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张春燕, 王东海, 庞紫豪, 等. 2022. 物理协调大气变分客观分析模型及其在青藏高原的应用II:那曲试验区云—降水、热量和水汽的变化特征[J]. 大气科学, 46(4): 936−952. doi: 10.3878/j.issn.1006-9895.2110.21078
引用本文: 张春燕, 王东海, 庞紫豪, 等. 2022. 物理协调大气变分客观分析模型及其在青藏高原的应用II:那曲试验区云—降水、热量和水汽的变化特征[J]. 大气科学, 46(4): 936−952. doi: 10.3878/j.issn.1006-9895.2110.21078
ZHANG Chunyan, WANG Donghai, PANG Zihao, et al. 2022. Physically Consistent Atmospheric Variational Objective Analysis Model and Its Applications over the Tibetan Plateau. Part II: Characteristics of Cloud–Precipitation, Heat, and Moisture in the Naqu Region [J]. Chinese Journal of Atmospheric Sciences (in Chinese), 46(4): 936−952. doi: 10.3878/j.issn.1006-9895.2110.21078
Citation: ZHANG Chunyan, WANG Donghai, PANG Zihao, et al. 2022. Physically Consistent Atmospheric Variational Objective Analysis Model and Its Applications over the Tibetan Plateau. Part II: Characteristics of Cloud–Precipitation, Heat, and Moisture in the Naqu Region [J]. Chinese Journal of Atmospheric Sciences (in Chinese), 46(4): 936−952. doi: 10.3878/j.issn.1006-9895.2110.21078

物理协调大气变分客观分析模型及其在青藏高原的应用II:那曲试验区云—降水、热量和水汽的变化特征

Physically Consistent Atmospheric Variational Objective Analysis Model and Its Applications over the Tibetan Plateau. Part II: Characteristics of Cloud–Precipitation, Heat, and Moisture in the Naqu Region

  • 摘要: 本文利用约束变分客观分析法构建的物理协调大气变分客观分析模型,通过融合地面、探空、卫星等多源观测资料和ERA-Interim再分析资料,建立了青藏高原那曲试验区5年(2013~2017年)长时间序列的热力、动力相协调的大气分析数据集,并以此分析那曲试验区大气的基本环境特征与云—降水演变和大气动力、热力的垂直结构。分析表明:(1)试验区350 hPa以上风速的季节变化非常明显,风速在冬季11月至次年2月达到最大(>50 m s−1),盛夏7~8月风速的垂直变化最弱,温度的垂直变化最强,大气高湿区在夏秋雨季位于350~550 hPa,在冬春干季升至300~400 hPa。(2)试验区6~7月上旬降水最多;春、秋、冬三季,300~400 hPa高度层作为大气上升运动和下沉运动的交界处,是云量的集中区;夏季,增多的水汽和增强的大气上升运动导致高云和总云量明显增多,中、低云减少。(3)夏季的地表潜热通量与大气总的潜热释放最强,大气净辐射冷却最弱,高原地区较强的地面感热导致试验区500 hPa以下的近地面全年存在暖平流,500 hPa以上则由于强烈的西风和辐射冷却存在冷平流。此外,试验区整层大气全年以干平流为主,但在夏季出现了较弱的湿平流。(4)视热源Q1具有明显的垂直分层特征:全年500 hPa以下大气表现为冷源,300~500 hPa和100~150 hPa表现为热源,150~300 hPa则在冬春干季表现为冷源,在夏秋雨季表现为热源,不同高度层的冷、热源的形成原因不同,其中夏季由于增强的上升运动、感热垂直输送和水汽凝结潜热以及高云的形成,因此几乎整层大气表现为热源。

     

    Abstract: This study sets up a long-term (2013–2017) dynamically and thermodynamically consistent atmospheric dataset over the Tibetan Plateau-Naqu analysis region that is derived by a constrained variational objective analysis with ground-based, sounding, and satellite measurements as well as ERA-Interim reanalysis data. Annual evolutions of atmospheric basic environments, cloud precipitation, and large-scale dynamic and thermal structures in the Naqu analysis region are analyzed using averaged results from the five-year dataset. Results show that: (1) The seasonal variation of the wind speed above 350 hPa is significant with a maximum (>50 m s−1) from November to February in the next year. The vertical variation of the wind speed is the weakest, while that of the temperature is the strongest from July to August. The high-humidity area is located at 350–550 hPa in summer and autumn but at 300–400 hPa in winter and spring. (2) There is rich precipitation in the analysis region from June to early July. The 300–400 hPa layer (as the junction of atmospheric ascending and descending motion) is the cloud concentration area in spring, autumn, and winter. However, the enhanced atmospheric ascending convection and water vapor in summer lead to an increase of high clouds and total clouds and a decrease of medium and low clouds. (3) The surface latent heat flux and the total air-column latent heat are the strongest, whereas the air-column net radiative cooling is the weakest in summer. The strong surface sensible heating in the plateau results in the horizontal warm advection below 500 hPa, while the strong westerly and radiative cooling cause the cold advection above 500 hPa. In addition, the analysis region is characterized by dry advection in the whole year. However, there is a weak moist advection in summer. (4) The apparent heat source Q1 has obvious vertical stratification characteristics, i.e., showing diabatic cooling below 500 hPa and diabatic heating in 300–500 hPa and 100–150 hPa in the whole year. Meanwhile, the 150–300 hPa layer has diabatic cooling in the dry seasons (winter and spring) and diabatic heating in the wet seasons (from the end of spring to autumn). In summer, the entire air column is almost dominated by the diabatic heating because of the enhanced ascending motion, net latent heating, transport of sensible heat by rising turbulence, and existence of high clouds.

     

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