. L. Desjardins J. I. Macpherson R. D. Kelly 《Boundary-Layer Meteorology》1990,50(1-4):109-138
Aircraft stacks were flown upwind and downwind of the First ISLSCP Field Experiment (FIFE) site in Kansas to measure the heat and moisture budgets of the boundary layer under fairly clear skies for four daytime periods. In this paper, we evaluate the terms in the conservation equation. The vertical flux divergence and advection do not account for the difference between surface and low-level aircraft flux estimates. Budget estimates of the surface fluxes using the aircraft data agree well with surface flux measurements, but extrapolation of the aircraft fluxes gives surface fluxes that are too low. With the 5 km cutoff filter used, the aircraft underestimate for sensible heat flux is about 40%, and for the latent heat flux about 30%. Part of the underestimation is attributable to long-wavelength contributions (longer than the 5 km filter), but more investigation is needed. 相似文献
18.
杜进 《高原山地气象研究》1999,19(2)
采用有关方法,分析了我市的光热水和土壤肥力等自然资源与冬小麦生产的关系,估算了气候土壤资源对作物具有的生产潜力,并阐明了影响潜在产量的主要自然因素,同时提出了相应的对策建议. 相似文献
19.
SSPs from an impact and adaptation perspective 总被引：1，自引：1，他引：0
The Shared Socioeconomic Pathways (SSPs) offer benefits for communities concerned with climate change adaptation research and actions (IAV), but some challenges need to be overcome in order to facilitate active IAV involvement in SSP use. This essay summarizes potential benefits, challenges, and possible strategies for enhancing the value of the SSP approach for IAV communities. 相似文献
20.
K.E. McConnell 《Climatic change》1997,37(1):121-139
This paper is concerned with nonmarket valuation in the context of global warming. First, concerning the impact of global warming: what are the prospects for the inclusion of nonmarket values in estimates of the damages of warming? The second question relates to the role of the Principles and Guidelines as the supporting document for water resource projects. Are tools for nonmarket valuation, as found in the Principles and Guidelines satisfactory for water resource project evaluation with a changing climate? The potential effects of climate change are so numerous and subtle that it would be prohibitively costly to measure them all. Thus a comprehensive program for including nonmarket damages as part of the costs of global warming seems ill-advised. Where specific concerns arise, researchers may learn from small scale studies. Many of the damages of global warming are diminished by the ability of humans to adapt at small costs, especially the nonuse component of nonmarket values. When the question concerns minor water resource projects, the gains from including extra effects induced by global warming seem to be small compared with the costs. The Principles and Guidelines does not reflect current practices in benefit estimation. However, it is not clear that this is a serious problem, because most practitioners continue to revise their understanding of valuation methods. If the Principles and Guidelines were to be revised, it would make sense to provide more current guidelines for all of the behavioral models and contingent valuation. Revisions of the Principles and Guidelines should not do anything special for anthropocentrically induced climate change. 相似文献