基于CLDAS强迫CLM3.5模式的新疆区域土壤温度陆面过程模拟及验证
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中国水利水电科学研究院,中国水利水电科学研究院,新疆大学 干旱生态环境研究所新疆 乌鲁木齐,中国气象局 国家气象信息中心 北京,中国科学院寒区旱区环境与工程研究所冰冻圈科学国家重点实验室,中国科学院新疆生态与地理研究所,中国气象局 华云信息技术工程有限公司

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水利部公益性行业科研专项经费(201301103);国家自然科学基金重点项目(41130531)


Simulation and verification of land surface soil temperatures in the Xinjiang Region by the CLM3.5 model forced by CLDAS
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School of Resources and Environment Science,Xinjiang University,Urumqi,,Institute of Arid Ecology and Environment,National Meteorological Information Center,China Meteorological Administration CMA,Beijing,,Xinjiang Institute of Ecology and Geography,Chinese Academy Sciences,Urumqi,

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    摘要:

    利用中国气象局国家气象信息中心研发的中国气象局陆面数据同化系统(China Meteorological Administration Land Data Assimilation System,CLDAS)大气近地面强迫资料,驱动美国国家大气研究中心公用陆面模式(Community Land Model,CLM3.5),对中国新疆地区土壤温度时空分布进行逐小时Off-line模拟(模拟时段为2009-2012年);利用国家土壤温度自动站(新疆区域105站点)数据验证CLDAS驱动场强迫下的CLM3.5模式在中国新疆地区3个土壤层(5cm、20cm和80cm)的土壤温度模拟能力。研究发现:在月变化方面,第1层(5cm)土壤温度模拟与实测值差异最大,在每年7月最大差异达5k左右;第2层(20cm)在每年7月达最大差异(3k左右),而第3层(80cm)在每年7月均模拟的很好。造成这种现象的原因可能因为新疆地区7月前后浅层土壤温度变化剧烈,温度白天最高可达300K以上,昼夜温差大,导致模式不能很好抓住浅层土壤温度的变化趋势。研究还发现,在80cm土壤深度,模式在1月、12月的模拟结果均较前两层差。在日变化方面,研究发现:较浅的两层(5cm和20cm)土壤温度模拟值在夏季和秋季均较差。与月变化模拟结果类似的是,80cm土壤层日变化在1、12月模拟较差,然而在其他时段却模拟的很好。在小时变化方面,分析发现:第1层土壤(5cm)模拟结果在每年的1-4月及9-11月的全天(即24 h),模式也会有不同的偏差:其中,在03UTC-21UTC之间主要表现为模式结果比观测结果偏高,而在日内21UTC-00UTC主要表现为模拟结果偏小。在每年的5-8月,全天模拟值都偏小,其中在09UTC达当日最大值。而距离第2层(20cm)处的土壤温度模拟值在大部分月份都偏差较小(-1K至1k之间),并在日内12UTC偏差达到当日最大值。研究发现,在土壤20cm处,模式模拟的最大值较观测值提前,而第3层(80cm)的土壤温度基本不受日内变化影响,表现较为平稳。造成这种影响的原因可能是因为新疆地区5-8月、9-11月为昼夜温差大,深层土壤温度较浅层土壤温度温差变化小,这也造成了模式对于浅层土壤模拟较深层差的主要原因。总体研究表明:CLDAS驱动场强迫下的CLM3.5模式可较为精确的模拟中国新疆地区多年平均土壤温度时空分布,并较为准确的反映中国新疆地区土壤温度的小时、日、月及年际的变化规律。模式浅温度模拟不好的原因可能与模式参数化方案及地表参数有关,后期将继续修正该问题。

    Abstract:

    This study modeled the spatial and temporal distribution of soil temperatures in the Xinjiang region of China, using atmospheric surface forcing data in the China Meteorological Administration Land Data Assimilation System (CLDAS, NMIC of China Meteorological Administration) to drive the Community Land Model (CLM3.5, National Center of Atmospheric Research USA) for hourly off-line simulations (from 2009 to 2012). To verify the CLM3.5 simulated soil temperatures, data from national automatic soil-temperature stations (105 in the Xinjiang region) were used at three soil layers (5 cm, 20 cm, and 80 cm). For monthly variation, simulated top layer (5cm) soil temperatures differed substantially from measured values, with the largest difference (±5℃) reaching the maximum in July each year. The difference (±3℃) between modeled and observed soil temperatures at the second layer (20 cm) reached the maximum in July for all years, whereas for the third layer (80 cm), simulated annual July soil temperatures were in accordance with the observed values. The large discrepancies in July soil temperatures in the top surface layers can be explained by the drastic surface temperature changes in the Xinjiang region during that month. With day-time temperatures that can reach above 30℃, combined with large diurnal temperature differences, it becomes very difficult to accurately capture surface temperature variation by using the model. In contrast, in January and December, the 80 cm soil depth simulations were less accurate than the results of simulations at the first two soil layers. Furthermore, simulated values of soil temperature at the top two layers (5 cm and 20 cm) did not fit well with observed values for the summer and autumn. However, similar to monthly variation, the daily variation in modeled soil temperature at 80 cm showed a bad fit with observed data in January and December, whereas the fit was good in other periods. For hourly variation at 5 cm soil depth, the simulated soil temperature values were higher than the observed ones from January to April and September to November between 03 UTC and 21 UTC the next day. In contrast, simulated results were slightly lower than the observed values between 21 UTC and 00 UTC the next day for this same layer and period. From May to August of every year, day-time simulated values are slightly lower, reaching a maximum at 09UTC. At 20 cm depth, simulated soil temperature had smaller deviations (between -1℃ and 1℃) for most months, and the daily maximum occurred at 12UTC, which is earlier than the observed values. At the 80 cm soil layer, little daily variation was simulated or observed in soil temperatures, giving this soil layer hardly any influence on the overall daily variation. In the Xinjiang region, the diurnal temperature difference is large from May to August and September to November, which can explain why the upper two soil layers show differences between modeled and observed hourly soil temperatures. Soil temperature at deep soil layers, however, will vary less with temperature differences, giving this layer a better fit than the other two. Overall, this study shows that the CLM3.5 model forced by a CLDAS driving field can simulate the multi-year spatial and temporal distribution of average soil temperatures in Xinjiang region precisely. It furthermore showed that this method could simulate and reflect the hourly, daily, monthly, and yearly patterns of soil temperature in the Xinjiang region. Finally, the poor simulation of temperatures at the surface layer may be caused by the parameterization scheme of the surface parameters in this model, which will be addressed and corrected in a later phase.

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孟现勇,王浩,刘志辉,师春香,刘时银,陈曦,龚伟伟.基于CLDAS强迫CLM3.5模式的新疆区域土壤温度陆面过程模拟及验证.生态学报,2017,37(3):979~995

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