Convective Boundary-Layer Entrainment: Short Review and Progress using Doppler Lidar

The entrainment of air from the free atmosphere into the convective boundary layer is reviewed and further investigated using observations from a 2 μm Doppler lidar. It is possible to observe different individual processes entraining air into the turbulent layer, which develop with varying stability of the free atmosphere. These different processes are attended by different entrainment-zone thicknesses and entrainment velocities. Four classes of entrainment parametrizations, which describe relationships between the fundamental parameters of the process, are examined. Existing relationships between entrainment-zone thickness and entrainment velocity are basically confirmed using as scaling parameters boundary-layer height and convective velocity. An increase in the correlation coefficient between stability parameters based on the stratification of the free atmosphere and entrainment velocity (and entrainment-zone thickness respectively) up to 200% was possible using more suitable length and velocity scales.     

Extremes and predictability in the European pre-industrial climate of a regional climate model

A high-resolution pre-industrial control simulation with the regional climate model REMO is analyzed in detail for different European subregions. To our knowledge, this is the first long pre-industrial control simulation by a regional climate model as well as at comparable resolution. We assess the ability of the climate model to reproduce the observed climate variability in various parts of the continent. In order to investigate the representation of extreme events in the model under pre-industrial greenhouse gas concentrations, selected seasons are examined with regard to the atmospheric circulation and other climatic characteristics that have contributed to the occurrences. A special focus is dedicated to land-atmosphere interactions. Extreme seasons are simulated by the model under various circumstances, some of them strongly resemble observed periods of extraordinary conditions like the summer 2003 or autumn 2006 in parts of Europe. The regional perspective turns out to be of importance when analyzing events that are constituted by meso-scale atmospheric dynamics. Moreover, the predictability of the European climate on seasonal to decadal time scales is examined by relating the statistics of surface variables to large-scale modes of variability impacting the North Atlantic sector like the Meridional Overturning Circulation, the El Niño Southern Oscillation, and the North Atlantic Oscillation. For this purpose, we introduce a measure of tail dependence that quantifies the correlation between extreme values in two variables that describe the state of the climate system. Significant dependence of extreme events can be detected in various situations.     

Explanation of the internal air pressure effect on the worden gravity meter dial constant

Summary A model, explaining the effect of air pressure changes in the space of the measuring system on the fine dial counter constant of the Worden and similar gravity meters, is presented. It is based on the changes of the bellows volume with compensating the gravity changes. It is shown that the resetting the gravity meter in the whole range has practically no influence on the fine dial counter constant.

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蒙古南戈壁中洛霍考夫阶(泥盆系)牙形刺的首次发现

蒙古南戈壁新金斯特(Shine Jinst)地区Ulaan-Shand 剖面的查干安普拉格(Tsagaanbulag)组以前曾划归志留系(文洛克统至普里多利统). 但在Tsagaanbulag组及其上部的阿曼采尔(Amansair)组发现了非常重要的牙形刺, 包括Lanea omoalpha, Amydrotaxis johnsoni, “Ozarkodina” planililingua, Pedavis sp., 清楚地指明这两个组应当归下泥盆统中洛霍考夫阶. 中洛霍考夫阶的海相地层在中国和蒙古国广泛分布. 志留系文洛克统和洛德罗统下部的海相地层在蒙古是否存在是值得注意的问题.     

Rainfall erosivity and erosivity density in Eastern Ghats Highland of east India

The rainfall erosivity (R-factor in USLE) is the long-term average of the sum of the product of rainfall kinetic energy and its maximum 30-min intensity. Therefore, at most 30-min time intervals pluviograph records are required to calculate R-factor. But, such high-resolution data are scarce in many parts of the world and require lengthy processing period. In this study, R-factor was correlated with daily, monthly and annual rainfall, and its spatial variability in Eastern Ghats Highland of east India was mapped. The result showed that power regression models predicted satisfactorily the daily, monthly and annual R-factor, of which annual R-factor model performed best (model efficiency 0.93). Mean monsoon season R-factor was 15.6 and 10.0 times higher than the pre- and post-monsoon season R-factor, and thus remained highly critical with respect to erosion. Annual R-factor values ranged from 3040 to 10,127 MJ mm ha^?1 h^?1 year^?1, with standard deviation of 1981 MJ mm ha^?1 h^?1 year^?1. Rainfall intensity was positively correlated with erosivity density, and numerical value of rainfall intensity was almost double of the erosivity density value. The combination of rainfall and erosivity density was used to identify flood, erosion and landslide-prone areas. The developed iso-erosivity, erosivity density and risk maps can be opted as a tool for policy makers to take suitable measures against natural hazards in Eastern Ghats Highland of east India and elsewhere with similar rainfall characteristics.

     

Detecting global atmospheric oscillations by seismic instruments

Izvestiya, Physics of the Solid Earth - We briefly overview the periodic atmospheric motions in the period range from 1 h to a few dozen days. It is shown that many oscillations recorded by...     

PV morphology of a frontal-wave development

Summary A case study is performed of a frontal-wave development on a trailing cold front in the Atlantic. The data base comprises principally the analysis and forecast fields of the global operational weather prediction model of the ECMWF, and the development itself is viewed from a potential vorticity (PV) perspective. It is shown that the ambient atmosphere contained three distinct and salient PV features: at the surface a frontal baroclinic zone; in the lower troposphere a co-aligned, moisture laden elongated band (2000 km long and 400 km wide) of enhanced PV; and at upper-levels a richly structured, southward extending PV pool. In the developments first phase a large-scale undulation of the surface frontal zone was accompanied by an in-phase movement of the upper-level anomaly. In a second phase two low-level wave features developed around 1000 km apart, and the resulting wave depressions were accompanied by a distortion of the baroclinic zone and the break-up of the low-level PV-band. In the subsequent mature phase the dominant secondary cyclone attained 500 km scale in the horizontal and acquired a coherent PV structure in the vertical.A PV-based diagnostic analysis provides evidence of both the self development of the PV features and their synergetic interplay. It also forms the basis for a comparison of the event with traditional and recent hypotheses for frontal-wave development.On the basis of the diagnosed relationship between the customarily depicted surface frontal-wave cups and the low-level PV-band, it is suggested that the segmentation of the latter provides a useful tool for monitoring and forecasting secondary developments. Also in the context of numerical weather prediction brief consideration is given to the sensivity of the frontal-wave development and structure to the spatial resolution of the associated forecast model and the specification of the initial fields.With 12 Figures     

Cyclic fluctuations of anoxia during Cretaceous time in the South Atlantic Ocean

The holes of the DSDP-IPOD program in the South Atlantic Ocean document two major anoxic events during Oxfordian to middle Albian times and secondly from late Cenomanian to Santonian times. The black shales formed during these two anoxic events differ in their rhythmicity and origin.During Lower Cretaceous time, the anoxic conditions resulted from the confined, euxinic nature of the basins. The rhythmicity of these black shales probably does not result from a global phenomenon (climatic or tectono-eustatic), but from local conditions resulting from the slender dimensions of the young ocean basin(s). The diversity and the diachroneity of the deposits from the south to the north precisely reflect the dynamics of the oceanic spreading.During Upper Cretaceous time, the anoxic conditions fluctuated in relation to a mid-water oxygen-minimum zone. The rhythmicity of black shale deposition seems to result from a global phenomenon, because of the widespread occurrence of the event. In the South Atlantic ocean, the cyclic fluctuations of anoxia were due to cyclic variations in the depth of the mid-water oxygen-minimum zone. There is no simple process to explain such rhythmicity. It probably results from the interplay of the three main variables which characterize the oceans at the time of the Cenomanian-Turonian boundary: the increased rate of sea floor spreading, high sea-levels and low water-circulation.