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An Assessment of Storage Terms in the Surface Energy Balance of a Subalpine Meadow in Northwest China

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Advances in Atmospheric Sciences 2011年第3期28卷 691-698页

作者：王润元张强 College of Atmospheric Sciences Lanzhou University key Open laboratory of arid climatic change and Disaster Reduction of CMA Institute of Arid MeteorologyChina Meteorological Administration key laboratory of arid climatic change and reducing Disaster of gansu province

The heat storage terms in the soil-vegetation-atmosphere system may play an important role in the surface energy *** this paper,we evaluate the heat storage terms of a subalpine meadow based on a ficld experiment conducted in the complex terrain of the eastern Qilian Mountains of Northwest China and their impact on the closure of the surface energy balance under such non-ideal *** the night, the average sum of the storage terms was -5.5 W m,which corresponded to 10.4%of net *** sum of the terms became positive at 0730 LST and negative again at about 1500 LST,with a maximum value of 19 W mobserved at approximately 0830 *** the day,the average of the sum of the storage terms was 6.5 W m,which corresponded to 4.0%of net *** to the slopes obtained when linear regression of the net radiation and partitioned fluxes was forced through the origin,there is an imbalance of 14.0%in the subalpine meadow when the storage terms are not considered in the surface energy *** imbalance was improved by 3.4%by calculating the sum of the storage *** soil heat storage flux gave the highest contribution(1.59%),while the vegetation enthalpy change and the rest of the storage terms were responsible for improvements of 1.04%and 0.77%,respectively.

关键词： subalpine meadow complex terrain surface energy balance storage terms

A Study of the Relationship between Air Pollutants and Inversion in the ABL over the City of Lanzhou

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Advances in Atmospheric Sciences 2011年第4期28卷 879-886页

作者：张强李宏宇 gansu key laboratory of arid climatic change and reducing Disaster Key Open Laboratory of Arid Climatic Change and Disaster Reduction of CMAInstitute of Arid MeteorologyChinese Meteorological Administration gansu Provincial Meteorological Bureau College of Atmospheric Sciences Lanzhou University

By analyzing the pollutant concentrations over the urban area and over the rural area of the city of Lanzhou, gansu province, China, the relationships between the daytime inversion intensity and the pollutant concentration in the atmospheric boundary layer （ABL） are studied with the consideration of wind speed and direction, potential temperature, specific humidity profiles, pollutant concentration in the ABL, the surface temperature, and global radiation on the ground. It was shown that the daytime inversion is a key factor in controlling air pollution concentration. A clear and positive feedback process between the daytime inversion intensity and the air pollutants over the city was found through the analysis of influences of climatic and environmental factors. The mechanisms by which the terrain and air pollutants affect the formation of the daytime inversion are discussed. The solar radiation as the essential energy source to maintain the inversion is analyzed, as are various out-forcing factors affecting the inversion and air pollutants. At last, a physical frame of relationships of air pollution with daytime inversion and the local and out-forcing factors over Lanzhou is built.

关键词： relationship Lanzhou City inversion pollutant out-forcing factors

Research on Water-Vapor Distribution in the Air over Qilian Mountains

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Acta meteorologica Sinica 2008年第1期22卷 107-118页

作者：张强张杰孙国武狄潇泓 key laboratory of arid climatic Changing and reducing Disaster of gansu province key Opening laboratory of arid climatic change and Disaster Reduction of CMA Institute of arid Meteorology China Meteorological Administration Lanzhou Regional Meteorological Centre

Based on the remote sensing data, the radiosonde data and precipitation data observed by weather stations, distributions of atmospheric water-vapor and cloud motion wind over the Qilian Mountains are analyzed. Moreover, on the basis of water-vapor and cloud motion wind analyses, relations of atmospheric water-vapor distribution with precipitation~ atmospheric circulation, and terrain are investigated. The results show that distributions of atmospheric water-vapor and precipitation in the Qilian Mountains are affected by the westerly belt, the southerly monsoon （the South Asian monsoon and plateau monsoon）, and the East Asian monsoon. In the northwest Qilian Mountains, water-vapor and precipitation are entirely affected by the westerly belt, and there is no other direction water-vapor transport except westerly watervapor flux, hence, the northwest region is regarded as the westerly belt region. In the south and middle of the mountaili, water-vapor is mainly controlled by the southerly monsoon, 37.7% of the total watervapor is from the south, especially in summer, the southerly water-vapor flux accounts for 55.9% of the total, and furthermore the water-vapor content in the southerly flow is more than that in the westerly flow. The southerly monsoon water-vapor is influenced by the South Asian monsoon from the Indian Ocean and the plateau monsoon in the Qinghai-Tibetan Plateau, thus, the south and middle region is called southerly monsoon region. But in the northeast Qilian Mountains, the East Asian monsoon is the main climate system affecting the water-vapor. Besides west and northwest water-vapor fluxes, there are a lot of easterly water-vapor fluxes in summer. The frequency of easterly cloud motion winds in summer half year accounts for 27.1% of the total, though the frequency is not high, it is the main water-vapor source of summer precipitation in this region, therefore, the northwest region is a marginal region of the East Asian monsoon. On the other hand, atmosp

关键词： satellite remote sensing data Qilian Mountains atmospheric water-vapor, cloud-motion wind, atmospheric circulation

Some Phenomena of the Interaction Between Vegetation and a Atmosphere on Multiple Scales

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Advances in Atmospheric Sciences 2006年第4期23卷 639-648页

作者：胡隐樵陈晋北郑元润李国庆左洪超 key laboratory of arid climatic change and reducing Disaste of gansu province Cold and arid Regions Environment and Engineering Institute CAS College of Atmospheric Sciences Lanzhou University Institute of Botany CAS

This article studies the response of the distribution pattern and the physiological characteristics of the ecosystem to the spontaneous precipitation and the interaction between vegetation and the atmosphere on multiple scales in arid and semi-arid zones, based on measured data of the ecological physiological parameters in the Ordas Plateau of northern China. The results show that the vegetation biomass and the energy use efficiency of photosynthesis are especially sensitive to the annual precipitation; strong and complex interactions exist between the vegetation and the atmosphere on multiple scales leading to supernormal thermal heterogeneity of the underlying surface, the strong vortex movement and turbulence. This study can facilitate understanding of the land surface processes and the influences of global climate change as well as human activities on the human environment in the arid and semi-arid zones. It also aids in improving the parameterization schemes of turbulent fluxes of a heterogeneous underlying surface for land surface processes in climate models.

关键词： climate arid zone precipitation ecosystem climate change

Using the Newtonian relaxation technique in numerical sensitivity studies

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Science China Earth Sciences 2016年第12期59卷 2454-2462页

作者： SHAO AiMei QIU ChongJian WANG XueJiao ZHANG YuXuan key laboratory of arid climatic changes and Disaster Reduction of gansu province Key Laboratory for Semi-Arid Climate Change of the Ministry of EducationCollege of Atmospheric SciencesLanzhou University

In model-based sensitivity studies,the growth of model error over long-term integrations may lead to serious deviations between the simulated and actual *** reduce these errors,we have developed a new modeling approach with application of the Newtonian relaxation technique,or *** this approach,an identical artificial Newtonian relaxation term that reflects the difference between the model reference state and its analysis(available in many sensitivity studies) is added to the prognostic equations of the two simulated states,the reference state and the perturbed state(for which observations are nonexistent).We have conducted idealized sensitivity experiments with a shallow-water model to evaluate the benefits and viability of this approach and to test its sensitivity to changes in the nudging period and error in the analysis *** experimental results confirm that this approach lead to more credible atmospheric responses to modified external forcing if the data error is within a reasonable *** results also indicate that a 12-hour period is more favorable for nudging than a 24-hour period.

关键词： Numerical simulation Sensitivity experiment Newtonian relaxation Shallow-water model

A piecewise-integration method for simulating the influence of external forcing on climate

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Progress in Natural Science:Materials International 2008年第10期18卷 1239-1247页

作者： Zhifu Zhang Chongjian Qiu Chenghai Wang key laboratory of arid climatic Changing and reducing Disaster of gansu province,College of Atmospheric Sciences,Lanzhou University.Lanzhou 730000.China key laboratory of arid climatic Changing and reducing Disaster of gansu province College of Atmospheric Sciences Lanzhou University Lanzhou 730000 China

Climate drift occurs in most general circulation models (GCMs) as a result of incomplete physical and numerical representation of the complex climate system,which may cause large uncertainty in sensitivity experiments evaluating climate response to changes in external *** solve this problem,we propose a piecewise-integration method to reduce the systematic error in climate sensitivity studies. The observations are firstly assimilated into a numerical model by using the dynamic relaxation technique to relax to the current state of atmosphere,and then the assimilated fields are continuously used to reinitialize the simulation to reduce the error of climate simulation. When the numerical model is integrated with changed external forcing,the results can be split into two parts,background and pertur- bation fields,and the background is the state before the external forcing is *** piecewise-integration method is used to con- tinuously reinitialize the model with the assimilated field,instead of the ***,the simulation error of the model with the external forcing can be *** this way,the accuracy of climate sensitivity experiments is greatly *** with a simple low-order spectral model show that this approach can significantly reduce the uncertainty of climate sensitivity experiments.

关键词： Climate model External forcing Sensitivity experiment Low-order spectral model Dynamic relaxation technique

A Multimodel Ensemble-based Kalman Filter for the Retrieval of Soil Moisture Profiles

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Advances in Atmospheric Sciences 2011年第1期28卷 195-206页

作者：张述文李得勤邱崇践 key laboratory for Semi-arid Climate change of the Ministry of Education College of Atmospheric Sciences Lanzhou University key laboratory of arid Climate change and reducing Disaster of gansu province

With the combination of three land surface models （LSMs） and the ensemble Kalman filter （EnKF）, a multimodel EnKF is proposed in which the multimodel background superensemble error covariance matrix is estimated by two different algorithms： the Simple Model Average （SMA） and the Weighted Average Method （WAM）. The two algorithms are tested and compared in terms of their abilities to retrieve the true soil moisture profile by respectively assimilating both synthetically-generated and actual near-surface soil moisture measurements. The results from the synthetic experiment show that the performances of the SMA and WAM algorithms were quite different. The SMA algorithm did not help to improve the estimates of soil moisture at the deep layers, although its performance was not the worst when compared with the results from the single-model EnKF. On the contrary, the results from the WAM algorithm were better than those from any single-model EnKF. The tested results from assimilating the field measurements show that the performance of the two multimodel EnKF algorithms was very stable compared with the single-model EnKF. Although comparisons could only be made at three shallow layers, on average, the performance of the WAM algorithm was still slightly better than that of the SMA algorithm. As a result, the WAM algorithm should be adopted to approximate the multimodel background superensemble error covariance and hence used to estimate soil moisture states at the relatively deep layers.

关键词： multimodel EnKF soil moisture land data assimilation land surface model

A variational method for correcting non-systematic errors in numerical weather prediction

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Science China Earth Sciences 2009年第10期52卷 1650-1660页

作者： SHAO AiMei XI Shuang QIU ChongJian key laboratory of arid climatic Changing and reducing Disaster of gansu province College of Atmospheric SciencesLanzhou UniversityLanzhou 730000China

A variational method based on previous numerical forecasts is developed to estimate and correct non-systematic component of numerical weather forecast error. In the method, it is assumed that the error is linearly dependent on some combination of the forecast fields, and three types of forecast combination are applied to identifying the forecasting error: 1) the forecasts at the ending time, 2) the combination of initial fields and the forecasts at the ending time, and 3) the combination of the forecasts at the ending time and the tendency of the forecast. The Single Value Decomposition (SVD) of the covariance matrix between the forecast and forecasting error is used to obtain the inverse mapping from flow space to the error space during the training period. The background covariance matrix is hereby reduced to a simple diagonal matrix. The method is tested with a shallow-water equation model by introducing two different model errors. The results of error correction for 6, 24 and 48 h forecasts show that the method is effective for improving the quality of the forecast when the forecasting error obviously exceeds the analysis error and it is optimal when the third type of forecast combinations is applied.

关键词： variational method non-systematic error Single Value Decomposition error correction shallow-water equation model

An explicit four-dimensional variational data assimilation method

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Science China Earth Sciences 2007年第8期50卷 1232-1240页

作者： QIU ChongJian ZHANG Lei SHAO AiMei key laboratory of arid climatic Changing and reducing Disaster of gansu province College of Atmospheric SciencesLanzhou UniversityLanzhou 730000China

A new data assimilation method called the explicit four-dimensional variational (4DVAR) method is proposed. In this method, the singular value decomposition (SVD) is used to construct the orthogonal basis vectors from a forecast ensemble in a 4D space. The basis vectors represent not only the spatial structure of the analysis variables but also the temporal evolution. After the analysis variables are ex-pressed by a truncated expansion of the basis vectors in the 4D space, the control variables in the cost function appear explicitly, so that the adjoint model, which is used to derive the gradient of cost func-tion with respect to the control variables, is no longer needed. The new technique significantly simpli-fies the data assimilation process. The advantage of the proposed method is demonstrated by several experiments using a shallow water numerical model and the results are compared with those of the conventional 4DVAR. It is shown that when the observation points are very dense, the conventional 4DVAR is better than the proposed method. However, when the observation points are sparse, the proposed method performs better. The sensitivity of the proposed method with respect to errors in the observations and the numerical model is lower than that of the conventional method.

关键词： data assimilation four-dimensional variation explicit method singular value decomposition shallow water equation