Heat tracing of heterogeneous hyporheic exchange adjacent to in‐stream geomorphic features

There are many field techniques used to quantify rates of hyporheic exchange, which can vary in magnitude and direction spatially over distances of only a few metres, both within and between morphological features. We used in‐stream mini‐piezometers and heat transport modelling of stream and streambed temperatures to quantify the rates and directions of water flux across the streambed interface upstream and downstream of three types of in‐stream geomorphic features: a permanent dam, a beaver dam remnant and a stream meander. We derived hyporheic flux estimates at three different depths at six different sites for a month and then paired those flux rates with measurements of gradient to derive hydraulic conductivity (K) of the streambed sediments. Heat transport modelling provided consistent daily flux estimates that were in agreement directionally with hydraulic gradient measurements and also identified vertical heterogeneities in hydraulic conductivity that led to variable hyporheic exchange. Streambed K varied over an order of magnitude (1·9 × 10^?6 to 5·7 × 10^?5 m/s). Average rates of hyporheic flux ranged from static (q < ±0·02 m/day) to 0·42 m/day. Heat transport modelling results suggest three kinds of flow around the dams and the meander. Copyright © 2010 John Wiley & Sons, Ltd.     

Variations of crop coefficient and its influencing factors in an arid advective cropland of northwest China

Understanding the variation and magnitude of crop coefficient (K_c) is important for accurate determination of crop evapotranspiration and water use. In this study, we calculated K_c in an irrigated maize field with ground mulching by eddy covariance evapotranspiration measurements during the whole growing periods in 2009 and 2010 in an arid region of northwest China. A semi‐empirical practical approach for estimating K_c was proposed by introducing the dynamic fraction of canopy cover and incorporating the effect of leaf senescence as a function of days after sowing. The contribution of arid advection of sensible heat resulting from irrigation to K_c and the response of K_c to canopy conductance (G_c) were investigated. The averaged values of daily K_c were lower than typical values obtained previously without mulching due to decreasing effect of mulching on K_c, with 0.82 and 0.80 for the 2 years, respectively. The maximum average K_c occurred at the heading stage, with 1.21 and 1.04 for the 2 years, respectively. The difference of K_c was attributed to the difference of leaf area index. The semi‐empirical practical approach could well estimate the variations of K_c, thus could be a robust and useful tool for the practical users and water managers. The contributions to daily K_c from the arid advection were 4.4–28.0% of the measured K_c. The G_c had stronger control on daily K_c at the early and later stages than at the middle stage. When G_c, leaf area index and relative soil extractable water were lower than the respective threshold values of 20 mm s^?1, 3.0 m² m^?2 and 0.5, the daily K_c increased significantly with the increase of the three factors, and almost remained constant when the three factors were beyond the threshold values. These results are helpful for quantifying contributions of individual factors to K_c, and subsequently improving water management practices according to K_c. Copyright © 2014 John Wiley & Sons, Ltd.     

Development mechanisms of an explosive cyclone over East Sea on 3–4 April 2012

The development mechanisms of the explosive cyclone that occurred during 3–4 April 2012 over East Sea (Sea of Japan) are examined through numerical simulation and sensitivity experiments using the Weather and Research Forecasting (WRF) model. The characteristics of this explosive cyclone are different from typical cyclonic features observed in this region, including its intensity, deepening rate, and formation time. Numerical simulation, reanalysis data, upper and surface weather charts, and satellite data indicate that the strong baroclinic instability and temperature advection associated with upper-level cut-off low and the interaction of potential vorticity (PV) anomalies between the lower- and upper-level are essential to explosive cyclogenesis.The sensitivity experiments of the explosive cyclone show that latent heat release (LHR) is an important factor in explosive cyclogenesis. The intensification, extent, and movement speed of the cyclone are amplified by LHR as well as the formation of an upper-level cut-off low. The role of LHR is primary important in the generation and evolution of the cyclone. Especially, the LHR contributes to roughly 50% of decrease in sea level pressure (SLP) and 50% of the central cyclone’s low-level PV generation in initial stage. During a 48-h simulation, the contributions of the LHR, surface heat flux, and their interaction on the decrease of SLP of the cyclone are found to be 40.6, −8.2, and 10.5%, respectively. These results reveal that the explosive cyclone has larger deepening rates than OJ cyclones, and develops with a large amount of LHR near the cyclone center.     

青藏高原热力强迫对中国东部降水和水汽输送的调制作用

从4个方面综述了有关青藏高原大地形热力“驱动”对中国东部雨带和水汽输送特征及其年代际变化的影响作用的研究进展:(1)中国三阶梯大地形热力过程变化与季风雨带季节演进;(2) 青藏高原地-气过程热力“驱动”及其季风水汽输送结构;(3) 青藏高原积雪冷源对中国东部水汽输送结构及其雨带分布的影响;(4) 青藏高原视热源变化与雨带年代际变化相关特征及其可能调制。其主要研究结论是:(1)中国西部高原特殊三阶梯大地形结构强化了海-陆热力差异,尤其是高原大地形使地-气热力差异季节变化有由青藏高原向东北方向大地形区域延伸变化趋势,且其与季风雨带由东南沿海移向西北朝青藏高原与黄土高原边缘同步演进,两者似乎存在类似季节内演进的一种“动态的吸引”。(2)中国东部雨带时空变化特征和季风强弱变化趋势均与青藏高原热源强弱异常变化相对应。青藏高原热源异常影响低纬度海洋向陆地的水汽传输路径和强度,进而调制中国东部降水时空演变。在青藏高原热源强和弱年,中国降水变率空间分布特征分别为“北涝南旱”和“南涝北旱”。青藏高原视热源强(弱)异常变化“强信号”将对东亚与南亚区域的季风水汽输送结构,以及夏季风降水时空分布的变异具有“前兆性”的指示意义。(3)长江中下游地区作为独特南北两支水汽流的汇合带,该地区夏季青藏高原热源与水汽通量相关矢特征呈类似于青藏高原多雪与少雪年水汽通量偏差场中水汽汇合区显著特征差异,揭示了冬季青藏高原积雪冷源影响中国东部夏季长江流域梅雨水汽输送结构特征。(4)中国降水的年代际变化基本型态为中国东部呈“南涝北旱趋势”,西北区域呈现出“西部转湿趋势”。但基于近10年青藏高原春季视热源出现“降后回升”趋势,中国东部“南涝北旱”的降水格局已出现转折趋势。     

Evaluation of CMIP5 Climate Models in Simulating 1979–2005 Oceanic Latent Heat Flux over the Pacific

The climatological mean state,seasonal variation and long-term upward trend of 1979–2005 latent heat flux(LHF) in historical runs of 14 coupled general circulation models from CMIP5(Coupled Model Intercomparison Project Phase 5) are evaluated against OAFlux(Objectively Analyzed air–sea Fluxes) data. Inter-model diversity of these models in simulating the annual mean climatological LHF is discussed. Results show that the models can capture the climatological LHF fairly well,but the amplitudes are generally overestimated. Model-simulated seasonal variations of LHF match well with observations with overestimated amplitudes. The possible origins of these biases are wind speed biases in the CMIP5 models. Inter-model diversity analysis shows that the overall stronger or weaker LHF over the tropical and subtropical Pacific region,and the meridional variability of LHF,are the two most notable diversities of the CMIP5 models. Regression analysis indicates that the inter-model diversity may come from the diversity of simulated SST and near-surface atmospheric specific humidity.Comparing the observed long-term upward trend,the trends of LHF and wind speed are largely underestimated,while trends of SST and air specific humidity are grossly overestimated,which may be the origins of the model biases in reproducing the trend of LHF.     

中国海及邻区盆地现今地温场特征及其影响因素

现今地温场是构造活动、岩石圈热状态的综合反应,对研究盆地的区域构造演化、深部岩石圈结构和评估油气潜力具有重要意义。地温梯度和大地热流是表征沉积盆地热状况的两个基本参数。虽然我国大陆地区地热数据较丰富,并已经过四次系统汇编,但中国海及邻区盆地地热数据报道较少,且未经过系统整理。本文基于近年来新增的钻井温度数据,新增计算研究区810个地温梯度数据,并收集了国内外数据库、期刊的地热数据,在此基础上,首次系统整理了中国海及邻区盆地地温梯度数据和大地热流数据,绘制了其等值线图,分析了研究区现今地温场特征并讨论了其影响因素。研究结果表明,中国海及邻区盆地平均地温梯度43.2±25.7℃/km,平均大地热流74.4±26.6 mW/m²,多数盆地平均大地热流高于65 mW/m²,属于“热盆”;地温场分布总体呈现较为明显的“两带性”,其中近岸带较冷,远岸带较热;研究区现今地温场特征直接或间接地受控于其所处的构造环境,整体上是太平洋板块等多板块作用下岩石圈伸展减薄的结果,局部地区的热异常可能与断裂活动、岩浆活动、泥-热流底辟活动等因素有关。     

淮北煤田现今地温场特征及大地热流分布

淮北煤田的高温热害问题愈发突出,但目前对该区系统的地温场特征及大地热流分布研究非常稀少.在系统分析淮北煤田大量地面钻孔井温测井数据和井下巷道围岩温度测试数据的基础上,结合72块岩石样品的热导率测试结果,全面阐述了该区现今地温梯度和大地热流的分布特征.研究表明:淮北煤田现今地温梯度众值介于1.80~2.80 ℃/100 m之间,平均地温梯度为2.42 ℃/100 m;大地热流值变化范围为39.52~74.12 mW/m2,平均热流值为55.72 mW/m2,地温梯度和热流值均低于同处华北板块的其他盆地以及南部的淮南煤田;大地热流受地温梯度控制明显,两者分布较为相似,整体表现为南高北低、西高东低的特点.结果表明,区内现今地温场和热流分布主要受区域地质背景和区内构造格局的控制.      

凌汛期槽蓄水增量过程模拟

为研究凌汛期槽蓄水增量来源,在分析实测冰情资料基础上,把槽蓄水增量分为水位壅高主河道蓄水量增大、主河道内河水转化为固体冰盖和上滩水形成冰盖及在冰下聚集等3部分,建立河冰动力学模型,模拟河冰生消及槽蓄水增量过程,利用2008/2009年度三湖河口—头道拐河段实测冰情资料对模型进行了验证,表明滩地冰盖及冰盖下滞洪是内蒙古河段槽蓄水增量的主要来源,占最大槽蓄水增量的63.44%,主河道水位壅高引起的槽蓄水增量占26.56%,主槽冰盖蓄水占10.0%。     

西南喀斯特地区地表水热过程研究进展与展望

西南喀斯特地区水文二元结构以及生境条件的异质性导致地表水热过程异常复杂。水热过程机理研究薄弱,已经成为生态系统退化关键过程识别、生态恢复重建推进的关键限制因素。首先从野外科学实验、陆面过程参数化、遥感反演技术3个方面简要论述了地表水热过程的研究方法,指出在喀斯特地区,目前亟需开展的工作是在样地和坡面尺度上对地表水热过程进行系统的观测和实验,以深化水热过程机理研究,并发展适用于喀斯特地区的陆面过程模式和遥感反演模型。进而评述西南喀斯特地区地表水热过程已有研究进展与存在问题:水分循环研究的重视,但在特殊的地质背景与复杂的生境条件下,土壤水分时空异质性及降雨入渗产流和土壤侵蚀过程的机理仍不明晰,而且水热耦合研究非常缺失。最后从地表水热过程机理、水热过程变化影响机制、生态系统恢复重建水热调控等方面展望了其未来发展趋势。     

淮南煤田现今地温场特征

在系统分析淮南煤田大量地面钻孔井温测井数据和井下巷道围岩温度测试数据的基础上,结合58块岩石样品的热导率测试结果,全面阐述了该区现今地温梯度和大地热流的分布特征。研究表明,淮南煤田现今地温梯度的众值介于2.50~3.50℃/hm之间,平均地温梯度为2.9℃/hm;大地热流值变化范围为31.87~83.9 m W/m2,平均热流值为63.69 m W/m2,地温梯度和热流值区均高于淮北煤田;大地热流受地温梯度控制明显,其变化特征和地温梯度分布较为相似,整体表现为中东部高,西部其次,东南部最小的特征。分析揭示,区内现今地温场和热流分布主要受区域地质背景和区内构造格局的控制。