Dust mobilization and transport in the northern Sahara during SAMUM 2006 – a meteorological overview     

By PETER KNIPPERTZ  ALBERT ANSMANN  DIETRICH ALTHAUSEN  DETLEF MÜLLER  MATTHIAS TESCHE  EIKE BIERWIRTH  TILMAN DINTER  THOMAS MÜLLER  WOLFGANG VON HOYNINGEN-HUENE  KERSTIN SCHEPANSKI  MANFRED WENDISCH  BERND HEINOLD  KONRAD KANDLER  REAS PETZOLD  LOTHAR SCHÜTZ  INA TEGEN 《Tellus. Series B, Chemical and physical meteorology》2009,61(1):12-31

The SAMUM field campaign in southern Morocco in May/June 2006 provides valuable data to study the emission, and the horizontal and vertical transports of mineral dust in the Northern Sahara. Radiosonde and lidar observations show differential advection of air masses with different characteristics during stable nighttime conditions and up to 5-km deep vertical mixing in the strongly convective boundary layer during the day. Lagrangian and synoptic analyses of selected dust periods point to a topographic channel from western Tunisia to central Algeria as a dust source region. Significant emission events are related to cold surges from the Mediterranean in association with eastward passing upper-level waves and lee cyclogeneses south of the Atlas Mountains. Other relevant events are local emissions under a distinct cut-off low over northwestern Africa and gust fronts associated with dry thunderstorms over the Malian and Algerian Sahara. The latter are badly represented in analyses from the European Centre for Medium–Range Weather Forecasts and in a regional dust model, most likely due to problems with moist convective dynamics and a lack of observations in this region. This aspect needs further study. The meteorological source identification is consistent with estimates of optical and mineralogical properties of dust samples.  相似文献   

翼龙类翼膜的折叠，褶皱以及物质特性     

Stefanie MONNINGER  Eberhard FREY  Ross ELGIN  Helmut TISCHLINGER  Julian SARTORI  Petra SCHNEIDER 《地球学报》2010,31(Z1):52-52

Preservation of wing membranes in pterosaurs is only reported from a few localities in the world, namely from the Karatau Hills, Kazakhstan (Upper Jurassic), from the Solnhofen Lithographic Limestone, Germany (Upper Jurassic), the Daohugou Beds of China (Upper Jurassic or Lower Cretaceous) and the Crato and Santana Formations, Chapada do Araraipe, NE Brazil (Lower Cretaceous).  相似文献   

Properties of dust aerosol particles transported to Portugal from the Sahara desert   总被引：1，自引：0，他引：1  

FRANK WAGNER  DANIELE BORTOLI  SÉRGIO PEREIRA  MARIA JOÃO COSTA  ANA MARIA SILVA  BERNADETT WEINZIERL  MICHAEL ESSELBORN  REAS PETZOLD  KATHI RASP  BERND HEINOLD  INA TEGEN 《Tellus. Series B, Chemical and physical meteorology》2009,61(1):297-306

Aerosol properties of mineral particles in the far field of an African desert dust outbreak were investigated that brought Saharan dust over the Mediterranean in different layers to Portugal. The measurements were performed inside the project Desert Aerosols over Portugal (DARPO) which was linked to the Saharan Mineral Dust Experiment (SAMUM). The maximum particle mass concentration was about 150 μg m⁻³ and the corresponding scattering coefficient was 130 M m⁻¹ which results in a mass scattering efficiency of 0.87 m² g⁻¹. The aerosol optical depth reached values up to 0.53 and the lidar ratio was between 45 and 50 in the whole dust loaded column. A comparison between particle size distributions and refractive indices derived from different instruments and models showed a general good agreement but some minor differences could also be observed. Measurements as well as calculations with a particle transport model suggest that there is a relatively higher concentration of very large particles in the upper region of the dust layer than on the surface which is likely connected with meteorological conditions at the observational site (Évora, Portugal).  相似文献   

Observations and modelling of the global distribution and long-term trend of atmospheric ¹⁴CO₂     

By INGEBORG LEVIN †  TOBIAS NAEGLER †  BERND KROMER  MORITZ DIEHL ‡  ROGER J. FRANCEY  ANGEL J. GOMEZ-PELAEZ  L. PAUL STEELE  DIETMAR WAGENBACH  ROLF WELLER  DOUGLAS E. WORTHY 《Tellus. Series B, Chemical and physical meteorology》2010,62(1):26-46

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GLACIER FLUCTUATIONS, SUSPENDED SEDIMENT FLUX AND GLACIO-LACUSTRINE SEDIMENTS   总被引：1，自引：0，他引：1  

PETER JANSSON  GUNHILD ROSQVIST  THOMAS SCHNEIDER 《Geografiska Annaler: Series A, Physical Geography》2005,87(1):37-50

ABSTRACT. In order to perform inverse modelling of climate variability based on palaeoclimate proxy records, the complexity of intermediate steps in the chain of processes from the climate forcing to the responding proxy has to be considered. In reconstructing climate-forced glacier fluctuations from proglacial lacustrine sediments it is important to understand how climate affects glacier dynamics. A glacier system is complex with many factors influencing sediment production, transport and deposition. Fluvial and mass movement processes in the proglacial environment may affect lake sedimentation substantially. We argue that it is easy to over-interpret glaciolacustrine sediment variability by ignoring these complications. The sediment records may contain individual layers resulting from single precipitation or melt events, as well as persistent changes in climate-forced glacier dynamics. We conclude that it is necessary to consider all possible influencing factors in order to derive reliable palaeoclimate data from lacustrine sediment sequences.  相似文献   

FREQUENCY WAVENUMBER APPROACH OF THE τ-p TRANSFORM: SOME APPLICATIONS IN SEISMIC DATA PROCESSING*     

S.D. BENOLIEL  W.A. SCHNEIDER  R.N. SHURTLEFF 《Geophysical Prospecting》1987,35(5):517-538

The τ-p transform is an invertible transformation of seismic shot records expressed as a function of time and offset into the τ (intercept time) and p (ray parameter) domain. The τ-p transform is derived from the solution of the wave equation for a point source in a three-dimensional, vertically non-homogeneous medium and therefore is a true amplitude process for the assumed model. The main advantage of this transformation is to present a point source shot record as a series of plane wave experiments. The asymptotic expansion of this transformation is found to be useful in reflection seismic data processing. The τ-p and frequency-wavenumber (or f-k) processes are closely related. Indeed, the τ-p process embodies the frequency-wavenumber transformation, so the use of this technique suffers the same limitations as the f-k technique. In particular, the wavefield must be sampled with sufficient spatial density to avoid wavenumber aliasing. The computation of this transform and its inverse transform consists of a two-dimensional Fast Fourier Transform followed by an interpolation, then by an inverse-time Fast Fourier Transform. This technique is extended from a vertically inhomogeneous three-dimensional medium to a vertically and laterally inhomogeneous three-dimensional medium. The τ-p transform may create artifacts (truncation and aliasing effects) which can be reduced by a finer spatial density of geophone groups by a balancing of the seismic data and by a tapering of the extremities of the seismic data. The τ-p domain is used as a temporary domain where the attack of coherent noise is well addressed; this technique can be viewed as ‘time-variant f-k filtering’. In addition, the process of deconvolution and multiple suppression in the τ-p domain is at least as well addressed as in the time-offset domain.  相似文献   

Environmental change during the Allerød and Younger Dryas reconstructed from Swiss tree-ring data     

MATTHIAS SCHAUB  KLAUS FELIX KAISER  DAVID CHARLES FRANK  ULF BÜNTGEN  BERND KROMER  SAHRA TALAMO 《Boreas: An International Journal of Quaternary Research》2008,37(1):74-86

Annually resolved tree-ring width variations and radiocarbon ages were measured from a collection of 120 Lateglacial pine stumps excavated on the Swiss Plateau. These data – representing the oldest absolutely dated wood samples worldwide – extend the absolute tree-ring chronology from Central Europe by 183 years back to 12 593 cal. yr BP (10 644 cal. yr BC). They also yield a 1420-year floating chronology covering the entire Allerød and the early Younger Dryas (14 170–12 750 cal. yr BP). Radiocarbon data suggest a 250-year jump in the ¹⁴C reservoir correction around the time of the Allerød to Younger Dryas transition, although calendric dating of the floating chronology – by filling a ∼150 year gap – is necessary for confirmation. Various subgroups, based on the year of germination, were used to assess temporal changes in growth characteristics along the Allerød to Younger Dryas transition. Comparison of these Lateglacial data with a reference data set of living and historic pines from the Swiss Valais (AD 940–2000) revealed differences in both growth trend and level. The generally slower Lateglacial growth was likely influenced by higher geomorphic activity and severe climatic conditions. After removal of the biological age-trend, a strong common signal found in the tree-ring data suggests some skill in estimating interannual to multidecadal Lateglacial climatic variations.  相似文献   

Evolving Perspectives on Abrupt Seasonal Changes of the General Circulation     

Jianhua LU  Tapio SCHNEIDER 《大气科学进展》2017,34(10):1185-1194

Professor Duzheng YE(Tu-cheng YEH) was decades ahead of his time in proposing a model experiment to investigate whether abrupt seasonal changes of the general circulation can arise through circulation feedbacks alone, unrelated to underlying inhomogeneities at the lower boundary. Here, we introduce Professor YEH's ideas during the 1950 s and 1960 s on the general circulation and summarize the results and suggestions of Yeh et al.(1959) on abrupt seasonal changes. We then review recent advances in understanding abrupt seasonal changes arising from model experiments like those proposed by Yeh et al.(1959). The model experiments show that circulation feedbacks can indeed give rise to abrupt seasonal transitions.In these transitions, large-scale eddies that originate in midlatitudes and interact with the zonal mean flow and meridional overturning circulations in the tropics play central roles.  相似文献   

FLOOD FREQUENCIES AS RELATED TO LAND USE     

William J. SCHNEIDER 《水文科学杂志》2013,58(4):36-39

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Late-glacial varved clays in the Bornholm Basin and Hanö Bay     

KLAUS DUPHORN  FRIEDRICH-C. KÖGLER  BERND STAY 《Boreas: An International Journal of Quaternary Research》1979,8(2):137-140

Distribution, thickness, lithology and stratigraphy of varved clays are discussed. The sediments were deposited in the Baltic Ice Lake during the Late Weichselian.  相似文献