Winds and waves in the middle atmosphere as observed by ground-based radars

Ground-based radars have proved to be powerful instruments for studying dynamical processes in the middle atmosphere. They have been used successfully in the last few years during Pre-MAP and MAP projects. This paper briefly reviews the following ground-based radar methods: the new MST radar technique for remote sensing of the mesosphere, stratosphere and troposphere, and the well known techniques for mesospheric measurements such as the ionospheric drift experiment, the meteor radar and the MF radar experiments. A survey of observational results obtained with the various techniques is presented. Particular emphasis is directed to winds and waves as well as their interaction, all of which play an important role in the structure and dynamics of the middle atmosphere.     

First calibration measurements with the dust impact detector DIDSY-IPM

The IPM detector consists of two separate impact ionization detectors, one of them covered by a 2.5 μm thick plastic film and a piezoelectric sensor mounted to the back of the joint impact plate. First impact tests, with iron projectiles in the mass range 10^?15 to 10^?9 g and in the speed range 1 km/s to 70 km/s, were performed with the calibration (FS) and the flight (F) model of this detector. The charge yield at 69 km/s impact speed (flyby speed of GIOTTO) has been extrapolated from the data and amounts to 400 Coulombs per gram. This corresponds to a preliminary sensitivity threshold for the impact ionization detector of about 6×10^?17 g. The penetration limit introduced by the plastic film is about 10^?14 g for iron particles. Only the biggest particles used for the test produced signals at the piezoelectric sensor. If one assumes an energy dependence of the piozoelectric signal, a preliminary sensitivity threshold of about 10^?13 g at 69 km/s can be established.     

Some aspects of temperature sounding of the atmosphere

Based on measurements with the interferometer spectrometer SI-1 on board of Meteor satellites the following problems are investigated: the systematic effect of the spectral response function in deriving effective radiation temperatures; the selection of ‘optimal’ spectral channels within the 15 μm region, and effects of additional molecular absorbers on the determination of the temperature profile. It can be shown that using broad-band window channels (half width ?20cm^?1) the derived surface temperature is significantly different from the surface temperature derived from narrow spectral band channels (e.g. for the HIRS window channel 8 this difference is about 1° C). Simulations of some combinations of spectral channels including one proposed as an optimal approach show no significant difference in the derived temperature profile. Neglecting the ozone absorption of the 14.1 μm band leads to a change in radiance of about 1.5 mW/m²sr cm^?1 and to a systematic error of the derived temperature of about ?2° C in the troposphere.     

Mission aspects of GRASP ESA's prospective gamma-ray astronomy satellite

Mission aspects of the project GRASP (Gamma-Ray Astronomy with Spectroscopy and Positioning) are described as documented in the ESA assessment study at the end of 1986. The goals of this study addressed scientific objectives, technical solutions and feasibility of the mission. Two accommodation studies accompanied the assessment study. Their results show that GRASP can be accommodated on two existing space platforms, EURECA-B and ROBUS, respectively.     

An attempt for objective analysis of TIROS-N images

An attempt for digital processing of analog images taken in the infrared channel (10.5–11.5 μm) from TIROS-N is presented. The data digitized to 8-bits are normalized by using SR Data Manipulator. The investigated period is November 3–4, 1979. The geographic rectification moves the data into a polar stereographic map. To estimate the cloud heights empirical relationships are applied. The following characteristics of the cloud field are produced: the cloud amount, the dominant cloud-type, the daily variation of IR brightness temperature and the cloud texture. The results are visualized on a colour display.     

The GRASP telescope

The GRASP mission Gamma-Ray Astronomy with Spectroscopy and Positioning addresses the scientific goals of fine spectroscopy with imaging and accurate positioning of gamma-ray sources, an unexplored area within gamma-ray astronomy. The assessment of GRASP as a future space astronomy mission in the mid-1990s has led to the design of the instrument outlined in this article. Thus GRASP is a third generation gamma-ray telescope and is designed to operate as a high quality spectral imager in the mid-1990s, when, following the GRO, SIGMA, and GAMMA-1 missions, there will be requirement for a more sophisticated instrument to maintain the momentum of advance in gamma-ray astronomy. The telescope will be capable of locating point sources with a precision of typically 1 arc min, whilst making a fine spectral analysis (E/E 1000) of any gamma-ray line features. The high sensitivity of this instrument and the long (> 2 year) lifetime of the mission will enable a large number ( 1000) of astronomical objects to be studied. The GRASP mission has the potential to move gamma-ray astronomy from an era of basic exploration to one in which detailed and novel measurements can be used to gain a better understanding of many astrophysical problems.     

Large-scale electric fields and currents and related geomagnetic variations in the quiet plasmasphere

At the end of the sixties it became obvious that two-dimensional dynamo models can explain nearly all facts, which had been found morphologically for mean annual Sq-fields. During the recent decade new or improved methods to measure electric fields (e.g. incoherent scatter facilities) and to investigate great data files have been developed. New informations received with these methods about the existence of regular variations of the Sq-field in dependence on season and universal time and about the electric field have been summarized in Section 2. All attempts to describe also these variations with a two-dimensional dynamo model did not lead to any success, but showed a strong theoretical over-estimation of the asymmetries. Therefore, it must be concluded that three-dimensional plasmaspheric current systems, taking into consideration the coupling between both hemispheres along the high-conducting magnetic field lines, are needed in order to explain the regular variations of the Sq -field. The basic equations for two- and three-dimensional dynamo models, different methods for the solution of these equations and the resulting models from different authors are compiled and discussed (Section 3).Based on all morphological and theoretical results a plasmaspheric-ionospheric current system has been constructed and some properties of the plasmaspheric field-aligned current distribution, have been derived.     

Cosmic Rays Beyond the Knee

We briefly review the available data on cosmic rays beyond the `knee, i.e., over the energy range from 10¹⁵ to more than 10²⁰ eV. We discuss the observational status of the field, review some of the current attempts to explain the origin of these particles, and briefly survey the prospects of future measurements.     

Evaluation of mixed mode-I/II criteria for fatigue crack propagation using experiments and modeling

In this study, in-plane mixed mode-I/II fatigue crack growth simulations and experiments are performed for the Al 7075-T651 aluminum alloy which is widely used in the aerospace industry. Tests are carried out under different mode mixity ratios to evaluate the applicability of a fracture criterion developed in a previous study to mixed mode-I/II fatigue crack growth tests. Results obtained from the analyses and experiments are compared with existing and developed criteria in terms of crack growth lives. Compact Tension Shear (CTS) specimens, which enable mixed mode loading with loading devices under different loading angles, are used in the simulations and experiments. In an effort to model and simulate the actual conditions in the experiments, crack surfaces of fractured specimens are scanned, crack paths are modeled exactly, and contacts are defined between the contact surfaces of a specimen and the loading device for each crack propagation step in the analyses. Having computed the mixed mode stress intensity factors from the numerical analyses, propagation life cycles are predicted by existing and the developed mixed mode-I/II criteria and then compared with experimental results.