Jiancun Gong

The Prediction of Maximum Amplitudes of Solar Cycles and the Maximum Amplitude of Solar Cycle 24

We present a brief review of predictions of solar cycle maximum ampli- tude with a lead time of 2 years or more. It is pointed out that a precise prediction of the maximum amplitude with such a lead-time is still an open question despite progress made since the 1960s. A method of prediction using statistical character- istics of solar cycles is developed: the solar cycles are divided into two groups, a high rising velocity (HRV) group and a low rising velocity (LRV) group, depending on the rising velocity in the ascending phase for a given duration of the ascending phase. The amplitude of Solar Cycle 24 can be predicted after the start of the cycle using the formula derived in this paper. Now, about 5 years before the start of the cycle, we can make a preliminary prediction of 83.2-119.4 for its maximum

On energetic electrons (>38 keV) in the central plasma sheet: Data analysis and modeling

The spatial distribution of >38 keV electron fluxes in the central plasma sheet (CPS) and the statistical relationship between the CPS electron fluxes and the upstream solar wind and interplanetary magnetic field (IMF) parameters are investigated quantitatively using measurements from the Geotail satellite (1998-2004) at geocentric radial distances of 9-30 RE in the night side. The measured electron fluxes increase with closer distance to the center of the neutral sheet, and exhibit clear dawn-dusk asymmetry, with the lowest fluxes at the dusk side and increasing toward the dawn side. The asymmetry persists along the Earths magnetotail region (at least to Geotails apogee of 30 RE during the period of interest). Both the individual case and the statistical analysis on the relationship between >38 keV CPS electron fluxes and solar wind and IMF properties show that larger (smaller) solar wind speed and southward (northward) IMF B(z) imposed on the magnetopause result in higher (lower) energetic electron fluxes in the CPS with a time delay of about 1 hour, while the influence of solar wind ion density on the energetic electrons fluxes is insignificant. Interestingly, the energetic electron fluxes at a given radial distance correlate better with IMF B(z) than with the solar wind speed. Based on these statistical analyses, an empirical model is developed for the first time to describe the 2-D distribution (along and across the Earths magnetotail) of the energetic electron fluxes (>38 keV) in the CPS, as a function of the upstream solar wind and IMF parameters. The model reproduces the observed energetic electron fluxes well, with a correlation coefficient R equal to 0.86. Taking advantage of the time delay, full spatial distribution of energetic electron fluxes in the CPS can be predicted about 2 hours in advance using the real-time solar wind and IMF measurements at the L1 point: 1 hour for the solar wind to propagate to the magnetopause and a 1 hour delay for the best correlation. Such a prediction helps us to determine whether there are enough electrons in the CPS available to be transported inward to enhance the outer electron radiation belt.

A regional ionospheric TEC mapping technique over China and adjacent areas on the basis of data assimilation

In this paper, a regional total electron content (TEC) mapping technique over China and adjacent areas (70 degrees E-140 degrees E and 15 degrees N-55 degrees N) is developed on the basis of a Kalman filter data assimilation scheme driven by Global Navigation Satellite Systems (GNSS) data from the Crustal Movement Observation Network of China and International GNSS Service. The regional TEC maps can be generated accordingly with the spatial and temporal resolution being 1 degrees x1 degrees and 5min, respectively. The accuracy and quality of the TEC mapping technique have been validated through the comparison with GNSS observations, the International Reference Ionosphere model values, the global ionosphere maps from Center for Orbit Determination of Europe, and the Massachusetts Institute of Technology Automated Processing of GPS TEC data from Madrigal database. The verification results indicate that great systematic improvements can be obtained when data are assimilated into the background model, which demonstrates the effectiveness of this technique in providing accurate regional specification of the ionospheric TEC over China and adjacent areas.

Ionospheric response to CIR-induced recurrent geomagnetic activity during the declining phase of solar cycle 23

This paper presents an epoch analysis of global ionosphere responses to recurrent geomagnetic activity during 79 corotating interaction region (CIR) events from 2004 to 2009. The data used were GPS total electron content (TEC) data from the Madrigal Database at the Massachusetts Institute of Technology Haystack Observatory and the electron density (Ne) data obtained from CHAllenging Minisatellite Payload (CHAMP) observations. The results show that global ionosphere responses to CIR events have some common features. In high and middle latitudes, the total electron content (TEC) showed a significant positive response (increased electron densities) in the first epoch day. A negative TEC response occurred at high latitudes of the American sector following the positive response. The CHAMP Ne showed a daytime positive response in all latitudes and a nighttime negative response in the subauroral region. These negative TEC and Ne responses were found to be related to thermospheric composition (O/N-2) changes during the storms. At all latitudes, the maximum of the TEC positive effect always occurred at 2-6 h after the CIR starting during local daytime and 10-18 h later for the CIR onset during local nighttime. Case studies indicate that the TEC and Ne positive response had a strong dependence on the southward component (Bz) of the interplanetary magnetic field and solar wind speed. This suggests that penetration electric fields that were associated with changes in solar winds might play a significant role in the positive ionospheric response to storms. During the recovery time of the CIR-produced geomagnetic activity, the TEC positive disturbance at low latitudes sometimes could last for 2-4 days, whereas at middle to high latitudes the disturbance lasted only for 1 day in most cases. A comparison of the ionospheric responses between the American, European and Asian sectors shows that the ionosphere response in the North American sector was stronger than that in the other two regions. The response of f(o)F(2) to the CIR events in middle to high latitudes showed a negative response for 2-3 days after the first epoch day. This is different from the response of TEC, which was mostly positive during the same period of time.

CONTRIBUTION OF VELOCITY VORTICES AND FAST SHOCK REFLECTION AND REFRACTION TO THE FORMATION OF EUV WAVES IN SOLAR ERUPTIONS

We numerically study the detailed evolutionary features of the wave-like disturbance and its propagation in the eruption. This work is a follow-up to Wang et al., using significantly upgraded new simulations. We focus on the contribution of the velocity vortices and the fast shock reflection and refraction in the solar corona to the formation of the EUV waves. Following the loss of equilibrium in the coronal magnetic structure, the flux rope exhibits rapid motions and invokes the fast-mode shock at the front of the rope, which then produces a type II radio burst. The expansion of the fast shock, which is associated with outward motion, takes place in various directions, and the downward expansion shows the reflection and the refraction as a result of the non-uniform background plasma. The reflected component of the fast shock propagates upward and the refracted component propagates downward. As the refracted component reaches the boundary surface, a weak echo is excited. The Moreton wave is invoked as the fast shock touches the bottom boundary, so the Moreton wave lags the type II burst. A secondary echo occurs in the area where reflection of the fast shock encounters the slow-mode shock, and the nearby magnetic field lines are further distorted because of the interaction between the secondary echo and the velocity vortices. Our results indicate that the EUV wave may arise from various processes that are revealed in the new simulations.

Operational Space Weather Services in National Space Science Center of Chinese Academy of Sciences

The National Space Science Center (NSSC) of Chinese Academy of Sciences (CAS) was established in 1958 with the mandate to develop the first artificial satellite of China, the DFH-1. NSSC is China’s gateway to space science and is the key institute responsible for planning, developing, launching, and operating China’s space science satellite missions. With the development of space exploration missions in China, highly needed are the space weather forecasting services, which can greatly help to prevent or reduce the risks caused by space environment disturbances. Therefore, providing operational space weather forecasting services in enabling and enhancing national preparedness for space weather disruption has become a priority in NSSC, which is indispensable in mitigating the impacts of space weather on China’s space missions and in safeguarding critical domestic infrastructure systems and technologies.

Verification of a Similar Cycle Prediction for the Ascending and Peak Phases of Solar Cycle 23

Reviews of long-term predictions of solar cycles have shown that a precise prediction with a lead time of 2 years or more of a solar cycle remains an unsolved problem. We used a simple method, the method of similar cycles, to make long-term predictions of not only the maximum amplitude but also the smoothed monthly mean sunspot number for every month of Solar Cycle 23. We verify and compare our prediction with the latest available observational results.

A regional ionospheric TEC mapping technique over China and adjacent areas: GNSS data processing and DINEOF analysis

A technique is developed to derive two-dimensional maps of total electron content (TEC) over China and adjacent areas using Global Navigation Satellite System (GNSS) data from the Crustal Movement Observation Network of China (CMONOC) and the International Global Navigation Satellite System Service (IGS). A revised self-calibration of pseudo-range errors (SCORE) algorithm is used to derive the TEC and to determine the Differential Code Biases (DCBs) simultaneously. The accuracy and validity of this technique is verified in two ways. Firstly, the estimated TEC is compared with the results derived using DCBs from Center for Orbit Determination of Europe (CODE) under different solar activity conditions and seasons; secondly, sample TEC along the receiver-to-satellite ray paths are simulated by NeQuick model and are reprocessed by this TEC derivation technique to make the accuracy test. Two-dimensional maps of vertical TEC of ionospheric pierce points (IPPs) are obtained accordingly with a time resolution of 30 s. The data interpolating empirical orthogonal functions (DINEOF) technique is then used to make the extrapolation for the unknown or missing data points. The optimal EOF modes for data reconstruction are specified via cross-validation method. The regional TEC distribution over China and adjacent areas is scaled into grid size of 1° × 1° for each 5 min, which can well reflect the characteristic of large-scale regional variations and temporal evolution as well as the small-scale local features of ionosphere.创新点1. 利用中国及周边区域的地基GNSS观测数据进行TEC解算, 并采用伪距误差自校正技术来计算硬件偏差, 得到高精度TEC星下点数据。2. 采用经验正交函数法插值法构建覆盖中国及周边区域的高分辨率TEC地图

Short-term prediction of solar proton events by neural network method☆☆☆

Abstract Based on a large number of statistical results, we study the prediction of solar proton events in depth. By summarizing the relations of the proton events with the area, position, McIntosh structure, magnetic structure of the active region, and the number of solar flare bursts which happened in the active region two days before, a short-term prediction model of solar proton events is built on the lines of artificial neural network. Tests on 12 samples later than 2000 indicate a prediction accuracy of about 83%. Further test predictions are made on the proton events which occurred in Jan.–Apr. 2002. It is found that all the 6 events that occurred in this period are correctly predicted. Among them, 3 are predicted 3 days ahead, 2 events — 2 days ahead, and 1 event — 1 day ahead.

Comparison of energetic electron flux and phase space density in the magnetosheath and in the magnetosphere

Whether energetic electrons (10s of keV) in the magnetosheath can be directly transported into the magnetosphere and further energized through radial diffusion is significant in understanding the physical mechanisms for producing the radiation belt electrons (>100s of keV) in the magnetosphere. In this study, we analyze more than two hundred magnetopause crossing events using the energetic electron and magnetic field measurements from Geotail and compare the flux and phase space density (PSD) of the energetic electrons on both sides of the magnetopause. It is found that for most of the events (>70%), the fluxes and PSDs of energetic electrons in the magnetosheath are less than those in the magnetosphere, suggesting that the energetic electrons in the magnetosheath cannot be a direct source sufficient for the energetic electrons inside the magnetosphere. In fact, our analysis suggests a possible leakage of the energetic electrons from inside to outside the magnetopause. By investigating the average energetic electron flux distribution in the magnetosheath, we find that the energetic electron fluxes are higher near the bow shock and the magnetopause than in between. The high energetic electron flux near the bow shock can be understood as due to energization of electrons when they go through the bow shock. The relatively low flux of the energetic electrons in between indicates that it is difficult for the energetic electrons to travel from the bow shock to the magnetopause and vice versa, possibly because the energetic electrons near the bow shock and the magnetopause are all on open magnetic field lines and these two relatively intense energetic electron populations in the magnetosheath rarely get mixed.