THE IMPACTS OF INTERACTION OF A TYPHOON WITH THE MIDLATITUDE TROUGH ON ITS TRACK AFTER THE RECURVATURE

Three typhoon cases are selected to conduct a series of simulations that are initialized from sequential analyses. The results show that the forecast error in crucial area where a tropical cyclone (TC) interactes with the upstream trough is highly correlated to the track forecast error after the TC recurvature. Furthermore, sensitivity experiments confirm that the developments of the midlatitude downstream circulations and then the TC track after its recurvature are highly sensitive to the TC intensity and its location relative to the upstream trough, which can give an example or one way of sensitivity of the TC track to the TC-trough interaction. If the TC interacts with the upstream trough more strongly (e.g., the TC being intensified or getting closer to the upstream trough), the downstream circulations will be more meridional, thus the TC track will be more northerly and westerly; otherwise, the downstream circulations will be more zonal, and the TC track will be more southerly and easterly.     

Propagation and influence on tropical precipitation of intraseasonal variation over mid-latitude East Asia in boreal winter

本文研究冬季东亚中纬度地区9–29天季节内变化的传播特征和其对热带降水的影响。分析发现风场的季节内信号既可以向东传播,也可以向南传播。向东传播时,风场的季节内信号主要限于中纬度地区,表现为气旋和反气旋的向东移动。向南传播时,源于中纬度的经向风扰动可以深入到低纬度地区,甚至到达赤道附近。伴随的辐合辐散引起赤道附近地区降水异常,形成南海南部和中国东部-日本之间一个南北向偶极型降水异常。一个异常经向翻转环流在连接热带和中纬度季节内风场和降水变化中起着重要作用。     

Early Holocene climate change and human occupation along the semiarid coast of north‐central Chile

The brief, terminal Pleistocene archaeological site at Santa Julia (SJ, 31° 50′ S; 71° 45′ W) is the only one with fluted projectile preforms and megafauna consumption known from the Chilean semiarid coastline. Here, we present the climatic history at SJ during the early Holocene reconstructed from pollen and charcoal analyses spanning 13.2–8.6 ka (=10³ calibrated ¹⁴C yr BP). Elevated charcoal concentrations confirm human activity by 13.2 ka. Human occupation decreased in intensity and charcoal practically disappears from the record after 10.6 ka, followed by wetland expansion at SJ between 10.5 and 9.5 ka. Local dominance of coastal shrubland reveals that dry phases occurred between >11.2–10.5 and 9.5–9.0 ka. Overall, these findings imply that by modulating available resources at both local and landscape levels climate change may have played an important role in explaining the peopling of semiarid coastal Chile. Copyright © 2010 John Wiley & Sons, Ltd.     

地球自转与北半球中纬度地面温度的年代际关系及其可能物理过程分析

利用地球日长（LOD）资料和美国环境预报中心/国家大气研究中心（NCEP/NCAR）的气象要素资料,统计分析发现1962-2010年LOD的变化和北半球中纬度地面温度均存在明显的十年以上的波动周期.相关分析、合成分析等统计方法均检测到LOD与中纬度地面温度的显著负相关关系,当地球自转速率加快时,北半球中纬度地面增温;反之,中纬度地面降温.小波功率谱和交叉谱分析则确定二者的相互关系属于准20年周期尺度上的年代际变化联系,并且LOD的变化超前于地面温度的变化大概3~4年.平均而言,LOD的变化可带来中纬度地面温度0.2℃的降温（或增温）.通过对大气相对角动量、纬向风场、海平面气压场的年代际合成分析,揭示了LOD与地面温度的年代际联系形成的具体物理过程.当地球自转加速时,北半球高低纬度经向温差梯度减弱,热带地区向极地扩展,造成北半球中纬度地区地面增温;地球自转减速时段相反,经向温差梯度增强,热带地区向赤道收缩,中纬度地区地面降温.     

The Kuroshio Extension System: Its Large-Scale Variability and Role in the Midlatitude Ocean-Atmosphere Interaction

The Kuroshio Extension and its recirculation gyre form an interconnected dynamic system. The system is located at a crossroads where the meso-scale and large-scale oceanic variability are highest, and where the ocean-atmosphere interaction is most active in the Pacific Ocean outside of the tropics. Following a brief review of the mean flow and meso-scale eddy variability, this study describes in detail the large-scale structural change (an oscillation between an elongated and a contracted state) observed in the Kuroshio Extension system. Causes for this structural change are explored next, and it is argued that the basin-wide external wind forcing and the nonlinear dynamics associated with the inertial recirculation gyre are both important factors. Data analysis results are reviewed and presented, emphasizing that the surface Kuroshio Extension is not simply a well-mixed layer passively responding to heat flux anomalies imposed by the atmosphere. It is argued that large-scale changes in the Kuroshio Extension system influence the surface ocean heat balance and generate wintertime sea surface temperature (SST) anomalies through both horizontal geostrophic heat advection and re-emergence to the surface mixed layer of sequestered mode water temperature anomalies. This revised version was published online in August 2006 with corrections to the Cover Date.     

Changing fire regimes in the temperate rainforest region of southern Chile over the last 16,000 yr

A high-resolution macroscopic charcoal record from Lago Melli (42°46′S, 73°33′W) documents the occurrence of forest fires in the lowlands of Isla Grande de Chiloé, southern Chile, over the last 16,000 yr. Our data suggest that fire activity in this region was largely modulated by the position/intensity of the southern westerlies at multi-millennial time scales. Fire activity was infrequent or absent between 16,000-11,000 and 8500-7000 cal yr BP and was maximal between ∼ 11,000-8500 and 3000-0 cal yr BP. A mosaic of Valdivian/North Patagonian rainforest species started at ∼ 6000 cal yr BP, along with a moderate increase in fire activity which intensified subsequently at 3000 cal yr BP. The modern transition between these forest communities and the occurrence of fires are largely controlled by summer moisture stress and variability, suggesting the onset of high-frequency variability in summer precipitation regimes starting at ∼ 5500 cal yr BP. Because negative anomalies in summer precipitation in this region are teleconnected with modern El Niño events, we propose that the onset of El Niño-like variability at ∼ 5700-6200 cal yr BP led to a reshuffling of rainforest communities in the lowlands of Isla Grande de Chiloé and an increase in fire activity.     

Land–sea correlations in the Australian region: 460 ka of changes recorded in a deep-sea core offshore Tasmania. Part 2: the marine compared with the terrestrial record

We present an array of new proxy data and review existing ones from core Fr1/94-GC3 from the East Tasman Plateau. This core is positioned at the southern extreme of the East Australia Current and simultaneously records changes in both oceanography and environments both in offshore and in southeastern Australia. Microfossils, including planktonic and benthic foraminifera, ostracods, coccoliths and radiolarians, were studied to interpret palaeo-oceanographic changes. Sea-surface temperature was estimated using planktonic foraminifera, alkenones and radiolaria. From the silicate sediment fraction, the mean grain size of quartz grains was measured to detect the changes in wind strength. An XRF scan of the entire core was used to determine the elemental composition to identify provenance of the sediment. We also compare these data with a pollen record from the same core provided in an accompanying article that provides the longest well-dated record of vegetation change in southeastern Australia. In an area of slow sedimentation, Fr1/94-GC3 provides a continuous record of change in southeastern Australia and the southern Tasman Sea over approximately the last 460?ka. We determine that the East Australian Current varied in intensity through time and did not reach the core site during glacial periods but was present east of Tasmania during all interglacial periods. The four glacial–interglacial periods recorded at the site vary distinctly in character, with Marine Isotope Stage (MIS) 9 being the warmest and MIS 5 the longest. Through time, glacial periods have progressively become warmer and shorter. Deposition of airborne dust at the core site is more substantial during interglacial periods than glacials and is believed to derive from mainland Australia and not Tasmania. It is likely that the source and direction of the dust plume varied significantly with the wind regimes between glacials and interglacials as mean effective precipitation changed.     

Climate variability over the last 9900 cal yr BP from a swamp forest pollen record along the semiarid coast of Chile

We present a fossil pollen analysis from a swamp forest in the semiarid coast of Chile (32°05′S; 71°30′W), at the northern influence zone of southern westerly wind belt. A ∼10,000 cal yr BP (calendar years before 1950) palynological sequence indicates a humid phase characterized by dense swamp forest taxa dated between ∼9900 and 8700 cal yr BP. The presence of pollen-starved sediments with only scant evidence for semiarid vegetation indicates that extreme aridity ensued until ∼5700 cal yr BP. The swamp forest recovered slowly afterwards, helped by a significant increase in moisture at ∼4200 cal yr BP. A new swamp forest contraction suggests that another slightly less intense drought occurred between ∼3000 and 2200 cal yr BP. The swamp forest expansion begins again at ∼2200 cal yr BP, punctuated by a highly variable climate. Comparisons between the record presented here with other records across the region imply major variations in the extent of the southern westerlies during the Holocene. This variability could have been caused either by latitudinal displacements from the present mean position of southern westerlies wind belt or by changes in the intensity of the South Pacific Subtropical Anticyclone, both of which affect winter precipitation in the region.     

晚第四纪风尘物质成分的变化及其环境意义

对长武和宜川晚第四纪黄土-古土壤序列的高分辨率铁含量分析表明,不同时期的风尘在化学成分上具有较明显的区别。在排除成壤过程中CaCO₃淋溶和淀积的相对影响后,研究剖面的铁含量基本反映了原始风尘的铁含量。已有研究表明,西部源区的气溶胶和现代地表流沙中铁的相对含量显著高于东部源区。本文认为,风尘铁含量的变化反映了西部沙漠风尘对黄土堆积的相对贡献。由于西风带北支是西部源区风尘的主要搬运者,风尘中全铁含量可能反映了西风带北支气流的强度,并明显存在着千年尺度的变化。