BoBBLE (Bay of Bengal Boundary Layer Experiment): Ocean⿿atmosphere interaction and its impact on the South Asian monsoon
Authors
P. N. Vinayachandran; Adrian J. Matthews; K Vijay Kumar; Alejandra Sanchez-Franks; V Thushara; Jenson V. George; V Vijith; Benjamin G. M. Webber; Bastien Y. Queste; Rajdeep Roy; Amit Sarkar; Dariusz B Baranowski; G. S Bhat; Nicholas P Klingaman; Simon C Peatman; C. Parida; Karen J Heywood; Robert Hall; Brian King; Elizabeth C Kent; Anoop Nayak; C. P Neema; P Amol; A Lotliker; A Kankonkar; D. G Gracias; S Vernekar; A. C. D'Souza; G. Valluvan; Shrikant M Pargaonkar; K. Dinesh; Jack Giddings; Manoj Joshi
A field experiment in the southern Bay of Bengal to generate new high-quality in situ observational data sets of the ocean, air⿿sea interface and atmosphere during the summer monsoon.
The 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 ⿿ July 2016. Physical and bio-geochemical observations were made using a CTD, five ocean gliders, a uCTD, a VMP, two ADCPs, Argo floats, drifting buoys, meteorological sensors and upper air radiosonde balloons. The observations were made along a zonal section at 8°N between 85.3°E and 89°E with a 10-day time series at 89°E, 8°N. This paper presents the new observed features of the southern BoB from the BoBBLE field program, supported by satellite data. Key results from the BoBBLE field campaign show the Sri Lanka Dome and the SMC in different stages of their seasonal evolution and two freshening events during which salinity decreased in the upper layer leading to the formation of thick barrier layers. BoBBLE observations were taken during a suppressed phase of the intraseasonal oscillation; they captured in detail the warming of the ocean mixed layer and preconditioning of the atmosphere to convection
Paper No
2
Publication ID : 656 & Year : 2016
Title
What Controls Seasonal Evolution of Sea Surface Temperature in the Bay of Bengal? Mixed Layer Heat Budget Analysis Using Moored Buoy Observations Along 90°E
Authors
Thangaprakash, V.P., M.S. Girishkumar, K. Suprit, N. Suresh Kumar, D. Chaudhuri,
K. Dinesh, A. Kumar, S. Shivaprasad, M. Ravichandran, J.T. Farrar, R. Sundar, and
R.A. Weller. 2016
Source
https://doi.org/10.5670/oceanog.2016.52
Abstract
Continuous time-series measurements of near surface meteorological and ocean variables obtained from Research Moored Array for African-Asian-Australian Monsoon Analysis and Prediction (RAMA) moorings at 15°N, 90°E; 12°N, 90°E; and 8°N, 90°E and an Ocean Moored buoy Network for Northern Indian Ocean (OMNI) mooring at 18°N, 90°E are used to improve understanding of air-sea interaction processes and mixed layer (ML) temperature variability in the Bay of Bengal (BoB) at seasonal time scales. Consistent with earlier studies, this analysis reveals that net surface heat flux primarily controls the ML heat balance. The penetrative component of shortwave radiation plays a crucial role in the ML heat budget in the BoB, especially during the spring warming phase when the ML is thin. During winter and summer, vertical processes contribute significantly to the ML heat budget. During winter, the presence of a strong barrier layer and a temperature inversion (warmer water below the ML) leads to warming of the ML by entrainment of warm subsurface water into the ML. During summer, the barrier layer is relatively weak, and the ML is warmer than the underlying water (i.e., no temperature inversion); hence, the entrainment cools the mixed layer. The contribution of horizontal advection to the ML heat budget is greatest during winter when it serves to warm the upper ocean. In general, the residual term in the ML heat budget equation is quite large during the ML cooling phase compared to the warming phase when the contribution from vertical heat flux is small.
