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.     

Numerical model of time-dependent hydrodynamic flows with mass loading

We study the influence of mass loading on the formation of shocks employing a time-dependent hydrodynamic model. Numerical examples illustrate in which way the formation and propagation of shocks in the plasma is affected by variations of the ionization rate (due to changes of solar wind parameters or of neutral gas production). It is found that mass loading may be an efficient mechanism to prevent the formation of discontinuities in hydrodynamic flows.     

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.     

Banded electron cyclotron harmonic instability-a first comparison of theory and experiment

A study, which is the first of its kind, uses information derived from simultaneously measured wave spectra and particle distributions as the input to a theoretical linear instability model of an electrostatic cyclotron harmonic wave event recorded on GEOS-1. The presence of a hot loss cone component of the particle distribution is established experimentally, and the model accounts reasonably for the observed frequencies and relative strengths of the (n+1/2)f _c and upper hybrid emission features.     

Effect of temperature on the adsorption of adenine

Equilibrium adsorption isotherms for the purine base adenine on the surface of graphite crystals have been obtained at 30, 40, 50, and 60 degrees C by frontal analysis using water as a mobile phase. These data were fitted to the Langmuir isotherm model and interpreted in terms of the well-characterized adsorbate monolayer structure. A van't Hoff plot was used to estimate the adsorption enthalpy, -delta H degree which we determined to be 20 kJ mol-1. The susceptibility of nucleic acid bases to aqueous-phase hydrolysis may have been a limiting feature for their inclusion in the primordial genetic architecture; our results suggest that the effects of temperature and the presence of inorganic solids must also be included when assessing the prebiotic availability of adenine.     

Observations of Irradiance Variations

Since November 1978 a complete set of total solar irradiance (TSI) measurements from space is available, yielding a time series of 21 years. From measurements made by different space radiometers (HF on NIMBUS-7, ACRIM I on SMM, ACRIM II on UARS and VIRGO on SOHO) a composite record of TSI can be compiled. The corrections which are needed for each radiometer, mainly to compensate for degradation, but also for operational influences are described. ACRIM I (1980–1989) and ACRIM II (1992–1995) are taken as reference because their degradation was monitored by inflight comparisons with spare radiometers; since 1996 VIRGO is used as reference. The scale of ACRIM II is adjusted to ACRIM I by comparison with NIMBUS-7 and ERBE. The reliability of this adjustment depends strongly on the stability of the HF and ERBE radiometer during the period of the gap between the ACRIMs which is discussed in detail together with an assessment of the overall precision of the composite.     

The Habitability of Venus

Space Science Reviews - Venus today is inhospitable at the surface, its average temperature of 750 K being incompatible to the existence of life as we know it. However, the potential for...