Marine Boundary-Layer Variability Over The Indian Ocean During Indoex (1998)

Abstract. Recent observations have shown the ubiquitous presence of iodine oxide (IO) in the Indian Ocean marine boundary layer (MBL). In this study, we use the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem version 3.7.1), including halogens (Br, Cl and I) sources and chemistry, to quantify the impacts of the observed levels of iodine on the chemical composition of the MBL. The model results show that emissions of inorganic iodine species resulting from the deposition of ozone (O3) on the sea surface are needed to reproduce the observed levels of IO, although the current parameterisations overestimate the atmospheric concentrations. After reducing the inorganic emissions by 40 %, a reasonable match with cruise-based observations is found. A strong seasonal variation is also observed, with lower iodine concentrations predicted during the monsoon period when clean oceanic air advects towards the Indian subcontinent, and higher iodine concentrations predicted during the winter period, when polluted air from the Indian subcontinent increases the ozone concentrations in the remote MBL. The results show that significant changes are caused by the inclusion of iodine chemistry, with iodine catalysed reactions leading to regional changes of up to 25 % in O3, 50 % in nitrogen oxides (NO and NO2), 15 % in hydroxyl radicals (OH), 25 % in hydroperoxyl radicals (HO2), and up to a 50 % change in the nitrate radical (NO3). Most of the large relative changes are observed in the open ocean MBL, although iodine chemistry also affects the chemical composition in the coastal environment and over the Indian subcontinent. These results show the importance of including iodine chemistry in modelling the atmosphere in this region.

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Observations of iodine oxide in the Indian Ocean marine boundary layer: A transect from the tropics to the high latitudes

Atmospheric Environment X ◽

10.1016/j.aeaoa.2019.100016 ◽

2019 ◽

Vol 1 ◽

pp. 100016 ◽

Cited By ~ 2

Author(s):

Anoop S. Mahajan ◽

Liselotte Tinel ◽

Shrivardhan Hulswar ◽

Carlos A. Cuevas ◽

Shanshan Wang ◽

...

Keyword(s):

Boundary Layer ◽

Indian Ocean ◽

Marine Boundary Layer ◽

High Latitudes ◽

The Indian Ocean ◽

The Tropics

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Thermodynamic structure of the Atmospheric Boundary Layer over the Arabian Sea and the Indian Ocean during pre-INDOEX and INDOEX-FFP campaigns

Annales Geophysicae ◽

10.5194/angeo-22-2679-2004 ◽

2004 ◽

Vol 22 (8) ◽

pp. 2679-2691 ◽

Cited By ~ 14

Author(s):

M. V. Ramana ◽

P. Krishnan ◽

S. Muraleedharan Nair ◽

P. K. Kunhikrishnan

Keyword(s):

Boundary Layer ◽

Indian Ocean ◽

Atmospheric Boundary Layer ◽

Mixed Layer ◽

Arabian Sea ◽

Trade Wind ◽

Back Trajectory ◽

Spatial And Temporal Variability ◽

Air Mass ◽

The Indian Ocean

Abstract. Spatial and temporal variability of the Marine Atmospheric Boundary Layer (MABL) height for the Indian Ocean Experiment (INDOEX) study period are examined using the data collected through Cross-chained LORAN (Long-Range Aid to Navigation) Atmospheric Sounding System (CLASS) launchings during the Northern Hemispheric winter monsoon period. This paper reports the results of the analyses of the data collected during the pre-INDOEX (1997) and the INDOEX-First Field Phase (FFP; 1998) in the latitude range 14°N to 20°S over the Arabian Sea and the Indian Ocean. Mixed layer heights are derived from thermodynamic profiles and they indicated the variability of heights ranging from 400m to 1100m during daytime depending upon the location. Mixed layer heights over the Indian Ocean are slightly higher during the INDOEX-FFP than the pre-INDOEX due to anomalous conditions prevailing during the INDOEX-FFP. The trade wind inversion height varied from 2.3km to 4.5km during the pre-INDOEX and from 0.4km to 2.5km during the INDOEX-FFP. Elevated plumes of polluted air (lofted aerosol plumes) above the marine boundary layer are observed from thermodynamic profiles of the lower troposphere during the INDOEX-FFP. These elevated plumes are examined using 5-day back trajectory analysis and show that one group of air mass travelled a long way from Saudi Arabia and Iran/Iraq through India before reaching the location of measurement, while the other air mass originates from India and the Bay of Bengal.

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Structure of the marine boundary layer over north western Indian Ocean during 1983 summer monsoon

Boundary-Layer Meteorology ◽

10.1007/bf00123183 ◽

1990 ◽

Vol 52 (1-2) ◽

pp. 177-191

Author(s):

M. R. Ramesh Kumar ◽

Y. Sadhuram ◽

G. S. Michael ◽

L. V. Gangadhara Rao

Keyword(s):

Boundary Layer ◽

Indian Ocean ◽

Summer Monsoon ◽

Marine Boundary Layer ◽

Western Indian Ocean ◽

North Western

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Modelling the impacts of iodine chemistry on the northern Indian Ocean marine boundary layer

Atmospheric Chemistry and Physics ◽

10.5194/acp-21-8437-2021 ◽

2021 ◽

Vol 21 (11) ◽

pp. 8437-8454

Author(s):

Anoop S. Mahajan ◽

Qinyi Li ◽

Swaleha Inamdar ◽

Kirpa Ram ◽

Alba Badia ◽

...

Keyword(s):

Boundary Layer ◽

Chemical Composition ◽

Indian Ocean ◽

Marine Boundary Layer ◽

Indian Subcontinent ◽

Winter Period ◽

Monsoon Period ◽

Mean Values ◽

Iodine Chemistry ◽

Inorganic Iodine

Abstract. Recent observations have shown the ubiquitous presence of iodine oxide (IO) in the Indian Ocean marine boundary layer (MBL). In this study, we use the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem version 3.7.1), including halogen (Br, Cl, and I) sources and chemistry, to quantify the impacts of the observed levels of iodine on the chemical composition of the MBL. The model results show that emissions of inorganic iodine species resulting from the deposition of ozone (O3) on the sea surface are needed to reproduce the observed levels of IO, although the current parameterizations overestimate the atmospheric concentrations. After reducing the inorganic emissions by 40 %, a reasonable match with cruise-based observations is found, with the model predicting values between 0.1 and 1.2 pptv across the model domain MBL. A strong seasonal variation is also observed, with lower iodine concentrations predicted during the monsoon period, when clean oceanic air advects towards the Indian subcontinent, and higher iodine concentrations predicted during the winter period, when polluted air from the Indian subcontinent increases the ozone concentrations in the remote MBL. The results show that significant changes are caused by the inclusion of iodine chemistry, with iodine-catalysed reactions leading to regional changes of up to 25 % in O3, 50 % in nitrogen oxides (NO and NO2), 15 % in hydroxyl radicals (OH), 25 % in hydroperoxyl radicals (HO2), and up to a 50 % change in the nitrate radical (NO3), with lower mean values across the domain. Most of the large relative changes are observed in the open-ocean MBL, although iodine chemistry also affects the chemical composition in the coastal environment and over the Indian subcontinent. These results show the importance of including iodine chemistry in modelling the atmosphere in this region.

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The structure of the haze plume over the Indian Ocean during INDOEX: tracer simulations and LIDAR observations

Atmospheric Chemistry and Physics ◽

10.5194/acp-6-907-2006 ◽

2006 ◽

Vol 6 (4) ◽

pp. 907-923 ◽

Cited By ~ 11

Author(s):

G. Forêt ◽

C. Flamant ◽

S. Cautenet ◽

J. Pelon ◽

F. Minvielle ◽

...

Keyword(s):

Boundary Layer ◽

Indian Ocean ◽

Arabian Sea ◽

Vertical Structure ◽

Atmospheric Modeling ◽

Airborne Lidar ◽

Layer Depth ◽

The Indian Ocean ◽

Ground Based Lidar ◽

Lidar Observations

Abstract. Three-dimensional, nested tracer simulations of a pollution plume originating from the Indian sub-continent over the Indian Ocean, in the framework of the Indian Ocean Experiment (INDOEX), between 5 and 9 March 1999, were performed with the Regional Atmospheric Modeling System (RAMS), to provide insight into the transport patterns of the pollutants, as well as to investigate the dynamical mechanisms controlling the vertical structure of the plume and its evolution in the vicinity of the Maldives Islands. Airborne and ground-based LIDAR observations of the structure of the haze plume made on 7 March 1999 were used to assess the quality of the simulations, as well as the impact of grid resolution on the vertical structure of the simulated plume. It is shown that, over the Arabian Sea, in the vicinity of the Maldives Islands, the pollutants composing the plume observed by the airborne LIDAR essentially originated from the city of Madras and that the vertical structure of the plume was controlled by the diurnal cycle of the continental boundary layer depth. A combination of tracer simulations and remote sensing observations (airborne LIDAR, ship-borne photometer, ground-based LIDAR in Goa) was used to analyse the diurnal evolution of the haze plume over the sea. We find evidence that the sea breeze circulation and orographic lifting taking place in the southern part of the Indian sub-continent during the daytime play a crucial role in the modulation of the continental boundary layer depth, and in turn, the haze plume depth. The eastward shift of the subtropical high from central India to the Bay of Bengal after 6 March lead to an increase in the tracer concentrations simulated over the Arabian Sea, in the region of intensive observations north of the Maldives, as transport pathways form Hyderabad and Madras were modified significantly. The nesting of a high horizontal resolution domain (5 km, with 39 vertical levels below 4000 m above mean seal level) allows for a better representation of local dynamics, the circulation of sea and mountains breezes, and therefore a noticeable improvement in the representation of the pollutants' plume in the simulation.

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