A dark October in Beijing 2016

In recent years, haze pollution events in Beijing have increased sharply, and the haze pollution of Beijing in October 2016 reached a new high. Meteorological conditions are thought to have influences on the haze occurrence, yet the associated atmospheric circulation of haze in October and why the most severe haze pollution occurred in 2016 is still unclear. Here, the authors show through daily observation and reanalysis data that key regions of North Atlantic and North Pacific sea surface temperature （SST） anomalies may be the main factors for this most severe haze event. Since 2013, the SSTs of these two key regions have increased dramatically and reached a peak, which could have induced the severe haze pollution by affecting the Eurasia teleconnection （EU） and the North Pacific Oscillation, with these factors then providing favorable dynamic and thermodynamic conditions for haze development.

North Atlantic forcing of autumn drought in Southwest China

Drought often lasts long and is thus closely related to slowly varying external forcing such as sea surface temperature(SST).Here,based on observed precipitation and SST data along with NCEP-DOE reanalysis data,the possible impacts of North Atlantic SST on drought formation in Southwest China are investigated.Results show that northeast-southwest-orientated dipole SST anomalies in the mid-high latitudes of the North Atlantic are closely related to autumn drought in Southwest China;the linear correlation coefficient between them reaches 0.48 during 1979-2020,significant at the 0.001 level.The dipole SST anomalies trigger southeastward-propagating Rossby waves and induce barotropic cyclonic circulation anomalies over India and the western Tibetan Plateau.This enhances the upward motion in northern India and the western Tibetan Plateau and causes a compensating downdraft,reduced precipitation,and consequent drought formation in Southwest China.

Why does the IOD-ENSO teleconnection disappear in some decades?

Lag correlations between sea surface temperature anomalies （SSTA） in the southeastern tropical Indian Ocean （STIO） in fall and Nifio 3.4 SSTA in the eastern equatorial Pacific in the following fall are subjected to decadal variation, with positive correlations during some decades and negative correlations during others. Negative correlations are smaller and of shorter duration than positive correlations. Variations in lag correlations suggest that the use of the Indian Ocean Dipole （IOD） as a predictor of the E1 Nifio- Southern Oscillation （ENSO） at a lead time of one year is not effective during some decades. In this study, lag correlations between IOD and ENSO anomalies were analyzed to investigate why the IOD-ENSO teleconnection disappears during decades with negative correlations. Anomalies induced by the IOD in the equatorial Pacific Ocean during decades with negative correlations are still present, but at a greater depth than in decades with positive correlations, resulting in a lack of response to oceanic channel dynamics in the cold tongue SSTA. Lag correlations between oceanic anomalies in the west Pacific warm pool in fall and the equatorial Pacific cold tongue with a one-year time lag are significantly positive during decades with negative correlations. These results suggest that oceanic channel dynamics are overwhelmed by ocean- atmosphere coupling over the equatorial Pacific Ocean during decades with negative correlations. Therefore, the Indonesian throughflow is not effective as a link between IOD signals and the equatorial Pacific ENSO.

Unprecedented East Asian warming in spring 2018 linked to the North Atlantic tripole SST mode

An unusually warm East Asia in spring 2018,when exceptionally high surface air temperatures were recorded in large areas of Asia,such as northern China,southern China,and Japan,was investigated based on the ERA-Interim reanalysis.The East Asian warming anomalies were primarily attributed to a tripole mode of North Atlantic SST anomalies,which could have triggered anomalous Rossby wave trains over the North Atlantic and Eurasia through modulating the North Atlantic baroclinic instability.Atlantic-forced Rossby waves tend to propagate eastward and induce anomalously high pressure and anticyclonic activity over East Asia,leading to a northward displacement of the Pacific subtropical high.As a result,descending motion,reduced precipitation,and increased surface solar radiation due to less cloud cover appear over East Asia,accompanied by remarkably warm advection from the ocean to southern China,northern China,and Japan.The transportation of anomalously warm advection and the feedbacks between soil moisture and surface temperature were both favorable for the recordbreaking warmth in East Asia during spring 2018.The seasonal‘memory’of the North Atlantic tripole SST mode from the previous winter to the following spring may provide useful implications for the seasonal prediction of East Asian weather and climate.

Expression responses of five cold tolerant related genes to two temperature dropping treatments in sea cucumber Apostichopus japonicus

Environmental conditions, including ambient temperature, play important roles in survival growth development, and reproduction of the Japanese sea cucumber, Apostichopus japonicus. Low temperatures result in slowed growth and skin ulceration disease. In a previous study, we investigated the effect of low temperature on gene expression profiles inA.japonicus by suppression subtractive hybridization （SSH）. Genes encoding Ferritin, Lysozyme, Hsp70, gp96, and AjToll were selected from a subtracted cDNA library of A. japonicus under acute cold stress. The transcriptional expression profiles of these genes were investigated in different tissues （coelomocyte, respiratory tree, intestine, longitudinal muscle） after exposure to acute and mild temperature dropping treatments. The results show that （1） the five cold-tolerance-related genes were found in all four tissues and the highest mRNA levels were observed in coelomocyte and respiratory tree; （2） under the temperature dropping treatments, three types of transcriptional regulation patterns were observed： primary suppression followed by up-regulation at -2℃, suppressed expression throughout the two treatments, and more rarely an initial stimulation followed by suppression; and （3） gene expression suppression was more severe under acute temperature dropping than under mild temperature dropping treatment. The five cold-tolerance-related genes that were ,distributed mainly in coelomocyte and respiratory tissues were generally down-regulated by low temperature stress but an inverse up-regulation event was found at the extreme temperature （-2℃）.

GEV指数表征的贵州夏旱分布特征及干旱事件的异常环流特征

利用贵州省81个台站的夏季降水资料、NCEP/NCAR再分析资料以及英国哈德雷中心(MOHC)提供的海温资料,基于广义极值分布理论(Generalized Extreme Value Distribution,GEVD),构建了一种新的干旱指数I_(Gev),研究了该指数所表征的贵州夏季干旱的时空分布特征,并对贵州夏季干旱时的环流背景进行了分析.结果表明:贵州省的夏季降水更接近于服从Weibull分布,且省内南部与东北部的夏季降水具有较大的年际变率;贵州夏季GEV干旱指数I_(Gev)具有显著的年际变化,就干旱事件的表征而言,季尺度的GEV干旱指数能够更好地反映贵州干旱事件的分布与发生发展特征;贵州夏季干旱的形成与对流层低层在中南半岛及南海地区上空出现的异常的气旋式环流以及西北太平洋日本南部洋面上空的异常反气旋式环流有关,且异常垂直环流中贵州地区受到显著的下沉运动控制,使得来自于南方的暖湿气流和来源于北方的冷空气较常年均有所偏弱,贵州省成为水汽通量的辐散区,不利于当地降水的形成,从而导致干旱的发生;最后,贵州夏季GEV干旱指数与同期印度洋北部及西北太平洋的海温的存在密切的关系,印度洋及西北太平洋海温的异常偏低可作为预测贵州夏季干旱的一个重要的前期信号.

Asymmetrical response of summer rainfall in East Asia to CO_(2)forcing

Understanding the regional hydrological response to varying CO_(2)concentration is critical for cost-benefit analysis of mitigation and adaptation polices in the near future. To characterize summer monsoon rainfall change in East Asia in a changing CO_(2)pathway, we used the Community Earth System Model(CESM) with28 ensemble members in which the CO_(2)concentration increases at a rate of 1% per year until its quadrupling peak, i.e., 1468 ppm(ramp-up period), followed by a decrease of 1% per year until the present-day climate conditions, i.e., 367 ppm(ramp-down period). Although the CO_(2)concentration change is symmetric in time, the amount of summer rainfall anomaly in East Asia is increased 42% during a rampdown period than that during a ramp-up period when the two periods of the same CO_(2)concentration are compared. This asymmetrical rainfall response is mainly due to an enhanced El Ni?o-like warming pattern as well as its associated increase in the sea surface temperature in the western North Pacific during a ramp-down period. These sea surface temperature patterns enhance the atmospheric teleconnections and the local meridional circulations around East Asia, resulting in more rainfall over East Asia during a ramp-down period. This result implies that the removal of CO_(2)does not guarantee the return of regional rainfall to the previous climate state with the same CO_(2)concentration.

嘉兴地区冬季雷暴天气特征分析

利用1972—2010年嘉兴地区6个测站观测资料及同期NCEP/NCAP日平均再分析资料,对该地区冬季(2月)雷暴天气进行统计和特征分析,发现嘉兴地区冬季典型雷暴发生日低层气温较常年显著偏高,最大偏离层在850 hPa,并在925～850 hPa存在一个垂直恒温层。典型雷暴日的环流特点是:500 hPa乌拉尔山以西地区高压增强,我国东北低槽(涡)较常年加深,同时日本区域为明显正距平。850 hPa长江下游到华南增温明显,而东北地区温度则比常年偏低。对于发生典型冬雷日年份从上年度7月份起赤道太平洋区域有一次逐渐增温并西传过程,至当年3月份结束。分析2月份雷暴发生次数与全球海温关系发现与同月我国东部近海海温有较好正相关,其范围与黑流流经区域基本吻合,另外,与上年9月份南太平洋区域表面海温呈明显负相关性。