Tropical Coastal Site Research Articles

Numerical Simulation of Horizontal Convective Rolls Over a Tropical Coastal Site Using WRF: Sensitivity to Land Surface Physics

Numerical Simulation of Horizontal Convective Rolls Over a Tropical Coastal Site Using WRF: Sensitivity to Land Surface Physics

Site-specific transfer parameters for the tritium transport model at a tropical site, Tarapur, west coast of India

The study of the fate of atmospheric release and transport of Tritium requires an understanding of the exchange/transfer of Tritium (HTO) from within the compartments; air, soil, and plant systems. The Tritium transfer parameters within these compartments are used in specific activity models to compute TFWT and OBT in terrestrial plants and are highly dependent on the site-specific conditions. Hence a study was carried out to generate site-specific Tritium transport model parameters in the tropical environment of Tarapur which receives the atmospheric releases of Tritium from nuclear facilities operating at this site, on the West coast of India. The paper presents the details of the study carried out in Tarapur, India. The transfer parameters generated through this study are soil water to air moisture HTO transfer ratio: CRs, plant water to air moisture HTO transfer ratio: Rpa, and plant water to soil water HTO transfer ratio: Rpw. The geometric mean and geometric standard deviation (GSD) of the transfer ratios, CRs, Rpa and Rpw determined were found to be 0.50 (GSD: 3.52), 0.53 (GSD: 2.51) and 1.12 (GSD: 2.58), respectively. In addition, the Tritium scavenging ratio, surface loading, and wet deposition velocity were also derived and were found to be 1.59 ± 1.32, 1.21 × 10−2 Bq m−2 s−1, and 7.91 × 10−2 m s−1, respectively. The study has generated a set of site-specific model input parameters for a tropical coastal site of Tarapur, India, and details are discussed in the manuscript.

Ozone chemistry and dynamics at a tropical coastal site impacted by the COVID-19 lockdown

The nationwide lockdown in India to curb the spread of Coronavirus disease 2019 (COVID-19) led to colossal reduction in anthropogenic emissions. Here, we investigated the impact of lockdown on surface ozone (O3) and nitrogen dioxide (NO2) over a tropical coastal station – Thumba, Thiruvananthapuram (8.5°N, 76.9°E). Daytime as well as night-time NO2 showed reduction by 0.8 (40%) and 2.3 (35%) ppbv, respectively during the lockdown period of 25–30 March 2020 as compared with the same period of previous 3 years. Unlike many urban locations, daytime surface O3 is found to be dramatically reduced by 15 ppbv (36%) with O3 production rate being lower by a factor of 3 during the lockdown. Interestingly, a feature of O3-hump during the onset of land breeze typically observed during 1997–1998 has reappeared with magnitude of 5–10 ppbv. A photochemical box model, capturing this feature, revealed that significant O3 sustained till onset of land breeze over the land due to weaker titration with NOx during lockdown. It is suggested that the transport of this O3 rich air with onset of land breeze led to the observed hump. Our measurements unravel a remarkable impact of the COVID-19 lockdown on the chemistry and dynamics of O3 over this tropical coastal environment.Supplementary InformationThe online version contains supplementary material available at 10.1007/s12040-021-01666-3.

The impact of eutrophication towards selected bacterial process rates in tropical coastal waters

The dissolved organic nutrient conditions and bacterial process rates at two tropical coastal sites in Peninsular Malaysia (Port Klang and Port Dickson) were initially studied in 2004–2005 period and later revisited in 2010–2011. We observed that dissolved organic nitrogen (DON) increased about two- and ten-fold at Port Klang and Port Dickson, respectively and resulted in a significant change in DOC:DON ratio (t ≥ 2.077, p < 0.05). Among the bacterial processes measured, bacterial respiration (BR) was lower in the 2010–2011 period at both stations (t ≥ 3.390, p < 0.01). BR also correlated to the DOC:DON ratio (R2 ≥ 0.259, p < 0.01). The increase in substrate quality enabled the bacteria to respire less in the dissolved organic matter degradation. As a result, the average bacterial growth efficiency increased slightly in the 2010–2011 period.

Salvando el planeta con biotecnología apropiada: 4. Cultivo de cocolitóforos e implementación

Cultivating coccolithophore algae for carbon sequestration is discussed. Coccolithophores have been major calcium carbonate producers in the world’s oceans for about 250 million years. Today, they account for about a third of the total marine CaCO3 production by coating their single cells externally with plates of microcrystalline CaCO3. The possibility that these algae could be used to trap atmospheric CO2 with existing technology has not been widely considered. There is scope for both high technology cultivation in bioreactors and low technology cultivation in terraced raceway ponds or lagoons on tropical coastal sites. The latter could produce a sludge of pure CaCO3 as a feedstock for cement production in place of the fossilised limestone currently used (cement production accounts for around 8% of industrial fossil CO2 emissions). On the high seas coccolithophores naturally produce extensive blooms, which emit the volatile gas dimethyl sulfide to the atmosphere, where it promotes formation of clouds that block solar radiation. The vision is for aquaculture nurseries onboard factory ships, cultivating both coccolithophores and bivalve molluscs, creating and maintaining blooms of coccolithophores in the oceanic high seas to sequester carbon from the atmosphere and generate cloud cover to cool the immediate environment.

Radiative characteristics of near-surface aerosols at a tropical site: An estimation based on concurrent measurements of their physico-chemical characteristics

This study is an attempt to estimate the radiative characteristics of aerosols, namely, the scattering coefficient (βsc), absorption coefficient (βab), extinction coefficient (βex), single scattering albedo (ω) and the phase function P(θ), on a seasonal basis, incorporating the concurrent measurements of aerosol mass loading, size distribution and chemical composition at the tropical coastal site, Thiruvananthapuram. The software package Optical Properties of Aerosols and Clouds (OPAC) has been made use for the estimation of the radiative parameters. This paper presents the seasonal features of aerosol chemical composition and their source characteristics also. Along with this, the association between size-resolved number density of aerosols and their chemical characteristics were also investigated through correlation analysis. The location is significantly influenced by human activities as seen from the dominance of the anthropogenic component which is highest in winter (22%) with comparable values in pre-monsoon and post-monsoon and minimum in monsoon (13%). The sea-salt contribution is found to peak in monsoon (~40%) and attain a minimum in winter. The source characterization using principal component analysis along with back-trajectory analysis showed the seasonally changing mixed aerosol sources over the region. Accordingly, the radiative properties of aerosols also exhibit significant seasonal variations. βsc varied from 0.04 to 0.14 km−1 and βab between 0.01 and 0.05 km−1 over a year. The single-scattering albedo exhibited significant seasonal differences being ~0.71 for winter and ~0.89 (0.55 μm) for monsoon season, indicating the presence of more absorbing aerosols in winter.

Comparative metagenomics study reveals pollution induced changes of microbial genes in mangrove sediments

Mangrove forests are widespread along the subtropical and tropical coasts. They provide a habitat for a wide variety of plants, animals and microorganisms, and act as a buffer zone between the ocean and land. Along with other coastal environments, mangrove ecosystems are under increasing pressure from human activities, such as excessive input of nutrients and toxic pollutants. Despite efforts to understand the diversity of microbes in mangrove sediments, their metabolic capability in pristine and contaminated mangrove sediments remains largely unknown. By using metagenomic approach, we investigated the metabolic capacity of microorganisms in contaminated (CMS) and pristine (PMS) mangrove sediments at subtropical and tropical coastal sites. When comparing the CMS with PMS, we found that the former had a reduced diazotroph abundance and nitrogen fixing capability, but an enhanced metabolism that is related to the generation of microbial greenhouse gases via increased methanogenesis and sulfate reduction. In addition, a high concentration of heavy metals (mainly Zn, Cd, and Pb) and abundance of metal/antibiotic resistance encoding genes were found in CMS. Together, these data provide evidence that contamination in mangrove sediment can markedly change microbial community and metabolism; however, no significant differences in gene distribution were found between the subtropical and tropical mangrove sediments. In summary, contamination in mangrove sediments might weaken the microbial metabolisms that enable the mangrove ecosystems to act as a buffer zone for terrestrial nutrients deposition, and induce bioremediation processes accompanied with an increase in greenhouse gas emission.

Simulation of atmospheric dispersion of airborne effluent releases at a tropical coastal site under sea-breeze circulation and internal boundary layer development

In this study the impact of land–sea breeze circulation and internal boundary layer (IBL) on the atmospheric dispersion of airborne effluent releases at the tropical coastal site Kalpakkam is simulated using mesoscale model WRF and Lagrangian particle dispersion model FLEXPART. Simulations with WRF are conducted for typical days in different seasons, i.e., 3 May 2011 (summer), 20 Sep 2010 and 20 Jun 2011 (southwest monsoon). Two K-based non-local turbulence closures (YSU, ACM) and two TKE-based local closures (MYNN, MYJ) in WRF are tested for simulating the sea breeze and IBL. Observations from a 50-m meteorological tower, GPS Sonde, and a Doppler SODAR are used for validation. Simulations indicate that the synoptic flow largely influences the characteristics of the sea breeze at the site. Results show that the sea breeze is more predominant with early onset and it is characterized by deep inland penetration, strong horizontal and vertical winds and is associated with formation of a deep IBL relative to monsoon with opposing large-scale flow. The YSU non-local diffusion scheme and the higher order local TKE closure (MYNN) simulated the sea breeze and IBL characteristics in good agreement with observations. Dispersion simulations with a hypothetical tracer release using FLEXPART showed relatively high ground-level concentrations during IBL formation in the daytime and during stable off-shore flow condition in the morning time. The coupled mesoscale dispersion model could simulate the plume trajectory and buildup of concentrations during sea-breeze time by realistically simulating the winds and mixed-layer characteristics at the coastal site.

Classification and seasonal distribution of rain types based on surface and radar observations over a tropical coastal station

An attempt has been made to classify stratiform and convective rain using an impact type disdrometer at a tropical coastal site based on (Testud et al., 2001) method. Using this classification scheme, all rain events were analysed and computed their duration (minutes) and accumulated water (mm) in convective, stratiform, transition and mixed rain types. For the first time, in this paper an atmospheric electric field mill was used for rain type classification. The classification results were confirmed with disdrometer, Micro Rain Radar (MRR), and atmospheric electric field mill (EFM) observations. In convective rain type, non-bright band and high electric field were correspondingly observed in MRR and EFM records. Whereas bright band and shallow electric fields were detected during stratiform rain in the above observations of instruments. Other supporting evidences were observed from disdrometer also in corresponding rain types. Seasonal variations in rain duration and associated accumulated water were investigated in the four seasons (winter, pre-monsoon, summer monsoon and post-monsoon) for different rain types. General and mixed rain events were identified depending on the presence of stratiform or convective type in them. Percentage of rain duration and events for the study period were analysed with respect to (a) mean monthly rain water availability and (b) the intensity pattern in the total rainfall encountered in each month. Among the four seasons, summer monsoon received maximum rainfall followed by post-monsoon. A bimodal variation in the rainfall with a primary peak in June and secondary peak in October was observed in the annual cycle. Rainfall was intense during the pre- and post-monsoon seasons and less intense during the summer monsoon season. Also, shorter duration rain events were repeated in summer monsoon and fewer rain events of longer duration are resulted during pre- and post-monsoon seasons. In this duration, mixed rain accounts second higher in all the seasons. It was more evident in summer monsoon and least in post-monsoon. Rainfall contribution from convective rain was dominant in all the seasons except in winter. In summer monsoon, mixed and transition rain types have contributed much water among the four seasons. In mixed and transition rain types, mixed rain contributed more in duration and transition contributed more to water. From day-night variation analysis, it was observed that there was day-high and night-low in pre-monsoon and its reversal in post-monsoon season, with almost same occurrence during the summer monsoon. In the case of number of rain events, general (mixed) events were less (more) during the summer monsoon. From statistical analyses, an increase was observed in the duration of rain events from winter to post-monsoon. About 20% of duration was aggregated by longer duration events in all the seasons except during the winter.

Thunderstorm induced changes in near-surface O3, NOx and CH4 and associated boundary layer meteorology over a tropical coastal station

The paper presents four cases of the response of near-surface O3, NOx and CH4 to thunderstorm activity at a tropical coastal site in India, occurred during pre-monsoon and post-monsoon seasons. The associated changes in boundary layer meteorology in terms of temperature, relative humidity (RH), wind and boundary layer height (BLH) are also examined. The meteorological parameters like temperature and RH respond very fast depicting changes during the initial phase of the thunderstorm activity, whereas a delayed response is observed in the wind direction (changing from the sea breeze to land breeze) and collapse of the BLH (1–1:30 h delay) at the mature phase of the activity. Associated with the thunderstorm activity, significant changes were observed in the mixing ratios of the near-surface O3, NOx and CH4. An increase in NOx (5.2–8.7 ppbv) and CH4 (36.7–134.6 ppbv) and reduction in O3 (9.9–18.8 ppbv) were recorded at the mature phase of the thunderstorm. The rise in NOx is attributed to the combined effect of thunderstorm activity and wind reversal whereas that in CH4 is attributed to the wind reversal and associated change in air mass. A post activity increase is observed in mixing ratio of O3 in all the four cases. This is attributed to the downdrafts characteristic of the dissipation phase of thunderstorm activity which brings in O3 rich upper air down.

Seasonal variation of atmospheric organochlorine pesticides and polybrominated diphenyl ethers in Parangipettai, Tamil Nadu, India: Implication for atmospheric transport

Past studies have reported several persistent organic pollutants (POPs) in different environmental matrices from a tropical coastal site, Parangipettai (PI), located along the bank of the Vellar River in Tamil Nadu, south India. Hence to fill the data gap after the strict ban on several POPs, high volume air sampling was conducted in PI to study the variability of atmospheric organochlorine pesticides (OCPs) and polybrominated diphenyl ethers (PBDEs) during summer, pre-monsoon and monsoon seasons. Emission source regions were tracked by using five days back trajectory analysis. Range of air concentrations in pg/m3 were: dichlorodiphenyltrichloroethane (DDT), 13 - 1976; hexachlorocyclohexane (HCH), 260–1135, hexachlorocyclobenzene (HCB), 52–135, chlordanes, 36–135 and endosulfans, 66–1013. Six PBDE congeners ranged between 25 and 155 pg/m3 with the highest concentration in summer followed by pre-monsoon and monsoon. Atmospheric DDT and HCH in PI have drastically reduced from the past report thereby showing the strict ban on agricultural use of these compounds. During monsoon, fresh source of o,p′‐DDT, trans‐chlordane and α‐endosulfan was evident. Higher level of endosulphan sulfate in PI seems to be likely affected by the air mass, originating from a neighbouring state Kerela, where endosulfan has been extensively used for cashew plantations. Similarly in summer, the day recorded with the highest level of PBDEs, the sample was concurrently impacted by air parcel comprised of two major clusters, 1 (25%) and 2 (49%) that traversed through the metropolitan cities like Bangalore and Chennai. Dominance of BDE-99 over BDE-47 in PI is in line with the PBDE profile reported from Chennai city during similar time frame. Average concentration of tetra and penta BDE congeners in summer samples were nearly 2–3 folds higher than pre-monsoon or monsoon. Given the fact that strong localised sources for heavier BDE congeners are lacking in PI, regional atmospheric transport from the strong emission source regions in Chennai might have impacted PBDE concentration in PI.

Evaluation of Soil Fertility Status Based on CEC and Variation across Disturbed and Intact Tropical Coastal Forests Sites in Tanzania

Evaluation of Soil Fertility Status Based on CEC and Variation across Disturbed and Intact Tropical Coastal Forests Sites in Tanzania

Season-dependent size distribution of aerosols over the tropical coastal environment of south-west India

This paper presents the results of a detailed study on the size characteristics of aerosols at the tropical coastal site Thiruvananthapuram based on the in-situ measurements of size resolved aerosol number density using an aerosol spectrometer, covering a period of 28 months from September 2011 to December 2013. The diurnal pattern of aerosol number density is characterized by day time low and a two-fold increase during nighttime and these changes are closely associated with the strong mesoscale features namely the sea breeze and land breeze prevailing at the site. Aerosol Number Size Distribution (NSD) depicts a multi-modal nature with two prominent modes, one ≤0.1 μm and other ∼1 μm. Two other less pronounced modes are also observed in the NSD, one ∼0.3–0.5 μm and other ∼5–8 μm. The NSDs also exhibited strong seasonal changes linked with the synoptic meteorological feature of this region namely the South Asian monsoon. The seasonal NSDs were parameterized and analyzed. In addition to this, the effects of meteorological parameters temperature, relative humidity, and wind speed and airflow patterns on aerosol number density as revealed by partial correlation analysis were found to be aerosol size dependent.

Particulate Matter Concentrations in the Southern Tip of India: Temporal Variation, Meteorological Influences, and Source Identification

Objective This study investigates the temporal variability of particulate matter (PM10 and PM2.5) concentrations at an inland tropical coastal site in Thiruvananthapuram (8.5°N, 76.9°E), which is in the province of Kerala in the southern part of India.

Observation and numerical simulation of submesoscale motions within sea breeze over a tropical coastal site: A case study

Submesoscale motions observed using SODAR and fast response anemometer data during sea breeze hours are studied. SODAR data indicates the presence of waves with period ~30min during the sea breeze hours. The observations are further verified by spectral analysis of sonic anemometer data using wavelet and FFT techniques. The analysis confirms that there are waves with periods of ~30min present throughout the sea breeze hours with varying intensity. The observed waves are simulated using high-resolution WRF-ARW model using the MYJ planetary boundary layer scheme. The conditions of occurrence of such motions are briefly discussed. It is also found that these motions are caused by horizontal convective rolls within the sea breeze layer.

Chemical Constituents of Carbonaceous and Nitrogen Aerosols over Thumba Region, Trivandrum, India.

Aerosol filter samples collected at a tropical coastal site Thumba over Indian region were analysed for water-soluble ions, total carbon and nitrogen, organic carbon (OC), elemental carbon (EC), and water-soluble organic carbon/nitrogen and their sources for different seasons of the year. For the entire study period, the order of abundance of ions showed the dominance of secondary ions, such as SO42-, NO3-, and NH4+. On average, Mg2+ (56%), K+ (11%), SO42- (8.8%), and Ca2+ (8.1%) contributions were from maritime influence. There was significant chloride depletion due to enhanced levels of inorganic acids, such as SO42- and NO3-. Total carbon contributed 21% of the aerosol total suspended particulate matter in which 85% is organic carbon. Primary combustion-generated carbonaceous aerosols contributed 41% of aerosol mass for the entire study period. High average ratios of OC/EC (5.5±1.8) and WSOC/OC (0.38±0.11) suggest that organic aerosols are predominantly comprised of secondary species. In our samples, major fraction (89±9%) was found to be inorganic nitrate in total nitrogen (TN). Good correlations (R 2≥0.82) were observed between TN with NO3- plus NH4+, indicating that nitrate and ammonium ions account for a significant portion of TN. The temporal variations in the specific carbonaceous aerosols and air mass trajectories demonstrated that several pollutants and/or their precursor compounds are likely transported from north western India and the oceanic regions.

Formulation of stability-dependent empirical relations for turbulent intensities from surface layer turbulence measurements for dispersion parameterization in a lagrangian particle dispersion model

Season- and stability-dependent turbulence intensity (σu/u*, σv/u*, σw/u*) relationships are derived from experimental turbulence measurements following surface layer scaling and local stability at the tropical coastal site Kalpakkam, India for atmospheric dispersion parameterization. Turbulence wind components (u′, v′, w′) measured with fast response UltraSonic Anemometers during an intense observation campaign for wind field modeling called Round Robin Exercise are used to formulate the flux–profile relationships using surface layer similarity theory and Fast Fourier Transform technique. The new relationships (modified Hanna scheme) are incorporated in a Lagrangian Particle Dispersion model FLEXPART-WRF and tested by conducting simulations for a field tracer dispersion experiment at Kalpakkam. Plume dispersion analysis of a ground level hypothetical release indicated that the new turbulent intensity formulations provide slightly higher diffusivity across the plume relative to the original Hanna scheme. The new formulations for σu, σv, σw are found to give better agreement with observed turbulent intensities during both stable and unstable conditions under various seasonal meteorological conditions. The simulated concentrations using the two methods are compared with those obtained from a classical Gaussian model and the observed SF6 concentration. It has been found that the new relationships provide comparatively higher diffusion across the plume relative to the model default Hanna scheme and provide downwind concentration results in better agreement with observations.

Atmospheric particle dry deposition of major ions to the South Atlantic coastal area observed at Baía de Todos os Santos, Brazil

The coastal atmosphere adjacent to large urban areas can be strongly affected by the emission of air pollutants, among them, major ions species. In this study, the chemical composition and sources of carboxylates and other water-soluble ions in fine and coarse aerosols as well as estimates of particle dry deposition fluxes were studied at a tropical coastal site affected by an urban environment. The mean concentrations of the total carboxylates were 78 ng m–3 in fine fraction and 81 ng m–3 in coarse fraction of particulate matter (PM). The corresponding values for the total inorganic ions were 2143 ng m–3 and 4880 ng m–3 respectively. Main sources for fine particles were: (i) photochemical formation of carboxylic acids in vapor phase and a posterior gas-to-particle conversion onto sea salt particles; (ii) emissions from anthropic sources with long range transportation processes; and (iii) the interchanging of volatile species among atmospheric phases. In turn, for coarse particles, the predominant sources were: (i) gas-phase species and ab/adsorbed onto pre-existing particles afterwards; (ii) primary emission of coarse particles from anthropogenic sources; and (iii) sea salt spray and/or soil resuspension. Finally, particle dry deposition was a very important mechanism representing air-to-sea fluxes of major species.

Formulation of TKE based empirical diffusivity relations from turbulence measurements and incorporation in a Lagrangian particle dispersion model

In this paper a turbulence kinetic energy (TKE) based empirical formulation for turbulent diffusion is developed from ultra sonic anemometer measurements at a tropical coastal site Kalpakkam situated on the southeast coast of India. The diffusivity relationship is validated against an independent observation from SODAR. This formulation for turbulent diffusion is incorporated in a particle trajectory model FLEXPART-WRF. Under this formulation the turbulent component of the motion of pseudo particles in the model can be related to the TKE. Two case studies of dispersion simulation are carried out by incorporating the new relationship in FLEXPART-WRF. In the first case the simulated plume spread is compared against a real smoke plume from an accidental oil tank fire obtained from satellite image (MODIS-TERRA). In the second case, observed plume in the Hanford tracer experiment is simulated and normalized concentration profiles at different arcs are compared with that of the simulation. Results demonstrate that the simulated TKE using Mellor–Yamada–Nakanishi–Niino scheme in the Weather Research & Forecasting along with the new relationships for TKE apportionment simulate the dispersion pattern better than the Hanna scheme based on surface layer parameterization.

Optical properties of the South Asian winter haze at a tropical coastal site in India

Every year during the winter and pre-monsoon periods most of the Indian peninsula, Bay of Bengal and the adjoining Indian Ocean are affected by a polluted regional haze, known as the South Asian Winter Haze (SAWH). This article is the first of a series of three papers collectively anticipated at the central idea of retrieving aerosol component type and effective radius of the SAWH by incorporating experimental data of ground-based solar radiometer into Mie theory, and validation by collocated in-situ measurements. The work presented in this paper provides an approach to retrieve optical depths and their spectral curvature for SAWH at a tropical coastal station, Visakhapatnam (17.7°N, 83.3°E). A dataset comprised of 92 wintertime atmospheric optical depths are obtained from spectral extinction measurements of direct solar flux by means of a Multi-Wavelength Solar Radiometer during the period of October 2002 to February 2004. The inter-channel correlations established a linear relation and the airmass conditions specific to this dataset suggested a two-component linear model; the stable and variable components of which are analysed to obtain the mentioned optical parameters. Results indicate that the spectral curvature is best represented by a Lorentz model with a central wavelength of 0.40425±0.02945μm, a width of 0.40382±0.10253μm, a constant of 0.92623±0.33793, and a wavelength independent component of 0.95778±0.15678. Resonance-like structure of the obtained spectral curvature resembles wavelength dependent extinction characteristic of absorbing soot particles; thereby supports the key findings from INDOEX campaign.