Due to the particularity of frozen soil media and the importance of soil moisture movement in it, the study of water movement in frozen soil has received attention from many countries in the world.

The seven international permafrost conferences that have been held have covered this aspect respectively. The U.S. Highway Research Department and similar organizations in other countries have organized relevant special meetings for many times. UNESCO has specially organized a workshop on water and soil issues in cold areas.

etc.

According to incomplete statistics, in addition to China, more than ten countries such as the former Soviet Union, the United States, Canada and Sweden are currently conducting such research.

In the past 20 years, researchers in various related disciplines have conducted multi-faceted studies on the migration of soil water and heat during the freezing and thawing process from different angles and research purposes, and have achieved many important results.

1. Overview of Permafrost Research Permafrost research includes permafrost physics, permafrost chemistry, permafrost mechanics, engineering permafrost science, permafrost environmental science and other disciplines.

The problem of water and heat migration during soil freezing and thawing belongs to the research scope of frozen soil physics.

Frozen soil physics is the basic research content of frozen soil science. Its research scope includes: the basic physical properties, structure, and structure of frozen soil, water migration, ice formation and frost heaving during soil freezing and thawing, salt migration and salt expansion

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More systematic research on permafrost began in the late 19th century.

In 1890, Russia established the Permafrost Research Committee and began to conduct relatively extensive research on permafrost.

After entering the 20th century, during the Soviet era, permafrost research developed rapidly (Tretovich, 1985; Friedman, 1982). The research content involved permafrost physics, permafrost mechanics, soil hydrothermal improvement, and engineering.

Stability etc.

In the United States, Canada and other countries, since the 20th century, the development and utilization of natural resources has directly promoted the continuous development of permaculture.

The first International Conference on Permafrost (ICOP) held in 1963 marked a new stage in permafrost research.

Since then, ICOP has been held every five years since 1973 to exchange research results in the field of permafrost from various countries.

At the Fourth ICOP held in 1983, China, Russia, the United States, and Canada initiated the establishment of the International Permafrost Association (IPA).

my country's permafrost research started late, but it has developed rapidly and is now among the most advanced in the world.

The main research units in my country include: Lanzhou Institute of Glaciation and Permafrost, Chinese Academy of Sciences, design and scientific research institutes in water conservancy, highways, railways, construction and other industries, and related colleges and universities.

China established the Glacier Permafrost Branch of the Chinese Geographical Society in 1982 and held the National Glacier Permafrost Conference to exchange research results in related fields at home and abroad, which played a great role in promoting the development of permafrost.

2. Research on water and heat exchange between the earth and air interface. From the perspective of energy balance process, various physical phenomena occurring in the lower atmosphere are basically formed under the influence of the underlying surface (such as soil, vegetation, water surface, etc.).

Different underlying surfaces have different physical properties. Complex material and energy exchange processes occur in the near-surface air layer and upper soil layer adjacent to the underlying surface, which have an important impact on the characteristics and formation rules of microclimate.

The underlying surface heats up by absorbing direct radiation from the sun and scattered radiation from the sky (short-wave radiation), and is also cooled by long-wave radiation.

The difference between shortwave radiation and longwave effective radiation is the net radiation obtained by the underlying surface.

During the day, solar short-wave radiation is generally greater than long-wave effective radiation. The net radiation obtained by the underlying surface will heat the air near the ground and the upper soil through the upward sensible heat flux and the downward soil heat flux respectively; at night, the underlying surface will

The surface net radiation is negative, and it needs to rely on the near-surface air and soil layers to supplement heat.

Therefore, the temperature conditions of the near-surface atmosphere and upper soil layers are strongly affected by the underlying surface.

The underlying surface is the main source of water vapor in the lower atmosphere.

When evapotranspiration occurs from the underlying surface and water vapor is transported to the atmosphere, a large amount of latent heat of evaporation is also consumed.

The latent heat of evaporation is also an important component of the heat balance of the underlying surface.

When condensation occurs on the underlying surface, corresponding latent heat will be released.

This moisture circulation process that depends on the underlying surface also plays an important role in the formation of microclimate.

The vertical distribution of temperature and humidity in the near-earth air layer is related to the balance of heat and moisture. Therefore, the upward and downward heat transport and moisture transport of the underlying surface are also basic factors that determine the climate characteristics of the near-earth air layer and the upper layer of soil.

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The water and heat exchange between the earth and air interface serves as the upper boundary condition for the water and heat transfer in frozen-thaw soil, and is essential for studying the law of soil water and heat transfer using mathematical physics methods.

The methods currently used to determine the water and heat exchange flux between the earth and air interface are mainly micrometeorological methods, including aerodynamic methods, energy balance methods, energy balance-aerodynamic methods, and vorticity correlation methods.

These methods all have certain application value in actual production, but each has its own advantages and disadvantages.

Among them, the comprehensive method combining energy balance and aerodynamics takes into account the characteristics of the underlying surface and the near-surface atmosphere. It has a good physical background and basis and is a basic method to understand the dynamic change process of surface water heat exchange and its influencing factors.

, has been widely used in the study of coupled migration processes of soil water and heat.