J. Meteor. Res.
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2019 Vol. 33, No. 2
Published: 2019-04-28

Regional and Global Land Data Assimilation Systems: Innovations, Challenges, and Prospects
Youlong XIA, Zengchao HAO, Chunxiang SHI, Yaohui LI, Jesse MENG, Tongren XU, Xinying WU, Baoqing ZHANG
2019, 33(2): 159-189 [Abstract]( 146 ) HTML PDF (1347 KB)  ( 154 Supplemental Material
Abstract:Since the North American and Global Land Data Assimilation Systems (NLDAS and GLDAS) were established in 2004, significant progress has been made in development of regional and global LDASs. National, regional, project-based, and global LDASs are widely developed across the world. This paper summarizes and overviews the development, current status, applications, challenges, and future prospects of these LDASs. We first introduce various regional and global LDASs including their development history and innovations, and then discuss the evaluation, validation, and applications (from numerical model prediction to water resources management) of these LDASs. More importantly, we document in detail some specific challenges that the LDASs are facing:quality of the in-situ observations, satellite retrievals, reanalysis data, surface meteorological forcing data, and soil and vegetation databases; land surface model physical process treatment and parameter calibration; land data assimilation difficulties; and spatial scale incompatibility problems. Finally, some prospects such as the use of land information system software, the unified global LDAS system with nesting concept and hyper-resolution, and uncertainty estimates for model structure, parameters, and forcing are discussed.
Evaluating Soil Moisture Predictions Based on Ensemble Kalman Filter and SiB2 Model
Xiaolei FU, Zhongbo YU, Ying TANG, Yongjian DING, Haishen LYU, Baoqing ZHANG, Xiaolei JIANG, Qin JU
2019, 33(2): 190-205 [Abstract]( 104 ) HTML PDF (1743 KB)  ( 69 Supplemental Material
Abstract:Soil moisture is an important variable in the fields of hydrology, meteorology, and agriculture, and has been used for numerous applications and forecasts. Accurate soil moisture predictions on both a large scale and local scale for different soil depths are needed. In this study, a soil moisture assimilation and prediction based on the Ensemble Kalman Filter (EnKF) and Simple Biosphere Model (SiB2) have been performed in Meilin watershed, eastern China, to evaluate the initial state values with different assimilation frequencies and precipitation influences on soil moisture predictions. The assimilated results at the end of the assimilation period with different assimilation frequencies were set to be the initial values for the prediction period. The measured precipitation, randomly generated precipitation, and zero precipitation were used to force the land surface model in the prediction period. Ten cases were considered based on the initial value and precipitation. The results indicate that, for the summer prediction period with the dee-per water table depth, the assimilation results with different assimilation frequencies influence soil moisture predictions significantly. The higher assimilation frequency gives better soil moisture predictions for a long lead-time. The soil moisture predictions are affected by precipitation within the prediction period. For a short lead-time, the soil moisture predictions are better for the case with precipitation, but for a long lead-time, they are better without precipitation. For the winter prediction period with a lower water table depth, there are better soil moisture predictions for the whole prediction period. Unlike the summer prediction period, the soil moisture predictions of winter prediction period are not significantly influenced by precipitation. Overall, it is shown that soil moisture assimilations improve its predictions.
Impacts of Soil Moisture on the Numerical Simulation of a Post-Landfall Storm
Feimin ZHANG, Zhaoxia PU, Chenghai WANG
2019, 33(2): 206-218 [Abstract]( 161 ) HTML PDF (1902 KB)  ( 103 Supplemental Material
Abstract:Surface heat and moisture fluxes are important to the evolution of a tropical storm after its landfall. Soil moisture is one of the essential components that influence surface heating and moisture fluxes. In this study, the impact of soil moisture on a pre-landfall numerical simulation of Tropical Storm Bill (2015), which had a much longer lifespan over land, is investigated by using the research version of the NCEP Hurricane Weather Research and Forecasting (HWRF) model. It is found that increased soil moisture with SLAB scheme before storm's landfall tends to produce a weaker storm after landfall and has negative impacts on storm track simulation. Further diagnoses with different land surface schemes and sensitivity experiments indicate that the increase in soil moisture inside the storm corresponds to a strengthened vertical mixing within the storm boundary layer, which is conducive to the decay of storm and has negative impacts on storm evolution. In addition, surface diabatic heating effects over the storm environment are also found to be an important positive contribution to the storm evolution over land, but their impacts are not so substantial as boundary layer vertical mixing inside the storm. The overall results highlight the importance and uncertainty of soil moisture in numerical model simulations of landfalling hurricanes and their further evolution over land.
Evaluation of the WRF-Lake Model over Two Major Freshwater Lakes in China
Yuanyuan MA, Yi YANG, Chongjian QIU, Chenghai WANG
2019, 33(2): 219-235 [Abstract]( 122 ) HTML PDF (3640 KB)  ( 63 Supplemental Material
Abstract:This paper evaluates the performance of the Weather Research and Forecasting (WRF) model coupled with a lake scheme over the Lake Poyang and Lake Dongting regions. We choose several cases with different weather characteristics, including winter with/without precipitation and summer with/without precipitation, and conduct a series of experiments (without the lake model, with the default lake model, and with a calibrated lake model that adjusts the water absorption, extinction coefficients, and surface roughness length) for each case. The results show that the performance of the lake model is significantly affected by the weather conditions. For the winter with precipitation cases, the performance of the default lake model is even worse than without the lake model, but the calibrated lake model can obviously reduce the biases of 2-m temperature and dew-point temperature. Although the performance of the default and new calibrated models is intricate for other cases, the new calibrated model has prominent advantages for 2-m dew-point temperature. Moreover, a long-term simulation of five months also shows that the new calibrated coupled lake model performs better than the default one. These imply that the new calibrated coupled lake model is more suitable to be used in studies of the effects of Lake Poyang and Lake Dongting on regional weather and climate.
The Representativeness of Air Quality Monitoring Sites in the Urban Areas of a Mountainous City
Minjin MA, Yue CHEN, Fan DING, Zhaoxia PU, Xudong LIANG
2019, 33(2): 236-250 [Abstract]( 107 ) HTML PDF (926 KB)  ( 46 Supplemental Material
Abstract:Lanzhou is a typical mountainous city with severe air pollution in northwestern China. This study uses hourly observational data of air pollutants at five air quality monitoring sites in Lanzhou from July to December 2015 to discuss data quality control and the representativeness of the monitoring sites (four urban sites and one suburban site). A fuzzy matrix is applied to study primary air pollutants. The results show that of the six routinely monitored pollutants, the primary pollutant is PM10 during the study period. Based on lag correlation analysis and one-way analysis of variance, it is concluded that there are redundant observations at the four urban sites for the timely diffusion and transport of air pollutants from the same general area. The coefficient of divergence (COD) method is then used to evaluate the spatial distribution differences, and the primary air pollutant PM10 shows differences at each site. COD can be used as a positive indicator to describe site representativeness. To evaluate the overall air pollution in the valley, correlation analysis is performed between the PM10 concentration retrieved from aerosol optical depth satellite data and the concentration from the four urban monitoring sites. Among these, the correlation between the workers' hospital site data and the retrieval data is the highest, passing the 90% confidence level. A new representative evaluation model for air quality monitoring sites, Rs=0.77COD + 0.23Rretrieval, is established by using COD and correlation coefficients between routine observations and satellite retrieval products. From this model, it can be concluded that the biological products institute site in Lanzhou is the most representative site for the evaluation of air pollution out of the four urban air quality monitoring sites from July to December 2015.
Coupling the Common Land Model to ECHAM5 Atmospheric General Circulation Model
Yufei XIN, Yongjiu DAI, Jian LI, Xinyao RONG, Guo ZHANG
2019, 33(2): 251-263 [Abstract]( 66 ) HTML PDF (4267 KB)  ( 64 Supplemental Material
Abstract:The ECHAM5 model is coupled with the widely used Common Land Model (CoLM). ECHAM5 is a state-of-the-art atmospheric general circulation model incorporated into the integrated weather and climate model of the Chinese Academy of Meteorological Sciences (CAMS-CSM). Land surface schemes in ECHAM5 are simple and do not provide an adequate representation of the vegetation canopy and snow/frozen soil processes. Two AMIP (Atmosph-eric Model Intercomparison Project)-type experiments using ECHAM5 and ECHAM5-CoLM are run over 30 yr and the results are compared with reanalysis and observational data. It is found that the pattern of land surface temperature simulated by ECHAM5-CoLM is significantly improved relative to ECHAM5. Specifically, the cold bias over Eurasia is removed and the root-mean-square error is reduced in most regions. The seasonal variation in the zonal mean land surface temperature and the in situ soil temperature at 20-and 80-cm depths are both better simulated by ECHAM5-CoLM. ECHAM5-CoLM produces a more reasonable spatial pattern in the soil moisture content, whereas ECHAM5 predicts much drier soils. The seasonal cycle of soil moisture content from ECHAM5-CoLM is a better match to the observational data in six specific regions. ECHAM5-CoLM reproduces the observed spatial patterns of both sensible and latent heat fluxes. The strong positive bias in precipitation over land is reduced in ECHAM5-CoLM, especially over the southern Tibetan Plateau and middle-lower reaches of the Yangtze River during the summer monsoon rainy season.
Influences of Physical Processes and Parameters on Simulations of TOA Radiance at UV Wavelengths: Implications for Satellite UV Instrument Validation
Shouguo DING, Fuzhong WENG
2019, 33(2): 264-275 [Abstract]( 223 ) HTML PDF (1881 KB)  ( 112 Supplemental Material
Abstract:Numerous factors can influence the radiative transfer simulation of hyper-spectral ultraviolet satellite observation, including the radiative transfer scheme, gaseous absorption coefficients, Rayleigh scattering scheme, surface reflectance, aerosol scattering, band center wavelength shifts of sensor, and accuracy of input profiles. In this study, a Unified Linearized Vector Radiative Transfer Model (UNL-VRTM) is used to understand the influences of various factors on the top of atmosphere (TOA) normalized radiance in the ultraviolet (UV) region. A benchmark test for Rayleigh scattering is first performed to verify the UNL-VRTM accuracy, showing that the model performances agree well with earlier peer-reviewed results. Sensitivity experiments show that a scalar radiative transfer approximation considering only ozone and a constant surface reflectance within the UV region may cause significant errors to the TOA normalized radiance. A comparison of the Ozone Mapping and Profiler Suite (OMPS) radiances between simulations and observations shows that the surface reflectance strongly influences the accuracy for the wavelengths larger than 340 nm. Thus, using the surface reflectivity at 331 nm as a proxy for simulating the whole OMPS hyperspectral ultraviolet radiances is problematic. The impact of rotational Raman scattering on TOA radiance can be simulated through using SCIATRAN, which can also reduce the difference between measurements and simulations to some extent. Overall, the differences between OMPS simulations and observations can be less than 3% for the entire wavelengths. The bias is nearly constant across the cross-track direction.
An Operational Precipitable Water Vapor Retrieval Algorithm for Fengyun-2F/VISSR Using a Modified Three-Band Physical Split-Window Method
Juyang HU, Shihao TANG, Hailei LIU, Min MIN
2019, 33(2): 276-288 [Abstract]( 66 ) HTML PDF (1669 KB)  ( 40 Supplemental Material
Abstract:The Visible and Infrared Spin-Scan Radiometer (VISSR) onboard the Fengyun-2 (FY-2) satellite can provide valuable thermal infrared observations to help create a precipitable water vapor (PWV) product with high spatial and temporal resolutions. The current FY-2/VISSR PWV product in operation is produced by using a traditional two-band physical split-window (PSW) method, which produces low quality results under dry atmospheric conditions. Based on the sensitivity characteristics of FY-2F/VISSR water vapor channel and two split-window channels to atmosphe-ric water vapor, this study developed a new, robust operational PWV retrieval algorithm for FY-2F to improve the operational precision of the current PWV product. The algorithm uses a modified three-band PSW method, which adds a scale for the water vapor channel in the improved three-band PSW method. Integrated PWV products from the radiosonde data in 2016 are used here to validate the precision of the PWV retrieved by the modified three-band and traditional two-band PSW methods. The mean bias, root mean square error (RMSE), and correlation coefficient of the PWV retrieved by the modified three-band PSW method are 0.28 mm, 4.53 mm, and 0.969, respectively. The accuracy is much better than the PWV retrieved by the two-band method, whose mean bias, RMSE, and correlation coefficient are 12.67 mm, 29.35 mm, and 0.23. Especially, in mid-or high-latitude regions, the RMSE of the PWV is improved from 10 to 2 mm by changing the inversion in the two-band method to the modified three-band PSW method. Furthermore, the modified three-band PSW results show a better consistency with the radiosonde PWV at any zonal belt and season than the two-band PSW results. This new algorithm could significantly improve the quality of the current FY-2F/VISSR PWV product, especially at sites where the actual PWV are lower than 15 mm.
An Analysis of the Discontinuity in Chinese Radiosonde Temperature Data Using Satellite Observation as a Reference
Yanjun GUO, Chengzhi ZOU, Panmao ZHAI, Guofu WANG
2019, 33(2): 289-306 [Abstract]( 100 ) HTML PDF (42013 KB)  ( 143 Supplemental Material
Abstract:Reconciling upper-air temperature trends derived from radiosonde and satellite observations is a necessary step to confidently determine the global warming rate. This study examines the raw and homogenized radiosonde observations over China and compares them with layer-mean atmospheric temperatures derived from satellite microwave observations for the lower-troposphere (TLT), mid-troposphere (TMT), upper-troposphere (TUT), and lower-stratosphere (TLS) by three research groups. Comparisons are for averages over China, excluding the Tibetan Plateau, and at individual stations where metadata contain information on radiosonde instrument changes. It is found that major differences between the satellite and radiosonde observations are related to artificial systematic changes. The radiosonde system updates in the early 2000s over China caused significant discontinuities and led the radiosonde temperature trends to exhibit less warming in the middle and upper troposphere and more cooling in the lower stratosphere than satellite temperatures. Homogenized radiosonde data have been further adjusted by using the shift-point adjustment approaches to match with satellite products for China averages. The obtained trends during 1979-2015 from the re-adjusted radiosonde observation are respectively 0.203 ±0.066, 0.128 ±0.044, 0.034 ±0.039, and -0.329 ±0.135 K decade-1 for TLT, TMT, TUT, and TLS equivalents. Compared to satellite trends, the re-adjusted radiosonde trends are within 0.01 K decade-1 for TMT and TUT, 0.054 K decade-1 warmer for TLT, and 0.051 K decade-1 cooler for TLS. The results suggest that the use of satellite data as a reference is helpful in identifying and removing inhomogeneities of radiosonde temperatures over China and reconciling their trends to satellite microwave observations. Future efforts are to homogenize radiosonde temperatures at individual stations over China by using similar approaches.
Assessment of the Capability of ENSEMBLES Hindcasts in Predicting Spring Climate in China
Yitong LIN, Haiming XU, Jing MA, Haijun LI
2019, 33(2): 307-322 [Abstract]( 45 ) HTML PDF (17468 KB)  ( 42 Supplemental Material
Abstract:Using the hindcasts provided by the Ensemble-Based Predictions of Climate Changes and Their Impacts (ENSEMBLES) project for the period of 1980-2005, the forecast capability of spring climate in China is assessed mainly from the aspects of precipitation, 2-m air temperature, and atmospheric circulations. The ENSEMBELS can reproduce the climatology and dominant empirical orthogonal function (EOF) modes of precipitation and 2-m air temperature, with some differences arising from different initialization months. The multi-model ensemble (MME) forecast of interannual variability is of good performance in some regions such as eastern China with February initialization. The spatial patterns of the MME interannual and inter-member spreads for precipitation and 2-m air temperature are consistent with those of the observed interannual spread, indicating that internal dynamic processes have major impacts on the interannual anomaly of spring climate in China. We have identified two coupled modes between inter-member anomalies of the 850-hPa vorticity in spring and sea surface temperature (SST) both in spring and at a lead of 2 months, of which the first mode shows a significant impact on the spring climate in China, with an anomalous anticyclone located over Northwest Pacific and positive precipitation and southwesterly anomalies in eastern China. Our results also suggest that the SST at a lead of two months may be a predictor for the spring climate in eastern China. A better representation of the ocean-atmosphere interaction over the tropical Pacific, Northwest Pacific, and Indian Ocean can improve the forecast skill of the spring climate in eastern China.
Springtime Convective Quasi-Biweekly Oscillation and Interannual Variation of Its Intensity over the South China Sea and Western North Pacific
Zhiqing XU, Ke FAN, Huijun WANG
2019, 33(2): 323-335 [Abstract]( 71 ) HTML PDF (4360 KB)  ( 47 Supplemental Material
Abstract:This study investigates characteristics of the convective quasi-biweekly oscillation (QBWO) over the South China Sea (SCS) and western North Pacific (WNP) in spring, and the interannual variation of its intensity. Convective QBWO over the WNP and SCS shows both similarities and differences. Convective QBWO over the WNP originates mainly from southeast of the Philippine Sea and propagates northwestward. In contrast, convective QBWO over the SCS can be traced mainly to east of the Philippines and features a westward propagation. Such a westward or northwestward propagation is probably related to n=1 equatorial Rossby waves. During the evolution of convective QBWO over the WNP and SCS, the vertical motion and specific humidity exhibit a barotropic structure and the vertical relative vorticity shows a baroclinic structure in the troposphere. The dominant mode of interannual variation of convective QBWO intensity over the SCS-WNP region in spring is homogeneous. Its positive phase indicates enhanced convective QBWO intensity accompanied by local enhanced QBWO intensity of vertical motion throughout the troposphere as well as local enhanced (weakened) QBWO intensity of kinetic energy, vertical relative vorticity, and wind in the lower (upper) troposphere. The positive phase usually results from local increases of the background moisture and anomalous vertical shear of easterlies. The latter contributes to the relationship between the dominant mode and QBWO intensities of kinetic energy, vertical relative vorticity, and wind. Finally, a connection between the dominant mode and the sea surface temperature anomalies in the tropical Pacific Ocean is demonstrated.
The Distribution and Uncertainty Quantification of Wind Profile in the Stochastic General Ekman Momentum Approximation Model
Bing YAN, Sixun HUANG, Jing FENG, Yu WANG
2019, 33(2): 336-348 [Abstract]( 64 ) HTML PDF (1751 KB)  ( 47 Supplemental Material
Abstract:The general Ekman momentum approximation boundary-layer model (GEM) can be effectively used to describe the physical processes of the boundary layer. However, eddy viscosity, which is an approximated value, can lead to uncertainty in the solutions. In this paper, stochastic eddy viscosity is taken into consideration in the GEM, and generalized polynomial chaos is used to quantify the uncertainty. The goal of uncertainty quantification is to investigate the effects of uncertainty in the eddy viscosity on the model and to subsequently provide reliable distribution of simulation results. The performances of the stochastic eddy viscosity and generalized polynomial chaos method are validated based on three different types of eddy viscosities, and the results are compared based on the Monte Carlo me-thod. The results indicate that the generalized polynomial chaos method can be accurately and efficiently used in uncertainty quantification for the GEM with stochastic eddy viscosity.
Characteristics of Near Surface Winds over Different Underlying Surfaces in China: Implications for Wind Power Development
Xi GONG, Rong ZHU, Lianshou CHEN
2019, 33(2): 349-362 [Abstract]( 68 ) HTML PDF (1819 KB)  ( 69 Supplemental Material
Abstract:Accurate wind and turbulence information are essential to wind energy research and utilization, among which wind shear and turbulence intensity/scale have seldom been investigated. In this paper, the observational data from the 100-m high wind towers in Xilinhot in Inner Mongolia (2009-10; grassland region), Huanghua in Hebei Province (2009-10; coastal flat region), and Xingzi County in Jiangxi Province (2010-11; mountain-lake region) are used to study the variations in near surface winds and turbulence characteristics related to the development of local wind energy over different underlying surfaces. The results indicate that (1) the percentage of the observed wind shear exponents exceeding 0.3 for the grassland region is 6%, while the percentage is 13% for the coastal flat region and 10% for the mountain-lake region. In other words, if the wind speed at 10 m is 10 m s-1, the percentage of the wind speed at 100 m exceeding 20 m s-1 for the grassland region is 6%, while the percentage is 13% for the coastal flat region and 10% for the mountain-lake region. (2) In terms of the turbulent intensity in the zonal, meridional, and vertical directions (Iu, Iv, and Iw, respectively), the frequencies of Iv/Iu < 0.8 in the grassland, coastal flat, and mountain-lake regions are 23%-29%, 32%-38%, and 30%-37%, respectively. Additionally, the frequencies of Iw/Iu < 0.5 in the grassland, coastal flat, and mountain-lake regions are 45%-75%, 52%-70%, and 43%-53%, respectively. The frequencies of Iv/Iu < 0.8 and Iw/Iu < 0.5 in each region mean that Iu is large and the air flow is unstable and fluctuating, which will damage the wind turbines. Therefore, these conditions do not meet the wind turbine design requirements, which must be considered separately. (3) At 50-and 70-m heights, the value of the turbulence scale parameter Λ in the grassland region is greater than that in the coastal flat region, and the latter is greater than that in the mountain-lake region. Therefore, under the same conditions, some parameters, e.g., the extreme directional change and extreme operating gust at the hub height in the grassland region, are greater than those in the coastal flat region, which are greater than those in the mountain-lake region. These results provide a reference for harnessing local wind energy resources and for the selection and design of wind turbines.
Projection of Heat Injury to Single-Cropping Rice in the Middle and Lower Reaches of the Yangtze River, China under Future Global Warming Scenarios
Xiaomin LYU, Guangsheng ZHOU, Mengzi ZHOU, Li ZHOU, Yuhe JI
2019, 33(2): 363-374 [Abstract]( 73 ) HTML PDF (3716 KB)  ( 50 Supplemental Material
Abstract:Based on simulation results from the 16 CMIP5 model runs under three Representative Concentration Pathways (RCP2.6, RCP4.5, and RCP8.5) in combination with the recent five years of growth-stage data from agrometeorological observation stations in the middle and lower reaches of the Yangtze River, changes in heat injury and spatial distribution patterns of single-cropping rice in China during the early (2016-35), middle (2046-65), and late (2080-99) 21st century were projected by using quantitative estimations. Relative to the reference period (1986-2005), the occurrence probabilities of heat injury to single-cropping rice under different RCP scenarios increased significantly, showing a trend of mild > moderate > severe. The occurrence probabilities increased with time and predicted emissions, especially the average and maximum occurrence probabilities, which were~48% and~80%, respectively, in the late 21st century under the RCP8.5 scenario. The spatial patterns of the occurrence probabilities at each level of heat injury to single-cropping rice did not change, remaining high in the middle planting region and low in the east. The high-value areas were mainly in central Anhui and southeastern Hubei provinces, and the areas extended to the northwest and northeast of the cultivation area over time. Under the RCP2.6, RCP4.5, and RCP8.5 scena-rios, the total area of heat injury to single-cropping rice showed a significant linear increasing trend of 7.4×103, 19.9×103, and 35.3×103 ha yr-1, respectively, from 2016 to 2099, and the areas of heat injury were greatest in the late 21st century, accounting for~25%,~40%, and~59% of the cultivation area.
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