Study On The Features Of Strong Precipitation Low-frequency Oscillation In South China

At first, we analyze the character of tow-frequency oscillation of precipitation inSouth China by using the method of Morlet wavelet. Then we analyze some relatedfactors which have relationship with precipitation, to look for the obvious mainfactors with the low-frequency character and study the relationship between thesefactors and precipitation. Then analyze the single process of strong precipitation tomake sure that how the key factors take part in the process of precipitation. Finally,based on the analytical results above, we research the anomalies relativity betweenlatitude windward of 850hpa and precipitation to find out the forecast signal, whichhave actual meaning for extension precipitation. The main results are as follows:(1)The character of low-frequency precipitation existent widely in South China.And the time from May to July is the most obvious period of the low-frequencyprecipitation. There is obvious difference between the year of more precipitation andthe year of less precipitation, In the year of more precipitation, the main cycle oflow-frequency precipitation is 10-20 day. But in the year of less precipitation, thecycle of low-frequency is more than 20 days. Above analytical enunciation, when10～20 day is main cycle of low-frequency precipitation, strong precipitation maybemore frequent and the precipitation may be more then average precipitation.(2) From the analysis of many factor relating with precipitation, we detect that, thefactors on 850hpa have the most obvious low-frequency characteristic, including850hpa latitude windward field, 850hpa perturbation kinetic energy and 850hpageopotential height. The low-frequency precipitation of these factors appear hugedifferent between the years of more precipitation and the years of less precipitation.And the difference of low-frequency is familiar with precipitation.(3) We chose several years to analyze the relationship between the factors of850hpa and the strong precipitation. And we find that three low-frequency mainfactor is the main element that infects strong precipitation remarkably. Among them,which have the most function for precipitation is the 850hpa low-frequency latitude windward field, almost during every occurrence of strong precipitation, the 850 hpathe low-frequency latitude windward field gathers in South China.(4) From above research, we can see that the process of strong precipitation hasmost close relationship with the movement and change of the 850hpa low-frequencylatitude windward field in South China. Meanwhile the 850hpa the low-frequencywind is the most typical element in daily forecast. So we make a further study of therelationship between the strong precipitation and the 850hpa low-frequency latitudewindward field. During the period of strong precipitation, the 850hpa low-frequencylatitude wind gathers in (15°N～25°N, 100°E～120°E),and the change of the swingof the 850hpa low-frequency latitude wind in this area conform to the variety ofprecipitation. So we can use this character as a signal of forecast.(5) From the correlative analyze of 850hpa low-frequency latitude wind and strongprecipitation, we detect that, when the precipitation occurrence for ex-15 days, alow-frequency latitude wind gather in Bay of Bengal. Then this extremum centermove towards east, when reach South Sea, it change to move towards north. Whenthe extremum center close up to South China, the heavy precipitation will happen inSouth China. So we can use the change of the way that 850hpa low-frequencylatitude wind moves to improve the accuracy rate of extension forecast.