The satellite cloud pictures are the most products in quantity provided by meteorological satellites and are divided into visible pictures (0.58-0.68¦Ìm) and infrared pictures (10.5-12.5¦Ìm). In particular, the picture of stationary meteorological satellite with high spacial resolution and time resolution is the most effective tool for monitoring, analyzing and forecasting the medium-scale system which causes torrential rain.
Cloudburst causing medium-scale system is expressed as a bright cloud cluster on the satellite picture. The area of the cloud cluster is closely related to the range of cloudburst. Heavy rainfall mostly comes from vigorous convection cloud area that has high cloud top and low temperature at the cloud top. Through the enhancement display of the infrared cloud picture, heavy precipitation center can be seen clearly according to thermal stratification, which becomes an important means for cloud burst forecast.
The water level of upper reaches of the Hanjiang River suddenly rose because of continuous rainstorm in the last ten days of July in 1983. On July 30, the discharge of flood peak in Ankang Station reached [TPB,+47mm¡£52mm,ZS,PY¡½ ¡¼TS(¡½¡¼WT5HZ¡½¡¼ST5HZ¡½ ¡¼JZ¡½Fig.1The picticre of the ¡¼JZ¡½average of cloudiness which ¡¼JZ¡½caused the catastro phic ¡¼JZ¡½cloudbursts in Jiang hui ¡¼JZ¡½Area in the summer of 1991[TS)] [TPC,+35mm¡£112mm,YS,PZ#¡½ ¡¼TS(¡½¡¼WT5HZ¡½¡¼ST5HZ¡½ ¡¼JZ¡½Fig.2The minimun variation with the time of average brigh ¡¼JZ¡½thess temperature in plum rains front cloud zend during cloud- ¡¼JZ¡½burst oclurred from June 27 to July 13,1991[TS)] [TPD,+47mm¡£52mm,YX,PZ#¡½ ¡¼TS(¡½¡¼WT5HZ¡½¡¼ST5HZ¡½ ¡¼JZ¡½Fig.3 The medium-and lower ¡¼JZ¡½level water vapor distribation ¡¼JZ¡½chart of Jiang huai cloud ¡¼JZ¡½burst in June,1991[TS)] [FL(3!K2]34000Mª¬3/s, damaged flood control dikes and inundated the cities. Related departments forecasted the rainstorms of July 27 and July 28, respectively according to the satellite cloud pictures and the leading departments decided to evacuate Ankang and other cities on July 31st, thus reduced casualties of the residents there.
Satellite data are very precious for the Qinghai-Xizang Plateau area. It is clearly to see in the satellite cloud picture that the tropical cloud system (monsoon cloud system and Bangladesh Bay cyclone and Arabian Sea Surge) could influence the plateau. On September 26, 1975, Indian monsoon low pressure westing along the Ganges and the cloud system of low pressure stretched to reach the Qinghai-Xizang Plateau and caused a strong precipitation. Its rainfall reached 97.9mm. ¡¼£×£Ô£µ£È£Ú¡½Cloudiness¡¼£×£Ô¡½The cloudiness data acquired from the geostationary satellite's infrared data are used to analyze the cause of cloudburst, which is a new method.
The picture of the average of cloudiness which caused the catastrophic
cloudbursts in Jianghuai Area in the summer of 1991 has several obvious
characteristics:
Figure 3 is the medium- and lower-level water vapor distribution chart of Jiang Huai Cloudburst in June, 1991, derived from the water vapor channel of the NOAA satellite. We can see that there are two water vapor channels (14h/kg Line) from the Bangladesh Bay and the South Sea respectively during the cloudburst period. The water vapor tongue of the former stretches from southwest to northeast, the latter from south to north. The area near 30-35¡ãW is the larger water vapor gradient area. On the south of this area, the whole southern mainland of China lies in the high humidity areas and the cloud cluster of cloudburst mostly generates and develops on the south of the large gradient area.
The sustained occurrence of water vapor tongue in that area is the characterization of sufficient ¡¼FL)¡½[LM] ¡¼TPK,+78mm¡£82mm,Z,PY¡½ ¡¼TS(¡½¡¼WT5HZ¡½¡¼ST5HZ¡½ [JZ]Fig.4The continuos visible for the aloud system\= [JZ]of deep depression reaching the wese of the Qing-\= [JZ]hai Xizang plateau at 09:52GMT Sep.25,1995[TS)] ¡¼TPK,+78mm¡£88mm,Y,PZ¡½ ¡¼TS(¡½¡¼WT5HZ¡½¡¼ST5HZ¡½ [JZ] Fig.5The continuos visible picture for the\= [JZ]cloud system moving eastnand slowly over\= [JZ]the plateau at 09:53 GMT Sep.26,1995[TS)] [FL(3!K2] ¡¼TPK,+92mm¡£112mm,ZX,PY,DY#¡½ ¡¼TS(¡½¡¼WT5HZ¡½¡¼ST5HZ¡½ [JZ] Fig.6The compre hen sive picture of water vapor and ose\= [JZ]fields during the cloudburst between 12 and 14 June,1991[TS)] water vapor condition during the sustained occurrence of Jianghuai cloudburst. The large water vapor gradient area provides us the position of the generation and development of the medium scale system of cloud burst, which is very advantageous to the forecast of the generation and development of cloudburst.
OLR data played an important role in precisely forecasting the heavy cloudburst occurred in Sichuan, Hubei in July, 1989.
The well-known El Nino phenomenon means the abnormal warming of the Pacific Ocean temperature, which is large-scale ocean abnormal phenomenon and has obvious influence on global atmospheric circulation, and ocean and climate abnormality. The analysis of EL Nino via ocean temperature data can forecast flood trend in a certain area.
At the end of May, 1993, it was found that the sea temperature in North Pacific Ocean [FL)] ¡¼TPK,+100mm¡£112mm,ZS,PY#¡½ ¡¼TS(¡½¡¼WT5HZ¡½¡¼ST5HZ¡½ [JZ]Fig.7 Apsendo-color visible picure in south ¡¼JZ¡½china at 08 26 GMT 7 September [TS)] rose obviously, which meant the strengthening of El Nino. But the sea temperature near the sea of Japan in the North Pacific Ocean Area was quite low and there was a frontal zone to the south of Pacific Ocean. The subtropical high pressure in summer is not easy to be found to the North, which is liable for the flood and waterlogging to occur in the Changjiang Basin.
On June 5, 1993, the report China Meteorological Bureau submitted to the State Council pointed out that in the flood control work in 1993 the stress should be put on the Changjiang River, not the Yellow River. The actual weather situation in 1993 proved that this conclusion was right.