Subjects: Geosciences >> Space Physics submitted time 2016-05-04
Abstract： OH airglow emissions are generated in the mesopause and low thermosphere (MLT) region in a layer centered near 87km.The OH rotational temperature is a good proxy for the kinetic temperature.So the rotational temperatures derived from ground-based observations of OH airglow emissions are used to investigate the temperature structure in the MLT.The OH airglow emission spectra were observed by the ground-based spectrometer from December 2011 to December 2013.The OH (8-3) band is used to calculate rotational temperature.The temperatures from SABER are weighted vertically by the weighting functions from its OH-A channel volume emission rates.Firstly, the rotational temperature is compared with the SABER.Secondly, the daily mean temperatures are fitted by the harmonic waves, and the temporal variation features during nights are analyzed.The comparison between OH rotational temperature and SABER shows that the mean rotational temperature of OH (8-3) band is 203.011.2Kwith 5.5Kwarmer than SABER′s.Both have obviously identical seasonal variations and the temperature variation of winter to summer can reach 60K.The annual and semiannual components are the two most significant variations, and the annual amplitude of 10.8Kis greater than semiannual amplitude of 2.7K.Their phases are respectively in December and March.It is shown that there are multiple temporal rotational variations during night, such as oscillations controlled by tides and shortperiod waves.The OH rotational temperature is a good proxy for the kinetic temperature in the MLT region.There are significant annual and semiannual variations in this region, and the temperatures during night have various temporal features.It is concluded that the temporal variations of ground-based rotational temperatures from OH (8-3) band are well correlated with the SABER temperatures.They have the same seasonal variations and the annual and semiannual oscillations are the two strongest components.The nocturnal rotational temperatures have multiple temporal features controlled by the various oscillations.
Peer Review Status:
Awaiting Review
Subjects: Geosciences >> Space Physics submitted time 2016-05-04
Abstract： Large planar plasma sheets with size of 60 cm*60 cm, maximum current of 3 A and duration of 200 mus, were obtained in a pulsed linear hollow cathode discharge device under 15 mT magnetic field confinement. The electron density 2-D distribution in the thickness direction and its evolution of plasma sheets with pressures between 90 Pa to 210 Pa were obtained by Langmuir probe using the fast frame function of oscilloscope and the rotating hollow cathode method. The effects of pressure on the time needed to reach the maximum peak density in the thickness direction, the maximum peak density and the full width at half maximum (FWHM) peak density, were investigated. The results show that, as the pressure decreased, the time reaching the maximum peak density in the thickness direction and the FWHM peak density diminished, while the maximum peak density in the thickness direction increased. These results could be utilized to manipulate the parameters of large planar plasma sheets.
Peer Review Status:Awaiting Review
Subjects: Geosciences >> Space Physics submitted time 2016-05-04
Abstract： Radiation risk of astronauts during the flight in low earth orbit (LEO) and deep space exploration is mainly from the exposure of galactic cosmic ray (GCR). The radiation dose from GCR is the basis for the assessment of astronauts' radiation risk. In 2013, a new estimation method for the assessment of astronauts' radiation dose was presented by the International Committee on Radiological Protection (ICRP), so as to improve the assessment's accuracy of the radiation dose from heavy ions in space. Based on this method, a Monte Carlo program was developed for simulation of the particle transportation in materials and a voxel phantom of Chinese adult male was realized in this program to represent the astronaut. With this program, the fluence to dose conversion coefficients for the organs of astronauts were calculated for the isotropic exposure by particles with the atomic number from 1 to 92. The radiation dose to astronauts in LEO from GCR was also estimated. �2015, Beijing University of Aeronautics and Astronautics (BUAA). All right reserved.
Peer Review Status:Awaiting Review
Subjects: Geosciences >> Space Physics submitted time 2016-05-04
Abstract： In order to choose the best detection efficiency of different formations, quantitative evaluation of different formations shall be employed. In this paper, the existing evaluation parameters of four-point cooperative detection are analyzed and summarized and then based on the definition of volumetric tensor, the five-point formation is divided into five tetrahedrons and one main tetrahedron plus a fifth point to evaluate the detection efficiency. Finally, orbit data of five-spacecraft in one orbit period is used to simulate and analyze the two methods, and result shows that the method works well in evaluating five-point formation.
Peer Review Status:Awaiting Review
Subjects: Geosciences >> Space Physics submitted time 2016-05-04
Abstract： This paper describes the design of an array antenna which can generate radio waves carrying orbital angular momentum (OAM) at 6 GHz.We consider the microstrip antenna with coaxial feed as the element to compose the circular antenna array which is excited with unit amplitude but with phase delay from element to element.According to the simulation and optimization with high frequency structure simulator(HFSS),we get different patterns of OAM modes depending on the different phase delay,and obtain the vortex electromagnetic wave carrying orbital angular momentum.
Peer Review Status:Awaiting Review
Subjects: Geosciences >> Space Physics submitted time 2016-05-03
Abstract： After spacecraft launched into space environment, molecule contamination and tiny particle contamination deposit on spacecraft surface and constitute the surface contamination layer. This contamination phenomenon has different levels of negative impacts on some technical systems. The on-orbit detection results of spacecraft surface contamination both in China and abroad were discussed. Surface contamination deposition changes and control factors were preliminarily evaluated. The result shows that deposition changes of surface contamination within the first 1 to 2 years after launch are controlled by the spacecraft outgassing mass by itself, outgassing rate, spacecraft surface temperature and air flow direction. The deposition mass within early period is larger, which is controlled by more surface outgassing by spacecraft itself within early period and higher deposition rate after launch. And the deposition mass is more in the ram area than in the yield area. The surface deposition in the later period shows obvious drop or slow fluctuations, and possesses omnidirectional characteristics. Some control factors with omnidirectional effect were discussed, among which high-energy particle flux and solar ultraviolet radiation flux may be the main control factors.
Peer Review Status:Awaiting Review
Subjects: Geosciences >> Space Physics submitted time 2016-05-03
Abstract： Gravity wave activity in the upper stratosphere is investigated using density data retrieved from the Rayleigh lidar of National Space Science Center, Chinese Academy of Sciences. Combining the Rayleigh lidar data with the wind data of National Centers for Environmental Prediction (NCEP) Global Forecast System (GFS), we study a mountain wave observed on November 11, 2013. The parameters of this mountain wave, such as propagation direction and propagation speed, have been calculated. Gravity wave perturbations are extracted from 0.5 h×1 km density profiles. The relative density perturbations are expressed by ρ'(z)=(ρ(z)-ρ0(z))/ρ0(z), where ρ(z) is the measured atmosphere density, and ρ0(z) is the background density which is calculated by fitting the logarithmic form of whole night mean density with 4 order polynomial. The background wind data are achieved by applying a linear polynomial fitting to the NCEP-GFS wind data between 20 to 48 km altitude. Using the data extracted from the complete density perturbations structure and the background wind data, we calculate the parameters of gravity waves observed on November 11, 2013 by the gravity wave dispersion equation. The complete density perturbation structure shows an obvious phenomenon of mountain gravity wave activity. The wave phases at same altitude remain unchanged in the whole night. The perturbation structure shows that vertical wavelength is about 5.5 km but changes with altitude. A group of over-determined equations can be established by substituting the data extracted from the complete density perturbations structure and the background wind data into the gravity wave dispersion equation. And two groups of solutions are obtained by using the least squares method to solve these over-determined equations. The wind profiles in the direction of two sets of solutions have been analyzed. A critical layer (zero wind layer) which will prevent the upward propagation of mounting waves is found in the wind profile in the direction of 37.9°(or 217.9°). Finally, the gravity waves observed on November 11, 2013 propagate in the direction of 52.4° from the north to the west, with a horizontal wavelength of 5.5 km. Compared with inertia waves, there is no downward-propagating or upward-propagating phase in the density perturbation structure. At the same altitude, the phase remains unchanged in the whole night. Such kind of gravity wave perturbation structures have been often observed in winter. Density data obtained by Rayleigh lidar and NCEP-GFS wind data at Beijing are used to analyze a mountain wave parameters observed on November 11, 2013. By analysis, we obtain terrain-generated gravity waves propagating in the direction of 52.4° from the north to the west, with a horizontal wavelength of 5.5 km and average vertical wavelength of 6.0 km. ©, 2015, Science Press. All right reserved.
Peer Review Status:Awaiting Review
Subjects: Geosciences >> Space Physics submitted time 2016-05-03
Abstract： The classical approaches for single event latchup (SEL) rate prediction are based on the rectangular parallelepiped (RPP) model of only one sensitive volume. However, the experiment results of SEL sensitivity mapping of static random access memory (SRAM) show that the device has not only one sensitive volume (SV). The in-flight SEL rate of the device was corrected using the experiment results of pulsed laser SEL sensitivity mapping of SRAM K6R4016V1D.The SEL sensitivity maps of the SRAM by pulsed laser were first obtained and then the SV number of the device was calculated. The SEL rates of the device were predicted and discussed for different space orbits, radiation particles, SV thicknesses and SV number in particular. The results show that SEL rate caused by heavy ion decreases with SV number. The correction of the SV number is essential for SEL rate due to proton direct ionization; otherwise, the contribution of direct ionization of protons to SEL rate would be greatly overestimated.
Peer Review Status:Awaiting Review
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