Differences among Space Physics, Atmospheric Physics and Astrophysics

Space physics

A subject that mainly uses spacecraft to directly detect and study space physical processes. A branch of space science. Extending from geophysics, atmospheric physics and astronomy. At first, people could only observe various physical phenomena such as auroras, meteors and noctilucent clouds in the sky on the ground. With the development of science and technology, people use balloons, rockets and other launching tools to detect the composition and density of the upper atmosphere, high-altitude magnetic field, high-energy particles, plasma and so on. And gradually formed high-level atmospheric physics, which is the basis of the formation and development of space physics. With the successful launch of man-made earth satellites from 65438 to 0957, human beings overcame the obstacles of the atmosphere for the first time and directly observed the vast space, thus entering the space age. With the development of space science and technology, the exploration field extends from near-earth space to the moon, planets and interplanetary space. With the research on the dynamic process of physical process, an independent discipline-space physics has gradually formed.

research objects

The research objects of space physics include: ① Upper atmosphere. Generally speaking, it refers to the earth's atmosphere more than 60 kilometers, which is the first research field of space physics. The subject that studies the composition, structure and dynamic process of the upper atmosphere is called upper atmospheric physics. ② Ionosphere. The ionization zone in the upper atmosphere of the earth is generally considered to be about 60 ~ 2000 kilometers high. The ionosphere is formed by the action of solar ultraviolet rays, X-rays and high-energy particles. The ionosphere can affect the propagation direction, velocity, phase, amplitude and polarization of radio waves. Studying the propagation of radio waves in the ionosphere can solve the problems in radio communication and radio speed measurement and positioning. Conversely, the ionospheric state can also be detected by the absorption, reflection, refraction, scattering, Doppler effect and Faraday effect of electric waves in the ionosphere. The basic theory of studying radio wave propagation in ionosphere is magnetic ion theory. ③ magnetosphere. In the 1960s, direct exploration and detailed study of the earth's magnetosphere began. The magnetosphere is directly related to the solar wind and interplanetary magnetic field. The influence of the solar wind is transmitted to the ionosphere and neutral atmosphere through the magnetosphere. Therefore, the magnetosphere is of great significance for exploring and studying the coupling process of solar atmosphere-interplanetary medium-magnetosphere-ionosphere-neutral atmosphere. The activities of satellites and spacecraft are influenced by magnetic fields, radiation belts and magnetospheric plasma. 4 sun ball. The space around the sun controlled by the solar wind and its interplanetary magnetic field. The interface between heliosphere and interstellar medium is called heliopause. The detection of heliosphere is mainly carried out near the ecliptic plane. ⑤ cosmic rays. Refers to the flow of high-energy particles from space. Part from the Milky Way and part from the sun. Cosmic rays interact with solar wind, interplanetary magnetic field and magnetosphere during their propagation in the solar circle, which has become an important tool for studying these fields. 6. Planets and their satellites. A comparative study of the atmosphere, ionosphere, magnetosphere, gravity field and magnetic field intensity of planets and their satellites in the solar system with that of the earth can inspire and promote the study of the origin of the solar system and some phenomena of the earth.

Space Physics Exploring space physics is a very observant subject. The main objects of space physics exploration are neutral particles, high-energy charged particles, plasma, solid particles, low-frequency electromagnetic waves and plasma waves, magnetic fields and electric fields. Through the detection of these physical phenomena, we can understand the basic structure of the earth's atmosphere, ionosphere, magnetosphere and interplanetary space, thus establishing the upper atmosphere model, ionosphere model, radiation belt model and solar spectrum, discovering the fan-shaped structure of interplanetary magnetic field and establishing the solar wind model. After expanding the depth and breadth of the detection range and obtaining the data of long-term change law, the law of space physical process is further analyzed to understand the reasons for the formation and change of space physical state. The means of space physical exploration include artificial earth satellites, artificial planets and interplanetary probes, high-altitude sounding balloons and rockets suitable for the earth's upper atmosphere, and a network of ground observation stations all over the earth's surface for continuous measurement. They have their own strengths and complement each other.

Space physics exploration satellites run in orbits hundreds of kilometers or even higher from the ground for a long time. The instruments carried by satellites are not affected by the atmosphere, and can directly detect the space physical environment, which has become the main means of space physical exploration. Because the main detection objects of satellites are different, in order to obtain the maximum detection range, the detection instruments are required to reach all points in the vast space directly, so the orbits of such satellites are uncertain, including polar orbits and low inclination orbits. The orbital height varies greatly, with perigee generally being several hundred kilometers and apogee reaching several thousand, tens of thousands and hundreds of thousands of kilometers. Because there are many kinds of space physics instruments used on satellites, there are different requirements for installation location, detection window, temperature control, electromagnetic compatibility between instruments, etc., and some special requirements are put forward for the shape and structure of satellites, so the shapes of space physics exploration satellites are also very different. The main series of space physics exploration satellites are Explorer, Orbital Geophysical Station, International Solar-Terrestrial Explorer and Cosmos. On September 20th, China 198 1 launched three satellites at the same time with one rocket, which was the first batch of space physics exploration satellites in China.

Atmospheric physics

Atmospheric physics is a branch of atmospheric science, which studies the physical phenomena, processes and evolution laws of the atmosphere. It mainly studies sound image, light image, electric image, radiation process, cloud and precipitation physics, near-surface atmospheric physics, stratosphere and mesosphere physics, etc. It is not only a basic theoretical part of atmospheric science, but also a part of environmental science.

People have paid attention to and studied many physical phenomena in the atmosphere for a long time, such as rainbow, halo, porcelain, lightning and so on, but their contents are scattered in physics, chemistry, astronomy, radio and other disciplines. Only in the last thirty or forty years have they been included in a discipline of atmospheric physics.

Since the 1940s, with the rapid expansion of human activities in the atmosphere, the research field of atmospheric physics has been expanding. For example, in order to improve the radio wave communication and light wave communication in the atmosphere and improve the missile guidance level, it is necessary to understand the atmospheric medium and its interaction, so it is necessary to study the sound, light, electricity and radio meteorology of the atmosphere; For another example, in order to avoid the plane crash caused by clear-sky turbulence, it is necessary to study atmospheric turbulence.

A large number of aerosols and pollutants discharged into the atmosphere by industrial production cause air pollution through diffusion, and some of them form acid rain through sedimentation or precipitation, which is sent to the ground, causing land and river pollution and seriously affecting plants and human beings. It is necessary not only to develop production, but also to make the atmosphere not exceed its ability to dilute pollutants, which requires a detailed study of the physical characteristics of the atmospheric boundary layer.

Production activities and other human activities affect the natural environment. For example, the content of carbon dioxide in the atmosphere is increasing year by year, which affects the radiation range of the atmosphere and the law of climate change. These in turn affect agricultural production, especially grain production. The food problem has aroused people's concern about climate change, which in turn has promoted the study of atmospheric radiation.

With the increase of industrial and agricultural water consumption year by year, it is necessary to make full use of the abundant water in the atmosphere, which requires the development of water resources in the atmosphere; In addition, in order to avoid or reduce weather disasters, it also promoted the extensive research of weather modification experiments, thus promoting the study of cloud and precipitation physics.

Since 1960s, remote sensing technology has developed rapidly, and radiation transmission is the basis of remote sensing, which has promoted the study of atmospheric radiation. The development of satellites and computers and the application of new technologies (such as laser, radar and microwave) have provided powerful detection tools for atmospheric physics research and obtained more detection data, thus greatly accelerating the development of atmospheric physics.

Atmospheric physics mainly includes atmospheric boundary layer physics, cloud and precipitation physics, radar meteorology, radio meteorology, atmospheric acoustics, atmospheric optics and atmospheric radiation, atmospheric electricity, stratosphere and mesosphere physics. They all have their own characteristics:

Atmospheric acoustics, atmospheric optics, atmospheric electricity and radio meteorology study the sound, light and electricity phenomena in the atmosphere and the propagation characteristics of sound waves and electromagnetic waves in the atmosphere; Radar meteorology studies the principle and method of detecting the atmosphere with meteorological radar, and its application in weather analysis and forecast, cloud and precipitation physics; Atmospheric radiation studies the transmission and transformation process and radiation balance of radiation in the earth's atmospheric system; Cloud and precipitation physics studies the formation, development and dissipation of clouds and precipitation; Atmospheric boundary layer physics studies the horizontal and vertical distribution of temperature, humidity, wind and other factors in the lower atmosphere, atmospheric turbulence and diffusion, water vapor and heat transfer. It is greatly affected by the ground. Stratospheric and mesospheric atmospheric physics studies the physical processes in the atmosphere from the tropopause (about 10 km) to 80 ~ 90 km. Atmospheric processes are often the result of many factors, so all aspects of atmospheric physics are often interrelated, such as atmospheric electricity and cloud and precipitation physics. Both have their own emphasis and are closely related.

Atmospheric physics is closely related to other branches of atmospheric science. For example, the process of atmospheric physics is restricted by the weather background, and the results of atmospheric physics research and detection are widely used in weather analysis and forecast, so it is closely related to meteorology; Cloud dynamics is a combination of atmospheric physics and atmospheric dynamics. Many contents of atmospheric physics involve the study of climate change; Atmospheric physics is the basis of atmospheric exploration and applied meteorology, and the development of these two disciplines enriches the content of atmospheric physics. For example, atmospheric physics provides a theoretical basis for meteorological radar observation, and radar meteorological information provides rich data for studying atmospheric physical processes.

Many new scientific and technological achievements have promoted the development of atmospheric physics and constantly put forward new requirements for atmospheric physics. Human activities in the atmosphere are frequent, affecting the atmosphere intentionally or unintentionally, making the atmospheric state more complicated. How to further understand the fine structure of the atmosphere, deeply understand the evolution of the three-dimensional space of the atmosphere, and effectively use, properly protect and constantly transform the atmosphere is a long-term important task of atmospheric physics.

Other branches of atmospheric science

Atmospheric science, climatology, phenology, paleoclimatology, tree climatology, atmospheric chemistry, dynamic meteorology, atmospheric physics, atmospheric boundary layer physics, cloud and precipitation physics, cloud microphysics, cloud dynamics, radar meteorology, radio meteorology, atmospheric radiation, atmospheric optics, atmospheric electricity, stratospheric atmospheric physics, atmospheric acoustics, meteorology, tropical meteorology, polar meteorology, satellite meteorology, biogeography.

theoretical astrophysics

A discipline that studies the physical properties and processes of celestial bodies by theoretical physical methods. 1859, Kirchhoff explained the Fraunhofer line of the solar spectrum according to the laws of thermodynamics, and asserted that some chemical elements on the sun are the same as those on the earth. This shows that the internal properties of celestial bodies can be separated from astronomical measurement results by using the universal laws of theoretical physics, which is the beginning of theoretical astrophysics. The development of theoretical astrophysics is closely dependent on the progress of theoretical physics, and almost every major breakthrough in theoretical physics will greatly promote the progress of theoretical astrophysics. The establishment of quantum theory in the early 1920s made it possible to deeply analyze the spectra of stars, thus establishing a systematic theory of stellar atmosphere. With the development of nuclear physics in 1930s, the problem of stellar energy was solved satisfactorily, and the theory of stellar internal structure developed rapidly. According to the measurement results of Herotto, the scientific theory of star evolution is established. 19 17 Einstein analyzed the structure of the universe with general relativity and founded relativistic cosmology. 1929, Hubble discovered the relationship between the red shift of spectral lines and the distance of extragalactic galaxies. Later, people used the gravity theory of general relativity to analyze the observation data of celestial bodies outside the river and explore the large-scale material structure and movement, forming modern cosmology. In the past two decades, in the field of theoretical astrophysics, we can see a wider and deeper combination of theoretical physics and astrophysics, including relativistic astrophysics, plasma astrophysics, high-energy astrophysics and so on.

From the relationship between theoretical physics and astrophysics, we can see the general situation of theoretical astrophysics at present.

Radiation theory studies the radiation of quasars, radio sources, galactic nuclei and other celestial bodies, as well as the emission mechanism of X-ray sources, gamma-ray sources and interstellar molecules.

Nuclear theory studies the structure and evolution of stars, the origin and nuclear synthesis of elements (see element synthesis theory), and cosmic rays.

Gravity theory discusses the structure and stability of compact stars, the problem of black holes, the kinematics and dynamics of cosmology.

The structures of radio source, supernova remnant, ionized hydrogen region, pulsar, planetary magnetosphere, interplanetary matter, interstellar matter and intergalactic matter are analyzed by plasma theory.

Basic particle theory studies supernova explosions, neutrino processes in celestial bodies (see neutrino astronomy), and the composition and state of ultra-dense matter.

Solid state (or condensed state) theory studies the phase transition in interstellar dust, dense stars and other solid processes.

The basic method of theoretical astrophysics is to apply the laws found in the laboratory on earth to the study of cosmic celestial bodies. This method is not only powerful for explaining and explaining known astronomical phenomena, but also can predict some unobserved astronomical phenomena or celestial bodies. For example, shortly after 1932 discovered neutrons, Landau and Oppenheimer predicted that stable and dense neutron stars might exist according to the theory of stellar balance and stability. Although the predicted celestial bodies are very different from all known celestial bodies at that time (unusually high density, etc.). ), the prediction was finally confirmed in 1967 more than 30 years later. On the other hand, many physical concepts are first obtained by studying astronomical phenomena, and then tested by astronomical phenomena. For example, at first, astrophysicists noticed that ionized matter filled the universe has a series of characteristics, which greatly promoted the establishment of plasma physics. For another example, in the study of star energy, the concept of thermonuclear fusion was put forward for the first time. Before the in-depth discussion, the forbidden line was also stimulated by the study of celestial spectra.

Due to the limitation of ground conditions, the verification of some physical laws can only be carried out through the laboratory of cosmic objects. A series of key observations and tests about the general theory of relativity are completed by studying the astronomical phenomena. Mercury perihelion precession, light deflection and radar echo delay are some early examples. Theoretical astrophysics is not only the "application" discipline of theoretical physics to celestial problems, but also the "basic" discipline of exploring basic physical laws with celestial phenomena. From the perspective of astronomy and physics, theoretical astrophysics is full of vitality.