scholarly journals Marine Heatwaves in the Arabian Sea

2021 ◽  
Author(s):  
Abhisek Chatterjee ◽  
Gouri Anil ◽  
Lakshmi R. Shenoy
Keyword(s):  
Indian Ocean ◽  
Arabian Sea ◽  
Heat Budget ◽  
Monsoon Season ◽  
Fold Increase ◽  
Recent Decade ◽  
Ocean Basin ◽  
Significant Heterogeneity ◽  
Indian Ocean Basin Mode ◽  
Budget Analysis

Abstract. Marine heatwaves (MHWs) are prolonged warm sea condition events that cause a destructive impact on marine ecosystems. The documentation of MHWs and assessment of their impacts are largely confined to a few regional seas or in global mean studies. The Indian Ocean received almost no attention in this regard despite the fact that this ocean basin, particularly the Arabian Sea, is warming at the most rapid pace among the other tropical basins in recent decades. This study shows the characteristics MHWs for the Arabian Sea during 1982–2019. Our analysis shows that the duration of MHWs exhibit a rapidly increasing trend of ~20 days/decade (1.5–2 count/decade) in the northern Arabian Sea and in the southeastern Arabian Sea close to the west coast of India; which is more than 15 fold increase in the MHW days from the early 80s'. At the same time increase in MHW frequency is ~1.5–2 count/decade i.e an increase of ~6 fold, indicating more frequent and much longer heatwave events in the recent decade. Notably, since the beginning of the satellite record, the year 2010 and 2016 saw the maximum number of heatwave days with more than 75 % of days of the pre-monsoon and summer monsoon season experienced heatwaves. The accelerated trend of the heatwave days is found to be driven by the rapid rise of the mean SST of the Arabian Sea in the recent decade. Moreover, longer heatwave days are also associated with the dominant climate modes and among them, Indian Ocean Basin mode via the decaying phase of the El-Niño is found to be the most influencing mode contributing in more than 70–80 % of observed heatwave days in this basin. Mixed layer heat budget analysis suggests significant heterogeneity in the dominant processes across the years; however, weakening of latent heat loss is in general one of the key mechanism in the genesis of most of the MHWs.

scholarly journals Seven year satellite observations of the mean structures and variabilities in the regional aerosol distribution over the oceanic areas around the Indian subcontinent

2005 ◽  
Vol 23 (6) ◽  
pp. 2011-2030 ◽  
Author(s):  
S. K. Nair ◽  
K. Parameswaran ◽  
K. Rajeev
Keyword(s):  
Indian Ocean ◽  
Southern Hemisphere ◽  
Bay Of Bengal ◽  
Arabian Sea ◽  
Indian Subcontinent ◽  
Monsoon Season ◽  
Dry Season ◽  
Aerosol Transport ◽  
Summer Monsoon Season ◽  
Aerosol Distribution

Abstract. Aerosol distribution over the oceanic regions around the Indian subcontinent and its seasonal and interannual variabilities are studied using the aerosol optical depth (AOD) derived from NOAA-14 and NOAA-16 AVHRR data for the period of November 1995–December 2003. The air-mass types over this region during the Asian summer monsoon season (June–September) are significantly different from those during the Asian dry season (November–April). Hence, the aerosol loading and its properties over these oceanic regions are also distinctly different in these two periods. During the Asian dry season, the Arabian Sea and Bay of Bengal are dominated by the transport of aerosols from Northern Hemispheric landmasses, mainly the Indian subcontinent, Southeast Asia and Arabia. This aerosol transport is rather weak in the early part of the dry season (November–January) compared to that in the later period (February–April). Large-scale transport of mineral dust from Arabia and the production of sea-salt aerosols, due to high surface wind speeds, contribute to the high aerosol loading over the Arabian Sea region during the summer monsoon season. As a result, the monthly mean AOD over the Arabian Sea shows a clear annual cycle with the highest values occurring in July. The AOD over the Bay of Bengal and the Southern Hemisphere Indian Ocean also displays an annual cycle with maxima during March and October, respectively. The amplitude of the annual variation is the largest in coastal Arabia and the least in the Southern Hemisphere Indian Ocean. The interannual variability in AOD is the largest over the Southeast Arabian Sea (seasonal mean AOD varies from 0.19 to 0.42) and the northern Bay of Bengal (seasonal mean AOD varies from 0.24 to 0.39) during the February–April period and is the least over the Southern Hemisphere Indian Ocean. This study also investigates the altitude regions and pathways of dominant aerosol transport by combining the AOD distribution with the atmospheric circulation. Keywords. Atmospheric composition and structure (Aerosols and particles) – Meteorology and atmospheric dynamics (Climatology) – Oceanography: physical (Ocean fog and aerosols)

Understanding the Weakening Relationship of the Pacific Decadal Oscillation and Indian Ocean Basin Mode During Boreal Winter

2021 ◽  
Author(s):  
Jin-Sil Hong ◽  
Sang-Wook Yeh ◽  
Young-Min Yang ◽  
Young-Kwon Lim ◽  
Kyu-Myong Kim
Keyword(s):  
Indian Ocean ◽  
Pacific Decadal Oscillation ◽  
Climate Model ◽  
Ocean Basin ◽  
Boreal Winter ◽  
Indian Ocean Basin Mode ◽  
The Pacific ◽  
Basin Mode ◽  
Relationship Of

Abstract While it is known that the Pacific Decadal Oscillation (PDO) leads the Indian Ocean Basin Mode (IOBM) with the same phase via the atmospheric bridge, we found that the relationship of PDO-IOBM during boreal winter is not stationary. Here, we investigated the PDO-IOBM relationship changes on low-frequency timescales by analyzing the observations, a long-term simulation of climate model with its large ensembles as well as the pacemaker experiments. A long-term simulation of climate model with its large ensemble simulations indicated that the non-stationary relationship of PDO-IOBM is intrinsic in a climate system and it could be at least partly due to internal climate variability. In details, we compared the PDO structures during the entire period with those during the period when the PDO-IOBM relationship was weak (i.e., 1976-2006). We found that the structures of sea surface temperature (SST) as well as its associated tropical Pacific convective forcing during the negative phase of PDO for 1976-2006 are far away from the typical structures of the negative PDO phase during the entire period, which were responsible for the weakening relationship of the PDO-IOBM in the observation. The results of the two pacemaker experiments support that a non-stationary relationship of PDO-IOBM is primarily due to the SST forcing in the Pacific.

scholarly journals Asymmetry of the Indian Ocean Dipole. Part I: Observational Analysis

2008 ◽  
Vol 21 (18) ◽  
pp. 4834-4848 ◽  
Author(s):  
Chi-Cherng Hong ◽  
Tim Li ◽  
LinHo ◽  
Jong-Seong Kug
Keyword(s):  
Indian Ocean ◽  
Mixed Layer ◽  
Indian Ocean Dipole ◽  
Heat Budget ◽  
Mature Phase ◽  
Budget Analysis ◽  
Nonlinear Advection ◽  
Negative Skewness ◽  
The Indian Ocean ◽  
The Asymmetry

The physical mechanism for the amplitude asymmetry of SST anomalies (SSTA) between the positive and negative phases of the Indian Ocean dipole (IOD) is investigated, using Simple Ocean Data Assimilation (SODA) and NCAR–NCEP data. It is found that a strong negative skewness appears in the IOD east pole (IODE) in the mature phase [September–November (SON)], while the skewness in the IOD west pole is insignificant. Thus, the IOD asymmetry is primarily caused by the negative skewness in IODE. A mixed-layer heat budget analysis indicates that the following two air–sea feedback processes are responsible for the negative skewness. The first is attributed to the asymmetry of the wind stress–ocean advection–SST feedback. During the IOD developing stage [June–September (JJAS)], the ocean linear advection tends to enhance the mixed-layer temperature tendency, while nonlinear advection tends to cool the ocean in both the positive and negative events, thus contributing to the negative skewness in IODE. The second process is attributed to the asymmetry of the SST–cloud–radiation (SCR) feedback. For a positive IODE, the negative SCR feedback continues with the increase of warm SSTA. For a negative IODE, the same negative SCR feedback works when the amplitude of SSTA is small. After reaching a critical value, the cold SSTA may completely suppress the mean convection and lead to cloud free conditions; a further drop of the cold SSTA does not lead to additional thermal damping so that the cold SSTA may grow faster. A wind–evaporation–SST feedback may further amplify the asymmetry induced by the aforementioned nonlinear advection and SCR feedback processes.

A study of biases in simulation of the Indian Ocean basin mode and its capacitor effect in CMIP3/CMIP5 models

2015 ◽  
Vol 46 (1-2) ◽  
pp. 205-226 ◽  
Author(s):  
Weichen Tao ◽  
Gang Huang ◽  
Kaiming Hu ◽  
Hainan Gong ◽  
Guanhuan Wen ◽  
...  
Keyword(s):  
Indian Ocean ◽  
Ocean Basin ◽  
Cmip5 Models ◽  
Indian Ocean Basin Mode ◽  
Basin Mode ◽  
The Indian Ocean

Anthropogenic iron deposition alters the ecosystem and carbon balance of the Indian Ocean over a centennial timescale

2020 ◽  
Author(s):  
Anh Pham ◽  
Takamitsu Ito
Keyword(s):  
Indian Ocean ◽  
Arabian Sea ◽  
Ocean Basin ◽  
Ecosystem Dynamics ◽  
Carbon Uptake ◽  
The South ◽  
Nutrient Deposition ◽  
The North ◽  
The Indian Ocean ◽  
The Impact

<p>Phytoplankton growth in the Indian Ocean is generally limited by macronutrients (nitrogen: N and phosphorus: P) in the north and by micronutrient (iron: Fe) in the south. Increasing anthropogenic atmospheric deposition of N and dissolved Fe (dFe) into the ocean can thus lead to significant responses from marine ecosystems in this ocean basin. Previous modeling studies investigated the impacts of anthropogenic nutrient deposition on the ocean, but their results are uncertain due to incomplete representations of Fe cycling. We use a state-of-the-art ocean ecosystem and Fe cycling model to evaluate the transient responses of ocean productivity and carbon uptake in the Indian Ocean, focusing on the centennial time scale. The model incorporates all major external sources and represents a complicated internal cycling process of Fe, thus showing significant improvements in reproducing observations. Sensitivity simulations show that after a century of anthropogenic deposition, increased dFe stimulates diatoms productivity in the southern Indian Ocean poleward of 50⁰S and the southeastern tropics. Diatoms production weakens in the south of the Arabian Sea due to the P limitation, and diatoms are outcompeted there by coccolithophores and picoplankton, which have a lower P demand. These changes in diatoms and coccolithophores productions alter the balance between the organic and carbonate pumps in the Indian Ocean, increasing the carbon uptake in the south of 50⁰S and the southeastern tropics while decreasing it in the Arabian Sea. Our results reveal the important role of ecosystem dynamics in controlling the sensitivity of carbon fluxes in the Indian Ocean under the impact of anthropogenic nutrient deposition over a centennial timescale.</p>

Response of the Indian Ocean Basin Mode and Its Capacitor Effect to Global Warming*

2011 ◽  
Vol 24 (23) ◽  
pp. 6146-6164 ◽  
Author(s):  
Xiao-Tong Zheng ◽  
Shang-Ping Xie ◽  
Qinyu Liu
Keyword(s):  
Global Warming ◽  
Indian Ocean ◽  
El Niño ◽  
El Nino ◽  
Ocean Basin ◽  
Northwest Pacific ◽  
Geophysical Fluid Dynamics Laboratory ◽  
Indian Ocean Basin Mode ◽  
Easterly Wind ◽  
The Indian Ocean

Abstract The development of the Indian Ocean basin (IOB) mode and its change under global warming are investigated using a pair of integrations with the Geophysical Fluid Dynamics Laboratory Climate Model version 2.1 (CM2.1). In the simulation under constant climate forcing, the El Niño–induced warming over the tropical Indian Ocean (TIO) and its capacitor effect on summer northwest Pacific climate are reproduced realistically. In the simulation forced by increased greenhouse gas concentrations, the IOB mode and its summer capacitor effect are enhanced in persistence following El Niño, even though the ENSO itself weakens in response to global warming. In the prior spring, an antisymmetric pattern of rainfall–wind anomalies and the meridional SST gradient across the equator strengthen via increased wind–evaporation–sea surface temperature (WES) feedback. ENSO decays slightly faster in global warming. During the summer following El Niño decay, the resultant decrease in equatorial Pacific SST strengthens the SST contrast with the enhanced TIO warming, increasing the sea level pressure gradient and intensifying the anomalous anticyclone over the northwest Pacific. The easterly wind anomalies associated with the northwest Pacific anticyclone in turn sustain the SST warming over the north Indian Ocean and South China Sea. Thus, the increased TIO capacitor effect is due to enhanced air–sea interaction over the TIO and with the western Pacific. The implications for the observed intensification of the IOB mode and its capacitor effect after the 1970s are discussed.

scholarly journals Variability of Ocean Features and their Impact on Cyclogenesis over Arabian Sea During Post Monsoon Season

2021 ◽  
Author(s):  
suchandra Aich Bhowmick ◽  
Anup Mandal
Keyword(s):  
Indian Ocean ◽  
Arabian Sea ◽  
Indian Subcontinent ◽  
Monsoon Season ◽  
Heat Content ◽  
North Indian Ocean ◽  
Post Monsoon ◽  
Positive Indian Ocean Dipole ◽  
South West Indian Ocean ◽  
Atmospheric Forcings

Abstract Arabian Sea (AS), the western sector of North Indian Ocean (NIO) produce smaller number of tropical cyclones as compared to Bay of Bengal. Though limited in numbers, the cyclones over Arabian sea are catastrophic by character. This make west coast of Indian subcontinent vulnerable to these hazards. The post-monsoon cyclogenesis over this region is known to be modulated by both monsoon rainfall and the El-Niño accompanied with positive Indian Ocean Dipole events. No single phenomena, however, can fully explain the variability observed in AS region. In this study, it is observed that apart from several known atmospheric forcings, inter-annual variability of ocean heat content (OHC) influence the post-monsoon AS cyclogenesis. The OHC of this region is partially modulated by the changes in salinity. Heat exchanges between the South West Indian Ocean (SWIO) and AS also modulates the OHC over AS. This remote influence is facilitated largely by the variability in the equatorial currents. Further it is seen that the recent trend of increased OHC post-2011 matches with the enhanced sea surface carbon over AS.

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