Index of assessment of the state of the earth's magnetic field. Geomagnetic field: features, structure, characteristics and history of research. SCR as the main source of radiation hazard in the OKP

Geomagnetic À, K, and Kp indices.

Regular daily variations in the magnetic field are mainly created by changes in currents in the Earth's ionosphere due to changes in the illumination of the ionosphere by the Sun during the day. Irregular variations in the magnetic field are created due to the impact of the solar plasma flow (solar wind) on the Earth's magnetosphere, changes within the magnetosphere, and the interaction of the magnetosphere and ionosphere

Geomagnetic activity indices are intended to describe variations in the Earth's magnetic field caused by these irregular causes. The K-index is a quasi-logarithmic (increases by one with an approximately twofold increase in disturbance) index calculated from the data of a particular observatory over a three-hour time interval. The index was introduced by J. Bartels in 1938 and represents values ​​from 0 to 9 for each three-hour interval (0-3, 3-6, 6-9, etc.) of world time. To calculate the index, the change in the magnetic field is taken over a three-hour interval, the regular part, determined by calm days, is subtracted from it, and the resulting value is converted into the K-index using a special table.

Since magnetic disturbances manifest themselves in different ways in different places on the globe, each observatory has its own table, constructed in such a way that different observatories, on average, give the same indices over a long time interval.

For the Moscow observatory, this table is given as follows:

Ap is a linear index (an increase in perturbation by several times gives the same increase in the index) and in many cases the use of the Ap index makes more physical sense.

Qualitatively, the state of the magnetic field depending on the Kp index can be approximately characterized as follows:

Planetary Kp and Ap indices have been available since 1932 and can be obtained on request via FTP from

Regular daily variations in the magnetic field are mainly created by changes in currents in the Earth's ionosphere due to changes in the illumination of the ionosphere by the Sun during the day. Irregular variations in the magnetic field are created due to the impact of the solar plasma flow (solar wind) on the Earth's magnetosphere, changes within the magnetosphere, and the interaction of the magnetosphere and ionosphere.

The solar wind is a stream of ionized particles flowing from the solar corona at a speed of 300–1200 km/s (the speed of the solar wind near the Earth is about 400 km/s) into the surrounding space. The solar wind deforms the magnetospheres of the planets, generates auroras and radiation belts of the planets. The solar wind intensifies during solar flares.

A powerful solar flare is accompanied by the emission of a large number of accelerated particles - solar cosmic rays. The most energetic of them (108-109 eV) begin to reach the Earth 10 minutes after the flare maximum.

An increased flux of solar cosmic rays near the Earth can be observed for several tens of hours. The invasion of solar cosmic rays into the ionosphere of the polar latitudes causes its additional ionization and, accordingly, the deterioration of short-wave radio communications.

The flare generates a powerful shock wave and ejects a cloud of plasma into interplanetary space. Moving at a speed of over 100 km/s, the shock wave and the plasma cloud reach the Earth in 1.5-2 days, causing sharp changes in the magnetic field, i.e. magnetic storm, increased auroras, ionospheric disturbances.

There is evidence that a noticeable rearrangement of the baric field of the troposphere occurs 2–4 days after a magnetic storm. This leads to an increase in the instability of the atmosphere, a violation of the nature of air circulation (in particular, cyclogenesis intensifies).

Geomagnetic Activity Indices

Geomagnetic activity indices are intended to describe variations in the Earth's magnetic field caused by irregular causes.

K indices

K index- three-hour quasi-logarithmic index. K is the deviation of the Earth's magnetic field from the norm during a three-hour interval. The index was introduced by J. Bartels in 1938 and represents values ​​from 0 to 9 for each three-hour interval (0-3, 3-6, 6-9, etc.) of world time. The K-index increases by one with an approximately twofold increase in perturbation.

Kp index is a three-hour planetary index introduced in Germany based on the K index. Kp is calculated as the average value of K indices determined at 16 geomagnetic observatories located between 44 and 60 degrees north and south geomagnetic latitudes. Its range is also from 0 to 9.

And the indices

A index- daily index of geomagnetic activity, obtained as an average of eight three-hour values, is measured in units of magnetic field strength nT - nanotesla and characterizes the variability of the Earth's magnetic field at a given point in space.

Recently, instead of the Kp index, the Ap index is often used. Ap index is measured in nanoteslas.

Ap- planetary index obtained on the basis of averaged data on A indices received from stations located around the world. Since magnetic disturbances manifest themselves in different ways in different places on the globe, each observatory has its own table of ratios and index calculations, built in such a way that different observatories give the same indices on average over a long time interval.

Qualitatively, the state of the magnetic field depending on the Kp index
Kp Kp = 2, 3 - weakly perturbed;
Kp = 4 - perturbed;
Kp = 5, 6 - magnetic storm;
Kp >= 7 - strong magnetic storm.

For the Moscow observatory:

G A geomagnetic storm is a disturbance of the geomagnetic field lasting from several hours to several days. Geomagnetic storms are one of the types of geomagnetic activity. They are caused by the arrival of perturbed solar wind streams in the vicinity of the Earth and their interaction with the Earth's magnetosphere. Geomagnetic storms cause rapid and strong changes in the Earth's magnetic field that occur during periods of increased solar activity. This phenomenon is one of the most important elements of solar-terrestrial physics and its practical part, usually denoted by the term "Space weather".

As a result of solar flares, a huge amount of matter (mainly protons and electrons) is ejected into outer space, some of which, moving at a speed of 400–1000 km/s, reaches the earth’s atmosphere in one or two days. The Earth's magnetic field captures charged particles from outer space. Too much particle flow perturbs the planet's magnetic field, causing the characteristics of the magnetic field to change rapidly and strongly.

The G-index is a five-point scale for the strength of magnetic storms, which was introduced by the US National Oceanic and Atmospheric Administration (NOAA) in November 1999. The G-index characterizes the intensity of a geomagnetic storm by the impact of variations in the Earth's magnetic field on people, animals, electrical engineering, communications, navigation, etc.

Magnetic storms also affect the health and well-being of people. They are dangerous primarily for those who suffer from arterial hypertension and hypotension, heart disease. Approximately 70% of heart attacks, hypertensive crises and strokes occur during solar storms.

Magnetic storms are often accompanied by headaches, migraines, heart palpitations, insomnia, poor health, decreased vitality, and pressure drops. Scientists attribute this to the fact that when the magnetic field fluctuates, capillary blood flow slows down and oxygen starvation of tissues occurs.

Soviet biophysicist A.L. Chizhevsky In his monograph "Earth echo of solar storms" he analyzed a large historical material and found a correlation between solar activity maxima and massive cataclysms on Earth. From this, a conclusion was made about the influence of the 11-year cycle of solar activity (periodic increase and decrease in the number of sunspots) on climatic and social processes on Earth. Chizhevsky established that during the period of increased solar activity (a large number of spots on the Sun), wars, revolutions, natural disasters, catastrophes, epidemics occur on Earth, and the intensity of bacterial growth increases (“Chizhevsky-Velkhover effect”).

• Solar cosmic rays (SCR) - protons, electrons, nuclei formed in flares on the Sun and reached the Earth's orbit after interaction with the interplanetary medium.
• Magnetospheric storms and substorms caused by the arrival of an interplanetary shock wave to the Earth associated with both CME and CME, as well as with high-speed solar wind streams;
• Ionizing electromagnetic radiation (IEI) of solar flares, which causes heating and additional ionization of the upper atmosphere;
• Increases in the fluxes of relativistic electrons in the outer radiation belt of the Earth, associated with the arrival of high-speed solar wind streams to the Earth.

Solar cosmic rays (SCR)

Energetic particles formed in flares - protons, electrons, nuclei - after interaction with the interplanetary medium can reach the Earth's orbit. It is generally accepted that the greatest contribution to the total dose is made by solar protons with an energy of 20-500 MeV. The maximum flux of protons with energies above 100 MeV from a powerful flare on February 23, 1956 amounted to 5000 particles per cm -2 s -1 .
(see more details on the topic "Solar cosmic rays").
Main source of SKL- solar flares, in rare cases - the decay of a prominence (filament).

SCR as the main source of radiation hazard in the OKP

Streams of solar cosmic rays significantly increase the level of radiation hazard for astronauts, as well as crews and passengers of high-altitude aircraft on polar routes; lead to loss of satellites and failure of equipment used on space objects. The harm that radiation causes to living beings is quite well known (for more details, see the materials to the topic "How does space weather affect our lives?"), but in addition, a large dose of radiation can also disable electronic equipment installed on spacecraft (see (more on lecture 4 and materials for topics on the impact of the external environment on spacecraft, their elements and materials).
The more complex and modern the microcircuit, the smaller the size of each element and the greater the likelihood of failures that can lead to its incorrect operation and even to the processor stop.
Let us give a clear example of how high-energy SCR flows affect the state of scientific equipment installed on spacecraft.

For comparison, the figure shows photographs of the Sun taken by the EIT (SOHO) instrument, taken before (07:06 UT on October 28, 2003) and after a powerful flare on the Sun that occurred at about 11:00 UT on October 28, 2003, after which The NES fluxes of protons with energies of 40-80 MeV increased by almost 4 orders of magnitude. The amount of "snow" in the right figure shows how much the recording matrix of the device is damaged by flare particle flows.

Influence of increases in SCR fluxes on the Earth's ozone layer

Since high-energy SCR particles (protons and electrons) can also be sources of nitrogen and hydrogen oxides, whose content in the middle atmosphere determines the amount of ozone, their influence should be taken into account in photochemical modeling and interpretation of observational data at the moments of solar proton events or strong geomagnetic disturbances.

Solar proton events

The role of 11-year GCR variations in assessing the radiation safety of long-term space flights

When evaluating the radiation safety of long-term space flights (such as, for example, the planned expedition to Mars), it becomes necessary to take into account the contribution of galactic cosmic rays (GCR) to the radiation dose (see Lecture 4 for more details). In addition, for protons with energies above 1000 MeV, the GCR and SCR fluxes become comparable. When considering various phenomena on the Sun and in the heliosphere over time intervals of several decades or more, the determining factor is the 11-year and 22-year cyclicity of the solar process. As can be seen from the figure, the GCR intensity varies in antiphase with the Wolf number. This is very important, since the interplanetary medium is weakly perturbed at the SA minimum, and the GCR fluxes are maximum. Having a high degree of ionization and being all-penetrating, during periods of minimum SA GCR determine the dose loads on humans in space and aviation flights. However, the processes of solar modulation turn out to be quite complex and cannot be reduced only to anticorrelation with the Wolf number. .

The figure shows the CR intensity modulation in the 11-year solar cycle.

solar electrons

High-energy solar electrons can cause volumetric ionization of spacecraft, as well as act as "killer electrons" for microchips installed on spacecraft. Due to SCR flows, short-wave communications in the polar regions are disrupted and failures occur in navigation systems.

Magnetospheric storms and substorms

Other important consequences of the manifestation of solar activity that affect the state of near-Earth space are magnetic storms are strong (tens and hundreds of nT) changes in the horizontal component of the geomagnetic field measured on the Earth's surface at low latitudes. magnetospheric storm- this is a set of processes occurring in the Earth's magnetosphere during a magnetic storm, when there is a strong compression of the magnetosphere boundary from the day side, other significant deformations of the magnetosphere structure, and a ring current of energetic particles is formed in the inner magnetosphere.
The term "substorm" was introduced in 1961. S-I. Akasof to designate auroral disturbances in the auroral zone with a duration of about an hour. Even earlier, bay-like perturbations were identified in the magnetic data, coinciding in time with a substorm in the auroras. magnetospheric substorm is a set of processes in the magnetosphere and ionosphere, which in the most general case can be characterized as a sequence of processes of energy accumulation in the magnetosphere and its explosive release. Source of magnetic storms− the arrival of high-speed solar plasma (solar wind) to the Earth, as well as the CW and the shock wave associated with them. High-velocity solar plasma flows, in turn, are divided into sporadic, associated with solar flares and CMEs, and quasi-stationary, arising above coronal holes. According to their source, magnetic storms are divided into sporadic and recurrent. (See lecture 2 for more details).

Geomagnetic indices - Dst, AL, AU, AE

Numerical characteristics reflecting geomagnetic disturbances are various geomagnetic indices - Dst, Kp, Ap, AA and others.
The amplitude of variations in the Earth's magnetic field is often used as the most general characteristic of the strength of magnetic storms. Geomagnetic index Dst contains information about planetary disturbances during geomagnetic storms.
The three-hour index is not suitable for studying substorm processes; during this time, a substorm can begin and end. The detailed structure of magnetic field fluctuations due to currents in the auroral zone ( auroral electrojet) characterizes auroral electrojet index AE. To calculate the AE index, we use magnetograms of H-components observatories located at auroral or subauroral latitudes and evenly distributed along longitude. At present, the AE indices are calculated from the data of 12 observatories located in the northern hemisphere at different longitudes between 60° and 70° geomagnetic latitude. For the numerical description of substorm activity, the geomagnetic indices AL (the largest negative variation of the magnetic field), AU (the largest positive variation of the magnetic field), and AE (the difference between AL and AU) are also used.

Dst-index for May 2005

Kr, Ar, AA indices

The index of geomagnetic activity Kp is calculated every three hours by measuring the magnetic field at several stations located in different parts of the Earth. It has levels from 0 to 9, each next level of the scale corresponds to variations 1.6-2 times greater than the previous one. Strong magnetic storms correspond to levels of Kp greater than 4. So-called superstorms with Kp = 9 occur quite rarely. Along with Kp, the Ap index is also used, which is equal to the average amplitude of geomagnetic field variations over the globe per day. It is measured in nanoteslas (the earth's field is approximately
50,000 nT). The level Kp = 4 approximately corresponds to Ap equal to 30, and the level Kp = 9 corresponds to Ap greater than 400. The expected values ​​of such indices constitute the main content of the geomagnetic forecast. The Ap-index has been calculated since 1932, therefore, for earlier periods, the AA-index is used - the average daily amplitude of variations calculated from two antipodal observatories (Greenwich and Melbourne) since 1867.

Complex influence of SCR and storms on space weather due to the penetration of SCR into the Earth's magnetosphere during magnetic storms

From the point of view of the radiation hazard posed by SCR flows for high-latitude parts of the ISS-type orbits, it is necessary to take into account not only the intensity of SCR events, but also the boundaries of their penetration into the Earth's magnetosphere(see more lecture 4.). Moreover, as can be seen from the figure, SCR penetrate deep enough even for small amplitude (-100 nT and less) magnetic storms.

Estimation of radiation hazard in high-latitude regions of the ISS trajectory based on data from low-orbit polar satellites

Estimates of radiation doses in high-latitude regions of the ISS trajectory, obtained on the basis of data on the spectra and boundaries of SCR penetration into the Earth's magnetosphere according to the Universitetsky-Tatiana satellite data during solar flares and magnetic storms in September 2005, were compared with doses experimentally measured on the ISS in high latitude regions. It is clearly seen from the figures that the calculated and experimental values ​​agree, which indicates the possibility of estimating radiation doses in different orbits from the data of low-altitude polar satellites.

Dose map on the ISS (SRK) and comparison of calculated and experimental doses.

Magnetic storms as a cause of radio communication disruption

Magnetic storms lead to strong disturbances in the ionosphere, which, in turn, adversely affect the states radio broadcast. In the subpolar regions and zones of the auroral oval, the ionosphere is associated with the most dynamic regions of the magnetosphere and, therefore, is most sensitive to such influences. Magnetic storms at high latitudes can almost completely block the radio for several days. At the same time, other areas of activity also suffer, for example, air traffic. Another negative effect associated with geomagnetic storms is the loss of orientation of satellites, the navigation of which is carried out in the geomagnetic field, which experiences strong disturbances during the storm. Naturally, during geomagnetic disturbances, problems also arise with radar.

The influence of magnetic storms on the functioning of telegraph lines and power lines, pipelines, railways

Variations in the geomagnetic field that occur during magnetic storms in polar and auroral latitudes (according to the well-known law of electromagnetic induction) generate secondary electric currents in the conducting layers of the Earth's lithosphere, in salt water, and in artificial conductors. The induced potential difference is small and amounts to about a few volts per kilometer, but in extended conductors with low resistance − communication and power lines (power transmission lines), pipelines, railway rails- the total strength of the induced currents can reach tens and hundreds of amperes.
The least protected from such influence are overhead low-voltage communication lines. Thus, significant interference that occurred during magnetic storms was already noted on the very first telegraph lines built in Europe in the first half of the 19th century. Geomagnetic activity can also cause significant trouble to railway automation, especially in the subpolar regions. And in pipes of oil and gas pipelines stretching for many thousands of kilometers, induced currents can significantly accelerate the process of metal corrosion, which must be taken into account when designing and operating pipelines.

Examples of the impact of magnetic storms on the operation of power lines

A major accident that occurred during the strongest magnetic storm in 1989 in the Canadian power grid clearly demonstrated the danger of magnetic storms for power lines. Investigations showed that transformers were the cause of the accident. The fact is that the direct current component introduces the transformer into a non-optimal mode of operation with excessive magnetic saturation of the core. This leads to excessive energy absorption, overheating of the windings and, in the end, to a failure of the entire system. The subsequent performance analysis of all power plants in North America revealed a statistical relationship between the number of failures in high-risk areas and the level of geomagnetic activity.

Impact of magnetic storms on human health

Currently, there are results of medical studies proving the presence of a human response to geomagnetic disturbances. These studies show that there is a fairly large category of people on whom magnetic storms have a negative effect: human activity is inhibited, attention is dulled, and chronic diseases are exacerbated. It should be noted that studies of the impact of geomagnetic disturbances on human health are just beginning, and their results are quite controversial and contradictory (for more details, see the materials to the topic "How does space weather affect our lives?").
However, most researchers agree that in this case there are three categories of people: geomagnetic disturbances have a depressing effect on some, on the contrary, they are exciting, while others do not have any reaction.

Ionospheric substorms as a space weather factor

Substorms are a powerful source electrons in the outer magnetosphere. The fluxes of low-energy electrons increase strongly, which leads to a significant increase in electrization of spacecraft(for details, see materials on the topic "Electrification of spacecraft"). During strong substorm activity, the electron fluxes in the outer radiation belt of the Earth (ERB) increase by several orders of magnitude, which poses a serious danger to satellites whose orbits cross this region, since a sufficiently large amount of space charge leading to failure of on-board electronics. As an example, we can cite problems with the operation of electronic instruments onboard Equator-S, Polag and Calaxy-4 satellites, which arose against the background of prolonged substorm activity and, as a result, very high fluxes of relativistic electrons in the outer magnetosphere in May 1998.
Substorms are an integral companion of geomagnetic storms, however, the intensity and duration of substorm activity has an ambiguous relationship with the power of a magnetic storm. An important manifestation of the "storm-substorm" relationship is the direct effect of the power of a geomagnetic storm on the minimum geomagnetic latitude at which substorms develop. During strong geomagnetic storms, substorm activity can descend from high geomagnetic latitudes, reaching middle latitudes. In this case, at middle latitudes, there will be a disruption in radio communication caused by the disturbing effect on the ionosphere of energetic charged particles generated during substorm activity.

Relationship between solar and geomagnetic activity - current trends

In some modern works devoted to the problem of space weather and space climate, the idea is expressed of the need to separate solar and geomagnetic activity. The figure shows the difference between the average monthly sunspot values, traditionally considered an indicator of SA (red), and the AA index (blue), showing the level of geomagnetic activity. It can be seen from the figure that the coincidence is not observed for all SA cycles.
The point is that sporadic storms, which are responsible for flares and CMEs, that is, phenomena occurring in regions of the Sun with closed field lines, account for a large proportion in SA maxima. But in SA minima, most storms are recurrent, caused by the arrival of high-speed solar wind streams to the Earth, flowing from coronal holes - regions with open field lines. Thus, the sources of geomagnetic activity, at least for SA minima, have a significantly different nature.

Ionizing electromagnetic radiation from solar flares

Ionizing electromagnetic radiation (ERR) from solar flares should be separately noted as another important factor in space weather. In quiet times, the IEI is almost completely absorbed at high altitudes, causing ionization of air atoms. During solar flares, EPI fluxes from the Sun increase by several orders of magnitude, which leads to warm up and additional ionization of the upper atmosphere.
As a result heating under the influence of IEI, the atmosphere “swells up”, i.e. its density at a fixed height increases greatly. This poses a serious danger for low-altitude satellites and manned OS, because, getting into the dense layers of the atmosphere, the spacecraft can quickly lose altitude. Such a fate befell the American space station Skylab in 1972 during a powerful solar flare - the station did not have enough fuel to return to its previous orbit.

Absorption of shortwave radio emission

Absorption of shortwave radio emission is the result of the fact that the arrival of ionizing electromagnetic radiation - UV and X-ray radiation of solar flares causes additional ionization of the upper atmosphere (for more details, see the materials on the topic "Transient light phenomena in the Earth's upper atmosphere"). This leads to a deterioration or even a complete cessation of radio communications on the illuminated side of the Earth for several hours. }