Relationship Between Moisture Disturbance And Heavy Rainfall Based On GPS Data And Multi-scale Analysis

From the three aspects of the observation, numerical simulation and precipitation forecasting application, the disturbance characteristics of atmospheric water vapor and its relationship with severe precipitation are investigated. Using hourly data set of ground-based GPS precipitable water vapor (PW) and automatic weather station (AWS) observation, the atmospheric moisture disturbance is analyzed with wavelet analysis method during the processes of heavy rainfall. The temporal and frequency spectral characteristics are revealed. The severe precipitation event on July21,2012was simulated by using the ARPS model with the initial fields assimilating the data of GPS total moisture. With the output data of the high-resolution numerical simulation, the relationship between the water vapor and precipitation was examined. The chief scales of water-vapor, dynamic and thermodynamic fields were focused on. The concept of potential shear-deformation wave-activity density was put forward. Finally, the wave-activity density was applied to the precipitation forecast experiment.This work provides the following conclusions.(1) In the case of heavy-rainfall event on July10,2004, the total water vapor of ground-station GPS was closely related to the development of precipitation. Companying with precipitation increasing or decreasing, the total moisture content appeared fluctuating. Before the precipitation occurred, the total moisture reached peak. At the end of precipitation, the total moisture drops to minimum. When the moisture was beyond the threshold of50mm, the precipitation will occurred in the next1-3hours. After the moisture fell below threshold of50mm, the precipitation ended. In the case of a squall line on1August,2007, the GPS slant water vapor (SW) got to its maximum when this squall line passed through the station. The largest difference is20%between SW and PW. The squall line locates outside of the line-of-sight path if the difference is smaller than±2mm. The GPS SW can infer the spatial and temporal movement of atmospheric systems.(2) The wavelet analysis with complex Gaussian mother function was applied to the hourly observations of GPS PW and AWS during July-August2012. The analysis of multiple temporal scales was conducted for the observation data. The surface temperature, potential temperature, pressure, horizontal wind, specific humidity and GPS PW presented the features of multiple temporal perturbations during all precipitation processes. Especially, the GPS PW varies with multiple temporal scales distinctly, during the heavy rainfall, which occured in July21,2012("12721"). The period is larger than13hr. The disturbance with83hr period is the most strong. The perturbation of GPS PW shows a closer correlation to the precipitation than the surface specific humidity. The GPS total moisture disturbance occurred mainly in the larger time scale, indicating the water vapor of GPS changed with a larger time period. The specific humidity of AWS can be divided into two parts, the stronger long-period disturbances and weaker short-period perturbations, and dominated by long-period disturbances. The gravity wave activity in this heavy rainfall event was recognized by using wavelet analysis and cross-spectral methods, In this case, the phase differences between the pressure, zonal and meridional wind with the potential temperature were close, indicating that the four meteorological elements meet the polarization of gravitational waves. This meant there existed gravity wave activity with long period.(3) It was shown that the assimilation of GPS total moisture can improve the performance of numerical simulation. The spatial relationship between moisture disturbance and precipitation was examined. The heavy precipitation resulted from the favorable configuration of high-and low-level jet streams, northwards lifting subtropical high, and westward moving Baikal trough. The event underwent the three stages of warm-area, transitional, cold-front precipitations. During the period of warm-area precipitation, LLJ matching with the high terrain played an important role in transportation of water vapor. There were two regions of high water vapor, one in the western region of Hebei province, was closely related to the southwest low-level Jet in the westsouth of low system which transported water vapor from Bay of Bengal. Another in the Bohai Bay was caused by the strong southeast winds between typhoon Wei Sente and subtropical high. The transportation vertically extended to10km altitude, and was significant below the height of4km. During the transitional stage, the specific humidity near surface ground increased in the southwest of Beijing, and appeared significantly perturbation under the altitude of2km. The perturbation rose along the high terrain and was characterized by the southeastwards propagation. During the cold-front stage, the water vapor over surface ground was reduced. The convective activity was not obvious and the precipitation tended to finish in the district of Beijing. Terrain played an important role of dynamic uplift and convergence in the precipitation process. On the one hand, the horseshoe-shaped topography dynamically lifted the warm and moist flow, enhanced the ascending motion. On the other hand, the topography blocked the low-level Jet, made the warm and moist flow convergent on the windward slope, accumulate more moisture and promote heavy rainfall increases. The humidity function was introducing to describe the intensity of relative humidity in convective clouds. Its horizontal gradient was used to represent the concentration of water vapor. It was indicated that the horizontal advection of relative-humidity horizontal gradient is the chief force of its local change and key physical processes dominating the local concentration of water vapor.(4) The multi-scale analysis and wave-activity density method were applied to the experiment of precipitation forecast. By using the multi-scale analysis method, the moisture and winds were broken down into seven components with different scales. It was revealed that the3rd horizontal scale was the key scales of water vapor and potential temperature perturbations, and the key scale of horizontal wind is the6th horizontal scale. Based on the decomposition, the potential shear deformation wave-activity density was proposed. On the spatial distribution and time evolution, the wave-activity density was closely related to the heavy rainfall. It was capable of indicating the development and movement of precipitation region. This meant that these dynamic and thermodynamic perturbation and moisture disturbance played an important role in the development of strong convection. A forecast equation of precipitation was established by using the wave-activity density. In the case of "12721" precipitation, the experiment of precipitation forecast based on the equation was conducted. It was shown that the precipitation forecast was always weaker than the observation. Nevertheless, the forecast of precipitation location, especially precipitation center performed well. To some extent, the equation performed better than the precipitation forecast of GFS model. This indicates the equation has prediction capability.