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Digital computer model was devised for determining thermal and solar radiation interchange factors. Program computes interchange factors among surfaces having any combination of following properties: diffuse emittance and reflectance, diffuse emittance and specular reflectance, diffuse emittance and components of diffuse and specular reflectance, and directional emittance and bidirectional reflectances.
A collisional electromagnetic dispersion relation is derived from two-fluid theory for the interchange mode coupled to the Alfven, acoustic, drift and entropy modes in a partially ionized plasma. The fundamental electromagnetic nature of the interchange model is noted; coupling to the intermediate Alfven mode is strongly stabilizing for finite k sub z. Both ion viscous and ion-neutral stabilization are included, and it was found that collisions destroy the ion finite Larmor radius cutoff at short perpendicular wavelengths.
A collisional electromagnetic dispersion relation is derived from two-fluid theory for the interchange mode coupled to the Alfven, acoustic, drift, and entropy modes in a partially ionized plasma. The fundamental electromagnetic nature of the interchange mode is noted: coupling to the intermediate Alfven mode is strongly stabilizing for finite perturbations of the magnetic field. Both ion-viscous and ion-neutral stabilization are included; and it is found that collisions destroy the FLR (finite Larmor radius) cutoff at short perpendicular wavelengths.
A rotation-dominated magnetosphere is unstable to magnetic flux-tube interchange motions if and only if the plasma content of a unit magnetic flux tube is a decreasing function of distance from the spin axis. For a spin-aligned dipole field, an approximate expression is obtained for the marginally stable distribution. Plasma filling the Jovian magnetosphere from internal sources would initially violate this stability criterion so that interchange motions would act to establish the marginally stable distribution.
Volume interchange factors are shown to be convenient in modeling the radiative processes in the wake of a hypersonic vehicle. Use of the factors facilitates calculating not just the radiative heating rates on afterbody surfaces but also the radiative de-excitation rates from stimulated emission and re-excitation rates from absorption in rarefied nonequilibrium flows. Sample calculations of volume interchange factors are presented for volume configurations modeling wake elements, and the numerical results are compared to limiting approximations to clarify the operation of the emission, transmission, and absorption processes.
Numerical simulations of the generalized Rayleigh-Taylor instability are presented. The model and simulations are applicable to bottomside and topside spread F, unstable barium cloud dynamics, and collisional interchange instability in general. The principal result is that the evolution of the instability tends to an anisotropic state consisting of nearly sinusoidal (quasi-periodic) variation along the effective electric field, and shocklike structures propagating perpendicular to E(eff) along the extrema of the quasi-periodic structures. The spectral properties of the nonlinear state are analyzed using one-dimensional power spectra calculated along spatial trajectories for selected angles to E(eff). In this way a direct comparison to in situ probe data can be made. The inherent anisotropy of the nonlinear state is reflected in major qualitative differences between the spectra taken parallel to and perpendicular to E(eff). The fundamental finding of the present work is that anisotropy in interchange dynamics is much greater than had been previously reported. This strong anisotropy can explain much of the spectral and spatial structural characteristics of both bottomside and topside spread F. In a companion paper a comparison of the simulation results to various in situ data sets is given.
The dynamical properties and spectral characteristics of the ionospheric interchange instability in the collisional and inertial regimes are investigated numerically and analytically, using a two-dimensional fluid model. This model, which describes the collisional and inertial dynamics of the F region ionosphere, is similar to the models of Ott (1978) and Kintner and Seyler (1985). By numerically integrating the model equations, the nonlinear evolution of three interchange unstable configurations in the collisional and inertial regimes are followed, and their dynamical and spectral properties are studied. The solutions indicate that the dynamical properties of a collision-dominated regime are distinctly different from those of an inertia-dominated regime. The qualitative characteristics of a plasma bubble in both regime-types are described.
The Infrared Space Observatory (ISO) is an ESA cornerstone mission for infrared astronomy. Schedules for launch in 1993, its four scientific instruments will provide unprecedented sensitivity and spectral resolution at wavelengths which are inaccessible using ground-based techniques. One of these, the Long Wavelength Spectrometer (LWS), will operate in the 45 to 180 micron region (Emery et. al., 1985) and features two Fabry-Perot interferometers mounted on an interchange mechanism. The entire payload module of the spacecraft, comprising the 60 cm telescope and the four focal plane instruments, is maintained at 2 to 4 K by an onboard supply of liquid helium. The mechanical design and testing of the cryogenic interferometer and interchange mechanisms are described.
The factors that affect the interchange instability of the earth's plasmapause are investigated using an extension of Richmond's (1973) procedure based on computing individual particle motions. The effects of particle inertia, centrifugal force, and gravity are estimated. A general differential equation is derived for the time variation of the perturbation potential characterizing an electrostatic ripple with no field-aligned potential drop, which can be solved as an eigenvalue problem to find the linear growth rate. Approximate analytic solutions to this equation were obtained from which it was deduced that the interchange instability is caused by the sharp change in plasma pressure at the plasmapause; its growth rate is limited by ionospheric conductivity and, for very short wavelengths, by the inertia of the magnetospheric particles.
Graphic illustration of midlatitude interchange of atmospheric angular momentum between distant regions is presented. An examination is conducted of the global distribution of atmospheric angular momentum during 1977-1978 and 1982-1983 in order to identify evidence of prominent short-term interchanges of relavitive atmospheric angular momentum between mid and high latitude zones in both hemispheres. Thirty-day detrended angular momentum time series, prepared from the NMC global zonal wind data, are examined in latitude bands. The results confirm that momentum can be selectively redistributed between tropical, temperate, and high latitudes in patterns indicative of the development and dissipation of interacting regions, described variously in studies on the index cycle, seesaws, and telecommunications.
The nonlinear evolution of the magnetic interchange or buoyancy instability of a differentially rotating disk threaded by an ordered vertical magnetic field is investigated. A 2D ideal fluid in the equatorial plane of a central mass in the corotating frame of reference is considered as a model for the disk. If the rotation rate of the disk is Keplerian, the disk is found to be stable. If the vertical magnetic field is sufficiently strong, and the field strength decreases with distance from the central object, and thus the rotation of the disk deviates from Keplerian, if is found that an instability develops. The magnetic flux and disk matter expand outward in certain ranges of azimuth, while disk matter with less magnetic flux moves inward over the remaining range of azimuth, showing a characteristic development of an interchange instability.
The Directory Interchange Format (DIF) is a data structure used to exchange directory-level information about data sets among information systems. In general the format consists of a number of fields that describe the attributes of a directory entry and text blocks that contain a descriptive summary of and references for the directory entry. All fields and the summary are preceded by labels identifying their contents. All values are ASCII character strings. The structure is intended to be flexible, allowing for future changes in the contents of directory entries. The manual is structured as follows: section 1 is a general description of what constitutes a directory entry; section 2 describes the content of the individual fields within the data structure, together with some examples. Also included in the six appendices is a description of the syntax used within the examples; samples of the directory interchange format applied to different data sets; the allowable discipline keywords; a current list of valid location keywords; a list of allowable parameter keywords; a list of acronyns and a glossary of terms used; and a description of the Standard Formatted Data Unit header, which may be added to the front of a DIF file to identify the file as a registered standard format.
The Consultative Committee for Space Data Systems (CCSDS) is developing Standards for the interchange of information between systems, including those operating under different environments. The objective is to perform the interchange automatically, i.e. in a computer interpretable manner. One aspect of the concept developed by CCSDS is the use of a separate data description to specify the data being transferred. Using the description, data can then be automatically parsed by the receiving computer. With a suitably expressive Data Description Language (DDL), data formats of arbitrary complexity can be handled. The advantages of this approach are: (1) that the description need only be written and distributed once to all users, and (2) new software does not need to be written for each new format, provided generic tools are available to support writing and interpretation of descriptions and the associated data instances. Consequently, the effort of 'hard coding' each new format is avoided and problems of integrating multiple implementations of a given format by different users are avoided. The approach is applicable in any context where computer parsable description of data could enhance efficiency (e.g. within a spacecraft control system, a data delivery system or an archive). The CCSDS have identified several candidate DDL's: EAST (Extended Ada Subset), TSDN (Transfer Syntax Data Notation) and MADEL (Modified ASN.1 as a Data Description Language -- a DDL based on the Abstract Syntax Notation One - ASN.1 - specified in the ISO/IEC 8824). This paper concentrates on ESA's development of MADEL. ESA have also developed a 'proof of concept' prototype of the required support tools, implemented on a PC under MS-DOS, which has successfully demonstrated the feasibility of the approach, including the capability within an application of retrieving and displaying particular data elements, given its MADEL description (i.e. a data description written in MADEL). This paper outlines the work done to date and assesses the applicability of this modified ASN.1 as a DDL. The feasibility of the approach is illustrated with several examples.
A recent assessment of suprathermal electron heat flux dropouts (HFDs) in the solar wind eliminated 90% as possible signatures of field lines disconnected from the Sun at both ends (Pagel et al., 2005b). The primary reason for elimination was the presence of a residual field-aligned strahl presumably signaling field lines connected to the Sun. Using high-time-resolution data from the Wind spacecraft, this paper tests whether the residual strahls were an artifact of averaging over pitch angle distributions (PADs) with and without strahls. An automated search for PADs without strahls (flat PADs) yields an occurrence rate of only 14% within HFDs, but a detailed case study shows that these flat PADs are imbedded within intervals of nearly flat PADs, that is, PADS with residual strahls that cannot be artifacts of averaging. An attractive alternative is that the residual strahls result from intermixing of originally back-scattered fluxes (haloes) of unequal intensities on field lines that have either disconnected or interchange reconnected at the Sun. A reevaluation of reported streaming of higher-energy electrons in HFDs suggests a similar cause. While the high-time-resolution data show high variability of PAD profiles within HFDs, this paper reopens the possibility that a substantial fraction signal disconnection or interchange reconnection. Estimated occurrence rates of fields having undergone these processes based upon published HFD rates are of the same order of magnitude as the surprisingly low values of 1-5% recently predicted by a model of a balanced heliospheric flux budget (Owens and Crooker, 2007).
The Digital Information Sub-project will hold a Technical Interchange Meeting (TIM) with JetBlue Airways to discuss potential collaboration opportunities as well as discuss upcoming NASA-led demonstrations. This interchange meeting will solicit feedback from JetBlue for consideration of the sub-project in upcoming development and to encourage future participation and collaboration.
The Digital Information Sub-project will hold a Technical Interchange Meeting (TIM) with Delta Airlines to discuss potential collaboration opportunities as well as discuss upcoming NASA-led demonstrations. This interchange meeting will solicit feedback from Delta for consideration of the sub-project in upcoming development and to encourage future participation and collaboration. Additionally, Delta will provide insight into airline operations to allow NASA to learn more about airline operations.
Context. The generation of the slow solar wind remains an open problem in heliophysics. One of the current theories among those aimed at explaining the injection of coronal plasma in the interplanetary medium is based on interchange reconnection. It assumes that the exchange of magnetic connectivity between closed and open fields allows the injection of coronal plasma in the interplanetary medium to travel along the newly reconnected open field. However, the exact mechanism underlying this effect is still poorly understood. Aims. Our objective is to study this scenario in a particular magnetic structure of the solar corona: a pseudo-streamer. This topological structure lies at the interface between open and closed magnetic field and is thought to be involved in the generation of the slow solar wind. Methods. We performed innovative 3D magnetohydrodynamic (MHD) simulations of the solar corona with a pseudo-streamer, using the Adaptively Refined MHD Solver (ARMS). By perturbing the quasi-steady ambient state with a simple photospheric, large-scale velocity flow, we were able to generate a complex dynamics of the open-and-closed boundary of the pseudo-streamer. We studied the evolution of the connectivity of numerous field lines to understand its precise dynamics. Results. We witnessed different scenarios of opening of the magnetic field initially closed under the pseudo-streamer: one-step interchange reconnection dynamics, along with more complex scenarios, including a coupling between pseudo-streamer and helmet streamer, as well as back-and-forth reconnections between open and closed connectivity domains. Finally, our analysis revealed large-scale motions of a newly opened magnetic field high in the corona that may be explained by slipping reconnection. Conclusions. By introducing a new analysis method for the magnetic connectivity evolution based on distinct closed-field domains, this study provides an understanding of the precise dynamics underway during the opening of a closed field, which enables the injection of closed-field, coronal plasma in the interplanetary medium. Further studies shall provide synthetic observations for these diverse outgoing flows, which could be measured by Parker Solar Probe and Solar Orbiter.
The purpose of this Technical Interchange Meeting (TIM) is to hold our second of several discussions on select DIP and AES-topics. The first AES- DIP Technical Interchange Meeting was an in-person event in Washington DC. This is a followup meeting to deep dive into some of the areas discussed during the 1st TIM