Kosa indicates the following weather phenomenon: Dust in inland deserts or dry zones in eastern Asia centered around People's Republic of China, is flung up into the air, for example, by a sandstorm, and is carried and falls over a wide area of eastern Asia centered around spring. Or the sand itself that causes this phenomenon.
It is considered that the kosa as a weather phenomenon occurs when the states of the earth and atmosphere, for example, the state of soil, from which dust is generated, and that of the airflow that carries dust together with sandstorms, meets certain conditions. The frequency with which kosa occurs depends on the season. In spring, kosa is generated frequently because the conditions are likely to be met, and has the tendency of being carried over a relatively long distance. However, kosa occurs in the seasons other than spring as well, although the frequency with which it occurs is extremely high in spring.
Damage due to kosa is not limited within a nation, being inflicted across nation boundaries, and in addition, the extent of the damage and the season in which it mostly occurs depends on the area. Kosa causes lots of damage described as in the following and the economical loss due to it is estimated to exceed 700 billion yen yearly: Dust from kosa adheres to things placed outdoors, making them dirty, degrades outdoor visibility, makes the sunlight reaching the ground weaker, obstructs traffic, and adversely affects the health of human beings and animals from inhaling the dust.
It is likely that, when an area is located closer to kosa occurrence areas, dust with larger grains falls on the area more frequently. In Mongolia, China, and the Republic of Korea, kosa sometimes causes significant damage to activities of the people and the economy in these areas, and it becomes socially important to take measures against kosa and to prevent kosa from occurring. It is said that damage due to kosa has become significant in eastern Asian nations recently, and some observational data backs up the situation. In addition, with interest in environmental problems being heightened, social interest in kosa has increased as well.
On the other hand, it is also pointed out that the movement of dust due to kosa plays an important role in the natural environment. In addition, the unique landscape produced by kosa has been targeted by cultural expressions. Furthermore, in some areas, the coming of kosa is said to be simply a seasonal charming sight.
The term actually includes more than one phenomenon when it is defined meteorologically, while they are collectively called 'kosa.'
In the area where kosa is being generated, kosa indicates 'a sandstorm' that causes kosa, the kosa floating in the air are 'ambient aerosol particles,' and the state in which lots of kosa is floating and falling is called 'drifting dust,' 'haze' or 'dust haze.'
Kosa is used as a phenomenon for classifying the degrees of visibility. In each eastern Asian nation, the meteorology-related organization defines 'kosa' and specifies the strength levels of kosa. However, they all differ slightly (refer to the section of kosa in various countries).
The areas where kosa is generated
The typical areas where kosa is generated are the following three areas, listed from the in order from the most western, the Takla Makan Desert (located in the western part of China), the Gobi Desert (located in the northern part of China and the southern part of Mongolia) and the Loess Plateau (located in the central part of China).
In addition to these, there are the following dry zones where kosa can occur:
The Saryesik-Atyrau Desert (located in the eastern part of Kazakhstan)
The Gurbantunggut Desert (located in Sinkiang Uigur Autonomous Region in China)
The Kumtag Desert (located across Sinkiang Uigur Autonomous Region and Gansu Province): Located adjacent to the Takla Makan Desert and is merging with this desert)
The Ordos Desert (located in the Inner Mongolia Autonomous Region of China)
Including the Mu-Us Desert and the Kubuchi Desert.
The Badain Jaran Desert (same as above, located in the Inner Mongolia Autonomous Region of China)
The Tengger Desert (located across the Inner Mongolia Autonomous Region of China, as above and Gansu Province)
The Ulan Buh Desert (same as above, located in the Inner Mongolia Autonomous Region of China)
The Sunite Basin (same as above, located in the Inner Mongolia Autonomous Region of China)
The Horqin desert (same as above, located in the Inner Mongolia Autonomous Region of China) (for reference: A description in the Chinese version of Wikipedia)
The Hunshandake Desert (same as above, located in the Inner Mongolia Autonomous Region of China)
The Qaidam Desert (located in Qinghai Province, China)
Almost all of these areas are located in eastern Asia, but some of them extend to central Asia. It is also pointed out that, in addition to those described above, the sources of kosa occurrence may also exist in the northeastern part of China (former Manchuria), the northern part of Mongolia and some parts of Russia. The total size of the areas where kosa originates is large (1.9 million square meters), more than five times that of Japan's land area, even when the areas are limited to the three main areas described above.
These areas where kosa originates are dry lands with an yearly amount of rain fall less than 500 mm or less than 100 mm in some places. Therefore, the surfaces of these areas are covered with sand. Although it is known that kosa originates in dry zones, there are the following three theories about the area where kosa actually originates: One of them limits the area to deserts alone, based on analysis of the dust that comes flying, another attributes the area to dry areas other than deserts, and the last one says that kosa originates in both deserts and dry areas (see the section of Components and shapes of kosa).
The occurrence of kosa
Today, it is considered that most of kosa dust is flung up into the air by sandstorms (dust storms) striking the dry areas where kosa can originate.
An investigation found that, in the Takla Makan Desert, the Gobi Desert, and the Loess Plateau, dust was flung up into the air when the average wind speed at the height of 10 m above the ground was 5 m/s or more. In addition to this, brief meteorological conditions such as the existence of a rising air current and the strength of sunlight in the area where kosa originates, are included in the conditions for making dust fly up. It is also pointed out that, in areas where kosa can originate that are surrounded by mountain ranges, for example, the Takla Makan Desert, a strong wind called yamatanikaze (mountain-valley wind) blows at the same time every day, making dust fly up.
Furthermore, when the wind strength is greater, a violent sandstorm called shachenbao in Chinese (沙塵暴 or 沙暴 in simplified Chinese characters) may be developed. An investigation found that shachenbao sandstorm occurred at a wind speed of 10 m/s in the Gobi Desert and at 6 m/s in the Takla Makan Desert and the Loess Plateau. Reportedly, it was observed that sand was flung up to a height of seven to eight kilometers by shachenbao sandstorm. However, it is not clear whether the value was correct, because the observation unit may sometimes malfunction.
A sandstorm (shachenbao) may sometimes grow quite strong. The meteorological authorities in China specify a sandstorm with an instantaneous wind speed of 25 m/s or more and a visible distance of 50 m or less as Kara Bran or 'black wind,' which is called 'black storm' popularly. When the atmosphere becomes unstable, for example, due to a passage of a cold front, a Kara Bran is generated triggered by a local gust, such as a downburst or a gust front. Horizontally, it covers a distance of several hundred meters to several hundred kilometers, and moves in a big vortex.
When approaching, it looks like 'a sand wall' with a height of several hundred meters
Entering within 'a sand wall,' the amount of sand flying around increases suddenly, and (when it is daytime), the surrounding area becomes darker while becoming more yellowish and reddish and the wind becomes stronger as well. For several tens of minutes, it remains dark outdoors and it is almost impossible even to walk. Even if you escape into a house, intrusion of sand makes it almost impossible to conduct ordinary household activities. Kara Bran rarely occurs. The latest one occurred on May 5, 1993 and inflicted significant damage (to be described later in further details).
How dust is flung up depends totally on the size of sand grains. It is said that sand with a gain size of 1mm or more rotates (see Fig. 1 on the left), those with a grain size of 1 mm to 0.05 mm (50 micrometers) jump, and those with a grain size of less then 0.05 mm float. The rotating sand of a kosa cannot move far from the place where the kosa originates, and constitutes a moving sand dune. The jumping sand is flung up for a short period of time and constitutes most of shachenbao sandstorm. The floating sand moves on the wind, reaching far away places.
In more details, the movement of the floating sand is as follows: The sand flung up into the air by a sandstorm ascends up 500 m to 2 km above the ground due to an ascending air current and moves at that height. Around the area where a kosa originates, the distribution of dust density and that of sand gain sizes are quite complicated. However, in the areas remote from the place where the kosa has originated, a high-density dust layer tends to be formed at a height of around 1 to 2 km above the ground. In these areas, the atmosphere under 500 m to 2 km above the ground is called the atmospheric boundary layer, and the air flow there is complicated. Above this layer, there exists a layer called the free atmosphere, and when some sand grains are lifted up to this layer, they are moved to far away places on a steady fast wind. However, when the air is churned by a strong wind, for example, by a movement of a growing low pressure, a high-density dust layer may be generated at a higher place, for example, a height of up to 6 to 7 km above the Japanese archipelago, moving the dust to far away places. Furthermore, the dust that is generated in daytime and floats in the atmospheric boundary layer remains at the same height, even when, entering the night, the boundary between the atmospheric boundary layer and the free atmosphere descends. Therefore, some of the dust enters the free atmosphere and is moved to far away places.
Westerlies flow in wide areas of eastern Asia and central Asia
However, westerlies have little affect on the atmosphere near to the ground. Therefore, dust can be moved in directions other than east, depending on the pressure pattern. However, dust at higher altitudes are affected by westerlies strongly, and the kosa that is flung up high into the air is moved to the east. Therefore, it is likely that kosa reaches areas to the east of the place where it has originated.
The falling of kosa
Through these processes, larger-grain sand in the dust falls first. An investigation found that the diameters of sand grains falling in Beijing are roughly 4 to 20 μm, and those falling in Japan three to four days later are around 4 μm. As a reference, it is said that, in an ordinary kosa, 30 percent of the dust flung up into the air falls and stays in the place where the kosa originates, 20 percent in its vicinity, and 50 percent is moved to, falls in and stays in far places like Japan, Korea and the Pacific Ocean.
However, when a kosa occurs in a place, areas located nearer to the place are affected more seriously. For example, most of the kosa observed in the Korean peninsula have been produced in the Loess Plateau, the Gobi Desert and others in its west, and rarely in the Takla Makan Desert. The Korean peninsula is far apart more than 5,000 km from the Takla Makan Desert, and the kosa originated in the desert can reach the peninsula only when a condition enabling the carriage of it for a long distance is met.
Concerning the kosa arriving in South Korea, the South Korean meteorological agency investigated 'the number of days between the occurrence of kosa and its arrival in Korea' and 'the average heights of the arriving kosa.'
According to the data, the kosa originated in the Takla Makan Desert reached Korea in four to eight days at 4 to 8 km altitude, the one in the dry area of northern part of China in three to five days at 1 to 5 km, the one in the Loess Plateau in two to four days at 1 to 4 km, and the one in Manchuria (the northeastern part of China) in one to three days at 1 to 3 km.
The amount of kosa produced, weather and seasons
Concerning the amount of kosa (in weight) produced yearly, it is estimated that 1 to 5 tons per a square kilometer fall in Japan yearly and around 15 tons per a square kilometer in Beijing monthly. However, it is considered that the actual amounts depend on the weather of the place where each of the kosa is produced.
When much rain falls in a place where kosa is supposed to occur, the occurrence frequency of kosa there tends to decrease thereafter. On the other hand, when little rain falls in a place where kosa is supposed to occur, the occurrence frequency of kosa there tends to increase thereafter. This is because, due to the amount of rainfall, the states of the soil, such as the dryness level of the land and the existence or nonexistence of snow or plants, change. However, the amount of kosa is more affected by the strength of wind due to a storm and the occurrence frequency of such winds, rather than the amount of rainfall. Therefore, before and after a strong low pressure passes a kosa generating area, sandstorms are generated frequently, increasing the amount of kosa produced as well. Furthermore, sand grain sizes of each kosa producing area affect the amount of kosa.
As for the season, kosa occurs in spring the most. Kosa is less likely to originate in the winter when rain falls little and the land surface becomes dry, because the weather during that season stays mild with no strong wind, due to the Siberian high pressure, and in addition, the surfaces of almost all of the dry areas are covered with snow. It is considered that kosa occurs more frequently in spring by the following conditions: Melting snow on the topsoil, being stronger westerlies by weaker high pressures, increasing windy days by passing of developing low pressure, and so on. Entering the middle of spring when the weather becomes warm, the amount of plants on the land increases, and in summer, the amount of rain fall also increases. Therefore, the soil become more fixed on the surface of the land and consequently the amount of kosa decreases gradually. Then it occurs in autumn the fewest.
For a reference, on a kosa producing site, there is statistical data about the number of days when a sandstorm was generated in the Sinkiang Uigur Autonomous Region. According to the data, maximum approx. 20 percent of the yearly occurrences were concentrated in April, with approx. 70 percent in the four-month period from March to June. According to statistical data about the number of days when a sandstorm was generated in the area from Dunhuang City to Hexi Corridor, slightly less than 50 percent of the occurrences were concentrated in the three months of spring. However, approx. 10 percent of the yearly sandstorms occurred in autumn as well, showing that sandstorms occurred throughout the year. On the other hand, in Japan where kosa is brought, approx. 90 percent of kosa arriving is concentrated in the four months from February to May corresponding to spring, with almost no kosa observed in July to September corresponding to summer. However, these statistical data is based on observations on the ground level, and it is observed that thin kosa is passed above Japan even in summer.
Recently, it has also become known that, even when no kosa is observed on the ground level because no visibility is affected there, thin dust is observed in the high-altitude atmospheric layer called the free atmosphere (also known as free troposphere).
This is called 'background kosa.'
It has become known that this type of kosa originates in the summer and autumn when almost no kosa is observed ordinarily on the ground level. In addition, it has also been made clear that this type of kosa is concerned with the neutralization acid fogs in high mountains. A feature of background kosa is that it originates even in the following conditions: No sandstorm is generated in its vicinity and not even low pressure that will fling up dust into the air. The components of background kosa are provided with the following feature: While Ca (calcium) in ordinary kosa exists in the form of CaSO4 (calcium sulphate), Ca in background kosa exists in the form of CaCO3 (Calcium carbonate). This indicates that background kosa is slightly mixed with SO42- (sulfide ion) included in air pollutants exhausted on the ground level and that this type of kosa is generated through paths different from those through which ordinary kosa is generated.
An occurrence of kosa and its strength level are judged totally based on observation data, including the color of the sky and humidity, in addition to visibility. It can be said that so far, meteorological observations are mostly based on visual ones.
Of the WMO-specified international symbols on weather charts, which are internationally usable for indicating meteorological phenomena, the following 11 can be used for kosa:
06: Dust or sand floats in the air over a wide area (not ones flung up by wind) =>
07: The dust or sand flung up into the air by wind =>
09: A sandstorm is visible or a sandstorm existed within the last one hour =>
30: A weak or ordinary-level sandstorm.
The dust density has decreased in the last one hour =>
31: A weak or ordinary-level sandstorm.
Has remained unchanged in the last one hour =>
32: A strong sandstorm:
The dust density has increased in the last one hour =>
33: A strong sandstorm:
The dust density has decreased in the last one hour =>
34: A strong sandstorm.
Has remained unchanged in the last one hour =>
35: A strong sandstorm.
The dust density has become increased in the last one hour =>
98: Thunder and lightning was observed.
Accompanied by a sandstorm =>
The above symbols are converted to a format, such as surface synoptic observations, and are transmitted globally from observation points in the meteorological data format for exchanging such data internationally. The data concerned, for example, about kosa densities, had not easily been exchanged internationally until several years ago. However, because China started providing information concerned, lots of data in a wide eastern Asia area has been able to be shared since the spring of 2008. Therefore, now, the accuracy of kosa forecast has increased.
For precise observations for the purpose of research or for monitoring atmospheric environments (for example, observations of air pollution), various instruments are used depending on the objective.
LIDAR (laser radars)
Enabling measuring kosa densities at various altitudes. Measurements can be conducted at all times and unmanned, but it sometimes happens that measurement becomes impossible in cloudy conditions or when the density is high.
Actinometers and radiometers
These instruments can be used for measuring optical characteristics and the sizes of sand grains of kosa and others.
Nephelometers and absorption spectrometers
These instruments can be used for measuring optical characteristics of kosa and others.
Particle counters and mass monitors
These instruments can be used for measuring, the mass, densities and sand grain sizes of kosa and others.
Time-of-Flight mass spectrometers
This instrument can be used for measuring chemical characteristics of kosa and others.
Use of this instrument allows visibility levels to be measured more precisely than visually.
The instruments described above are installed on the ground level. Observations are also conducted on airplanes, on helicopters, on flying balloons, on ships or at highlands at an altitude of more than 2000 m (where an atmospheric layer called free troposphere exists, and the layer has an air flow different from that of others, because no friction with the ground surface exists there). It is also conducted to gather sample kosa grains and to analyze them. In addition, data from artificial satellites, which allow observations over wide areas, has also been used.
Analysis on Geological Survey
It is considered that kosa fell in Japan in the last glacial period at least 70 thousand years ago. The amount of dust sent by wind in the period from 70 to 60 thousand years ago (the sand and dust carried over to and accumulated in Japan, including kosa) was 12 g per 10 square centimeters. The amount in the period from 10 thousand years ago to today, corresponding to the Holocene epoch, was 3 to 4 g. In other words, it is estimated that the amount in the last glacial period was three or four times that of today. Furthermore, there is also the data that the amount of accumulated kosa increased 18 thousand years ago as well.
Concerning relationships with weather, it is supposed that, when the earth was in a cold period, the amount of kosa increased because the land became increasingly dry, and in the warm period, the amount decreased because the humidity level of the land increased. Research based on dust-falling frequencies in the last 1,000 years (between 1000 to 1999, roughly the last 1,000 years) showed that an increase in the dust-falling frequency was inversely proportional to an increase in the temperature, supporting this theory. As a factor that increased kosa in the cool periods, it is said that, in these periods, cool air advanced southward more frequently due to changes in the air flow, increasing the frequency of dust storm occurrences.
It is considered that the Loess Plateau, which is a kosa producing place, was formed by wind-sent dust that started falling there 2.5 million years ago and whose amount increased starting 2 million years ago. It is considered that these changes in the amount of kosa or wind-sent dust occurred, because climate changes and crustal changes altered wind, rainfall or land shape patterns.
Approx. 1,000m thick mudstone layers called kucha (Shimajiri Mudstone in the scientific name) exist on the Nansei (Southwestern) Islands of Japan, and it is considered that the layers include sand grains that originated in kosa. The Shimajiri Mudstone layer was formed in the Neogene period, or from approx. 25 million years ago to approx. 2 million years ago, suggesting that the kosa might have arrived in this area in that period as well.
An analysis of sediments showed that kosa originated as early as in the latter half of the Cretaceous period, or from approx. 70 million years ago.
Appearances in historical documents
It is known that, in China, present kosa was called 'chenyu' (dust rain) in around 1150 BC. In addition, the terms of 'wutu' (raining dirt), 'wusha' (raining sand), 'tumai' (raining mud), and 'huangwu' (yellow fog) are also found in historical documents. Furthermore, a document recording kosa from 300 BC also exists.
In Korea, the term of 'wutu' is included in descriptions for around 174 A.D. in "Samguk Sagi" (History of the Three Kingdoms) in the Silla period. It was believed that an angry god made it fall instead of rain or snow. There also remains a record that red snow, considered being snow mixed with kosa, fell around 644.
In Japan, descriptions of kosa started appearing around the Edo period, with the terms of 'dei-u' (mud rain), 'beni-yuki' (red snow), or 'Ki-yuki' (yellow snow). As kigo (season-indicating words) for haiku poems, 'tsuchifuru' (also referred as 'bai,' dark sky due to dust), 'yonagumori' (dark sky due to dust) and 'baifu' (a strong wind flinging up sand) are used. In "Honcho Nendaiki" (the Chronicle of the Dynasty), it is recorded that beni-yuki (red snow) fell in 1477.
Changes that have occurred entering the 20th century
It is frequently reported that the occurrence of kosa has been increasing recently. It is said that the occurrence frequency of kosa offers an important viewpoint for considering the advance of global warming and desertification. However, to know how the occurrence frequency has changed needs data over a long period of time.
Major data available is described below:
In the area in the west of the Takla Makan Desert, kosa has occurred more frequently corresponding to an increase in the occurrence frequency of strong wind and also corresponding to a decrease in the snow-falling area.
In the northwestern area of China, the occurrence frequency of kosa has shown a decreasing trend for 40 years from the 1960s, in particular between the 1980s and 1990s. However, the frequency in each area was considerably different in around 1970s.
In the Huabei Plain of China, the occurrence frequency had continued decreasing until 1990s, but has increased entering the 21st century.
In South Korea, the following are found from data available for the last approx. 100 years: The occurrence frequency of kosa in the period from the latter half of 1930s to the first half of 1940s was almost the same level or more than that in the period after the latter half of 1990s, the frequency was in a decreasing trend in around the period from the latter half of 1940s to 1950s, and it has been in an increasing trend thereafter, with the occurrence of kosa increasing in the season from the late autumn to the early spring.
The Japan Meteorological Agency has observed kosa since 1967, and the data obtained there shows the following: Both the number of kosa occurrences and the total number of days when kosa was observed were maximum in 2002, but the long-term trend is not clear because the data changed considerably depending on the year.
Concerning data other than changes in the occurrence frequency of kosa, research shows that the occurrence frequency of dust storms and that of high-density kosa have been increasing.
It is found that the strength of kosa and its occurrence frequency have changed in the order of several years to several tens of years and that these changes have depended on the area. On the whole, it can be said that the occurrence frequency has been in an increasing trend since 1950s in South Korea and entering the 21st century in China.
It is said that changes in the amount of rainfall, the amount of snow-covered area, the period when the land is covered by snow and changes of kosa-flying paths constitute the major factors causing these changes concerned with kosa. However, it is also said that desertification and an increase of dry weather areas in China constitutes a factor of increasing the occurrence frequency of kosa. In 2007, 18 percent of the total land area of China, approx. 1.74 million square km, was desert. However, it is said that this desertification originated in agriculture-related problems, such as excessive pasturing and an enlargement of arable land, and in living and economy related problems. Therefore, this phenomenon is sometimes considered as an environmental problem. It is pointed out that both central and local governments of China have employed policies to accelerate the extent of making the land drier, leading to the expansion of dry area. On the other hand, there also exists a view of considering that Korea and Japan, which have been affected by kosa, are responsible indirectly as well, for example, through importation of woods and agricultural products.
In some cases, the soil polluted due to contaminated water and waste has killed plants, expanding dry areas. In Kazakhstan, as known from the example in the Aral Sea, inappropriate agricultural policies caused underground water and wake water to be pumped excessively, expanding dry areas. It is said that, in the Inner Mongolia Autonomous Region and some other areas, excessive pasturing and industrial pollution have expanded dry areas, becoming kosa generating areas.
In addition, there is also another theory that global warming has been related to an increase in kosa in the following way: Global warming has caused the amount of rainfall in the inner land to decrease and has also caused the atmospheric pressure patterns to change, consequently expanding dry area and increasing the occurrence of strong winds. It is also pointed out that El Nino and the occurrence frequency of kosa may be related.
However, the following still remains unclear: Kosa and changes in damage due to kosa, and changes in the natural environments and artificial factors that are considered constituting the cause. There is also the aspect that air pollution, not directly related to kosa, has increased bad effects of kosa.
The following phenomena, mostly accompanying a sandstorm, resemble kosa considerably: Dry high-temperature wind from the Sahara Desert in Africa (called ghibli in Libya, or scirocco in Italy), harmattan that is dry cool wind in the area from the Gulf of Guinea to Cape Verde, haboob that are sandstorms in Sudan, and khamsin that is dry high-temperature wind in Egypt. Scirocco resembles kosa in the following sense: It brings the falling of red rain that includes dust, and is considered contributing to the generation of terra rossa, the red clay distributed widely in the Mediterranean region. For the phenomena described above, their names are related to the wind or sandstorms, unlike kosa that is related to sand.
The areas where large-scale dust like kosa is produced include northern America and Australia, in addition to central Asia (where kosa and others are generated) and Africa (ghibli, scirocco and others are generated).
The sizes of sand gains of the kosa that comes flying over a long distance from its source place, for example, to Japan are around 0.5 µm to 5 µm (0.0005 mm to 0.005 mm) that is slightly larger than those of grains in smoke from tobacco (0.2 µm to 0.5 µm) and slightly smaller than the diameters of human red blood cells (6 µm to 8 µm). In geology, these sizes of grains are classified as mud rather than sand.
The sand gains observed in China are mostly larger, and those in Japan are mostly smaller. In an investigation conducted in 1934 over the area from China to Japan, the sand grain sizes were concentrated in the range of 0.001 mm to 0.5 mm (note that optical microscopes used could not measure minute grain sizes). An analysis of kosa conducted in Nagoya in 1979 showed that most of the sand grain sizes are distributed roughly between 1 μm to 30 μm, with its distribution peak at 4μm. Based on these investigations, it is supposed that particles of kosa are cohered clay particles or comparatively large mineral particles to which clay particles are stuck.
The colors of kosa are near to ocher, yellowish brown, or reddish brown.
Composition and components
The composition mostly includes quartz, feldspar, mica, chlorite, kaolinite, calcite (Calcium carbonate), gypsum (calcium sulphate), and ammonium sulfate. Because lots of gypsum exists in deserts but no gypsum in ocher, there is a view of considering that kosa originates in deserts. However, it is known that, when Calcium carbonate, a major component of limestone, reacts with ammonium sulfate, gypsum is generated (to be described in details in the following sentence). Therefore, there is also a view of considering that kosa not necessarily originates in deserts. A component analysis of aerosol conducted in April, 2002 at a kosa-producing place and a kosa-falling place showed that the ratio of gypsum included in calcium minerals was larger in more eastern places.
Various particles stick to kosa, although how easily particles are stuck to kosa depends on the type of the particles. In major cities of China, such as Beijing, the amount of aerosol increases in the winter when kosa also increases. Therefore, it is considered that most of the aerosol comes from kosa. However, when the components of the aerosol in the soil of the place where kosa was produced was compared with those in major cities in China, it was found that the latter included more sulfide ion, more nitrate ion and more lead (a heavy metal). Based on experiments, it was also found that sulfur dioxide gas adheres to the surfaces of kosa particles, with kosa particles working as a catalyst, and that the ammonium sulfate, much included in the air of major cities in China, adheres to kosa in high-humidity conditions and becomes calcium sulphate (gypsum) through the process in which calcium in kosa reacts with ammonia.
Kosa adheres to various particles in the air while floating in the sky. Therefore, it is considered that the components depend on the place where the kosa is generated and on the areas where it passes. It is considered that sulfur oxide and nitrogen oxide adhere to the kosa passing over industrial zones in China, Korea or Japan. Actually, according to an investigation in which both the components of the kosa captured in China and those in Tsukuba City, Ibaragi Prefecture in Japan, were analyzed, the kosa in Tsukuba City included more nitrogen dioxide (NO2) and hydrogen sulfate (HSO4), supporting the relationship described above.
According to component analyses of kosa conducted in 2001 at the three typical kosa source places (the western area of China, the northern area of China and the Loess Plateau) in Asia, the kosa included, in the larger mass order, silicon (24 to 30 percent), calcium (7 to 12 percent), aluminum (7 percent), iron (4 to 6 percent), potassium (2 to 3 percent) and magnesium (1 to 3percent). In addition, minute amounts of manganese, titanium, and phosphorus were also detected.
Tottori Prefectural Institute of Public Health and Environmental Science investigated the components of the kosa-including air in April, 2005. In the investigation, the amount of arsenic included was 22 times the average value, that of manganese 13 times the average value, that of chromium 7 times the average value and that of nickel 3 times the average value, each quite a high value compared with the average value, were detected, suggesting that the components of the air in the time when kosa is falling are different from those of the ordinary air.
There is also an investigation showing that the density of dioxin and dioxin-like particles in the air increased when kosa arrived. In Taiwan, it is reported that the density of such components in the air increased by 35 percent compared with that in the ordinary air condition. In Busan, an investigation in 2001 showed that the density of such components in dust was 2.5 times that in the ordinary condition. In an investigation in 2007 also in Busan in which the amount of these components taken into human bodies was measured, it was found that 0.028 to 0.038 pg-TEQ/kg/day was taken in the day when kosa fell, more than double 0.01pg-TEQ/kg/day that was taken in an ordinary day.
An investigation conducted by the Rural Development Administration of South Korea for sampled kosa showed that, although depending on the area, the samples included bacteria with a density of 7 to 22 times more than that of the ordinary air and mold with a density of 15 to 26 times that of the ordinary air. The reason is considered that, when kosa came floating, bacteria and mold stuck to kosa particles and multiplied themselves in a condition of an appropriate temperature and humidity for them.
However, their effects on human beings, livestock and plants are a concern
Also in South Korea, it is reported in 2003 that analyses of urine samples in epidemiological investigations conducted before and after kosa arrived showed that carcinogens belonging to polycyclic aromatic hydrocarbon (PAH) increased by 25 percent on average when kosa arrived.
It has been known in Japan that stem rust, a disease damaging barley and wheat, increases after kosa arrives. However, it has also been known through research that spores of strip rust, a disease damaging barley and wheat as well, have flown to Japan together with kosa.
Research also found that silicon dioxide, which causes inflammation when taken into lungs, and β glucan, one configuration of the mycelium mold, were included in kosa.
It is considered that some of the bacteria in kosa are killed by ultraviolet rays included in sunlight. However, there is also concern about chemicals that might decompose into dangerous ones.
Effects of kosa
It has been confirmed that kosa causes various kinds of damage listed below:
The damaged areas confirmed cover a wide area in eastern Asia. In Mongolia, China and South Korea, the damage due to kosa is considerable, becoming a social problem. In Japan, the damage is not so serious compared with these nations, and kosa is usually taken up as an environmental problem.
Kosa constitutes a typical cross-nation-boundary problem that causes damage to areas far away from the problem source place. Kosa is closely related to economical progress in China and there is a view of considering that political measures to be taken are the key to solving the problem. Some call it "Yellow dust terrorism."
Furthermore, from measurements of kosa and estimates based on a kosa-scattering model, it has also been known that soot and carbon monoxide generated in eastern Asia have flown to Japan as well. In this way, it has also become known that similar across-boarder problems exist in other areas of Asia as well.
Physical or economical damage
When the density of kosa in the air is relatively low, slightly yellowish mist is generated and visibility is affected slightly, but everyday lives are not affected seriously. However, when the density becomes high, outdoor landscape becomes yellowish or reddish, visibility becomes affected seriously, and various kinds of damages are reported. Damage is generated even when the amount of kosa is small, but the damage becomes more serious when the amount becomes larger.
The kosa that falls and accumulates causes various kinds of physical damage, such as making building windows and washed clothes dirty and hindering the growth of agricultural products. When kosa accumulates on vinyl plastic houses or on skylight windows of buildings, damage is sometimes caused because it hinders the penetration of sunlight.
When kosa enters rainy clouds or snowy clouds, the kosa absorbed there may fall mingled with rain or snow particles. Quite minute particles are included in kosa. Therefore, when these particles are mixed with rain, they become a muddy substance and are sometimes stuck strongly to buildings and cars.
The substance stuck is more difficult to remove than the kosa mingled with no rain
When kosa is mingled with snow, the accumulating snow may become yellow or red.
Kosa remains in the air for a long time together with air-polluting substances and makes the color of the clouds around it brownish. In some cases, the brown clouds, which have been suspected of damaging agricultural products, are generated. When a large-scale kosa is produced, it is sometimes included in pictures taken by weather satellites.
Deteriorating visibility, high-density kosa sometimes obstructs flights of airplanes, traffic of vehicles, railway operations and the walking of human beings. Covering the sky, it also sometimes obstructs weather observations. In addition, such kosa sometimes reflects terrestrial radio wave irregularly, causing receiving failures or abnormal transmission of the radio wave. In China and South Korea, the driving speeds of passenger vehicles are sometimes restricted in high-density kosa conditions.
In factories for precision machinery or for semiconductors, the intrusion of minute particles included in kosa may cause damage that generates defective products. Serious economic losses, such as those due to speed restriction or traffic disruption and to various kinds of damage, including damage to health, and the cost of dealing with the sand and dust, are generated.
Sandstorms called Kara Bran near places where kosa is produced accompany lots of sand and strong wind. Therefore, buildings may be destroyed or buried, utility posts may be tumbled down, and electric power outage may occur due to the breaking of electric wires.
In some parts of the desert where kosa occurs, the extent of damage due to kosa is by far more serious, because accompanying sandstorms may move sand dunes, may bury dwelling places, may make roads unusable, and may resultantly make a whole village inhabitable.
It is difficult to remove kosa, even if it is dry, and in addition, kosa is likely to be solidified like mud, making the coating and windows of vehicles dirty. On the other hand, if the kosa that has become dry is wiped with wipers or a towel, the wiped surfaces are likely to be damaged, sometimes causing irreparable damage to be generated. It is said that a better measure to be taken against this situation is to wash as frequently possible, using water in particular.
Damage to health
Fine sand grains, the substances stuck to sand grains, and the chemicals coming flying together with kosa (refer to the description of Shapes and components of kosa) inflict various kinds of damage on health.
Damage to respiratory organs, eyes and ears, such as the generation of cough, phlegm, asthma, soreness, snivel, and itching is conspicuous. On a day when strong kosa arrives, the states of allergic diseases, such as hay fever, asthma, and atopy, may become worse. However, even in the same pollution level, the states of diseases depend on the individual.
In an epidemiological survey conducted in South Korea between 1995 and 1998, death rate in the higher age range increased by 2.2 percent and the persons who visited or were admitted to hospitals due to diseases related to respiratory organs, circulatory organs or eyes increased, when kosa arrived flying. According to a newspaper report in China, it was found that, when dust is scattered, infectious diseases, cardiovascular diseases, cardiac infarction, hypertension, and cerebral strokes increased (according to an article on May 28, 2002 of "Xin Sheng net"). In Japan, no epidemiological survey has been conducted.
The sizes of sand grains of the kosa flying to Japan are so minute that it is said that the grains reach the ends of lungs. However, it is said that they are so minute that their total amount would not be large. Although kosa itself is not allergen, the following possibility is pointed out: When pollutants stick to kosa, some synergistic effects are generated and the bad effects that the pollutants would affect human bodies are amplified.
In China and South Korea, public organizations announce information to recommend wearing a mask or to urge people to avoid going outdoors, when a high-density kosa arrives.
Through sand and the substances stuck to sand, minerals are supplied to soil and sea and consequently the growth of plants and phytoplankton is advanced, and therefore, it is pointed out that kosa provides effects which enrich the quality of soil. There is also research showing that phosphorous and iron constituting kosa are related to the growth of plankton in the sea and that of forests in Hawaii. Calcium carbonate included in kosa is provided with a neutralization ability. Therefore, when the flying kosa meets rain, the rain is neutralized because acid and base are produced. Consequently, kosa also contributes to a reduction in the damage due to acid rain.
However, it is also known that kosa helps the generation of stem rust and strip rust, diseases of barley and wheat. Various substances are stuck to kosa and are carried with the kosa, but the damage and environmental pollution caused by harmful substances of them are considered constituting a problem.
Kosa affects climate in various ways. Today, the following are known as effects caused by kosa, but it is not known clearly how kosa works completely: When being placed over forests or sea, kosa grains provide the so-called umbrella effect to prevent the penetration of the sunlight (cooling effect); When being placed on snow areas or glaciers, they provide the effect of warming the air through absorbing sunlight (heating); Being able to become nuclei of generating clouds, they provide the effect of controlling the distribution of clouds above the earth; Because substances included in kosa affect the growth of plants and planktons, kosa also provides the effect of affecting the carbon cycle.
Celestial color changes
The sun and the moon, and so on, sometimes appear in different colors due to the kosa that covers the sky. The color of the sun sometimes appears silver, or blue accompanied by a blue halo around it. The color of the moon also sometimes appears blue accompanied by a blue halo around it.
Although rarely seen, such phenomena were actually observed in Japan as well as in the northern part of China.
These appearance-changing phenomena occur because kosa sand grains prevent the penetration of some of the sunlight, reducing the strength of the light, and scatter the remaining light. It is considered that the change to blue color is caused mainly by Mie scattering, and due to a similar principle, Mars looks blue in the evening glow.
Measures to be taken against kosa
Measures against damage due to kosa are taken in various areas. In areas near places where kosa occurs, the measure to prevent falling sand from entering buildings and that to prevent too heavy sand from accumulating on roofs or similar structural places are taken. Measures are taken to close windows, to remove kosa stuck to clothes and to do cleaning after kosa ceases falling are considered.
When lots of kosa is falling, it is considered to take the following measures against damage to health: Wearing eye glasses and a mask to prevent fine sand particles from entering the body, gargling and washing your hands and face, and avoiding going outdoors.
There is also the view of considering that kosa is a natural phenomenon having occurred at least last several tens of thousand years and it is impossible to prevent damage due to it completely. However, it is considered that the amount of kosa can be reduced by taking appropriate measures, and various measures have been taken centered on the prevention of desertification of the areas where kosa occurs.
Preventing desertification and preventing land from becoming dry
Also refer to water crisis in China, water supply and sanitary states in China, desertification problems in China and environmental problems in China.
It is considered that kosa can be originated in almost all of the desert and dry land in China. It is considered that the major factors contributing to desertification in the last several tens of years in China were the dry climate due to climate changes in addition to artificial factors, such as policy failures in cutting trees, pasturing, farming and water usage.
Desertification and advancing the dry state of land mostly starts when plants are blighted due to a slight shortage of water, for example, caused by dry weather. Therefore, it is considered important to prevent desertification at this stage, because desertification can be prevented more efficiently at this stage. However, water becomes necessary to take measures necessary for the prevention, but there exist limitations in taking such measures because lots of water is unavailable.
On the other hand, to nourish the rapidly growing population, it has been necessary to increase production power and economic power. Therefore, in the northern part and western part of China, the way of farming and livestock-farming has been changed from the moving type to the stationary type, though use of the stationary type is likely to change areas in these parts into desert.
In the Loess Plateau where slightly more rain than in desert falls, the traditional rain-fed farming method, in which, relying solely on rainfall, fallow land was used for accumulating rain, was originally utilized (particles of loess and of kosa are so fine that surface tension enables water to be accumulated among the particles, providing them with a water-retaining characteristic). However, as in other areas, an increase in the population of these areas has caused excessive farming and the accumulation of salt due to irrigation. Therefore, it is considered that dry land has expanded in these areas as well.
Based on these backgrounds, so far it is considered important, to prevent desertification, to take measures centered on planting tress in deserts and improving farming methods. More specifically, these measures include planting trees more properly, securing fuel, such as more energy-efficient firewood, managing livestock, preventing soil erosion, irrigation, using resources more effectively, re-using energy, using land more properly or changing the farming method to more proper ones, and preventing sand from moving. Therefore, it is necessary to develop the technologies needed for these measures and to guide people by specialists concerned, to make the activities for preventing desertification continue for a long period of time.
However, many of these measures include those that would force burden to be placed on the residents concerned or that would change their lives themselves. Therefore, it is not easy to prevent desertification or to prevent land from becoming dry. For example, the one-child policy of China has played a significant role for controlling the population. However, the measure alone is not enough, and it is considered that steady activities, including planting trees in desert, are required as measures against kosa. The nations where no kosa is produced, such as Japan, can also aid the activities to plant trees in deserts and to guide farming methods, and such activities have actually been done in various places. On the other hand, there is a view of considering that the speed of dry land expansion is higher than that of planting trees and it is not easy to make the effects of the measures taken against kosa visible.
Researches and international activities
Kosa has been observed in various areas as part of weather observations. However, the observation points are not placed uniformly nor weather observations alone are enough for understanding kosa phenomena thoroughly. Therefore, it is necessary to conduct more precise and more systematic measurement. Until now, researches concerned have been conducted by individuals or small-sized groups. However, since the reality of kosa phenomena became known in details in 1990s, it became gradually clear that, to grasp the reality of kosa phenomena, it is necessary to deploy a monitoring system for a long period of several tens of years.
The following information is provided for the general public now:
Information about kosa, and weather information about kosa
Provided by Japan Meteorological Agency or the meteorology laboratory.
Kosa forecasts and precaution-requiring information (using three stages)
Provided by South Korea's weather agency.
Sandstorm forecasts and warning
Provided by the China Meteorological Administration. The forecasts were only for a short-time period, or today and the next day. Therefore, a numerical forecasting system has been developed by the Chinese Academy of Sciences and its operation has started.
In addition, large-scale projects have been organized by governmental organizations and by research organizations.
ADB/GEF projects of countermeasures against kosa
Participated in by the eight parties of UNEP (United Nations Environment Programme), UNEP (Economic and Social Commission for Asia and the Pacific), UNCCD (United Nations Convention to Combat Desertification), ADB (Asian Development Bank), China, South Korea, Mongolia, and Japan. This project has achieved some results, for example, the compilation of a plan to combat kosa (refer to the web site concerned).
Surveys of the reality of kosa
Projects by Ministry of the Environment (refer to the web site concerned).
Meetings by the ministers of the environments of Japan, China and South Korea
Consensuses about kosa problems have been built there as well.
A director-level conference of countermeasures against kosa among Japan, China, and South Korea.
International workshops for dust storms
International meetings concerning kosa research.
Many universities, research institutes, and government organizations in Mongolia, China, South Korea, and Japan are engaged in the research and observations concerned. Among these nations, cooperation has been made concerning aid for observation instruments and funds concerned, and cooperation has been also made about planting trees and providing guidance for farming. Concerning planting trees and providing guidance for farming, there also exist projects participated in by private bodies, such as non-government organizations.
Remaining problems and future problems to be tackled
It is pointed out that the recognition of kosa as well as the definition and classification of kosa (refer to the section of kosa in various countries) depends on the nation and the differences constitute one factor of delaying taking necessary measures. For example, the concept of damage by kosa is considered quite different in each nation as follows: Sand-hits in Mongolia, sandstorm-hits in China, damage by weather phenomena in South Korea, and air pollution in Japan.
In addition, it can be said that there is still no clear scientific explanation available about the problems of what generates desertification, considered the main cause of producing kosa, and of where the responsibility of desertification resides.
It has been caused by a decrease in rainfall due to global warming, and the responsibility resides in advanced nations.
It has been caused because no appropriate actions have been taken for farming and controlling water, and the responsibility resides in the residents, governments and administrations concerned.
Japan and South Korea, where no kosa is produced, are concerned with kosa as well because the factories of companies in these nations generate air pollutants that stick to kosa and because they import wood, agricultural products and livestock products that may cause desertification, and therefore, they are also responsible.
As described above, there are many opinions, and the opinions of China and Mongolia, where kosa is produced, are totally different from those of South Korea and Japan, where damage is inflicted by kosa.
The following are considered as future problems to be tackled: Continuing surveying the water amount and state of flora on the earth surface, the kinds and distribution of crops, the distribution of livestock, and the continuous survey of the state in which underground water is taken up, deploying advanced observation instruments, enabling observed data to be shared anytime, unifying the definitions and classifications of kosa, improving kosa-forecasting technologies, and evaluating the measures taken.
Kosa in various countries
The following terms are used for indicating kosa in various languages:
Japan (in Japanese)
黄砂,' pronounced 'kosa.'
The pronounce of 'osa' is wrong. The expression of '黄沙' is also used, though rarely.
The People's Republic of China (in Chinese)
黄沙' or '黄砂,' and both are pronounced 'hoansha' (binin, Huángshā). In addition, it is also provided with the expressions of '洲粉塵,' '黄塵,' '黄河風,' or '中國沙塵暴' (shachenbao in China). However, in China, the term of '黄沙' is mostly used among the researchers concerned, and the term indicating the kosa phenomena as a whole, for example, the one corresponding to 'kosa' in Japan, is hardly used. Instead, 'shachenbao' indicating only a sandstorm (due to kosa) alone is used.
English language regions
China dust,' 'Asian dust,' 'Yellow dust,' 'Yellow sand,' 'Yellow wind,' or 'China dust storms.'
Republic of Korea (South Korea) and Democratic People's Republic of Korea (North Korea) (in Korean)
황사,' '黄沙,' or '黄砂,' each of which is pronounced 'fansa' equally.
Vietnam (in Vietnamese)
Hoàng sa'(黃砂) or 'bão cát vàng.'
Mongolia (in Mongolia)
Tweilin' (in pronunciation) is used for indicating the sandstorms that cause kosa, although not expressing kosa itself.
In academic areas, the terms in English are used widely regardless of the language used. Furthermore, another term of 霾 (pronounced, bai or tsuchifuru) is also used in songs or poems, and in addition, some area-dependent terms of '灰西' (literally, dust from the west), '赤霧' (red mist), '山霧' (mountain mist) or '粉雨' (dust rain) are also used.
China and Mongolia
In weather observations in the People's Republic of China, kosa is included in 'dust weather,' the air state in which the visibility (horizontal one) is within 10 km and the wind is weak is called 'floating dust,' the air state in which the wind is strong and the visibility is in the range of 10 to 1 km is called 'floating sand,' and the air state in which the wind is strong and the visibility is within 1 km is called 'shachenbao.'
Shachenbao is further classified into class 3 (weak), class 2 (medium), class 1 (strong) and class 0 (especially strong). In particular, class 0 (especially strong) Shachenbao with an instantaneous wind speed of 25 m/s or more and with a visibility of less than 50 m is called "black wind" or Kara Bran.
Such Kosa is observed frequently in the eastern areas of China. When falling in city areas, kosa and smog, generated due to recent economic progress, produce a synergistic effect, sometimes limiting the visibility considerably. Located near deserts where kosa is produced, Beijing and Tianjin have been attacked frequently by large-scale kosa recently.
Damage has often been inflicted even on areas located relatively far apart from the places where kosa is originated. In Shanghai, the largest amount of kosa in the past of 623µg per cubic meter and the worst air pollution index in the past of 500 and were observed on April 2, 2007. Because a value between 0 and 500 is used for the air pollution index, with values of 300 or more considered 'serious,' this was the worst value recorded until now. In Huabei (the North China) and northeastern part of China, index values of around 100 are observed almost everyday and the index value of 500 was once recorded there. However, it was the first 'serious' index for Shanghai. Even in Taiwan located in the south, kosa in the level of 500 µg per cubic meter are observed centered on spring.
However, in the inner part of China and Mongolia located near places where kosa is produced, damage due to sandstorms is more serious than the simple falling of kosa. Kosa covers farm products with sand, causing bad harvests. In addition, the sand intrudes into dwellings, and the low visibility due to the sand sometimes even causes persons to be killed by ensuing traffic accidents.
The most serious damage in the past was done by Kara Bran produced in the northwestern area of China (Ningxia Huizu Autonomous Region, the Alashan province of Inner Mongolia, and Gansu Province) on May 5, 1993. In this case, the number of killed or missing persons reached 112, the number of injured persons 386, the number of killed or missing livestock, horses and cattle 483 thousand, the number of tumbled electric poles 4,600, the size of damaged farm land area 210 thousand hectares, the size of damaged forests 180 thousand hectares, and the total economic loss 6.6 billion yen. In addition, many roads and railway roads were seriously damaged by being buried under sand. Many of the dead were children returning from schools. In this case, a record kosa density of 22.9 mg per cubic meter (22,900 μg per cubic meter) was observed in Gansu Province.
According to the Forest Management Office of China, approx. 400 million persons are affected by kosa, and the amount of damage reaches 54 billion yuan (approx. 84 billion yen), even if the damage is limited to those directly inflicted. According to another estimate, the yearly damage due to kosa was 1.5 billion yuan in 1980s (according to Yang and Lu, in 2001).
In the Republic of Korea, the strength of kosa is classified into three stages of strength 0, strength 1, and strength 2.
Visibility is slightly hindered.
The sky looks dirty and yellow dust accumulates on the surface of materials slightly.
The sky looks yellowish brown, the strength of the sunlight is lessened, and yellow dust accumulates on the surface of materials slightly.
Based on the average prediction per hour of the PM10 density obtained from the observation network of the Ministry of Environment, Republic of Korea, South Korea's weather agency issues a three-stage warning when it is predicted that a specified density will continue for two or more hours. The warning is issued for each area necessary, as for information about precaution-needing weather and warning for weather.
Information about kosa
Issued when the density is 300 µg per cubic meter or more and it is necessary to provide the information.
It is urged that aged persons, children, and persons with respiratory disease should avoid doing outdoor activities, that kindergartens and elementary schools should avoid doing outdoor activities, and that the general public should avoid doing strenuous sports outdoors.
Information about precaution for kosa
Issued when the density is 400 µg per cubic meter or more.
It is urged that the general public should avoid doing strenuous sports outdoors. It is urged that senior adults, children, and persons with respiratory disease should be prohibited from doing outdoor activities and that kindergartens and elementary schools should be prohibited from doing outdoor activities. It is guided so that people should wear long-sleeved clothes in going outdoors and should keep clean.
Warning for kosa
Issued when the density is 800 µg per cubic meter or more.
It is urged that senior adults, children, and persons with respiratory disease should be prohibited from going outdoors and that the general public should be prohibited from doing outdoor activities, should avoid going outdoors and should stop or postpone outdoor sport events. It is urged that kindergartens and elementary schools should be prohibited from doing outdoor activities and should shorten their class hours or should be closed. It is urged that people should wear long-sleeved clothes when going outdoors and should wear goggles and a mask to keep themselves clean. It is guided how to protect livestock barns and livestock, how to cover farm products and fodder, and how to prevent fine particles from intruding in electronic or precision machines.
The standards described above were revised on February 10, 2007, based on an increase in the amount of damage due to kosa.
In April, 2002, the worst kosa in history of 2,070 µg per cubic meter fell.
A local newspaper reported that 'the visibility was only 1 to 2 km and it was difficult even to breathe.'
In April, 2006, a kosa of 2,015 µg per cubic meter was observed, causing six domestic flights to be canceled in South Korea.
According to South Korea's weather agency, the kosa coming to Korea is produced mostly in Inner Mongolia, the Gobi Desert, or the Loess Plateau, and reaches Korea in around one to eight days after it is produced in these areas. On the other hand, the kosa produced in the northeastern part of China, the nearest kosa-producing place reaches Korea only in half a day.
According to an estimate by the South Korean government, the yearly economic loss due to kosa amounts to three to five trillion won. According to another estimate, the total of the amount of damage due to kosa in the medical and welfare areas and of the cost needed for the measures taken against kosa is 364 billion won yearly (according to Kang, 2004).
The reality of Kosa in the Democratic People's Republic of Korea (North Korea) is little known, because almost all of the information about the nation is not announced externally. However, media in the neighboring nations have reported that kosa has affected human bodies, animals, plants, farm products and factories in the county or that it has been pointed out that such situations may occur.
In Japan, the Meteorological Agency defines kosa as the phenomenon in which visibility is reduced to less than 10 km due to soil particles originating on the continent. When an occurrence of kosa is predicted, the Meteorological Agency announces to each prefecture 'weather information: weather information for disaster prevention' (by the Meteorological Agency).
Kosa is frequently observed between February and May, especially in April, with the occurrence diminishing at the lowest level in summer. Kosa is observed more frequently in the western part of Japan and on the Japan Sea side. In the eastern part of Japan, on the Pacific Ocean side and in the inner areas, located across mountain ranges, kosa is sometimes observed though not so often.
The maximum kosa density ever observed in Japan was 0.79 mg per cubic meter (790µg per cubic meter) in 2002, although the value is to be used only as a reference, because it actually is a density value of suspended particulate matter (SPM) including kosa.
In Japan, the number of days when kosa was observed in a year was around 20 on average since 1967, but the number increased considerably to around 50 from 2000 to 2002. In the years when the number of days when kosa was observed in Japan increased, there was a tendency that low pressure was likely to be generated in the northeastern part of China and western wind was strong. Even if kosa is observed in Japan, it only causes the sky to become slightly hazy and causes a small amount of sand to be accumulated on the ground, with hardly any serious damage reported. However, minor physical damage and minor damage to heath have been reported. In weather observations, kosa is classified as smog or dust haze.
Although no ground-level data observed is available, it is considered, based on analyses of images observed with satellites, that Enkai shu (Russian maritime provinces) and Sakhalin in Russia also constitutes a kosa-passing route.
The far away places where kosa has been observed include the State of Hawaii and mainland of the United States of America, and Canada.
The kosa produced in the early April, 2001 reached Salt Lake City on April 15, the Rocky Mountains from Canada to the State of Arizona on April 18, around the Great Lakes on April 19, and over Atlantic Ocean off Canada on April 20.
It was also reported that the sand and soil particles considered originating in kosa were found in Greenland and the Alps as well.
Kosa and culture
Kosa-concerned poems, haiku poems or waka poems have been made since old times, or it can be said that kosa has affected the sphere of culture.
The mist that is generated due mostly to kosa is called harugasumi (spring mist). In addition to 'harugasumi' and 'tsuchifuru' (being cloudy due to flung-up dust) that is an old term for kosa, there are many other terms indicating kosa, such as 'yonagumori' (霾曇 or 霾晦, cloudy with kosa), 'baifu' (kosa wind), 'baiten' (kosa sky), 'kojinbanjo' (with "kojin" meaning "yellow dust"), 'mokokaze' (Mongolian wind), 'tsuchikaze' (dust wind), 'tsuchigumori' (cloudy due to dust), 'yonabokori' (kosa dust), and 'kosa' (with "sa" meaning "sand"). These terms express kosa emotionally and have been used in waka poems and haiku poems from old times. Being caused by kosa, a hazy moon is often observed in spring nights.
When having entered Futo (a wind-related place), dust falls from the edges of clouds'
It is said that, in "鄭駙馬宅宴洞中," a Qi-yan-shi (a Chinese poem of eight lines, with seven characters in each line) made by Du Fu, this line expressed the state that wind containing dust was blowing from the edges of clouds. The phrase 'dust falls from the edges of clouds' of this line was also quoted in "the Narrow Road to the Deep North" by Basho MATSUO. Basho used it for expressing apprehension about passing a mountainous area on the way going from a village in Iwate to another village in Mogami. Shuson KATO, Teijo NAKAMURA, Akito ARIMA, and Fusei TOMIYASU also made haiku poems concerning kosa or tsuchifuru.
Today, the term of 'kosa' itself is used in waka poems or haiku poems. Each of these terms is handled as a term concerning spring.