陕北安塞县黄土丘陵区露水凝结时间与频率

露水凝结时间和频率是开发利用气态水资源的基本参数.根据2015和2016年黄土丘陵典型地区陕西安塞县的实地近地表露水监测数据,分析露水凝结时间和发生频率及其大气影响因子.结果表明: 研究区露水凝结时间长且具有周期性.就日周期而言,露水呈现“昼伏夜出”的典型特点,主要凝结时段为21:00至次日8:00,其中,4:00—6:00是露水最易凝结时段;就季周期而言,夏秋季是露水的频发期,春冬季是露水低发期;就年周期而言,6—11月是露水最易凝结时段.相比降雨,露水具有发生频率高、稳定性强的特点.露水的形成是下垫面和多种气象因素综合作用的结果,在相对湿度>80%、气温-露点差为1～3 ℃及风速为0～1 m·s^-1时露水发生频率更高.单就安塞地区而言,风向为120°～150°和240°～300°时更有利于露水凝结.

Dew condensation time and frequency in the loess hilly region of Ansai County,northern Shaanxi Province,China

Dew condensation time and frequency are basic parameters for exploring the vapor phase of water resources. According to an in-situ monitoring of near-surface dew occurrence between 2015 and 2016 in a typical loess hilly region of Ansai County, Shaanxi Province, the dew condensation time, frequency and their atmospheric influencing factors were analyzed. Results showed that the dew condensation time was long and occurred in cyclic patterns. Over the daily cycle, dew manifested a typical “night-time show and day-time no-show” pattern, and it mainly occurred between 21: 00 and 8: 00 while the most frequently condensed dew period was between 4:00 and 6:00. Over the seasonal cycle, summer and fall had the higher frequency, whereas spring and winter had the lower frequency. Over the annual cycle, the most frequent dew period was from June to November. Compared to rainfall, dewfall had characteristics of higher frequency and stronger stability. A variety of substrate and meteorological factors contributed to the formation of dew, e.g. dew occurred more frequently when the atmospheric relative humidity was greater than 80%, air temperature-dew point difference was between 1 and 3 ℃, and wind speed was between 0 and 1 m·s^-1. In Ansai, wind directions ranging among 120°-150° and 240°-300° were more favorable to dew condensation.