西北干旱区绿洲—戈壁资料同化数据集的建立与分析

利用美国气象环境预报中心和美国国家大气研究中心(NCEP/NCAR)共同开发的天气研究和预报系统WRF模式3.1版本,结合地球观测系统的中分辨率成像光谱仪EOS-MODIS反演的下垫面土地利用/植被类型资料,并同化2008年夏季金塔绿洲野外观测试验所取得的气象资料,对绿洲系统陆—气水热交换过程进行模拟,最终生成金塔高分辨率资料同化再分析数据集。此数据集包括黑河流域金塔绿洲2008年6-8月逐时水平分辨率1 km的土地利用类型、19层风温湿压、4层土壤温湿度以及地表植被覆盖、辐射分量、热通量等资料。同时,利用金塔绿洲观测期内的地表气压、地面气温和相对湿度实测值对该数据集进行初步验证,并分析了绿洲—戈壁系统的"冷湿岛效应"、平均大气环流特征和空气温湿度长期变化规律。结果表明,绿洲和戈壁下垫面的热力差异明显,绿洲和戈壁平均地表温度白天和夜间分别相差21℃和3℃;10 cm土壤温度白天最大相差17℃,并且绿洲比戈壁滞后3 h达到峰值;戈壁相对湿度比绿洲平均约低11%;白天绿洲的"冷岛效应"和"湿岛效应"影响高度平均可达2000 m和1500 m;夜间绿洲的近地层500 m以下则表现出弱的"冷岛效应";夜间绿洲上空的平均垂直气流为上升气流,白天出现大范围下沉气流,平均最大下沉气流速度可达-0.3 m·s-1。

基于高分辨率资料同化数据对青藏高原极端低温特征分析

为进一步研究青藏高原极端低温事件的影响,本文利用WRF模式输出的2015~2020年的逐小时气温高分辨率同化数据计算了两类极端气温指数,研究了其空间分布规律,并根据指数分布规律将青藏高原分为四个区域,研究了高原极端低温的区域特征。结果表明:1) 高原整体呈现出东暖西冷的特征,气温以昆仑山脉与塔里木盆地的交界地带为低值中心,向四周逐渐增暖,霜冻日数和冰封日数也逐步减少。2) 以藏北为主的一区气温最低,以川西为主的四区气温最高,而以青海为主的二区和以藏南为主的三区气温最接近,一区和二区为年内气温变化最为剧烈的两个区域。四个区域霜冻与冰封日数的分布规律与气温相对应,一区最多,三区次之,二区较少,四区最少。3) 四个区域霜冻和冰封日数的季节变化相一致,冬季最多,春季次之,秋季较少,夏季最少。对霜冻日数而言,冬季,不同区域间日数的差异最小;温度越高的区域,霜冻日数的季节差异越明显;冰封日数与霜冻日数相反。

Northward expansion of the western Pacific Warm Pool in late 1990s and early 2000s

Based on 48-year (1958-2006) ocean reanalysis data of Simple Ocean Data Assimilation and 23-year (1984-2006) global ocean-surface heat flux products developed by the Objectively Analyzed Air-Sea Heat Flux Project, meridional variation of the western Pacific Warm Pool (WPWP) is addressed. The results show that there is a significant expansion of the northern edge of the WPWP in the late 1990s and early 2000s. This variation is mainly within 120°E-160°E by 8°N-20°N, we define this region (120°E-160°E by 8°N-20°N) as the core region. Furthermore, analyses on upper ocean heat budget show that the short wave radiation plays a key role in the northward expansion of the northern edge of the WPWP in the core region. It is proved that the northward expansion may be caused by the change of the mixed layer which became shallower in 1994-2006 compared with 1984-1993 in the study region. The short wave radiation flux distribution within the shallower mixed layer leads to a positive anomaly in seawater temperature, promoting the northward expansion of the WPWP.

Relationship between oceanic heat content and sea surface height on interannual time scale

The relationship between heat content and the interannual time scale is examined with satellite sea surface height （SSH） in the global ocean on altimeter measurements, historical hydrography, and model assimilation outputs. Results show that correlation between altimetric SSH and heat content in the upper 700 m calculated from Ishii data is geographically nonuniform. In the tropical ocean, heat content and SSH are strongly correlated and exhibit nearly the same interannual variations. In the polar ocean, their correlation is relatively weak. Further analysis with Simple Ocean Data Assimilation outputs shows that such nonuniform distribution is not from dynamical origin but from the limited integral depth selected to calculate heat content. The integral depth of 700 m is inadequate to capture variation of the deep main thermocline in the polar region. The halosteric effect also contributes to the nonuniform pattern of correlation, because saline contraction becomes significant in the polar ocean owing to low temperature.

External Weather Data Assimilation to Simulate Wind and Temperature Fields in the Region of Gualeguaych~, Argentina

This work shows the comparison between the results of wind and temperature simulation and data weather measurements in low layers near Gualeguaychfi City, Argentine, for 12 h in January 1, 2011. The model ARPS （advanced regional prediction system） with two options in the boundary conditions is used. In such conditions, wave-radiating open （radiative） with relaxation to the initial state were used while otherwise used absorbing boundary conditions data forced from MBLM （meso-scale boundary layer model） operational forecasters used by the National Weather Office. The results of both simulations are compared with data measured by three weather stations located around of the Uruguay River. As both simulations are initialized using the same data, there is a better agreement between the values obtained by forcing the boundary conditions for which are using ＂radiative＂ boundary conditions after 2 h physical time from the start of the simulation.

A review on evapotranspiration data assimilation based on hydrological models

Accurate estimation of evapotranspiration(ET),especially at the regional scale,is an extensively investigated topic in the field of water science. The ability to obtain a continuous time series of highly precise ET values is necessary for improving our knowledge of fundamental hydrological processes and for addressing various problems regarding the use of water. This objective can be achieved by means of ET data assimilation based on hydrological modeling. In this paper,a comprehensive review of ET data assimilation based on hydrological modeling is provided. The difficulties and bottlenecks of using ET,being a non-state variable,to construct data assimilation relationships are elaborated upon,with a discussion and analysis of the feasibility of assimilating ET into various hydrological models. Based on this,a new easy-to-operate ET assimilation scheme that includes a water circulation physical mechanism is proposed. The scheme was developed with an improved data assimilation system that uses a distributed time-variant gain model(DTVGM),and the ET-soil humidity nonlinear time response relationship of this model. Moreover,the ET mechanism in the DTVGM was improved to perfect the ET data assimilation system. The new scheme may provide the best spatial and temporal characteristics for hydrological states,and may be referenced for accurate estimation of regional evapotranspiration.

GRACE terrestrial water storage data assimilation based on the ensemble four-dimensional variational method PODEn4DVar:Method and validation

Seasonal and interannual changes in the Earth's gravity field are mainly due to mass exchange among the atmosphere,ocean,and continental water sources.The terrestrial water storage changes,detected as gravity changes by the Gravity Recovery and Climate Experiment(GRACE) satellites,are mainly caused by precipitation,evapotranspiration,river transportation and downward infiltration processes.In this study,a land data assimilation system LDAS-G was developed to assimilate the GRACE terrestrial water storage(TWS) data into the Community Land Model(CLM3.5) using the POD-based ensemble four-dimensional variational assimilation method PODEn4 DVar,disaggregating the GRACE large-scale terrestrial water storage changes vertically and in time,and placing constraints on the simulation of vertical hydrological variables to improve land surface hydrological simulations.The ideal experiments conducted at a single point and assimilation experiments carried out over China by the LDAS-G data assimilation system showed that the system developed in this study improved the simulation of land surface hydrological variables,indicating the potential of GRACE data assimilation in large-scale land surface hydrological research and applications.

Using the GPS observations to reconstruct the ionosphere three-dimensionally with an ionospheric data assimilation and analysis system(IDAAS)

Using an international reference ionosphere(IRI)model as a background ionosphere and applying the Kalman filter to update the state with observations,we develop an ionosphere data assimilation analysis system(IDAAS)to reconstruct a three-dimensional(3D)ionosphere with the GPS slant TEC and ionosonde data over east-south Asia.The preliminary results with the GPS data collected over east-south Asia on 30 June 2005 showed that inversed slant TEC has very good correlation with the observations both for the GPS sites being and not being involved in reconstruction.The inversed NmF2 and vertical TEC both demonstrate great improvement of agreement with those observed from ionosondes and TOPEX satellite independently.