Contrast in monsoon precipitation over oceanic region of north Bay of Bengal and east equatorial Indian Ocean

2018 ◽  
Vol 38 ◽  
pp. e1061-e1075 ◽  
Author(s):  
Samir Pokhrel ◽  
Anupam Hazra ◽  
Subodh Kumar Saha ◽  
Hemantkumar S. Chaudhari ◽  
Abirlal Metya ◽  
...  
Keyword(s):  
Indian Ocean ◽  
Bay Of Bengal ◽  
Equatorial Indian Ocean ◽  
Monsoon Precipitation ◽  
Oceanic Region

Importance of wind variations and intersecting waveguides near Sri Lanka for the intraseasonal sea level variability along the west coast of India

2020 ◽  
Author(s):  
Iyyappan Suresh ◽  
Jerome Vialard ◽  
Matthieu Lengaigne ◽  
Takeshi Izumo ◽  
Muraleedharan Pillathu Moolayil
Keyword(s):  
Sri Lanka ◽  
Indian Ocean ◽  
Sea Level ◽  
Bay Of Bengal ◽  
West Coast ◽  
Equatorial Indian Ocean ◽  
Direct Connection ◽  
Local Wind ◽  
The West ◽  
Eastern Equatorial Indian Ocean

<p>Remote wind forcing plays a strong role in the Northern Indian Ocean, where oceanic anomalies can travel long distances within the coastal waveguide. Previous studies for instance emphasized that remote equatorial forcing is the main driver of the sea level and currents intraseasonal variability along the west coast of India (WCI). Until now, the main pathway for this connection between the equatorial and coastal waveguides was thought to occur in the eastern equatorial Indian Ocean, through coastal Kelvin waves that propagate around the Bay of Bengal rim and then around Sri Lanka to the WCI. Using a linear, continuously stratified ocean model, the present study demonstrates that two other mechanisms in fact dominate. First, the equatorial waveguide also intersects the coastal waveguide at the southern tip of India and Sri Lanka, creating a direct connection between the equator and WCI. Rossby waves reflected from the eastern equatorial Indian Ocean boundary indeed have a sufficiently wide meridional scale to induce a pressure signal at the Sri Lankan coast, which eventually propagates to the WCI as a coastal Kelvin wave. Second, local wind variations in the vicinity of Sri Lanka generate strong intraseasonal signals, which also propagate to the WCI along the same path. Sensitivity experiments indicate that these two new mechanisms (direct equatorial connection and local wind variations near Sri Lanka) dominate the WCI intraseasonal sea level variability, with the “classical” pathway around the Bay of Bengal only coming next. Other contributions (Bay of Bengal forcing, local WCI forcing) are much weaker.</p><p>We further show that the direct connection between the equatorial waveguide and WCI is negligible at seasonal timescale, but not at interannual timescales where it contributes to the occurrence of anoxic events. By providing an improved understanding of the mechanisms that control the WCI thermocline and oxycline variability, our results could have socio-economic implications for regional fisheries and ecosystems.</p>

scholarly journals Seasonal prediction of cyclonic disturbances over the Bay of Bengal during summer monsoon season : Identification of potential predictors

MAUSAM ◽  
2021 ◽  
Vol 61 (4) ◽  
pp. 469-486
Author(s):  
M. MOHAPATRA ◽  
S. ADHIKARY
Keyword(s):  
Indian Ocean ◽  
Bay Of Bengal ◽  
Large Scale ◽  
Monsoon Season ◽  
Equatorial Indian Ocean ◽  
Seasonal Prediction ◽  
Reanalysis Data ◽  
Scale Field ◽  
Large Scale Field ◽  
Cyclonic Disturbances

The cyclonic disturbances (CD) over the Bay of Bengal during monsoon season have significant impact on rainfall over India. On many occasions, they cause flood leading to loss of lives and properties. Hence, any early information about the frequency of occurrence of such disturbances will help immensely the disaster managers and planners. However, the studies are limited on the seasonal prediction of CD over the Bay of Bengal unlike other Ocean basins of the world. Hence, a study has been undertaken to find out the potential predictors during the months of April and May for prediction of frequency of cyclonic disturbances over the Bay of Bengal during monsoon season (June – September). For this purpose, best track data of India Meteorological Department and large scale field parameters based on NCEP/NCAR reanalysis data have been analyzed for the period of 1948 – 2007.  The linear correlation analysis has been applied between frequency of CD and large scale field parameters based on NCEP/NCAR reanalysis data to find out the potential predictors.   The large scale field parameters over the equatorial Indian Ocean, especially over west equatorial Indian Ocean and adjoining Arabian Sea (up to 15° N) should be favourable in April and May with lower mean sea level pressure (MSLP), lower geopotential heights and stronger southerlies in lower and middle levels, along with stronger northerly components at upper level for higher frequency of CD during subsequent monsoon season. Consequently, there should be increase in relative humidity (RH) and precipitable water content and decrease in outgoing longwave radiation (OLR) and temperature at lower levels over this region during April and May for higher frequency of CD during subsequent monsoon  season. Comparing the area of significant correlation between frequency of CD and large scale field parameters and its stability from April to September, MSLP and geopotential heights are most influencing parameters followed by OLR, sea surface temperature, air temperature and RH at 850 hPa level.

scholarly journals Cloud climatology of the Indian Ocean based on ship observations

MAUSAM ◽  
2022 ◽  
Vol 52 (3) ◽  
pp. 527-540
Author(s):  
M. RAJEEVAN ◽  
R. K. PRASAD ◽  
U. S. DE
Keyword(s):  
Indian Ocean ◽  
Bay Of Bengal ◽  
Cloud Cover ◽  
Monsoon Season ◽  
Equatorial Indian Ocean ◽  
Enso Events ◽  
Decadal Scale ◽  
Low Cloud ◽  
The Indian Ocean ◽  
Low Cloud Cover

Surface cloud data based on synoptic observations made by Voluntary Observing Ships (VOS) during the period 1951-98 were used to prepare the seasonal and annual cloud climatology of the Indian Ocean. The analysis has been carried out by separating the long-term trends, decadal and inter-annual components from the monthly cloud anomaly time series at each 5° × 5° grids.   Maximum zone of total and low cloud cover shifts from equator to northern parts of India during the monsoon season. During the monsoon season (June-September), maximum total cloud cover exceeding 70% and low cloud cover exceeding 50% are observed over north Bay of Bengal. Maximum standard deviation of total and low cloud cover is observed near the equator and in the southern hemisphere. Both total and low cloud cover over Arabian Sea and the equatorial Indian Ocean are observed to decrease during the ENSO events. However, cloud cover over Bay of Bengal is not modulated by the ENSO events. On inter-decadal scale, low cloud cover shifted from a "low regime" to a "high regime" after 1980 which may be associated with the corresponding inter-decadal changes of sea surface temperatures over north Indian Ocean observed during the late 1970s.

Seasonal and interannual variabilities of chlorophyll across the eastern equatorial Indian Ocean and Bay of Bengal

2021 ◽  
pp. 102661
Author(s):  
Yi Xu ◽  
Ying Wu ◽  
Huiwu Wang ◽  
Zhenqiu Zhang ◽  
Jian Li ◽  
...  
Keyword(s):  
Indian Ocean ◽  
Bay Of Bengal ◽  
Equatorial Indian Ocean ◽  
Eastern Equatorial Indian Ocean

scholarly journals Intraseasonal-to-semiannual variability of sea-surface height in the astern, equatorial Indian Ocean and southern Bay of Bengal

2017 ◽  
Vol 122 (5) ◽  
pp. 4051-4067 ◽  
Author(s):  
Xuhua Cheng ◽  
Julian P. McCreary ◽  
Bo Qiu ◽  
Yiquan Qi ◽  
Yan Du
Keyword(s):  
Indian Ocean ◽  
Bay Of Bengal ◽  
Equatorial Indian Ocean ◽  
Sea Surface Height ◽  
Sea Surface

scholarly journals Modeling Salinity Exchanges Between the Equatorial Indian Ocean and the Bay of Bengal

Oceanography ◽  
2016 ◽  
Vol 29 (2) ◽  
pp. 92-101 ◽  
Author(s):  
Tommy Jensen ◽  
Hemantha Wijesekera ◽  
Ebenezer Nyadjro ◽  
Prasad Thoppil ◽  
Jay Shriver ◽  
...  
Keyword(s):  
Indian Ocean ◽  
Bay Of Bengal ◽  
Equatorial Indian Ocean

scholarly journals Correlation between subsurface salinity anomalies in the Bay of Bengal and the Indian Ocean Dipole and governing mechanisms

2020 ◽  
Author(s):  
Zheen Zhang ◽  
Thomas Pohlmann ◽  
Xueen Chen
Keyword(s):  
Indian Ocean ◽  
Bay Of Bengal ◽  
Indian Ocean Dipole ◽  
Equatorial Indian Ocean ◽  
Ocean Model ◽  
Subsurface Temperature ◽  
Remote Forcing ◽  
Salinity Variability ◽  
Eastern Equatorial Indian Ocean ◽  
The Indian Ocean

Abstract. Lead-lag correlations between the subsurface temperature/salinity anomalies in the Bay of Bengal (BoB) and the Indian Ocean Dipole (IOD) are revealed in model results, ocean synthesis, and observations. Mechanisms for such correlations are further investigated using the Hamburg Shelf Ocean Model (HAMSOM), mainly on the salinity variability. It is found that the subsurface salinity anomaly of the BoB positively correlates to the IOD with a lag of three months on average, while the subsurface temperature anomaly negatively correlates. The model results suggest the remote forcing from the equatorial Indian Ocean dominates the interannual subsurface salinity variability in the BoB. The coastal Kelvin waves carry signals of positive (negative) salinity anomalies from the eastern equatorial Indian Ocean and propagate counterclockwise along the coasts of the BoB during positive (negative) IOD events. Subsequently westward Rossby waves propagate these signals to the basin at a relatively slow speed, which causes a considerable delay of the subsurface salinity anomalies in the correlation. By analyzing the salinity budget of the BoB, it is found that the diffusion dominates the salinity changes near the surface, while the advection dominates the subsurface; the vertical advection of salinity contributes positively to this correlation, while the horizontal advection contributes negatively. These results suggest that the IOD plays a crucial role in the interannual subsurface salinity variability in the BoB.

scholarly journals Principal component analysis of monthly mean Area surface temperature over the Arabian Sea, Bay of Bengal and north Indian Ocean for two Contrasting sets of monsoon years

MAUSAM ◽  
2021 ◽  
Vol 44 (1) ◽  
pp. 69-76
Author(s):  
T. K. BALAKRISHNAN ◽  
A. K. JASWAL ◽  
S.S.. SINGH ◽  
H. N. SRIVASTAVA
Keyword(s):  
Indian Ocean ◽  
Bay Of Bengal ◽  
Arabian Sea ◽  
Monsoon Rainfall ◽  
Equatorial Indian Ocean ◽  
Principal Component ◽  
North Indian Ocean ◽  
Orthogonal Function ◽  
The North ◽  
Extreme North

The spatial distribution and temporal variation of the monthly mean SSTA over the Arabian Sea, Bay of Bengal and the north Indian Ocean were investigated for a set of contrasting years of monsoon over the period 1961-80 for months April through July using Empirical Orthogonal Function (EOF) technique with a view to identify regions that are significantly related to the monsoon rainfall. Over 75% of the total variance is, explained by the first mode EOF. SSTA over the north and northeast Arabian Sea during pre-monsoon months were found to be possible indicators of the ensuing monsoon activity. The higher eigen vectors in May over northeast Arabian Sea may signal good monsoon and vice versa. In June there is a marked contrast in the distribution of SST over the Arabian Sea between the two sets of the years the eastern Arabian Sea IS warmer for the deficient monsoon years while the entire Arabian Sea except over the extreme north Arabian Sea is cool during good monsoon years. There is formation of SSTA over the equatorial Indian Ocean area close to Indonesian island commencing from May which is more marked in June and is positively correlated with seasonal rainfall activity over India.  

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