热带大气ISO在几种再分析资料中的对比分析

利用NCEP/NCAR, NCEP/DOE和ERA40 3套再分析资料的逐日200 hPa纬向风数据,选取1961—1990年、1971—2000年和1981—2010年3种不同气候态,对比分析了3种气候态下热带大气季节内振荡 (ISO) 的基本气候特征及其在不同再分析资料中的异同。研究表明:1981—2010年气候态下,热带大气ISO冬春强、夏秋弱的年循环特征更加明显,东传短波能量增强,起始北传时间偏晚。NCEP/NCAR与NCEP/DOE资料所表征的热带大气ISO在空间分布、强度和能量传播方面的一致性较好。NCEP/NCAR资料反映的热带大气ISO强度在热带印度洋和热带西太平洋地区较ERA40资料偏弱,在赤道东太平洋地区较ERA40资料偏强;ERA40资料反映的热带大气ISO强度在12月—次年3月中旬较NCEP/NCAR资料偏强,而在3月中旬—11月偏弱;ERA40资料反映的热带大气ISO振荡位相较NCEP/NCAR资料超前10 d左右;NCEP/NCAR资料反映的东传谱能量弱于ERA40资料,西传能量强于ERA40资料;7月中旬,NCEP/NCAR资料反映的东亚地区大气ISO经向北传较ERA40资料偏晚。     

南半球气候锋的统计特征分析

本文利用 1995 - 97年 NCEP全球 2 .5°× 2 .5°经纬网格点再分析资料对南半球的温度梯度和厚度梯度的分布特征进行了分析 ,给出了南半球副热带洋面上锋面的产生与厚度、温度梯度的关系 ,从而得出南半球气候锋活动规律、发生源地及其基本特征 ,并概括出南半球气候锋存在的依据     

乌鲁木齐大气边界层结构的四季特征初探

利用乌鲁木齐市2011～2012年08时、20时L波段(1型)雷达探测的高空资料建立了乌鲁木齐大气边界层气象要素数据库,分析了乌鲁木齐边界层内气温、风向、风速和相对湿度的垂直分布及其时间变化特征。结果表明：边界层内温度廓线的日变化和季节变化比较显著,各月均有逆温出现,且08时较20时更易出现逆温,冬季08时逆温层厚度较厚且强度最大。边界层内夏、冬两季风速随高度变化波动较大,春、秋两季变化较小。近地层春、夏、秋三季08时盛行西南偏南风,冬季盛行偏东风和西南风;20时春季盛行东北风,夏秋盛行偏北风和西北风,冬季则盛行东风和东北偏东风。08时、20时风向均随高度的增加呈明显的向右偏转趋势,且日风向的变化具有明显的“山谷风”特点。08、20时的相对湿度冬季最大,夏季最小,且随高度增加,春、夏两季08、20时相对湿度的变化较大。     

4种再分析月降水数据在内蒙古地区的适用性分析

利用1981—2020年气象台站的实测降水数据,对CRA40、ERA5、JRA55和MERRA2这4种再分析月降水数据在内蒙古地区的降水分布特征,与实测降水的相关性和误差进行分析。结果表明：（1）内蒙古地区4种再分析降水数据的空间分布与台站降水基本一致,误差分析表明CRA40与MERRA2的数据质量较高,ERA5次之,而JRA55数据质量相对较差。（2）CRA40和MERRA2在1983—1986年存在明显的降水低估,ERA5在2005年之后的内蒙古中东部出现明显的降水低估,JRA55在115°E以东存在明显降水高估,在115°E以西则以降水低估为主。（3）4种再分析月降水数据的年内最大均方根误差和绝对误差均集中在6—8月,与台站降水相关系数的年内最小值均出现在7月,内蒙古夏季汛期是再分析降水误差产生的主要时段。     

L波段雷达资料在雾的边界层逆温特征中的应用

本文利用沙坪坝基本气象站2005~2010年逐日08,20时L波段雷达探空资料,对不同类型雾日期间边界层逆温特征进行分析。结果表明:从季节上来看雾日主要发生在秋冬季节,雾日期间不论是08时还是20时均有多层逆温存在,各类型雾日逆温温差均为08时大于20时,而逆温强度表现为20时大于08时,不论是雾日,轻雾日还是浓雾日,08时逆温层厚度都比20时要厚。总的来说,浓雾日的逆温层各要素都体现逆温特征较为明显的特点,逆温温差越大,逆温层厚度越厚,也就更容易形成浓雾,同时08时的各逆温要素均高于20时,08时逆温特征也更为明显,在这时段也就更容易形成雾。      

CMA-GFS全球模式海洋边界层高度的主要偏差特征

海洋边界层高度是表征海洋上空大气的水汽、热量、物质等垂直分布的重要特征量，同时在气候、污染、模式预报上有关键作用。然而，利用海洋边界层高度观测对数值天气预报模式进行诊断的研究很少。因此，本文利用2019—2020年GPS掩星资料计算出的海洋边界层高度的分布特征，对CMA GFS全球模式的预报性能进行分析，同时借助ERA5再分析资料对CMA GFS模式的偏差进行讨论。主要结论如下：①CMA GFS全球模式在西太平洋、南太平洋、南大西洋绝大部分海域预报的边界层高度比较合理;②模式在热带辐合带海域和南太平洋辐合带存在高估预报，初步分析与模式对热带深对流的抬升凝结高度的预报偏高有关。③模式和ERA5在南半球层积云所在区域均存在边界层高度预报偏低，初步分析可能是模式对南半球层积云顶辐射冷却驱动的湍流扩散偏小造成。④模式在有云的大气下主要呈现为预报偏高，中心值在200 m左右，而在晴空区域模式预报较为合理，偏差值范围较小，ERA5也存在类似的特点。     

ERA5再分析资料对中国大陆区域近地层风速气候特征及变化趋势再现能力的评估

基于台站观测资料,评估了欧洲中期天气预报中心（ECMWF）最高时空分辨率的第五代大气再分析资料（ERA5）对1979～2018年间中国大陆区域10 m高度风速的气候特征及其变化趋势的再现能力,并同步对比分析了ERA5资料100 m高度风速的特征和长期趋势。结果表明,ERA5资料10 m和100 m风速在空间分布、年—季节—月尺度演变的气候特征方面与台站观测非常一致,10 m风速气候态空间相关系数达到0.66。观测和再分析资料均显示,中国近地层风速呈现出显著的区域性特征,风速大值区主要分布在内蒙古、东北地区西部、新疆北部以及青藏高原西部地区,上述区域的风速季节差异也相对明显,春季风速最大。台站观测、ERA5资料10 m和100 m全国平均风速在4月达到最大值,分别为2.6、3.0、4.5 m s–1,8月为最小值,分别为2.0、2.4、3.5 m s–1。从月平均序列来看,ERA5资料的10 m风速较台站观测偏高0.3～0.5 m s–1,而100 m的风速较10 m风速整体偏高1.2～1.4 m s–1。在风速变化方面,台站观测风速在中国陆地区域整体呈下降趋势–0.4 m s–1（39 a）–1,春季下降趋势最显著[–0.5 m s–1（39 a）–1],且1979～1992年冬季风速降幅最大[–0.7 m s–1（14 a）–1],2013年以后风速逐渐增强。ERA5资料两个高度层的风速在整个中国区域均没有明显的长期变化趋势,4个季节风速变化趋势的空间分布与观测也存在差异,100m风速的长期变化趋势与10 m一致但变化幅度大于10 m风速。总之,ERA5资料对中国大陆区域气候平均风速具有较好的再现能力,但无法呈现台站观测风速的长期变化趋势。     

ERA5再分析10m风速数据在“两洋一海”的适用性分析北大核心CSCD

西太平洋-南海-东印度洋(以下简称“两洋一海”)地区对我国的天气气候、国家安全和社会经济有重要影响,但由于资料条件的限制,现有的海上高风速事件研究主要集中于近海,导致对“两洋一海”地区远洋高风速事件的时空分布、变化特征及其机理仍然不够了解,急需利用新的高分辨率资料进行深入的研究。目前欧州中期天气预报中心第五代全球大气再分析资料(ERA5)再分析近地面10 m风速数据与现场观测风速的比较研究还相对较少,因此本文将“两洋一海”地区的国际海洋大气综合数据集(ICOADS)锚定浮标观测资料与ERA5进行了对比分析。结果表明:ERA5再分析10 m风速数据能够较好地表现出海面风场的分布特点和变化特征。ERA5再分析资料具有较高的时空分辨率、较长的时间序列以及完整的数据记录,将其用于海上高风速事件的气候分析是可行的,且具有一定的优势。需要注意的是,ERA5再分析风速总体上存在低估实测风速的系统偏差,尤其是实测风速较大时,ERA5偏离于实测风速的现象更为明显。     

2021年陕西极端秋雨事件环流特征及成因

利用国家气候中心提供的88项环流指数资料、 陕西省101个气象站逐日降水资料、NCEP/NCAR 25°×25°逐日再分析资料,分析了2021年陕西极端秋雨期间的大气环流特征及成因,结果表明：持续受冷暖气流共同影响,陕西出现了长达52 d的秋雨事件,秋雨出现早、结束晚,呈现自北向南增多的空间分布特征,较气候态降水量异常偏大;500 hPa高度场距平在中高纬“东高西低”的环流分布形态和巴尔喀什湖到贝加尔湖地区的显著负异常区,有利于引导高空槽底部分裂冷空气南下;低纬度异常偏强、偏西、偏大的副热带高压有利于外围暖湿气流向西北地区东部输送水汽和能量;850 hPa风场上东北地区东部存在的异常反气旋环流引导偏东路径的冷湿气流与来自孟加拉湾、南海及西北太平洋的充沛暖湿气流在西北地区形成水汽汇,造成陕西降水偏多;陕西持续位于40°N的高空急流入口区南侧,具备高空辐散、低层辐合的有利动力条件;稳定维持在105°E～110°E的θse能量锋区,多次受弱冷空气侵入,是导致秋雨中出现暴雨的主要原因。     

两套土壤湿度再分析资料在黑河流域的对比分析

利用黑河流域少量观测台站的实测降水和土壤湿度资料, 对比分析了欧洲中心ERA40及美国NCEP R-1两套常用的土壤湿度再分析资料在黑河流域的空间分布、 年际变化和季节循环特征, 结果表明:两套资料在黑河流域均能表现出“南湿北干”的分布格局, 湿度高值中心位于祁连山区东南部\.以此为中心, 土壤湿度从上游山区向中下游递减。ERA40土壤湿度在祁连山区年际变化明显, 与降水的响应关系要好于NCEP资料, 在中下游站点, NCEP 10 cm层土壤湿度对降水的响应好于ERA40。祁连站ERA40土壤湿度在6~8月接近观测值, 在额济纳站两套资料对于土壤湿度的描述都不理想。     

近中性条件下青藏高原行星边界层厚度及其特征分析

本文利用1979年5—8月常规气象资料,采用三种不同定义的确定边界层厚度的方法,得到近中性弱稳定条件下夏季青藏高原平均边界层厚度为600m左右。     

Impact of Boundary-Layer Processes on Near-Surface Turbulence Within the West African Monsoon

High frequency measurements of near-surface meteorological data acquired in north Benin during the 2006 West African monsoon seasonal cycle, in the context of the African Monsoon Multidisciplinary Analysis (AMMA) experiment, offer insight into the characteristics of surface turbulence in relation to planetary boundary-layer (PBL) processes. A wide range of conditions is encountered at the lower and upper limits of the PBL: (i) from water-stressed to well-fed vegetation, and (ii) from small to large humidity and temperature jumps at the PBL top inversion, due to the Saharan air layer overlying the monsoonal flow. As a result, buoyant convection at the surface and entrainment at the PBL top play very different roles according to the considered scalar. We show that, when the boundary-layer height reaches the shear level between the monsoonal and Harmattan flows, the temperature source and humidity sink at the boundary-layer top are sufficient to allow the entrainment to affect the entire boundary layer down to the surface. This situation occurs mainly during the drying and moistening periods of the monsoon cycle and affects the humidity statistics in particular. In this case, the humidity turbulent characteristics at the surface are no longer driven solely by buoyant convection, but also by entrainment at the boundary-layer top. Consequently, the Monin–Obukhov similarity theory appears to fail for the parameterisation of humidity-related moments.     

绿洲与荒漠相互影响下大气边界层特征的模拟

用发展的二维中尺度土壤－植被－大气连续体数值模式模拟了绿洲与荒漠相互影响下的大气边界层特征。得到了绿洲和临近荒漠之间的边界层高度、风螺线、风速廓线、位温廓线和比湿廓线的差别,并给出了绿洲对其上游和下游荒漠大气的不同影响。基本再现了白天绿洲大气逆温和临近绿洲的荒漠大气逆湿。模拟实验研究不仅验证了外场观测结果,而且也使我们对复杂下垫面边界层结构有了一些新的认识。     

The effect of ocean mixed layer depth on climate in slab ocean aquaplanet experiments

The effect of ocean mixed layer depth on climate is explored in a suite of slab ocean aquaplanet simulations with different mixed layer depths ranging from a globally uniform value of 50–2.4 m. In addition to the expected increase in the amplitude of the seasonal cycle in temperature with decreasing ocean mixed layer depth, the simulated climates differ in several less intuitive ways including fundamental changes in the annual mean climate. The phase of seasonal cycle in temperature differs non-monotonically with increasing ocean mixed layer depth, reaching a maximum in the 12 m slab depth simulation. This result is a consequence of the change in the source of the seasonal heating of the atmosphere across the suite of simulations. In the shallow ocean runs, the seasonal heating of the atmosphere is dominated by the surface energy fluxes whereas the seasonal heating is dominated by direct shortwave absorption within the atmospheric column in the deep ocean runs. The surface fluxes are increasingly lagged with respect to the insolation as the ocean deepens which accounts for the increase in phase lag from the shallow to mid-depth runs. The direct shortwave absorption is in phase with insolation, and thus the total heating comes back in phase with the insolation as the ocean deepens more and the direct shortwave absorption dominates the seasonal heating of the atmosphere. The intertropical convergence zone follows the seasonally varying insolation and maximum sea surface temperatures into the summer hemisphere in the shallow ocean runs whereas it stays fairly close to the equator in the deep ocean runs. As a consequence, the tropical precipitation and region of high planetary albedo is spread more broadly across the low latitudes in the shallow runs, resulting in an apparent expansion of the tropics relative to the deep ocean runs. As a result, the global and annual mean planetary albedo is substantially (20 %) higher in the shallow ocean simulations which results in a colder (7C) global and annual mean surface temperature. The increased tropical planetary albedo in the shallow ocean simulations also results in a decreased equator-to-pole gradient in absorbed shortwave radiation and drives a severely reduced (≈50 %) meridional energy transport relative to the deep ocean runs. As a result, the atmospheric eddies are weakened and shifted poleward (away from the high albedo tropics) and the eddy driven jet is also reduced and shifted poleward by 15° relative to the deep ocean run.     

The sensitivity of k-ɛ model computations of the neutral planetary boundary layer to baroclinicity

While the importance of baroclinicity in determining the structure of the planetary boundary layer (PBL) is well recognized, the actual effect of baroclinicity on the structure is not well understood. Results based on simulations obtained using the turbulent kinetic energy-dissipation rate of turbulent kinetic energy closure model of the turbulent flow in a neutral baroclinic PBL provide additional insight into the role of baroclinicity. The baroclinic PBL is characterized by significant shear production of turbulent kinetic energy throughout the complete boundary-layer depth. The turbulent mixing length is bounded by the presence of a stable temperature inversion layer indicating that the depth of the baroclinic PBL is determined by the inversion height. Significant turbulent shear stresses exist throughout the baroclinic PBL and the air is relatively well-mixed except in the surface layer.     

Aircraft study of aerosol vertical distributions over Beijing and their optical properties

A set of 152 vertical profiles of aerosol number concentration and size distribution with diameter ranging from 0.12 to 3.0 μm observed by the airborne optical spectrometer probe in Beijing, China, between February 2005 and September 2006 is analysed and discussed. The statistic of aerosol number concentration ( N _a) reveals a high aerosol number density in this region with average surface level number concentration ( N ₀) of about 6600 cm⁻³ (0.12–3.0 μm). The average vertical profile of N _a approximately satisfies an exponential decline function with a scale height of 1419 m. The N _a profiles are influenced by the structures of planetary boundary layer (PBL) significantly and two typical types of N _a profile under different conditions of PBL are presented and parametrized in this study. The observations of aerosol size distribution show that, in most cases the aerosol size distributions are not very sensitive to altitude, with effective radii ranging from 0.16 to 0.28 μm. Comparison between aircraft-derived aerosol optical depth (AOD) and Moderate Resolution Imaging Spectroradiometer-derived AOD shows good agreement. The Mie model calculations suggest that the surface level number concentration, the PBL height and the structure of PBL can influence the AOD significantly.     

Land-Surface Heterogeneity Effects in the Planetary Boundary Layer

We investigate the cumulative added value of assimilating temperature, moisture, and wind observations in the three-dimensional non-hydrostatic Fifth-Generation Pennsylvania State University/National Center for Atmospheric Research Mesoscale Model MM5 and use these forecasts to analyze the relationship between surface forcing and planetary boundary-layer (PBL) depth. A data assimilation methodology focused on the surface and the PBL, previously tested in a one-dimensional version of MM5, is applied to 29 May, 6 June, and 7 June 2002 during the International $\hbox {H}_{2}\hbox {O}$ Project over the Southern Great Plains. Model-predicted PBL depth is evaluated against PBL depth diagnosed from data across 4,800 km of airborne lidar data (flight tracks 100–300 km long). The forecast with data assimilation verifies better against observations and is thus used to investigate the environmental conditions that govern PBL depth. The spatial structure in PBL depth is found to be most affected by spatial variations in surface buoyancy flux and capping inversion strength. The spatial scales of surface flux forcing reflected in the PBL depth are found through Fourier analysis and multiresolution decomposition. Correlations are ${<}0.50$ at scales of 64 km or less and increase at larger scales for 29 May and 6 June, but on 7 June low correlations are found at all scales, possibly due to greater within-PBL wind speeds, a stronger capping inversion on this day, and clouds. The results suggest a minimum scale, a function of wind speed, below which heterogeneity in surface buoyancy fluxes is not reflected directly in PBL depth.     

The theoretical distribution of wind in the planetary boundary layer with circular isobars

The equations of motions are solved for concentric circular flow in the planetary boundary layer (PBL) under the assumption of K = l ₂|?v/?z| and gradient wind independent of radius r. The theoretical distribution of wind is obtained for r ≥ 300 km. Other parameters of the PBL are also calculated. Finally, equilibrium of the forces in the PBL is analyzed.     

Uncertainties in simulating regional climate of Southern Africa: sensitivity to physical parameterizations using WRF

This study aims at quantifying seasonal biases of regional climate model outputs during southern African summer, against a dense in situ measurement network (daily rain-gauge and surface air temperature records, and 12?h UTC radiosondes), and uncertainties associated with some physical parameterizations. Using the non-hydrostatic Advanced Research Weather Forecast (WRF) laterally forced by ERA40 reanalysis, twenty-seven experiments configured with three schemes of cumulus (CU), planetary boundary layer (PBL) and microphysics (MP), are performed at 35?km horizontal resolution during the core of a summer rainy season (December 1993 to February 1994 season) representative of the South African rainfall climatology. WRF simulates accurately seasonal large-scale rainfall patterns, as well as seasonal gradients of South African rainfall and 2-m temperature, and seasonal vertical profiles of the air temperature and humidity. However seasonal biases fluctuate strongly from an experiment to another, denoting considerable uncertainties generated by the physical package. Rainfall amounts are the most sensitive parameter to the tested schemes. Their geography, intensity, and intraseasonal characteristics are predominantly sensitive to CU schemes, and much less to PBL and MP schemes. Some CU-PBL combinations produce additive effects, which can dramatically either reduce or increase biases. Satisfactory configurations are found for South African climate, which would not have been possible without testing numerous physical parameterizations.     

北京地区夏季边界层结构日变化的高分辨模拟对比

使用WRF中尺度数值模式, 分别选用两种不同的边界层参数化方案 (MYJ, YSU) 和3种陆面参数化方案 (SLAB, Noah, RUC), 对2004年7月1日08:00—7月4日20:00 (北京时) 北京地区夏季边界层结构进行1 km的高分辨模拟。对比分析了近地面层风场、温度场以及边界层的日变化特征, 结果发现:WRF模式基本模拟出了北京夏季边界层的日变化特征; 在边界层方案中, MYJ方案描述的边界层结构较YSU方案合理; Noah陆面模式较好地反映了城市的热岛效应; 无降水时, 风速及边界层高度对于陆面过程不敏感, 而降水发生后, 陆面过程对于边界层结构的影响增大; 各方案模拟的城区风速明显偏大, 这是因为没有充分考虑城市建筑物的阻力作用。