Abstract Climate model simulations and observations show that there is a poleward expansion of the Hadley Circulation (HC) as well as a strengthening of the hydrological cycle in a warming climate. However, to establish a relation between the two phenomena in present day climate, simultaneous investigations of the HC and hydrological cycle changes using observational/reanalysis data are necessary, which is limited as compared to model simulations. In this regard, the present study employs relative humidity (RH), cloud fraction (CF) and precipitation (RF) parameters of the hydrological cycle and analyse their long term changes within the HC ascending and descending regions, simultaneously. Long term RH and CF data (1979–2016) are obtained from ERA-I reanalysis, and RF from GPCP precipitation dataset. The boundaries of the HC are identified using the meridional Mass Stream Function (MSF) metric, a metric that can track the mass motion in the atmosphere in the meridional direction. The analysis brings out the spatial pattern of the distribution of trends in hydrological parameters within the HC boundaries. The trends are observed to be significantly positive at the edges of the HC ascending region and significantly negative in the regions near the HC edges, insignificant (and in some cases, negative) in the deep tropics. This pattern is more or less consistent in RH, CF, as well as RF parameters. Thus the study shows that there are regions of positive as well as negative trends within the both ascending and descending regions. The results are found to be in accordance with the poleward expansion of HC and strengthening of the hydrological cycle. Besides, a northward shift in the HC ascending regions are also indicated from the analysis of the annual cycle of trend in precipitation. The current investigation is thus envisaged to contribute to further exploration on the relation between the HC changes and the intensification of the hydrological cycle in a warmer climate.

中文翻译：

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哈德利环流上升和下降分支中水分、云和降水的长期变化特征

摘要 气候模式模拟和观测表明，在气候变暖的情况下，哈德利环流（HC）向两极扩张，水文循环加强。然而，要在当今气候中建立这两种现象之间的关系，需要使用观测/再分析数据同时调查 HC 和水文循环变化，这与模型模拟相比是有限的。在这方面，本研究利用水文循环的相对湿度 (RH)、云量 (CF) 和降水 (RF) 参数，同时分析它们在 HC 上升和下降区域内的长期变化。长期 RH 和 CF 数据（1979-2016）来自 ERA-I 再分析，RF 来自 GPCP 降水数据集。HC 的边界是使用子午质量流函数 (MSF) 度量确定的，该度量可以跟踪大气中子午方向的质量运动。该分析显示了 HC 边界内水文参数趋势分布的空间格局。观察到趋势在 HC 上升区域的边缘显着为正，在 HC 边缘附近的区域显着为负，在深热带地区不显着（在某些情况下为负）。这种模式在 RH、CF 以及 RF 参数中或多或少是一致的。因此，研究表明，在上升和下降区域内都存在积极和消极趋势的区域。发现结果与HC向极地扩张和水文循环的加强是一致的。此外，从降水年际变化趋势分析也表明，HC上升区有北移。因此，目前的调查预计将有助于进一步探索 HC 变化与温暖气候下水文循环加剧之间的关系。