Tidal effects on phytoplankton assemblages in a near‐pristine estuary: a trait‐based approach for the case of a shallow tropical ecosystem in Brazil

The study of near‐pristine estuaries can be used as a tool for mitigation projects of harmful effects in anthropogenic eutrophic systems, since one can analyze the effect of temporal and spatial variations generated mainly by natural forces. Phytoplankton taxonomy has been used as a classical indicator to assess changes in transitional water communities, however alternative methods based on morphological, behavioral and physiological traits offer the opportunity to compare sites or moments with different taxonomic compositions. Our goal, in this context, is to evaluate phytoplankton community short‐term and seasonal variability in a near‐pristine estuary, Barra Grande estuary (Ilha Grande, RJ, Brazil), through species functional traits and thus community functional diversity. Samplings were carried out in a mooring in complete tidal cycles, seasonally during 2012. Our results showed a diverse phytoplankton community with 38 frequent and abundant taxa, marked by density variation (1.2 × 10.4–2 × 10.7 cell L^?1) in depth, with abundance inversely related to tidal currents. The functional structure of the phytoplankton community measured by functional diversity (FD), varied seasonally in and across a gradient of tidal energy. A core community, mainly represented by flagellates and dinoflagellates, occurred in all observations and was highly functional (high FD), exploiting a variety of habitats. The chain‐forming diatoms were associated with high tidal energy, and occurred in higher densities during summer. Phytoplankton cell size, cell shape, and the ability to form colonies are extremely plastic traits that can be regulated by the environment, however, isolated tychopelagic diatoms were present in the study area across all seasons, with higher contributions in autumn and winter, reflecting the shallow characteristic of this system. During the winter, an exposed sandbar was formed, and the lack of connection with the ocean resulted in an abundance of riverine and brackish water taxa. In this near‐pristine estuary the densities and occurrences of HAB phytoplankton are low. Trait‐based analyses add information about community structure, which can be impacted by anthropogenic actions in urbanized coastal systems. Thus the information provided by this study regarding phytoplankton functional diversity and its relation to nutrients and hydrography in Barra Grande Estuary can be applied as a baseline model for the development of public policies.     

我国南极科考站附近气旋的特征分析

本文基于欧洲中心的ERA-Interim再分析数据,采用雷丁大学的气旋自动识别与追踪算法,建立了1979-2013年中国南极科学考察站长城站、中山站以及泰山站划定的统计区域内气旋数据集。基于这套数据,分析了3个站区附近气旋的气候特征,包括:气旋数量、空间分布、强度、加深率等,并研究了达到爆发性发展的气旋的时空特征。分析表明,长城站以及中山站气旋数量均有增加趋势,但都未达到显著水平;泰山站气旋数量的减少趋势达到显著性水平。3个站区的气旋统计表明,长城站统计区域内气旋活动最频繁,且爆发性气旋活动相对较多;中山站、长城站气旋的数量和空间分布具有季节变化,气旋数量夏季较其他3个季节偏少、偏弱;泰山站气旋活动最少,并且大部分影响到该站的气旋都处于消亡阶段,气旋的强度较弱,故气旋活动对该站的影响较弱。     

热带气旋温湿非对称结构的比较研究

利用NCEP的CFSR 0.5 °再分析资料和日本东京台风中心的最佳路径集,对西北太平洋和南海海域1979—2010年间的热带气旋温湿水平非对称和垂直非均匀结构等进行了合成和对比分析。(1) 热带气旋流场的非对称随着气旋增强逐渐趋于轴对称化,而外包区及外围区比湿场的非对称性逐渐增强。(2) 热带气旋普遍具有“双暖心”的垂直非均匀分布结构特征;弱热带气旋的低层暖心相对较强而TY及以上强度的热带气旋高层暖心相对较强。(3) “暖心”的水平范围和形态随气旋的增强而扩大并更趋于轴对称,200 hPa高度场上较弱的热带气旋暖心附近为弱高压中心、较强热带气旋暖心附近为一低压中心。(4) 热带气旋的“湿心”主要位于700～850 hPa的低层,湿心强度随着气旋强度等级增加而增强,0.8 g/kg的比湿距平范围随TC强度增强而不断向高层延伸。(5) 气旋不同区域的各个层次假相当位温随气旋增强而增加,且各个强度级别的气旋不同区域增温速率均为内核区最大、外包区次之和外围区最小。      

2012-2013年中国西南地区秋、冬、春季持续干旱的成因

利用多种资料从大尺度大气环流、水汽输送、热带海表温度、北极涛动、平流层极涡等方面分析了2012-2013年中国西南地区秋、冬、春季持续干旱的成因。结果表明, 西南水汽输送偏弱、高纬度地区南下冷空气路径偏东、冷暖空气难以在西南地区上空交汇, 是此次持续干旱的直接原因。这段时间西南地区大都受平直西风气流控制, 孟加拉湾和中南半岛地区位势高度较常年偏高, 不利于这些地区气旋性环流的发展;热带海表温度异常变化,特别是冬春季印度洋海表温度的持续偏高, 使得菲律宾地区上空低层反气旋异常环流增强。这些都导致了西南向水汽输送偏弱。此外, 北极涛动异常变化对西南地区的干旱也有重要影响, 北极涛动持续处于负位相, 不仅使南支槽减弱变浅, 西南水汽输送减少, 还导致贝加尔湖高压脊偏弱, 使北方南下冷空气主体偏东。冬季平流层极涡强度的变化在各个高度的位势高度场和位势涡度场上都有体现, 其变化对冷空气的强度及路径有明显影响。     

Radar-based Characteristics and Formation Environment of Supercells in the Landfalling Typhoon Mujigae in 2015

This study presents the radar-based characteristics and formation environment of supercells spawned by the tornadic landfalling Typhoon Mujigae(2015)in October 2015.More than 100 supercells were identified within a 24-hour period around the time of the typhoon’s landfall,of which three were tornadic with a rotational intensity clearly stronger than those of non-tornadic supercells.The identified supercells were concentrated within a relatively small area in the northeast quadrant beyond 140 km from the typhoon center.These supercells were found more likely to form over flat topography and were difficult to maintain in mountainous regions.During the study period,more supercells formed offshore than onshore.The mesocyclones of the identified supercells were characterized by a small diameter generally less than 5 km and a shallow depth generally less than 4 km above ground level.An environmental analysis revealed that the northeast quadrant had the most favorable conditions for the genesis of supercell in this typhoon case.The nondimensional supercell composite parameter(SCP)and entraining-SCP(E-SCP)were effective in separating supercell from non-supercell environment.Even though the atmosphere in the typhoon’s northeast quadrant was characterized by an E-SCP/SCP value supportive of supercell organization,orography was an impeditive factor for the supercell development.These findings support the use of traditional parameters obtained from midlatitude supercells to assess the supercell potential in a tropical cyclone envelope.     

Tropical cyclone risk perceptions in Darwin,Australia: a comparison of different residential groups

Different individuals and groups perceive risk differently. This can significantly affect risk management and mitigation practices and requirements. This paper presents findings from a study of tropical cyclone risk perceptions in the city of Darwin in the Northern Territory of Australia. Primary in-depth interview data and other secondary data are analysed, focussing in particular on wind damage, storm surge and life safety risk perceptions of residents since Cyclone Tracy, which impacted in 1974, and perceptions of future climate change as it relates to tropical cyclone risk. The analysis reveals that a number of perceptions prevail. In particular, the study reveals a wide difference of perceptions between short-term residents (Group 1) and long-term and expert residents (Group 2) in relation to wind damage, storm surge and life safety risk. It also reveals a large division between laypersons (Group 3) and expert residents’ (Group 4) perceptions of climate change risk as it relates to tropical cyclone risk. The author recommends that flexible, multiple and integrative management and mitigation approaches are required to deal with such different perceptions and divisions in the resident population.     

Analysis of cyclogenesis parameter for developing and nondeveloping low-pressure systems over the Indian Sea

A cyclone genesis parameter, termed the genesis potential parameter (GPP), for the Indian Sea is proposed. The parameter is defined as the product of four variables, namely vorticity at 850 hPa, middle tropospheric relative humidity, middle tropospheric instability, and the inverse of vertical wind shear. The variables are calculated using the National Centers for Environmental Prediction (NCEP), USA, reanalysis data, averaged within a circle of 2.5° radius around the centre of cyclonic system. The parameter is tested with a sample dataset of 35 nondeveloping and developing low-pressure systems that formed over the Indian Sea during the period 1995–2005. The result shows that there is a distinction between GPP values for nondeveloping and developing systems in more than 85% cases. The composite GPP value is found to be around three to five times greater for developing systems than for nondeveloping systems. The analysis of the parameter at early development stage of a cyclonic storm appears to provide a useful predictive signal for intensification of the system.     

末次盛冰期太平洋赤道辐合带对暖池外热带海表温度变化的敏感性

利用美国NCAR CAM3大气环流模式,分析了末次盛冰期（LGM）两个不同的热带海表温度重建方案中,北半球冬季热带中、西太平洋对流活动及大气环流对暖池外（赤道东太平洋和热带大西洋）热带SST异常的敏感性。结果表明：  1）SST异常首先引起大气环流的改变。  赤道东太平洋对流层下沉增强,而作为经向补偿,副热带东太平洋上升运动增强,其中南半球尤为明显,同时南半球热带中、西太平洋上升运动增强,加剧了该区纬向逆时针环流,说明冰期热带海气耦合过程受气候背景场（如SST）影响很大;   2）大气环流格局改变引起热带中西太平洋的大气加热、对流活动、表层风场及降雨的巨大变化。  140°E以西的婆罗洲和菲律宾区域,总的大气加热减少是由于对流与辐射加热减少所致,对应于该区风场辐散和降雨减少;   而140°E以东的南半球热带中、西太平洋,大气吸收热量增加,对流与辐射加热均增强,总降雨量也随之增加,反映该区赤道辐合带南移并增强。该项研究为探索热带太平洋在冰期/间冰期旋回中的古海洋学变化提供了新的数据支撑。此外,不同重建SST对赤道辐合带的影响比较大,因此利用重建SST进行数值模拟或者利用耦合模式研究LGM热带海气相互作用时,应该十分重视全球热带SST分布特征。     

热带森林植被生物量遥感估算探讨

该文以我国云南省西双版纳的热带森林植被为例,对热带森林植被生物量的遥感地学估算进行初步探讨。研究表明,只用LANDSAT TM的波段数据建立生物量的回归估算模型时,其模型的复相关系数只有0．118,而利用其主成分或植被指数建立回归估算模型时,其模型的复相关系数不仅没有提高,反而在一定程度上有所降低。原始波段与其主成分结合能提高估算模型的复相关系数,其效果比原始波段与植被指数结合的效果要好。模型中如果考虑气象因子中的年平均降雨量,能在很大程度上提高其复相关系数。在此基础上引入地形因子,未能显著提高模型的复相关系数。有气象因子参与建立的遥感气象模型和遥感地学模型在0．01水平上回归显著。     

Tracking surface cyclones with moist potential vorticity

1. Introduction There have been two di?erent approaches used fortracking extratropical cyclones. The traditional andmost common approach is to follow the minimum sur-face pressure of a cyclone (e.g., Petterssen, 1956; Car-nell and Senior, 1998; Serreze…