5The Bay of Bengal (BoB) plays a fundamental role in controlling the weather systems that make up the South Asian summer monsoon system. In particular, the southern BoB has cooler sea surface temperature (SST) that influence ocean-atmosphere interaction and impact on the monsoon. Compared to the southeast, the southwestern BoB is cooler, more saline, receives much less rain, and is influenced by the Summer Monsoon Current (SMC). To examine the impact of these features on the monsoon, the BoB Boundary Layer Experiment (BoBBLE) was jointly undertaken by India and the UK during June
The strong stratification of the Bay of Bengal (BoB) causes rapid variations in sea surface temperature (SST) that influence the development of monsoon rainfall systems. This stratification is driven by the salinity difference between the fresh surface waters of the northern bay and the supply of warm, salty water by the Southwest Monsoon Current (SMC). Despite the influence of the SMC on monsoon dynamics, observations of this current during the monsoon are sparse. Using data from high-resolution in situ measurements along an east–west section at 8°N in the southern BoB, we calculate that the northward transport during July 2016 was between 16.7 and 24.5 Sv (1 Sv ≡ 106 m3 s−1), although up to ⅔ of this transport is associated with persistent recirculating eddies, including the Sri Lanka Dome. Comparison with climatology suggests the SMC in early July was close to the average annual maximum strength. The NEMO 1/12° ocean model with data assimilation is found to faithfully represent the variability of the SMC and associated water masses. We show how the variability in SMC strength and position is driven by the complex interplay between local forcing (wind stress curl over the Sri Lanka Dome) and remote forcing (Kelvin and Rossby wave propagation). Thus, various modes of climatic variability will influence SMC strength and location on time scales from weeks to years. Idealized one-dimensional ocean model experiments show that subsurface water masses advected by the SMC significantly alter the evolution of SST and salinity, potentially impacting Indian monsoon rainfall.
During the Bay of Bengal (BoB) Boundary Layer Experiment (BoBBLE) in the southern BoB, time series of microstructure measurements were obtained at 8 • N, 89 • E from 4-14 July, 2016. These observations captured events of barrier layer (BL) erosion and re-formation. Initially, a three-layer structure was observed: a fresh surface mixed layer (ML) of thickness 10-20 m; a BL below of 30-40 m thickness with similar temperature but higher salinity; a high salinity core layer, associated with Summer Monsoon Current. Each of 93 reason for this is the lack of direct turbulence and mixing observations, particularly in 94 the BoB. In the BoB, measurements of vertical mixing have been made in the north (Lu-95 cas et al. 2016; Mahadevan et al. 2016) and near Sri Lanka (Jinadasa et al. 2016). Here 96 we present micro-structure measurements that captured the erosion of the barrier layer 97 and its re-formation during a 10-day time series in the southern BoB during the summer 98 monsoon of 2016. The data have been used to understand the characteristics of mixing 99 5in the barrier layer, and the mechanism of barrier layer formation and erosion. Our data 100 suggest that the advection of high salinity surface waters by the SMC to the southern 101 BoB has an important role in the barrier layer erosion.
102The paper is organized as follows: The measurements and methodologies are de-103 scribed in Section 2. Observations of barrier layer formation and erosion are presented 104 in Section 3. Formation mechanisms of the barrier layer and its turbulent characteristics 105 are addressed in Section 4. Section 5 details the mechanism of barrier layer erosion. 106 A 1D model analysis is presented in Section 6. The summary and conclusions of the 107 present study are given in Section 7. 108 2. Methods and field campaign 109
The longer persistence of the high water level around high tide implies that a storm surge is more likely to coincide with the high tide, leading to a greater chance of destruction. Since the stands are associated with an amplification of the 4-hourly and 6-hourly constituents, storm surges that have a similar period are also likely to amplify more during their passage through the SES.
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