Introduction
Chennai is one of the four largest Metropolitan cities of India and located on the east coast of Tamilnadu state. The city has two large operating coal fired thermal power stations situated on the northern coast, away from the urban habitation. A programme to survey and study the ambient air quality has been initiated, focusing mainly on the influences of the coastal meteorological condition on it.
Two prominent phenomena of mesoscale nature namely the sea breeze circulation and the associated Thermal Internal Boundary Layer (TIBL) are known to have influence on the air borne pollution release and resultant ground level concentration (GLC) profile in this area (Lyons and Cole, 1973). The sea breeze is likely to bring back pollutants transported over sea during the night hours and the TIBL fumigates the plume from tall stacks of the power plants increasing the GLC (Bouchlaghem et al., 2007). Estimation of the flow field and spatial variation of the height of TIBL w.r.t inland distance is vital for accurate assessment of GLC. It is too difficult to estimate the non homogeneous wind field based on measurement. Alternatively one can use a numerical model for simulating the same using minimum available routine measurements like the surface level temperatures over land and sea and vertical wind and temperature stratification from a single radiosonde as input.
Several numerical mesoscale atmospheric models are founds in the literature in the recent past to describe the boundary layer characteristics at the time of sea breeze hours in coastal terrain. To quote a few example, a dynamic Colorado State University Regional Atmospheric Modeling System (RAMS) is described by Pielke et al. (1992) and its outputs are compared with comprehensive data sets of field study PACIFIC 93 carried out in the Lower Fraser Valley B C, Canada. On the other hand, a simple diagnostic Applied Slab Model (SASM) of Gryning and Batchvarova (1996) estimates TIBL height without detailed hydrodynamic simulation and has been tested with the same data set of PACIFIC 93 as well as inter-compared with RAMS (Batchvarova et al., 1999) estimates. Internal Boundary Layer (IBL) profile development is diagnosed from the vertical profile of turbulent kinetic energy (TKE) in RAMS where as in SASM, top of the IBL is identified by means of potential temperature jump. A comparison between these two methods is also discussed by Prabha et al. (1999) using tethered balloon measurements and the method based on TKE is recommended for TIBL height determination. Numerous operational models like PSU/NCAR Mesoscale Model (MM5), Advanced Regional Prediction System (ARPS), Regional Atmospheric Modeling System (RAMS), Weather Research and Forecasting (WRF)etc are also available through open sources for simulating the wind field and boundary layer structure. Literature is abundant on the sea breeze modelling study. Among others, a study on Chicago lake breeze carried out by Harris and Kotamarthi (2005) using MM5 and a trajectory model showed that the general characteristics could be modelled by MM5 where as the single day event simulation was in an error with in the range of natural variability.
A simple numerical mesoscale model is developed at IGCAR Kalpakkam to quickly generate the necessary and sufficient input data for dispersion models that can be run together on a PC. The model called Mesoscale Atmospheric Model (MAM-1) is based on shallow water hydrostatic equations for mean meteorological variables and turbulent kinetic energy — mixing length closure scheme (widely known as k−l closure scheme) for eddy diffusion. The model was partially validated with measurements using Tower and Sodar based wind profile data at Kalpakkam as well as using a full-fledged benchmark data set from Øresund field experiment (Prabha et al., 1999). Earlier study using MAM-1 coupled with a particle dispersion model for a 100m stack release showed that the coastal fumigation effect enhanced the GLC up to 10km inland (Venkatesan et al., 2002) by a factor of 2.3.
The objective of the present study is to highlight sea breeze characteristics from the meteorological field data collected during the air quality study program at the northern rural suburb of coastal city Chennai, and to attempt to simulate them using MAM-I. A comparison of MAM-1 performance with a widely used operational model MM5 is also made in order to validate MAM-1. The data is not sufficient for a detailed analysis of the structure of the sea breeze and atmospheric boundary layer such as the ESCOMPTE experiment (Puygrenier et al., 2005). However it is a useful case study to test the performance of model prediction of the wind field. A brief account of the meteorological measurements carried out is described in the first section. In subsequent sections, an outline of MAM-1 model, comparison of model results with measurement as well as inter-comparison with MM5 is presented.
Section snippets
Brief outline of the study programme
An air-quality study programme near the coastal site was performed during the month of April and May, 2005. The objective is to assess the impact of coastal meteorological condition on tall stack emissions and evolve methodology to account it in regulatory, monitoring and site selection applications. The study area Ennore (latitude N 13°12′, longitude E80°18′) is located in the rural coastal plain north of city Chennai. The shoreline profile is approximately linear and oriented itself in the
Brief outline of MAM-I
MAM-I is a numerical model developed to simulate the sea-land breeze circulation and TIBL structure for a coastal terrain, which are used as input in coastal atmospheric dispersion models. The model is formulated using the system of governing equations for the atmospheric boundary layer and the numerical solution procedure is based on Finite Difference Method (FDM) of solving the fundamental partial differential equations of temperature, specific humidity, pressure, turbulent kinetic energy
Major features
The model is integrated for 48h to simulate the land-sea breeze. The overall performance of the model is examined first by analysing the spatio-temporal pattern of the mean meteorological parameters. Simulation of the wind and temperature profiles at a single location over land (10km inland) and another over water (6km off-shore) are shown in Fig. 7. The locations correspond to the horizontal (x) grid 32 and grid 38 respectively in the model. The land-sea breeze circulation and the diurnal
Summary and conclusion
The present study focuses on the meteorological data observed near a semi-rural coastal site at North Chennai during the pre-monsoon summer period. Land-sea breeze common to the site has been observed with typical features like sudden increase and steep turning of the wind during onset of sea breeze, delay in on set times at different down wind locations, damping of the upper level temperature rise at the coastal site due to marine air intrusion etc. The climatological analysis at a similar
Acknowledgements
This study is part of the project funded by the University Grant Commission (UGC) under the scheme of major research project. Authors thank the Director, IGCAR for encouraging interaction with expertise at the Centre and duly acknowledge Dr. R. Indira, Head, RSD for permitting to use the instruments and tower accessories for the study. Thanks are also due to the Panchayat chief and people at Kattupalli coastal fishermen Kuppam who, despite the Tsunami devastation and loss, rendered their
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The surface wind field is characterized by weak (~ 2 m s− 1) southwesterly to westerly and northwesterly wind (land breeze) during 00:00 and 09:00 LT of the day. However, it turns north-northeasterly in winter and southeasterly in summer at ~ 10:00 LT under the influence of synoptic wind, and then accelerates (from 2 m s− 1 to 7 m s− 1) during noon hours (12:00–14:00 LT) as a result of the onset of sea breeze (Srinivas et al., 2006; Venkatesan et al., 2009). During the study periods, the winds at the sampling site were relatively calm, except for 15 February, and mostly N/SW in winter whereas in summer the winds showed a shift from SW to SE (Fig. 1b).
To better understand the photochemical production and diurnal distributions of organic and inorganic aerosols in the tropical coastal Indian atmosphere, the aerosol (TSP) samples were collected every 3h during 30–31 January, 14–15 February and 28–29 May 2007 from Chennai and studied for total carbon (TC) and nitrogen (TN) and their stable isotope ratios (δ13CTC and δ15NTN), carbonaceous components, inorganic ions, diacids, ketoacids and α-dicarbonyls. Time-resolved distributions of bulk parameters, inorganic ions, and diacids and related compounds, except for few species, did not show any clear diurnal trend but showed peaks at 6–9h during all the study periods, except for the peak at 15–18h on 28 May. SO42−, C2−C6 diacids, ketoacids and α-dicarbonyls in February and on 29 May showed a diurnal trend. δ13CTC and δ15NTN stayed relatively constant during the study periods but showed 13C depletion (in January) and 15N enrichment when TC and TN peaked. Based on these results together with air mass trajectories, we found that the diurnal distributions of Chennai aerosols are mainly influenced by land/sea breeze and the aged (photochemically processed) air masses, although in situ photochemical production and nighttime chemistry of secondary aerosol species, particularly C2–C4 diacids and SO42−, are significant. The characteristics of seasonal variations of carbonaceous components, and diacids and related compounds and comparisons of δ13CTC and δ15NTN of Chennai aerosols with the isotopic signatures of the point sources inferred that biofuel/biomass burning in South and Southeast Asia are the major sources of aerosols (TSP).
Study on deep inland penetration of sea breeze over complex terrain in the tropics
2012, Atmospheric Research
Citation Excerpt :
Penetration of sea breeze circulation over inland around 75 km along the west-coast of India during pre-monsoon season is reported by Indira et al. (2009). Also Venkatesan et al. (2009) has reported sea-breeze circulations over Chennai, a station located on east-coast of Indian peninsular region. Flow over complex terrain is important in understanding the links between large-scale synoptic flow situation and small-scale turbulent flow associated with a particular surface geometry, wind strength and direction.
Characteristics of sea breeze circulations over a tropical Indian station have been studied, based on one year of observations, by Doppler Sound Detection and Ranging (SODAR) system at National Atmospheric Research Laboratory, Gadanki (13.5°N, 79.2°E), India. The effect of sea breeze circulations on the dynamics of low level flow patterns in atmospheric boundary layer over complex terrain in tropics is investigated. The study reveals that a sea-breeze front develops well along the eastern coastal plain of southern peninsular India and propagates over inland up to the distance about 80km. It is found that the sea-breeze signal is well recognized during the months of February, March and April due to the presence of tropical easterlies. In these three months, SODAR observations indicate a late afternoon intensification of sea-breeze flow in the height range 0.2–0.6km during 1400 and 2000 local time (LT). The decrease in temperature of 2°C and increase in relative humidity of 20% at surface level are observed on a sea breeze day as compared to a non-sea breeze day. Sea-breeze inland propagation is absent for the rest of the months due to the opposing meso-flow direction. ERA-Interim reanalysis U-velocity data over south-Asia grid also corroborates the deep-inland penetrations of sea breeze circulations over this site.
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2018, Pure and Applied Geophysics
(Video) India Meteorological Department achievement in successful prediction of Cyclones - In Hindi PART 1Water-soluble organic carbon, dicarboxylic acids, ketoacids, and α-dicarbonyls in the tropical Indian aerosols
2010, Journal of Geophysical Research Atmospheres
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