东亚中纬度夏季陆面增暖与土壤湿度异常的联系

利用1979—2015年ERA-Interim再分析土壤湿度、云量资料,NCEP/NCAR再分析环流资料和CPC土壤湿度资料,分析了东亚中纬度夏季陆面热力异常的时空分布特征及其与前期春季土壤湿度异常的联系,探讨了前期春季土壤湿度影响东亚中纬度夏季陆面增暖的可能途径。结果表明,东亚中纬度夏季土壤表层温度呈全区一致增暖趋势,其中贝加尔湖及以南地区温度变化最剧烈、增暖最迅速,且1990年代中期前后存在一个明显由冷向暖的年代际转变。进一步分析发现,春、夏季西西伯利亚到贝加尔湖北部地区的土壤湿度与夏季贝加尔湖及以南地区的土壤表层温度在年代际和年际尺度上均存在紧密联系:西西伯利亚到贝加尔湖北部地区土壤湿度异常偏高,通常对应贝加尔湖及南部地区夏季土壤表层温度偏高。西西伯利亚到贝加尔湖北部地区春、夏土壤湿度异常可以引起夏季大气环流异常,从而对东亚夏季中纬度陆面热力异常产生影响:春、夏土壤湿度偏高时,贝加尔湖及其南部地区上空位势高度为正异常,对应为反气旋性异常环流,云量减少,有利于东亚中纬度陆面增暖;反之,则对应为气旋性异常环流,不利于陆面增暖。     

Soil moisture influence on summertime surface air temperature over East Asia

Soil moisture influence on surface air temperature in summer is statistically quantified across East Asia using the Global Land Data Assimilation System soil moisture and observational temperature. The analysis uses a soil moisture feedback parameter computed based on lagged covariance ratios. It is found that significant negative soil moisture feedbacks on temperature mainly appear over the transition zones between dry and wet climates of northern China and Mongolia. Over these areas, the feedbacks account for typically 5–20% of the total temperature variance, with the feedback parameter of ?0.2°C to ?0.5°C (standardized soil moisture)^?1. Meanwhile, positive feedbacks may exist over some areas of Northeast Asia but are much less significant. These findings emphasize the importance of soil moisture-temperature feedbacks in influencing summer climate variability and have implications for seasonal temperature forecasting.     

Land response to atmosphere at different resolutions in the common land model over East Asia

Towards a better understanding of hydrological interactions between the land surface and atmosphere, land surface models are routinely used to simulate hydro-meteorological fluxes. However, there is a lack of observations available for model forcing, to estimate the hydro-meteorological fluxes in East Asia. In this study, Common Land Model (CLM) was used in offline-mode during the summer monsoon period of 2006 in East Asia, with different forcings from Asiaflux, Korea Land Data Assimilation System (KLDAS), and Global Land Data Assimilation System (GLDAS), at point and regional scales, separately. The CLM results were compared with observations from Asiaflux sites. The estimated net radiation showed good agreement, with r =0.99 for the point scale and 0.85 for the regional scale. The estimated sensible and latent heat fluxes using Asiaflux and KLDAS data indicated reasonable agreement, with r = 0.70. The estimated soil moisture and soil temperature showed similar patterns to observations, although the estimated water fluxes using KLDAS showed larger discrepancies than those of Asiaflux because of scale mismatch. The spatial distribution of hydro-meteorological fluxes according to KLDAS for East Asia were compared to the CLM results with GLDAS, and the GLDAS provided online. The spatial distributions of CLM with KLDAS were analogous to CLM with GLDAS, and the standalone GLDAS data. The results indicate that KLDAS is a good potential source of high spatial resolution forcing data. Therefore, the KLDAS is a promising alternative product, capable of compensating for the lack of observations and low resolution grid data for East Asia.     

土壤湿度对东亚夏季气候潜在可预报性影响的数值模拟

利用全球大气环流模式NCARCAM3进行了在给定的观测海温条件下的22a（1979—2000年）5—8月的2组集合试验。运用方差分析方法,分析了在气候态和年际变化的表层土壤湿度情况下,CAM3模式模拟的东亚夏季气候潜在可预报性及其差异。结果表明：在给定的观测海温条件下,采用气候态的土壤湿度时,CAM3模式模拟的东亚夏季气候的潜在可预报性偏低;而采用年际变化的土壤湿度时,模拟的夏季气候潜在可预报性有所提高,尤其是在中国西北地区;后者模拟的中国西北地区夏季降水和气温的潜在可预报性比前者的模拟结果提高0．1以上。其原因可能是：采用年际变化的土壤湿度时,模式可以更好地模拟出中国西北地区的地表蒸发量和湍流热通量的年际变化,进而使得模式对该地区夏季气候的预报技巧得到提高。     

Use of a land surface model to evaluate the observed soil moisture of grassland at the Tongyu reference site

A land surface model driven by the continuous three-year observed meteorological data with a time interval of 30 minutes at the Tongyu station, a reference site of the Coordinated Enhanced Observing Period （CEOP）, was used to evaluate the observation bias of soil moisture （SM） data and analyze the variation of SM at different time scales. The saline-alkaline soil of the grassland at the Tongyu site makes the measured SM too high, especially in boreal summer of 2003-05. The simulated annual mean SM has the lowest value in 2004 and its three-year variation corresponds to the change of precipitation, whereas the observation shows the increasing trend from 2003 to 2005. Compared to the variation range between -60% and 40% for the anomaly percentage of the simulated daily mean SM during May-October of 2004, the measured data show the higher values more than 40%. The magnitude of the variation trend of the observed daily mean SM in 2003 and 2005 is generally consistent with the simulation. The largest deficiency for the soil moisture observation of the grassland is the overestimated value in the drought year with less precipitation. The simulated monthly mean SM has the lowest value in March due to the large contribution of evaporation relative to precipitation and this phenomenon can not be reproduced in the observation.     

陆面热力异常与东亚夏季中纬度气旋年代际变化的联系

基于欧洲中期预报中心的再分析数据ERA-interim,利用统计学方法分析了1979—2013年期间东亚中纬度地区气旋生成频率和陆面热力异常的年代际变化及两者的可能联系。结果表明,东亚中纬度地区存在气旋活动频繁的气旋源地,该地区的温带气旋生成频率具有明显的年代际变化,1990年之前气旋生成频率偏多,1990s至今偏少,而且东亚中纬度地区陆面热力异常的变化有明显的年代际增暖信号;进一步的分析发现,东亚夏季中纬度气旋活动的年代际变化与陆面异常异常之间存在密切的联系,东亚中纬度地区陆面年代际增暖,是引起温度气旋活动年代际减弱的一个重要原因。由于陆面增暖的非均匀性,在50°N以北存在一个影响中纬度气旋生成频率的关键区,关键区陆面的年代际异常增暖,导致气旋源地温度经向梯度减弱,大气斜压性随之减弱,从而使得气旋生成频率年代际减少。     

厄尔尼诺衰减年东亚夏季大气环流和降水异常的耦合模式后报试验

利用中国科学院大气物理研究所大气科学和地球流体力学数值模拟国家重点实验室(LASG)新一代耦合气候模式(FGOALS)进行了气候异常季节后报试验,通过对1982—2005年7个个例的分析,探讨了厄尔尼诺衰减年夏季东亚大气环流和降水异常发生的物理机制。分析结果表明:FGOALS可以模拟出厄尔尼诺衰减年夏季相关气候场的异常态特征,表现为在西北太平洋为负海温异常,在热带印度洋为正海温异常,从而导致西北太平洋地区大气中低层异常反气旋环流的维持,其反气旋的西南部及西部的偏南及西南气流造成中国长江中下游地区降水的异常增多。在提前3—9个月的预测模拟中,模式可以模拟出气候场的异常演变,随着预测时间的延长,产生局地耦合的西北太平洋海表温度异常信号变弱,使得模拟出的西北太平洋反气旋异常偏弱、中心东移,从而导致影响东亚降水的气候场的异常变弱,降水异常区偏东。模拟结果也揭示出,西北太平洋海表温度负异常是厄尔尼诺异常信号的转换模态,并且,由于局地海-气相互作用,热带海温异常信号可以持续到第2年夏季,从而引起东亚大气环流和降水异常。对于东亚降水的季节预测出现误差可能是模式对ENSO的模拟偏差造成的,随着预测时间延长,模式模拟的厄尔尼诺信号偏弱,这将使得海表温度异常偏弱,同时相关物理场的异常响应也减弱。     

Derivation of regression coefficients for sea surface temperature retrieval over East Asia

Among the regression-based algorithms for deriving SST from satellite measurements, regionally optimized algorithms normally perform better than the corresponding global algorithm. In this paper,three algorithms are considered for SST retrieval over the East Asia region (15°-55°N, 105°-170°E),including the multi-channel algorithm (MCSST), the quadratic algorithm (QSST), and the Pathfinder algorithm (PFSST). All algorithms are derived and validated using collocated buoy and Geostationary Meteorological Satellite (GMS-5) observations from 1997 to 2001. An important part of the derivation and validation of the algorithms is the quality control procedure for the buoy SST data and an improved cloud screening method for the satellite brightness temperature measurements. The regionally optimized MCSST algorithm shows an overall improvement over the global algorithm, removing the bias of about -0.13℃ and reducing the root-mean-square difference (rmsd) from 1.36℃ to 1.26℃. The QSST is only slightly better than the MCSST. For both algorithms, a seasonal dependence of the remaining error statistics is still evident. The Pathfinder approach for deriving a season-specific set of coefficients, one for August to October and one for the rest of the year, provides the smallest rmsd overall that is also stable over time.     

Assessment of the biospheric contribution to surface atmospheric CO2 concentrations over East Asia with a regional chemical transport model

A regional chemical transport model, RAMS-CMAQ, was employed to assess the impacts of biosphere–atmosphere CO2 exchange on seasonal variations in atmospheric CO2 concentrations over East Asia. Simulated CO2 concentrations were compared with observations at 12 surface stations and the comparison showed they were generally in good agreement. Both observations and simulations suggested that surface CO2 over East Asia features a summertime trough due to biospheric absorption, while in some urban areas surface CO2 has a distinct summer peak, which could be attributed to the strong impact from anthropogenic emissions. Analysis of the model results indicated that biospheric fluxes and fossil-fuel emissions are comparably important in shaping spatial distributions of CO2 near the surface over East Asia. Biospheric flux plays an important role in the prevailing spatial pattern of CO2 enhancement and reduction on the synoptic scale due to the strong seasonality of biospheric CO2 flux. The elevation of CO2 levels by the biosphere during winter was found to be larger than 5ppm in North China and Southeast China, and during summertime a significant depletion( 7 ppm) occurred in most areas,except for the Indo-China Peninsula where positive bioflux values were found.     

东亚地区冬季地面气温延伸期概率预报研究

利用TIGGE资料中的ECMWF、NCEP、UKMO三个中心集合预报系统以及由此构成的多中心集合预报系统所提供的地面2 m气温10~15 d延伸期集合预报产品,建立贝叶斯模式平均(Bayesian Model Averaging,BMA)概率预报模型,对东亚地区冬季地面气温进行延伸期概率预报研究。采用距平相关系数、均方根误差、布莱尔评分、等级概率评分等指标分别对BMA确定性结果与概率预报进行评估。结果表明,BMA方法明显地改进了原始集合预报结果,预报技巧优于原始集合预报,且多中心BMA预报优于单中心BMA预报,最佳滑动训练期取35 d。BMA预报为气温的延伸期概率预报提供了更合理的概率分布,定量描述了预报的不确定性。     

中国夏季气温对东亚土壤湿度异常响应的统计评估

基于欧亚夏季土壤湿度变化特征及其与中国夏季气温的相关分析,选取东亚地区作为土壤湿度异常影响中国夏季气温的陆面关键区,采用广义平衡反馈分析方法(GEFA)探讨了我国夏季气温对东亚地区土壤湿度异常的可能响应,并初步讨论了相关的物理过程。结果表明:中国夏季气温与东亚地区初夏和同期的土壤湿度异常具有密切的联系;进一步分析表明,夏季气温距平场对土壤湿度第一模态的响应最显著:当东亚中纬度及我国东部地区土壤湿度异常偏干时,夏季气温表现为一致增暖;而土壤湿度第二模态对长江流域至我国西部地区的气温有较弱的强迫作用;气温对第三模态的响应主要表现为华南地区的显著降温。并以对气温影响最为显著的土壤湿度异常第一模态为例,初步探讨了气温对土壤湿度异常响应的可能物理过程。当贝加尔湖以南以及我国东部的土壤偏干时,地表异常加热容易引起我国北方高层大气出现明显正异常和低层的反气旋性异常环流,上述环流异常容易导致温度偏高,同时不利于该区域降水的发生,进而导致土壤湿度偏低,上述正反馈机制可能是该区域土壤湿度与大气之间联系的一种可能途径。     

大尺度土地利用变化对东亚地表能量、水分循环及气候影响的敏感性试验

利用NCAR大气环流模式CAM4.0,针对潜在植被和当代植被的分布情形进行了两组25 a的积分试验,探讨了土地利用变化对东亚地区地表能量平衡、水分循环和气候的可能影响.结果表明:以森林退化、农田迅速增加为主的当代土地利用变化,显著改变地表属性,使得东亚地区不同季节的地表反照率均明显增加,并显著改变东亚地区的冬、春季节的地表能量和水分循环.此外,当代大尺度土地利用变化对东亚地区大气环流也有一定影响,可引起东亚冬季风环流显著加强和东亚夏季较弱的偏南风异常.当代土地利用变化未能引起东亚地区近地面气温的显著变化,但可引起东亚北(南)部地区春季降水的显著增加(减小).     

2020年6-7月长江中下游极端梅雨天气特征分析

利用逐小时地面、风廓线和天气雷达观测资料,对局地分析与预报系统的再分析产品（Local Analysis and Prediction System-Live Products,Laps_Live）和欧洲中期天气预报中心的第五代再分析产品（The fifth Generation ECMWF Reanalysis,ERA5）在2020年梅雨期的日变化特征进行检验和分析。结果表明：LAPS_LIVE地面要素日变化与实况的相关性普遍比ERA5高。LAPS_LIVE对武陵山区地面温、湿度日变化再现能力不如ERA5,对大别山区海平面气压和地面温、湿度的日变化再现能力明显优于ERA5。两种再分析资料在江汉平原区的海平面气压和地面温、湿度的日变化均与实况误差很小。LAPS_LIVE地面平均风场的误差比ERA5小,但风场日变化幅度明显偏小、风速偏低;ERA5地面风场的日变化幅度和风速则比实况显著偏强。LAPS_LIVE低空风廓线的惯性振荡特征与观测一致,对上午时段低层风场的时间演变和垂直切变的再现能力强于ERA5,但对夜间低空急流的再现能力不足。ERA5低空风场高估上午时段的偏北风和凌晨时段的西南低空急流,但ERA5的低空风廓线平均场比LAPS_LIVE更接近探测值。

     

东亚陆地星载微波成像仪新增通道观测质量评估

基于2014年8月1—16日AMSR-2的观测资料,采用谱差法重点对东亚陆地低频7.3 GHz的无线电频率干扰(RFI)进行识别与分析。研究发现,东亚地区7.3 GHz通道观测存在无线电频率干扰,其中韩国京畿道、大邱市,孟加拉国,越南及柬埔寨东南部地区的干扰源是稳定、持续的地面主动源。日本地区7.3 GHz通道RFI仅出现在AMSR-2升轨观测上,而降轨观测则几乎不受干扰,且RFI污染区出现的位置与强度随时间及辐射计扫描角度周期性变化,探究其污染源,发现主要来自地面反射的静止通信/电视卫星信号对星载微波被动传感器观测的干扰。     

GRIST模式夏季气候回测试验中东亚降水季节内特征的评估

将自主研发的包含对流参数化、宏观云凝结、云微观物理参数化在内的湿物理过程（简称PhysCN）引入全球-区域一体化预测系统（Global-to-Regional Integrated forecast SysTem,GRIST）。通过大气模式比较计划（AMIP）10 a连续积分考察了PhysCN较原有方案（简称PhysC）对模拟的全球气候基本态的影响。结果显示,PhysCN更真实地重现了热带降水的气候分布特征和季节变化。相比PhysC,PhysCN减少了赤道辐合带（ITCZ）、热带太平洋和印度洋上空的虚假降水,改善了双ITCZ偏差。PhysCN在热带对流层顶附近和中、高纬度地区形成了比PhysC更多的冰云,增强了长波云辐射效应。但另一方面,由于单冰云微物理方案中采用一个变量类别考虑所有冰相粒子,导致中、高纬度低层云冰比湿比PhysC中更大。宏观云凝结中采用基于冰面相对湿度的方法诊断冰云量,使低云更密实,减弱了短波云辐射效应,也使全球净辐射收支偏差大于PhysC模拟结果。研究证明了PhysCN湿物理方案在GRIST模式中的稳定性与合理性,但也展示出冰云诊断和云微物理参数化的协调性有待进一步改进。     

Synoptic-scale reversal of dipole surface temperature anomalies over East Asia and Central Siberia in November 2021

In early-to-mid November 2021, a pronounced reversal of surface air temperature (SAT) anomalies (SATAs) occurred over East Asia and Central Siberia, with extreme SATAs that reached up to about 10 °C. Such a synoptic-scale reversal of SATAs was characterized by the alternate emergence of the “colder Central Siberia–warmer East Asia” pattern and the “warmer Central Siberia–colder East Asia” pattern in November 2021. Coinciding with the reversals of the meridional dipole SATAs, large-scale atmospheric circulation anomalies experienced reversed changes. The development of the anomalous cyclonic (anticyclonic) flow over East Aisa (Central Siberia) was crucial for the occurrence of the “warmer Central Siberia–colder East Asia” pattern. Moreover, as the leading mode of daily SAT variability in approximately 56% of the Novembers during 1979–2021, the meridional dipole pattern of warmer (colder) anomalies over Central Siberia and colder (warmer) anomalies over East Asia may be one of the dominant modes of November SAT variability over Eurasia on the synoptic scale.摘要2021年11月, 东亚与中西伯利亚经历了相反的冷暖异常转换, 表现为“中西伯利亚偏冷, 东亚偏暖”与“中西伯利亚偏暖, 东亚偏冷”的交替出现. 该偶极型气温异常的天气尺度反转伴随着大尺度大气环流异常的反转. 进一步分析表明, 东亚与中西伯利亚的偶极型气温异常反转是1979–2021年期间11月欧亚气温日变化的主导模态之一(发生概率超过56%).     

基于TIGGE资料的东亚地面气温预报的不一致性研究

基于TIGGE资料中欧洲中期天气预报中心(ECMWF)、美国国家环境预报中心(NCEP)和中国气象局(CMA)3个集合预报系统的地面气温集合预报资料,运用跳跃指数研究了3个集合预报系统中东亚地面气温的控制预报及集合平均预报的不一致性。结果表明,各个集合预报系统地面气温预报的时间平均不一致性指数差异较大。ECM WF时间不一致性指数最小,NCEP次之,CM A最大。另外NCEP的控制预报、ECM WF的控制预报和集合平均预报,这三者的时间平均不一致性指数随预报时效延长而增加,且集合平均预报一致性优于控制预报。而对于CMA预报的不一致性,无论是控制预报还是集合平均预报总体上都稳定地保持在较高的水平。此外,ECMWF的地面气温冬(夏)季预报的不一致性相对较强(弱),且单点跳跃随预报时效延长变化不明显,而控制预报和集合平均预报的异号两点跳跃以及三点跳跃出现的频率总体上随预报时效延长略有增加。     

Variation of surface albedo and soil thermal parameters with soil moisture content at a semi-desert site on the western Tibetan Plateau

Almost three years of continuous measurements taken between January 2001 and May 2003 at the Gaize (or Gerze) automatic weather station (32.30 °N, 84.06 °E, 4420 m), a cold semi-desert site on the western Tibetan Plateau, have been used to study seasonal and annual variations of surface albedo and soil thermal parameters, such as thermal conductivity, thermal capacity and thermal diffusivity, and their relationship to soil moisture content. Most of these parameters undergo dramatic seasonal and annual variations. Surface albedo decreases with increasing soil moisture content, showing the typical exponential relation between surface albedo and soil moisture. Soil thermal conductivity increases as a power function of soil moisture content. The diffusivity first increases with increasing soil moisture, reaching its maximum at about 0.25 (volume per volume), then slowly decreases. Soil thermal capacity is rather stable for a wide range of soil moisture content.