Differences About Low-frequency Characteristics Of Precipitation In The Yangtze River And The Yellow River Basin And Possible Differences In Mechanism

Using the global sea surface temperature (SST) from Hadley Climate Prediction and Research Center, NCEP\NCAR daily wind field and specific humidity, and 753-station daily precipitation and 160-station monthly precipitation data from national meteorological information center, the differences about low-frequency characteristics of precipitation and its related moisture transport path in the Yangtze River and the Yellow River basin in the following summer of eastern Pacific(EP) and center Pacific (CP) type El Ni(?)o events are analyzed, For convenience, precipitation is also called EP type and CP type respectively. The relationship between atmospheric low frequency element field (water vapor flux field, height field, flow function, potential function, vertical velocity) and low frequency precipitation in the Yangtze River and the Yellow River Basin are studied. The results show that,(1) Different types of El Ni(?)o events in the summer of the Yangtze River and the Yellow River Basin, the main low frequency cycle and the Warp direction and weft direction water vapor fluxes are also different. 1) The EP type precipitation in the 7-year average sequence existed 10-20 d and 20-30 d significant cycles, but CP type precipitation only existed for 10-20 d significant low frequency cycle. 2) In the comparison of the two types of events, the 10-20 d (20-30 d) low frequency period is significant in the EP type and CP type, but the EP type in the 30-60 d cycle is higher than the CP type (30-60 d) low frequency cycle EP type is slightly weaker (stronger) than CP type.(2) Affect the EP 10-20d low frequency precipitation circulation system are mainly: the anomalous anti-cyclonic water vapor circulation near the Philippine Islands; the anomalous cyclone type, the anti-cyclonic water vapor circulation in the southwest of the Japanese archipelago and the northeastern part of the Japanese archipelago; Abnormal cyclone water vapor circulation in the northeastern part of the Lake Balkhash, north airflow on the west side of the Lake Baikal. The main low-frequency water vapor circulation systems that affect the CP type 10-20d low-frequency precipitation are: anomalous cyclone water vapor circulation west of the Bay of Bengal, Sumatra; anti-cyclonic water vapor circulation near the Philippines; the anomalous cyclone and anti-cyclonic water vapor circulation pair near the Bohai Sea, the southeastern side of the Japanese archipelago, Abnormal Cyclone, Anti - cyclonic Circulation on Both Sides of Lake Baikal.(3) EP type precipitation mainly has three water vapor passages. Cold air passage: The reference point for the water vapor signal is the west side of West Siberia and Lake Baikal (formed at 0 d), the Northwest Pacific (always present). Warm wet water vapor channel: water vapor signal reference source for the South China Sea (-2d when the basic formation). CP type precipitation has four water vapor channel. Cold air channel: water vapor signal reference source for the Eastern European plain (0d when the formal formation), the Northwest Pacific (only trace water vapor to reach the key area). Warm water vapor channel: water vapor signal reference source for the Arabian Sea, the Indian Ocean (-4d began to form), the Western Pacific (-2d when the basic formation).(4) The distribution of 10-20 d low frequency height field in EP-E1 Ni(?)o event is as follows:1) 500hPa, the height field in the middle and high latitudes is two ridge and one trough, and the western Pacific subtropical high is banded. The ridge is located at (135° E, 25 ° N). 2) 200hPa,South Asia high pressure is located between 20?35°N,showing east-west zonal distribution,the eastern ridge point near 130° E. CP type El Ni(?)o event: 1) 500hPa, the middle and high latitudes Eurasia showed two ridge-trough, and the western Pacific subtropical high was banded, with ridge points at (125° E, 25° N) , compared with the EP-type events, the subtropical high position is more partial west, more conducive to a large number of warm and humid water into the Yangtze River - the Yellow River basin. 2) 200hPa, South Asia high pressure is located between 20?35°N, showing east-west zonal distribution, the eastern ridge point near 122° E.(5) The distribution of 10-20d low frequency flow function in the El Ni(?)o event is: 1) 850hPa,the system affecting the precipitation is the anti-cyclonic circulation near the southern part of the Philippine Islands, the cyclonic circulation in the northern part of the Japanese archipelago, the northern part of the Yangtze River and the Yellow River of the cyclonic circulation. 2) 200hPa, the system that affected the precipitation has the anti-cyclone circulation from the west side of the Ural Mountains to the west of the Okhotsk Sea, the cyclone circulation from the south China to the southern part of the Bering Sea. CP type El Ni(?)o events: 1) 850hPa, the system affecting the precipitation is Mascalin anti-cyclone, the cyclone circulation near Sumatra, the cyclone circulation from Bering sea south to the northern part of the Japanese archipelago, the cyclone circulation from the Indian peninsula to the Okhots sea. 2) 200 hPa, the system affecting the precipitation from the Bay of Bengal to the Bering Sea anti-cyclonic circulation.(6) The characteristics of the 10-20d low frequency potential function of the EP El Ni(?)o event are: 1) 850hPa, the system affecting the precipitation is the convergence zone in the northwest of the Bohai Sea, the convergence belt in the northeastern side of the Philippine Islands and the divergent center near the Bohai Bay. 2) 200hPa, the system affecting the precipitation is the divergent gas flow belt from the Ural Mountains to the northern part of Japan, the convergence belt near the Yangtze River and the Yellow River basin, from the Qinghai-Tibet Plateau to Japan's convergence center. CP type El Ni(?)o events: 1) 850hPa, the system affecting the precipitation is the the convergence zone on the south side of Japanese islands, divergence center near the Bohai Bay. 2) 200hPa, the system affecting the precipitation is the divergent center on the west side of the Yangtze River - the Yellow River basin, the convergence belt in the eastern part of the Japanese archipelago, and the convergence zone from the Yangtze River to the eastern part of the Japanese archipelago.(7) The characteristics of the 10-20d low frequency vertical velocity of the EP El Nifo event are: The intensity of the rising air flow between the Yangtze River and the Yellow River is weak and the altitude is low, which leads to weak EP precipitation. CPtype El Ni(?)o event: The intensity of the rising airflow between the Yangtze River and the Yellow River is stronger and higher, which leads to the precipitation of CP type.(8) EP El Ni(?)o event 850hpa wind field seasonal oscillation intensity seasonal variation characteristics: Asia-Pacific region perennial strong seasonal oscillation, the strongest in spring and winter, the largest at the northern hemisphere. CP El Ni(?)o event : The intensity of the oscillation in the wind field has experienced a decrease from the winter to the autumn. The intracontinental oscillations in the northern hemisphere are mainly located in the Eurasian continent (perennial) and the northwest Pacific region (spring and summer). The oscillation of the southern hemisphere is mainly located in the South Indian Ocean and the South Pacific (summer)and Oceania (winter and spring).