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  • Article
    Corrigendum to “Formation and erosion of the seasonal thermocline in the Kuroshio Extension Recirculation gyre” [Deep-Sea Res. II 85 (2013) 62–74]
    (Elsevier, 2016-08-08) Cronin, Meghan F. ; Bond, Nicholas A. ; Farrar, J. Thomas ; Ichikawa, Hiroshi ; Jayne, Steven R. ; Kawai, Yoshimi ; Konda, Masanori ; Qiu, Bo ; Rainville, Luc ; Tomita, Hiroyuki
  • Article
    Formation and erosion of the seasonal thermocline in the Kuroshio Extension Recirculation Gyre
    (Elsevier Ltd., 2012-07-21) Cronin, Meghan F. ; Bond, Nicholas A. ; Farrar, J. Thomas ; Ichikawa, Hiroshi ; Jayne, Steven R. ; Kawai, Yoshimi ; Konda, Masanori ; Qiu, Bo ; Rainville, Luc ; Tomita, Hiroyuki
    Data from the Kuroshio Extension Observatory (KEO) surface mooring are used to analyze the balance of processes affecting the upper ocean heat content and surface mixed layer temperature variations in the Recirculation Gyre (RG) south of the Kuroshio Extension (KE). Cold and dry air blowing across the KE and its warm RG during winter cause very large heat fluxes out of the ocean that result in the erosion of the seasonal thermocline in the RG. Some of this heat is replenished through horizontal heat advection, which may enable the seasonal thermocline to begin restratifying while the net surface heat flux is still acting to cool the upper ocean. Once the surface heat flux begins warming the ocean, restratification occurs rapidly due to the low thermal inertia of the shallow mixed layer depth. Enhanced diffusive mixing below the mixed layer tends to transfer some of the mixed layer heat downward, eroding and potentially modifying sequestered subtropical mode water and even the deeper waters of the main thermocline during winter. Diffusivity at the base of the mixed layer, estimated from the residual of the mixed layer temperature balance, is roughly 3×10−4 m2/s during the summer and up to two orders of magnitude larger during winter. The enhanced diffusivities appear to be due to large inertial shear generated by wind events associated with winter storms and summer tropical cyclones. The diffusivity's seasonality is likely due to seasonal variations in stratification just below the mixed layer depth, which is large during the summer when the seasonal thermocline is fully developed and low during the winter when the mixed layer extends to the top of the thermocline.
  • Article
    Novel and flexible approach to access the open ocean: Uses of sailing research vessel Lady Amber during SPURS-2.
    (Oceanography Society, 2019-06-14) Rainville, Luc ; Centurioni, Luca R. ; Asher, William E. ; Clayson, Carol A. ; Drushka, Kyla ; Edson, James B. ; Hodges, Benjamin A. ; Hormann, Verena ; Farrar, J. Thomas ; Schanze, Julian J. ; Shcherbina, Andrey Y.
    SPURS-2 (Salinity Processes in the Upper-ocean Regional Study 2) used the schooner Lady Amber, a small sailing research vessel, to deploy, service, maintain, and recover a variety of oceanographic and meteorological instruments in the eastern Pacific Ocean. Low operational costs allowed us to frequently deploy floats and drifters to collect data necessary for resolving the regional circulation of the eastern tropical Pacific. The small charter gave us the opportunity to deploy drifters in locations chosen according to current conditions, to recover and deploy various autonomous instruments in a targeted and adaptive manner, and to collect additional near-surface and atmospheric measurements in the remote SPURS-2 region.
  • Article
    From salty to fresh—salinity processes in the Upper-ocean Regional Study-2 (SPURS-2) : diagnosing the physics of a rainfall-dominated salinity minimum
    (The Oceanography Society, 2015-03) Schmitt, Raymond W. ; Asher, William E. ; Bingham, Frederick ; Carton, James A. ; Centurioni, Luca R. ; Farrar, J. Thomas ; Gordon, Arnold L. ; Hodges, Benjamin A. ; Jessup, Andrew T. ; Kessler, William S. ; Rainville, Luc ; Shcherbina, Andrey Y.
    One of the notable features of the global ocean is that the salinity of the North Atlantic is about 1 psu higher than that of the North Pacific. This contrast is thought to be due to one of the large asymmetries in the global water cycle: the transport of water vapor by the trade winds across Central America and the lack of any comparable transport into the Atlantic from the Sahara Desert. Net evaporation serves to maintain high Atlantic salinities, and net precipitation lowers those in the Pacific. Because the effects on upper-ocean physics are markedly different in the evaporating and precipitating regimes, the next phase of research in the Salinity Processes in the Upper-ocean Regional Study (SPURS) must address a high rainfall region. It seemed especially appropriate to focus on the eastern tropical Pacific that is freshened by the water vapor carried from the Atlantic. In a sense, the SPURS-2 Pacific region will be looking at the downstream fate of the freshwater carried out of the SPURS-1 North Atlantic region. Rainfall tends to lower surface density and thus inhibit vertical mixing, leading to quite different physical structure and dynamics in the upper ocean. Here, we discuss the motivations for the location of SPURS-2 and the scientific questions we hope to address.
  • Article
    Salinity and temperature balances at the SPURS central mooring during fall and winter
    (The Oceanography Society, 2015-03) Farrar, J. Thomas ; Rainville, Luc ; Plueddemann, Albert J. ; Kessler, William S. ; Lee, Craig M. ; Hodges, Benjamin A. ; Schmitt, Raymond W. ; Edson, James B. ; Riser, Stephen C. ; Eriksen, Charles C. ; Fratantoni, David M.
    One part of the Salinity Processes in the Upper-ocean Regional Study (SPURS) field campaign focused on understanding the physical processes affecting the evolution of upper-ocean salinity in the region of climatological maximum sea surface salinity in the subtropical North Atlantic (SPURS-1). An upper-ocean salinity budget provides a useful framework for increasing this understanding. The SPURS-1 program included a central heavily instrumented mooring for making accurate measurements of air-sea surface fluxes, as well as other moorings, Argo floats, and gliders that together formed a dense observational array. Data from this array are used to estimate terms in the upper-ocean salinity and heat budgets during the SPURS-1 campaign, with a focus on the first several months (October 2012 to February 2013) when the surface mixed layer was becoming deeper, fresher, and cooler. Specifically, we examine the salinity and temperature balances for an upper-ocean mixed layer, defined as the layer where the density is within 0.4 kg m–3 of its surface value. The gross features of the evolution of upper-ocean salinity and temperature during this fall/winter season are explained by a combination of evaporation and precipitation at the sea surface, horizontal transport of heat and salt by mixed-layer currents, and vertical entrainment of fresher, cooler fluid into the layer as it deepened. While all of these processes were important in the observed seasonal (fall) freshening at this location in the salinity-maximum region, the variability of salinity on monthly-to-intraseasonal time scales resulted primarily from horizontal advection.
  • Article
    ASIRI : an ocean–atmosphere initiative for Bay of Bengal
    (American Meteorological Society, 2016-11-22) Wijesekera, Hemantha W. ; Shroyer, Emily L. ; Tandon, Amit ; Ravichandran, M. ; Sengupta, Debasis ; Jinadasa, S. U. P. ; Fernando, Harindra J. S. ; Agrawal, Neeraj ; Arulananthan, India K. ; Bhat, G. S. ; Baumgartner, Mark F. ; Buckley, Jared ; Centurioni, Luca R. ; Conry, Patrick ; Farrar, J. Thomas ; Gordon, Arnold L. ; Hormann, Verena ; Jarosz, Ewa ; Jensen, Tommy G. ; Johnston, T. M. Shaun ; Lankhorst, Matthias ; Lee, Craig M. ; Leo, Laura S. ; Lozovatsky, Iossif ; Lucas, Andrew J. ; MacKinnon, Jennifer A. ; Mahadevan, Amala ; Nash, Jonathan D. ; Omand, Melissa M. ; Pham, Hieu ; Pinkel, Robert ; Rainville, Luc ; Ramachandran, Sanjiv ; Rudnick, Daniel L. ; Sarkar, Sutanu ; Send, Uwe ; Sharma, Rashmi ; Simmons, Harper L. ; Stafford, Kathleen M. ; St. Laurent, Louis C. ; Venayagamoorthy, Subhas K. ; Venkatesan, Ramasamy ; Teague, William J. ; Wang, David W. ; Waterhouse, Amy F. ; Weller, Robert A. ; Whalen, Caitlin B.
    Air–Sea Interactions in the Northern Indian Ocean (ASIRI) is an international research effort (2013–17) aimed at understanding and quantifying coupled atmosphere–ocean dynamics of the Bay of Bengal (BoB) with relevance to Indian Ocean monsoons. Working collaboratively, more than 20 research institutions are acquiring field observations coupled with operational and high-resolution models to address scientific issues that have stymied the monsoon predictability. ASIRI combines new and mature observational technologies to resolve submesoscale to regional-scale currents and hydrophysical fields. These data reveal BoB’s sharp frontal features, submesoscale variability, low-salinity lenses and filaments, and shallow mixed layers, with relatively weak turbulent mixing. Observed physical features include energetic high-frequency internal waves in the southern BoB, energetic mesoscale and submesoscale features including an intrathermocline eddy in the central BoB, and a high-resolution view of the exchange along the periphery of Sri Lanka, which includes the 100-km-wide East India Coastal Current (EICC) carrying low-salinity water out of the BoB and an adjacent, broad northward flow (∼300 km wide) that carries high-salinity water into BoB during the northeast monsoon. Atmospheric boundary layer (ABL) observations during the decaying phase of the Madden–Julian oscillation (MJO) permit the study of multiscale atmospheric processes associated with non-MJO phenomena and their impacts on the marine boundary layer. Underway analyses that integrate observations and numerical simulations shed light on how air–sea interactions control the ABL and upper-ocean processes.
  • Article
    Autonomous multi-platform observations during the Salinity Processes in the Upper-ocean Regional Study
    (Oceanography Society, 2017-06) Lindstrom, Eric ; Shcherbina, Andrey Y. ; Rainville, Luc ; Farrar, J. Thomas ; Centurioni, Luca R. ; Dong, Shenfu ; D'Asaro, Eric A. ; Eriksen, Charles C. ; Fratantoni, David M. ; Hodges, Benjamin A. ; Hormann, Verena ; Kessler, William S. ; Lee, Craig M. ; Riser, Stephen C. ; St. Laurent, Louis C. ; Volkov, Denis L.
    The Salinity Processes in the Upper-ocean Regional Study (SPURS) aims to understand the patterns and variability of sea surface salinity. In order to capture the wide range of spatial and temporal scales associated with processes controlling salinity in the upper ocean, research vessels delivered autonomous instruments to remote sites, one in the North Atlantic and one in the Eastern Pacific. Instruments sampled for one complete annual cycle at each of these two sites, which are subject to contrasting atmospheric forcing. The SPURS field programs coordinated sampling from many different platforms, using a mix of Lagrangian and Eulerian approaches. This article discusses the motivations, implementation, and first results of the SPURS-1 and SPURS-2 programs.
  • Article
    Bay of Bengal intraseasonal oscillations and the 2018 monsoon onset
    (American Meteorological Society, 2021-10-01) Shroyer, Emily L. ; Tandon, Amit ; Sengupta, Debasis ; Fernando, Harindra J. S. ; Lucas, Andrew J. ; Farrar, J. Thomas ; Chattopadhyay, Rajib ; de Szoeke, Simon P. ; Flatau, Maria ; Rydbeck, Adam ; Wijesekera, Hemantha W. ; McPhaden, Michael J. ; Seo, Hyodae ; Subramanian, Aneesh C. ; Venkatesan, Ramasamy ; Joseph, Jossia K. ; Ramsundaram, S. ; Gordon, Arnold L. ; Bohman, Shannon M. ; Pérez, Jaynise ; Simoes-Sousa, Iury T. ; Jayne, Steven R. ; Todd, Robert E. ; Bhat, G. S. ; Lankhorst, Matthias ; Schlosser, Tamara L. ; Adams, Katherine ; Jinadasa, S. U. P. ; Mathur, Manikandan ; Mohapatra, Mrutyunjay ; Rama Rao, E. Pattabhi ; Sahai, Atul Kumar ; Sharma, Rashmi ; Lee, Craig ; Rainville, Luc ; Cherian, Deepak A. ; Cullen, Kerstin ; Centurioni, Luca R. ; Hormann, Verena ; MacKinnon, Jennifer A. ; Send, Uwe ; Anutaliya, Arachaporn ; Waterhouse, Amy F. ; Black, Garrett S. ; Dehart, Jeremy A. ; Woods, Kaitlyn M. ; Creegan, Edward ; Levy, Gad ; Kantha, Lakshmi ; Subrahmanyam, Bulusu
    In the Bay of Bengal, the warm, dry boreal spring concludes with the onset of the summer monsoon and accompanying southwesterly winds, heavy rains, and variable air–sea fluxes. Here, we summarize the 2018 monsoon onset using observations collected through the multinational Monsoon Intraseasonal Oscillations in the Bay of Bengal (MISO-BoB) program between the United States, India, and Sri Lanka. MISO-BoB aims to improve understanding of monsoon intraseasonal variability, and the 2018 field effort captured the coupled air–sea response during a transition from active-to-break conditions in the central BoB. The active phase of the ∼20-day research cruise was characterized by warm sea surface temperature (SST > 30°C), cold atmospheric outflows with intermittent heavy rainfall, and increasing winds (from 2 to 15 m s−1). Accumulated rainfall exceeded 200 mm with 90% of precipitation occurring during the first week. The following break period was both dry and clear, with persistent 10–12 m s−1 wind and evaporation of 0.2 mm h−1. The evolving environmental state included a deepening ocean mixed layer (from ∼20 to 50 m), cooling SST (by ∼1°C), and warming/drying of the lower to midtroposphere. Local atmospheric development was consistent with phasing of the large-scale intraseasonal oscillation. The upper ocean stores significant heat in the BoB, enough to maintain SST above 29°C despite cooling by surface fluxes and ocean mixing. Comparison with reanalysis indicates biases in air–sea fluxes, which may be related to overly cool prescribed SST. Resolution of such biases offers a path toward improved forecasting of transition periods in the monsoon.