Stratospheric Aerosol Extinction Profile Retrieval from SCIAMACHY Limb Measurements

Stratospheric aerosol extinction profiles are retrieved from Scanning Imaging Absorption Spectrome- ter for Atmospheric Cartography （SCIAMACHY） limb scatter measurements. In the process of retrieval, the SCIATRAN radiative transfer model is used to simulate the limb scattering radiation received by the SCIAMACHY instrument, and an optimal estimation algorithm is used to calculate the aerosol extinction profiles. Sensitivity analy- ses are performed to investigate the impact of the surface albedo on the accuracy of the retrieved aerosol extinction profiles in the northern midlatitudes. It is found that the errors resulting from the bias of the assumed surface albedo in the retrieval are generally below 6%. The retrieved SCIAMACHY aerosol extinction profiles are compared with corresponding Stratospheric Aerosol and Gas Experi- ment （SAGE） II measurements, and the results indicate that for the zonal mean profiles, the SCIAMACHY retrievals show good agreement with SAGE II measurements, with the absolute differences being less than 2.3 × 10-5 km-1 from 14-25 km, and less than 5.9×10-6 km-1 from 25-35 km; and the relative differences being within 20% over the lati- tude range of 14-35 km.     

Programme of the US.-Swiss conference on internal waves in geophysical contexts

Abstract

Evidence from radio polarization measurements is reviewed that indicates that most galactic magnetic field structures fall into one of two categories: axisymmetric spiral and bisymmetric spiral. The resultant challenges to dynamo theorists is stated. Estimates of the magnetic field strengths based on equipartition of field and cosmic ray energies are given, but deviations from equipartition are inferred. Possible goals for future research are suggested.     

Propeller underwater radiated noise: A comparison between model scale measurements in two different facilities and full scale measurements

The prediction of propeller induced pressure fluctuations and underwater radiated noise is a subject of great and increasing interest in marine engineering. Nevertheless, the full-scale prediction of these negative effects, even though based on dedicated model scale tests represents still a challenging task. This is due to different phenomena, among which scale effects on cavitation and ship wake, confined environment and near field effects in model tests play an important role; the analysis of these problems is made difficult by the rather limited amount of available data from sea trials and to the complexities of the phenomena, most of which related to cavitation on the propeller blades, that are present in the measurements carried out in cavitation tunnels, depressurized towing tanks or circulating channels.In the present work, the subject has been studied with reference to a four blades conventional CP propeller of a coastal tanker.Cavitation tunnel tests have been carried out in two rather different facilities, at UNIGE cavitation tunnel and at SSPA large cavitation tunnel.Results from model scale tests processed with different treatments are then compared with full scale measurements performed by SSPA on the same propeller in terms of cavitation extension and radiated noise.The analysis is aimed at assessing the effectiveness of different experimental setups, testing procedures and scaling laws.     

EPR and SQUID magnetometry study of Cu2FeSnS4 (stannite) and Cu2ZnSnS4 (kesterite)

An EPR and SQUID magnetometry study of Cu₂FeSnS₄ (stannite) and Cu₂ZnSnS₄ (kesterite) has been performed in order to gain a deeper insight into the crystal chemistry of these minerals, in which the mixed character of bonds lends uncertainty to the determination of the metal valence states. EPR investigations were performed down to almost liquid nitrogen temperature on both natural and synthetic samples of stannite and kesterite. The interpretation of their parameters (g- and T-tensors) was refined by computer simulation. The main feature of all the spectra is the unstructured signal centered at about 0.310 T due to the presence of Cu(II). The absence of structure in the signal is due to spin-spin exchange interaction between Cu(II) and Fe(II), pointing to a diluted distribution of Cu(II). The temperature dependence of the Cu(II) signal can be related to a topological variation of the first-neighbors coordination. The SQUID measurements, while allowing a more precise interpretation of the EPR data, led to a full characterization of magnetic behavior of stannite and kesterite down to liquid helium temperature, evidencing antiferromagnetic interactions between the Fe(II) ions in all samples but in synthetic kesterite. From the EPR and SQUID experimental data no evidence was provided for the existence of two different structures for stannite and kesterite. Received: 2 August 1999 / Accepted: 7 January 2000     

塔里木盆地北部油田古应力的AE法测量

本文在阐述了声发射(简称AE-Acoustic Emission)法测量古构造应力的可行性之后,着重介绍了测量古应力与测量现今应力在方法上的不同之处。作者采用AE法测量了塔里木盆地北部油田古应力,并得出该区喜马拉雅期有2幕主要构造运动;燕山期有3幕主要构造运动;古生代有2-3幕主要构造运动的认识。喜马拉雅构造运动在该区占主导地位。      

Long-Term Measurements of Light Hydrocarbons (C2–C5) at Schauinsland (Black Forest)

Long-term measurements of light hydrocarbons(C₂–C₅ HCs) were performed in the courseof the EUROTRAC sub-project TOR (Tropospheric Ozone Research) in thesouthern part of the Black Forest in southwest Germany. The measurementscover a time period of five years (January 1989–January 1994) and theair samples were analyzed onsite by an automated GC-system. Pronouncedannual cycles with maxima in late winter and minima in late summer wereobserved in the case of the slowly reacting hydrocarbons ethane, propane andacetylene, reflecting the fact that the seasonal variation of these speciesis photochemically driven. For the shorter lived compounds the seasonalvariations are considerably weaker, connected with a stronger scatter of theindividual measurements, which is caused by different distances to theirmain sources for different wind vectors as well as by varying sourcestrengths. From a detailed characterization of the hydrocarbon patterns theinfluence of two different sources could be distinguished. An extrapolationto photochemical age of zero and completion of our data with those from aspeciated VOC inventory yields an estimated [VOC]/NO_x sourceratio for Schauinsland of 5 [ppbC/ppb]. Comparable[VOC]/NO_x ratios are observed in automobile exhaust gasesunder low speed conditions, which points to the important role of trafficunder conditions, when freshly polluted air masses from a near-by city areadvected to the site. From an investigation of the photochemical age of theadvected air masses it becomes clear that there must exist biogenic sourcesof light olefins in the vicinity of the observatory during the vegetationperiod. For propene and the butenes we are able to estimate a lower limit oftheir contributions in terms of reactivity to the total reactivity( [HC](i) k_OH(i),i=C₂-C₅) of the measured hydrocarbons. Forlowest pollution levels in summer (acetylene <300 ppt, about 40%of the summer values) this source is found to be responsible for15–20% of the total C₂–C₅reactivity observed at Schauinsland. On the average, this source accountsfor 5–10% of the total C₂–C₅reactivity.     

Humidity Measurements in Cold and Humid Environments

Recent studies have shed new light on humidity conditions in the polar atmospheric boundary layer, and cast doubt on the reliability of humidity measurements above the frost point humidity. These issues are addressed herein by considering the processes that affect humidity and its measurement in cold climate conditions and by analyzing observations from two sites, at which the relative humidity is frequently above 100% at sub-freezing temperatures, as shown by repeatedly observed in-cloud icing events. Humidity measurements were made at these two sites by the commonly used Vaisala HMP35 probe and HMP233 capacitance probes respectively and simultaneously by the same manufacturer’s HMP243 probe that determines the frost point by a heated capacitance sensor. The results confirm that the relative humidity is frequently well above the frost point, both due to radiative cooling and to the advection of moist air, and that the conventional humidity measurements are unable to detect these events. Furthermore, after such events, the iced sensors show too high a humidity. The false values occur due to ice growth on the probe and cannot be corrected by any algorithm. Our results indicate that these problems, inherent to conventional humidity measurements in cold and humid environments, are avoided by the use of HMP243, which has a heated humidity probe.     

Correcting Distortions in Measurements of Atmospheric Pressure Fluctuations

Although recognized as important, measurements of turbulent atmospheric pressure are considered difficult and are conducted infrequently. Here we discuss the essential elements in the design of an instrument for measuring turbulent fluctuations of atmospheric pressure. Our analysis of the instrument’s dynamics is focused on the signal distortions resulting from a pneumatic filter, a necessary element in the instrument’s design. Such distortions substantially affect the observed spectral scaling of the pressure field as well as other quantities of physical interest, such as pressure-velocity 〈p, v〉 and pressure-wave 〈p, η〉 covariances. We propose a computationally efficient discrete-time signal processing method for complete compensation of pneumatic filter distortions and review the criteria for selecting the instrument parameters (sampling frequency and time constant), so that digital filter distortions, precision degradation, clipping, and over-damping, are simultaneously avoided. This correction method must be an inherent part of the instrument’s design.     

In Situ Trace Gas and Particle Measurements in the Summer Lower Stratosphere during STREAM II: Implications for O3 Production

In situ aircraft measurements of O₃, CO,HNO₃, and aerosol particles are presented,performed over the North Sea region in the summerlower stratosphere during the STREAM II campaign(Stratosphere Troposphere Experiments by AircraftMeasurements) in July 1994. Occasionally, high COconcentrations of 200-300 pbbv were measured in thelowermost stratosphere, together with relatively highHNO₃ concentrations up to 1.6 ppbv. The particlenumber concentration (at standard pressure andtemperature) between 0.018-1 m decreased acrossthe tropopause, from >1000 cm^-3 in the uppertroposphere to <500 cm^-3 in the lowermoststratosphere. Since the CO sources are found in thetroposphere, the elevated CO mixing ratios areattributed to mixing of polluted tropospheric air intothe lowermost extratropical stratosphere. Further wehave used a chemical model to illustrate that nitrogenoxide reservoir species (mainly HNO₃) determinethe availability of NO_x (=NO + NO₂) andtherefore largely control the total net O₃production in the lower kilometers of thestratosphere. Model simulations, applying additionalNO_x perturbations from aircraft, show that theO₃ production efficiency of NO_x is smallerthan previously assumed, under conditions withrelatively high HNO₃ mixing ratios, as observedduring STREAM II. The model simulations furthersuggest a relatively high O₃ productionefficiency from CO oxidation, as a result of therelatively high ambient HNO₃ and NO_xconcentrations, implying that upward transport of COrich air enhances O₃ production in the lowermoststratosphere. Analysis of the measurements and themodel calculations suggest that the lowermoststratosphere is a transition region in which thechemistry deviates from both the upper troposphere andlower stratosphere.     

Vertical profiles of acetylene in the troposphere and stratosphere

Stratospheric measurements of acetylene up to altitudes of 30 km are presented. The air samples were collected during three different balloon flights, two of them at 44°N, one at 32°N using balloon borne, liquid neon-cooled, cryosamplers. Their acetylene concentration was measured in the laboratory by flame ionisation gaschromatography. The different profiles at 32°N and 44°N are discussed with respect to possible vertical exchange processes and compared with published model calculations.