PROGRESS IN GEOGRAPHY ›› 2013, Vol. 32 ›› Issue (3): 447-454.

Characteristics of the changes of springtime cumulonimbus (Cb) clouds in Qilian Mt. Region under the background of global warming

SHI Guangpu1,2,3,4, SHI Yuanyuan4, Guo Junting4, CHEN Shaoyong4, LIN Shu1,2,3, WANG Yinhua4

1. 1. Institute of Arid Meteorology, CMA, Lanzhou, Lanzhou 730020, China;
2. Key Laboratory of Arid Climatic Change and Reducing Disaster of Gansu Province, Lanzhou 730020, China;
3. Key Open Laboratory of Arid Climate Change and Disaster Reduction of CMA, Lanzhou 730020, China;
4. Baiyin Meteorological Bureau, Baiyin 730900, China
• Received:2012-05-01 Revised:2012-11-01 Online:2013-03-25 Published:2013-03-25

Abstract: Based on meteorological data of springtime cloud shape and surface air temperature at 26 meteorological stations during 1961-2005 in Qilian Mountain and the surrounding areas, using linear regression analysis and wavelet analysis , the characteristics of temporal variation and spatial distribution of the frequency of Springtime Cb clouds and its relationship with climatic warming are analyzed. The NCEP/NCAR global reanalysis data in the corresponding period are selected for the analysis of the circulation of Springtime Cb clouds in Qilian Mt. Region. The results indicate that: (1) The frequency of springtime Cb clouds in Qilian Mt. Region is obviously higher than that in Hexi corridor and Qaidam basin. (2) The springtime mean air temperature in Qilian Mt. Region increased 0.9 ℃ with an increase rate of 0.18 ℃/10a over the recent 45 years, and the increase tendency has become clearer since the 1990s. (3) The frequency of springtime Cb clouds in Qilian Mt. Region decreased weakly over the recent 45 years, and the decreased tendency has become clearer since the 1990s. (4) In the time scale of 25 years, the frequency of springtime Cb clouds and the springtime mean air temperature showed a pattern of anti- phase variation mainly in Qilian Mt. Region. However, in the time scale of 6 years with the strongest air temperature surge, the frequency of springtime Cb clouds and the spring mean air temperature showed a pattern of in-phase variation. (5) There was a significant difference in the 500 hPa atmospheric circulation between the years with abundant springtime Cb clouds and the years with scarce springtime Cb clouds in Qilian Mt. Region, and the frequency of springtime Cb clouds in Qilian Mt. Region changed in response to the anomaly of 500 hPa circulation in the Eurasian areas. In abundant years, with the Eastern Asia deep trough relatively weaker and the Ural high pressure ridge relatively stronger than in other years, guided by the north-northwest airflow on the front side of the ridge, Polar Cold Air moved to the northwestern China through a northwest path; the low-value systems from Central Asia continuously developed and moved to Qinghai-Tibet Plateau. At the same time, movement of the warm and wet airflow from the South China Sea and the East China Sea toward the inland areas strengthened remarkably, and it collided with the cold air from the northern Plateau. More frequent convergences of strengthening warm and cold airflows caused the increase of the frequency of springtime Cb clouds in Qilian Mt. Region. In scarce years, warm anticyclones from West Siberia to Qinghai-Tibet Plateau abnormally strengthened, and the Eastern Asia deep Trough is relatively stronger than in other years. The path of cold airflow leaned to the east; the regions from Asian continent to western Pacific showed significant winter monsoon characteristics. Northwest wind strengthened and blocked the movement of warm and wet airflow from the Southeast to the Northwest of China. Less frequent collisions of the warm and cold airflows in Qilian Mt. Region caused the decrease of the frequency of springtime Cb clouds in the region.