A wind profiler radar at 205 MHz is operational since January 2017, at Cochin ( $$10.04^\circ \hbox {N}$$ 10 . 04 ∘ N ; $$76.33^\circ \hbox {E}$$ 76 . 33 ∘ E ), a region lying in the west coast of Southern Peninsular India, which also is the entry point of the Indian summer monsoon. Using the radar wind profiles obtained during April to September, the detailed vertical structure of wind during the pre-monsoon and monsoon period was studied for the years 2017 and 2018. The gradual transition from pre-monsoon to monsoon season as manifested by the development of monsoon circulations in the lower and upper troposphere is well captured by the radar observations. Parameters which characterize the strength of monsoon circulations have been derived which are shown to be potential predictors for declaring the monsoon onset over Kerala in an objective manner. The monsoon circulation during the year 2018 was studied in detail in the backdrop of extreme heavy rainfall over Kerala. It is observed that there is an anomalous decrease in the core height, but with high core speed in the Low-level Jet stream (LLJ) during 2018 as compared to year 2017. Owing to this unique placement of LLJ, it can be concluded that intense orographic lifting could have played a role in causing heavy rainfall over Kerala in 2018. The transitions in LLJ prior to heavy rainfall over south-west coast are aptly captured by the radar observations which opens up the possibility of predicting heavy rainfall events through continuous monitoring of monsoon circulation using radar.

中文翻译：

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205-MHz风廓线雷达观测的季风环流垂直结构与演化

205 MHz 的风廓线雷达自 2017 年 1 月起在科钦开始运行 ( $10.04^\circ \hbox {N}$$ 10 . 04 ∘ N ; $76.33^\circ \hbox {E}$$ 76 . 33 ∘ E )，位于印度半岛南部西海岸的地区，也是印度夏季风的入口。利用 4 月至 9 月期间获得的雷达风廓线，研究了 2017 年和 2018 年季风和季风期间风的详细垂直结构。雷达观测很好地捕捉到了对流层低层和高层的季风环流。已经推导出表征季风环流强度的参数，这些参数被证明是客观地宣布喀拉拉邦季风开始的潜在预测因子。在喀拉拉邦极端强降雨的背景下，对 2018 年的季风环流进行了详细研究。据观察，与 2017 年相比，2018 年低空急流 (LLJ) 的核心高度异常下降，但核心速度较高。由于 LLJ 的这种独特位置，可以得出结论：强烈的地形抬升可能在 2018 年导致喀拉拉邦的强降雨中发挥了作用。