###### Abstract  
The Yangtze River region is the main production area for famous, high-quality tea in China. Radiation frost frequently occurs in this region, especially in the early spring during calm and clear nights, and it causes substantial damage to crops, which leads to huge economic losses for tea growers. The formation of frost is difficult to experimentally control due to the complexity and variability of the agro-micrometeorological environment. The objective of this study was to evaluate an artificial radiation frost chamber based on the temperature difference between leaf and air dew point, which was designed for advanced frost-related research. Micro-meteorological data and the frost formation process were monitored in an experimental tea field during typical radiation frost nights to mimic declining temperatures that are consistent with nature. The radiation frost chamber model and main parameters were determined by theoretical calculations and computational fluid dynamics (CFD) simulation. A frost-forming experiment was conducted to evaluate the performance of the frost chamber. The observation results showed that the greatest temperature difference between leaf and air dew point (\(T_{diff\sigma}\)) was \(-2.3\)\({}^{\circ}\)C. The simulation results showed that the desublimation cooling rate of the air vapor was greater than sublimation, and the \(T_{diff\sigma}\) should be greater than \(-3.2\)\({}^{\circ}\)C, which could cause frost to easily form on the leaf. The performance testing results showed that leaf temperature slowly declined after a rapid decrease, which is similar to the natural condition, which results in noticeable frost formation on the leaf. air dew point; CFD simulation; leaf-air temperature difference; leaf temperature; radiation-frost chamber +
Footnote †: journal: Applied Physics Letters  
article  
Radiation frosts can be categorized into \"hoar frost\" and \"black frost\". A \"hoar frost\" occurs when water vapor deposits onto the surface and forms a white coating of ice that is commonly called \"frost\". A \"black\" frost occurs when the temperature falls below 0 \({}^{\circ}\)C and no ice forms on the surface. Black frost occurs when the humidity is sufficiently low. When the humidity is high, ice is more likely to deposit and a \"hoar frost\" can occur. Radiation frosts occur because of heat losses in the form of radiant energy [3]. Under clear night-time skies, more heat is radiated away from the surface than is received, which thus causes the air temperature to decrease [9]. The air temperature decreases faster near the radiating surface, causing the formation of a temperature inversion. The sensible heat content of the soil surface and air near the surface decreases, as there is a net loss of energy through radiation from the surface. There is a flux of sensible heat downward from the air and upward from within the soil to the surface to replace the lost sensible heat. The dew point is the temperature at which air must be cooled to become saturated with water vapor. When further cooled, the airborne water vapor will condense to form liquid water [10]. When air cools to its dew point through contact with a surface that is colder than the air, water will condense on the surface. When the air temperature is below the freezing point of water, the dew point is called the frost point, as frost is formed rather than dew point [2; 11]. Recent research on radiation frost focused on the mechanism of frost formation, critical temperature measurement, and the freezing injury of radiation frost [9; 12; 13; 14]. The use of artificial radiation-frost chamber is crucial to frost research, as it simulates a natural radiation frost environment. However, most of the frost studies used an incubator based on the convective heat transfer between plants and the air to decrease the environment temperature [15; 16; 17]; this is inconsistent with the mechanism of a natural radiation frost event, and thus will negatively affect the experimental accuracy.