Study On Multi-timescale Variability And Local Features Of Precipitation In Shandong

Precipitation caused by all kinds of elements interacting with each other in the climate system is one of the key elements in describing the climate system and its variability. The variation of precipitation shows a strong random and multi-timescale feature. The climate study of local precipitation usually focuses on precipitation or the variability of its deviation. The oscillation of precipitation shows a great range. It includes the high frequency oscillations, such as diurnal and annual, as well as the low frequency oscillations, i.e., inter-annual and inter-decadal. The present study mainly focuses on the multi-timescale variability and local features of precipitation of Shandong in climatology. In rainy seasons, the intra-seasonal and inter-decadal variations of precipitation show no difference in Shandong province. However, the diurnal variation of precipitation in summer and precipitation in winter shows evident local characteristics. Based on the inherent laws of climate change, four climatological patterns has been analyzed from the annual precipitation by using multi-year surface and upper air observations, reanalysis data from National Center for Environmental Prediction (NCEP)/National Center for Atmospheric Research (NCAR) as well as statistical methods. The four patterns are annual cycle, seasonal variation,30to70-day intra-seasonal oscillation,10to28-day intra-monthly oscillation, which are named climatological modes. The correlation and difference of precipitation between Shandong province and its surrounding area are analyzed in terms of multi-timescale processes. The relationship between the precipitation in Shandong and east Asian high level jets was analyzed. The outset and end of flood seasons, the precipitation as well as the variation of the variance contribution in multi-timescale were analyzed. The relationship between the precipitation anomalies in main rainy seasons and low frequency oscillation transportation of atmospheric circulations was analyzed. Besides, the diurnal variation of precipitation and regional characteristics as well as the regional precipitation difference between Shandong peninsula and inland in winter were analyzed. It is very important for improving the capabilities of predicting rainfall and disaster prevention and mitigation to understand the rules of climate change and climate background of rainfall disaster.1) The diurnal variation of precipitation in Shandong shows regional, seasonal and inter-annual characteristics. It can be classified into three types:inland type, southern peninsula type, northern peninsula type. It shows a twin-peak pattern in inland type and northern peninsula type, whereas in southern peninsula type, it shows a single-peak pattern. It also suggested that the diurnal variation of precipitation in summer, especially in July and August, varies significantly, of which in flood years it is close to multi-year mean level, whereas in drought years it is far away from the climatological mean level. The probably reason for forming the midnight-early morning peaks is analyzed.2) The summits of annual cycle shows the northward advancement of the main precipitation belt, those of seasonal variation reflect main rainy seasons in different regions in east of China. There is only one main flood season in Shandong. Huaihe River Basin and North China. As for climatic intra-seasonal oscillation (CISO), Shandong and Huaihe River Basin have the same phase from April to Mid July, but different phase from late July to late September. In summer half year, CISOs of Shandong and north part of North China have reverse phase. For intra-monthly oscillation, precipitation have reverse phase in the first half of August and have similar phase at start and end at of the main flood season in Shandong and north part of North China. Precipitation of Shandong is closely related to atmosphere circulations in terms of any climate modes. East Asian westerly jet index(EAWJI). The phase of annual mode and seasonal mode is reverse to those of EAWJI. For CISO mode, precipitation and EAWJI have similar phase in summer half year.3) The low-frequency oscillation of precipitation in Shandong in summer half year, i.e., May to September, is stronger than that in winter. Its amplitude in summer is bigger than that in winter. The precipitation in rainy season from May to September mainly shows three sudden changes. The first and third changes mark the outset and end date of the flood seasons in Shandong. Combining with the annual cycle and intra-seasonal variations, the fact that intra-monthly oscillations modulate CISO leads to these three changes. The intra-monthly oscillations play an essential role in these changes.4) The inter-decadal variation of precipitation in main flood seasons varies significantly. Before1975, the precipitation is more than the mean level. In the following20years, the precipitation is less than the mean level. After2000, the precipitation is increasingly intensified. The periods of inter-annual and inter-decadal oscillations of precipitation are2-3year and11-year, respectively. The two sudden changes of inter-annual variation of precipitation happened around1976and2005, respectively. The former is closely related to the11-year period oscillation. The later is caused by the interactions of two oscillations.5) The deviations and variances of amplitudes and phases in every mode of the past years from the climatological mean level are different. This is the main reason for leading to the strong inter-annual variations of precipitation in the main rainy seasons. The start and end dates are statistically related to the precipitation anomalies. If the main rainy seasons start late, the precipitation is probably less than normal. The precipitation is positively related to the end date and the lasting time of the main rainy seasons. The deviation of the start and end dates of the main rainy seasons is larger in the drought years of the inter-decadal oscillation.6) The distribution of Sea surface temperature anomaly (SSTA) in the north Pacific suggested that starting from spring, it is colder in the south and warmer in the north in the flood years of the main rainy seasons. The pattern lasted until fall and could probably lead to the weakening of the Hardley cell. Consequently, the subtropical high is located in higher latitudes in500-hPa in summer. Hence, this leads to more precipitation and vice versa. In500-hPa, the geopotential height is significantly higher from Shandong peninsula to south of Japan in the flood years of main rainy seasons. However, it is significantly lower from Lake Baikal to south of Lake Balkhash. It suggested that if the subtropical high is in higher latitudes, the troughs could easily develop in the westerly belt. The geopotential height in200-hPa along the40°N shows a positive CGT-like wave distribution. In the upper level of east Asian, the westerly jets are intensified north of40°N and weakened south of40°N.7) The anomalies of precipitation in the flood seasons were significantly related to the variances of the annual cycle and seasonal change (>99.9%). However, the anomalies of precipitation in the main rainy seasons are mainly caused by the low frequency oscillation. In the typical flood year (1998), the transportation signal of the intra-seasonal oscillation of the atmospheric circulation is very significant. The precipitation peak of the intra-seasonal oscillation happened in the same time as the wind peaked at the (35°N,120°E). The phase of the zonal and meridional winds is consistent. However, the phenomena only happened in some period. In the typical drought years, the situation is different. The low-frequency oscillations of the atmosphere circulation in the drought and flood years show significant differences. In the flood years,it is that not only the westward transportation of the intra-seasonal oscillation, but also of the intra-monthly oscillations is more obvious than that in the drought years.8) Precipitation in winter in Shandong inland and its surrounding area, especially northern China, shows great consistency, whereas in the northeastern area of Shandong peninsula precipitation has local characteristics. The local climatology phenomena is not only caused by the so-called "peninsula effect" and the peninsula topography. The regional sub-synoptic scale constant disturbance formed in the lower-level atmosphere of the Yellow and Bohai Seas caused by the continental topography and land-sea distribution plays an important role in the local climatology phenomena. The following configuration, such as stable middle and upper atmospheric layer, unstable low level atmosphere layer, moistures and heat transported from ocean to atmosphere, leads to the precipitation in the northeastern Shandong peninsula due to the shallow convection.