The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Jiangyu Mao - One of the best experts on this subject based on the ideXlab platform.
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Decadal changes in interannual dependence of the bay of bengal summer monsoon onset on enso modulated by the Pacific Decadal Oscillation
Advances in Atmospheric Sciences, 2019Co-Authors: Jiangyu MaoAbstract:Interannual variations of the Bay of Bengal summer monsoon (BOBSM) onset in association with El Nino-Southern Oscillation (ENSO) are reexamined using NCEP1, JRA-55 and ERA20C atmospheric and Hadley sea surface temperature (SST) reanalysis datasets over the period 1900–2017. Decadal changes exist in the dependence of the BOBSM onset on ENSO, varying with the Pacific Decadal Oscillation (PDO). A higher correlation between the BOBSM onset and ENSO arises during the warm PDO epochs, with distinct late (early) onsets following El Nino (La Nina) events. In contrast, less significant correlations occur during the cold PDO epochs. The mechanism for the PDO modulating the ENSO-BOBSM onset relationship is through the variations in SST anomaly (SSTA) patterns. During the warm PDO epochs, the superimpositions of the PDO-related and ENSO-related SSTAs lead to the SSTA distribution of an El Nino (La Nina) event exhibiting significant positive (negative) SSTAs over the tropical central-eastern Pacific and Indian Ocean along with negative (positive) SSTAs, especially over the tropical western Pacific (TWP), forming a strong zonal interoceanic SSTA gradient between the TWP and tropical Indian Ocean. Significant anomalous lower tropospheric easterlies (westerlies) together with upper-tropospheric westerlies (easterlies) are thus induced over the BOB, favoring an abnormally late (early) BOBSM onset. During the cold PDO epochs, however, the superimpositions of PDO-related SSTAs with El Nino-related (La Nina-related) SSTAs lead to insignificant SSTAs over the TWP and a weak zonal SSTA gradient, without distinct circulation anomalies over the BOB favoring early or late BOBSM onsets.
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interDecadal variability of early summer monsoon rainfall over south china in association with the Pacific Decadal Oscillation
International Journal of Climatology, 2017Co-Authors: Jiangyu MaoAbstract:The interDecadal variability of early summer South China (SC) monsoon rainfall (SCMR) is investigated based on several long-term rainfall data sets from 1926 to 2013. Both correlation and composite analyses suggest a significant out-of-phase relationship between interDecadal fluctuations of SCMR and the preceding wintertime Pacific Decadal Oscillation (PDO), with negative (positive) PDO epochs favouring above-normal (below-normal) SCMR. The physical mechanism relating the wintertime PDO to the interDecadal variability of SCMR appears to take place via atmospheric and oceanic teleconnections. The below-normal SCMR is characterized by a meridionally arranged vortex (MAV) pattern across the East Asia–western North Pacific (WNP) sector, with an anomalous cyclone, an anomalous anticyclone and an anomalous cyclone occurring alternately over the South China Sea (SCS)–WNP, Yangtze Basin and Lake Baikal in the early summer. This may respond to the PDO-related positive sea surface temperature (SST) anomalies locally over the SCS–WNP and remotely over the tropical eastern Pacific, with the latter forcing anomalous Hadley and Walker circulations. SC is located directly under the divergent moisture environment of anomalous northeasterlies between the anomalous cyclone over the SCS–WNP and the anticyclone over the Yangtze Basin. Again, the below-normal SCMR is preceded by negative (positive) SST anomalies in the midlatitude North Pacific (tropical eastern Pacific) associated with positive PDO in wintertime. Such an anomalous SST pattern subsequently induces a strengthened and northward-shifted upper-tropospheric jet in early summer, leading to significant upper-tropospheric convergence over SC. The out-of-phase relationship between SCMR and wintertime PDO as well as related physical processes are validated by coupled model simulations.
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interDecadal modulation of enso related spring rainfall over south china by the Pacific Decadal Oscillation
Climate Dynamics, 2016Co-Authors: Jiangyu MaoAbstract:The interDecadal modulation of the relationship between El Nino–Southern Oscillation (ENSO) and the South China spring rainfall (SCSR) by the Pacific Decadal Oscillation (PDO) is investigated using long-term observational datasets. When ENSO and PDO are in-phase [i.e., El Nino events during warm PDO (EN_WPDO) and La Nina events during cold PDO (LN_CPDO)], the positive correlations between ENSO and SCSR are enhanced significantly, with above-normal (below-normal) SCSR generally following EN_WPDO (LN_CPDO) events. In contrast, the ENSO–SCSR relationship becomes ambiguous when ENSO and PDO are out-of-phase [i.e., El Nino events during cold PDO (EN_CPDO) and La Nina events during warm PDO (LN_WPDO)]. The PDO modulates the ENSO–SCSR relationship through the impact of variations in the lower-tropospheric subtropical anticyclone over the western North Pacific (WNP) and upper-tropospheric westerly jets over East Asia and the midlatitude North Pacific. An EN_WPDO (LN_CPDO) event induces an enhanced subtropical anticyclone (cyclone) over the WNP and intensified (weakened) subtropical westerly jet around the southern Tibetan Plateau due to modification by the PDO-forced anomalous circulation. Thus, South China falls just under the influence of the anomalous lower-tropospheric southwesterlies (northeasterlies) and upper-tropospheric divergent (convergent) environment, leading to above-normal (below-normal) SCSR. In contrast, the SCSR anomalies exhibit no wet or dry preference following EN_CPDO (LN_CPDO) events, because ENSO-induced and PDO-forced circulation anomalies tend to cancel each other out. These modulating effects by the PDO on the ENSO–SCSR relationship and related physical processes are also examined with coupled model simulations.
Yongqi Gao - One of the best experts on this subject based on the ideXlab platform.
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modulation of the Pacific Decadal Oscillation on the summer precipitation over east china a comparison of observations to 600 years control run of bergen climate model
Climate Dynamics, 2015Co-Authors: Tore Furevik, Odd Helge Ottera, Yongqi GaoAbstract:Observations show that the summer precipitation over East China often goes through Decadal variations of opposite sign over North China and the Yangtze River valley (YRV), such as the “southern flood and northern drought” pattern that occurred during the late 1970s–1990s. In this study it is shown that a modulation of the Pacific Decadal Oscillation (PDO) on the summer precipitation pattern over East China during the last century is partly responsible for this characteristic precipitation pattern. During positive PDO phases, the warm winter sea surface temperatures (SSTs) in the eastern subtropical Pacific along the western coast of North American propagate to the tropics in the following summer due to weakened oceanic meridional circulation and the existence of a coupled wind–evaporation–SST feedback mechanism, resulting in a warming in the eastern tropical Pacific Ocean (5°N–20°N, 160°W–120°W) in summer. This in turn causes a zonal anomalous circulation over the subtropical–tropical Pacific Ocean that induces a strengthened western Pacific subtropical high (WPSH) and thus more moisture over the YRV region. The end result of these events is that the summer precipitation is increased over the YRV region while it is decreased over North China. The suggested mechanism is found both in the observations and in a 600-years fully coupled pre-industrial multi-century control simulations with Bergen Climate Model. The intensification of the WPSH due to the warming in the eastern tropical Pacific Ocean was also examined in idealized SSTA-forced AGCM experiments.
Jianqi Sun - One of the best experts on this subject based on the ideXlab platform.
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footprints of Pacific Decadal Oscillation in the interDecadal variation of consecutive cloudy rainy events in southern china
Atmospheric Research, 2021Co-Authors: Jianqi Sun, Mengqi ZhangAbstract:Abstract Consecutive Cloudy-Rainy Events (CCREs) in spring have a disastrous impact on agriculture and the natural ecosystem over southern China. In this study, the variability of the frequency of spring CCREs in southern China from 1961 to 2016 and the underlying mechanism of these phenomena are explored. The results indicate that the dominant mode of the CCRE frequency in southern China varies in a uniform spatial pattern, and the time series exhibits a strong interDecadal variation, with a higher frequency between the late 1970s and late 1990s and a lower frequency in the other periods. Such an interDecadal variation in the CCRE frequency varies well in–phase with the Pacific Decadal Oscillation (PDO). Further dynamic diagnosis and numerical simulation both suggest that the PDO is linked with CCREs in southern China through two physical processes. On the one hand, the anomalous PDO is associated with the anomalous North Pacific Oscillation (NPO). The westward extension of the NPO is accompanied by anomalous East Asian westerly jet (EAWJ) and West Pacific subtropical high (WPSH). On the other hand, the eastward development process associated with the PDO variation can excite a Rossby wave train over the Northern Hemispheric mid-latitudes. The PDO-related Rossby wave train can alter East Asian atmospheric circulations, leading to anomalous EAWJ. The changes in the EAWJ and WPSH can further lead to anomalous upward motion over southern China and moisture transportation from the South China Sea to southern China. Through these physical processes, the positive–phase (negative–phase) PDO provides a favorable (unfavorable) condition for the occurrence of CCREs in southern China.
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contribution of the phase transition of Pacific Decadal Oscillation to the late 1990s shift in east china summer rainfall
Journal of Geophysical Research, 2015Co-Authors: Yali Zhu, Tao Wang, Huijun Wang, Jianqi SunAbstract:Based on our previous study, the interDecadal changes in summer rainfall over East China in the late 1990s are further explored here. The increased local rising motion is implicated as the dominant factor of increased rainfall in the lower Huang-Huai River valley (LHR). Both the observation and numerical experiments using Community Atmosphere Model, version 4 suggest that the negative Pacific Decadal Oscillation (PDO) mode can result in rising anomalies and thus more rainfall in the LHR. The East Asian westerly jet stream (EAWJS) is suggested as a bridge to link the Pacific sea surface temperature anomalies and East Asian summer rainfall. Model results reveal that the negative PDO mode can lead to significant easterly anomalies over East Asia. As a result, the EAWJS is weakened and shifts poleward, which coincides with observed changes in EAWJS after the late 1990s. In addition, weakened and poleward shifted EAWJS can result in an anomalous ascending motion to its south (in the LHR) by modulating the jet-related secondary meridional-vertical circulation. Consequently, rainfall increased in the LHR after the late 1990s. Besides, the positive Atlantic Meridional Oscillation can only induce insignificant changes over East Asia and partly counteract the negative PDO effect there.
Hong S He - One of the best experts on this subject based on the ideXlab platform.
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solar activity global surface air temperature anomaly and Pacific Decadal Oscillation recorded in urban tree rings
Annals of Forest Science, 2007Co-Authors: Xingyuan He, Zhenju Chen, Wei Chen, Xuemei Shao, Hong S HeAbstract:A tree ring width chronology developed from 58 samples taken from Chinese pine trees (Pinus tabulaeformis Carr.) growing in Shenyang city was studied to analyze the effects of solar activity, Global Surface Air Temperature Anomalies (GSATA) and the Pacific Decadal Oscillation (PDO) on annual radial growth. An excellent response of tree rings to solar activity and global environmental change was revealed, indicating that these urban Chinese pine trees are a suitable proxy for Sun-Earth system research despite their location in Shenyang, an industrial city. The information derived from annual growth rings of urban Chinese pine trees coincides with records from undisturbed trees in a natural location, and demonstrates significant synchronous response to solar activity in the periodic bands of 5–8, 10–12 and 20–30 years. The wave signal of tree growth was also affected and amplified by the combined effect of the PDO from 1900 to 2004 and GSATA from 1880 to 2004 with a short lag time, revealing 5–8, 11–13, and 20–23 year oscillatory modes. At 20–30 year timescale, Chinese pines validated the strong GSATA influence signal at 20.8 years, and may be the primary cause of the 20 and 23 year periodic waves of tree rings. Shenyang urban tree ring growth also showed high frequency variation (2—4 y) that may be due to low periodicity of solar activity, GSATA, PDO and local climate variations, especially in the 2–4 years band width.
Koji Yamazaki - One of the best experts on this subject based on the ideXlab platform.
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Decadal scale variation of south asian summer monsoon onset and its relationship with the Pacific Decadal Oscillation
Journal of Climate, 2014Co-Authors: Takeshi Watanabe, Koji YamazakiAbstract:The variation of the summer monsoon onset over South Asia was investigated by using long-term data of the onset over Kerala, India, during the 64-yr period from 1948 to 2011. It was found that the onset over Kerala shows variation on a multiDecadal scale. In early-onset years, the sea surface temperature (SST) anomaly over the northern Pacific Ocean was very similar to the negative Pacific Decadal Oscillation (PDO). The stationary wave train related to the negative PDO reaches into central Asia and generates a warm anomaly, thereby intensifying the land‐sea thermal contrast, which promotes summer monsoon onset over South and Southeast Asia.ThecorrelationbetweentheonsetdateoverKeralaandthePDOhasstrengthenedsince1976.Analysisof zonal wind in the upper-level troposphere for the period 1958‐2002 indicates that the change in the correlation is related to the change in the wave train path. The wave train propagating from the northern Pacific Ocean to western Russia could propagate eastward more easily in 1976‐2002 than in 1958‐75.
