Diagnostic analysis of two dos-à-dos extreme northeast monsoon seasons with dipolar rainfall performance

Abstract

Northeast monsoon season over the southern peninsular India during October–December 2015 and 2016 saw two back-to-back extreme seasonal rainfall performances with excess rainfall leading to floods in 2015 and largely deficient rainfall leading to drought conditions in 2016. Contrasting climate settings and Asian winter monsoon circulation features and the modulations in the seasonal flow pattern over the peninsular India and the dynamical and thermo-dynamical features associated with such contrasting seasons are discussed. During 2015, strong El Nino and positive IOD led to strengthening of easterlies over the peninsular India which resisted the eastward propagation of MJO and confined it mostly in phase 2–4. Associated with positive IOD, enhanced warming prevailed over western Indian Ocean, which led to anomalous ascending motion over the Arabian Sea and adjoining southern peninsula in the winter monsoon Walker circulation feature with anomalous upper tropospheric divergent outflow over these regions. During 2016, weak La Nina, negative to neutral IOD, MJO in the other half of the hemisphere, anomalous low-level cyclonic circulation over the central parts of southern Bay of Bengal and anomalous subsidence over the peninsular India in the Walker circulation with the upper tropospheric divergent outflow shifted to east of 100° E were associated with weakening of easterlies and penetration of continental northerlies into the southern peninsula. Associated with good rainfall activity, there was mid-tropospheric warming of about 1–3 K/day during November 2015, but, in 2016, only a heat sink is observed over most parts of the peninsular India in the mid-troposphere.