Danqing Huang

Impact of the Middle and Upper Tropospheric Cooling over Central Asia on the Summer Rainfall in the Tarim Basin, China

AbstractThe changes in summer rainfall over the Tarim Basin, China, and the underlying mechanisms have been investigated using the observed rainfall data at 34 stations and the NCEP–NCAR reanalysis data during the period of 1961–2007. Results show that the summer rainfall over the Tarim Basin, which exhibits a significant increasing trend during the last half century, is closely related to the summer middle and upper tropospheric cooling over central Asia. Mechanism analysis indicates that the middle and upper tropospheric cooling over central Asia results in a location farther south of the subtropical westerly jet over western and central Asia with anomalous southerly wind at lower levels and ascending motion prevailing over the Tarim Basin. Such anomalies in the atmospheric circulations provide favorable conditions for the enhanced summer rainfall over the Tarim Basin. Further analysis suggests that the weakened South Asian summer monsoon (SASM) could be potentially responsible for the middle and upper ...

Changes of the Annual Precipitation over Central Asia in the Twenty-First Century Projected by Multimodels of CMIP5

AbstractBased on the outputs of historical and future representative concentration pathway (RCP) experiments produced by 28 models from phase 5 of the Coupled Model Intercomparison Project (CMIP5), future changes in climatic mean, interannual standard deviation (ISD), and long-term trends of the annual precipitation over central Asia (CA) have been estimated. Under different emission scenarios during the twenty-first century, the climatic mean and ISD (long-term trends) of the annual precipitation over CA projected by the five best models’ ensemble mean show very similar (quite different) spatial patterns to those in the twentieth century. Relatively stronger increasing rates (over 3 mm decade−1 in RCP2.6 and over 6 mm decade−1 in RCP4.5 and RCP8.5) are located over northern CA and the northeastern Tibetan Plateau. Compared to the situations in the twentieth century, the climatic mean, ISD, and long-term trends of the projected annual precipitation over most of CA under different emission scenarios exhibi...

The Different Configurations of the East Asian Polar Front Jet and Subtropical Jet and the Associated Rainfall Anomalies over Eastern China in Summer

AbstractTo investigate the concurrent impacts of the East Asian polar front jet (EAPJ) and subtropical jet (EASJ) on the summer rainfall over eastern China, positive (strengthened EAPJ with weakened EASJ) and negative (weakened EAPJ with strengthened EASJ) configurations are identified. In the positive configuration, rainfall decreases in the northern part of eastern China and increases in the southern part, vice versa in the negative configuration. The possible mechanisms maintaining the two jet configurations are further proposed from the perspectives of sea surface temperature (SST) and synoptic-scale transient eddy activities (STEA). In the positive configuration, meridional distributed cold–warm SST anomalies over the eastern North Pacific may induce regional circulation and meridional temperature gradient anomalies, which can strengthen the EAPJ and weaken the EASJ. The central Pacific La Nina–like SST anomalies are related with the Arctic vortexlike anomalies in the stratosphere, which may strength...

The Impact of the East Asian Subtropical Jet and Polar Front Jet on the Frequency of Spring Persistent Rainfall over Southern China in 1997–2011

AbstractSpring persistent rainfall (SPR) over southern China has great impact on its society and economics. A remarkable feature of the SPR is high frequency. However, SPR frequency obviously decreases over the period of 1997–2011. In this study, the possible causes have been investigated from the perspective of the individual and concurrent effects of the East Asian subtropical jet (EASJ) and East Asian polar front jet (EAPJ). A close relationship is detected between SPR frequency and EASJ intensity (but not EAPJ intensity). Associated with strong EASJ, abundant water vapor is transported to southern China by the southwesterly flow, which may trigger the SPR. Additionally, frequencies of both strong EASJ and weak EAPJ events are positively correlated with SPR frequency. Further investigation of the concurrent effect indicates a significant positive correlation between the frequencies of SPR and the strong EASJ–weak EAPJ configuration. Associated with this configuration, southwesterly flow strengthens in ...

Spatial differences in seasonal variation of the upper-tropospheric jet stream in the Northern Hemisphere and its thermal dynamic mechanism

NCEP/NCAR reanalysis daily data from 1951 to 2008 are used in this study to reveal the spatial-asymmetric features in the seasonal variation of the upper-tropospheric jet stream (UTJS) and its thermal dynamic forcing mechanism. The jet occurrence percentage distribution of the UTJS demonstrates a spiral-like pattern in winter, but it is quasi-annular in summer. The jet occurrence percentage in the Eastern Hemisphere is larger than that in the Western Hemisphere, and its maximum area is located further south. The polar front jet stream (PJS) and subtropical jet stream (SJS) can be distinguished over the Northern Africa and Asian regions, whereas only one jet stream can be observed over the Western Pacific and Atlantic Ocean. Furthermore, a single peak pattern is found in the seasonal variation of the SJS occurrence frequency with the highest jet occurrence appearing in winter and the lowest in summer, while a double peak pattern is observed in the seasonal variation of the PJS occurrence, i.e., the jet occurrence reaches its peaks in autumn and spring for the PJS. Based on the thermal wind theory, air temperature gradient and atmospheric baroclinicity are calculated and compared with the jet occurrence variation to explore the thermal dynamic forcing mechanism for the UTJS variation. In addition, synoptic-scale transports of eddy heat and momentum are also calculated. The results indicate that the SJS variation is primarily determined by the air temperature gradient and atmospheric baroclinicity, while the PJS variation is under great influence of the transport of eddy heat and momentum over Northern Africa and East Asia. The UTJS variation over the area from 140E to 70W cannot be well individually explained by the air temperature gradient and atmospheric baroclinicity. Further analysis indicates that UTJS variation over this area is largely under control of combined effect of the transport of eddy heat and momentum as well as the atmospheric baroclinicity.

Recent heterogeneous warming and the associated summer precipitation over eastern China

The recent heterogeneous warming and the associated summer precipitation over eastern China are investigated in this study. In 1990–1999, there exist warming over northwestern Pacific and cooling over eastern equatorial Pacific, which can be quantified by temperature gradient index (TGI). Positive and negative cases are chosen based on TGI. In positive cases, a “southern flood and northern drought” summer rainfall pattern dominates over eastern China. The atmospheric circulations show that associated with the southward receding of western Pacific subtropical high (WPSH), ascending motion accompanied with more water vapor exists over southern China. Furthermore, cold–warm air activity affected by weakened East Asian subtropical jet (EASJ) and strengthened East Asia polar front jet (EAPJ) may also be responsible for this rainfall anomaly pattern. In negative cases, significant positive Meiyu-like rainfall anomaly concentrated over Yangtze Huaihe River Basin (YHRB). Associated with the northward shift of WPSH, more water vapor is transported to YHRB. Additionally, the enhanced ascending motion over YHRB may be related with the northward shift of the EAPJ and westward shift of the EASJ. The results reinforce the notion that the configuration of EASJ and EAPJ in both intensity and position has large impacts on the precipitation variations over eastern China.

Changes in the frequencies of record‐breaking temperature events in China and its association with East Asian Winter Monsoon variability

The daily maximum and minimum temperatures observed at the 1897 meteorological stations of China over the past 60 years (1951–2010) are analyzed in this study to examine the interdecadal variation of frequency for record-breaking event (RBE) of temperature in the context of global warming. The results indicate that the frequency of record-breaking high temperature in the first decade of the 21st century is the highest in the three decades from the 1980s to the 2000s, implying a distinct warming trend. Meanwhile, frequencies of record-breaking low temperature in the 1990s and the beginning of the 21st century are also significant. In particular, the RBEs of low temperature occurred over most of China in the 1990s but concentrated in northern China during the 2000s. To understand why the record low temperatures in northern China are repeatedly broken in the 2000s, the related East Asian Winter Monsoon (EAWM) variability is investigated. The empirical orthogonal function analysis of surface air temperature reveals that the northern mode of the EAWM variability, which is highly associated with the Arctic Oscillation (AO) activities at both interdecadal and interannual timescales, has been intensifying since late 1990s. Corresponding to the intensification of the northern mode of the EAWM variability and the negative phase of AO in the 2000s, the Siberian High and East Asian trough intensify while the polar-front jet stream strengthens and the subtropical westerly jet stream abnormally shifts northward. As a result, anomalously strong cold air masses, originated from Siberia, intrude into East Asia but are blocked by the enhanced northward subtropical westerly jet and cannot reach low-latitude area. Therefore, the extremely strong cold air masses are amassed in mid-high latitudes of East Asia, resulting in RBEs of low temperature in this area.

Recent Winter Precipitation Changes over Eastern China in Different Warming Periods and the Associated East Asian Jets and Oceanic Conditions

AbstractGlobal-mean surface temperature has experienced fast warming during 1985–98 but stabilized during 1999–2013, especially in boreal winter. Climate changes over East Asia between the two warming periods and the associated mechanisms have not been fully understood. Analyses of observation and reanalysis data show that winter precipitation has decreased (increased) over southern (northeastern) China from 1985–98 to 1999–2013. Winds at 300 hPa over East Asia strengthened during 1999–2013 around 30°–47.5°N but weakened to the north and south of it. This change pattern caused the East Asian polar front jet (EAPJ) and the East Asian subtropical jet (EASJ) to shift, respectively, equatorward and poleward during 1999–2013. Associated with these jet displacements, the Siberian high enhanced and the East Asian trough shifted westward. The enhanced Siberian high strengthened the East Asian winter monsoon and weakened southwesterly winds over the South China Sea, leading to precipitation decreases over southern...

Changes of Meiyu system in the future under A1B scenario simulated by MIROC_Hires model

The Meiyu/Baiu/Changma is an important and unique persistent rainfall over East Asian during the northward progress of the East Asian summer monsoon (EASM) from late spring to middle summer. In this study, changes of Meiyu system under global warming are examined by MIROC_Hires coupled model. The results reveal that the Meiyu system becomes weaker in the warmer future: the large precipitation center shifts to northern China; ratio of Meiyu rainfall to total summer precipitation ratio decreases. For the three-dimensional atmospheric circulation, the configuration of upper and lower jets benefits the heavy rainfall located over the northern China, associated with abundant water vapor transporting to northern China. The heterogeneous warming over land and sea may be a possible reason for the changes of Meiyu system. Larger thermal contrast is indicated between the Asian continent and the western Pacific during the Meiyu period, which may result in the enhanced southerly with abundant water vapor arriving at northern China. Therefore, rainfall over Meiyu region may be suspended.

The heterogeneity of Meiyu rainfall over Yangtze–Huaihe River valley and its relationship with oceanic surface heating and intraseasonal variability

Increasing heavy concentrated Meiyu precipitation over the Yangtze–Huaihe river valley (YHRV) during recent years has been previously reported. In fact, the concentrated Meiyu rainfall occurring in a small region or a certain period easily results in floods, thus it is worthy to analyze the heterogeneity of Meiyu rainfall over YHRV. In this study, we use both of precipitation concentration period (PCP) and precipitation concentration degree (PCD) based on vector analysis to identify the heterogeneity of Meiyu rainfall over YHRV. On the climatological mean, the concentrated heavy precipitation occurs in late summer over the Yangtze River Delta, where is usually suffered by floods. The dominant two patterns of PCP and PCD variations are northeast–southwest dipole pattern, homogeneous anomalies and homogeneous variation, north–south dipole pattern, respectively. In addition, the relationship on heterogeneity of Meiyu rainfall with sea surface temperature (SST) and the low level summer intraseasonal oscillation (ISO) are investigated. Two key regions of SST activities are found: Bay of Bengal (BOB) and Equatorial eastern Pacific. From BOB, more abundant water vapor has been brought. On the El Niño-Southern Oscillation variation, it is closely relative with PCD–PC1 during the decaying phase of El Niño, while PCP–PC2 is accompanied with developing phase of La Nina events, suggesting a negative feedback of PCP–PC2 on the Niño3.4 SST, and changes to positive during the later winter. On the ISO activities, the robust regions are located over the high-latitude areas, which are closely related with northeastern cold vortex. The north “cold and dry” air southwardly invaded with the lower-level strong warm air in the rainy area, and easily formed an “upper-wet and lower-dry” unstable layer. Under the trigger of the upward motion, the concentrated heavy rainfall easily occurred over YHRV. In all, the homogeneity variation of the concentrated heavy precipitation over YHRV is closely associated with both of the heating forcing (SST) and dynamical atmospheric forcing (low-level ISO).