The Analysis Of The Trend Characteristic Of The MJO In Summer And Winter From1982-2009

Based on the20-70d filtered NOAA daily outgoing long-wave radiation (OLR) data from1982to2009, NECP monthly reanalysis data (2.5×2.5), the ECMWF data (1.5×1.5) and Hadley monthly sea surface temperature (1.0×1.0),the intensity of the MJO activity in summer and winter are investigated. Based on these, the characteristics of the intensity of the MJO in summer, its impact factor and the possible linkage between the summer’s MJO and the ENSO are analysised by the statistical methods.The main conclusions are follow:1. The OLR data of the tropic (60°E-180°E,10°S-25°N) in summer are analysised by using the empirical orthogonal function (EOF) analysis. The EOF2’s spatial mode is15°latitudes backward to the EOF1’s spatial mode; EOF2’s times series is10days(almost1/4MJO’s activity period) backward to the EOF1’s. EOF’s spatial mode and times series indicate that the northward mechanism of the MJO in summer is significant.2. The OLR date of the tropic (40°E～120°W,15°S～15°N) in winter are analysised by using the empirical orthogonal function(EOF) analysis. The EOF2’s spatial mode is20°longitudes backward to the EOF1’s spatial mode; EOF2’s times series is12days (almost1/4MJO’s activity period) backward to the EOFl’s. EOF’s spatial mode and times series indicate that the eastward mechanism of the MJO in winter is significant.3. Based on the calculate on the MJO in summer and winter, the standardization annual mean amplitude of the MJO in summer and winter are achieved. The intensity of the MJO activity in summer has a significant gradually enhancing trend(tendency coefficient is0.027), whereas the trend of the MJO in winter isn’t significant(tendency coefficient is0.008). 4. Start from the previous year before the intensity of the MJO in summer enhances, on the west and central part of the Pacific Ocean, there is obvious positive anomaly of SST. The regression coefficient of SST is greatest in the previous winter, there is obvious westward transfer of water vapor above the equatorial Pacific Ocean, whereas above the equatorial Indian Ocean there is obvious eastward transfer of water vapor, the westward and eastward water vapor converge above the west part of the equatorial Pacific Ocean, these are the reason that the content of the water vapor above the west part of the equatorial Pacific Ocean is relatively great, and the intensity of the MJO in summer enhances.5. When there is a significant gradually enhancing trend of the MJO in summer from1982to2009, the SST of the coastal of the East Asian has a persistence tendency of enhancing, the water vapor is continued great above925hPa, especially in winter; and the regression coefficient of SST is the greatest. The westward water vapor above the east part of the equatorial Pacific Ocean, the southwest towards water vapor above the southeast edge of the north Pacific Ocean geopotential height field and the eastward water vapor above the equatorial Indian Ocean converge above the west part of the equatorial Pacific Ocean, and this field’s positive anomaly of the specific humidity also is the greatest. In winter, the SST of the east of the equatorial Pacific Ocean is continued cold, the negative anomaly of the SST is the greatest, the divergence of the water vapor is gradually enhancing and westward continued, the negative anomaly of the specific humidity is also the greatest. Under the global warming, the SST of the east part of the equatorial Pacific Ocean is continued warming, the content of water vapor is continued enlarging. In the winter and spring of the28years, the SST of the east part of the equatorial Pacific Ocean is continued cold, and the content of water vapor is continued reducing, these have a great affect on the enhancing trend of the MJO in summer in these28years.6. In order to analysis the summer MJO’s interannual change, we find that there is obvious negative anomaly of SST on the east part of the Pacific Ocean and the regression coefficient is the greatest. The water vapor above the east and central of the Pacific Ocean diverge strongly. The diverged water vapor go to the equatorial west Pacific Ocean. There is a positive anomaly of the water vapor above the west Pacific Ocean.In the previous winter, the SST and the content of water vapor of the east Pacific Ocean have a significant effect on the intensity of the MJO in summer. The SST of the east Pacific Ocean in winter is an important characterization of ENSO. When the SST of the east Pacific Ocean raises anomaly, the content of water vapor reduces anomaly, the intensity of the summer MJO declines, the vapor of the mainland of South American, the Southeast coastal and the middle and lower reaches of the Yangtze River in China increase; when the SST of the Equator Eastern Pacific cooled down anomaly in the preceding winter, the vapor of this region decreased, the intensity of the MJO in summer is strengthen, and the vapor of the mainland of South American, the Southeast coastal and the middle and lower reaches of the Yangtze River in China decrease.7. Results indicate that the boreal summer ISO has a significant intensifying trend each year, whereas there was little evidence on the trend of the Madden-Julian Oscillation (MJO) in winter. Results show that from1982to2009, the Western and Central Pacific SSTs continued to increase, and the upward motion over the Equatorial Western Pacific exhibits an increasing tendency. As a result, the anti-Walker circulation from the Western Pacific to the Indian Ocean has been reinforced, the easterly vertical shear of the equatorial central Indian Ocean has been increased, thereby amplifying the Rossby waves. The amplified Rossby waves could affect the intensity of BSISO activity through the development of Kelvin-Rossby waves. Although the Western and Central Pacific SSTs increased in winter with the enhanced upward motion, the major MJO patterns are related to Kelvin waves that have little relationship with the easterly vertical shear. Thus, the increased SSTs did not contribute to the MJO intensity changes.