791 research outputs found
Interplanetary double-shock ensembles with anomalous electrical conductivity
Similarity theory is applied to the case of constant velocity, piston-driven, shock waves. This family of solutions, incorporating the interplanetary magnetic field for the case of infinite electric conductivity, represents one class of experimentally observed, flare-generated shock waves. This paper discusses the theoretical extension to flows with finite conductivity (presumably caused by unspecified modes of wave-particle interactions). Solutions, including reverse shocks, are found for a wide range of magnetic Reynolds numbers from one to infinity. Consideration of a zero and nonzero ambient flowing solar wind (together with removal of magnetic considerations) enables the recovery of earlier similarity solutions as well as numerical simulations. A limited comparison with observations suggests that flare energetics can be reasonably estimated once the shock velocity, ambient solar wind velocity and density, and ambient azimuthal Alfven Mach number are known
Overview of STIP intervals 15-19
Five STIP Intervals for special scientific study of solar and interplanetary phenomena were designated between February 1984 and March 1986. The first two intervals were selected retrospectively after unusual periods of solar activity; the remaining three intervals were selected in advance in conjunction with anticipated spacecraft configurations and measurements. In this overview the historical background of these STIP Intervals and a summary of the rationale in the selection of these particular time periods for concentrated studies are presented
A simulation of the IPS variations from a magnetohydrodynamical simulation
Calculations of the variations of interplanetary scintillation (IPS) from a disturbance simulated by a 3-D magnetohydrodynamical (MHD) model of the solar wind are presented. The simulated maps are compared with observations and it is found that the MHD model reproduces the qualitative features of observed disturbances. The disturbance produced by the MHD simulation is found to correspond in strength with the weakest disturbance which can be reliably detected by existing single station IPS observations
A simulation study of two major events in the heliosphere during the present sunspot cycle
The two major disturbances in the heliosphere during the present sunspot cycle, the event of June to August, 1982, and the event of April to June, 1978, are simulated by the method developed by Hakamada and Akasofu (1982). Specifically, an attempt was made to simulate the effects of six major flares from three active regions in June and July, 1982, and April and May, 1978. A comparison of the results with the solar wind observations at Pioneer 12 (approximately 0.8 au), ISEE-3 (approximately 1 au), Pioneer 11 (approximately 7 to 13 au) and Pioneer 10 (approximately 16 to 28 au) suggests that some major flares occurred behind the disk of the sun during the two periods. The method provides qualitatively some information as to how such a series of intense solar flares can greatly disturb both the inner and outer heliospheres. A long lasting effect on cosmic rays is discussed in conjunction with the disturbed heliosphere
A serial queuing model for the Navy Advanced Traceability and Control (ATAC) system
The purpose of this thesis was to develop a preliminary simulation model of the Advanced Traceability and Control (ATAC) process. The motivation was the need to evaluate significant policy decisions such as, Defense Management Review Decision (DMRD) 901's "ship or hold" decision. An analysis of the operation of ATAC and the data base maintained by Navy Material Transportation Office (NAVMTO) were made to provide necessary details for constructing the model. Significant data base problems were discovered that precluded the development of an elaborate simulation model.. Although the simulation model is very simple, it does show that more detailed and accurate ATAC data are needed to effectively measure and monitor the ATAC system.http://archive.org/details/serialqueuingmod00dryeLieutenant, United States NavyApproved for public release; distribution is unlimited
Alternator and voltage regulator-exciter for a Brayton cycle space power system. Volume 1 - Design and development
Alternator and voltage regulator for Brayton cycle space power syste
A statistical study of the performance of the Hakamada-Akasofu-Fry version 2 numerical model in predicting solar shock arrival times at Earth during different phases of solar cycle 23
The performance of the Hakamada
Akasofu-Fry, version 2 (HAFv.2) numerical model, which provides predictions
of solar shock arrival times at Earth, was subjected to a statistical study
to investigate those solar/interplanetary circumstances under which the
model performed well/poorly during key phases (rise/maximum/decay) of solar
cycle 23. In addition to analyzing elements of the overall data set (584
selected events) associated with particular cycle phases, subsets were
formed such that those events making up a particular sub-set showed common
characteristics. The statistical significance of the results obtained using the
various sets/subsets was generally very low and these results were not significant
as compared with the hit by chance rate (50%). This implies a low level
of confidence in the predictions of the model with no compelling
result encouraging its use. However, the data
suggested that the success rates of HAFv.2 were higher when the background
solar wind speed at the time of shock initiation was relatively fast. Thus,
in scenarios where the background solar wind speed is elevated and the
calculated success rate significantly exceeds the rate by chance, the
forecasts could provide potential value to the customer.
With the composite statistics available for solar cycle 23,
the calculated success rate at high solar wind speed, although clearly above
50%, was indicative rather than conclusive. The RMS error
estimated for shock arrival times for every cycle phase and for the
composite sample was in each case significantly better than would be
expected for a random data set. Also, the parameter "Probability of
Detection, yes" (PODy) which presents the Proportion of Yes observations
that were correctly forecast (i.e. the ratio between the shocks correctly
predicted and all the shocks observed), yielded values for the
rise/maximum/decay phases of the cycle and using the composite sample of
0.85, 0.64, 0.79 and 0.77, respectively. The statistical results obtained
through detailed analysis of the available data provided insights into how
changing circumstances on the Sun and in interplanetary space can affect the
performance of the model. Since shock arrival predictions are widely
utilized in making commercially significant decisions re. protecting space
assets, the present detailed archival studies can be useful in future
operational decision making during solar cycle 24. It would be of added
value in this context to use Briggs-Rupert methodology to estimate the cost
to an operator of acting on an incorrect forecast
Slow shock interactions in the heliosphere using an adaptive grid MHD model
International audienceA one-dimensional (1-D), time-dependent, adaptive-grid MHD model with solar wind structure has been used in the past to study the interaction of shocks. In the present study, we wish to study some fundamental processes that may be associated with slow shock genesis and their possible interactions with other discontinuities. This adaptive-grid model, suitable for appropriate spatial and temporal numerical simulations, is used for this purpose because its finer grid sizes in the vicinity of the steep gradients at shocks make it possible to delineate the physical parameters on both sides of the shocks. We found that a perturbation with deceleration of solar wind will generate an ensemble consisting of a forward slow shock, a fast forward wave and a reverse slow shock. On the other hand, a perturbation with an increase in acceleration of solar wind will generate both a slow shock and a fast shock. These two perturbations, although not unique, may be representative of momentum and pressure changes at the solar surface. During the transition of a fast shock overtaking a slow shock from behind, the slow shock might disappear temporarily. Also, during the process of the merging of two slow shocks, a slow shock-like structure is formed first; later, the slow shock-like structure evolves into an intermediate shock-like structure. This intermediate shock-like structure then evolves into an intermediate wave and a slow shock-like structure. Finally, the slow shock-like structure evolves into a slow shock, but the intermediate wave disappears by interacting with the non-uniform solar wind. This complex behavior demonstrates the non-unique nature of the formation of slow shocks, intermediate shocks and their derivative structures. We emphasize the main aim of this work to be both: (a) non-unique input physical parameters to explain the paucity of observed slow shocks, as well as (b) the impossibility of backward tracing to the history of input boundary conditions in view of the present inability to describe unambiguous inputs at the Sun
A numerical study of transient, thermally-conductive solar wind
A numerical analysis of transient solar wind starting at the solar surface and arriving at 1 AU is performed by an implicit numerical method. The model hydrodynamic equations include thermal conduction terms for both steady and unsteady simulations. Simulation results show significant influence of thermal conduction on both steady and time-dependent solar wind. Higher thermal conduction results in higher solar wind speed, higher temperature, but lower plasma density at 1 AU. Higher base temperature at the solar surface gives lower plasma speed, lower temperature, but higher density at 1 AU. Higher base density, on the other hand, gives lower velocity, lower temperature, but higher density at 1 AU
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