Winter precipitation variability over Korean Peninsula associated with ENSO

In this study, winter precipitation variability associated with the El Niño-Southern Oscillation (ENSO) over the Korean Peninsula was investigated using a 5-pentad running mean data because significant correlation pattern cannot be revealed using seasonal-mean data. It was found a considerably significant positive correlation between Niño3 sea-surface temperature and precipitation during early winter (from Mid-November to early-December), when the correlation coefficient is close to 0.8 in early-December; the correlation is distinctively weakened during late winter. It is demonstrated that such sudden intraseasonal change in relation to ENSO is associated with the presence of anticyclonic flow over the Kuroshio extension region (Kuroshio anticyclone). In early winter, there is strong southerly wind over the Korean Peninsula, which is induced by the Philippine Sea anticyclone and Kuroshio anticyclone. However, in January, although the Philippine Sea anticyclone develops further, the Kuroshio anticyclone suddenly disappears; as a result, the impact of ENSO is considerably weakened over the Korean Peninsula. These results indicate that the Kuroshio anticyclone during El Niño peak phase plays a critical role by strongly affecting Northeast Asia climate, including the Korean Peninsula. In addition, it is also found that there are distinctive interdecadal changes of the relationship between ENSO and precipitation over the Korean Peninsula. In particular, the strong correlation in early winter is clearer in the recent 30 years than that in the previous period of 1950–1979.     

西北地区3-9月降水量与ENSO的联系

利用1950-2005年全球陆地月平均降水资料,分析了中国西北地区3-9月平均降水量(Rm)与ENSO的统计关系.结果表明:在全球变暖背景下,厄尔尼诺当年(次年)西北地区Rm偏少(偏多)的关系依然稳定存在,并且随着全球增暖,该关系表现得更稳定.西北地区,尤其是西北地区东部是同纬度带主要干旱半干旱区中Rm与ENSO联系最紧密、最稳定的区域.北半球主要干旱半干旱区中,厄尔尼诺当年Rm偏少,次年Rm偏多的关系仅存在于中国北部地区.我国西北地区东部厄尔尼诺事件当年(次年)Rm偏少(偏多),我国西北地区西部38°N以南厄尔尼诺事件当年(次年)Rm偏多(偏少),存在着明显的东西部差异.     

Interannual variability of summer monsoon precipitation over the Indochina Peninsula in association with ENSO

The interannual variability of summer monsoon precipitation (1979–2011) over the Indochina Peninsula (ICP) is characterized using the first empirical orthogonal function of 5-month total precipitation (May to September). The leading mode, with a monopole pattern, accounts for 30.6 % of the total variance. Dynamic composites and linear regression analysis indicate that the rainy season precipitation over the ICP is linked to El Niño–Southern Oscillation (ENSO) on interannual scales. The preceding winter [D(?1)JF(0)] negative sea surface temperature (SST) over the Niño-3.4 region is predominantly correlated with the rainy season precipitation over the ICP. Notably, the simultaneous correlation between remote SST anomalies in the Niño-3.4 region and the rainy season precipitation over the ICP is weak. The interannual variation of tropical cyclones modulated by ENSO is a significant contributing factor to the rainy season precipitation over the ICP. However, this relationship is not homogeneous over the ICP if ENSO is considered. Before removing the ENSO signal, enhanced precipitation is present over the northeastern part of the ICP and reduced precipitation appears in the western ICP, especially in coastal areas. In contrast, after removing ENSO, only a minor significant positive precipitation anomaly occurs over the northeastern part of the ICP and the negative anomaly appears particularly in the western and eastern coastal regions. The results obtained through the present study are useful for our understanding of circulation mechanisms and provide information for assessing the ability of regional and global climate models in simulating the climate of Southeast Asia.     

Precipitation over eastern South America and the South Atlantic Sea surface temperature during neutral ENSO periods

The dominant mode of coupled variability over the South Atlantic Ocean is known as “South Atlantic Dipole” (SAD) and is characterized by a dipole in sea surface temperature (SST) anomalies with centers over the tropical and the extratropical South Atlantic. Previous studies have shown that variations in SST related to SAD modulate large-scale patterns of precipitation over the Atlantic Ocean. Here we show that variations in the South Atlantic SST are associated with changes in daily precipitation over eastern South America. Rain gauge precipitation, satellite derived sea surface temperature and reanalysis data are used to investigate the variability of the subtropical and tropical South Atlantic and impacts on precipitation. SAD phases are assessed by performing Singular value decomposition analysis of sea level pressure and SST anomalies. We show that during neutral El Niño Southern Oscillation events, SAD plays an important role in modulating cyclogenesis and the characteristics of the South Atlantic Convergence Zone. Positive SST anomalies over the extratropical South Atlantic (SAD negative phase) are related to increased cyclogenesis near southeast Brazil as well as the migration of extratropical cyclones further north. As a consequence, these systems organize convection and increase precipitation over eastern South America.     

Decadal Changes in Climatological Intraseasonal Fluctuation of Subseasonal Evolution of Summer Precipitation over the Korean Peninsula in the mid-1990s

Decadal changes in the subseasonal evolution and the phase-locked climatological intraseasonal fluctuation of summertime rainfall over the Korean Peninsula before and after the mid-1990s are investigated.The activity and the migration speed of the monsoon rain band over the East Asian region are altered in the recent decade,resulting in the drier conditions in late spring and the earlier onset of Changma.In early August when a climatological monsoon break was clear in the earlier decade,the precipitation has increased dramatically with a meridional coherency.The response to the enhanced convection over the South China Sea and southeastern China provides a favorable condition for more precipitation in early August through the changes in moisture transport and tropical cyclone passage.     

Effect of ENSO on landfalling tropical cyclones over the Korean peninsula

The effect of ENSO on landfalling tropical cyclones (TCs) over the Korean Peninsula is examined. It is found that although the landfalling frequency does not show any statistically significant difference among ENSO phases, the landfalling tracks are shifted northward in response to the decrease in Niño-3.4 index. In the neutral ENSO phase, many TCs pass through mainland China before landfalling over the Korean Peninsula due to the westward expansion of the western North Pacific subtropical high. Therefore, the landfalling TC intensity over the Korean Peninsula in the neutral phase is similar to that in the La Niña phase because more than half of those TCs made landfall over mainland China. However, it is found that the preceding winter ENSO phases are not related to the landfalling TC activity over the Korean Peninsula during summer.     

Projected Heat Wave Characteristics over the Korean Peninsula During the Twenty-First Century

Climate change is expected to increase temperatures globally, and consequently more frequent, longer, and hotter heat waves are likely to occur. Ambiguity in defining heat waves appropriately makes it difficult to compare changes in heat wave events over time. This study provides a quantitative definition of a heat wave and makes probabilistic heat wave projections for the Korean Peninsula under two global warming scenarios. Changes to heat waves under global warming are investigated using the representative concentration pathway 4.5 (RCP4.5) and 8.5 (RCP8.5) experiments from 30 coupled models participating in phase five of the Coupled Model Inter-comparison Project. Probabilistic climate projections from multi-model ensembles have been constructed using both simple and weighted averaging. Results from both methods are similar and show that heat waves will be more intense, frequent, and longer lasting. These trends are more apparent under the RCP8.5 scenario as compared to the RCP4.5 scenario. Under the RCP8.5 scenario, typical heat waves are projected to become stronger than any heat wave experienced in the recent measurement record. Furthermore, under this scenario, it cannot be ruled out that Korea will experience heat wave conditions spanning almost an entire summer before the end of the 21st century.     

Strategy for the meteorological and environmental airborne observations over the Korean Peninsula

Aircraft campaigns for the meteorological and environmental research have been conducted in regional and global scales. The aircraft is increasingly considered as one of the best platforms to get the atmospheric three-dimensional information, especially over sea. We discuss the airborne observation plan and payloads designed for the aircraft campaigns over the Korean Peninsula. The main goals of the campaigns are to (i) conduct precipitation (snow) enhancement experiments with observations of the microphysical properties of clouds, dominantly in winter, (ii) monitor the severe weather generally in summer, (iii) characterize the climate change composition and the outflow of pollution from the Asian continent of the troposphere over the Korean Peninsula generally in spring or fall, and (iv) validate satellite and ground-based remote measurements of tropospheric composition generally in spring or fall.     

昌都地区汛期降水与ENSO事件的关系

利用昌都地区7站1980~2010年逐日、逐月降水资料与NCEP再分析资料,对昌都地区汛期(5~9月)降水进行分析,分析结果表明:昌都地区汛期降水在厄尔尼诺-南方涛动(NESO)事件的不同阶段存在显著差异,在ENSO发展阶段昌都地区汛期降水除八宿县外,各地均偏少。影响逐月降水的原因在于降水日数的变化,降水偏多月份中雨与大雨的降水日数增多,大雨日数增加明显;降水偏少月份,中雨与小雨降水日数偏少。对ENSO发展阶段和常年的大气环流对比得出,南亚高压偏东是影响汛期降水偏少的主要原因。     

A global analysis of austral summer ocean wave variability during SAM–ENSO phase combinations

Anticipating and mitigating wave-related hazards rely heavily on understanding wave variability drivers. Here, we describe wave conditions related to concurrent Southern Annular Mode (SAM) and El Niño–Southern Oscillation (ENSO) phases during the austral summer. To identify such conditions, significant wave height (Hs) and peak wave period (Tp) daily anomalies were composited during different SAM–ENSO phase combinations over the last four decades (1979–2018). Surface wind anomalies were also composited to assist in the interpretation of wave conditions. The composites show significant wave variability across all ocean basins and in several semi-enclosed seas throughout the different SAM–ENSO phase combinations. The Southern, Indian, and Pacific Oceans generally experience the strongest Tp anomalies during combinations of SAM phases with El Niño, and the weakest Tp anomalies during combinations of SAM phases with La Niña. The anomalously large waves observed in the south-western Pacific, Tasman Sea, and the Southern Ocean, previously ascribed to ENSO conditions, seem to be instead associated with the SAM variability. SAM-related atmospheric conditions are found to be able to modulate the intensity of ENSO-related winds over the South China Sea, which, in turn, alter the magnitude of waves in that region. These and other wave anomaly structures described here, especially those contrasting the behaviour expected for a given ENSO phase, such as the one found along the California coast, stress the importance of understanding relationships between wave parameters and climate patterns interactions.     

Winter daily precipitation variability over the South West Peninsula of England

Summary Daily precipitation totals for five consecutive winters (1995–99) were obtained for 127 stations in Devon and Cornwall to explore spatial variations in rainfall. This dataset was assembled with the explicit aim of assessing the appropriateness of current arrangements for daily rainfall forecasts in the SW Peninsula of England. Firstly, the extent to which fundamental geographic variables determine precipitation was investigated by correlating each station’s mean wet day amount (WDA) and percentage of wet days (PERWET) with altitude, latitude, longitude and distance from the coast. Altitude emerged as the most important control on precipitation, with a two-variable multiple linear regression model containing altitude and latitude being able to explain 39.3% (29.8%) of the variance in WDA (PERWET) values. The main spatial modes of variability in the region’s precipitation field were identified by using S mode principal components analysis (PCA). Six PCs were statistically significant and explained 83.4% of the geographic variance in precipitation over Devon and Cornwall. The components were interpreted physically by examining the synoptic flow environment (pressure and wind anomalies) on days with high positive and negative PC scores. Explaining 25.1% of the variance, the most important pattern (PC1) depicts a location’s degree of exposure or shelter in a moist, unstable W–NW airflow. The higher PCs describe modes of variability that accentuate rainfall in East Devon (PC2), Cornwall (PC3), Dartmoor and Bodmin Moor (PC4), South Devon (PC5), and North Cornwall and NW Devon (PC6) relative to other areas of the Peninsula. Finally, a winter precipitation regionalisation was derived by applying agglomerative hierarchical cluster analysis to the PC loadings of the significant components. In most cases, the six coherent precipitation regions do not reflect the familiar administrative or topographic areas used for forecasting, suggesting that forecasts issued on such a basis are likely to be insufficiently detailed and misleading.     

A Comparison of GPS- and NWP-derived PW Data over the Korean Peninsula

Precipitable Water (PW) derived from Global Positioning System (GPS)measurements and numerical weather prediction (NWP) model analysis data werecompared to further evaluate the efficacy of applying GPS-derived PW to theNWP model. The spatial and temporal variations of GPS-derived PW during arainfall event were also examined.GPS-derived PW measurements show good agreement with the behavior of watervapor at a high spatial resolution during the analysis period. Temporalanomalies of GPS-derived PW moving along with the front are successfullydetected by the GPS array. Large positive anomalies of GPS-derived PW areindicated immediately before a rainfall event, and the intensity of thesepositive anomalies do not seem to decrease significantly as theprecipitation system passes. These results indicate that the Korean GPSnetwork may have great potential as a PW sensor over the Korean Peninsula.In contrast with GPS-derived PW, NWP-derived PW shows negative biases. Thesebiases appear to stem mainly from the differences between modeled and actualGPS site elevations, as GPS sites were generally located at elevations lowerthan those employed by the NWP model. However, there still exists adiscernable dry bias after a PW correction is applied to NWP-derived PW.GPS-derived PW better reflects the spatial and temporal moisture variationsof precipitation systems, as compared to NWP-derived PW. These resultsprovide entirely new information for improving the regional NWP system,since GPS-derived PW produced with data from the Korean GPS network may beincorporated into the NWP model to improve rainfall forecasts.     

ENSO对中国南方降水低频变率的可能影响

利用1979—2012年Hadley中心海表温度、中国2 474个台站逐日降水和NCEP/NCAR全球再分析资料,分析了不同类型ENSO事件秋冬季和次年春季中国南方地区10~30 d降水低频变率的变化特征。结果表明,中国南方地区10~30 d降水低频变率对不同类型ENSO事件的响应存在显著的季节差异。EP型El Ni1o的冬季和次年春季,低频降水变率显著增强; CP型El Ni1o秋冬季低频降水强度呈现相反的异常,秋季低频降水偏弱,而冬季则偏强; La Ni1a事件期间中国南方低频降水变率的变化较小且不稳定。进一步分析发现,ENSO对南方地区10~30 d低频降水变率的影响与西北太平洋地区季节平均大气环流背景场对ENSO的响应密切相关。相比正常年份,EP型El Ni1o冬春季菲律宾反气旋性异常环流的强度较强且范围较大,其西侧的异常西南风向中国南方地区输送了大量水汽,从而有利于低频降水的增强; CP型El Ni1o年秋季西北太平洋表现为气旋性环流异常,抑制了热带水汽向东亚大陆的输送,而冬季却产生了与EP型El Ni1o年类似的异常反气旋环流,只是强度有所减弱,因此中国南方地区低频降水强度在秋冬季呈相反异常。La Ni1a年菲律宾附近虽然存在气旋性环流异常,但强度较弱,因而我国南方地区低频降水变率的响应也较弱。     

广西极端降水事件气候态及其对ENSO的潜在响应

本研究利用日本人文与自然研究所和日本气象厅气象研究所发布的0.25°×0.25°亚洲区域高解析度观测集成降水数据（APHRODITE),并结合NOAA发布的Niño3.4区海温指数和美国国家环境预报中心NCEP再分析数据,分析了广西地区不同极端降水事件的气候平均态和气候倾向率的时空分布,并通过快速傅里叶变换方法分析了不同极端降水逐月区域平均值的气候变率。在此基础上,对ENSO不同位相的周期交替对广西不同极端降水的逐月区域平均值周期的影响及其滞后性进行交叉相关分析,并得出不同极端指标对不同ENSO位相的潜在响应及其显著性特征。结果表明1951-2007年广西全区除无雨日数呈现增加趋势外,暴雨日数、连续干期和湿期均呈减少趋势。不同极端指标在3~7 a的傅里叶谱周期内均呈现显著的周期性变率,说明其与ENSO的潜在联系。交叉相关分析表明Niño3.4指数与无雨日数（暴雨日数）和连续干（湿）期具有显著的负（正）相关特征,其滞后期约为6~18个月,但不同极端指标与ENSO相关程度具有差异。通过滞后6~18个月的平均Ni?o3.4指数所确定的不同ENSO位相,发现相对于拉尼娜冷位相,广西无雨日数（暴雨日数）和连续干（湿）期在厄尔尼诺暖位相下总体呈现减少（增多),但该响应的统计显著性在全区分布不普遍。这可能与湿静力稳定度、低层温度露点差与中层湿位涡正压项等热力因子的响应不利于极端降水增加有关。     

ENSO与南海SST关系的年代际变化

基于NOAA重建的海面温度（sea surface temperature, SST）资料和NCEP再分析大气资料,研究了ENSO（El Niño-Southern Oscillation）与南海SST关系的年代际变化。结果表明：ENSO影响南海SST的冬、夏季“双峰”现象发生了显著的年代际变化,即冬季的“峰值”自20世纪80年代显著减弱,而夏季的“峰值”稳定持续且在20世纪70年代之后增强;冬季“峰值”的减弱可能与冬季西北太平洋反气旋的年代际变化有关,夏季“峰值”的维持和增强可能与20世纪70年代之后印度洋SST“电容器”效应的增强有关。     

ENSO发展和衰亡阶段中非线性项的作用

利用哈得来中心海表温度（HadISST）和美国马里兰大学海洋同化（Simple Ocean Data Assimilation,SODA 2.2.4）数据集,分析了1979-2015年赤道太平洋地区海表温度异常的偏度特征;并通过诊断混合层热量收支平衡方程着重探讨了非线性项在不同类型ENSO发展衰亡过程中起的不同作用。研究结果表明,中部型厄尔尼诺和拉尼娜事件的偏度很弱,且符号相反、强度相当,而东部型厄尔尼诺的偏度为很强的正值,即ENSO的强度非对称性主要来自东部型厄尔尼诺的贡献,中部型厄尔尼诺和拉尼娜的海表温度异常呈现准对称特征。在ENSO事件的发展阶段,非线性项对东部型厄尔尼诺和拉尼娜均有很强的正贡献,而对中部型厄尔尼诺的正贡献相对较弱,这会促进东部型厄尔尼诺强度的增强而抑制拉尼娜振幅的发展,从而有利于ENSO强度非对称性的产生;在ENSO事件的衰亡阶段,非线性项对拉尼娜维持正贡献但强度大为减弱,对东部型厄尔尼诺和中部型厄尔尼诺的衰减则分别起促进和抑制作用,这可能是东部型厄尔尼诺衰减速度较快而中部型厄尔尼诺衰减速度较慢的重要原因之一。      

Snowstorm over the Southwestern Coast of the Korean Peninsula Associated with the Development of Mesocyclone over the Yellow Sea

This study investigates the characteristics of a heavy snowfall event over the southwestern part of the Korean Peninsula on 4 December 2005. The snowstorm was a type of mesoscale maritime cyclone which resulted from barotropic instability, and diabatic heating from the warm ocean in continental polar air masses. Based on surface observations, radiosonde soundings, MTSAT-1R satellite data and the 10-km grid RDAPS （Regional Assimilation and Prediction System based on the PSU/NCAR MM5） data, the evolution of the mesocyclone is explained by the following dynamics; （1） In the initial stage, the primary role in the cyclogenesis process of the mesocyclone is a barotropic instability in the horizontal shear zone. （2） In the developing stage, the mesocyclone moves and deepens into a baroclinic zone corresponding to the surface heating and moistening. （3） In the mature stage, it is found that the mesocyclone is intensified by the destabilization caused by enhanced low-level heating and condensation, the moisture flux convergence, and the interaction between upper and lower-level potential vorticity anomalies. We suggest that a checklist with stepwise indicators responsible for development be prepared for the forecasting of heavy snowfall over the southwestern part of the Korean Peninsula.     

ENSO事件对珠海市降水的影响

统计1960~2006年间的ENSO事件,将厄尔尼诺细分为早发型、晚发型及东部型、中部型。统计珠海市近47年的逐日降水资料,通过距平分析及显著性检验方法,研究ENSO影响期间珠海市降水的变化特征,降水异常与ENSO的关系,发现ENSO影响期间珠海市各时段降水出现了一定的异常,并且不同类型厄尔尼诺事件的影响存在差异,但并不是每种异常都与ENSO关系密切。结果表明:厄尔尼诺当年和次年及拉尼娜年珠海市年降水量明显偏多,早发型及东部型厄尔尼诺当年前汛期降水量明显偏多,早发型厄尔尼诺年当年汛期降水量显著偏多。但晚发型厄尔尼诺次年前汛期降水量却比常年明显偏少。