天气现象自动化观测资料可用性分析与应用探讨

通过对北京地区天气现象组网试验资料的可用性分析以及在精细化预报业务中的应用,发现自动观测天气现象资料连续时长多于20 min以上时,数据可信度较高,对预报员有较高的参考价值。自动观测系统对雨、雾、霾现象的识别结果正确率总体较好,其高频次的探测数据对低频次的人工观测起到补充作用。但在天气现象识别算法、质控、雷暴和降水性质识别、现象识别连续性等方面还存在不足,需要进一步改进。     

2018年一次温带气旋入海爆发性增强时期的集合预报对比分析

基于实况观测资料、欧洲中期天气预报中心(European Centre for Medium-Range Forecast, ECMWF)0.5°（纬度）×0.5°（经度）水平分辨率的再分析数据和集合预报数据,对2018年2月一次入海爆发性气旋在黄海南部的爆发性增强时期的动力和热力因子进行了对比分析。根据气旋路径、强度和海面风的检验结果挑选出两组集合成员——好成员组和坏成员组。通过组间对比分析得到如下主要 结论 1）在气旋入海之后爆发性增强时,500 hPa高空槽和850 hPa中低层低涡迅速加强,同时低层和高层的西南急流均明显加大,中高层系统快速增强,上述因子均为气旋出现爆发性发展提供有利条件。2）气旋入海之后上升运动快速增强,这加剧了低层辐合与高层辐散,有利于地面降压,促使地面气旋的爆发性发展。水汽在中低层辐合后随气流上升发生凝结并释放潜热,这加强了高层辐散、低层辐合以及上升运动,促使气旋进一步爆发性发展。与此同时,对流层顶的高值位涡下传增强,低层大气斜压性受气旋上空冷暖平流的增强而增大,导致垂直稳定度减小,地面气旋性涡度增强,也有利于气旋爆发性发展。最终此次气旋快速增强并达到中等爆发性气旋的强度。3）虽然集合预报两组成员的平均场均比分析场弱,但是好成员组抓住了气旋上空中高层天气系统的快速增强过程,以及垂直运动、温度平流、水汽条件、位涡等预报因子和物理量的快速增强过程,其预报效果在气旋强度和路径等方面均显著优于坏成员组。     

2010-07-23陕西中西部大暴雨天气诊断分析

分析结果表明：①山西北部的暴雨云团在850hPa暖切变线南部生成、发展,并在地面切变线附近合并;山西南部的MCC由3个B中尺度对流云团发生、发展、合并形成,β中尺度对流云团在700hPa次天气尺度切变线上触发生成;MCC发展、成熟阶段,α中尺度云团沿925hPa暖切变线东移;减弱阶段,随副高的南压而南压。②副高西进北抬背景下,同一次暴雨过程中,MCC发生在5880gpm边缘弱的斜压环境里,高层则出现在高压北侧的反气旋环流中;一般暴雨云团发生在5840gpm边缘较强的斜压环境里,高层则出现在急流人口区的右侧。③MCC作为大型的中尺度对流系统,不但对低层高温高湿能量的需求比一般暴雨云团更多,而且在垂直方向上,要求湿层、高能舌、暖温结构更深厚。④南部MCC影响区及5880gpm线边缘为负地闪覆盖区,正地闪主要出现在北部一般暴雨云团影响区及5840gpm线附近。一般暴雨云团影响下比MCC影响下,局地闪电开始及闪电峰值的出现较降水的开始及降水峰值的出现有更多的提前量。⑤山西北部暴雨云团出现在气柱水汽总量梯度的大值区及水汽锋上;山西南部MCC则出现在水汽锋的南侧气柱水汽总量的大值区。气柱水汽总量对0811暴雨过程有36h的提前量,对暴雨的落区有很好的指示意义。     

Sedimentology,sequence stratigraphy and syn-rift model of younger part of Washtawa Formation and early part of Kanthkot Formation,Wagad, Kachchh basin,Gujarat

The 600 m thick prograding sedimentary succession of Wagad ranging in age from Callovian to Early Kimmeridgian has been divided into three formations namely, Washtawa, Kanthkot and Gamdau. Present study is confined to younger part of the Washtawa Formation and early part of the Kanthkot Formation exposed around Kanthkot, Washtawa, Chitrod and Rapar. The depositional architecture and sedimentation processes of these deposits have been studied applying sequence stratigraphic context. Facies studies have led to identification of five upward stacking facies associations (A, B, C, D, and E) which reflect that deposition was controlled by one single transgressive — regressive cycle. The transgressive deposit is characterized by fining and thinning upward succession of facies consisting of two facies associations: (1) Association A: medium — to coarse-grained calcareous sandstone — mudrocks alternations (2) Association B: fine-grained calcareous sandstone — mudrocks alternations. The top of this association marks maximum flooding surface as identified by bioturbational fabrics and abundance of deep marine fauna (ammonites). Association A is interpreted as high energy transgressive deposit deposited during relative sea level rise. Whereas, facies association B indicates its deposition in low energy marine environment deposited during stand-still period with low supply of sediments. Regressive sedimentary package has been divided into three facies associations consisting of: (1) Association C: gypsiferous mudstone-siltstone/fine sandstone (2) Association D: laminated, medium-grained sandstone — siltstone (3) Association E: well laminated (coarse and fine mode) sandstone interbedded with coarse grained sandstone with trough cross stratification. Regressive succession of facies association C, D and E is interpreted as wave dominated shoreface, foreshore to backshore and dune environment respectively. Sequence stratigraphic concepts have been applied to subdivide these deposits into two genetic sequences: (i) the lower carbonate dominated (25 m) transgressive deposits (TST) include facies association A and B and the upper thick (75m) regressive deposits (HST) include facies association C, D and E. The two sequences are separated by maximum flooding surface (MFS) identified by sudden shift in facies association from B to C. The transgressive facies association A and B represent the sediments deposited during the syn-rift climax followed by regressive sediments comprising association C, D and E deposited during late syn-rift stage.     

Spatially variable sedimentary responses to orbitally driven pluvial climate during Marine Oxygen Isotope Stage 5.1, Dakhla Oasis region, Egypt

Pleistocene basinal sediments (PBS) in the Dakhla region of Egypt's hyperarid Western Desert comprise four facies: (A) fluvio-lacustrine, (B) mixed lacustrine/pluvio-eolian, (C) pluvio-eolian, and (D) mixed eolian/pluvio-eolian. Contiguity of basins containing each facies, and their stratigraphic position between two bajada gravel formations, P/B-II and P/B-III, confirm their equivalence. Facies A and B, with lacustrine components, are attributed to orbitally forced poleward incursion of the Intertropical Convergence Zone (ITCZ), resulting in increased summer insolation/temperature/precipitation. Facies C and D, comprising pluvio-eolian and eolian sediments, reflect geologic/topographic influences overprinted on regional 'pluvial' conditions, eliminating lacustrine response. A Th/U age of ∼ 62 ka on lacustrine marl within Facies B is minimal, and an OSL age of 110 ± 18 ka on sediments immediately below Facies B is maximal. Since bajada gravels P/B-III are the youngest Pleistocene formation, they must represent the final strong incursion of the ITCZ into the Dakhla region at MIS 5.1, ∼ 80 ka. Because PBS Facies A pass rapidly up into P/B-III bajada gravels, PBS are assigned to the rising limb of the MIS 5.1 insolation/temperature/precipitation curve, slightly younger than 80 ka.     

Fluvial braidplain to shallow marine transition in the early Neoproterozoic Morar Group,Fannich Mountains,northern Scotland

The early Neoproterozoic Morar Group in northern Scotland forms the lower part of the Moine Supergroup, deformed and metamorphosed within the Precambrian Knoydartian and Lower Palaeozoic orogenies. It has remained uncertain whether it was deposited in a shallow-marine ‘failed rift’ basin within Rodinia or a foreland basin on the margin of the Grenville orogen, which is important to determine for tectonic reconstructions. In that context, we assess the sedimentology, depositional environment and tectonic setting of the middle part of the Morar Group in the Fannich Mountains. A ca. 4–6 km thick fining-upward facies succession contains three psammite dominated lithofacies (LF): LF1, at the base, contains amalgamated and multi-storey sets of trough and tabular cross beds, which passes upwards into LF2 consisting of trough and tabular cross-bedded units arranged in coarsening and fining-upward sequences with minor pelitic rocks. The stratigraphically highest lithofacies, LF3, contains finer and more complex coarsening-upward packages of rhythmically interbedded pelite and psammite. Palaeoflow develops from broadly unimodal NW–NE flow in LF1, to weakly bimodal NW–SE flow in LF3. The data indicate that this part of the Morar Group records deposition in a distal fluvial braidplain to tidally influenced shallow-marine setting. All facies and palaeocurrent transitions are gradual and occur systematically over many hundreds of metres vertically; such characteristics are incompatible with a rift-basin setting. We suggest that, instead, deposition occurred in a transition between a foreland basin to the Grenville orogen and a marine basin associated with the Asgard Sea between Baltica and Laurentia.     

新一代天气雷达与TWR01小天气雷达在一次强降水天气过程中的对比分析

通过对贵阳多普勒雷达和独山TWR01小天气雷达资料在一次强降水天气过程中四个时段的观测资料和四个时段的自记降水资料进行分析对比．得出新一代多普勒天气雷达由于贵州地形影响等原因．存在一定的探测盲区,而TWR01小雷达对小范围的对流云层观测更清楚、更接近当时天空的实际情况,是多普勒天气雷达很好的补充。     

Deposit architecture and dynamics of the 2006 block‐and‐ash flows of Merapi Volcano,Java, Indonesia

The internal architecture of the 2006 block‐and‐ash flow deposits of Merapi volcano (Java, Indonesia) was investigated using data collected from 27 stratigraphic sections measured immediately after flow emplacement, and after one and two rainy seasons of erosion. Identification of different depositional units and their longitudinal and lateral facies variations provide detailed information about: (i) the distribution, volumes and sedimentological characteristics of the different units; (ii) flow types and mobility as inferred from associated deposits; and (iii) changes in the dynamics of the different flows and their material during emplacement. Two main types of block‐and‐ash flows (short‐runout to medium‐runout block‐and‐ash flows and long‐runout block‐and‐ash flows) are defined based on flow generation mechanism, flow volume, travel distance, deposit morphology, distribution, lithology and grain‐size distribution. Conceptual models for the transport and depositional mechanisms of these two types of block‐and‐ash flows are presented. Variations in the runout distances observed for short‐runout to medium‐runout block‐and‐ash flows are linked directly to different initial flow volumes, degree of fragmentation and material properties of the moving mass during transport, with the largest and finer grained flows having the greatest mobility. Deposition occurs only over a narrow range of basal inclinations close to the angle of repose for pyroclastic material, indicating that such flows behave in a similar way to granular‐free surface flows on unconfined planes. The flow mechanisms of long‐runout block‐and‐ash flows at Merapi are interpreted to be similar, in many respects, to unsteady, cohesionless grain flows with an inertial flow regime where collisional forces largely overcome frictional forces. Flow unsteadiness causes the main body to be segmented into different pulses that run closer to each other as the flow moves downslope. Deposition occurs stepwise, with rapid aggradation of stacked sub‐units from different parts of the major flow pulses. In such a model, the arrival of each flow pulse front at selected sites in the main river valley controls the generation and development of highly mobile, unconfined pyroclastic flows outside valley regions and their associated overbank deposits.     

Mid- to late Holocene environmental and climatic changes in New Caledonia, southwest tropical Pacific, inferred from the littoral plain Gouaro-Déva

Multiproxy analysis of three littoral cores from western New Caledonia supports the hypothesis that the main controlling factors of environmental changes are sea-level change, ENSO variability and extra-tropical phenomena, such as the Medieval Warm Period (MWP) marked by a tendency for La Niña-like conditions in the tropical Pacific. The record starts during the late Holocene sea-level rise when the terrestrial vegetation indicated wet and cool conditions. The site was a coastal bay definitely transformed into a freshwater swamp at around 3400 cal yr BP, after the rapid drawdown of sea level to its current level. Sediments and foraminiferal assemblages indicated subsequent episodes of freshwater infillings, emersion or very high-energy conditions, likely related to climatic changes and mostly controlled by ENSO variability. Between 2750 and 2000 cal yr BP, relatively dry and cool climate prevailed, while wetter conditions predominated between ca. 1800 and 900 cal yr BP. The Rhizophoraceae peak between ca. 1080 and 750 cal yr BP, coeval with the MWP, may indicate a global phenomenon. Microcharcoal particles present throughout the record increased after 1500 cal yr BP, suggesting an anthropogenic source. From ca. 750 cal yr BP the appearance of current type of vegetation marks the human impact.