河南一次西南涡暴雨的大气排熵指数特征分析

应用耗散结构理论,基于广义相当位温构建大气排熵指数,利用常规观测资料、地面加密自动站雨量资料、NCEP/NCAR 1°×1°再分析资料等,对2008年7月21—23日一次西南低涡东移造成的河南省大范围暴雨过程的大气排熵指数进行诊断分析,结果表明:大气排熵指数的演变与此次西南涡暴雨落区和雨强关系密切,暴雨落在负排熵指数中心偏南一侧,大雨以上降水分布在排熵指数负值中心轴线附近及其偏南侧;强降水开始前,排熵指数明显减小,强降水持续时间与排熵指数低值维持时间联系紧密;雨强不仅与排熵指数低值有关,且与低值维持时间、6h变化量也有密切关系。排熵指数低值中心位置和中心值的强弱变化与该个例中西南低涡中心位置和其强弱变化具有较好一致性。     

冬小麦农田裸温与气温差异分析及其应用

以矮秆代表作物冬小麦为研究对象,利用郑州农业气象试验站2010年10月15日—2011年6月2日农田小气候观测的各层裸温、气温、总辐射和覆盖度资料,采用对比差值、温度垂直梯度等方法统计分析,并对温度对比差值和总辐射曝辐量相关关系和温度的垂直梯度分布特征进行了研究,结果表明:25cm、150cm和300cm高度的日平均裸温和气温变化趋势基本一致,其对比差值呈由小变大趋势;各层裸温和气温的日分布符合温度日变化分布的一般规律,垂直梯度变化比较明显;各层对比差值呈单峰分布,峰值出现在正午12时左右;裸温和气温的对比差值与总辐射曝辐量呈线性相关。裸温与气温的垂直梯度变化有很好的一致性,可利用裸温不同层次间垂直梯度变化特征确定气温传感器合理的安装高度;根据麦田裸温垂直梯度变化特征,考虑到温度防辐射罩高度限制,矮秆作物田间小气候气温应在距离地表面25cm、50cm和150cm高度附近分别设置观测层次。     

利用TMI资料估计西北太平洋热带气旋强度的客观方法

利用2007—2009年热带降雨测量卫星(TRMM)微波成像仪(TMI)观测的亮温资料,建立一种西北太平洋热带气旋强度(Tropical Cyclone,TC)的估计模型,对2010年热带气旋进行独立估计试验,并对估计误差进行分析。结果表明:该模型对强度小于强台风TC的拟合效果较好,均方根误差约为5 m/s,平均绝对误差约为4 m/s;对强台风和超强台风TC的拟合误差较大,均方根误差分别为9.65和6.60 m/s,平均绝对误差分别为7.76和5.49 m/s;对强台风及以上强度的TC,模型的拟合误差在日(夜)间减小(增大),误差最小(大)值为6.00 m/s(11.96 m/s),说明估计值在日(夜)间偏大(小)。     

CMIP5西北太平洋气候变率的模拟评估

利用观测海温资料和CMIP5模式模拟结果分析西北太平洋(120°E~120°W,20~60°N)海表温度的气候态和年代际变化特征。结果表明,所选22个模式可以较好地模拟出西北太平洋海表温度的气候特征及其年际、年代际变化特征;模式模拟的海表温度总体标准偏差在黑潮延伸体区域最大;绝大多数模式能模拟出海表温度的第一EOF模态;西北太平洋海表温度具有较明显的年代际振荡现象,13/22的模式模拟的海表温度存在明显的年代际振荡,同时海表温度气候态的模拟偏差对其周期振荡模拟的影响较大,尤其在黑潮延伸体区域。     

夏季云顶高于对流层顶事件对东亚天气型及上对流层-下平流层大气结构的影响

采用A-Train系列卫星的AURA/MLS水汽、温度资料,CALIPSO/CALIOP云物理资料,结合ECMWF气象再分析资料,分析了东亚地区云顶高于对流层顶事件(Cloud Top Above the Tropopause,CTAT)的区域分布,及其对上对流层-下平流层(Upper Troposphere and Lower Stratosphere,UTLS)水汽和温度结构的影响。结果表明:亚洲季风区的夏季CTAT发生率是30%~55%,为全球最强区域;东北亚的夏季CTAT发生率是15%~20%,为中纬度最强分布区。以CTAT为指标的合成结果表明:15~30°N的东亚-西太平洋UTLS,水汽呈"上干下湿"的异常分布,温度呈"上冷下暖"的异常分布,该结构与该区域热带气旋合成的结果一致,说明热带气旋是该区域CTAT形成的主要天气系统;35~50°N的东北亚UTLS,水汽呈"上干下湿"的异常分布,温度呈"上暖下冷"的异常分布,该结构与该区域温带气旋合成的结果一致,说明温带气旋是该区域CTAT形成的主要天气系统。     

Interannual and Decadal Variations of Surface Solar Radiation over East China in the First Half of the 20th Century

Variability and long-term trends of sunshine duration(SSD) and total cloud cover(TCC) were studied based on surface observations from 10 meteorological stations over East China in the first half of the 20 th century. The correlation coefficients between SSD and diurnal temperature range(DTR), as well as TCC, were analyzed. SSD experienced a significant increasing trend(0.16 h d-1 per decade) from 1908 to 1936, and the maximum brightening was in autumn(0.33 h d-1 per decade). The good agreement between the variability of SSD and DTR, supported by the correlation coefficient between them of 0.72, implies that the SSD measurements were reliable. TCC showed a decreasing trend(-0.93% per decade) and was significantly inversely related to SSD(-0.74), indicating the variation of SSD was attributable to changes in cloud cover. The result was obviously different to that since the 1960 s, when clouds could not account for the decadal trend of surface solar radiation in China.     

Performance of the seasonal forecasting of the Asian summer monsoon by BCC_CSM1.1(m)

This paper provides a comprehensive assessment of Asian summer monsoon prediction skill as a function of lead time and its relationship to sea surface temperature prediction using the seasonal hindcasts of the Beijing Climate Center Climate System Model, BCC_CSM1.1(m). For the South and Southeast Asian summer monsoon, reasonable skill is found in the model's forecasting of certain aspects of monsoon climatology and spatiotemporal variability. Nevertheless, deficiencies such as significant forecast errors over the tropical western North Pacific and the eastern equatorial Indian Ocean are also found. In particular, overestimation of the connections of some dynamical monsoon indices with large-scale circulation and precipitation patterns exists in most ensemble mean forecasts, even for short lead-time forecasts. Variations of SST, measured by the first mode over the tropical Pacific and Indian oceans, as well as the spatiotemporal features over the Niño3.4 region, are overall well predicted. However, this does not necessarily translate into successful forecasts of the Asian summer monsoon by the model. Diagnostics of the relationships between monsoon and SST show that difficulties in predicting the South Asian monsoon can be mainly attributed to the limited regional response of monsoon in observations but the extensive and exaggerated response in predictions due partially to the application of ensemble average forecasting methods. In contrast, in spite of a similar deficiency, the Southeast Asian monsoon can still be forecasted reasonably, probably because of its closer relationship with large-scale circulation patterns and El Niño-Southern Oscillation.     

Simulation of the equatorially asymmetric mode of the Hadley circulation in CMIP5 models

The tropical Hadley circulation (HC) plays an important role in influencing the climate in the tropics and extra-tropics. The realism of the climatological characteristics, spatial structure, and temporal evolution of the long-term variation of the principal mode of the annual mean HC (i.e., the equatorially asymmetric mode, EAM) was examined in model simulations from the Coupled Model Intercomparison Project Phase 5 (CMIP5). The results showed that all the models are moderately successful in capturing the HC's climatological features, including the spatial pattern, meridional extent, and intensity, but not the spatial or temporal variation of the EAM. The possible reasons for the poor simulation of the long-term variability of the EAM were explored. None of the models can successfully capture the differences in the warming rate between the tropical Southern Hemisphere (SH) and Northern Hemisphere (NH), which is considered to be an important driver for the variation of the AM. Most of the models produce a faster warming in the NH than in the SH, which is the reverse of the observed trend. This leads to a reversed trend in the meridional gradient between the SH and NH, and contributes to the poor simulation of EAM variability. Thus, this aspect of the models should be improved to provide better simulations of the variability of the HC. This study suggests a possible reason for the poor simulation of the HC, which may be helpful for improving the skill of the CMIP5 models in the future.     

Synergistic contribution of precipitation anomalies over northwestern India and the South China Sea to high temperature over the Yangtze River Valley

This study explores the characteristics of high temperature anomalies over eastern China and associated influencing factors using observations and model outputs. Results show that more long-duration (over 8 days) high temperature events occur over the middle and lower reaches of the Yangtze River Valley (YRV) than over the surrounding regions, and control most of the interannual variation of summer mean temperature in situ. The synergistic effect of summer precipitation over the South China Sea (SCS) region (18°-27°N, 115°-124°E) and the northwestern India and Arabian Sea (IAS) region (18°-27°N, 60°-80°E) contributes more significantly to the variation of summer YRV temperature, relative to the respective SCS or IAS precipitation anomaly. More precipitation (enhanced condensational heating) over the SCS region strengthens the western Pacific subtropical high (WPSH) and simultaneously weakens the westerly trough over the east coast of Asia, and accordingly results in associated high temperature anomalies over the YRV region through stimulating an East Asia-Pacific (EAP) pattern. More precipitation over the IAS region further adjusts the variations of the WPSH and westerly trough, and eventually reinforces high temperature anomalies over the YRV region. Furthermore, the condensational heating related to more IAS precipitation can adjust upper-tropospheric easterly anomalies over the YRV region by exciting a circumglobal teleconnection, inducing cold horizontal temperature advection and related anomalous descent, which is also conducive to the YRV high temperature anomalies. The reproduction of the above association in the model results indicates that the above results can be explained both statistically and dynamically.