A two-dimensional energy balance climate model on Mars

A two-dimensional energy balance climate model has been built to investigate the climate on Mars.The model takes into account the balance among solar radiation,longwave radiation,and energy transmission and can be solved analytically by Legendre polynomials.With the parameters for thermal diffusion and radiation processes being properly specified,the model can simulate a reasonable surface atmospheric temperature distribution but not a very perfect vertical atmospheric temperature distribution compared with numerical results,such as those from the Mars Climate Database.With varying solar radiation in a Martian year,the model can simulate the seasonal variation of the air temperature on Mars.With increasing dust content,the Martian atmosphere gradually warms.However,the warming is insignificant in the cold and warm scenarios,in which the dust mixing ratio varies moderately,whereas the warming is significant in the storm scenario,in which the dust mixing ratio increases dramatically.With an increasing albedo value of either the polar cap or the non-ice region,Mars gradually cools.The mean surface atmospheric temperature decreases moderately with an increasing polar ice albedo,whereas it increases dramatically with an increasing non-ice albedo.This increase occurs because the planetary albedo of the ice regions is smaller than that of the non-ice region.

基于NPP VIIRS数据和SEBS模型的河南省冬小麦蒸散量估算与时空特征

农田蒸散量(evapotranspiration,ET)是农田水热交换过程的关键变量,准确估算农田ET对了解农田土壤水分变化动态,监测预测作物旱情,指导科学灌溉等具有重要作用。将Suomi NPP(National Polar-orbiting Partnership)卫星的新型遥感数据源可见光红外成像辐射仪(visible infrared imaging radiometer suite,VIIRS)数据用于ET反演,基于地表能量平衡理论,将NPP VIIRS反演的地表温度、地表反照率等参数和优化计算的VIIRS NDVI(normalized difference vegetation index)数据,与SRTM DEM数据和气象观测数据输入地表能量平衡系统(surface energy balance system,SEBS)模型,估算了2016—2018年河南省冬小麦关键生育时期——返青期至灌浆期的农田ET(VIIRS ET)。分别对比了VIIRS ET与彭曼公式(Penman-Monteith,P-M)计算的P-M ET、大型土壤蒸渗仪实测Real ET和MODIS(moderate-resolution imaging spectroradiometer)数据估算ET(MODIS ET)的结果,并进行了ET时空变化特征分析。结果表明,VIIRS ET与Real ET的RMSE为0.203 mm·d^(–1),且VIIRS ET与P-M ET和MODIS ET均具有较高的一致性。该方法可为利用NPP VIIRS数据和SEBS模型估算ET提供方法、技术上的支持。研究区冬小麦关键生育时期ET的时间特征表现为自返青期后逐日上升,抽穗期达到最大值,灌浆期开始下降的趋势,与冬小麦生长发育规律具有较好的一致性。综合空间特征来看,在关键生育时期河南省冬小麦ET均呈现中部和东南部较高,向西北部和西南部逐渐降低的趋势,与灌溉条件具有较强的对应性。河南省冬小麦ET时空特征可为河南省农业水资源管理、分配和高效利用等提供重要依据。

基于MODIS产品影像及陆面能量平衡系统(SEBS)的河北平原区域蒸散估算(英文)

地表蒸散是区域水文循环的重要组成部分之一,传统的地表蒸散估算一般基于点上的气象观测数据,当用于区域地表蒸散评价时,具有一定的局限性。随着遥感技术的发展,利用遥感影像能够对大区域进行观测的优势进行区域地表蒸散估算已成为可能。地表能量平衡系统(SEBS)是根据地表能量平衡估算地表蒸散量的一种方法,该方法由于提出了地表能量传输过程中关键制约因素热传导粗糙度的估算模型而在遥感蒸散计算方面具有较高的精度。本文在SEBS模型的基础上,以河北平原为例,采取中分辨率成像光谱辐射仪(MODIS)产品影像,根据研究区下垫面的实际情况进行了参数估算,进行了区域实际蒸发蒸腾量计算及模型精确度评价,并在SEBS模型的基础上,提出了新的"标准化温度差-反照率"特征空间分析方法,对研究区内地表土壤水分现状进行了评价;最后,对河北平原地表蒸散时空分布进行了分析。计算结果表明,在所选取的晴空乌云条件下,根据SEBS模型计算所得的地表蒸散与研究区内利用大型承重式蒸渗仪所测量的地表实际蒸散量具有很好的一致性,说明SEBS模型在遥感蒸散计算方面据有较高的可信度。然而,由于地表蒸散的遥感估算是以所获取的遥感影像单元为基础,计算误差不可避免,尤其是使用低分辨率遥感影像的时候,每个影像单元所反映的地表蒸散为单元内各种地表覆盖的综合反映,当与只反映一种地表覆盖蒸散的大型承重式蒸渗仪测量结果进行比较时,误差是显而易见的,因此,若着重考虑模型精度验证,尚需在以后的研究中考虑使用高分辨率的遥感影像。地表土壤水分或湿度状况是地表能量交换及蒸散发生的主要控制因素。利用地表温度与植被指数的关系对区域地表湿度状况进行监测在实践中被广泛利用,然而,由于不用地区地表属性的千差万别,当利用这种方法进行区域地表湿度评价时,"地表温度-植被指数"特征空间的边界很难确定。本文在SEBS模型的基础上,提出新的"标准化温度差-反照率"特征空间分析方法,对研究区内地表土壤水分现状进行评价,结果显示,由于在SEBS模型中考虑了干限和湿限两种极端情况下的能量平衡,"标准化温度差-反照率"特征空间的边界问题很容易被确定,利用修正的特征空间,可以对区域土壤水分或湿度状况进行客观的评价。下垫面的几何特征参数的精确反演是进行地表能量平衡模拟的基础,目前多根据有关经验公式利用遥感影像进行下垫面几何特征参数估算,由于已有的经验公式多基于不同研究区域获得,当应用到新的研究区时,其具体参数需要进一步调整,以获得对下垫面的几何特征的精确描述。由于缺乏相关实测资料,本研究中利用经验公式进行下垫面几何特征参数,误差不可避免,需要在以后的研究中进行深入探索。另外,地表蒸散的计算只是进行区域水资源评价、农业节水措施评价以及全球变化等研究的一个中间环节,需要在以后的研究中根据具体研究目的进行进一步研究。

SEBS模型在黄淮海地区地表能量通量估算中的应用

在对SEBS模型的有关参数进行订正的基础上,利用MODIS遥感数据结合地表气象观测数据,对黄淮海地区地表能量通量进行了估算。将SEBS估算结果先与北京顺义定量遥感综合试验(QRSLSP/Shunyi)实测结果进行对比分析,然后与郑州的大孔径闪烁仪(LAS)观测的感热通量进行对比分析。结果表明,SEBS估算的通量与二者的实测结果相当一致。因此,利用改进后的SEBS模型估算的黄淮海地区地表能量通量具有一定的精度,可满足区域日蒸散量计算等的需求。

北京大学陆面过程模式PKULM(Peking University Land Model)介绍及检验

陆面过程模式是气候模式和天气模式的核心组成部分之一.在土壤—植被—大气耦合模式(Soil-PlantAtmosphere Model,SPAM)的基础上,发展了新一代北京大学陆面过程模式PKULM(Peking University Land Model).本文首先介绍了PKULM的辐射传输、湍流输送、光合作用、土壤水热输送等过程的参数化方案;采用隐式迭代计算框架,发展并应用了一个快速的线性方程组求解算法,提高了模式计算稳定性;提出并使用了二分搜索算法计算气孔阻抗,避免了CLM(Community Land Model)等使用的迭代方法在干旱区不稳定的情况,提高了模式的适用性;采用水势为基础的土壤水分扩散方程,使模式能够模拟土壤饱和区的水分输送过程,为进一步与水文过程模式耦合奠定了基础;还发展了一个地表积水与径流过程的机理模型,提高了模式对地表水分平衡过程的模拟能力;最后,使用"中国西北干旱区陆—气相互作用观测试验"平凉站的资料对模式进行了检验并与NOAH(National Center for Environmental Prediction,Oregon State University,Air Force,and Hydrology Lab model)陆面过程模式的模拟结果进行了比较,结果表明PKULM能够较好地模拟西北半干旱区农田下垫面地气交换过程.

基于SEBS模型的干旱区流域蒸散发估算探究

水资源在干旱区的经济社会发展中占据着举足轻重的地位,被利用的水资源通过蒸散发进入大气,定量估算区域的蒸散发对区域的水资源分配管理、旱情监测等具有一定的指导意义。应用SEBS模型估算了2015年5～9月艾比湖流域的蒸散发,按照流域的分水岭划分研究区范围,根据土地覆被类型将研究区划分为乔木林地、灌木林地、牧草地、耕地、水域及其他6大类,分析了流域内蒸散发的时间与空间变化以及不同土地覆被的蒸散发情况。结果表明:(1)整体而言,流域范围内日均蒸散量在生长季内呈单峰型分布,7月中旬达到顶峰,平均值为4.35 mm·d-1,最大值为5.63 mm·d-1,对气温的变化最敏感。(2)研究区蒸散发的高低分布与土地覆被类型分布存在高度一致性,日均蒸散量大小依次为:水域>耕地>牧草地>乔木林>其他>灌木林。(3)蒸散发在不同土地覆被具有不同的峰值分布,乔木林的峰值分别出现在1.20 mm和6.80 mm左右,灌木林的峰值分别出现在3.5 mm和6.00 mm左右,牧草地分别出现在4.00 mm和6.80 mm左右。耕地、水域的峰值分别在6.60 mm、7.20 mm左右。(4)SEBS模型在干旱区流域具有较高应用价值。

基于SEBS模型和Landsat 8数据的黑河下游蒸散发时空特性分析

对黑河下游地区蒸散发量的估算及其时空特性的研究,有助于进一步了解流域水循环,合理利用水资源,防止生态环境进一步恶化。利用SEBS模型估算了黑河下游额济纳绿洲2014年15天的日蒸散量,将SEBS估算的日蒸散与不同下垫面5个站点的EC实测值进行对比,其均方根误差和确定性系数分别为1.2 mm、0.85(5个站点),0.5 mm、0.96(2个站点),表明SEBS模型的结果是合理的,可以适用于黑河下游额济纳绿洲地区的地表蒸散量的估算。同时分析了黑河下游蒸散发的时空变化规律,结果表明,黑河下游额济纳绿洲地区,蒸散发在时间上存在明显的季节变化规律:夏季>春季>秋季>冬季;空间上呈现明显的沿河分布的趋势。不同土地覆被类型蒸散发有相似的季节变化特征,但其季节变化幅度并不相同,规律为:水体>耕地>灌丛地>草地>裸土地>沙地。

Inter-comparisons of thermodynamic sea-ice modeling results using various parameterizations of radiative flux

Radiative fluxes are of primary importance in the energy and mass balance of the sea-ice cover. Various parameterizations of the radiative fluxes are studied in a thermodynamic sea-ice model. Model outputs of the surface radiative and heat fluxes and mass balance are compared with observations. The contribution of short-wave radiation is limited to a long part of winter. Therefore, simple schemes are often sufficient. Errors in estimations of the short-wave radiation are due mainly to cloud effects and occasionally to multi-reflection between surface and ice crystals in the air. The long-wave radiation plays an important role in the ice surface heat and mass balance during most part of a winter. The effect of clouds on the accuracy of the simple radiative schemes is critical, which needs further attention. In general, the accuracy of an ice model depends on that of the radiative fluxes.

Characteristics of land-atmosphere energy and turbulentfluxes over the plateau steppe in central Tibetan Plateau

The land-atmosphere energy and turbulence exchange is key to understanding land surface processes on the Tibetan Plateau(TP). Using observed data for Aug. 4 to Dec. 3, 2012 from the Bujiao observation point(BJ) of the Nagqu Plateau Climate and Environment Station(NPCE-BJ), different characteristics of the energy flux during the Asian summer monsoon(ASM) season and post-monsoon period were analyzed. This study outlines the impact of the ASM on energy fluxes in the central TP. It also demonstrates that the surface energy closure rate during the ASM season is higher than that of the post-monsoon period. Footprint modeling shows the distribution of data quality assessments(QA) and quality controls(QC) surrounding the observation point. The measured turbulent flux data at the NPCE-BJ site were highly representative of the target land-use type. The target surface contributed more to the fluxes under unstable conditions than under stable conditions. The main wind directions(180° and 210°) with the highest data density showed flux contributions reaching 100%, even under stable conditions. The lowest flux contributions were found in sectors with low data density, e.g., 90.4% in the 360° sector under stable conditions during the ASM season. Lastly, a surface energy water balance(SEWAB) model was used to gap-fill any absent or corrected turbulence data. The potential simulation error was also explored in this study. The Nash-Sutcliffe model efficiency coefficients(NSEs) of the observed fluxes with the SEWAB model runs were 0.78 for sensible heat flux and 0.63 for latent heat flux during the ASM season, but unrealistic values of-0.9 for latent heat flux during the post-monsoon period.

Estimations of Land Surface Characteristic Parameters and Turbulent Heat Fluxes over the Tibetan Plateau Based on FY-4A/AGRI Data

Accurate estimates of land surface characteristic parameters and turbulent heat fluxes play an important role in the understanding of land-atmosphere interaction. In this study, Fengyun-4A (FY-4A) Advanced Geostationary Radiation Imager (AGRI) satellite data and the China Land Data Assimilation System (CLDAS) meteorological forcing dataset CLDAS-V2.0 were applied for the retrieval of broadband albedo, land surface temperature (LST), radiation flux components, and turbulent heat fluxes over the Tibetan Plateau (TP). The FY-4A/AGRI and CLDAS-V2.0 data from 12 March 2018 to 30 April 2018 were first used to estimate the hourly turbulent heat fluxes over the TP. The time series data of in-situ measurements from the Tibetan Observation and Research Platform were divided into two halves-one for developing retrieval algorithms for broadband albedo and LST based on FY-4A, and the other for the cross validation. Results show the root-mean-square errors (RMSEs) of the FY-4A retrieved broadband albedo and LST were 0.0309 and 3.85 K, respectively, which verifies the applicability of the retrieval method. The RMSEs of the downwelling/upwelling shortwave radiation flux and downwelling/upwelling longwave radiation flux were 138.87/32.78 W m^(−2) and 51.55/17.92 W m^(−2), respectively, and the RMSEs of net radiation flux, sensible heat flux, and latent heat flux were 58.88 W m^(−2), 82.56 W m^(−2) and 72.46 W m^(−2), respectively. The spatial distributions and diurnal variations of LST and turbulent heat fluxes were further analyzed in detail.

The Representation of Soil Moisture−Atmosphere Feedbacks across the Tibetan Plateau in CMIP6

Thermal processes on the Tibetan Plateau(TP)influence atmospheric conditions on regional and global scales.Given this,previous work has shown that soil moisture−driven surface flux variations feed back onto the atmosphere.Whilst soil moisture is a source of atmospheric predictability,no study has evaluated soil moisture−atmosphere coupling on the TP in general circulation models(GCMs).In this study,we use several analysis techniques to assess soil moisture−atmosphere coupling in CMIP6 simulations including:instantaneous coupling indices;analysis of flux and atmospheric behaviour during dry spells;and a quantification of the preference for convection over drier soils.Through these metrics we partition feedbacks into their atmospheric and terrestrial components.Consistent with previous global studies,we conclude substantial inter-model differences in the representation of soil moisture−atmosphere coupling,and that most models underestimate such feedbacks.Focusing on dry spell analysis,most models underestimate increased sensible heat during periods of rainfall deficiency.For example,the model-mean bias in anomalous sensible heat flux is 10 W m−2(≈25%)smaller compared to observations.Deficient dry-spell sensible heat fluxes lead to a weaker atmospheric response.We also find that most GCMs fail to capture the negative feedback between soil moisture and deep convection.The poor simulation of feedbacks in CMIP6 experiments suggests that forecast models also struggle to exploit soil moisture−driven predictability.To improve the representation of land−atmosphere feedbacks requires developments in not only atmospheric modelling,but also surface processes,as we find weak relationships between rainfall biases and coupling indexes.

西北内陆河流域实际蒸散发对干旱的响应及其影响因素

通过对西北内陆河流域实际蒸散发(ET)的研究以解决研究区内水资源短缺问题以及有限水资源的合理利用.利用西北内陆河流域80个气象站点的气象数据和中分辨率成像光谱仪遥感产品数据,采用基于地表能量平衡理论的地表能量平衡系统(SEBS)模型,对2000-2020年西北内陆河流域ET进行定量化估算,分析其时空分布特征和对干旱状况的响应,探讨不同气候因子对ET的影响.结果表明,西北内陆河流域2000-2020年各年平均蒸散量先减小后增加,多年平均值为157.97mm.不同季节,不同土地覆被类型条件下ET均值变化为夏季>春季>秋季>冬季,水域>耕地>林地>草地>其他.西北内陆河流域干旱程度空间分布差异较为明显,ET和温度植被干旱指数有着相反的变化趋势,2000-2020年流域经历了干旱先增强后减弱的一个过程,ET为先减小后增加的趋势.21a来,西北内陆河流域平均气温、地表温度、相对湿度与蒸散发均呈正相关关系,日照时数仅在冬季与蒸散发呈负相关关系,且影响因子与蒸散发的相关性随着季节的变化而改变.通过彭曼公式和蒸发皿数据对SEBS模型模拟值进行精度验证,ET模拟值精度较高,说明模拟结果适用于本研究区.

Modeling diurnal variation of ground thermal radiance images using energy balance model and endmember composing technique

Modeling and analyzing dynamic changes of land thermal radiance scenes play an important role in thermal remote sensing.In this paper,the diurnal variation of ground surface thermal scene is mainly discussed.Firstly,based on the land surface energy balance equation,the diurnal variation of land surface temperatures(LSTs) over bare land covers were simulated by an analytical thermal model with second harmonic terms,and the diurnal LST variation of vegetation canopy was simulated using the Cupid model.Secondly,normalized difference vegetation index(NDVI),normalized difference water index(NDWI),and ratio resident-area index(RRI) were used to evaluate the endmember abundance of four land cover types including vegetation,bare soil,impervious and water area,which were calculated from IKONOS visible and near infrared(VNIR) bands.Finally,the thermal radiance scenes at various times and view angles were modeled based on the linear-energy-mixing hypothesis.The results showed that the simulated daily LST variations for vegetated and bare surfaces are correlated with the measured values with a maximum standard deviation of 2.7°C,that land thermal radiant textures with high-resolution are restored from the linear-energy-mixing method,and that the information abundance of the scene are related to the distribution of land cover,the imaging time,and the view angle.

应用遥感技术反演流域尺度的蒸散发

利用MODIS遥感数据结合地表气象观测,在对SEBS模型物理参数进行计算和灵敏度分析的基础上,得到黑河流域春、夏、秋、冬四季不同气象条件和不同下垫面条件下的地表蒸散发。依靠黑河流域综合研究站—临泽站蒸散发仪观测的蒸散发验证遥感反演的精度,结果表明遥感反演的地表蒸散发精度较高,模型参数方案可行。这一方法可以在流域尺度上揭示出流域不同下垫面的蒸散发随季节变化的空间特征。最后,利用遥感反演的蒸散发与地面站点蒸发器实测的水面蒸发量和Penman-Monteith公式计算的蒸发量进行对比分析不同下垫面条件不同季节地表潜在蒸发能力和干湿状况。

地表蒸散遥感反演双层模型的研究方法综述

通过遥感方法反演表面温度来计算地表蒸散量是定量遥感的一个很有潜力的应用领域。这种方法已成功地应用于植被完全覆盖的地表蒸散的监测,然而对于植被稀疏的地区,利用该方法模拟通量和观测通量之间存在很大的差异。产生这种差异的原因是假设辐射表面温度可以用来代替空气动力学温度。在这种假设条件下,植被完全覆盖的地表的通量计算能够得到较为满意的结果,但对于稀疏植被地表却是不成立的。对此,国内外许多学者提出了将土壤和植被分开计算的双层模型以求得到更加准确的通量结果。介绍了当前国内外几种常用的地表蒸散遥感估算双层模型,讨论了这些模型的物理基础和假设并讨论了目前双层模型在计算通量时存在的一些问题和难点,并对今后的工作重点和研究方向提出了建议。

三种下垫面温度及结冰预报模型研究

应用地表热量平衡方程,考虑太阳短波辐射、大气和地面的长波辐射、潜热、感热传输等能量之间的平衡,并考虑水汽、气溶胶、浮尘以及云等对太阳短波辐射的吸收和散射,建立了一种较实用的下垫面温度预报模型.应用湖北省恩施和金沙2009年冬季2月对土壤、水泥、沥青三种不同下垫面温度和自动气象站的常规气象要素观测进行模拟分析,并与该时段内所测到的三种下垫面温度进行对比,结果表明:两地三种下垫面温度的预测值与实测值的相关系数均在0.95以上,标准差均小于2,预报误差在±3℃以内的频率高达95.20%、96.41%、93.57%和91.19%、94.16%、88.18%,表明模型具有较高的预报水平,且对冬季不同天气条件下下垫面温度预报结果均较好,特别对于低于0℃时的预报准确性较高,可以运用于冬季高速公路路面结冰状况的实际预报中.

冬季高速公路路桥温度变化规律及能量平衡分析

利用2009年10月—2010年3月湖北省武英高速凤凰关水库自动气象站逐时路、桥面温度和常规气象资料,分析了冬季典型天空状况(晴空、阴天)和天气过程(雾、降雨、降雪)中气温、路面温度和桥面温度的变化规律。结果表明,夜间桥面温度与气温接近,比路面温度低2℃,桥面0℃以下的低温维持时间为路面维持时间的2倍左右。利用下垫面能量平衡模型,分别计算冬季夜间晴空和阴天时路、桥面辐射能量收支变化情况,分析了夜间路面和桥面温度变化差异的原因,并对桥面比路面更易结冰的现象给出了理论解释。

植被覆盖度对兰州地区气象场影响的模拟研究

利用WRF(Weather Research and Forecasting)模式耦合Noah陆面过程模式,模拟了兰州地区冬季气象场,并用观测资料对模拟结果进行了检验。利用2006年中分辨率成像分光辐射计(MODIS)植被归一化指数(NDVI)计算得到的植被覆盖度替换模式默认的植被覆盖度,研究了植被覆盖度对WRF模式模拟结果的影响。结果表明,新的植被覆盖度数据使研究区域的地表反照率减小,发射率增加,感热通量白天增加、夜间减小;还明显地改进了WRF模式对近地面温度和风速的模拟;植被覆盖度对地表蒸发有很大影响,冬季干旱半干旱地区的植被基本处于休眠状态,地表蒸发以直接蒸发为主,使用新的植被覆盖度数据后,模拟区域的植被覆盖度增加,地表蒸发减小,近地面水汽含量减少,WRF模式模拟的边界层高度增大。

基于遥感技术的绿地耗水估算与蒸散发反演

为研究北京市五环范围内的绿地耗水总量和空间分布情况,该文应用高分辨率遥感影像、长时间序列气象数据、植被耗水规律研究成果等资料,进行绿地提取、耗水估算和蒸散发反演。主要步骤包括:预处理遥感影像,分析典型地物的光谱特征,层次分类提取绿地分布,估算不同气象条件、植被覆盖条件下的耗水量,以遥感技术为基础反演日蒸散发量。遥感技术提取的北京市五环内绿地面积为197.3km2,估算年耗水量为1.61亿m3。特枯年、枯水年、平水年和丰水年的净灌溉水量分别为1.09、0.75、0.59和0.35亿m3。应用地表能量平衡模型反演典型日蒸散发结果表明,城市水体、高植被覆盖率区和低植被覆盖率区的ET均值分别为11.1、5.7和4.0mm/d。五环内城区夏季典型日蒸散总量为126.6万m3,二环内、二三环间、三四环间、四五环间的绿地日ET总量分别为:10.3、14.2、20.4和81.7万m3,该研究可为城市绿地灌溉系统设计提供耗水总量和空间分布的信息。

基于SEBAL模型的扎龙湿地蒸散量反演

以扎龙湿地为研究对象,利用SEBAL模型结合ETM+遥感影像、DEM及研究区附近12个站点的气象数据,反演得到净辐射量、土壤热通量、感热通量等地表能量通量;然后通过能量平衡方程得到潜热通量,并推算得到日蒸散量值。结合2001年的土地利用图分析了不同土地利用类型的日蒸散量特征,发现水体、沼泽地具有较高的日蒸散量,水田、草地、林地次之,旱地、未利用地、居民点较低,符合蒸散规律,说明SEBAL模型在区域蒸散量估算方面具有较大的实用性。