Spectral aerosol optical characteristics during the northeast monsoon over the Arabian Sea and the tropical Indian Ocean: 1. Aerosol optical depths and their variabilities

2004 ◽  
Vol 109 (D19) ◽  
Author(s):  
S. Ramachandran
Keyword(s):  
Indian Ocean ◽  
Arabian Sea ◽  
Tropical Indian Ocean ◽  
Optical Characteristics ◽  
Northeast Monsoon

Interannual monsoon wind variability over the South tropical Indian ocean drives East African small pelagic fisheries

2020 ◽  
Author(s):  
Fatma Jebri ◽  
Zoe Jacobs ◽  
Dionysios Raitsos ◽  
Meric Srokosz ◽  
Stuart Painter ◽  
...  
Keyword(s):  
Indian Ocean ◽  
Phytoplankton Biomass ◽  
Critical Role ◽  
Tropical Indian Ocean ◽  
Nutrient Concentrations ◽  
Northeast Monsoon ◽  
The South ◽  
East African ◽  
Monsoon Wind ◽  
Pelagic Fisheries

<p>Small pelagic fisheries play a critical role in food security and economic stability for East African coastal communities ― a region of least developed countries. Using satellite and field observations together with modelling, we show the links between the small pelagic fisheries along the East African coast and the changes in Western Indian Ocean currents due to the interannual variability of the monsoonal wind field. The annual variations in phytoplankton biomass and fisheries yield are strongly associated. During the Northeast monsoon, the enhanced phytoplankton biomass is triggered by local wind-driven upwelling. During the Southeast monsoon, however, the enhanced phytoplankton biomass is due to two current induced mechanisms: coastal “dynamic uplift” upwelling; and westward advection of waters with higher nutrient concentrations. This biological response to the Southeast monsoon is greater than that to the Northeast monsoon. Interannually, an extreme increase (decrease) in chlorophyll concentrations is induced by strengthened (weakened) surface currents, which occur during anomalously “strong” (“weak”) Southeast monsoon years. For years where the effects of El Niño / La Niña are weak, the Southeast monsoon wind strength over the south tropical Indian Ocean is the main driver of year-to-year variability. Such changes have important implications for the predictability of fisheries yield, its response to climate change, policy and resource management.  </p>

scholarly journals Remote-Sensing-Based Estimation of Surface Nitrate and Its Variability in the Southern Peninsular Indian Waters

2011 ◽  
Vol 2011 ◽  
pp. 1-16 ◽  
Author(s):  
R. K. Sarangi
Keyword(s):  
Indian Ocean ◽  
Bay Of Bengal ◽  
Arabian Sea ◽  
Nitrate Concentration ◽  
Southwest Monsoon ◽  
Northeast Monsoon ◽  
Northern Indian Ocean ◽  
Noaa Avhrr ◽  
Nitrate Concentrations ◽  
High Nitrate Concentration

A relationship between sea surface temperature (SST) and surface nitrate concentrations has been obtained for the first time based on in situ datasets retrieved from U.S. JGOFS (1991–96) and Indian cruises (2000–2006) in the Arabian Sea, Bay of Bengal and Indian Ocean region around the southern Indian tip. The dataset includes 1537 points. A sigmoid relationship obtained with value 0.912. NOAA-AVHRR pathfinder satellite monthly averaged SST data retrieved from the PODAAC/JPL/NASA archive during July 1999–June 2004. The datasets imported in the ERDAS-Imagine software and SST images generated on monthly and seasonal scales, for latitudes 5–12°N and longitudes 75–85°E. The ocean surface nitrate images retrieved based on the established sigmoid relationship with SST. The nitrate concentrations ranged between 0.01–3.0 μM and categorized into five ranges. The significant seasonal upwelling zone around the southwest coast of India (Kerala coast, Latitude 80.10–9.30°N and Longitude 75.60–76.20°E) was identified during July–September 1999–2004 with very high nitrate concentration (~1.00 μM). Low nitrate and nitrate-depleted zones observed during summer (March–May). In the Arabian Sea and northern Indian Ocean, high nitrate concentration (~0.50 μM) observed during the southwest monsoon (SWM), whereas the Bay of Bengal was marked with high nitrate (~0.50 μM) during the northeast monsoon (NEM). SST was high (~29°C) in the Bay of Bengal and low (~26°C) in the Arabian Sea and northern Indian Ocean during SWM and vice versa during the NEM. There is a clear inverse relationship between nitrate and SST in the study area during July 1999–June 2004.

scholarly journals The Strengthening Relationship between ENSO and Northeast Monsoon Rainfall over Sri Lanka and Southern India

2006 ◽  
Vol 19 (8) ◽  
pp. 1567-1575 ◽  
Author(s):  
Lareef Zubair ◽  
C. F. Ropelewski
Keyword(s):  
Sri Lanka ◽  
Indian Ocean ◽  
El Niño ◽  
Monsoon Rainfall ◽  
El Nino ◽  
Southern Oscillation ◽  
Tropical Indian Ocean ◽  
Northeast Monsoon ◽  
Peninsular India ◽  
The Relationship

Abstract Recently, it was reported that the relationship of the Indian southwest monsoon rainfall with El Niño–Southern Oscillation (ENSO) has weakened since around 1980. Here, it is reported that in contrast, the relationship between ENSO and the northeast monsoon (NEM) in south peninsular India and Sri Lanka from October to December has not weakened. The mean circulation associated with ENSO over this region during October to December does not show the weakening evident in the summer and indeed is modestly intensified so as to augment convection. The intensification of the ENSO–NEM rainfall relationship is modest and within the historical record but stands in contrast to the weakening relationship in summer. The intensification of the circulation is consistent with the warming of surface temperatures over the tropical Indian Ocean in recent decades. There is modestly intensified convection over the Indian Ocean, strengthening of the circulation associated with ENSO (Walker circulation), and enhanced rainfall during El Niño episodes in a manner consistent with an augmented ENSO–NEM relationship.

Summer Rainfall Variability in Low-Latitude Highlands of China and Subtropical Indian Ocean Dipole

2014 ◽  
Vol 27 (2) ◽  
pp. 880-892 ◽  
Author(s):  
Jie Cao ◽  
Ping Yao ◽  
Lin Wang ◽  
Kui Liu
Keyword(s):  
Water Vapor ◽  
Indian Ocean ◽  
Arabian Sea ◽  
Tropical Indian Ocean ◽  
Summer Rainfall ◽  
Wind Component ◽  
Vertical Circulation ◽  
Low Latitude ◽  
Divergent Wind ◽  
Rainfall Variations

Abstract Based on reanalysis and observational datasets, this study proposes a reasonable mechanism for summer rainfall variations over the low-latitude highlands (LLH) of China, in which a subtropical Indian Ocean dipole (SIOD)-like pattern is the key external thermal forcing. In summers with a positive SIOD-like pattern, sea surface temperature (SST) anomalies may lead to lower-tropospheric divergence over the tropical Indian Ocean and convergence over the subtropical southwestern Indian Ocean and Arabian Sea. The convergence over the Arabian Sea can induce easterly anomalies of the divergent wind component off the eastern coast of the Bay of Bengal (BOB), while the divergence over the tropical Indian Ocean can change the interhemispheric vertical circulation and produce a descending motion over the same area and cyclonic anomalies in the rotational wind component over the Indian peninsula. The combined effect of the divergent and rotational wind anomalies and enhanced interhemispheric vertical circulation facilitates easterly anomalies and weakens climatological water vapor flux to the northern BOB. Therefore, anomalous water vapor divergence and less precipitation are observed over the LLH. In summers with a negative SIOD-like pattern, the situation is approximately the same but with opposite polarity and a weaker role of the divergent wind component. Further analyses indicate that the summertime SIOD-like pattern can be traced to preceding seasons, especially in positive SIOD-like years. The SST–wind–evaporation feedback mechanism could account for maintenance of the SIOD-like pattern. These results provide efficient prediction potential for summer rainfall variations over the LLH.

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