Intraseasonal Oscillation Of East Asian Subtropical Westerly Jet In Winter And Its Relationship With Precipitation In South China

Based on European center(ECMWF) ERA- Interim daily reanalysis data, experience in using orthogonal function decomposition(EOF), power spectrum analysis, Butterworth filter, synthetic analysis, correlation analysis and other statistical methods, analyzes the winter east Asian subtropical upper westerly jet oscillation characteristics of the season, and their formation mechanism are discussed from thermal aspects, as well as the preliminary analysis of the east Asian subtropical westerly jet in the season of oscillation and the relationship between precipitation in south China. Now the following conclusions:(1) East Asian subtropical westerly jet in winter has significant 30-60 day oscillation period, the seasonal changes in the largest area in its export zones, rapids change guide in the season of east-west oscillating jet. Winter east Asian subtropical westerly jet exit area oscillation propagation characteristics of no significant, but to increase or decrease in place. Export zones zonal wind season changes related to its north and south on both sides of the variable temperature within 30 to 60 days after filtering of zonal wind cooling on the northern side of enhancement is more depends on its export zones, the regional weather scale upward movement(below 30 days), north and south, adiabatic temperature increased the temperature gradient. In addition of synoptic-scale wind field to measure the temperature field of cold advection also have larger contribution to the north of cooling. Exit westerlies strengthen season in scale, its south is heating up, the same as the weather scale subsidence movement as a result. Export zones of rapids season had a great effect on the change of precipitation in south China. In 30 to 60 days scale, when the west wind is abnormal, southeast China and in the southeast area less rainfall. The main reason is the jet anomaly by east, southern China region controlled by high pressure from the north, the cold air south, water vapor can't delivery at this point, high moisture conditions, conducive to production of precipitation, and the entire south vertical circulation are sinking movement, unable to meet the conditions of rainfall, thus causing fewer precipitation in south China; Conversely, when the west wind negative anomaly, southeast China and in southeast area, the more the rainfall corresponding jet anomaly by west, southern region are located in the south of the jet entrance area in our country, the control is a wide range of low pressure, cold air southward, and southwest airflow from the bay of Bengal and southeast air current from the western Pacific region in the south of China, guide the water vapor convergence here, produce upward movement, is conducive to the occurrence of precipitation.(2) In the east Asian subtropical westerly jet entrance area in winter season change relative to the export zones. Entrance area within the season change is the biggest area in the DHS 30-40 DHS N, 110 DHS- 130 DHS E area, and the jet entrance area in winter 200 h Pa zonal wind oscillation period, it has two season respectively for 30 to 60 days and 10 to 30 days. For the entrance area near 30-60 day oscillation, the propagation characteristics of no significant but to increase or decrease in place, and exports area is relatively similar. Entrance area anomalies west H wind enhancement, also depends on its temperature, in the south of the north and significant temperature drop is given priority to with cool north. Export area north of the average airflow to measure the temperature of cold advection and export area south of average air temperature of weather scale warm advection is the temperature change is the most main reason. Within 30 to 60 days rapids season change has significant effect on the precipitation in south China. For the entrance area west wind was abnormal, to southeast Asia region precipitation on the southeastern coast of China, the more the central areas in China and Japan peninsula near less rainfall; Oscillations in the entrance area west wind season for negative anomaly, fewer precipitation on the southeastern coast of China, the central region precipitation bullish. Entrance area zonal wind 30 to 60 days of the change and the closely related to precipitation in China. Within the season as the entrance area zonal wind, precipitation area move from west to east, the middle troposphere, visible across the Lake Baikal in places such as control by abnormal trough, strong cold air forces, and in the lower troposphere is abundant water vapor transport, which have more precipitation in south China When zonal westerly winds reach the strongest, the north for abnormal trough, the south for abnormal ridge, zonal westerly winds began to taper off, from the middle troposphere, abnormal in eastern China in the ridge, the lower troposphere are abnormal north risk control system, is not conducive to the generation of precipitation. Near the jet stream, the second level circulation, significantly increase with the decrease of precipitation all over with zonal wind anomalies caused by the secondary circulation.(3) East Asian subtropical westerly jet entrance area 10 to 30 days season change also guide the jet oscillation east-west oscillation, and oscillation jet 10-30 days have relatively significant transmission characteristics, and the intensity will be stronger or weaker. On 10 to 30 days in scale, the entrance area zonal wind oscillation caused by the most significant reason is the temperature change on the northern side of the region.10-30 days scale zonal westerly enhancement with the regional weather scale(below 10 days) upward movement adiabatic temperature which influence on the temperature gradient. In addition the characterized by cold advection, the cold advection is by scale cold center under the impetus of the average airflow. South exit area to heat up, the same as the weather scale warm center under the impetus of the average flow of warm advection. At the same time, the area of synoptic-scale sinking motion adiabatic heating will also affect the temperature change. Winter east Asian subtropical westerly jet entrance area 10 to 30 days seasonal oscillation of positive anomaly, in southeast China and its east of the sea area rainfall less; When the entrance area rapids seasonal oscillation of positive anomaly, precipitation bullish on the southeastern coast of China. But in 10 to 30 days scale, precipitation in south China, there is no significant correlation with zonal wind field.