Abstract:

The climate in the Liupan Mountain area, northwest China changes from south to north (from a semihumid zone to a semiarid zone to an arid zone) and has the characteristics of both a continental and a marine monsoon edge climate. As an important water conservation area of the Loess Plateau, the Liupan Mountain area is relatively rich in water vapor, and because of the uplift of the terrain, topographic clouds often form around the mountains, producing precipitation. Thus, the development and utilization of the mountains as air resources and artificial increase in the precipitation in this mountainous area have become key figure assignments in the region. To develop the atmospheric water resources over the Liupan Mountain area using precipitation enhancement techniques, it is necessary to first understand the atmospheric water vapor field in the region and characteristics of the liquid water content in the clouds that produce precipitation. To date, however, there has been little research undertaken in this area. In this paper, data collected between 2018 and 2019 by a microwave radiometer (RPG-HATPRO-G4, RPG for short) situated at the Longde National meteorological station in the west valley of the Liupan Mountain area (in the southern Ningxia Hui Autonomous Region of China) were used to explore the characteristics of the changes on the atmospheric water vapor content [RPG integrated water vapor (IWV)] and the cloud liquid water content [RPG liquid water path (LWP)] seen over time in the west valley of the Liupan Mountain area, with statistical analysis methods conducted on 92 precipitation events of varying natures and precipitation levels. One significant characteristic of the results obtained is the curves seen in the LWPs; the LWPs jumped before raining on the ground in the in situ observations, and 87.0% of all precipitation events had an IWV value of more than 12 mm before raining; this IWV value increased with the amount of precipitation. The results also show that this jumping phenomenon was stronger in spring and summer than in autumn and winter and that the advanced time seen in different precipitation events changed with the varying natures and levels of precipitation. The IWV and LWP values also changed significantly according to the season. The maximum levels were always seen in summer, reaching 23.44 mm, which accounts for 47.7% of the annual average. Additionally, the diurnal variations show that the IWV and LWP curves include one valley and one peak; this peak came shortly after midday Beijing time in spring, summer, and autumn, but at 22:00 in winter. These preliminary findings are provided as a technical reference in the prediction of the proximity of precipitation and whether a cloud system is in its precipitation generation stage. The results of this paper are of greatest importance in the provision of a theoretical basis and technical support for the timing of weather modification operations. However, as a practical matter, it is necessary to further inspect the index using other meteorological observation instruments.

Key words: microwave radiometer, atmospheric water vapor content, cloud liquid water content, Liupan Mountain area