Editor’s note: “There are still many unknown mysteries to be explored in the vast sky”, for this reason, the Voice of the Chinese Academy of Sciences and the National Center for Space Science of the Chinese Academy of Sciences jointly opened the “Call Space” science column, for you to tell interesting stories, introduce some knowledge related to space science and space. In layman’s terms, the space environment, also known as the space environment, is the sum of all the material conditions in solar-Earth space that can affect human life or technological systems. The space environment is the fourth environment for human existence, except on land, oceans and atmosphere.
The space range referred to in the space environment usually refers to the vast area of the universe above the surface of the sun at altitudes of tens of kilometers above the ground, and the origin of the occurrence of the event of the space environment disaster is mainly from the sun. When the sun produces explosive activity, it may cause a series of space disaster events such as solar proton events, geomagnetic storms, high-energy electron storms, which may have serious impact on human space systems, radio link systems, power and energy systems.
In 2019, by the end of the 24th solar activity week, solar activity levels are low and solar eruptions are rare. However, the solar coronal hole still causes some geomagnetic stormevents from time to time, while high-energy electron stormevents near geosynchronous orbits are never absent. Let’s take a look back at the turbulent space environment of the year.
1, unusually silent sun
Sunspots, refers to where the magnetic field on the surface of the sun’s light sphere gathers, and is the most prominent phenomenon that can be seen on the surface of the sun. To the naked eye, the sunspot is darker than its surroundings, like a small speck. Sunspots are an important indicator of solar activity and the most important source of solar eruption activity. When we are at the height of solar activity, the sun is like a freckle, and there are often many sunspots on his face. And when we are at a low level of solar activity, the face of the sun is whitened again, clean and clean.
Figure 1 Solar activity high and low years of the sun
In 2019, the 24th/25th solar activity week is already at the end of the 24th solar activity week, which is approaching the new 25th solar activity week. The number of sunspots has been completely reduced to the trough. Its monthly average was below 1 in July-November and even 0 in February. The monthly mean of the Solar F10.7 index, which characterizes solar radiation levels, has also dropped to 67sfu, near historical lows.
Figure 2 Number of sunspots during solar activity weeks 24 and 25
The average annual number of sunspots in 2019 was 3.7, down 42% from 2018, while the f10.7 average was 69.7, a slight decrease (see table 1).
Table 1 Comparison of solar activity 2017-2019
As the level of solar activity continues to decrease, the number of sunspots in the sun is greatly reduced, and the sunless day (i.e. a sunspot on the surface of the sun) continues to appear. The number of sunspots in the sun throughout the year is only 24, a 35% decrease from 2018. Sunspot-free day 2019 is 284 days, and more than three-quarters of the year there are no sunspots.
The decrease in sunspots also means less solar eruption activity such as solar flares and coronal mass ejections. Only 32 C-class flares were produced in 2019, all concentrated in the first half of the year, with out of M-class flares and above. Of these, 12 C-level flares were produced in each of the two sunspot activity areas numbered AR2740 and AR2743. On May 15, the last C2 flare in the sun’s active area AR2741 erupted, and the sun was left dead, even without a C-level flare. Solar proton events have not been observed in 2019.
Figure 3 Solar X-ray Flow (Descriptive Flares) and Solar Proton Flow (Characterization Proton Events) 2019
Figure 4 Comparison of Solar Outbreak Activity in 2019
2, occasionally bright geomagnetic activities
Geomagnetic storm, is a violent global magnetic field disturbance phenomenon, is the most important kind of Earth magnetic disturbance change type, but also a kind of harsh space environment event. It can cause strong changes in the environment of the magnetosphere, ionosphere and mid-upper atmosphere, which can cause various hazards to spacecraft. For low-orbit spacecraft, the increase in atmospheric density caused by geomagnetic storms can lead to the enhancement of atmospheric damping, which will change the normal orbit of spacecraft and increase the error of spacecraft orbit ingressandand.
A variety of indices are used to describe geomagnetic activity, most commonly including Ap, Kp, Dst index, etc., where ap and Kp indices are used to measure global geomagnetic activity.
In 2019, the overall disturbance level of the Earth’s magnetic field will be very weak. From the multiple indicators in Table 2, the level of geomagnetic activity is significantly lower than in 2018. From January to December 2019, the average monthly geomagnetic Ap index is only more than 10 in September, with other months fluctuating between 4-9. The ap index’s annual average is just 6.9, 11.5% lower than in 2018, and the number of days in The Ap-15 is only 22 days, 16 days less than in 2018.
Table 2 Comparison of geomagnetic activity 2017-2019
The level of geomagnetic storms in 2019 is also relatively weak, from the Kp index indicating the level of geomagnetic storms, the number of days for small geomagnetic storms (Kp-5) occurs throughout the year is 14 days, the number of days for moderate magnetic storms (Kp-6) is 2 days, and only one day there is a geomagnetic storm (Kp-7).
Table 3 Geomagnetic storm days statistics for 2019
In general, the sources of geomagnetic storms can be divided into two types: coronal mass ejection (CME) and coronary hole high-speed flow (CHH). Among them, CME has the occasionality and strongness, mostly produced in the high years of solar activity, causing most of the geomagnetic storms, in the low years of solar activity occasionally caused geomagnetic storms;
Solar activity in 2019 is weak, but the solar surface mass ejection that broke out on May 10th and 11th caused the only geomagnetic storm of the year.
Figure 5 The coronal mass ejection in May triggered the only geomagnetic storm in 2019
Figure 6 Geomagnetic Ap Index and Kp Index 2019
If the first half of 2019, the CME caused the year’s only geomagnetic storm, the unique trend, then the second half of 2019 is the performance time of the coronation hole, after which we will focus on a large coronary hole spanning multiple solar rotation weeks (27 days).
3, high-energy electronic storm – “killer” electronic never absent
High-energy electron storm, refers to the occurrence of the extraterrestrial radiation zone region of high-energy electron flux suddenly increased thousands of times, or even tens of thousands of times the event.
The impact of high-energy electrons in space on spacecraft is very serious. Just as radioactive material produced by the atomic bomb explosion can penetrate into the human body, high-energy electrons can penetrate the surface of the spacecraft instrument into internal transmission, resulting in deep charging and other effects, so that the spacecraft produces the wrong action, resulting in abnormal or malfunctioning spacecraft, more serious charge and discharge can cause circuit breakdown, and even make the spacecraft fail. Deep charging has the greatest impact on navigation satellites, followed by synchronous orbiting satellites. In recent years, many satellites have caused satellite failure and failure due to the deep charging effect, which has caused great impact.
In the low years of solar activity, do not be blinded by the words “low level of solar activity, no activity area on the sun surface” and so on, relax the alertness of high-energy electronic storms. Due to the modulation of solar activity, high-energy electron bursts occur more frequently during the decline period of solar activity week – “killer” electrons are never absent.
In 2019, there were 66 days of small high-energy electronic storms, 10 days of moderate high-energy electronic storms, no strong high-energy electronic storms, high-energy electronic stormtotal days of 76 days, accounting for 21% of the total number of days of the year.
Table 4 Statistics on the number of days of high-energy electronic storms in 2019
In 2019, there have been several high-energy electronic storms that last for many days. August 6-11, high-energy electronic storm lasted 11 days, the daily credit flux is up to 1.1E plus 09 / cm2.sr.day. August 31 – September 12, high-energy electronic storm lasted 13 days, the daily integral flux of the maximum of 2.9E plus 09 / cm2.sr.day, close to the strong high-energy electronic storm event threshold.
Figure 7 Percentage of high-energy electronic storms in 2019
4, the “wind and clouds” of the year – the crown hole
In the previous section, we have mentioned that the coronary hole high-speed flow is the main cause of the major geomagnetic storms in 2019. Thus, in the second half of 2019, a coronal hole near the sun’s equator will be the annual “wind and clouds” of solar activity.
The coronal hole, which was generated on the sun in July, continued to expand and strengthen, and as the sun’s periodic self-turned to the sun for a 27-day rotation, several times toward situating towards the Earth, caused a number of geomagnetic storms in early August, early September, late September and late October, and caused a total of 8 days of moderate high-energy electron storms, 33 days of small high-energy electronic storms, accounting for 54% of the year’s high-energy electronic storm days.
Figure 8 The Coronation Hole passes through the center of the sun on August 2, August 29, September 26 and October 22
Figure 9 Geomagnetic storms caused by the great coronal hole in early August, early September, late September and late October
5, summary and outlook
In 2019, the overall level of solar activity slowly declined, with very few eruptions occurring, the overall level of geomagnetic steam also continued to decline, and the number and intensity of geomagnetic stormevents decreased, although more active, the frequency and intensity of occurrences decreased. As the above iconic events are drawing to a low, it is basically announced that the 24th Solar Activity Week is nearing its end.
Looking ahead to 2020, we are approaching our 25th week of activity, with the sun expected to gradually wake up and begin a new outburst, and we look forward to working with you on the occurrence of new space environment events.