INFORMATION ASPECTS OF STATISTICAL ANALYSIS OF METEOCHARACTERISTICS DURING SALT AND DUST STORMS ON THE DRY BOTTOM OF THE ARAL SEA

ABSTRACT

In this paper, in order to identify the meteorological patterns of the occurrence of salt-dust storms on the drained bottom of the Aral Sea, a statistical analysis of the three-day dynamics of meteorological elements, temperature, air humidity, atmospheric pressure and wind speed is given. As the first stage of the necessary research to predict salt-dust storms, the daily dynamics of meteorological elements is considered separately. The difference between the standard data of weather stations the day before and during the dust storm is determined, then the distribution series of these differences and the mathematical expectation. Their distribution function is also calculated to determine the characteristic values of meteorological elements during a dust storm. Long-term data of standard meteorological measurements of weather stations, synoptic maps, images from the Earth's satellite were used, methods of synoptic and statistical analysis were used.

АННОТАЦИЯ

В данной работе с целью выявления метеорологических закономерностей протекания солепылевых бурь на осушенном дне Аральского моря, приводится статистический анализ трехсуточной динамики метеоэлементов, температуры, влажности воздуха, атмосферного давления и скорости ветра. Как первый этап необходимых исследований для прогнозирования солепылевых бурь суточная динамика метеоэлементов рассматривается по отдельности. Определяется разность стандартных данных метеостанций за день до пылевой бури и во время нее, затем ряд распределения этих разниц и математическое ожидание. Рассчитывается также их функция распределения для определения характерных значений метеоэлементов во время пылевой бури. Использованы многолетние данные стандартных метеорологических измерений метеостанций, синоптические карты, снимки со спутника Земли, применялись методы синоптического и статистического анализа.

Keywords: Drained bottom of the Aral Sea, salt-dust storm, meteorological characteristics, statistical and synoptic analysis, distribution function, mathematical expectation.

Ключевые слова: Осушенное дно Аральского моря, пылевая буря, солепылевая буря, метеохарактеристики, статистический и синоптический анализ, функция распределения, математическое ожидание.

Introduction. Researchers of the Aral Sea crisis recognized the wind removal of salts from the drained bottom to adjacent territories as the most socially and environmentally dangerous consequence of it due to its proven impact on public health [17, p.5; 20, p.78], biocenosis, climate, and soil salinity [1, p.183; 18, p.5]. The huge spatial and quantitative scales [16, p.209] of this process exacerbate its negative significance.

Well known that the Southern Aral Sea region is experiencing the maximum impact of the Aral crisis. The amount of dust falling on the soil in the Southern Aral Sea region is ten times greater than in the irrigated zone, in which the content of sulfate salts reaches 25-48%, chloride - 18-30%, carbonate - 10-20%. [11, p.57]. Due to the prevailing regional wind regime, the removal of salts from the drained bottom of the Aral Sea occurs mainly in a southerly direction. The greatest ecological transformations under the influence of changes in the hydro regime of the Amu Darya also occur in the Southern Aral Sea region. Accordingly, Uzbekistan owns most of the initiatives to prevent and mitigate the consequences of the Aral Sea crisis. On the dry bottom of the Aral Sea, about 700 thousand hectares are covered by forest reclamation. Within the framework of the Comprehensive Program of Measures to Mitigate the Consequences of the Aral Catastrophe and the Development of the Aral Sea Region, designed for 2013-2017, more than 500 projects have been implemented, more than half of which are of a national character. It should also be noted that a national action plan for 2021-2024 has been developed to prevent and mitigate the consequences of sand and dust storms in the Republic of Uzbekistan.

Many works [4, p.136; 6, p.239; 8, p. 6; 12, p.8] have been devoted to studies of salt removal from the drained bottom of the Aral Sea. A large spread in the estimates of this complex process indicates the need to continue research in this direction.

A particularly relevant aspect of the removal of salts from the drained bottom of the Aral Sea remains the prediction of salt-dust storms, since the bulk of salts (about 83%) are removed during dust storms of varying intensity [13, p. 12; 20, p.78]. At the same time, this aspect remains poorly understood, as evidenced in particular by the absence of the Ministry of Emergency Situations-warnings about dust storms.

In this regard, the main goal of this study is a statistical analysis of a priori weather conditions that precede the occurrence of storm winds on the drained bottom of the Aral Sea. In addition, a posteriori meteorological conditions are analyzed for the presence of precipitation immediately after salt-dust storms that create particularly dangerous consequences for terrestrial plants.

Undoubtedly, for a reasonable forecast, it is necessary to consider such processes of the general circulation of the atmosphere as cyclones, cold intrusions, which determine the scale of salt removal, etc.

Materials and Methods. The work used the methods of statistical and synoptic analysis, the method of analogies [3, p.255, 19] and the materials of long-term data of standard meteorological measurements of the Aral weather stations, synoptic maps and images of an artificial Earth satellite (Fig. 1).

The analysis used data from the weather station for 1993-2021, in terms of wind speed and direction, pressure, precipitation, humidity and air temperature. Mathematical expectation, series and distribution functions calculated for all indicators.

Figure 1. Synthesized image of the salt-dust storm to the left in April 29, 2008 and to the right in March 24, 2020 (worldview.earthdata.nasa.gov).

A dust storm is characterized as a dangerous meteorological phenomenon when a large amount of dust, sand, and dry soil particles rises into the air, leading to turbidity of the air, a significant deterioration in visibility and the destruction of the fertile soil layer. At the same time, dust (sand) rises into the air and at the same time dust settles over a large area.

The definition dust storm is usually used when a storm occurs over clay and loamy soil. Despite the fact that dust storms appear mainly in summer, in the absence of precipitation and rapid drying of the soil, they also occur in spring. When storms occur in sandy deserts, especially in the Sahara [5, p.26], Australia [9, p.12], as well as in the Karakum, Kyzylkum, etc. [7, p.9; 10, p.10], when, in addition to small particles that reduce visibility, the wind also carries millions of tons above the surface larger sand particles, the term sandstorm is used [2, 14 , p.4, 15 , p.7].

In view of the peculiarities of the transported substance from the drained bottom of the Aral Sea, we introduce a special term salt-dust storm.

The horizontal extent of areas covered by sandstorms can vary from a few hundred meters to thousands of kilometers. The duration of sandstorms varies from a few seconds to several days. The weight concentration of dust particles in the air during dust storms significantly exceeds the background concentration. The paper describes a dust storm on the Great Plains with an average daily concentration of 843 µg/m³. For one case of a storm in Texas, a dust concentration above 2500 µg/m³ was obtained over a large area east of the Mississippi. Concentrations above 500 µg/m³ have been repeatedly recorded along the entire southeastern coast of the Atlantic. Consequently, the dust concentration of the order of thousands of µg/m³ can be considered normal, statistically average for dust storms.

The main reason for the formation of dust storms is turbulence due to the structure of the wind, which contributes to the rise of dust and sand particles from the earth's surface. In this case, the degree of vertical instability of the air mass, in which the dust storm develops, plays an important role.

In desert regions, dust and sand storms are most often caused by thunderstorm downdrafts and the associated increase in wind speed. The vertical dimensions of the storm are determined by the stability of the atmosphere and the weight of the particles. In some cases, dust and sand storms can be limited to a relatively thin layer due to the temperature inversion effect.

The uniqueness of wind salt transfer from the drained bottom of the Aral Sea and the difference between salt-dust storms in this region and dust storms in other parts of the world predetermine the little-studied of this phenomenon. For the occurrence of salt transfer, in addition to the usual storm conditions, the necessary conditions are sufficient dryness of the underlying surface, low relative humidity of the air, and, of course, salt accumulation on the drained bottom. These conditions are most typical for April-June, and to a lesser extent for September-October, when favorable conditions for salt accumulation are created: the alternation of precipitation and sunny days, which, as is known, intensifies the capillary rise of salts from groundwater to the surface.

In the conditions of Central Asia, storms are formed when warm and cold air masses meet. Moreover, in the lower reaches of the Amu Darya, the predominant wind direction during dust storms is northeast and west. Here the average duration of storms is 6 hours. If we consider the annual course of dust storms in Muynak, it turns out that their minimum number occurs in January, and the maximum - in April.

Atmospheric processes in storm conditions are extremely complex and systemic: the slightest change in one meteorological characteristic immediately causes a change in the rest. Therefore, for the purposes of short-term forecasting, systemic and factorial analyzes of the dynamics of meteorological characteristics (atmospheric pressure, air temperature and humidity, wind speed, etc.) are necessary.

In this paper, the daily dynamics of these meteorological elements is considered separately, as the first stage of the necessary research to predict salt-dust storms. The difference between the standard data of meteorological stations a day before and during a dust storm is calculated, and then the distribution series of these differences is determined. The same procedure is performed for posterior weather conditions. In order to identify the characteristic values of meteorological elements during a dust storm, their distribution function is also calculated.

Results and Discussion. It was revealed that changes in meteorological elements a day before a dust storm, during it and a day later, occur according to the normal law. By the most characteristic values (mathematical expectation) also indicated in the figure, an important conclusion can be drawn for the correct construction of forecasts of dust storms. With a reliability of 74%, we can say that the weather conditions changed a day before the salt and dust storm. Figures 2 and 3 show the series and distribution functions of the differences in standard weather station data a day before, during, and a day later a dust storm (- mathematical expectation).

Figure 2. The day before and during the dust storm

There was an increase in atmospheric pressure by 2.6 hPa, the air temperature increased by 2.8 ° C, and the relative humidity of the air decreased by 3.4%. The wind speed decreased by 1.9 m /s, this is due to the fact that during dust storms, wind speeds vary in a relatively wide range from 6-10 m/s to 20 m/s or more, and at different stations the maximum repeatability of different speeds falls at different intervals.

Figure 3. During the dust storm and the day later

A posteriori meteorological conditions are extremely important for assessing the consequences of a dust storm: they characterize the propagation distance of salt particles, the time of atmospheric purification, and in the event of precipitation, the possibility of damage to ground vegetation and one-time soil salinization. The most probable values of meteorological elements after a salt-dust storm are explained by a drop in atmospheric pressure by 2.2 hPa, an increase in air temperature by 0.8 ° C, a decrease in relative air humidity by 0.6% and an increase in wind speed by 4.1 m/s;

Conclusion. On the territory of the drained bottom of the Aral Sea, a significant increase in salt-dust storms has been observed for several decades.  Statistical analysis of meteorological characteristics in salt-dust storms showed that changes in meteorological elements occur according to the normal law.  Analysis of a posteriori weather conditions after salt-dust storms for the presence of precipitation, led to dangerous consequences for plants. A conclusion was made about the correct construction of the forecast of salt-dust storms using characteristic values.

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