Seasonal Variations in the Vertical Structure of Water Vapor Optical Depth in the Lower Troposphere over a Tropical Station

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Comparison of Surface Wind Stress Anomalies over the Tropical Pacific Simulated by an AGCM and by a Simple Atmospheric Model

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On the Forcing of the Radial-vertical Circulation within Cyclones-Part 1: Concepts and Equations

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Monsoons over China

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Numerical Simulation for the Impact of Deforestation on Climate in China and Its Neighboring Regions

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Vertical Structure of Beta Gyres and Its Effect on Tropical Cyclone Motion

ＶｅｒｔｉｃａｌＳｔｒｕｃｔｕｒｅｏｆＢｅｔａＧｙｒｅｓａｎｄＩｔｓＥｆｆｅｃｔｏｎＴｒｏｐｉｃａｌＣｙｃｌｏｎｅＭｏｔｉｏｎＴｉａｎＹｏｎｇｘｉａｎｇ（田永祥）ａｎｄＬｕｏＺｈｅｘｉａｎ（罗哲贤）（ＮａｍｉｎｇＩｎｓｔｉｔｕｔｅｏｆＭｅｔｅｏｒｏｌ...     

An analytical study on the urban boundary layer

ＡｎＡｎａｌｙｔｉｃａｌＳｔｕｄｙｏｎｔｈｅＵｒｂａｎＢｏｕｎｄａｒｙＬａｙｅｒ①①ＴｈｉｓｐｒｏｊｅｃｔｗａｓｓｕｐｐｏｒｔｅｄｂｙＬＡＳＧ,ＣｈｉｎｅｓｅＡｃａｄｅｍｙｏｆＳｃｉｅｎｃｅｓ．ＬｉｎＮａｉｓｈｉ（林乃实）,ＺｈｏｕＺｕｇａｎｇ（周祖...     

Vertical Ozone Profile over Tibet Using Sage I and II Data

ＶｅｒｔｉｃａｌＯｚｏｎｅＰｒｏｆｉｌｅｏｖｅｒＴｉｂｅｔＵｓｉｎｇＳａｇｅＩａｎｄＩＤａｔａ①ＺｏｕＨａｎ（邹捍）ａｎｄＧａｏＹｏｎｇｑｉ（郜永祺）ＩｎｓｔｉｔｕｔｅｏｆＡｔｍｏｓｐｈｅｒｉｃＰｈｙｓｉｃｓ，ＣｈｉｎｅｓｅＡｃａｄｅｍｙｏｆＳｃｉｅ...     

Signatures of a Universal Spectrum for Nonlinear Variability in Daily Columnar Total Ozone Content

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A Diagnostic Study of Explosive Development of Extratropical Cyclone over East Asia and West Pacific Ocean

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Tropical-temperate interactions over southern Africa simulated by a regional climate model

The Weather Research and Forecasting model (WRF) forced by ERA40 re-analyses, is used to examine, at regional scale, the role of key features of the local atmospheric circulation on the origin and development of Tropical Temperate Troughs (TTTs) representing a major contribution to South African rainfall during austral summer. A cluster analysis applied on 1971–2000 ERA40 and WRF simulated daily outgoing longwave radiation reveals for the November–February season three coherent regimes characteristic of TTTs over the region. Analyses of WRF simulated TTTs suggest that their occurrence is primarily linked with mid-latitude westerly waves and their phasing. Ensemble experiments designed for the case of austral summer 1996/1997 allow to examine the reproducibility of TTT events. The results obtained illustrate the importance of westerly waves phasing regarding the persistence of rain-producing continental TTT events. Moreover, oceanic surface conditions prevailing over the Agulhas current regions of the South West Indian Ocean (SWIO) are also found to influence TTT persistence for regional experiments with an oceanic mixed layer, warmer sea surface temperatures being associated with increased moisture advection from the SWIO where latent heat release is enhanced, favoring baroclinic instability and thus sustaining convection activity locally.     

An index for tropical temperate troughs over southern Africa

Strong cases of the tropical temperate troughs (TTT) that are responsible for the most of the summer rainfall over subtropical southern Africa are analyzed. An index for identifying the TTT is introduced for the first time using anomalies of outgoing longwave radiation (OLR) and the wind. The TTT is associated with a ridge-trough-ridge wave-like structure in the lower troposphere over southern Africa and the adjoining Indian Ocean. Therefore, the index considers physical processes that occur over southern Africa, adjoining the Atlantic and Indian Oceans to depict the variability of the TTT events. Unusually strong TTT events are identified when the standard deviations of the TTT indices defined by the OLR and wind anomalies in the selected regions are above 1.5 and 0.5 respectively. After applying this criterion and filtering out consecutive events, 55 TTT events are identified during the study period of December–January–February seasons from 1980–1981 to 2009–2010. From the composite analyses of those 55 events, it is found that the TTTs evolve with suppressed (enhanced) convection over the southwest Indian Ocean adjacent to Madagascar (southern Africa). The suppressed convection is, in turn, found to be associated with the enhanced convection around Sumatra in the southeast tropical Indian Ocean. This may explain why more TTT events occur in La Niña years as compared to El Niño years. Time evolution of the canonical TTT event shows that it starts 3 days prior to the mature phase of the event, suggesting possible predictability. After reaching a matured state, the system moves east toward the Indian Ocean and decays within the subsequent couple of days. In addition, the intertropical convergence zone (ITCZ) structure changes over Southern Africa/Madagascar during the TTT event and remains similar to climatology over other regions. The results indicate that the continental part of the ITCZ intensifies prior to the TTT event and then spreads southward following the mid-latitude influence during and after the event.     

Interactions between synoptic, intraseasonal and interannual convective variability over Southern Africa

After removing the annual cycle, a principal component analysis is applied to the daily outgoing longwave radiation anomaly field, used here as a proxy for atmospheric convection. The analysis is carried out over the southern African region (7.5°E–70°E, 10°S–40°S) for austral summer (November through February) for the period 1979–1980 to 2006–2007. The first five principal components (PC) are retained. The first two PCs describe spatial patterns oriented north-west to south-east from tropical southern Africa (SA) to the mid-latitudes. They are interpreted to be different possible locations for synoptic-scale tropical–temperate troughs (TTT), one dominant rainfall-producing synoptic system in the region. The phase relationship between these two PCs describes a tendency for these TTT to propagate eastwards from SA to the Mozambique Channel and southern Madagascar. The next three PCs describe convective fluctuations, respectively, located over the north-west, the south and the centre of SA. Their time series are significantly associated with Madden–Julian oscillation (MJO) activity in the tropics. However, we find that TTT systems are statistically independent of the MJO, i.e. they are equally liable to occur during any phase of the MJO. Three PCs out of five also show a significant association with El Niño southern oscillation, confirming that El Niño years mostly coincide with suppressed convection at the intraseasonal time-scales, a result consistent with its impact on seasonal averages diagnosed in previous studies.     

不同阶曲线拟合扰动场对下平流层重力波气候特征影响研究

重力波参数气候特征是确定大气模式中重力波参数化方案的重要条件之一,高垂直分辨率探空资料扰动场是获取重力波参数气候特征的基础数据;目前,获取扰动场的方法较多,但基于不同方法计算的扰动场对重力波参数气候特征影响的研究较少。基于2014—2017年山西太原气象台高垂直分辨率探空资料,利用2—4阶曲线拟合方法获取下平流层（17—24 km高度）温度扰动场、纬向风扰动场和经向风扰动场,经统计发现2阶与3阶曲线拟合方法的扰动场相似程度较高;在此选取相似度较高的2阶、3阶曲线拟合方法的扰动场分别计算大气重力波参数,并对大气重力波参数间的气候差异特征进行研究。结果表明:（1）不同阶曲线拟合方法扰动场的变化振幅及随高度变化趋势存在差异,且扰动场间的相关较弱;（2）2阶、3阶曲线拟合方法扰动场得到的重力波参数大小、年内变化趋势及在不同区间范围内占有率均存在差异,且相关较弱;（3）1—12月,相对3阶曲线拟合方法的扰动场,基于2阶曲线拟合方法的扰动场得到的重力波群速、水平波长、垂直波长、周期、固有相速均较大,而重力波能量上传百分比在某些月份较大。因此,不同阶曲线拟合方法扰动场间存在差异,会导致计算得到的大气重力波参数气候特征存在差异,最终对研制大气模式中的大气重力波参数化方案产生影响。      

Circulation anomalies associated with tropical-temperate troughs in southern Africa and the south west Indian Ocean

Daily rainfall variability over southern Africa (SA) and the southwest Indian Ocean (SWIO) during the austral summer months has recently been described objectively for the first time, using newly derived satellite products. The principle mode of variability in all months is a dipole structure with bands of rainfall orientated northwest to southeast across the region. These represent the location of cloud bands associated with tropical temperate troughs (TTT). This study objectively identifies major TTT events during November to February, and on the basis of composites off NCEP reanalysis data describes the associated atmospheric structure. The two phases of the rainfall dipole are associated with markedly contrasting circulation patterns. There are also pronounced intra-seasonal variations. In early summer the position of the temperate trough and TTT cloud band alternates between the SWIO and southwest Atlantic. In late summer the major TTT axis lies preferentially over the SWIO, associated with an eastward displacement in the Indian Ocean high. In all months, positive events, in which the TTT cloud band lies primarily over the SWIO, are associated with large-scale moisture flux anomalies, in which convergent fluxes form a pronounced poleward flux along the cloud band. This suggests that TTT events are a major mechanism of poleward transfer of energy and momentum. Moisture transport occurs along three principle paths: (1) the northern or central Indian Ocean (where anomalous fluxes extend eastward to the Maritime Continent), (2) south equatorial Africa and the equatorial Atlantic, (3) from the south within a cyclonic flow around the tropical-temperate trough. The relative importance of (2) is greatest in late summer. Thus, synoptic scale TTT events over SA/SWIO often result from large-scale planetary circulation patterns. Hovmoeller plots show that TTT development coincides with enhanced tropical convection between 10°–30°E (itself exhibiting periodicity of around 5 days), and often with convergence of eastward and westward propagating convection around 40°E. Harmonic analysis of 200 hPa geopotential anomalies show that TTT features are forced by a specific zonally asymmetric wave pattern, with wave 5 dominant or significant in all months except February when quasi-stationary waves 1, 2 and 3 dominate. These findings illustrate the importance of tropical and extratropical dynamics in understanding TTT events. Finally, it is suggested that in November–Januar TTT rainfall over SA/SWIO may be in phase with similar rainfall dipole structures observed in the South Pacific and South Atlantic convergence zones. Received: 11 August 1998 / Accepted: 28 May 1999     

Land-Air Interaction over Arid/Semi-arid Areas in China and Its Impact on the East Asian Summer Monsoon. Part I： Calibration of the Land Surface Model （BATS） Using Multicriteria Methods

To improve the land surface simulation in the arid and semi-arid areas of northern China, the observational data from two field experiments in Dunhuang and Tongyu are used to optimize the parameters in the land surface model, BATS, through calibration with the multicriteria method. Sensitivity analysis to the parameters in Dunhuang and Tongyu indicates that different parameters need to be calibrated in two sites with different environmental and climate regimes. Comparison of observed sensible heat flux, latent heat flux, and ground surface temperature with the simulated ones shows the simulations with the optimized parameters have been substantially improved. Especially, the holistic simulations with the calibration of the parameter values are much closer to the observations in the arid region (Dunhuang), and the energy partition with the calibrated parameters can also be simulated well in the semi-arid region (Tongyu). Whole results demonstrate that the parameter calibration of the land surface model is important when the model is to be used to investigate the land-air interaction.     

云闪放电过程中雨滴增长的数值试验研究

利用二维数值模式,对雨滴在云闪放电条件下的增长进行了试验研究。分别讨论了在不同的电场、荷电量和电场角度时雨滴的增长演变及其运动状况。结果表明：二维模式中闪电放电对雨滴增长的影响与一维有明显不同。电场和荷电量作单因子变化时,雨滴在二维中随参量取值的增加变化较大。两者同时变化时,其乘积愈大雨滴增长幅度愈大。雨滴对电场角度绝对值变化的反应较为缓慢。其运动轨迹在不同的条件下均为准周期的。     

Cloud bands over southern Africa: seasonality, contribution to rainfall variability and modulation by the MJO

Tropical-extratropical cloud band systems over southern Africa, known as tropical temperate troughs (TTTs), are known to contribute substantially to South African summer rainfall. This study performs a comprehensive assessment of the seasonal cycle and rainfall contribution of TTTs by using a novel object-based strategy that explicitly tracks these systems for their full life cycle. The methodology incorporates a simple assignment of station rainfall data to each event, thereby creating a database containing detailed rainfall characteristics for each TTT. This is used to explore the importance of TTTs for rain days and climatological rainfall totals in October–March. Average contributions range from 30 to 60 % with substantial spatial heterogeneity observed. TTT rainfall contributions over the Highveld and eastern escarpment are lower than expected. A short analysis of TTT rainfall variability indicates TTTs provide substantial, but not dominant, intraseasonal and interannual variability in station rainfall totals. TTTs are however responsible for a high proportion of heavy rainfall days. Of 52 extreme rainfall events in the 1979–1999 period, 30 are associated with these tropical-extratropical interactions. Cut-off lows were included in the evolution of 6 of these TTTs. The study concludes with an analysis of the question: does the Madden-Julian Oscillation influence the intensity of TTT rainfall over South Africa? Results suggest a weak but significant suppression (enhancement) of intensity during phase 1(6).     

CALMET模式不同参数化方案对江西省山地风场模拟的对比分析

通过降尺度模式CALMET不同参数化方案对江西山地风场测风塔风速风向模拟结果的对比分析,选取出适合山地风场模拟的最优参数化方案,并进行连续一年的模拟效果检验。结果表明:CALMET模式以不采用地形动力效应参数调整和Froude数调整,采用下坡气流效应调整和O’Brien垂直风速调整时,对江西省境内山地风场50 m以上高度层风场模拟效果最佳。最优参数化方案不仅能较好地模拟出山地风场测风塔逐时风速,并且对全年风速段分布模拟有较好的结果。CALMET模式能模拟出实际测风塔全年主导风向,但模拟与实测结果主导风向分布约有一个方位的偏差,主导风向频率有7%~8%的偏差。     

WOFOST作物生长模型在国内应用研究进展

WOFOST模型是利用计算机技术对不同生产水平下一年生作物的生长发育和产量形成进行定量分析的模拟模型,学者在WOFOST模型以及模型应用方面做了大量研究,总结WOFOST模型在我国的应用研究成果,可为保障粮食安全和农业的可持续发展提供技术支撑。本文采用分类归纳法,简要阐述了WOFOST模型在我国的应用研究历程及进展,应用研究主要涉及对WOFOST模型参数的敏感性分析、模型的适用性分析、模型的改进以及对模型的应用等4个方面。针对模型应用中存在的薄弱环节及发展所需,加强对模型参数的敏感性分析、加强对模型的本地化应用或改进、加强对模型参数的升尺度研究、加强模型与多学科多技术融合4个方面将是今后WOFOST模型的研究重点。