The Strong Upwelling Event off the Southern Coast of Sri Lanka in 2013 and Its Relationship with Indian Ocean Dipole Events

2021 ◽  
Vol 34 (9) ◽  
pp. 3555-3569
Author(s):  
Yuhui Li ◽  
Yun Qiu ◽  
Jianyu Hu ◽  
Cherry Aung ◽  
Xinyu Lin ◽  
...  
Keyword(s):  
Sri Lanka ◽  
Indian Ocean ◽  
Wind Stress ◽  
Indian Ocean Dipole ◽  
Remote Sensing Data ◽  
Southwest Monsoon ◽  
Ekman Pumping ◽  
Southern Coast ◽  
Northwesterly Wind ◽  
Upwelling Event

ABSTRACTMultisource satellite remote sensing data have been used to analyze the strong upwelling event off the southern coast of Sri Lanka in 2013 and its relationship with Indian Ocean dipole (IOD) events. The upwelling area in 2013 is 5.7 times larger than that in a normal year and lasts from June to August, with the peaks of the cooling anomaly reaching −1.5°C and the positive chlorophyll a concentration anomaly exceeding 3.1 mg m−3. In 2013, the negative unseasonable IOD (IODJJA) event enhances the southwest monsoon, while the blocking of the monsoon wind by the island results in a stronger westerly/northwesterly wind stress off the southern coast of Sri Lanka and a weaker westerly/northwesterly wind stress over the eastern Sri Lanka waters. This causes stronger offshore transport and positive Ekman pumping off the southern coast, forming a strong upwelling event there. Further analysis indicates that the interannual variability of the upwelling, as represented by a newly constructed index based on satellite observations, is primarily caused by the variations of local wind associated with the IOD. The upwelling off the southern coast of Sri Lanka weakens (strengthens) in the positive (negative) IOD years. However, an analysis based on 21 IOD events during 1982–2019 demonstrates that the effects of the three types of IOD events, including IODJJA, prolonged IOD (IODLONG), and normal IOD (IODSON), on the upwelling are different. Compared to the IODSON events, the IODJJA and IODLONG events tend to have stronger influences due to their earlier developing phases.

scholarly journals SURFACE CHLOROPHYLL-A VARIATIONS ALONG THE SOUTHERN COAST OF JAVA DURING TWO CONTRASTING INDIAN OCEAN DIPOLE EVENTS: 2015 AND 2016

2021 ◽  
Vol 16 (3) ◽  
pp. 116-127
Author(s):  
NETTY KURNIAWATI ◽  
◽  
QURNIA WULAN SARI ◽  
RIZA YULIRATNO SETIAWAN ◽  
EKO SISWANTO ◽  
...  
Keyword(s):  
Indian Ocean ◽  
Chlorophyll A ◽  
Indian Ocean Dipole ◽  
Southern Coast

scholarly journals Blue whales off the Southern coast of Sri Lanka during the Southwest Monsoon Season

2020 ◽  
Vol 21 (1) ◽  
pp. 1-7
Author(s):  
Grace Russell ◽  
Marcus Bridge ◽  
Maja Nimak-Wood
Keyword(s):  
Sri Lanka ◽  
Monsoon Season ◽  
Weather Conditions ◽  
Southwest Monsoon ◽  
Lower Latitude ◽  
Northeast Monsoon ◽  
Southern Coast ◽  
Northern India ◽  
Blue Whales ◽  
Southwest Monsoon Season

Observations of 37 individual blue whales (Balaenoptera musculus) were recorded off the southern coast of Sri Lanka during the Southwest Monsoon Season (SWM). Sightings were made during a scientific geophysical survey campaign conducted in July and August 2017. Whilst blue whales are regularly recorded on the continental slope of southern Sri Lanka during the Northeast Monsoon Season (NEM) (December - March) and during the two inter-monsoonal periods (March - April and September - October), limited data is available for the SWM (May - September) mostly due to unfavourable weather conditions and very little survey effort. In the northern hemisphere blue whales undertake seasonal migrations from higher latitude feeding grounds to lower latitude breeding and wintering areas. However it has been suggested that a population of blue whales in the Northern India Ocean (NIO) remains in lower latitudes year round taking advantage of the rich upwelling areas off Somalia, southwest Arabia and western Sri Lanka. Data from this study nevertheless support a theory that a certain number of individuals remain off the southern coast off Sri Lanka during the SWM, suggesting that the productivity in this region is sufficient to support their year-round presence. This study therefore fills a knowledge gap regarding the presence and movement of blue whales in the NIO highlighting the importance of data obtained from platforms of opportunity.

scholarly journals Impact of Equatorial Wind Stress on Ekman Transport During the Mature Phase of the Indian Ocean Dipole

2021 ◽  
Author(s):  
Linfang Zhang ◽  
Yaokun Li ◽  
Jianping Li
Keyword(s):  
Indian Ocean ◽  
Wind Stress ◽  
Zonal Wind ◽  
Indian Ocean Dipole ◽  
Meridional Overturning Circulation ◽  
Ekman Transport ◽  
Zonal Wind Stress ◽  
Mature Phase ◽  
The Indian Ocean ◽  
The Impact

Abstract This paper investigates the impact of equatorial wind stress on the equatorial Ekman transport during the Indian Ocean dipole (IOD) mature phase. The results show that the equatorial zonal wind stress directly drives the meridional motion of seawater at the upper levels. In normal years, the zonal wind stress south of the equator is easterly and that north of the equator is westerly, which contributes to southward Ekman transport at the upper levels to form the climatological Indian Ocean shallow meridional overturning circulation. During the years of positive IOD events, abnormal easterly winds near the equator bring southward Ekman transport south of the equator while they bring northward Ekman transport north of the equator. This causes the seawater to move away from the equator and hence induces upwelling near the equator, which forms a pair of small circulation cells that are symmetric about the equator at the upper levels (approximately 100 m deep). The abnormal circulation cell south (north) of the equator strengthens (weakens) the southward (southward) motion south (north) of the equator. During years with negative IOD events, the opposite occurs. In addition, during the mature period of IOD, the remote sea surface temperature anomaly (SSTA) such as El Niño–Southern Oscillation (ENSO) may exert some influence on equatorial wind stress and Ekman transport anomaly but the influence is weak.

scholarly journals Effect of Indian Ocean Dipole (IOD) Events on the Second Inter-monsoonal Rainfall in the Wet Zone of Sri Lanka

2021 ◽  
Vol 32 (3) ◽  
pp. 287
Author(s):  
A. B. Abeysekera ◽  
B. V. R. Punyawardena ◽  
B. Marambe ◽  
I. M. S. P. Jayawardena ◽  
T. Sivananthawerl ◽  
...  
Keyword(s):  
Sri Lanka ◽  
Indian Ocean ◽  
Indian Ocean Dipole ◽  
Wet Zone

scholarly journals Streamflow Variability in Mahaweli River Basin of Sri Lanka during 1990–2014 and Its Possible Mechanisms

Water ◽  
2019 ◽  
Vol 11 (12) ◽  
pp. 2485 ◽  
Author(s):  
Sherly Shelton ◽  
Zhaohui Lin
Keyword(s):  
Sri Lanka ◽  
Indian Ocean ◽  
River Basin ◽  
Southern Oscillation ◽  
Southwest Monsoon ◽  
Seasonal Rainfall ◽  
Northeast Monsoon ◽  
Total Rainfall ◽  
Factors Affecting ◽  
Streamflow Variability

This study investigates the variation of seasonal streamflow and streamflow extremes in five catchments of the Mahaweli River Basin (MRB) Sri Lanka from 1990 to 2014, and the relationship between streamflow and seasonal rainfall in each catchment is then examined. Furthermore, the influence of Indian Ocean Dipole (IOD) and El Nino and Southern Oscillation (ENSO) on the seasonal rainfall and streamflow in the upper (UMRB) and lower reaches (LMRB) of MRB are explored. It’s found that the rainfall amount in southwest monsoon (SWM) season contributes 29.7% out of annual total rainfall in the UMRB, while the LMRB records 41% of the total rainfall during the northeast monsoon (NEM) season. The maximum streamflow of upper (lower) Mahaweli catchments is observed in the SWM (NEM) season. Catchments in the UMRB (LMRB) recorded strong interannual variability of seasonal overall flow (Q50), Maximum 10-day, and 30-day flows during the SWM (NEM) season. It’s further revealed that the catchment streamflow in the UMRB is closely correlated with the SWM rainfall in the interannual time scale, while streamflow of catchments in the LMRB is closely associated with the NEM rainfall. The effects of ENSO and IOD on streamflow are consistent with their impacts on rainfall for all catchments in MRB, with strong seasonal dependent. These suggested that the sea surface temperature anomalies in the both Indian Ocean and tropical Pacific Ocean are important factors affecting the streamflow variability in the MRB, especially during the SWM season.

scholarly journals A biological Indian Ocean Dipole event in 2019

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Wei Shi ◽  
Menghua Wang
Keyword(s):  
Biological Activity ◽  
Indian Ocean ◽  
Indian Ocean Dipole ◽  
Infrared Imaging ◽  
Equatorial Indian Ocean ◽  
The West ◽  
Indian Ocean Dipole Event ◽  
Chl A ◽  
Positive Indian Ocean Dipole ◽  
Dipole Response

AbstractThe 2019 positive Indian Ocean Dipole (IOD) event in the boreal autumn was the most serious IOD event of the century with reports of significant sea surface temperature (SST) changes in the east and west equatorial Indian Ocean. Observations of the Visible Infrared Imaging Radiometer Suite (VIIRS) onboard the Suomi National Polar-orbiting Partnership (SNPP) between 2012 and 2020 are used to study the significant biological dipole response that occurred in the equatorial Indian Ocean following the 2019 positive IOD event. For the first time, we propose, identify, characterize, and quantify the biological IOD. The 2019 positive IOD event led to anomalous biological activity in both the east IOD zone and west IOD zone. The average chlorophyll-a (Chl-a) concentration reached over ~ 0.5 mg m−3 in 2019 in comparison to the climatology Chl-a of ~ 0.3 mg m−3 in the east IOD zone. In the west IOD zone, the biological activity was significantly depressed. The depressed Chl-a lasted until May 2020. The anomalous ocean biological activity in the east IOD zone was attributed to the advection of the higher-nutrient surface water due to enhanced upwelling. On the other hand, the dampened ocean biological activity in the west IOD zone was attributed to the stronger convergence of the surface waters than that in a normal year.

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