Multi-wavelength coordinated observations of ionospheric irregularity structures from an anomaly crest location during unusual solar minimum of the 24th cycle

The present paper reports coordinated ionospheric irregularity measurements at optical as well as GPS wavelengths. Optical measurements were obtained from Tiny Ionospheric Photometer (TIP) sensors installed onboard the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) satellites. GPS radio signals were obtained from a dual frequency GPS receiver operational at Calcutta (22.58°N, 88.38°E geographic; geomagnetic dip: 32.96°; 13.00°N, 161.63°E geomagnetic) under the SCIntillation Network Decision Aid (SCINDA) program. Calcutta is located near the northern crest of Equatorial Ionization Anomaly (EIA) in the Indian longitude sector. The observations were conducted during the unusually low and prolonged solar minima period of 2008–2010. During this period, four cases of post-sunset GPS scintillation were observed from Calcutta. Among those cases, simultaneous fluctuations in GPS Carrier-to-Noise ratios (C/N_o) and measured radiances from TIP over a common ionospheric volume were observed only on February 2, 2008 and September 25, 2008. Fluctuations observed in measured radiances (maximum 0.95 Rayleigh) from TIP due to ionospheric irregularities were found to correspond well with C/N₀ fluctuations on the GPS links observed from Calcutta, such effects being noted even during late evening hours of 21:00–22:00 LT from locations around 40° magnetic dip. These measurements indicate the existence of electron density irregularities of scale sizes varying over several decades from 135.6 nm to 300–400 m well beyond the northern crest of the EIA in the Indian longitude sector during late evening hours even in the unusually low solar activity conditions.     

Solar flares,CMEs and solar energetic particle events during solar cycle 24

We present here a study of Solar Energetic Particle Events (SEPs) associated with solar flares during 2010–2014 in solar cycle 24. We have selected the flare events (≥GOES M-class), which produced SEPs. The SEPs are classified into three categories i.e. weak (proton intensity?≤?1?pfu), minor (1?pfu?<?proton intensity?<?10?pfu) and major (proton intensity?≥?10?pfu). We used the GOES data for the SEP events which have intensity greater than one pfu and SOHO/ERNE data for the SEP event less than one pfu intensity. In addition to the flare and SEP properties, we have also discussed different properties of associated CMEs.     

Classification of solar wind structures and intense geomagnetic storm alarms with self-organizing maps

Intense geomagnetic storms (D_st < −100 nT) usually occur when a large interplanetary duskward-electric field (with Ey > 5 mV m⁻¹) lasts for more than 3 h. In this article, a self-organizing map (SOM) neural network is used to recognize different patterns in the temporal variation of hourly averaged Ey data and to predict intense storms. The input parameters of SOM are the hourly averaged Ey data over 3 h. The output layer of the SOM has a total of 400 neurons. The hourly Ey data are calculated from solar wind data, which are provided by NSSDC OMNIWeb and ACE spacecraft and contain information on 143 intense storms and a fair number of moderate storms, weak storms and quiet periods between September 3, 1966 and June 30, 2002. Our results show that SOM is able to classify solar wind structures and therefore to give timely intense storm alarms. In our SOM, 21 neurons out of 400 are identified to be closely associated with the intense storms and they successfully predict 134 intense storms out of the 143 ones selected. In particular, there are 14 neurons for which, if one or more of them are present, the occurrence probability of intense storms is about 90%. In addition, several of these 14 neurons can predict big magnetic storm (D_st  −180 nT). In summary, our method achieves high accuracy in predicting intense geomagnetic storms and could be applied in space environment prediction.     

三维非线性撕裂模耦合和快速磁场重联

基于三维不可压缩电阻性ＭＨＤ方程，在长柱形位型下，数值研究了电阻撕裂模不稳定性所引起的磁场重联过程。研究结果表明，撕裂模的非线性相互作用和耦合，将产生许多模式的强裂解稳和导致快速的磁场重联。这一过程的进一步发展，导致具有螺旋形结构，不同模式的磁岛磁力线重叠，从而引起较大区域内的磁场各态经历和磁力线随机走向，形成撕裂模端动。     

Structure and development of quiet loops in the solar corona

X-ray emission from solar coronal loops changes on two different timescales: a) flare loops and transient active region brightenings show a rapid variability, b) quiet region loops are quasi-steady and change only slowly with time. This different time behavior has been analyzed on the basis of Yohkoh SXT observations and we report here on the results from our analysis, mainly focussing on quiet loop variability.     

1982年12月30日日浪

介绍了１９８２年１２月３０日太阳视面上Ｓ１０Ｗ２０处伴随耀斑产生的日浪形态，并给出其速度场随时间演变的特征．光谱观测结果表明，日浪上升过程中有旋转运动，速度为２０—３０ｋｍ／ｓ，旋转速度随时间而减小．     

LANDSAT-7卫星的有效载荷ETM

LANDSAT-7卫星的主要有效载荷——改进型主题测绘仪(Enhanced Thematic Map-per Plus)ETM 是在landsat-4和Landsat-5卫星的主要有效载荷主题测绘仪(Thematic Map-per)的基础上改进的。ETM 相对TM的主要不同之处在于它增加了1个金色谱段和2个增益区域,增加了太阳定标器,并提高了红外谱段的分辨率,文章简要介绍ETM 的性能和主要组件。     

航天器太阳电池阵热真空试验技术

文章叙述了进行太阳电池阵热真空试验的重要性、一般要求及相关的主要试验技术.     

Experiments on unsteady vortex flowfield of typical rotor airfoils under dynamic stall conditions

A new experiment for airfoil dynamic stall is conducted by employing the advanced particle image velocimetry(PIV) technology in an open-return wind tunnel. The aim of this experimental investigation is to demonstrate the influences of different motion parameters on the convection velocity, position and strength of leading edge vortex(LEV) of airfoil under different dynamic stall conditions. Two different typical rotor airfoils, OA209 and SC1095, are measured at different free stream velocities, oscillation frequencies, and angles of attack. It is demonstrated by the measured data that the airfoil with larger leading edge radius could notably decrease the strength of LEV. The angle of attack(Ao A) of airfoil can obviously influence the dynamic stall characteristics of airfoil,and the LEV would be effectively inhibited by decreasing the mean pitch angle. In addition, the convection velocity of LEV is estimated in this measurement, and the results demonstrate that the influence of airfoil shape on convection velocity of LEV is limited, but the convection velocity of LEV would be increased by enlarging the oscillation frequency. Meanwhile, the convection velocity of LEV is a time variant value, and this value would increase as the LEV convects to the trailing edge of airfoil.