ABSTRACT

Madi was a category-2 cyclonic storm formed over the south-western Bay of Bengal (BoB) in December 2013. It formed on 6th December as a depression, and by 8^th December it became a very severe cyclonic storm. Some unique features of Madi were: (a) an unexpected reduction in the intensity during its north-westward movement, (b) sudden change in track by almost 180^o in a south-westerly direction, and (c) swift dissipation in the open ocean while moving over cold-core eddies during its south-westward movement. The rapid weakening in intensity before track reversal occurred mainly due to its passage over cold-core eddies, where the upper-ocean heat content was reduced due to eddy-pumping of cold water from the subsurface. An analysis of the eddy-feedback factor reiterated that the slower movement of the cyclone was due to the cold-core eddy. When the cyclone entered into the cold-core eddy region, it slowed-down and changed its track towards a south-westerly direction under the influence of prevailing north-easterly winds. The biogeochemical response of Madi estimated using the satellite remote sensing and Bio Argo data showed an increase in Chlorophyll-a (Chl-a) concentration from 0.2-0.4–2.7 mg/m³, while the net primary productivity (NPP) increased from 320 to 2500 mg C/m² /day, both of which were about 7 and 8 times respectively higher than the before-cyclone values. The CO₂ flux showed a 4 times increase from its pre-cyclone value of 3.5 mmol/m² /day, indicating that BoB becomes a strong source to the atmosphere during the cyclone Madi period.

摘要

马迪是 2013 年 12 月在孟加拉湾西南部 (BoB) 上空形成的 2 级气旋风暴。它于 12 月 6 日以低气压形式形成，到 12 月 8^日成为非常严重的气旋风暴。Madi 的一些独特特征是：(a) 在其向西北运动期间强度出人意料地降低，(b) 轨道突然变化近 180^度在西南方向，以及 (c) 在其西南运动过程中在冷芯涡流上移动时在开阔海洋中迅速消散。轨道反转前强度的迅速减弱主要是由于它通过冷芯涡流，由于从地下冷水的涡流抽吸，上层海洋的热量减少了。对涡流反馈因素的分析重申，气旋运动较慢是由于冷芯涡流。气旋进入冷芯涡流区后，在盛行的东北风影响下减速并转向西南方向。使用卫星遥感和 Bio Argo 数据估计的马迪生物地球化学响应显示叶绿素-a增加(Chl-a) 浓度从 0.2-0.4–2.7 mg/m ³，而净初级生产力 (NPP) 从 320 提高到 2500 mg C/m ² /天，分别是 7 倍和 8 倍。旋风前的值。CO _{2通量比旋风前的3.5 mmol/m} ² /天增加了4倍，表明BoB在旋风马迪时期成为大气的强源。