Climate Characteristics Of Sea Surface Temperature (SST) Variation In The Changjiang Estuary

Based on the monthly average SST data for 42 years (1959.9~2001.10) and thedaily average SST data for one year (1998.1.1~ 1998.12.31) at Yin-shuichuan oceanstation in the Changjiang estuary, the monthly average SST data for 23 years(1977.10 ~ 2000.4) and the daily average SST data for one year (1998.1.1 ~1998.12.31) at Da-jishan ocean station in the Changjiang estuary , the monthlyaverage Changjiang runoff discharge data for 32 years(1968.1 ~ 1999.12) at Da-tonghydrological station in AnHui Province, the monthly average reanalysis data ongeneral circulation from the NCEP/NCAR for 43 years(1959~2001),it is analyzedthe climate characteristics of the SST variation in the Changjiang estuary. It isstudied the daily, monthly ,seasonal, interannual and decadal years SST variation inthe Changjiang estuary. It is mainly discussed the important factors that effect theseasonal and interannual SST variation in the Changjiang estuary : it includes theaffect of the East-Asia monsoon and the Changjiang runoff to the SST variation.The studies on SST variation provide reliable evidence for short, medium, long termforecast and climatic prediction of SST in the Changjiang estuary ,it also benefits thefish production in the Changjiang estuary.1 Firstly it is analyzed the daily SST variation in the Changjiang estuary. Among four seasons the most daily SST deficit appears in spring at Yin-shuichuan station with 4.7℃ and in early summer and early autumn at Da-jishan station with 2.5℃ .By the weather chart, it is found that the Changjiang estuary is controlled by the center of high pressure on the most max daily SST deficit day. The Sun radiation is the main factor of SST daily variation.2 The seasonal SST variation in the Changjiang estuary is studied .The highest SST appears in August and the lowest SST in February among a year. Spring and Autumn are transition seasons in a year. In Spring the SST rises from March to May. In Autumn the SST declines from September to November. The biggest distribution of SST variance is in winter with being in January at Yin-shuichuan station and in December at Da-jishan station. The Sun radiation , the East Asia monsoon and changjiang run-off are the main affecting factors.3 By power spectrum analysis, it is showed that there are about 2-year and 3~ 5 year oscillations for SST annual variation in the Changjiang estuary. This conclusion corresponds with the results of China sea SST that many researchers havediscovered.4 The interdecade variation is divided into two periods: from 60s to the end of 80s of 20 century, SST was relatively "cold times" that in most of years SSTA(SST anomaly) are negative , from the end of 80s of 20 century to the early 21-century, SST was relatively "warm times" that in most of years SSTA(SST anomaly) is positive. The SST variation become warmer, the SST was lowest in 70s in the last century, and most of years are "cold -water" year. The SST was the highest in 90s in the last century and most of years are "warm -water" year. The abrupt change year for SST took place in 1989.5 By the compose analysis , it is studied the East-Asian monsoon influence to the SST annual variation in the Changjiang estuary. According to the analysis of 500hPa heights 850hPa wind velocity and sea surface pressure, it is showed that in winter the strong winter monsoon year is corresponded with cold water year and weak monsoon year is corresponded with warm water year for SST in the Changjiang estuary. In summer when the year is strong summer monsoon year, the SST is abnormally higher. When the year is weak summer monsoon year, the SST is abnormally lower.6 Based on correlation analysis, it is studied that the Changjiang run-off effects the seasonal and annual SST variation in the Changjiang estuary. The direct influence of Changjiang run-off to the SST seasonal variation appears in March and April in dry season. In flash season the Changjiang run-off has indirect influence to the SST of the Changjiang estuary after one^ two^ three month. The Changjiang run-off discharge have 6.9a ^ 3.5a and 1.5a oscillations . The Changjiang run-off also effects the annual SST variation: when the yearly-mean run-off discharge is bigger, the SST in the Changjiang estuary is higher. Others the SST is lower.