CHARACTERISTICS AND RELATIONS OF LIGHTNING AND RADAR ECHOES FOR STRONG CONVECTIVE RAINSTORMS IN YUNNAN

Based on cloud-ground lightning data and Doppler weather radar echo products, both thecharacteristics and the relations of lightning and radar echoes for strong convective rainstorms over Yunnanare analyzed during the flood season of 2007. The results show that most rainstorms are convective in whichlightning is mostly negative and the negative lightning number accounts for more than 90% of the total.Although the correlation between precipitation and the lightning number is small on the rainstorm day, thelarge day-lightning frequency usually produces heavy precipitation. Hourly evolution of precipitation andlightning frequency shows peak-style characteristics. And their evolution is very coherent in strongrainstorm, but lightning often occurs before precipitation, whose peaks are in phase with or 1-to-2-hourlagged behind that of lightning frequency. Meanwhile the peaks of positive frequency are in phase with orfall behind that of precipitation. When the wind field is heterogeneous in radial velocity, it is conducive toboth the development of convection echoes and occurrence of lightning. Strong lightning-producingconvective rainstorms correspond to strong echo fields and usually result in reflectivity above 30 dBZ andecho top ET of more than 9 km, respectively.

Trends in sunshine duration and atmospheric visibility in the Yunnan-Guizhou Plateau,1961-2005

Using the observed data from 184 stations over the Yunnan-Guizhou Plateau (YGP) from 1961 to 2005,the long-term trends in sunshine duration,cloud amount,dry visibility (Vd),dry extinction,and water vapor over the YGP are analyzed.The results show that 85% of the stations recorded shortening annual sunshine duration,with the decrease rates between -12.2 and -173.7 h/10yr.Results of Mann-Kendall tests indicate that,among the stations with decreasing sunshine duration,63.7% of them experienced an abrupt change that started in the 1970s and peaked in the 1980s.This decreasing trend has reversed in the early years of the 21st century.The cloud cover and water vapor content in the mid and lower levels over the YGP had no obvious changes during the study period.The annual averages of Vd declined from 34 km in the 1960s to 27 km at present.The annual mean dry extinction coefficient trended upward,from 0.176 to 0.190,on the YGP from 1980 to 2005.Analyses of cloud cover,water vapor,atmos-pheric visibility,and dry extinction coefficient revealed that emitted tropospheric aerosols (including air pollutants) resulting from increased energy consumption over the YGP could be a major factor influencing the reductions of sunshine duration and atmospheric visibility.

MESOSCALE ANALYSIS OF YUNNAN SUCCESSIVE HEAVY PRECIPITATION AROUSED BY THE STORM OVER THE BAY IN EARLY SUMMER

By using regular meteorological data, physical quantity fields, satellite pictures and Doppler radarecho data, we analyze the mesoscale features and the conditions of 4 successive heavy precipitation processes inYunnan aroused by the storm over the Bay in the early summer. The results show that the life of the storm overthe Bay is usual 2 or 3 days and the cloud top temperature of the storm is always below -65°C. The storm overthe Bay affects Yunnan by mesoscale convective cloud clusters, cloud system in peripheral or weaken itselfmoving to the northeast. The Tibetan Plateau shear lines and vortexes, NE-SW convergence channels andsouthwest wind convergence supply favorable circulation background and dynamical conditions. There are manycommon features about Doppler radar echoes, the flocculent echoes with intensity about 35-45 dBZ move to theeast to produce successive precipitation in Yunnan, and the mesoscale features of southwest jet and wind veeringwith altitude not only are favorable to transport warm and moist airflow brought to the north by the storm overthe Bay, but also are favorable to convective development.

THE CCA BETWEEN 500 hPa GEOPOTENTIAL HEIGHT FIELDS OVER NORTHERN HEMISPHERE AND RAINFALL OF CHINA IN MAY

Based on the theory of Canonical Correlation Analysis (CCA), the correlation between 500 hPa geopotential height (H) fields over the Northern Hemisphere (NH) and a 15-region rainfall (R) field of China in May is studied. The results indicate that: (1) there is a strong relationship between the H fields in January / May and the R field in China, (2) the variation of the general circulation over the whole NH (especially the 500 hPa H field over Europe and Asia) can affect the R in China, (3) in January and February the atmospheric general circulation can affect the R mainly by means of planetary waves, while in April and May the main control mechanism can be due to some teleconnections, and (4) the characteristic vectors for R in May and H from January to May have wave train structure, alternating sign from south to north.