Differential patterns of surface winds over Bay of Bengal   during the various phases of Indian northeast monsoon   derived from QuikSCAT data, 1999-2008

Thermodynamic structure of atmospheric boundary layer during October - December covering southwest and northeast monsoon activities over interior Tamilnadu (ITN), coastal Tamilnadu (CTN) and adjoining Bay of Bengal (BOB) has been studied using TIROS Operational Vertical Sounder (TOVS) data of 1996-98. Heights of neutral stratified mixed layer, cloud layer and planetary boundary layer (PBL) have been estimated through available standard pressure level data. Highest PBL occurs during active northeast monsoon. Cloud layer thickness during weak northeast monsoon over interior Tamilnadu is significantly higher than that over coastal Tamilnadu and also over Bay of Bengal. Convective stability (instability) of the atmosphere in 850-700 hPa layer is associated with weak / withdrawal (active) phase of northeast monsoon. One of the plausible reasons for subdued rainfall activity during weak northeast monsoon over interior Tamilnadu could be convective instability seen over this region in 850-700 hPa layer. But the same is absent in CTN and BOB where no rainfall activity exists during weak monsoon phase. Virtual temperature lapse rate in 850-700 hPa layer exceeding (less than) 6oK/km is associated with active (weak) phase of northeast monsoon over the interior, coastal Tamilnadu and Bay of Bengal.

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The Seasonal Cycle of Upper-Ocean Mixing at 8°N in the Bay of Bengal

Journal of Physical Oceanography ◽

10.1175/jpo-d-19-0114.1 ◽

2020 ◽

Vol 50 (2) ◽

pp. 323-342 ◽

Cited By ~ 2

Author(s):

D. A. Cherian ◽

E. L. Shroyer ◽

H. W. Wijesekera ◽

J. N. Moum

Keyword(s):

Bay Of Bengal ◽

Seasonal Cycle ◽

Sea Water ◽

Turbulent Transport ◽

Low Frequency ◽

Salt Flux ◽

Strong Mixing ◽

Northeast Monsoon ◽

Order Of Magnitude ◽

Episodic Mixing

AbstractWe describe the seasonal cycle of mixing in the top 30–100 m of the Bay of Bengal as observed by moored mixing meters (χpods) deployed along 8°N between 85.5° and 88.5°E in 2014 and 2015. All χpod observations were combined to form seasonal-mean vertical profiles of turbulence diffusivity KT in the top 100 m. The strongest turbulence is observed during the southwest and postmonsoon seasons, that is, between July and November. The northeast monsoon (December–February) is a period of similarly high mean KT but an order of magnitude lower median KT, a sign of energetic episodic mixing events forced by near-inertial shear events. The months of March and April, a period of weak wind forcing and low near-inertial shear amplitude, are characterized by near-molecular values of KT in the thermocline for weeks at a time. Strong mixing events coincide with the passage of surface-forced downward-propagating near-inertial waves and with the presence of enhanced low-frequency shear associated with the Summer Monsoon Current and other mesoscale features between July and October. This seasonal cycle of mixing is consequential. We find that monthly averaged turbulent transport of salt out of the salty Arabian Sea water between August and January is significant relative to local E − P. The magnitude of this salt flux is approximately that required to close model-based salt budgets for the upper Bay of Bengal.

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Upper layer thermohaline structure of the Bay of Bengal during the 2013 northeast monsoon

Deep Sea Research Part II Topical Studies in Oceanography ◽

10.1016/j.dsr2.2019.07.018 ◽

2020 ◽

Vol 172 ◽

pp. 104630 ◽

Cited By ~ 2

Author(s):

Emily L. Shroyer ◽

Arnold L. Gordon ◽

Gualtiero Spiro Jaeger ◽

Mara Freilich ◽

Amy F. Waterhouse ◽

...

Keyword(s):

Bay Of Bengal ◽

Northeast Monsoon ◽

Thermohaline Structure

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ASIRI: An Ocean–Atmosphere Initiative for Bay of Bengal

Bulletin of the American Meteorological Society ◽

10.1175/bams-d-14-00197.1 ◽

2016 ◽

Vol 97 (10) ◽

pp. 1859-1884 ◽

Cited By ~ 44

Author(s):

Hemantha W. Wijesekera ◽

Emily Shroyer ◽

Amit Tandon ◽

M. Ravichandran ◽

Debasis Sengupta ◽

...

Keyword(s):

Boundary Layer ◽

High Resolution ◽

Indian Ocean ◽

Bay Of Bengal ◽

Regional Scale ◽

Ocean Dynamics ◽

Coastal Current ◽

Northeast Monsoon ◽

Low Salinity ◽

Salinity Water

Abstract 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.

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Low-Frequency Currents from Deep Moorings in the Southern Bay of Bengal

Journal of Physical Oceanography ◽

10.1175/jpo-d-16-0113.1 ◽

2016 ◽

Vol 46 (10) ◽

pp. 3209-3238 ◽

Cited By ~ 14

Author(s):

H. W. Wijesekera ◽

W. J. Teague ◽

D. W. Wang ◽

E. Jarosz ◽

T. G. Jensen ◽

...

Keyword(s):

Bay Of Bengal ◽

Low Frequency ◽

Southwest Monsoon ◽

Naval Research ◽

Northeast Monsoon ◽

Intraseasonal Oscillations ◽

The Indian Ocean ◽

Inertial Currents ◽

Large Eddies ◽

Measurement Period

AbstractHigh-resolution currents and hydrographic fields were measured at six deep-water moorings in the southern Bay of Bengal (BoB) by the Naval Research Laboratory as part of an international effort focused on the dynamics of the Indian Ocean. Currents, temperature, and salinity were sampled over the upper 500 m for 20 months between December 2013 and August 2015. One of the major goals is to understand the space–time scales of the currents and physical processes that contribute to the exchange of water between the BoB and the Arabian Sea. The observations captured Southwest and Northeast Monsoon Currents, seasonally varying large eddies including a cyclonic eddy, the Sri Lanka dome (SLD), and an anticyclonic eddy southeast of the SLD. The observations further showed intraseasonal oscillations with periods of 30–70 days, near-inertial currents, and tides. Monthly averaged velocities commonly exceeded 50 cm s−1 near the surface, and extreme velocities exceeded 150 cm s−1 during the southwest monsoon. Tides were small and dominated by the M2 component with velocities of about 3 cm s−1. The average transport into the BoB over the measurement period was 2 Sv (1 Sv ≡ 106 m3 s−1) but likely exceeded 15 Sv during summer of 2014. This study suggests the water exchange away from coastal boundaries, in the interior of the BoB, may be largely influenced by the location and strength of the two eddies that modify the path of the Southwest Monsoon Current. In addition, there is a pathway below 200 m for transport of water into the BoB throughout the year.

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Onset of northeast monsoon over South Peninsular India

MAUSAM ◽

10.54302/mausam.v71i3.51 ◽

2021 ◽

Vol 71 (3) ◽

pp. 503-512

Author(s):

SATYANARAYANA G C ◽

NAIDU C V ◽

RAO D V BHASKAR ◽

UMAKANTH N ◽

NAVEENA N

Keyword(s):

Bay Of Bengal ◽

Arabian Sea ◽

Grid Point ◽

India Meteorological Department ◽

Onset Date ◽

Data Sets ◽

Northeast Monsoon ◽

Peninsular India ◽

Northern Latitudes ◽

High Pressure Zone

The onset dates of the northeast monsoon over South Peninsular India are determined using the wind data at 850 hPa and 200 hPa, OLR, mean sea level pressure data for the domain 40° E to 120° E, 0° to 40° N. These three data sets are sourced from NCEP/NCAR reanalysis daily data sets. Further the daily grid point (0.25° Lat. × 0.25° Long.) rainfall data over India from Indian Meteorological Department is considered for delineation of rainfall pattern. The total length of the data of the above mentioned parameters is 21 years (1994 to 2014). Pentad distributions of the above parameters for the domain considered are prepared for examining the circulation patterns and rainfall activity. The pentads taken for the study are from 55th (28th September - 2nd October) pentad to 65th (17-21 November) pentad. In the determination of the northeast monsoon over South Peninsular India, the following points are considered: (i) The persistence of the northeasterlies at 850 hPa level, (ii) Occurrence of the rainfall over the South Peninsular India, (iii) Presence of east-west oriented trough [Intertropical Convergence Zone (ITCZ)] in the lower latitudes from Ethiopia region to Malaysia region passing through South Arabian Sea, southern region of South Peninsular India and South Bay of Bengal, (iv) The presence of low pressure over the southwest Bay of Bengal at the surface, (v) Persistence of a high pressure zone in northern latitudes of India (extending from the Saudi Arabia/Jordan region to the Head Bay of Bengal running through North Arabian Sea, Gujarat and Orissa), (vi) Presence of subtropical ridge at 200 hPa level around 17.5° N, (vii) Presence of north-south ridge over theeastern parts of China and (viii) Presence of relatively low OLR values over South Peninsular India when compared to the northern latitudes. If any pentad satisfies the above points, the middle date of the pentad is considered as the date of onset of northeast monsoon over South Peninsular India. If any pentad satisfies all the points except point number 2, importance is given to the persistence of northeasterlies and the middle date of the pentad will be declared as the onset date. By following the criteria, the dates of onset of northeast monsoon are determined for the latest 21 years. These dates are compared with those of the India Meteorological Department.

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Bay of Bengal: 2013 Northeast Monsoon Upper-Ocean Circulation

Oceanography ◽

10.5670/oceanog.2016.41 ◽

2016 ◽

Vol 29 (2) ◽

pp. 82-91 ◽

Cited By ~ 18

Author(s):

Arnold Gordon ◽

Emily Shroyer ◽

Amala Mahadevan ◽

Debasis Sengupta ◽

Mara Freilich

Keyword(s):

Ocean Circulation ◽

Bay Of Bengal ◽

Upper Ocean ◽

Northeast Monsoon

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Bay of Bengal currents during the Northeast Monsoon

Geophysical Research Letters ◽

10.1029/98gl52115 ◽

1998 ◽

Vol 25 (15) ◽

pp. 2769-2772 ◽

Cited By ~ 37

Author(s):

Peter Hacker ◽

Eric Firing ◽

Julia Hummon ◽

Arnold L. Gordon ◽

J. C. Kindle

Keyword(s):

Bay Of Bengal ◽

Northeast Monsoon

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Contrasting movement of wind based equatorial trough and equatorial cloud zone over Indian southern peninsula and adjoining Bay of Bengal during the onset phase of northeast monsoon

MAUSAM ◽

10.54302/mausam.v58i1.1126 ◽

2021 ◽

Vol 58 (1) ◽

pp. 33-48

Author(s):

Y. E. A. RAJ ◽

R. ASOKAN ◽

P. V. REVIKUMAR

Keyword(s):

Bay Of Bengal ◽

Tamil Nadu ◽

Southwest Monsoon ◽

Monsoon Onset ◽

Northeast Monsoon ◽

Peninsular India ◽

Zonal Winds ◽

The North ◽

Latitudinal Position ◽

Onset Phase

ABSTRACT. The northeast monsoon sets in over southern parts of peninsular India after the retreat of southwest monsoon and in association with the southward movement of equatorial trough. The INSAT satellite imageries scrutinised during the past several years revealed that the cloud bands at the time of northeast monsoon onset moved from south Bay into the southern peninsula, a feature that contrasts with the north to south movement of the equatorial trough. The paper investigates this aspect based on a dataset of lower level upper winds of the peninsula, rainfall data and INSAT OLR data for the 20 year period 1981–2000. The super epoch profiles of zonal winds, latitudinal position of equatorial trough with reference to northeast monsoon onset dates have been derived and studied. The region with OLR values less than 230 W/m2 was defined as the equatorial cloud zone and the movement of northern limit of ECZ was studied based on the normal pentad OLR data and also the superposed epoch profiles. From these analysis it has been established that at the time of northeast monsoon onset, the wind based equatorial trough moves south of Comorin whereas the cloud zone in the Bay of Bengal moves from south to north. Reasons for the occurrence of such a contrasting feature have been ascribed to features such as decreasing strength of lower level easterlies from north to south over coastal Tamil Nadu, reversal of temperature gradient between Chennai and Thiruvananthapuram at the time of onset and the dynamics of 40-day oscillation. The northeast monsoon activity over coastal Tamil Nadu has been found to be negatively correlated with the low level zonal winds over the coast, the degree of relation decreasing from north to south and also from October to December. Based on the results derived in the study and also the other known features of northeast monsoon a thematic model of northeast monsoon onset listing the events that precede and succeed the onset has been postulated.

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Seasonal and annual variability in chlorophyll-a in the shelf region of the Northern Bay of Bengal using MODIS-Aqua data

Oceanological and Hydrobiological Studies ◽

10.1515/ohs-2020-0035 ◽

2020 ◽

Vol 49 (4) ◽

pp. 398-407

Author(s):

Muhammad Abdur Rouf ◽

Al-Hasan Antu ◽

Imran Noor

Keyword(s):

Satellite Data ◽

Bay Of Bengal ◽

River Discharge ◽

Monsoon Season ◽

Northeast Monsoon ◽

Discharge Data ◽

Annual Variability ◽

Northern Bay Of Bengal ◽

Shelf Region

AbstractChlorophyll-a (Chl-a) concentration is an important issue in ocean ecosystem management and research. This study investigates seasonal and annual variability in Chl-a and its relationship with sea surface temperature (SST) and river discharge in the shelf region of the Northern Bay of Bengal (BoB), as well as validates satellite data against in-situ data. Moderate Resolution Imaging Spectroradiometer (MODIS) Aqua satellite data on Chl-a concentration and SST from 2002–2018 were used in this study. River discharge data were obtained from the Bangladesh Water Development Board (BWDB). The annual Chl-a concentration ranged from 2.08 to 2.94 mg m−3, with an average of 2.43 ± 0.24 mg m−3. The Chl-a concentration was found higher (2.21 ± 0.56 mg m−3) during the northeast monsoon (October–February) and lower (1.81 ± 1.14 mg m−3) during the pre-monsoon season (March–May). The study revealed a declining trend in Chl-a concentration from 2002 to 2018, and the rate of change was −0.0183 mg m−3 year−1. Chl-a concentration showed a weak inverse relationship with SST, both annually and seasonally, especially in the pre-monsoon season. River discharge masked the effect of SST on Chl-a variability during the southwest and northeast monsoon. A reasonable correlation (r = 0.78) was found between the MODIS-Aqua data and in-situ Chl-a observations.

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