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Indian Journal of Marine Sciences



ISSN: 0379-5136




MARCH 2004




Special Issue


Aerosols and Trace Gases over the Oceans




Satellite observations of the regional aerosol distribution and transport over the Arabian Sea, Bay of Bengal, and Indian Ocean



K. Rajeev, Sandhya K Nair, K. Parameswaran, & C. Suresh Raju


[IPC Code : Int.Cl.7 C09K 3/30, G01B 11/22]




INDOX: An overview


A. P. Mitra


[IPC Code : Int.Cl.7 C09K 3/30, B01D 53/00]




Aerosol loading over the Indian Ocean and its possible impact on regional climate


Chul Eddy Chung & V. Ramanathan


[IPC Code : Int.Cl.7 C09K 3/30, G01B 11/22]




Atmospheric deposition fluxes of 7Be, 210Pb and chemical species to the Arabia Sea and Bay of Bengal



R. Rengarajan & M. M. Sarin


[IPC Code : Int.Cl.7 C09K 3/30]




Ocean-atmosphere biogeochemical interactions: A two-way coupling under ‘SOLAS’



Adele L. Chuck & Peter S. Liss


[IPC Code : Int.Cl.7 C09K 3/30]




Atmospheric chemistry in the coastal ocean: A synopsis of processing, scavenging and inputs



T. M. Church & T.D. Jickells


[IPC Code : Int.Cl.7 C09K 3/30]




Air-sea exchange of nitrous oxide and methane in the Arabian Sea: A simple model of the seasonal variability



Hermann W. Bange


[IPC Code : Int.Cl.7 C09K 3/30]




Severe weather conditions in the Arabian Sea and their impact on atmospheric N2O budget



 Prabir K. Patra & Shamil Maksyutov


[IPC Code : Int.Cl.G01W 1/16, C09K 3/30]




Trace gases over marine region around India


M. Naja, D. Chand, L. Sahu & S. Lal


[IPC Code : Int.Cl.7 C09K 3/30]






Indian Journal of Marine Sciences

Vol. 33(1), March 2004, pp. 11-29


Satellite observations of the regional aerosol distribution and transport over the Arabian Sea, Bay of Bengal and Indian Ocean

*K. Rajeev, Sandhya K. Nair, K. Parameswaran, & C .Suresh Raju


The aerosol optical depth (AOD) derived from the NOAA14-AVHRR data and the tropospheric circulation obtained from the NCEP-NCAR reanalysis were used to study the regional distribution and long-range transport of aerosols over the oceanic areas around the Indian subcontinent during the Asian dry period (November – April) and the southwest monsoon season (June-September). Due to the contrasting airmass types, the aerosol properties over the oceanic areas around the Indian subcontinent are distinctly different during the Asian dry period compared to that during the summer monsoon season. Strikingly, the oceanic areas around the Indian subcontinent in the northern hemisphere in general, and the Arabian Sea in particular are always under the influence of continental aerosols throughout the year, despite the large annual migration of ITCZ and the presence of the vast oceanic areas at the south of the continental areas. The study demonstrates the transport of aerosols from the continental areas in the northern hemisphere to the oceanic region during the Asian dry season and a much larger-scale aerosol transport from the Arabian desert region to the Arabian Sea during the summer monsoon period. Bay of Bengal and the tropical Indian Ocean are significantly influenced by the aerosol transport from the Indian subcontinent and southeast Asia. However, the continental aerosol transport remains more or less confined to the Arabian Sea, Bay of Bengal and northern hemisphere Indian Ocean. Throughout the year, spatial gradient in AOD is large over Arabian Sea and Bay of Bengal, particularly in the meridional direction across ~5°N to 10°N. Associated with the El Nino related forest fires in the Indonesian region, a substantially large aerosol plume, with AOD exceeding 1.0, was observed over the tropical Indian Ocean during September-November 1997. The contribution of natural aerosols to the observed AOD during each season, the long-term changes in the aerosol loading, and the interaction between aerosols and clouds further needs to be investigated.


[Key words: Aerosols, regional aerosol distribution, transport, satellite observations, AVHRR, Indian Ocean, Arabian Sea, Bay of Bengal, forest fires]


[IPC Code:  Int. Cl.7 C09K 3/30,   G01B 11/22 ]





Indian Journal of Marine Sciences

Vol. 33(1), March 2004, pp. 30-39


Indian Ocean Experiment [INDOEX]: An overview

A. P. Mitra


An overview of the Indian Ocean Experiment, INDOEX, the first comprehensive campaign to study aerosol and trace gas distribution in the Indian Ocean Region, is presented. The main phase of INDOEX was in 1999 with a field phase in 1998 and preliminary observations in 1996 and 1997 (mainly because of Indian initiative). This was a major international initiative with participation from many institutions and agencies of India, the USA, Europe, and from Maldives and Mauritius. It was a multi-platform campaign combining ground based, shipborne, satellite and aircraft observations and had the single objective of reducing uncertainties in radiative forcing of aerosols, both direct and indirect. The campaign covered both aerosols and trace gases (O3, CO, NOx, SO2 etc), although subsequent analysis has been concentrated more on aerosols than on trace gases. The surprising result of an extensive haze layer with an appreciable component of black carbon, evidence of long distances transport of both aerosols and trace species and possible impacts on climate, health and agriculture have created much interest and some controversy. We present here an overview of some of the results, the implications of these in climate forcing, the unresolved aspects of sources of these pollutants, and a few comments on policy implications.


[Key words: INDOEX, aerosols, trace gases, radiative forcing]

[IPC Code: Int.Cl.7 C09K3/30, B01D53/00]





Indian Journal of Marine Sciences

Vol. 33(1), March 2004, pp. 40-55


Aerosol loading over the Indian Ocean and its possible impact on regional climate

Chul Eddy Chung* & V. Ramanathan


This paper provides a review of aerosol forcing results from the Indian Ocean Experiment (INDOEX) and also summarizes the follow-on modeling studies that examine the impact of the haze on regional climate. Every dry season from November to May, anthropogenic haze spreads over most of the northern Indian Ocean, and South and Southeast Asia. The INDOEX documented this Indo-Asian haze at various scales during 1995-2001. The haze particles consisted of several inorganic and carbonaceous species, including absorbing black carbon clusters, fly ash and mineral dust. Because of black carbon contributing as much as about 14% to the fine particle mass, the single-scattering albedo estimated by several independent methods was consistently around 0.9 both inland and over the open ocean. Anthropogenic sources contributed as much as 75% (±10%) to the aerosol loading and the optical depth. The regional aerosol forcing resulting from the direct and indirect effects was derived by integrating the multi-platform observations of satellites, aircraft, ships, surface stations and balloons with 1- and 4-D models. The haze layer reduces the net solar flux at the surface by as much as 20 to 40 Wm-2 on a monthly mean basis and heats the lowest 3 km atmosphere by as much as 0.4 to 0.8 K/day, which enhances the solar heating of this layer by 50 to 100%.

The INDOEX also documented year-to-year fluctuations of the haze forcing. For instance, the southernmost extent of the haze varied from about 10°S to about 5°N. In assessing the haze impacts on the cold dry-season regional climate, we conducted two CCM3 experiments with two extreme locations of the forcing: 1) extended haze forcing (EHF) and 2) shrunk haze forcing (SHF). Over India where the forcing is centered, the simulated climate changes are very similar between EHF and SHF. The most important effect of the haze is a surface cooling, and a strengthening of the inversion in the lower troposphere. The surface cooling has been confirmed by observations. The stabilization of the boundary layer results in a reduction of evaporation and sensible heat flux from the land. Rainfall patterns get substantially disrupted in local and remote regions, with the disruption being very sensitive to the southern extent of the imposed haze forcing. Both forcings lead to global circulation/precipitation perturbations; and the EHF produces about an order of magnitude larger responses. One key remote response to the haze is the suppression of convection in the western equatorial Pacific, which has implications for ENSO variability. Since the western Pacific convection suppression would weaken the trade winds over the Pacific and induce warm anomalies in the eastern basin, we speculate that the Great Indo-Asian haze might have an important role in the amplitude and frequency of El Nińo events during the recent decades. The haze-ENSO connection is further demonstrated by the Cane-Zebiak Pacific Ocean/atmosphere model. The focus of the studies thus far has been on the dry season (November to May) aerosols. The role of anthropogenic aerosols during the wet season from June to September is to be explored.


[Key words: Absorbing aerosols, INDOEX, climate, Indian Ocean, haze, ENSO, modelling, Asian Brown  Cloud]


[IPC Code: Int.Cl.7 C09K3/30, G01B11/22]




Indian Journal of Marine Sciences

Vol. 33(1), March 2004, pp. 56-64


Atmospheric deposition fluxes of 7Be, 210Pb and chemical species to the Arabian Sea and Bay of Bengal

 R. Rengarajan* & M. M. Sarin


Aerosol samples collected close to the air-sea interface, between February 1997 to February 1999, over the Arabian Sea and Bay of Bengal were analyzed to determine the atmospheric dry-deposition of Fe (dust inputs), anthropogenic constituents (NO3-, SO42-) and environmental nuclides (7Be, 210Pb). In general, aerosol 210Pb concentrations showed a good correlation with 7Be, suggesting the long-range transport of 210Pb from the continents (via upper troposphere) and similarities in the processes governing their deposition through the marine boundary layer (MBL). The relatively low 7Be/210Pb ratios observed over the Bay of Bengal, during February 1999, are dominated by aerosol transport from the continental surface sources. The dry deposition fluxes of 210Pb and 7Be, to these two oceanic regions, average around 245 and 1860 Bq m-2 y-1, respectively. The non-sea-salt (nss) SO42- (range: 1.7 to 9.4 µg m-3) and NO3- (range: 0.6 to 4.1 µg m-3) are uncorrelated in the MBL, presumably because continental pollution sources for SO42- overwhelm the transport of NO3- from crustal dust and biomass burning. The oceanic biogenic emission (DMS) constitutes a very minor source for nss-SO42-. The enhanced concentrations of aerosol NO3- and Fe observed over the Arabian Sea are attributed to dust storm activities from the adjacent desert areas (Saudi Arabia and Thar). Significant scatter in the linear regression analyses indicate that the aerosol composition along the coastal tracks is different from those transported to the open ocean. On average, dry deposition fluxes of N-NO3 and non-marine SO42- are 150 and 1225 mg m-2 y-1, respectively. In contrast, dry deposition of Fe over the Arabian Sea (255 mg m-2 y-1) far exceeds that over the Bay of Bengal (93 mg m-2 y-1). Thus, dust from desert regions appears to be a potential source of micronutrients (Fe) to the surface Arabian Sea.


[Key words: Arabian Sea, Bay of Bengal, aerosol composition, atmospheric deposition fluxes chemical species, Be, Pb, nuclides]


[IPC Code: Int.Cl.7 C09K3/30]




Indian Journal of Marine Sciences

Vol. 33(1), March 2004, pp 65-70


Ocean-atmosphere biogeochemical interactions: A two-way coupling under ‘SOLAS’

*Adele L. Chuck & Peter S. Liss


The Surface Ocean-Lower Atmosphere Study (SOLAS) is a new international research programme which aims to address our understanding of the coupled ocean-atmosphere system and the biogeochemical and physical interactions within it. The following examples of research topics to be studied under SOLAS are presented in the paper: the DMS-climate linkage, organo-iodine compounds and new particle formation, alkyl nitrates and oxygenated trace gases and atmospheric inputs mediating ocean biogeochemistry. Finally, we give a brief outline of the science agenda of the SOLAS programme.


[Key words: SOLAS; ocean-atmosphere interactions; trace gases; atmospheric inputs]


[IPC Code: Int. Cl.7 C09K 3/30]





Indian Journal of Marine Sciences

Vol. 33(1), March 2004, pp. 71-76


Atmospheric chemistry in the coastal ocean: A synopsis of processing,
scavenging and inputs

T. M. Church*and T. D. Jickells


The coastal atmosphere provides a complicated chemical environment that can have global implications for climate. For example, the continents transport an array of gases and aerosols, both natural dusts and pollutant species, which can interact with sea-salt and affect coastal clouds and their processing for deposition. Once over the coastal ocean, different mixtures of acids, bases, minerals, sea-salt and water under different solar irradiation can induce a host of heterochemical chemical reactions. Deposition of the products of these reactions can make a significant contribution of nutrient inputs to coastal waters and impact coastal ecosystems. However, the steep gradients and complex physical and chemical processes occurring in this transitional area between terrestrial and marine atmospheric domains complicate the quantification of these inputs. This synopsis considers a group of key processes such as interaction of climatic aerosols that operate to regulate atmospheric scavenging and deposition to the coastal environment


[Key words: Coastal, atmosphere, chemistry, aerosols, precipitation, dimethyl sulfide]


IPC Code:  Int. Cl.7 C09K 3/30 ]




Indian Journal of Marine Sciences

 Vol. 33(1), March 2004, pp 77-83


Air-sea exchange of nitrous oxide and methane in the Arabian Sea:A simple model of the seasonal variability

Hermann W. Bange


With a simple box model the seasonal variability of N2O and CH4 were simulated in surface layers in the central and western Arabian Sea. The model was able to reproduce the N2O measurements except for times when cold water filaments occur (i.e., during the SW monsoon). Based on the comparison of model results and measurements, it is concluded that the saturation of N2O in the surface layer of the Arabian Sea is mainly controlled by (i) the wind-driven air-sea exchange during the SW monsoon, (ii) entrainment of N2O from the subsurface layer, and (iii) sea surface temperature variability. However, the contribution of the factors listed above to the seasonality of the N2O saturations is different in the selected areas. The overall good agreement of model results and the majority of N2O measurements suggest that N2O formation in the surface layer of the Arabian Sea is negligible. The comparison of model’s results and CH4 measurements revealed a more complex situation, partly due to considerable inconsistencies in the available CH4 data. Thus, the situation for CH4 remains unresolved and inconclusive.


[Key words: Nitrous oxide, methane, Arabian Sea, air-sea exchange, box model]


[IPC Code: Int. Cl.7 C09K 3/30]




Indian Journal of Marine Sciences

 Vol. 33(1), March 2004, pp. 84-94


Severe weather conditions in the Arabian Sea and their impact
on atmospheric N2O budget

Prabir K. Patra* & Shamil Maksyutov and Takakiyo Nakazawa


Influences of tropical cyclones and wide spread south-west monsoon on the ocean-atmosphere fluxes of nitrous oxide (N2O) in the Arabian Sea are estimated. The NCEP/NCAR reanalysed wind speeds during a cyclone event are used to calculate N2O fluxes from the Arabian Sea. It is found that net emission of N2O from the Arabian Sea in a span of about 7 cyclonic days can contribute about 5.3% of its annual sources. This emission rate is about the same as that was observed (earlier estimates) during the south-west monsoon season in the Arabian Sea. The NIES/FRSGC global transport model is used to compute the tracer transport of monthly-mean high resolution fluxes to verify the significance of the Arabian Sea N2O emission in comparison with 9 other source types of N2O. The results show that the effect of N2O flux from the Arabian Sea on its concentration at a coastal station is larger than some of the global scale anthropogenic sources. The transport model simulations suggest that some natural phenomena in the oceanic regions can even produce the fluctuations in the N2O time-series observed in the southern hemisphere.


[Key words: Nitrous oxide, Arabian Sea, transport modelling, Indian summer monsoon, tropic cyclones]


[IPC Code: Int.Cl.7 G01W1/16, C09K3/30]




Indian Journal of Marine Sciences

Vol. 33(1), March 2004, pp.  95-106


Trace gases over marine regions around India

M. Naja1*, D. Chand2, L. Sahu3 & S. Lal3


Measurements of O3, CO, CH4, NO and SF6 were made during four ship cruises in January, February and March months of years 1996, 1997, 1998, and 1999 over the Arabian Sea and the Indian Ocean. Measurements were also made over the Bay of Bengal in February and March of the year 2001. All the measured trace gases show systematic gradient with decrease in their mixing ratios from the Coastal India to the South Indian Ocean. Transport of these gases also takes place from the surrounding countries over the marine regions.  Ozone and CO show higher values over the Bay of Bengal than over the Arabian Sea, indicating stronger transport of polluted air-masses from northeast India and south Asia. Dramatic increase in ozone levels in the marine boundary layer (MBL) while showing no signature of in-situ photochemical production indicates the role of dynamical processes. The diurnal patterns in ozone are very different over the marine environments when compared with continental site, which is due to the nature and levels of pollutants transported from the continental regions and emissions of certain gases over the marine regions.  Estimate shows that ozone production over India is less efficient, when compared to mid latitude.


[Key words :  Trace gases, ozone, marine region, Asia, photochemistry, transport, Bay of Bengal, Arabian Sea, Indian Ocean, INDOEX, BOBEX]


[ IPC Code: Int. Cl.7 C09K 3/30 ]