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The Global Positioning System (GPS) cycle slip has a marked impact on the application of communication and navigation systems and therefore is one of the main concerns of the user and designer of terminal systems. In this study, we analyzed the temporal and spatial characteristics of cycle slip events using the GPS data detected from 260 observations in the China sector during the period of the year 2015–2018. The results show that the temporal variations of cycle slips are dependent on the local time, seasons, and solar activity. It occurs from 20:00 LT to midnight and more frequently in the equinox months, especially in solar maximum years. The spatial distribution occurs mainly at southern sector below 25°N, which should be associated with the solar condition and ionospheric irregularities in the equatorial region, and the case analyses reveal that the variation of cycle slips has a similar tendency with the ionospheric scintillation monitored at low‐latitude station Guangzhou explaining this relationship. Our results reflect the performance of the GPS signals monitored in the China area during the declining period of solar activity to some degree. Plain Language Summary: The cycle slip is one of the main impacts on communication and navigation systems and is also the main concern of space weather researches. To understand the distribution characteristics of the cycle slip over China mainland and adjacent region, we detect it using a specialized method and analyze the results of the cycle slip event. We find that the cycle slips are dependent on the local time, seasons, solar activity, and latitude. The cycle slip occurs in solar maximum years much more frequently. In solar maximum years, cycle slips occurrence more frequently in the equinox months than in other months and mainly occurs from 20:00 LT to midnight. The spatial distribution results indicate that most cycle slip events occur in the southern sector (below 25° at latitude). Moreover, we analyze the relationship between cycle slip and solar activity and ionospheric scintillation, and it is important to understand because the China longitudinal sector is one interesting transitional zone where the scintillation event is active. This study can contribute to space weather researchers and GNSS users to analyze the characteristics of the cycle slips, and is also used to evaluate the ionospheric effect on GPS to improve positioning performance in GPS application. Key Points: The temporal and spatial characteristics of cycle slips are analyzed using the GPS data detected from almost 260 observations in the China sector during the period of the year 2015–2018The variations of cycle slip are dependent on the local time, seasons, solar activity, and latitudesThe feature of cycle slip occurrence is related to the solar activity and distribution of ionospheric scintillation above a certain intensity level over the China region [ABSTRACT FROM AUTHOR]

In this study, we present a statistical analysis of equatorial plasma irregularities (EPIs) by using in situ plasma density measurements of the Swarm constellation from December 2013 to December 2019. The occurrence patterns for both postsunset and postmidnight EPIs with respect to longitude, season, local time, latitude, solar activity, and geomagnetic activity level are investigated. The main findings are as follows: (1) The postsunset/postmidnight EPIs occurrence rates exhibit different longitudinal and seasonal dependence: The postsunset EPIs have the maximum occurrence rate over the American‐Atlantic sectors during the December solstice and equinoxes, and the postmidnight EPIs have the maximum occurrence rate during the June solstice, especially over the African sector. (2) The postsunset EPIs occurrence rates have a positive correlation with solar activity, while the postmidnight EPIs are negatively correlated with it. (3) The latitudinal distribution of EPIs exhibits a double‐peak structure around ±5° magnetic latitude with a more significant peak in the summer hemisphere. (4) The EPIs occurrence rate increases with increasing geomagnetic activity level. (5) The main controlling factors for the distribution of postsunset EPIs are the magnetic declination angle, equatorial vertical E × B drift, and thermospheric zonal wind. For the postmidnight EPIs, the main controlling factors are likely to be atmospheric gravity waves and equatorward thermospheric meridional wind associated with midnight temperature maximum. Key Points: The postsunset EPI occurrence rate is positively correlated with solar activity, while the postmidnight EPI is negatively correlated with itThe postsunset (postmidnight) EPIs are more prominent during the equinoxes (June solstice) over the American‐Atlantic (African) sectorThe latitudinal variation of EPIs exhibits an asymmetric double‐peak distribution pattern that prevails in the summer hemisphere [ABSTRACT FROM AUTHOR]

A statistical analysis of the topside main ionospheric trough is implemented by using the Swarm constellation in situ plasma density measurements from December 2013 to November 2019. The key features of the main trough, such as the occurrence rate, minimum position, width, and depth, are characterized and quantified. The distribution patterns of these parameters are investigated with respect to magnetic local time, season, longitude, solar activity, and geomagnetic activity levels, respectively. The main results are as follows: (1) The diurnal variation of the trough occurrence rate usually exhibits a primary peak in the early morning, a subsidiary peak in the late evening, and a slight reduction around midnight especially in the Northern Hemisphere. (2) The seasonal variation of the nighttime trough has maximum occurrence rates around equinoxes, higher than those in local winter. (3) The trough distribution has an evident hemispherical asymmetry. It is more pronounced in the Northern Hemisphere during the winter and equinoctial seasons, with its average nighttime occurrence rate being 20–30% higher than that in the Southern Hemisphere. The trough minimum position and the trough width also exhibit more significant fluctuation in the Northern Hemisphere. (4) The longitudinal pattern of the trough shows clear east‐west preferences, which has a higher occurrence rate in eastern (western) longitudes around the December (June) solstice. (5) Conditions for the trough occurrence are more favored in low solar activity and high geomagnetic activity periods. Key Points: The occurrence rate of the main ionospheric trough at 450–550 km exhibits a slight midnight reduction comparing with evening/morning peaksThe trough has a longitudinal preference with higher occurrence rate in the eastern (western) longitudes around the December (June) solsticeConditions for the trough occurrence are more favored in equinoxes than local winter and in Northern Hemisphere than Southern Hemisphere [ABSTRACT FROM AUTHOR]

High-level surface-charging events are frequently observed on spacecrafts in aurora region. Besides the sunlit condition, two major factors causing charging events are the ambient plasma density and the precipitating electron flux. For the first factor, when the ambient plasma density is relatively low due to weak solar UV output during solar minimum, more surface-charging events are reported to occur for polar satellite. Moreover, the increased energetic electron precipitation during high geomagnetic activities in solar cycle decent years, may also contribute to the charging events. To evaluate these two factors comprehensively, we present a statistical survey of over 2000 surface charging events recorded by Defense Meteorological Satellite Program (DMSP) satellites over one solar cycle. The relationship between charging events and Kp index, F10.7 index, and monthly average sunspot number is investigated. It is shown that the occurrence frequency of charging events is larger at descending years of solar cycle. In addition, the conditional probabilities of the charging events increase as Kp increase. There is a threshold for Kp index, under which most of the charging events cannot occur, and this threshold grows as F10.7 increases. Finally, it is demonstrated that the surface charging potential is strongly correlated with the Kp index. Although there is no obvious correlation between the surface charging potential and F10.7 index, we still observe a decreasing trend of the surface potential range as F10.7 increases. [ABSTRACT FROM AUTHOR]

In space weather forecasting, forecast verification is necessary so that the forecast quality can be assessed. This paper provides an example of how to choose and devise verification methods and techniques according to different space weather forecast products. Solar proton events (SPEs) are hazardous space weather events, and forecasting them is one of the major tasks of the Space Environment Prediction Center (SEPC) at the National Space Science Center of the Chinese Academy of Sciences. Through analyzing SPE occurrence characteristics, SPE forecast properties, and verification requirements at SEPC, verification methods for SPE probability forecasts are identified, and verification results obtained. Overall, SPE probability forecasts at SEPC exhibit good accuracy, reliability, and discrimination. Compared with climatology and persistence forecasts, the SPE forecasts are more accurate. However, the forecasts for SPE onset days are substantially underestimated and need to be considerably improved. [ABSTRACT FROM AUTHOR]

In this study, the advantages and the limitations of previous low-latitude magnetopause empirical models are discussed. In order to overcome their limitations and inherit their advantages, a new continuous function for the influence of the interplanetary magnetic field (IMF) Bz on the magnetopause, the Shue model function and the 613 low-latitude magnetopause crossings are used to construct a new low-latitude magnetopause model parameterized by the solar wind dynamic pressure (Dp) and IMF Bz. In comparison with the previous low-latitude magnetopause models, it is found that the new model improves the prediction capability and has a large range of validity for the low-latitude magnetopause. In addition, it is also demonstrated that the new model and the previous low-latitude magnetopause models are not appropriate for predicting the high-latitude magnetopause. [ABSTRACT FROM AUTHOR]

Full-disk solar chromospheric and photospheric images are widely used to monitor solar activity. Flat-fielding is a basic step during scientific data production. Here, a Gaussian-type diffuser is used to measure the flat-field of full-disk solar chromospheric and photospheric images. The effectiveness of the method is verified by theoretical simulation and practical measurement. First, the uniformity of the light source generated by the Gaussian diffuser and the sunlight, with a field of view the same as the full-disk solar image, is calculated. The full width at half maximum (FWHM) of the scatter angle of the Gaussian diffuser is one degree, such that the light source presents a Gaussian distribution. After the correction of the Gaussian background, the uniformity of the area light source is 99.6%, which can be regarded as a uniform area light source. Second, experiments are conducted on full-disk solar telescopes at Huairou solar observing station and Yangbajing station. The diffuser covers the entire entrance aperture when taking flat-field frames. Through qualitative and quantitative analysis of experimental results, it is confirmed that a revised flat-field frame can modify uniformity caused by various aspects of the telescope, including vignetting, non-uniformities of filters, and contamination of optical components. [ABSTRACT FROM AUTHOR]