Суточная динамика градиента рефракции в нижнем десятиметровом слое приземной тропосферы
Authors: Базарова А.С. , Базаров А.В. , Кураков С.А. , Атутов Е.Б. , Сычев Р.С. , Башкуев Ю.Б. , Доржиева С.М. 
Published: February 2025

В нормальной атмосфере рефракция УКВ уменьшается на 0,04 N-ед. на каждый метр высоты. В работе показано, что в приземном десятиметровом слое центральной области Селенгинского среднегорья Республики Бурятия значения градиента рефракции изменяются от –0,249 до +0,285 1/м. Измерения метеопараметров проводились с использованием атмосферно-почвенного измерительного комплекса, установленного на Радиофизическом научном стационаре «Хурамша» Института физического материаловедения СО РАН. На их основе рассчитана рефракция на высотах 1 и 10 м, построена суточная динамика градиента рефракции по пятилетним данным с 2017 по 2021 год. Показана значительная изменчивость градиента в течение суток для центральных месяцев сезонов года: января, апреля, июля, октября. Вероятно, такие значения градиент рефракции в самом нижнем слое приземной атмосферы до 10 м приобретает под влиянием атмосферно-почвенных связей.

Introduction. Variations in atmospheric heterogeneity significantly complicate the radio wave propagation process. They cause the bending (refraction) of the beam trajectory within the atmosphere, resulting in increased propagation time for radio waves between signal transmission and reception points. Furthermore, these variations lead to changes in the amplitude, phase, and frequency of the waves. Such phenomena can introduce interference when making high-precision trajectory or angular measurements using radio equipment, and hence, they need to be considered when analyzing radio communication conditions. Aerological studies of the lower layers of the atmosphere reveal that the distribution of temperature and humidity, which influences the variability of the radio wave refractive index, can change significantly at various altitudes. The condition of the lower layer of the surface atmosphere is primarily determined by the exchange of radiation between the surface and the atmosphere in the infrared range. The Earth's surface, heated by direct solar radiation (which passes through the atmosphere with minimal loss), emits infrared radiation that is subsequently absorbed by the atmosphere. Changes in temperature and humidity in the lower atmosphere layer are influenced by factors like the temperature difference between the soil and the air during the day, the temperature gradient, and the concentration of greenhouse gases, including water vapor and carbon dioxide. Consequently, these variations can impact the daily fluctuations in the refractive gradient within the air layer directly adjacent to the ground. The study aims to develop methods for monitoring daily variations in the refraction gradient. This is based on meteorological data from an atmospheric-soil measuring complex (ASMC) located at the Radiophysical Research Station “Khurumsha”, which is part of the Institute of Physical Materials Science within the Siberian Branch of the Russian Academy of Sciences. This research station is situated in the central region of the Selenga midlands in the Republic of Buryatia. We've introduced the concept of a "typical day," allowing us to describe the daily data cycle. In our analysis, we present the results of a five-year study, spanning from 2017 to 2021. This study covers the central months of each season: January, April, July, and October. Specifically, we focus on the distribution of the refractive gradient data (gN) in the lower layer of the surface atmosphere during these months. The study has revealed that atmospheric-soil interactions play a significant role in influencing the refractive gradient. Notably, in January and April, the refraction gradient exhibited more pronounced daily fluctuations, ranging from -0.249 to 0.429 N-units. For this period, it took negative values only during the morning and nighttime hours. On the other hand, in July and October, the refraction gradient consistently held positive values, suggesting a decrease in the range of radio signal propagation. This specific pattern of atmospheric refraction seems to be a characteristic feature of the lower 10-meter layer in the dry steppes of the Selenga midlands, particularly in areas directly adjacent to the soil surface. It's worth noting that in more humid coastal regions and over bodies of water, we typically observe superrefraction and, consequently, tropospheric waveguides. To further enhance this research, there are plans to conduct additional studies in various areas with different climatic characteristics within the region.