Characterization of the slow wind in the outer corona

The study concerns the streamer belt observed at high spectral resolution during the minimum of solar cycle 23 with the Ultraviolet Coronagraph Spectrometer (UVCS) onboard SOHO. On the basis of a spectroscopic analysis of the O VI doublet, the solar wind plasma parameters are inferred in the extended corona. The analysis accounts for the coronal magnetic topology, extrapolated through a 3D magneto-hydrodynamic model, in order to define the streamer boundary and to analyse the edges of coronal holes. The results of the analysis allow an accurate identification of the source regions of the slow coronal wind that are confirmed to be along the streamer boundary in the open magnetic field region.     

基于LOLA数据的Aristarchus高原光照特性初步研究

改进了月面中低纬度地区光照分析算法,以Aristarchus高原（AP）为例,使用LRO卫星获得的高分辨率、高精度的LOLA数据和DE/LE430月球行星历表,同时基于月球天平动模型,定量计算和分析了AP地区的光照特性。结果表明：AP地区的光照率都在0.35以上,平坦地区的光照条件较好,受到地形的影响不同位置的光照率相差很大。光照率最大值点（B）要比最小值点（A）高出30%以上。考虑典型的长周期天平动效应,18.6年光照数据的分析结果表明,每个位置的光照率变化较小且趋于稳定,这对月球表面演化研究是一个重要的参考。     

基于STK的星座设计与性能评估

分析了区域性覆盖星座的任务要求及设计特点，结合我国周边地区的地理情况，提出了一种利用太阳同步回归轨道的低轨道区域性覆盖星座设计方案，并应用STK仿真软件完成了该星座的设计与性能评估。仿真结果表明，该星座完全满足对区域性覆盖的任务要求。     

Multi-scale reconnections in a complex CME

A series of three flares of GOES class M, M and C, and a CME were observed on 20 January 2004 occurring in close succession in NOAA 10540. Types II, III, and N radio bursts were associated. We use the combined observations from TRACE, EIT, Hα images from Kwasan Observatory, MDI magnetograms, GOES, and radio observations from Culgoora and Wind/ WAVES to understand the complex development of this event. We reach three main conclusions. First, we link the first two impulsive flares to tether-cutting reconnections and the launch of the CME. This complex observation shows that impulsive quadrupolar flares can be eruptive. Second, we relate the last of the flares, an LDE, to the relaxation phase following forced reconnections between the erupting flux rope and neighbouring magnetic field lines, when reconnection reverses and restores some of the pre-eruption magnetic connectivities. Finally, we show that reconnection with the magnetic structure of a previous CME launched about 8 h earlier injects electrons into open field lines having a local dip and apex (located at about six solar radii height). This is observed as an N-burst at decametre radio wavelengths. The dipped shape of these field lines is due to large-scale magnetic reconnection between expanding magnetic loops and open field lines of a neighbouring streamer. This particular situation explains why this is the first N-burst ever observed at long radio wavelengths.     

Very low thrust station-keeping for low Earth orbiting satellites

Traditional station-keeping for Earth observation satellites with chemical thrusters generally involves maneuvers every couple months that are able to change significantly the semi-major axis and the inclination. These strategies do not scale down to very low thrust level (a few hundreds of μN) electrical thrusters. This paper presents both in-plane and out-of-plane strategies that spread corrections over very long arcs and discretize them to tiny maneuvers every couple orbits, taking into account mission-constraints on maneuvers locations. These strategies scale up to medium thrust strategies, filling the gap between propulsion technologies. The out-of-plane strategy although features a new no-deadband property and controls the full orbital momentum. All strategies allow control very close to the reference (a few hundreds meters in osculating parameters) and very low cost.     

Evolutionary features of polar and non-polar coronal holes during solar cycle 24 and the rising phase of cycle 25

This paper presents the results of the analysis of the evolution of coronal holes (CHs) on the Sun during the period May 13, 2010 – March 20, 2022, covering Solar Cycle 24. Our study uses images in the extreme-ultraviolet iron line (Fe XII 193 Å) obtained with the Atmospheric Imager Assembly of the Solar Dynamics Observatory (AIA/SDO). To localize CHs and determine their areas, we used the Heliophysics Event Knowledgebase (HEK). We separate the CHs into polar and non-polar and study the evolutionary features of each group. During this period, an asymmetry between the Northern (N) and Southern (S) Hemispheres (N-S or hemispheric asymmetry) is detected both in the solar activity (SA) indices and in the localization of the maximum areas of the polar and non-polar CHs. It is shown that the hemispheric asymmetry of the areas of polar and non-polar CHs varies significantly over time and that the nature of these changes is clearly related to the SA cycle. We find that for most of the period, the polar CHs were predominated generated in the S- hemisphere while the non-polar CHs were dominant in the N- hemisphere. It is found that the maximum and minimum of the hemispheric imbalance in the areas of non-polar CHs are close in time to the maximum and minimum of the asymmetry of the SA indices (the number and areas of sunspots). The maximum hemispheric imbalance of the polar CH areas is observed at the maximum of Cycle 24, and the minimum imbalance is found at the cycle minimum. These results confirm our assumption that these two types of CHs are of a different nature and that the non-polar CHs, like sunspots, are elements of the general magnetic activity.     

Decline of geomagnetic and ionospheric activity at earthquake during spotless Sun

We investigate the geomagnetic and ionospheric effects of seismic activity during 1954 Sun spotless days (SSL) from 1995 to 2020. Two subsets of earthquakes (EQ) are evaluated for 676 events observed with the depth D1 ≤ 30 km and 1278 events with D2 > 30 km and the total set SSL. Newly developed 1 h geomagnetic index Hpo and the ionospheric W_EQ index are used for the comparisons with the daily peak earthquake. The ionosphere W_EQ index is derived at the EQ epicenter from JPL GIM-TEC map within the cell of 2.5°×5°, in latitude φ and longitude λ surrounding the epicenter at radius of about 200 km. We use the method of superposed epoch with the zero epoch time t₀ taken at EQ to extract peak values of Hpo and W_EQ during t₀-24 h ≤ t < t₀ (preEQ) and t₀ < t ≤ t₀ + 24 h (postEQ). It is found that the magnitude of Hpo(t₀) is less that the both peaks of Hpo(preEQ) and Hpo(postEQ) in 91 % of events independent of EQ’s depth. Similar effect is observed with the peak of the positive/negative ionosphere indices and the absolute values of |W(preEQ)| and |W(postEQ)| the both exceeding |W_EQ| in 77 % of events. The seismic activity tends to increase towards the solar minimum when SSLs occur. Our results provide evidence that EQ-related geomagnetic and ionospheric activities experience decline of intensity at the time of EQ under SSL.     

Where is the base of the Transition Region? Evidence from TRACE,SDO, IRIS and ALMA observations

Classic solar atmospheric models put the Chromosphere-Corona Transition Region (CCTR) at $～2$ Mm above the ${\tau }_{5000}=1$ level, whereas radiative MHD (rMHD) models place the CCTR in a wider range of heights. However, observational verification is scarce. In this work we review and discuss recent results from various instruments and spectral domains. In SDO and TRACE images spicules appear in emission in the 1600, 1700 and 304 Å bands and in absorption in the EUV bands; the latter is due to photo-ionization of H i and He i, which increases with wavelength. At the shortest available AIA wavelength and taking into account that the photospheric limb is $～0.34$ Mm above the ${\tau }_{5000}=1$ level, we found that CCTR emission starts at $～3.7$ Mm; extrapolating to $\lambda =0$, where there is no chromospheric absorption, we deduced a height of $3.0\pm 0.5$ Mm, which is above the value of 2.14 Mm of the Avrett and Loeser model. Another indicator of the extent of the chromosphere is the height of the network structures. Height differences produce a limbward shift of features with respect to the position of their counterparts in magnetograms. Using this approach, we measured heights of $0.14\pm 0.04$ Mm (at 1700 Å), $0.31\pm 0.09$ Mm (at 1600 Å) and $3.31\pm 0.18$ Mm (at 304 Å) for the center of the solar disk. A previously reported possible solar cycle variation is not confirmed. A third indicator is the position of the limb in the UV, where IRIS observations of the Mg ii triplet lines show that they extend up to $～2.1$ Mm above the 2832 Å limb, while AIA/SDO images give a limb height of $1.4\pm 0.2$ Mm (1600 Å) and $5.7\pm 0.2$ Mm (304 Å). Finally, ALMA mm-$\lambda$ full-disk images provide useful diagnostics, though not very accurate, due to their relatively low resolution; values of $2.4\pm 0.7$ Mm at 1.26 mm and $4.2\pm 2.5$ Mm at 3 mm were obtained. Putting everything together, we conclude that the average chromosphere extends higher than homogeneous models predict, but within the range of rMHD models..     

Numerical simulations of a continuously injected relativistic electron beam relaxation into a plasma with large-scale density gradients

In this paper the influence of large-scale decreasing and increasing gradients of the density of magnetized plasma on the relaxation process of a continuously injected relativistic electron beam with an energy of 660 keV ($v_b=0.9c$) and a pitch-angle distribution is studied using particle-in-cell numerical simulations. It is found that for the selected parameters in the case of a smoothly decreasing gradient and in a homogeneous plasma the formation of spatially limited plasma oscillations of large amplitude occurs. In such cases, modulation instability develops and a long-wave longitudinal modulation of the ion density is formed. In addition, the large amplitude of plasma waves accelerates plasma electrons to energies on the order of the beam energy. In the case of increasing and sharply decreasing gradients, a significant decrease in the amplitude of plasma oscillations and the formation of a turbulent ion density spectrum are observed. The possibility of acceleration of beam electrons to energies more than 2 times higher than the initial energy of the beam particles is also demonstrated. This process takes place not only during beam propagation in growing plasma density, but also in homogeneous plasma due to interaction of beam particles with plasma oscillations of large amplitude.