Research On Yiwu Precipitation Background Based On TBB

Precipitation is closely related to the occurrence and development of clouds. Cloud states such as cloud shape, cloud amount, cloud base height and cloud top temperature are directly related to the occurrence and strength of precipitation. Thereamong, the cloud top temperature obtained by meteorological satellite infrared detection channel, is outward radiation of cloud top and Earth's surface where there are no clouds or less clouds, it can generate infrared cloud images and a variety of enhanced cloud images and is expressed as blackbody temperature (Black-Body Temperature, abbreviated as TBB). In cloud area, TBB is cloud top blackbody radiation temperature. Generally, its values≤0℃, and lower TBB indicates higher cloud top, thicker clouds, more vigorous convection, and greater precipitation potentiality. Therefore, it can infer the intensity and events of weather systems, and imaginable corresponding changes in weather and precipitation according to the changes of cloud top temperature.Yiwu city is selected as the study area. Based on the Planck radiation law, this paper has used FY-2C geostationary meteorological satellite infrared channel 1 information, inverted the cloud top temperature of the region from June to August, then combined with conventional meteorological data and surface mesa-scale auto-observation meteorological operational obtained from routine meteorological operational system, got the relationship between TBB and the precipitation, at last it has studied the precipitation background of Yiwu summer precipitation cloud system. The conclusions are that: The daily variation of cloud top temperature is not unimodal, low value appears twice in a day; It is easy to rain when cloud top temperature are between 214-265K; The relationship between cloud top temperature and precipitation is nonlinear, within a certain temperature range, they are negatively correlated; the hourly cloud-top temperature difference also has nonlinear relation with surface rainfall, and mathematical relationship between them has been obtained; With different cloud top temperature, the precipitation probability is different, and along with the cloud top temperature lower, the chance of light rain reduces, the chances of moderate rain, heavy rain, torrential rain increase; Different precipitation have different corresponding cloud top temperature indicators, which vary depending on months and seasons.Then the paper uses mathematical relationship between the hourly cloud-top temperature difference and precipitation, selects a certain period of heavy precipitation process, and exemplify it, finds that the estimated precipitation and observed precipitation have similar trends, two values are closed, the heavy precipitation is corresponding to the low value of TBB.Finally, the conclusions are raised that the "time window" for artificial precipitation is from 16:00 to 19:00 pm, the " cloud seeding temperature window" of the cloud top temperature is between-10~-24℃,the corresponding TBB values are between 263K-249K, at which point the chemical catalysts have the optimal nucleation .Especially, when the cloud top temperature are or near 255.2K, 244.9K, 240.9K, it is necessary to properly catalyze, it is likely to appear moderate rain (2.0-6.9mm/h),heavy rain (7.0-14.9mm/h), torrential rain (≥15.0mm/h) on the ground, but there are different TBB indexes on different months, so different indexes should be judged and selected at the right time.