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青藏高原中东部春季地表感热增强过程的多尺度特征—基于多源数据的对比分析

Multiscale Characteristics of the Surface Sensible Heat Enhancement Process in the Central and Eastern Tibetan Plateau in Spring: A Comparative Analysis Based on Multi-source Datasets

  • 摘要: 多源地表感热资料在青藏高原的适用性评估,对准确揭示该区域热力异常的气候效应尤为重要。本文基于地面气象站实测资料、JRA-55、ERA5和MERRA2再分析资料,对1982-2020年青藏高原中东部春季地表感热增强过程多尺度特征进行了分析,评估了 JRA-55、ERA5和MERRA2等多源地表感热通量逐日资料在青藏高原的适用性。研究表明:(1)青藏高原中东部地表感热年内由弱转强时间(T1)平均出现在第14-17候(3月上、中旬),之后持续增强,峰值时间(T2)均出现在第30候之前,其春季增强过程平均持续14候(70天)左右的时间,增强强度(Q)在45-60W/m2;在季节内演变上,地表感热增强过程具有显著的准双周振荡特征,主周期为10-20天,可解释总季节变率的30%~50%,在位相演变上,以单极子型变化为主;T1和T2在2000年前后存在趋势突变,表现为先提早后推迟特征,Q在2000年前后存在气候态整体减弱特征。(2)对3套再分析资料的春季地表感热日增量和候增量评估表明,相较于JRA-55和ERA5,MERRA2在季节内准双周振荡强度和位相演变,以及T1、T2和Q的年际变化上均与站点观测值显著相关,在青藏高原中东部具有最佳适用性,其次是JRA-55,ERA5的表现相对较弱。(3)对春季地面风速和地气温差增量的评估表明,3套再分析资料均能较好表现地面风速的年际变化和空间分布,有50%以上的站点与观测值显著相关,但ERA5均值整体偏小一半,而JRA-55和MERRA2在青藏高原西南部存在异常偏大;在地气温差增量上,MERRA2的空间分布与站点观测最为相似,而JRA-55和ERA5由于地表温度增量和空气温度增量与观测值偏差的不一致,出现气候态的异常偏小(JRA-55)和偏大(ERA5);MERRA2在地面风速和地气温差增量上的综合表现均优于JRA-55和ERA5,这可能是其在地表感热增强过程的季节内演变和年际变化上表现较好的主要原因。研究结果为青藏高原地表感热逐日资料的选取提供了参考,同时为深入揭示青藏高原春季地表感热增强过程异常的气候影响奠定了基础。

     

    Abstract: Thermal anomalies of the Tibetan Plateau (TP) plays a critical role in driving the Asian monsoon system and global atmospheric circulation. However, the selection of heat source data for the TP has been controversial in its climate impact research. Therefore, the evaluation of the suitability of multi-source data on the TP is of particular importance. Based on station observations and reanalysis datasets (JRA-55, ERA5, and MERRA2), this study systematically analyzed the multi-scale characteristics of the springtime surface sensible heat (SH) enhancement process in the central-eastern TP (CETP) from 1982 to 2020 and evaluated the applicability of multi-source daily surface SH flux data in the TP region. The results have shown that: (1) On average, the time (T1) when the surface sensible heat (SH) over the CETP changes from weak to strong within a year occurs during the 14th - 17th pentads (early and mid - March). Subsequently, it keeps increasing. The peak time (T2) always occurs before the 30th pentad. The average duration of its increasing process in spring is approximately 14 pentads (70 days), and the increasing intensity (Q) ranges from 45 to 60 W/m2. In terms of intraseasonal evolution, the SH enhancement process exhibits a pronounced quasi-biweekly oscillation with a dominant periodicity of 10–20 days, accounting for 30% to 50% of the total seasonal variance. Regarding phase evolution, the pattern is primarily characterized by a single-pole mode. Both T1 and T2 undergo a trend shift around 2000, characterized by an initial decrease followed by an increase. Meanwhile, Q displays a notable weakening in its climatological state around the same period. (2) Evaluation of three surface sensible heat (SH) flux reanalysis datasets reveals that, compared to JRA-55 and ERA5, MERRA2 exhibits significantly higher correlations with station observations in both the intensity and phase evolution of quasi-biweekly oscillations during the spring SH enhancement process and the interannual variations of T1, T2, and Q. This indicates the best applicability of MERRA2 over the CETP, followed by JRA-55, whereas ERA5 performs relatively poorly. (3)Evaluation of spring surface wind speed and surface-air temperature difference increments shows that all three reanalysis datasets capture the interannual variability and spatial distribution of surface wind speed well, with over 50% of stations showing significant correlations with station observations. ERA5 has a mean value roughly half the observed, while JRA-55 and MERRA2 show anomalously large values over the southwestern Tibetan Plateau. For the temperature difference increment, MERRA2 has the most similar spatial distribution to station observations; JRA-55 and ERA5 show climatologically small and large values, respectively, due to inconsistent deviations in surface and air temperature increments. MERRA2 outperforms the other two in both variables, which may explain its better performance in intraseasonal and interannual variations of the surface sensible heat enhancement process. The findings provide a valuable reference for selecting daily SH flux data over the TP and lay the foundation for a more comprehensive understanding of the climatic impacts of anomalies in the spring surface sensible heat enhancement process in this region.

     

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