Modeling seasonal variations of subsurface chlorophyll maximum in South China Sea

In the South China Sea(SCS), the subsurface chlorophyll maximum(SCM) is frequently observed while the mechanisms of SCM occurrence have not been well understood. In this study, a 1-D physical-biochemical coupled model was used to study the seasonal variations of vertical profiles of chlorophyll-a(Chl-a) in the SCS. Three parameters(i.e., SCM layer(SCML) depth, thickness, and intensity) were defined to characterize the vertical distribution of Chl-a in SCML and were obtained by fitting the vertical profile of Chl-a in the subsurface layer using a Gaussian function. The seasonal variations of SCMs are reproduced reasonably well compared to the observations. The annual averages of SCML depth, thickness, and intensity are 75 ± 10 m, 31 ± 6.7 m, and 0.37 ± 0.11 mg m-3, respectively. A thick, close to surface SCML together with a higher intensity occurs during the northeastern monsoon. Both the SCML thickness and intensity are sensitive to the changes of surface wind speed in winter and summer, but the surface wind speed exerts a minor influence on the SCML depth; for example, double strengthening of the southwestern monsoon in summer can lead to the thickening of SCML by 46%, the intensity decreasing by 30%, and the shoaling by 6%. This is because part of nutrients are pumped from the upper nutricline to the surface mixed layer by strong vertical mixing. Increasing initial nutrient concentrations by two times will increase the intensity of SCML by over 80% in winter and spring. The sensitivity analysis indicates that light attenuation is critical to the three parameters of SCM. Decreasing background light attenuation by 20% extends the euphotic zone, makes SCML deeper(~20%) and thicker(12% – 41%), and increases the intensity by over 16%. Overall, the depth of SCML is mainly controlled by light attenuation, and the SCML thickness and intensity are closely associated with wind and initial nitrate concentration in the SCS.     

东海西部陆架海域水团的季节特征分析

On the basis of the CTD data and the modeling results in the winter and summer of 2009, the seasonal characteristics of the water masses in the western East China Sea shelf area were analyzed using a cluster analysis method. The results show that the distributions and temperature-salinity characteristics of the water masses in the study area are of distinct seasonal difference. In the western East China Sea shelf area, there are three water masses during winter, i.e., continental coastal water（CCW）, Taiwan Warm Current surface water（TWCSW） and Yellow Sea mixing water（YSMW）, but four ones during summer, i.e., the CCW, the TWCSW, Taiwan Warm Current deep water（TWCDW） and the YSMW. Of all, the CCW, the TWCSW and the TWCDW are all dominant water masses. The CCW, primarily characterized by a low salinity, has lower temperature, higher salinity and smaller spatial extent in winter than in summer. The TWCSW is warmer, fresher and smaller in summer than in winter, and it originates mostly from the Kuroshio surface water（KSW） northeast of Taiwan, China and less from the Taiwan Strait water during winter, but it consists of the strait water and the KSW during summer. The TWCDW is characterized by a low temperature and a high salinity, and originates completely in the Kuroshio subsurface water northeast of Taiwan.     

山东荣成天鹅湖大叶藻形态和生长的季节性变化研究

2012年8月至2013年7月,作者逐月对天鹅湖大叶藻(Zostera marina L.)的形态特征、植株密度、生物量和生产力进行了监测。结果表明,大叶藻周年株高最高值和最低值分别出现在7月和1月;叶鞘高度、叶鞘宽度和叶宽的最高值均出现在7月,叶鞘高度最低值出现在1月,叶鞘宽度和叶宽最低值均出现在2月;大叶藻顶枝、侧枝和花枝的周年密度最大值分别出现在6月、4月和5月,最小值分别出现在1月、8月和7月;单株生物量和地上部分生物量最大值均出现在7月,地下部分出现在10月,而单株生物量和地上部分生物量最小值均出现在1月,地下部分生物量最小值出现在3月;单株地上和地下生产力最大值均出现在6月,最小值则分别出现在1月和2月。分析显示,大叶藻在冬季由于水温较低导致生长缓慢,且植株较小,在春季随水温上升,生长开始加快。水温在夏初达到大叶藻的最适生长水温,大叶藻的生物量和初级生产力达到最高值,而夏末和初秋由于水温过高导致大叶藻个体生物量、密度和初级生产力开始降低。这种季节性变化与水温的季节性变化密切相关。     

Heat budget of the south-central equatorial Pacific in CMIP3 models

ABSTRACT Using data from 17 coupled models and nine sets of corresponding Atmospheric Model Intercomparison Project （AMIP） results, we investigated annual and seasonal variation biases in the upper 50 m of the south-central equatorial Pacific, with a focus on the double-ITCZ bias, and examined the causes for the amplitude biases by using heat budget analysis. The results showed that, in the research region, most of the models simulate SSTs that are higher than or similar to observed. The simulated seasonal phase is close to that observed, but the amplitudes of more than half of the model results are larger than or equal to observations. Heat budget analysis demonstrated that strong shortwave radiation in individual atmospheric models is the main factor that leads to high SST values and that weak southward cold advection is an important mechanism for maintaining a high SST. For seasonal circulation, large surface shortwave radiation amplitudes cause large SST amplitudes.     

Chinese Contribution to CMIP5：An Overview of Five Chinese Models’Performances

An overview of Chinese contribution to Coupled Model Intercomparison Project-Phase 5 （CMIP5） is presented. The performances of five Chinese Climate/Earth System Models that participated in the CMIP5 pro ject are assessed in the context of climate mean states, seasonal cycle, intraseasonal oscillation, interan-nual variability, interdecadal variability, global monsoon, Asian-Australian monsoon, 20th-century historical climate simulation, climate change pro jection, and climate sensitivity. Both the strengths and weaknesses of the models are evaluated. The models generally show reasonable performances in simulating sea surface tem-perature （SST） mean state, seasonal cycle, spatial patterns of Madden-Julian oscillation （MJO） amplitude and tropical cyclone Genesis Potential Index （GPI）, global monsoon precipitation pattern, El Ni-no-Southern Oscillation （ENSO）, and Pacific Decadal Oscillation （PDO） related SST anomalies. However, the perfor-mances of the models in simulating the time periods, amplitude, and phase locking of ENSO, PDO time periods, GPI magnitude, MJO propagation, magnitude of SST seasonal cycle, northwestern Pacific mon-soon and North American monsoon domains, as well as the skill of large-scale Asian monsoon precipitation need to be improved. The model performances in simulating the time evolution and spatial pattern of the 20th-century global warming and the future change under representative concentration pathways pro jection are compared to the multimodel ensemble of CMIP5 models. The model discrepancies in terms of climate sensitivity are also discussed.     

Quality assessment and hydrogeochemical characteristics of groundwater in Agastheeswaram taluk,Kanyakumari district,Tamil Nadu,India

The present study investigates the hydrogeochemical characteristics of groundwater quality in Agas- theeswaram taluk of Kanyakumari district, Tamil Nadu, India. A total of 69 groundwater samples were collected during pre- and post-monsoon periods of 2011-2012. The groundwater quality assessment has been carried out by evaluating the physicochemical parameters such as pH, EC, TDS, HCO3, Cl, SO42-, Ca2＋, Mg2＋, Na＋ and K＋ for both the seasons. Based on these parameters, groundwater has been assessed in favor of its suitability for drinking and irrigation purpose. Dominant cations for both the seasons are in the order of Na＋〉 Ca2＋〉 Mg2＋ 〉 K＋ while the dominant anions for post monsoon and pre monsoon have the trends of CI 〉 HCO3 〉 SO42- and HCO3- 〉 CI 〉 SO42-, respectively. Analytical results observed from various indices reveal that the groundwater quality is fairly good in some places. Analytical results of few samples show that they are severely polluted and incidentally found to be near the coasts, estuaries and salt pans in the study area. The Gibbs plot indicates that the majority of groundwater samples fall in rock dominant region, which indicates rock water interaction in the study area. The United States salinity （USSL） diagram shows that the groundwater is free from sodium hazards but the salinity hazard varies from low to very high throughout the study area. This reveals that the groundwater is moderately suitable for agricultural activities. The observed chemical variations in pre-monsoon and post-monsoon seasons may be the effect to rock-water interactions, ion-exchange reactions, and runoff of fertilizers from the surrounding agricultural lands.     

基于GEE和遥感大数据的1986—2015年全球城镇用地扩张占用水体时空特征

以全球年度城市动态数据（GAUD）和全球地表水动态数据集（GSW）为基础数据,利用Google Earth Engine（GEE）解析了1986—2015年全球城镇用地扩张占用永久性和季节性水体的时空分布特征。研究发现：30 a间全球城镇用地扩张直接占用水体的面积为1 033.2 km²,其中包括季节性水体711.7 km²和永久性水体321.5 km²,呈现先增加后降低的变化趋势。亚洲是城镇用地扩张占用水体面积最多的大洲,其次是北美洲和欧洲,占用水体的面积分别为799.4 km²、122.5 km²和61.1 km²。欧洲是唯一以占用永久性水体为主的大洲。陆地面积排名前十的国家中,中国、美国和印度是城镇用地扩张占用水体面积最多的国家,占用水体的面积分别为573.1 km²、109.6 km²和24 km²。以占用永久性水体为主的国家是俄罗斯和阿尔及利亚。尽管世界各国在水资源保护方面做出了巨大努力,但实现联合国可持续发展目标背景下,需防控更多的水体因城镇用地扩张而消失。     

沙丘形态及表沙粒度特征对风况和地表植被变化的响应

以毛乌素沙地3种沙丘（新月形沙丘、抛物线形沙丘和反向沙丘）为研究对象,对其形态、表沙粒度特征和区域风况进行了量化分析,探讨了沙丘表沙物理运动过程及其形态对外界条件（风况和地表植被）变化的反馈,揭示了沙丘表沙粒度特征对不同沙丘形态的响应机制。结果表明：新月形沙丘表沙平均粒径由迎风坡底部向顶部逐渐变小,分选呈现逐渐变好趋势, 但粒径较小和分选较差的表沙样出现在沙丘迎风坡中部。随着地表植被覆盖度的增加,新月形沙丘逐渐向抛物线形沙丘转变,近地表输沙能力和沙丘上风向沙源的供应同样受到限制,致使抛物线形沙丘由迎风坡底部向顶部呈现表沙平均粒径变大,而分选逐渐变好的趋势。毛乌素沙地内季节性风况（春季盛行强劲西北风,夏季盛行较弱东南风）的变化不仅促进了反向沙丘的发育,并且重组了西北盛行风影响下的表沙粒度特征。在夏季反向风风蚀的作用下,沙丘落沙坡顶部出现反向堆积和脊线反向移动的现象,同时其顶部呈现平均粒径由小变大、分选逐渐变好的趋势。     

1981—2018年内蒙古典型草原季节性冻土对气候变化的响应

以1981—2018年内蒙古典型草原季节性冻土为研究对象,通过气候倾向率、Mann-Kendall法、多元线性回归等方法,分析最大冻土时空分布特征、年际、年代际变化,研究影响最大冻土深度变化的气象因子。结果表明：（1） 内蒙古典型草原季节性冻土冻结初日在9—11月,终日在4—6月,年内最大冻土深度出现在2—3月,深度在100~280 cm之间。（2） 最大冻土深度年际变化分为下开口抛物线型、上开口抛物线型、正弦曲线型,从最大冻土深度气候倾向率看呈现减小趋势的站点有68%。（3） 最大冻土深度年代际变化分为逐年代递减、减-增型和无明显变化规律,50%的站点在1989年以后最大冻土深度发生突变。（4） 多元线性回归表明气温冻结指数、年平均风速、年极端最低气温对最大冻土深度产生显著影响。该研究揭示了最大冻土深度存在退化的事实,为草原应对气候变化提供指导,为陆地土壤和大气碳循环交换的研究给出提示。     

A GIS-based method for defining snow zones: application to the western United States

This study maps the geographic extent of intermittent and seasonal snow cover in the western United States using thresholds of 2000–2010 average snow persistence derived from moderate resolution imaging spectroradiometer snow cover area data from 1 January to 3 July. Results show seasonal snow covers 13% of the region, and intermittent snow covers 25%. The lower elevation boundaries of intermittent and seasonal snow zones increase from north-west to south-east. Intermittent snow is primarily found where average winter land surface temperatures are above freezing, whereas seasonal snow is primarily where winter temperatures are below freezing. However, temperatures at the boundary between intermittent and seasonal snow exhibit high regional variability, with average winter seasonal snow zone temperatures above freezing in west coast mountain ranges. Snow cover extent at peak accumulation is most variable at the upper elevations of the intermittent snow zone, highlighting the sensitivity of this snow zone boundary to climate conditions.