Through analyzing the mesoscale disturbance field of a Meiyu rainstorm, it is found that there are close relations between the development and propagation of inertia-gravitational waves, rain belts and low vortex. The propagating patterns of inertia-gravitational waves are different in the upper and lower levels. In the early period of precipitation, convective instability triggers the inertia-gravitational waves. When there are inertia-gravitational waves propagating southward in the upper and lower levels, it is favorable to form multi-rain belts. In the mid of precipitation, the inertia-gravitational waves in the upper-layer rotate anticlockwise with the lower-layer vortex center, and precipitation strengthens and moves eastward in the meantime. The inertia-gravitational waves propagating northward in the upperlayer may result in the development of the lower-layer vortex and precipitation.
The helicity of a severe sandstorm happened in Northwest China was analyzed by using global reanalysis grid data of NCEP/NCAR for 4 times a day. As an important physical parameter in analyzing and predicting severe convective weather, the helicity also has good indication in the forecasting of sandstorm. The distribution of helicity over the sandstorm area was negative at higher levels and positive at lower levels. There was definite relationship between the evolvement of helicity's negative value at higher levels and the occurrence of sandstorm.
Using CMAP, daily observatory rainfall data and NCEP/NCAR reanalysis data, climatic features of moisture transport and its differences between flood years and drought years during the first rainy season of South China (SC) are discussed. Results show that moisture transport influencing South China exhibit distinct difference before South China Sea Summer Monsoon (SCSSM) onset and after SCSSM onset. Therefore the first rainy season of SC should be divided into two stages: from April to SCSSM onset and from SCSSM to June. Variations of moisture transport from the West Pacific and North China have important effects on flood or drought of SC. But that from Arabian Sea-Bay of Bangle mainly influences local rainfall instead of abnormal rainfall over SC.
Drought is one of the major meteorological disasters to agriculture in north China so that the development of methods for effectively monitoring droughts is of great significance to dry land crops. This paper makes analysis of products of energy and water balances retrieved from LAS (Large Aperture Scintillometer) measurements, indicating that the structural parameter of LAS refractive index shows regular difference in daily variation between different weather backgrounds and remarkable difference in sensible heat flux on a seasonal basis, with higher negative correlation between such flux and soil humidity at 0 ~ 50 cm depth.
Drought is a principal agrometeorological disaster to winter wheat zones in North China. From the correlation of wheat yield to rainfall the drought indices are determined that correspond to varying levels of severities on an agricultural basis. In wheat growing season, when rainfall displays its negative anomalies of <15, 15-35, 36-55 and <55%, there occurs a slight, moderate, heavy and extreme drought, leading to yield drop by <10, 10-20, 21-30 and <30%, respectively. The economic loss consists of yield reduction and drought-fighting input like irrigation. A drought-caused loss model is presented from historical meteorological and wheat yield datasets, with which to make the distribution of economic losses in the last 30 years over the province of Henan. Evidence suggests that in years of heavy droughts the loss was between 450 to 675 (<250) RMB yuans per hectare in the NE (west − SW) segment of the province.