春夏季青藏高原与伊朗高原地表热通量的时空分布特征及相互联系

伊朗高原和青藏高原热力作用对东亚区域气候具有重要影响。基于1979—2014年欧洲中心ERA-interim月平均再分析地表热通量资料，分析了春、夏季青藏高原与伊朗高原地表热通量的时、空分布特征以及春、夏季青藏高原与伊朗高原地表热通量的关系。结果表明，春、夏季青藏高原与伊朗高原地表热通量在季节、年际和年代际尺度上具有不同的时、空分布特征。对于青藏高原，春、夏季地表感热呈西部大东部小、地表潜热呈东部大西部小；地表感热在春季最大且大于地表潜热，地表潜热在夏季最大且大于地表感热。在年际时间尺度上，春、夏季青藏高原地表热通量异常的年际变化在东、西部不一致，青藏高原西部，地表感热与地表潜热有较强的负相关关系。青藏高原地表感热异常具有很强的持续性，当春季地表感热较强（弱）时，夏季高原地表感热同样较强（弱）。青藏高原东部与西部地表热通量的年代际变化有明显差异，春（夏）季青藏高原东部地表感热呈显著的年代际减弱趋势，1998（2001）年发生年代际转折，由正异常转为负异常；而青藏高原西部地表感热在春季则有显著的增大趋势，2003年发生年代际转折，由负异常转为正异常。青藏高原东部地表潜热仅在春季为显著减弱趋势，2003年出现年代际转折，由正异常转为负异常；青藏高原西部地表潜热在春、夏季都有显著减弱趋势，年代际转折出现在21世纪初，由正异常转为负异常。对于伊朗高原，春、夏季地表热通量的空间分布在整个区域较一致，地表感热在夏季最大，地表潜热在春季大、夏季小，但各季节地表感热都大于地表潜热。相对于青藏高原地表感热，伊朗高原地表感热在各月都更大。在年际时间尺度上，春、夏季伊朗高原各区域地表热通量异常的年际变化较一致；地表感热与潜热有很强的负相关关系；伊朗高原地表感热、潜热异常都具有持续性，当春季地表感热（潜热）通量较强（弱）时，夏季地表感热（潜热）通量同样较强（弱）。伊朗高原北部与南部地表热通量的年代际变化存在差异。其中，春、夏季伊朗高原北部地表感热（潜热）呈显著增强（减弱）趋势，在20世纪末发生了年代际转折，春、夏季北部地表感热（潜热）由负（正）异常转为正（负）异常。而伊朗高原南部春、夏季地表热通量无显著变化趋势，但春季地表感热、潜热与夏季地表感热同样在20世纪末存在年代际转折，地表感热（潜热）由负（正）异常转为正（负）异常。春、夏季两个高原地区地表热通量的关系主要表现为:就春季同期变化而言，伊朗高原地表感热与青藏高原西部地表感热具有同相变化关系，与青藏高原东部地表感热具有反相变化关系，伊朗高原地表潜热与青藏高原东部地表潜热具有同相变化关系；就非同期变化而言，春季伊朗高原地表感热与夏季青藏高原东部地表感热存在反相变化关系。 

Spatial and temporal distribution characteristics of surface heat fluxes over both Tibetan Plateau and Iranian Plateau in boreal spring and summer and their relationships

Elevated heat sources over the Tibetan Plateau (TP) and the Iranian Plateau (IP) have significant impacts on East Asian climate. Based on monthly mean surface heat fluxes extracted from the ERA-interim reanalysis data for the period of 1979 to 2011, surface thermal characteristics during boreal spring and summer over both TP and IP and their relationships were analyzed. The results show that the basic spatial and temporal characteristics of surface heat fluxes over TP and IP are different in the spring and summer, and surface heat fluxes in specific regions of these two plateaus exhibit different characteristics on interannual and interdecadal time scales. Over TP, surface sensible heat flux (SH) in the western part is stronger than that in the eastern part during the spring and summer, whereas the spatial distribution of surface latent heat flux (LH) is opposite with larger values in the eastern part. SH peaks in the spring and exceeds LH before the summer, but LH is larger than SH in the summer. On the interannual time scale, SH is negatively correlated with LH in western TP during the spring and summer, and SH anomalies over western TP can persist from spring to summer. On the interdecadal time scale, there is a significant difference in surface heat fluxes between eastern and western parts of TP. Springtime (summertime) SH over eastern TP exhibits a significant decreasing trend and experienced an interdecadal change in 1998 (2001), switching from positive to negative anomaly. However, springtime SH over western TP exhibits a significant increasing trend and experienced a negative-to-positive interdecadal change in 2003. The LH over eastern TP displays a significant decreasing trend only in the spring and exhibited a positive-to-negative interdecadal change in 2003. The LH over western TP exhibits a significant decreasing trend in both the spring and summer and experienced an interdecadal change at the beginning of the 21st century, switching from positive to negative anomaly. Over IP, both SH and LH are uniformly distributed during the spring and summer. SH peaks in the summer, LH is strong in the spring but weak in the summer, and it is smaller than SH all year round. SH over IP is stronger than SH over TP in each season. On the interannual time scale, spring and summer SH (LH) anomalies over the entire IP are uniformly positive (negative). There is a significant negative correlation between SH and LH over IP. SH and LH anomalies over IP can persist for quite a while. A significant difference is found in the interdecadal variability of surface heat flux between northern and southern parts of IP. The spring and summer SH (LH) over northern IP exhibits a significant increasing (decreasing) trend and experienced an interdecadal shift in the end of the 20 century, when the anomaly of SH (LH) switched from negative (positive) to positive (negative). There is no significant trend in SH and LH over southern IP during the spring and summer. However, SH over southern IP in the spring and summer experienced a negative-to-positive interdecadal change,while springtime LH experienced a positive-to-negative interdecadal change at the end of the 20th century. The relationship between surface heat fluxes over these two Plateaus is as follows:SH over IP is positively correlated with SH over western TP and is negatively correlated with SH over eastern TP in the spring; LH over IP is positively correlated with LH over eastern TP in the spring; SH over IP in the spring is negatively correlated with SH over eastern TP in the subsequent summer.