Bay of Bengal Intraseasonal Oscillations and the 2018 Monsoon Onset

Abstract In the Bay of Bengal, warm, dry boreal spring concludes with onset summer monsoon and accompanying southwesterly winds, heavy rains, variable air–sea fluxes. Here, we summarize 2018 using observations collected through multinational Monsoon Intraseasonal Oscillations in Bengal (MISO-BoB) program between United States, India, Sri Lanka. MISO-BoB aims to improve understanding intraseasonal variability, field effort captured coupled response during a transition from active-to-break conditions central BoB. The active phase ∼20-day research cruise was characterized by warm sea surface temperature (SST > 30°C), cold atmospheric outflows intermittent rainfall, increasing winds (from 2 15 m s −1 ). Accumulated rainfall exceeded 200 mm 90% precipitation occurring first week. following break period both clear, persistent 10–12 wind evaporation 0.2 h . evolving environmental state included deepening ocean mixed layer ∼20 50 m), cooling SST (by ∼1°C), warming/drying lower midtroposphere. Local development consistent phasing large-scale oscillation. upper stores significant heat BoB, enough maintain above 29°C despite fluxes mixing. Comparison reanalysis indicates biases fluxes, which may be related overly cool prescribed SST. Resolution such offers path toward improved forecasting periods monsoon.