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Search Results: 1 - 10 of 34384 matches for " Lu Riyu "
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Linear relationship between the interdecadal and interannual variabilities of North China rainfall in rainy season
Riyu Lu
Chinese Science Bulletin , 2003, DOI: 10.1007/BF03184223
Abstract: Interdecadal and interannual timescales are dominant in the North China rainfall in rainy season (July and August). On the interdecadal timescale, the North China rainfall exhibited an abrupt decrease at the end of 1970s. In this study, we examined the effect of this abrupt rainfall decrease on the association between rainfall and circulation on the interannual timescale, and found that the interdecadal variation does not change the physical mechanism responsible for the interannual variation of North China rainfall. There is a linear relationship between the interdecadal and interannual variabilities of North China rainfall in rainy season.
Precursory SST anomalies associated with the convection over the western Pacific warm pool
Riyu Lu
Chinese Science Bulletin , 2002, DOI: 10.1360/02tb9158
Abstract: The convection over the tropical western Pacific warm pool influences significantly the atmospheric circulation and climate in East Asia. Thus, the precursory signals of the convection may be used in the forecast of summer climate in China. According to the present results, the June-July-August (JJA) mean convection intensity over the warm pool is significantly related to the precursory positive and negative sea surface temperatures (SSTs) in the warm pool and in the equatorial central and eastern Pacific, respectively. It is also related to the simultaneous negative surface temperatures west to the Philippines. The analysis on the SSTs associated with the convection over the warm pool in individual month of summer shows that for the convection in June and July, there are precursory SST signals in the warm pool and the equatorial central and eastern Pacific. Therefore, this study shows that only the convection in June and July, rather than that in August, has precursory SST signals, despite the existence of the precursory signals of the JJA mean convection. Accordingly, it is implied that the interaction among the warm pool, equatorial central and eastern Pacific, and the region west to the Philippines may exhibit distinct features in the precursory period (preceding winter and spring) and in the simultaneous period.
Indices of the Summertime Western North Pacific Subtropical High
夏季西北太平洋副热带高压指数

Lu Riyu,
Lu
,Riyu

大气科学进展 , 2002,
Abstract: By averaging June-July-August (JJA) mean geopotential height anomalies at 850 hPa over the specified areas, the author proposes two innovative and succinct parameters to objectively define the zonal and meridional displacements of the western North Pacific subtropical high (WNPSH) in summer, respectively.Thus, these two indices and the present results may provide a basis for validating atmospheric general circulation models simulating the WNPSH. For the zonal index, the specified area is the west edge (110°-150°E,10°-30°N) of the WNPSH. For the meridional index, the specified area is the northwest edge (120°-150°E,30°-40°N) of the WNPSH. The interannual variations of these two indices are found to be independent. The results from a composite analysis based on the meridional index are in good agreement with previous studies based on case analyses.The two indices are compared with the existing indices announced by the National Climate Center (NCC) in China, on the interannual timescale. Despite slight differences, the interannual variations of the presented indices are basically similar to those of the NCC indices, and thus the circulation and precipitation associated with the present indices exhibit similar features to those associated with the NCC indices.Furthermore, an analysis of the differences between the associations of the present indices and the NCC indices shows that the presented indices are better than the NCC indices. An important result is that the zonal index is related to a more outstanding anomaly of precipitation, especially in East Asia and the Philippine Sea,both based on the presented indices and the NCC indices.The two indices can also be used to describe the seasonal march of the WNPSH during summer,namely, the poleward and eastward shifts. It is found that climatologically, the WNPSH shifts poleward and eastward rapidly in middle July, but the amplitudes of the poleward and eastward shifts are more remarkable in the summers when the WNPSH is located poleward and eastward in average.
Atmospheric Circulations and Sea Surface Temperatures Related to the Convection over the Western Pacific Warm Pool on the Interannual Scale
与西太平洋暖池上空对流年际变化相关联的大气环流和海温

Lu Riyu,
Lu
,Riyu

大气科学进展 , 2001,
Abstract: The difference is examined in atmospheric circulation and Sea Surface Temperatures (SSTs) in the tropics and subtropics between weak and strong convection over the tropical western Pacific warm pool (signified as WPWP). The WPWP is chosen as the region (110-160°E, 10-20°N), where the Outgoing Longwave Radiation (OLR) shows a great year-to-year variance. A composite study was carried out to examine the differences in atmospheric circulation and SSTs between weak and strong convection over WPWP. First,NCEP/NCAR re-analysis data and satellite-observed OLR data are used to examine the differences.ERA data, in which the OLR data are calculated, are then used for re-examination. The composite results show that the differences are remarkably similar in these two sets of data. The difference in circulations between weak and strong convection over WPWP is significantly associated with westward extension of the North Pacific subtropical anticyclone and stronger westerlies at the northwestern edge of the subtropical anticyclone. It also corresponds with the significant easterly anomaly and the descent anomaly in situ, i.e., over the WPWP. The most prominent characteristics of the difference of SSTs between weak and strong convection over the WPWP are the significant positive SST anomalies in the Indian Ocean,the Bay of Bengal and the South China Sea. In WPWP, however, there are only weak negative SST anomalies. Thus, the anomaly of OLR over WPWP is weakly associated with the SST anomalies in situ, while closely associated with the SST anomalies west of WPWP.
Anomalies in the Tropics Associated with the Heavy Rainfall in East Asia during the Summer of 1998
Lu Riyu,
Lu
,Riyu

大气科学进展 , 2000,
Abstract: The summer of 1998 was characterised by a severe flood in East Asia. The possible linkages were examined among the anomalies in the tropics that may be associated with the severe flood. The anomalies of 1998 are obtained by removing the climatology, which is the average of the ECMWF (European Centre for Medium Range Weather Forecasts) Re-Analysis (ERA) data over 15 years from 1979 to 1993, from the corresponding fields of 1998, which are obtained from the ECMWF operational analyses.In comparison to the results of Nitta (1990), it was found that there are considerable similarities in the atmospheric circulation anomalies between the summers of 1998 and 1988, in the tropics as well as in middle-high latitudes. It was shown that the atmospheric convection is slightly suppressed over the tropical western Pacific. In general, the suppressed convection corresponds to a negative anomaly of SST in the warm pool region. In the summers of 1998 and 1988, however, there are positive anomalies of SSTs in the tropical western Pacific, corresponding to the suppressed convection over there. This slightly suppressed convection may not provide a viable forcing mechanism for the severe flood in East Asia. It was postulated that the zonal wind anomalies in the tropics, in addition to the atmospheric convection over the tropical western Pacific, influence the position and intensity of the North Pacific subtropical high.In both summers of 1998 and 1988, while the stronger convection occurs over the warmer tropical Indian Ocean, the suppressed convection corresponds to the positive anomalies of SSTs in the tropical western Pacific. A possible explanation was given for the broken relationship between SSTs and OLR, (Outgoing Longwave Radiation) by analyzing the large-scale atmospheric circulation anomalies in the tropics.The heat fluxes at the surface in the warm pool of the tropical western Pacific and tropical Indian Ocean were also examined by using the ERA-15 data. To avoid the inconsistency between the ERA-15 and the operational analyses, the anomalies of the heat fluxes at the surface in the warm pool region in the summer of 1988, instead of the summer of 1998, were examined. The anomalous latent heat flux and the net solar radiation flux are the main reason for the positive anomalies of SSTs in the tropical Indian Ocean and in the tropical western Pacific, respectively. The suppressed convection over the tropical western Pacific allows more solar radiation fluxes downward at the surface, which would increase the SSTs.
Projected change in the relationship between East Asian summer rainfall and upper-tropospheric westerly jet
Yi Dai,RiYu Lu
Chinese Science Bulletin , 2013, DOI: 10.1007/s11434-012-5540-1
Abstract: The authors analyzed the interannual variability in summer precipitation and the East Asian upper-tropospheric jet (EAJ) over East Asia under the Historical and Representative Concentration Pathways Scenarios (RCPs, including RCP4.5 and RCP8.5), using outputs of 17 Coupled Model Intercomparison Project phase 5 (CMIP5) coupled models. The analyzed results indicate that the models can reasonably reproduce relatively stronger interannual variability in both East Asian summer rainfall (EASR) and EAJ. These models can also capture the relationship between the rainfall anomaly along the East Asian rain belt and meridional displacement of the EAJ. Projected results suggest that the interannual variabilities in precipitation along the East Asian rain belt and in the EAJ are enhanced under the scenarios RCP4.5 and RCP8.5 in the 21st century, which is consistent with the previous studies. Furthermore, it is found that the relationship between the East Asian rainfall and the meridional displacement of the EAJ is projected to be stronger in the 21st century under the global warming scenarios, although there are appreciable discrepancies among the models.
Linear relationship between the interdecadal and interannual variabilities of North China rainfall in rainy season
Lu Riyu,
LURiyu

科学通报(英文版) , 2003,
Abstract: Interdecadal and interannual timescales are dominant in the North China rainfall in rainy season (July and August). On the interdecadal timescale, the North China rainfall exhibited an abrupt decrease at the end of 1970s. In this study, we examined the effect of this abrupt rainfall decrease on the association between rainfall and circulation on the interannual timescale, and found that the interdecadal variation does not change the physical mechanism responsible for the interannual variation of North China rainfall. There is a linear relationship between the interdecadal and interannual variabilities of North China rainfall in rainy season.
Interannual Meridional Displacement of the East Asian Upper-tropospheric Jet Stream in Summer
LIN Zhongda,LU Riyu,
LIN Zhong
,LU Riyu

大气科学进展 , 2005,
Abstract: On the interannual timescale, the meridional displacement of the East Asian upper-tropospheric jet stream (EAJS) is significantly associated with the rainfall anomalies in East Asia in summer. In this study, using the data from the National Centers for Environmental Prediction-Department of Energy (NCEP/DOE) reanalysis-2 from 1979 to 2002, the authors investigate the interannual variations of the EAJS's meridional displacement in summer and their associations with the variations of the South Asian high (SAH) and the western North Pacific subtropical high (WNPSH), which are dominant circulation features in the upper and lower troposhere, respectively. The result from an EOF analysis shows that the meridional displacement is the most remarkable feature of the interannual variations of the EAJS in each month of summer and in summer as a whole. A composite analysis indicates that the summer (June-JulyAugust, JJA) EAJS index, which is intended to depict the interannual meridional displacement of the EAJS, is not appropriate because the anomalies of the zonal wind at 200 hPa (U200) in July and August only, rather than in June, significantly contribute to the summer EAJS index. Thus, the index for each month in summer is defined according to the location of the EAJS core in each month. Composite analyses based on the monthly indexes show that corresponding to the monthly equatorward displacement of the EAJS, the South Asian high (SAH) extends southeastward clearly in July and August, and the western North Pacific subtropical high (WNPSH) withdraws southward in June and August.
Numerical Simulation of the Effect of the SST Anomalies in the Tropical Western Pacific on the Blocking Highs over the Northeastern Asia
Lu Riyu,Huang Ronghui,
Lu Riyu
,Huang Ronghui

大气科学进展 , 1996,
Abstract: The effects of the sea surface temperature (SST) anomalies in the tropical western Pacific on the atmospheric cir-culation anomalies over East Asia are simulated by the IAP-GCM with an observed and idealized distributions of the SST anomalies in the tropical western Pacific, respectively Firstly, the atmospheric circulation anomalies during July and August, 1980 are simulated by three anomalous experiments including the global SST anomaly experiment, the tropical SST anomaly experiment and the extratropical SST anomaly experiment, using the observed SST anomalies in 1980. It is shown that the SST anomalies in the tropical ocean greatly influence the formation and maintenance of the blocking high over the northeastern Asia, and may play a more important role than the SST anomalies in the extratropical ocean in the influence on the atmospheric circulation anomalies Secondly, the effects of the SST anomalies in the tropical western Pacific on the atmospheric circulation anoma?lies over East Asia are also simulated with an idealized distribution of the SST anomalies in the tropical western Paci?fic. The simulated results show that the negative anomalies of SST in the tropical western Pacific have a significant ef?fect on the formation and maintenance of the blocking high over the northeastern Asia.
The ENSO''s Effect on Eastern China Rainfall in the Following Early Summer
The ENSO’s Effect on Eastern China Rainfall in the Following Early Summer

LIN Zhongda,LU Riyu,
LIN Zhong
,LU Riyu

大气科学进展 , 2009,
Abstract: ENSO's effect on the rainfall in eastern China in the following early summer is investigated by using station precipitation data and the ERA-40 reanalysis data from 1958 to 2002. In June, after the El Ni\~no peak, the precipitation is significantly enhanced in the Yangtze River valley while suppressed in the Huaihe River-Yellow River valleys. This relationship between ENSO and the rainfall in eastern China is established possibly through two teleconnections: One is related to the western North Pacific (WNP) anticyclonic anomaly in the lower troposphere leading to enhanced precipitation in the Yangtze River valley, and the other is related to the southward displacement of the Asian jet stream (AJS) in the upper troposphere resulting in suppressed precipitation in the Huaihe River-Yellow River valleys. This southward displacement of the AJS is one part of ENSO's effect on the zonal flow in the whole Northern Hemisphere. After the El Ni\~no peak, the ENSO-related warming in the tropical troposphere persists into the following early summer, increasing the meridional temperature gradient and through the thermal wind balance, leads to the enhancement of westerly flow in the subtropics south of the westerly jet stream and results in a southward displacement of the westerly jet stream.
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