Seasonal climatology of cloud at resolute (75°N)     

A. Henderson‐Sellers  K. McGuffie  J.G. Cogley 《大气与海洋》2013,51(1):80-93

Abstract

An analysis of surface observations of cloud characteristics from a selected high‐latitude station, Resolute (N.W.T., Canada), is described. The data set has a high temporal resolution (1 h) and is extensive although here we report only on an analysis of 10 years: 1970–1979, inclusive. The pattern of cloudiness variations is more complex than previous studies of Arctic data have suggested. The predominant reported low‐level cloud type is stratocumulus, not stratus. The generally overcast summer conditions are found to extend over a considerable period when cloud cover is composed of several layers, often of types other than stratus. This observation of multilayering suggests that middle and high cloud layers may occur more frequently than they can be observed. Clearly a more accurate awareness of hidden cloud is important for improving solutions of the planetary radiation budget. The surface radiation budget is found to be strongly affected by the development of the summertime overcast but also exhibits features caused by the mid‐summer break‐up of the lower cloud layer.  相似文献   

Permafrost hydrology in North America 1     

Ming‐ko Woo 《大气与海洋》2013,51(3):201-234

Abstract

This paper reviews hydrologic processes in the permafrost regions of northern North America. Much work has recently been done at specific experimental plots to parallel the progress in laboratory investigations, improving our understanding of the heat and water fluxes in thawed and frozen grounds, infiltration in frozen soils, evaporation in a cold environment, interaction between snow and its frozen substrate, and the dynamics of storage in the active layer. Field research on permafrost slopes and in northern research basins adds to our knowledge of permafrost groundwater hydrology, runoff generating processes, river freeze‐up and breakup processes and allows more precise definition of basin water balance. Sufficient hydrometric data are now available to analyse the streamflow characteristics in an area with permafrost, and more work should be done along this line. It is urged that process studies be continued to gain a better understanding of the effect of permafrost upon the hydrologic cycle. Further research is needed to predict the impacts of human activities on the movement and redistribution of water.  相似文献   

Climate and climate change in western canada as simulated by the Canadian regional climate model     

Rene Laprise  Daniel Caya  Michel Giguere  Guy Bergeron  Hélène Côté  Jean‐Pierre Blanchet 《大气与海洋》2013,51(2):119-167

Abstract

A þrst climate simulation performed with the novel Canadian Regional Climate Model (CRCM) is presented. The CRCM is based on fully elastic non‐hydrostatic þeld equations, which are solved with an efþcient semi‐implicit semi‐Lagrangian (SISL) marching algorithm, and on the parametrization package of subgrid‐scale physical effects of the second‐generation Canadian Global Climate Model (GCMII). Two 5‐year integrations of the CRCM nested with GCMII simulated data as lateral boundary conditions are made for conditions corresponding to current and doubled CO₂ scenarios. For these simulations the CRCM used a grid size of 45 km on a polar‐stereographic projection, 20 scaled‐height levels and a time step of 15 min; the nesting GCMII has a spectral truncation of T32, 10 hybrid‐pressure levels and a time step of 20 min. These simulations serve to document: (1) the suitability of the SISL numerical scheme for regional climate modelling, (2) the use of GCMII physics at much higher resolution than in the nesting model, (3) the ability of the CRCM to add realistic regional‐scale climate information to global model simulations, and (4) the climate of the CRCM compared to that of GCMII under two greenhouse gases (GHG) scenarios.  相似文献   

Potential for small scale added value of RCM’s downscaled climate change signal   总被引：1，自引：1，他引：0  

Alejandro Di Luca  Ramón de Elía  René Laprise 《Climate Dynamics》2013,40(3-4):601-618

In recent decades, the need of future climate information at local scales have pushed the climate modelling community to perform increasingly higher resolution simulations and to develop alternative approaches to obtain fine-scale climatic information. In this article, various nested regional climate model (RCM) simulations have been used to try to identify regions across North America where high-resolution downscaling generates fine-scale details in the climate projection derived using the “delta method”. Two necessary conditions were identified for an RCM to produce added value (AV) over lower resolution atmosphere-ocean general circulation models in the fine-scale component of the climate change (CC) signal. First, the RCM-derived CC signal must contain some non-negligible fine-scale information—independently of the RCM ability to produce AV in the present climate. Second, the uncertainty related with the estimation of this fine-scale information should be relatively small compared with the information itself in order to suggest that RCMs are able to simulate robust fine-scale features in the CC signal. Clearly, considering necessary (but not sufficient) conditions means that we are studying the “potential” of RCMs to add value instead of the AV, which preempts and avoids any discussion of the actual skill and hence the need for hindcast comparisons. The analysis concentrates on the CC signal obtained from the seasonal-averaged temperature and precipitation fields and shows that the fine-scale variability of the CC signal is generally small compared to its large-scale component, suggesting that little AV can be expected for the time-averaged fields. For the temperature variable, the largest potential for fine-scale added value appears in coastal regions mainly related with differential warming in land and oceanic surfaces. Fine-scale features can account for nearly 60 % of the total CC signal in some coastal regions although for most regions the fine scale contributions to the total CC signal are of around ～5 %. For the precipitation variable, fine scales contribute to a change of generally less than 15 % of the seasonal-averaged precipitation in present climate with a continental North American average of ～5 % in both summer and winter seasons. In the case of precipitation, uncertainty due to sampling issues may further dilute the information present in the downscaled fine scales. These results suggest that users of RCM simulations for climate change studies in a delta method framework have little high-resolution information to gain from RCMs at least if they limit themselves to the study of first-order statistical moments. Other possible benefits arising from the use of RCMs—such as in the large scale of the downscaled fields– were not explored in this research.  相似文献   

Nonparametric analysis of high wind speed data     

Mario Francisco-Fernández  Alejandro Quintela-del-Río 《Climate Dynamics》2013,40(1-2):429-441

In this paper, nonparametric curve estimation methods are applied to analyze time series of wind speeds, focusing on the extreme events exceeding a chosen threshold. Classical parametric statistical approaches in this context consist in fitting a generalized Pareto distribution (GPD) to the tail of the empirical cumulative distribution, using maximum likelihood or the method of the moments to estimate the parameters of this distribution. Additionally, confidence intervals are usually computed to assess the uncertainty of the estimates. Nonparametric methods to estimate directly some quantities of interest, such as the probability of exceedance, the quantiles or return levels, or the return periods, are proposed. Moreover, bootstrap techniques are used to develop pointwise and simultaneous confidence intervals for these functions. The proposed models are applied to wind speed data in the Gulf Coast of US, comparing the results with those using the GPD approach, by means of a split-sample test. Results show that nonparametric methods are competitive with respect to the standard GPD approximations. The study is completed generating synthetic data sets and comparing the behavior of the parametric and the nonparametric estimates in this framework.  相似文献   

Real-time multi-model decadal climate predictions   总被引：1，自引：1，他引：0  

Doug M. Smith  Adam A. Scaife  George J. Boer  Mihaela Caian  Francisco J. Doblas-Reyes  Virginie Guemas  Ed Hawkins  Wilco Hazeleger  Leon Hermanson  Chun Kit Ho  Masayoshi Ishii  Viatcheslav Kharin  Masahide Kimoto  Ben Kirtman  Judith Lean  Daniela Matei  William J. Merryfield  Wolfgang A. Müller  Holger Pohlmann  Anthony Rosati  Bert Wouters  Klaus Wyser 《Climate Dynamics》2013,41(11-12):2875-2888

We present the first climate prediction of the coming decade made with multiple models, initialized with prior observations. This prediction accrues from an international activity to exchange decadal predictions in near real-time, in order to assess differences and similarities, provide a consensus view to prevent over-confidence in forecasts from any single model, and establish current collective capability. We stress that the forecast is experimental, since the skill of the multi-model system is as yet unknown. Nevertheless, the forecast systems used here are based on models that have undergone rigorous evaluation and individually have been evaluated for forecast skill. Moreover, it is important to publish forecasts to enable open evaluation, and to provide a focus on climate change in the coming decade. Initialized forecasts of the year 2011 agree well with observations, with a pattern correlation of 0.62 compared to 0.31 for uninitialized projections. In particular, the forecast correctly predicted La Niña in the Pacific, and warm conditions in the north Atlantic and USA. A similar pattern is predicted for 2012 but with a weaker La Niña. Indices of Atlantic multi-decadal variability and Pacific decadal variability show no signal beyond climatology after 2015, while temperature in the Niño3 region is predicted to warm slightly by about 0.5 °C over the coming decade. However, uncertainties are large for individual years and initialization has little impact beyond the first 4 years in most regions. Relative to uninitialized forecasts, initialized forecasts are significantly warmer in the north Atlantic sub-polar gyre and cooler in the north Pacific throughout the decade. They are also significantly cooler in the global average and over most land and ocean regions out to several years ahead. However, in the absence of volcanic eruptions, global temperature is predicted to continue to rise, with each year from 2013 onwards having a 50 % chance of exceeding the current observed record. Verification of these forecasts will provide an important opportunity to test the performance of models and our understanding and knowledge of the drivers of climate change.  相似文献   

组合压气机中尾迹与势流同频/异频干涉的叠加特性     

赵奔  杨策  老大中  张卫正 《贵州气象》2013,(4):477-485

为揭示多级压气机中上下游叶轮对中间叶片叠加气动影响特性,阐述不同叠加干涉情况下下游叶轮进气角度变化,采用数值方法模拟了一级轴流和一级离心组成的组合压气机非定常流场。详细讨论了上游动叶尾迹和下游动叶势流对中间导流叶栅段气流非定常流动的异频和同频叠加干涉特性,依据计算结果,直观地展示了静叶通道中两种干涉间相互激励和抑制作用的位置和时间,与数学公式的推导结果相互印证。研究结果表明:当上下游动叶对中间静叶段异频干涉时,干涉的激励、抑制区域的轴向位置随时间发生变化;当上下游动叶对中间静叶干涉频率相同时,干涉的相互激励、抑制区域的轴向位置不随时间发生变化,但干涉的激励、抑制区域的轴向位置受时序位置影响。另外,上游动叶尾迹与下游离心叶轮势流的不同叠加情况,决定着下游离心叶轮进口相对气流角的大小及波动幅值。   相似文献   

Fine-Scale Characteristics of Temperature, Wind, and Turbulence in the Lower Atmosphere (0–1,300 m) Over the South Peruvian Coast     

Ben B. Balsley  Dale A. Lawrence  Ronald F. Woodman  David C. Fritts 《Boundary-Layer Meteorology》2013,147(1):165-178

We report results of preliminary high-resolution in situ atmospheric measurements through the boundary layer and lower atmosphere over the southern coast of Perú. This region of the coast is of particular interest because it lies adjacent to the northern coastal edge of the sub-tropical south-eastern Pacific, a very large area of ocean having a persistent stratus deck located just below the marine boundary layer (MBL) inversion. Typically, the boundary layer in this region during winter is topped by a quasi-permanent, well-defined, and very large temperature gradient. The data presented herein examine fine-scale details of the coastal atmosphere at a point where the edge of this MBL extends over the coastline as a result of persistent onshore flow. Atmospheric data were gathered using a recently-developed in-house constructed, GPS-controlled, micro-autonomous-vehicle aircraft (the DataHawk). Measured quantities include high-resolution profiles of temperature, wind, and turbulence structure from the surface to 1,300 m.  相似文献   

The droughts of 1997 and 2005 in Amazonia: floodplain hydrology and its potential ecological and human impacts     

Javier Tomasella  Patrícia F. Pinho  Laura S. Borma  José A. Marengo  Carlos A. Nobre  Olga R. F. O. Bittencourt  Maria C. R. Prado  Daniel A. Rodriguez  Luz A. Cuartas 《Climatic change》2013,116(3-4):723-746

It is well known that most of the severe droughts in Amazonia, such as that of 1997, are El Niño-related. However, in 2005, the Amazon was affected by a severe drought that was not El Niño-related, as most of the rainfall anomalies that have happened in southwestern Amazonia are driven by sea surface temperature anomalies in the tropical North Atlantic. Earlier studies have analyzed both droughts in terms of their meteorological causes and impacts in terra firme (non-flooded) forests. This study compares the hydrological effects of both droughts on the Amazonian floodplain and discusses their potential ecological and human impacts based on an extensive literature review. The results revealed that the effects of the 2005 drought were exacerbated because rainfall was lower and evaporation rates were higher at the peak of the dry season compared to the 1997 drought. This induced a more acute depletion of water levels in floodplain lakes and was most likely associated with higher fish mortality rates. Based on the fact that the stem growth of many floodplain species is related to the length of the non-flooded period, it is hypothesized that the 1997 drought had more positive effects on floodplain forest growth than the 2005 drought. The fishing community of Silves in central Amazonia considered both droughts to have been equally severe. However, the 2005 drought was widely broadcasted by the press; therefore, the governmental mitigation efforts were more comprehensive. It is suggested that the availability of new communication technology and greater public awareness regarding environmental issues, combined with the new legal framework for assessing the severity of calamities in Brazil, are among the primary factors that explain the difference in societal response between the two droughts.  相似文献   

Climate change impacts on invasive potential of pink hibiscus mealybug, Maconellicoccus hirsutus (Green), in Chile     

Valentina Jara  Francisco J. Meza  Tania Zaviezo  Rodrigo Chorbadjian 《Climatic change》2013,117(1-2):305-317

Maconellicoccus hirsutus (Green) (Hemiptera:Pseudoccidae) is an important pest in many countries being responsible for considerable economic loses. Although it is not currently present in Chile, the chance that it could be accidentally introduced rises with the list of infested countries increasing over the last years. In addition, climate change projections indicate that a larger region would fit as potential habitat for this pest, allowing it to persist over time and colonize a larger proportion of the Chilean territory. In this study the geographic distribution and the number of generations this mealybug would develop in Chile were determined, under current temperatures and under two projected climatic scenarios. Cumulative degree days were calculated for current and future scenarios using a lower temperature threshold of 14.5 °C, with 624.5 degree-days as the thermal requirement for the species to complete one generation. The results show that under current climate conditions M. hirsutus could develop up to three generations in the north of the country (i.e. 18° South) and one generation in the region near 37° South. Under future scenarios’ conditions the pest could develop up to five generations in the north, and one generation around the 42° South. Present climate conditions in Chile would allow the establishment of the pink hibiscus mealybug, if the pest enters the country. Climate change conditions would allow the potentially invaded area to expand south, and would promote the development of more generations per year of the mealybug in the studied territory.  相似文献