青藏高原大气热源在春季的形成， 标志着高原对区域和全球天气气候热力强迫的开始。本文基于1981 -2010年台站观测和JRA-55大气环流再分析资料， 研究了春季青藏高原大气热源季节内尺度的时空变化特征。发现高原大气热源在春季存在显著的10~20天准双周振荡， 在空间分布上表现为纬向偶极子型与单极子型异常模态之间的交替出现。其中， 偶极子模态表现为凝结潜热异常在高原西北部和东南部的反相变化， 而单极子模态则表现为高原上空感热异常一致性变化。在单极子模态的位相下， 高原感热异常势必诱发低层环流异常， 改变了高原东、 西部的水汽输送， 从而引起局地降水和凝结潜热异常， 产生偶极子型的大气热源分布； 随后， 这种偶极子型大气热源异常又导致近地面纬向风调整， 令高原整体感热异常不断加强， 造成水汽输送再次改变， 凝结潜热加热随之逐渐减弱， 由此高原大气热源恢复单极子模态。因此， 春季高原上空感热、 凝结潜热和局地环流的相互作用是维持高原大气热源准双周振荡的关键机制。
The formation of atmospheric heat source over the Qinghai-Xizang Plateau （QXP） in boreal spring indicates the beginning of the QXP thermal forcing on regional and global weather and climate.Based on the JRA-55 atmospheric reanalysis and station-based observation data from 1981 to 2010， the present study investigated the spatial and intraseasonal variations of the spring atmospheric heat source over the QXP.A significant 10-20-day intraseasonal oscillation （ISO） was found in the atmospheric heat source over the QXP in boreal spring.It featured an alternation between zonal dipole and monopole mode of the spring atmospheric heat source over the QXP.The dipole mode was characterized by the inverse change of anomalous condensation latent heat between the northwestern and southeastern QXP.While the monopole mode exhibited a predominantly positive or negative sensible heat anomalies over the QXP.In the phases with the dominant monopole mode， the anomalous sensible heat over the QXP could produce the low-level circulation anomaly.It gave rise to the distinct water vapor transport between the eastern and western QXP， inducing the opposite variation of the local precipitation and condensation latent heat anomaly over the eastern and western QXP.The ISO thus entered its zonal dipole mode.As the atmospheric response to the anomalous condensation latent heat in the zonal dipole mode， the near-surface zonal wind was changed to facilitate the sensible heat anomaly over the QXP.In turn， the water vapor transport was altered over the eastern and western QXP but reversed its original property.As a result， the condensation latent heat anomaly decreased gradually over the QXP.On the one hand， the zonal dipole mode started to weaken.On the other hand， the response of the near-surface wind to the zonally asymmetric condensation heat anomaly could enhance the anomalous sensible heat over the QXP.Therefore， the atmospheric heat source over the QXP returned to the monopole mode with the homogeneous sensible heat anomaly.Finally， the interaction among sensible heat， condensation latent heat and local circulation maintained the quasi-biweekly ISO of the atmospheric heat source over the QXP in boreal spring.In addition， the zonal dipole mode of the quasi-biweekly ISO of the atmospheric heat source over the QXP led the significant anomaly of spring rainfall to the south of the Yangtze River by one phase （about 3 days）.It implicated that the biweekly ISO over the QXP could be treated as a potential subseasonal predicting precursor of the spring rainfall over East China.
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