Observation of fluxes over mountain areas in Chongqing and analysis of their variation characteristics in different time scales

Based on the flux observation, adjacent automatic meteorological observation and ERA5-Land reanalysis data for rainstorm cases in Western Chongqing, the reliability and applicability of flux observation over mountain areas in Chongqing are discussed. Additionally, the variation characteristics of fluxes in different time scales in 2019 are analyzed. The results are as follows. (1) Flux stations have similar meteorological background with the adjacent meteorological stations, and flux observations can better represent the temporal evolution of surface sensible heat and latent heat fluxes during precipitation than ERA5-land reanalysis data, indicating that the flux observations are reliable. The precipitation at flux stations can be replaced by the average precipitation at neighboring stations. (2) The three fluxes and their increments have different correlations with temperature, relative humidity, wind speed and precipitation. Momentum flux is positively correlated with precipitation and wind speed. The sensible and latent heat fluxes are positively correlated with temperature and wind speed, and negatively correlated with relative humidity. The increment of latent and sensible heat fluxes at Caoshang is negatively correlated with local precipitation. All these characteristics indicate that flux observations can be used in the study of this rainstorm. (3) The seasonal and monthly variations of sensible heat flux and latent heat flux indicate that the ground surface is mainly characterized by heating and evaporation in the long-term time scale. The seasonal variation of momentum flux indicates that the turbulent motion is the strongest in spring and the weakest in autumn. The diurnal variation of momentum flux is mainly unimodal, which indicates that the turbulence activity is stronger in the daytime and weaker at night. The diurnal variation of momentum flux at Jinfoshan shows a bimodal pattern in spring, summer and autumn, which indicates that the turbulence activity increases at night.