University Events

Description: The School for Marine Science and Technology
Department of Estuarine and Ocean Sciences
PhD Proposal Defense Announcement

"On The Diurnal Warm Layers in the Bay of Bengal"

by
Siddhant Kerhalkar

Advisor:
Dr. Amit Tandon, School for Marine Science & Technology, University of Massachusetts Dartmouth

Committee Members:
Dr. Miles Sundermeyer, SMAST, University of Massachusetts Dartmouth
Dr. J. Thomas Farrar, Physical Oceanography Department, Woods Hole Oceanographic Institution
Dr Kenneth Hughes, College of Earth, Ocean and Atmospheric Sciences, Oregon State University

Monday, August 23, 2021
2:00 pm-3 pm
SMAST E, Rooms 101,102,103
And via Zoom

Abstract:
Monsoons over the Indian subcontinent result in copious seasonal rainfall during May to September. The rain is dominated by inherent intra-seasonal oscillations with periods of a few weeks. These Monsoon Intra-Seasonal Oscillations (MISO) traverse the Bay of Bengal (an ocean basin located to the east of India, BoB hereafter) at various time scales bringing periods of relatively high rainfall, or active phases, followed by periods of little or no rainfall, called Break phases. The air-sea interaction during the phases is also dramatically different. MISO are not well predicted, and errors in simulating and predicting MISO affect the weather
forecasting across the globe.
Recent studies show that improvements in MISO forecasting requires (i) better understanding of the ocean-atmosphere coupling at multiple scales, and (ii) better representation of upper ocean stratification. The competition between stratifying effect of daytime trapping of solar heating, and the destabilizing effect of momentum trapped by winds, leads to diurnal warm layers (DWL) formation, which has not been studied before for the BoB. In addition, BoB is anomalously fresh and thus salinity plays a unique role. DWL evolution has an impact on the diel cycle of SSTs and air-sea interaction at sub-daily scales. Since they affect both (I) and (ii), in this thesis, we will understand and characterize DWLs in BoB and their interactions with other mesoscale and submesoscale processes. The observations analyzed in this work are from an international USA-India collaboration, MISOBOB (Monsoon Intra-Seasonal Oscillations in BoB), which
brought teams of scientists from both countries to intensively observe air-sea interaction and upper ocean processes using many autonomous and ship-based assets.
In Chapter 2, we describe the meteorological forcing and upper ocean vertical structure from the observational cruise. We also evaluate the spatial gradients in the diel cycles of SST for an oceanic mesoscale eddy O(500 km) across. During the break phase, DWLs are prominent. We explore the vertical structure of DWLs in BoB and compare them to Western Pacific. Salinity governed stratification modifies the nature of DWLs.
In Chapter 3, we propose to explore in greater detail two curious cases of DWLs in BoB. observations show different deepening rates of DWLs. We aim to understand the reasons behind this using 1-D and 3-D ocean models. In the second case, we observe large differences in the diel cycles of SST at two different drifter locations. Our working hypothesis is that these differences in diel cycles are due to the differences in background
stratification and the differences in optical properties of water. We propose to explore the DWLs in coastal waters using models.
In Chapter 4, we explore the lateral inhomogeneities in the DWL. Trapping of momentum within the DWL leads to the formation of a diurnally
varying jet which can cause lateral advection. Hence DWLs near a front could re-stratify the ocean. We aim to study the interaction of DWLs and fronts using process ocean models.
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Join Zoom Meeting
https://umassd.zoom.us/j/97864820665?pwd=Ums4T1BwSGJqN2RHYWNHZEZtL0dyQT09
Meeting ID: 978 6482 0665
Passcode: 465533
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For more information please contact Sue Silva-s1silva@umassd.edu