Retrieval of mixing height and dust concentration with lidar ceilometer   总被引：4，自引：2，他引：4  

Christoph Münkel  Noora Eresmaa  Janne Räsänen  Ari Karppinen 《Boundary-Layer Meteorology》2007,124(1):117-128

The Vaisala ceilometers CT25K and CL31 are eye-safe single lens lidar systems reporting attenuated backscatter profiles; they often operate 24 h a day in fully automated, hands-off operation mode. These profiles can be used for more than just cloud-base height determination. In dry weather situations, there is a fairly good correlation between the ceilometer near-range backscatter and in situ PM10 concentration readings. The comparison of mixing height values based on soundings and on ceilometer backscattering profiles indicates that ceilometers are suitable instruments for determining the convective mixing height. Its enhanced optics and electronics enables the CL31 ceilometer to detect fine boundary-layer structures whose counterparts are seen in temperature profiles.  相似文献   

Analysis of Low-Frequency Turbulence Above Tall Vegetation Using a Doppler Sodar     

Christoph Thomas  Jens-Christopher Mayer  Franz X. Meixner  Thomas Foken 《Boundary-Layer Meteorology》2006,119(3):563-587

This study applies acoustic sounding to observe coherent structures in the roughness sublayer (RSL) above tall vegetated surfaces. Data were collected on 22 days during two separate field experiments in summer 2003. A quality control scheme was developed to ensure high data quality of the collected time series. The data analysis was done using both discrete and continuous wavelet transform. The flow in the RSL was found to be a superposition of dynamic Kelvin–Helmholtz instabilities and convective mixing. The characteristic time scales for coherent structures resulting from the dynamic instabilities were observed to be approximately 20–30 s while thermal eddies have much larger time scales of 190–210 s. The degree of vertical coherency in the RSL increases with the flow evolving from neutral to near-convective conditions. This increase in the degree of organisation is attributed to the evolution of attached thermal eddies. The coherent structures resulting from instabilities were found to be present throughout the RSL but do not contribute to the increased vertical coherency. An alternative conceptual approach for the definition of the RSL is proposed, which yields its maximum vertical extent to five times the canopy height.  相似文献   

A Case Study on the Effects of Heterogeneous Soil Moisture on Mesoscale Boundary-Layer Structure in the Southern Great Plains, U.S.A. Part I: Simple Prognostic Model     

Ankur R. Desai  Kenneth J. Davis  Christoph J. Senff  Syed Ismail  Edward V. Browell  David R. Stauffer  Brian P. Reen 《Boundary-Layer Meteorology》2006,119(2):195-238

The atmospheric boundary-layer (ABL) depth was observed by airborne lidar and balloon soundings during the Southern Great Plains 1997 field study (SGP97). This paper is Part I of a two-part case study examining the relationship of surface heterogeneity to observed ABL structure. Part I focuses on observations. During two days (12–13 July 1997) following rain, midday convective ABL depth varied by as much as 1.5 km across 400 km, even with moderate winds. Variability in ABL depth was driven primarily by the spatial variation in surface buoyancy flux as measured from short towers and aircraft within the SGP97 domain. Strong correlation was found between time-integrated buoyancy flux and airborne remotely sensed surface soil moisture for the two case-study days, but only a weak correlation was found between surface energy fluxes and vegetation greenness as measured by satellite. A simple prognostic one-dimensional ABL model was applied to test to what extent the soil moisture spatial heterogeneity explained the variation in north–south ABL depth across the SGP97 domain. The model was able to better predict mean ABL depth and variations on horizontal scales of approximately 100 km using observed soil moisture instead of constant soil moisture. Subsidence, advection, convergence/divergence and spatial variability of temperature inversion strength also contributed to ABL depth variations. In Part II, assimilation of high-resolution soil moisture into a three-dimensional mesoscale model (MM5) is discussed and shown to improve predictions of ABL structure. These results have implications for ABL models and the influence of soil moisture on mesoscale meteorology  相似文献   

Freshwater pulses in the eastern Arctic Ocean during Saalian and Early Weichselian ice-sheet collapse     

Jochen Knies  Christoph Vogt 《Quaternary Research》2003,60(3):243-251

Improved multiparameter records from the northern Barents Sea margin show two prominent freshwater pulses into the Arctic Ocean during MIS 5 that significantly disturbed the regional oceanic regime and probably affected global climate. Both pulses are associated with major iceberg-rafted debris (IRD) events, revealing intensive iceberg/sea ice melting. The older meltwater pulse occurred near the MIS 5/6 boundary (∼131,000 yr ago); its ∼2000 year duration and high IRD input accompanied by high illite content suggest a collapse of large-scale Saalian Glaciation in the Arctic Ocean. Movement of this meltwater with the Transpolar Drift current into the Fram Strait probably promoted freshening of Nordic Seas surface water, which may have increased sea-ice formation and significantly reduced deep-water formation. A second pulse of freshwater occurred within MIS 5a (∼77,000 yr ago); its high smectite content and relatively short duration is possibly consistent with sudden discharge of Early Weichselian ice-dammed lakes in northern Siberia as suggested by terrestrial glacial geologic data. The influence of this MIS 5a meltwater pulse has been observed at a number of sites along the Transpolar Drift, through Fram Strait, and into the Nordic Seas; it may well have been a trigger for the North Atlantic cooling event C20.  相似文献   

Book Review     

Christoph  Clauser 《Geophysical Journal International》2003,153(2):508-509

  相似文献   

Wei-Chyung Wang, Ivar S. A. Isaksen (eds): Atmospheric Ozone as a Climate Gas, General Circulation Model Simulations     

Christoph Brühl 《Journal of Atmospheric Chemistry》1998,30(2):313-314

  相似文献   

Dissipation and mixing in a coastal jet: A Baltic Sea case study     

Christoph Zülicke  Eberhard Hagen  Adolf Stips 《Aquatic Sciences - Research Across Boundaries》1998,60(3):220-235

  相似文献   

Stalagmite from the Austrian Alps reveals Dansgaard-Oeschger events during isotope stage 3:: Implications for the absolute chronology of Greenland ice cores     

Christoph Spötl  Augusto Mangini 《Earth and Planetary Science Letters》2002,203(1):507-518

A mass-spectrometric uranium-series dated stalagmite from the Central Alps of Austria provides unprecedented new insights into high-altitude climate change during the peak of isotope stage 3. The stalagmite formed continuously between 57 and 46 kyr before present. A series of ‘Hendy tests’ demonstrates that the outer parts of the sample show a progressive increase of both stable C and O isotope values. No such covariant increase was detected within the axial zone. This in conjunction with other observations suggests that the continuous stable oxygen isotope profile obtained from the axial zone of the stalagmite largely reflects the unaltered isotopic composition of the cave drip water. The δ¹⁸O record shows events of high δ¹⁸O values that correlate remarkably with Interstadials 15 (a and b), 14 and 12 identified in the Greenland ice cores. Interstadial 15b started rapidly at 55.6 kyr and lasted ∼300 yr only, Interstadial 15a peaked 54.9 kyr ago and was even of shorter duration (∼100 yr), and Interstadial 14 commenced 54.2 kyr ago and lasted ∼3000 yr. This stalagmite thus represents one of the first terrestrial archives outside the high latitudes which record precisely dated Dansgaard-Oeschger (D/O) events during isotope stage 3. Provided that rapid D/O warmings occurred synchronously in Greenland and the European Alps, the new data provide an independent tool to improve the GRIP and GISP2 chronologies.  相似文献   

Xenoliths of lawsonite-ferroglaucophane rocks from a Quaternary volcano of Milos (Aegean Sea,Greece)     

Christoph Hoffman  Jörg Keller 《Lithos》1979,12(3):209-219

Xenoliths of metamorphic rocks with ferroglaucophane + albite + stilpnomelane + muscovite ± lawsonite ± pumpellyite are described fromn the rhylolitic tephra deposits of the Late Quaternary Phyriplaka Volcano, Milos, Aegean Island, Greece. The chemical bulk analyses reveal metabasaltic parent rocks with strongly modified chemical compositions. Unusual for common fresh basalt types is extreme Na₂O combined with low K₂O and rather low CaO. These are chemical characteristics of spilitic basalts. High iron in the bulk rock and very high Fe/Mg is probably the cause of extreme ferroglaucophane compositions. The metamorphic assemblages point to a high-p/low-T metamorphism in the pressure range 4–8 kb and with temperatures of about 350°C. Phyriplaka Volcano is likely to have only a shallow explosive center and ferroglaucophane rocks were ejected from the immediate basement of the island, which was uplifted after the metamorphic event.  相似文献   

Granites and migmatites of the Damara belt,South West Africa. Petrography and melting experiments     

Dr. Christoph Hoffmann 《International Journal of Earth Sciences》1976,65(1):939-966

In the central area of the early paleozoic Damara belt migmatites and some types of granites (sensu lato) crop out. Conventional petrographic data were collected and melting experiments were carried out with 63 samples of such rocks. Based on these data, migmatite genesis can be classified as follows:

1. Formation by partial melting and separation of more liquid and more crystalline fractions, the melting behaviour of these fractions has to be principally similar then.
2. Formation by injection of “geologically liquid” crystal-melt mixes into rocks of (incidentally) similar or (more frequently) dissimilar melting behaviour.
3. Formation by partial melting of metasediments of originally different composition. The method is applied and demonstrated for outcrops with complicated interrelations and it is shown that temperature estimates are possible thereby (670° to 710° at 4–5 kb H₂O pressure in the central Damara belt).

  相似文献