北大西洋涛动和南半球环状模不同位相配置对我国南方夏季降水的协同影响

利用我国气象台站观测资料和再分析格点数据,诊断研究了前期春季(4-5月份)北大西洋涛动(North Atlantic Oscillation,NAO)和南半球环状模(Southern Annular Mode,SAM)在不同位相配置下对我国南方夏季降水异常变化的协同影响作用.分析结果表明,在剔除ENSO最强信号影响后,我国南方夏季降水异常分布显著地依赖于前期春季两个较为独立的年际变率主模态(NAO和SAM)位相的不同配置,即降水异常型主要表现为两个因子单独作用的叠加效果,当前春SAM正位相偏强而NAO负位相偏强时,二者的影响呈现协同正效应,我国南方夏季(6-7月份)降水表现为全区正异常,特别在长江中下游及其以南附近地区最为显著;反之,当前春SAM呈偏强的负位相而NAO偏强的正位相配置时,二者的影响呈现协同负效应,对应我国夏季长江中下游地区降水表现为显著负异常.对其可能的影响机理研究表明,在SAM与NAO位相相反情况下,二者均会通过海气相互作用过程影响到热带大西洋北部海温的异常变化,进而形成协同作用,增强北大西洋海温三极子模态异常信号,从而通过欧亚大陆的遥相关波列对东亚夏季风和我国南方降水产生显著影响.相比之下,当SAM与NAO同位相时,可能表现为抵消效应,不利于北大西洋海温三极子发展,从而削弱对我国南方夏季降水的影响,此方面还有待进一步研究.     

内蒙古东南部地区夏季旱涝的环流特征分析及预测

主要从与内蒙古东南部地区(指赤峰市和通辽市)夏季旱涝关系密切的西太平洋副高、亚洲地区环流和蒙古冷涡三个主要的天气系统入手,分析旱涝年的环流差异。结果表明:⑴夏季蒙古冷涡偏多、副热带高压偏强和北半球盛行经向环流,是造成夏季降水偏多的主要环流形势;⑵冬季北半球极涡纬度和亚洲地区的环流指数对夏季环流形势有一定的指示意义;二者相互动态地影响了夏季旱涝,据此建立夏季旱涝预测模型。经过1995—2008年14年的实际应用,趋势准确率为85.7%。     

丽水山地夏季避暑旅游气候适宜度评价

利用2015—2019年丽水市283个气象观测站的逐日和逐时资料,采用中国气象局“避暑旅游气候适宜度评价方法”行业标准,在研究避暑旅游气候适宜度时空分布的基础上,运用GIS平台建立不同地形条件下避暑旅游适宜度地理推算模型,对丽水避暑旅游气候适宜度进行区划。结果表明,丽水山地夏季避暑旅游气候适宜等级为很适宜,所占区域居绝对比重。6月丽水各站避暑适宜度为很适宜,以海拔800 m为界,随着海拔高度的升高,适宜度先增后减。7—8月避暑旅游气候适宜度随海拔高度增加而提升,300 m以上为较适宜及以上级别。地理推算模型表明,丽水避暑旅游气候适宜度与海拔高度密切相关,庆元适宜及以上等级区域面积占比为全市最高,避暑旅游气候条件最优,其次景宁、遂昌、龙泉避暑旅游气候适宜度也较优越。     

Remote forcing of Indian Ocean warming on Northwest Pacific during E1 Nino decaying years： a FOAM model approach

This paper attempts to analyze in detail the remote influence of the Indian Ocean Basin warming on the Northwest Pacific （NWP） during the year of decaying E1 Nifio. Observation data and the Fast Ocean- Atmosphere coupled Model 1.5 were used to investigate the triggering conditions under which the remote influence is formed between the positive sea surface temperature （SST） anomaly in the North Indian Ocean and the Anomalous Northwest Pacific anticyclone （ANWPA）. Our research show that it is only when there is a contributory background wind field over the Indian Ocean, i,e., when the Indian Summer Monsoon （ISM） reaches its peak, that the warmer SST anomaly in the North Indian Ocean incites significant easterly wind anomalies in the lower atmosphere of the Indo-West tropical Pacific. This then produces the remote influence on the ANWPA. Therefore, the SST anomaly in the North Indian Ocean might interfere with the prediction of the East Asia Summer Monsoon in the year of decaying E1 Nifio. Both the sustaining effect of local negative SST anomalies in the NWP, and the remote effect of positive SST anomalies in the North Indian Ocean on the ANWPA, should be considered in further research.     

基于多点树轮序列的1768—2006年甘肃降水量变化

选择12个树木年轮宽度年表和28个气象站的降水量资料分别建立甘肃树轮宽度场和降水量场。树轮气候响应分析发现树轮宽度场第一主成分与甘肃28个气象站上年7月至当年6月降水量第一主成分有较好相关性,相关系数为0.580 (p<0.001)。利用线性回归模型重建甘肃上年7月至当年6月降水量第一主成分,方差解释量为33.6% (1961—2006年)。在1768—2006年期间甘肃有11个降水量较多的时期(高于多年平均值)和11个降水量较少的时期(低于多年平均值),分别反映了东亚夏季风较强和较弱的时期。同时,降水量重建序列的低值与西北地区极端干旱历史事件有着良好的一致性。空间相关分析表明该重建序列能够表征甘肃大范围的降水量变化,与实测降水量资料的第一主成分空间变化较为一致。多窗谱分析发现,甘肃降水量具有36.6年(95%)、11.2年 (95%)、4.8年(95%)、3.4年 (95%)、3.1年(95%)、2.6年(95%)和2.4年(99%)的周期变化。甘肃降水量与亚洲中纬度西风区、季风区树轮降水量序列之间存在一定的关联性,甘肃降水量变化与季风降水量的关联要大于与西风区降水量。     

QBO 与南海夏季风爆发的关系

利用1979—2001 年ECMWF 再分析资料和NOAA 海温资料,通过相关分析和合成分析等统计方法,分析了平流层准两年周期振荡(QBO)与南海夏季风建立时间的关系。结果表明,QBO 位相与南海夏季风爆发时间有显著的相关关系:超前南海夏季风爆发约18 个月的QBO 西(东)风位相对应着季风爆发时间偏早(晚)。QBO 与南海夏季风爆发的联系要比ENSO 与南海夏季风爆发的联系更密切。      

大兴安岭和长白山地形影响东北夏季降水的数值模拟研究

利用区域数值模式WRF-ARW（V3.9）开展高分辨率数值模拟试验,研究了东北地区大兴安岭和长白山地形对该地区夏季降水的单独和共同影响。结果表明,东北地区两大山脉地形可以显著影响东北及其周边区域的大气环流和降水。大兴安岭和长白山地形的阻挡作用使得夏季偏南气流在两个山脉的迎风坡一侧堆积,引起局地水汽增加并产生上升运动,因此两个山脉的迎风坡一侧降水增加;而在两个山脉的背风坡一侧,局地水汽减少并伴随下沉运动,因此两个山脉的背风坡一侧降水减少。大兴安岭地形的存在使得其东侧到松嫩平原地区夏季降水增加1.09 mm d?1（相较参照试验增幅为30%）,而使其西侧蒙古东部地区夏季降水减少0.69 mm d?1（相较参照试验减幅为24%）;长白山地形的存在使得长白山南侧到朝鲜半岛地区夏季降水增加1.76 mm d?1（相较参照试验增幅为26%）,而使其北侧三江平原地区夏季降水减少0.81 mm d?1（相较参照试验减幅为22%）。当大兴安岭与长白山同时存在时,两者的协同作用会减弱蒙古东部、松嫩平原和朝鲜半岛地区夏季降水的响应,而增强三江平原地区夏季降水的响应。该研究结果对于理解东北地区当代气候的形成具有重要的科学意义。     

A diagnostic analysis of the weakening of West Pacific subtropical anticyclone during the period of South China Sea summer monsoon onset in 1998

The onset of South China Sea summer monsoon in 1998 occurred on May 21st. Using the U.S. National Centers for Environmental Prediction reanalysis data, this paper examines the physical process of the weakening of a subtropical anticyclone in West Pacific during the onset period using the Zwack-Okossi vorticity equation. Results show that during the pre-onset period, the positive vorticity advection in front of an upper tropospheric trough was the most dominant physical mechanism for the increase of the cyclonic vorticity on the 850-hPa layer over the South China Sea and its nearby region. The secondary contribution to the increase of the cyclonic vorticity was the warm-air advection. After the onset, the magnitude of the latent-heat warming term rapidly increased and its effect on the increase of the cyclonic vorticity was about the same as the positive-vorticity advection. The adiabatic term and divergence term contributed negatively to the increase of the cyclonic vorticity most of the time. Thus, the positive vorticity advection is the most important physical mechanism for the weakening of the West Pacific subtropical anticyclone over the South China Sea during the onset period.     

东亚副热带急流与东北夏季降水异常的关系

利用东北地区88个气象站点观测的7、8月(夏季)降水量和NCEP/NCAR再分析资料,分析了东北地区夏季降水与同期东亚副热带西风急流之间的关系,发现东北地区夏季降水异常偏多年,位于青藏高原上空200 hPa西风急流中心强度偏强,东北地区上空急流轴向东北方向倾斜;东北地区夏季降水异常偏少年,青藏高原上空200 hPa西风...     

A chironomid-based reconstruction of summer temperatures in NW Iceland since AD 1650

Few studies currently exist that aim to validate a proxy chironomid-temperature reconstruction with instrumental temperature measurements. We used a reconstruction from a chironomid percentage abundance data set to produce quantitative summer temperature estimates since AD 1650 for NW Iceland through a transfer function approach, and validated the record against instrumental temperature measurements from Stykkishólmur in western Iceland. The core was dated through Pb-210, Cs-137 and tephra analyses (Hekla 1693) which produced a well-constrained dating model across the whole study period. Little catchment disturbance, as shown through geochemical (Itrax) and loss-on-ignition data, throughout the period further reinforce the premise that the chironomids were responding to temperature and not other catchment or within-lake variables. Particularly cold phases were identified between AD 1683–1710, AD 1765–1780 and AD 1890–1917, with relative drops in summer temperatures in the order of 1.5–2°C. The timing of these cold phases agree well with other evidence of cooler temperatures, notably increased extent of Little Ice Age (LIA) glaciers. Our evidence suggests that the magnitude of summer temperature cooling (1.5–2°C) was enough to force LIA Icelandic glaciers into their maximum Holocene extent, which is in accordance with previous modelling experiments for an Icelandic ice cap (Langjökull).