On the association between aerosol optical depths and surface meteorological conditions in a tropical coastal environment

Columnar aerosol spectral optical depth data, estimated using a ground based passive multi-wavelength solar radiometer at the tropical coastal station of Thumba, Thiruvananthapuram (Trivandrum) (8.55°N, 77°E) during the period November 1985 to May 1991, are examined to study the association of the seasonal variations in the optical depths and their association with the prevailing meteorological conditions. A systematic seasonal variation has been observed, with the optical depths maximising in the summer/pre-monsoon season and reaching a minimum in the winter season. Significant association has been observed between the seasonal variations of aerosol spectral optical depths with those of the (on-shore) surface wind speed and the rainfall. The implications of the findings are discussed.

Atmospheric water vapour and its effect on aerosol Extinction at a coastal station – Visakhapatnam

Integrated atmospheric water vapour content. has been evaluated from the spectral optical depths around the PaT band of water vapour by making directly transmitted solar flux measurements at 800, 935 and 1025 nm. The temporal variation of the total precipitable water vapour shows significant seasonal variation with maximum during~ pre-monsoon and monsoon months and minimum during winter months. The integrated content shows a positive correlation with surface humidity parameters and the correlation is better during monsoon months compared to other seasons. The experimentally derived variations of water vapour are compared with the model variations formulated using radiosonde data. The aerosol extinctions derived from the, multi-spectral solar flux measurements in the visible and near IR regions increase with increasing atmospheric water vapour and this increase shows .a seasonal dependence the surface temperature also seems to affect the, aerosol extinction probably through Its effect on the mixing heights.

On applicability of Frontier Regression to nowcast surface meteorological parameters at Chennai and Trichy airports in Tamilnadu

An advanced statistical forecasting technique, viz., Frontier regression (FR) has been explored to augment the forecasting capacity in nowcasting of meteorological parameters for aviation flight planning at Chennai airport. As maritime effects strongly influence weather over a coastal station like Chennai, the model contemplated in this study has been tried for an inland airport station, viz., Trichy also to assess its efficacy.

Forecasting maximum and minimum temperature over airports with special relevance to aviation in flight planning

Forecasting of maximum temperature and minimum temperature for aviation and non-aviation purpose has been attempted through auto regression and by employing the method of adaptive filtering and Kalman filtering during the hot weather season (March to May) over Madras. The filtering techniques have been outlined and the results are compared with the method of climatology and persistence. The Kalman filter using the model output of adaptive filtering. forecasts well the day-to-day variability of maximum and minimum temperature during hot weather season over Madras with an efficiency close to 90%. As the model performs reasonably well over Madras. a coastal station. the same has been tried over Trichy (300 km southwest of Madras), an inland airport station in Tamilnadu to ascertain its efficacy. The efficiency is better than 90% in predicting maximum and minimum temperature within an accuracy of 2°C).

Ecology and seasonality of Pseudo-nitzschia species (Bacillariophyceae) in the northwestern Adriatic Sea over a 30-years period (1988–2020)

The ecology and seasonality of Pseudo-nitzschia species and their contribution to phytoplankton community were analysed for the first time at the coastal station of the LTER-Senigallia-Susak transect (north-western Adriatic Sea) from 1988 to 2020. Species composition was addressed using DNA sequence data obtained from 106 monoclonal strains isolated from January 2018 to January 2020. The mean annual cycle of total phytoplankton in the study period (Feb 1988–Jan 2020) showed maximum abundances in winter followed by other peaks in spring and autumn. Diatoms were the main contributors in terms of abundance during the winter and the spring blooms. The autumn peak was due to phytoflagellates and diatoms. In summer phytoflagellates dominated the community, followed by diatoms and dinoflagellates, which in this season reached their annual maximum. Pseudo-nitzschia spp. represented on average 0.4–17.6% of diatom community, but during their blooms they could reach up to up to 90% of the total diatom abundances with 106 cells l-1. By LM, six different taxa were recognized: Pseudo-nitzschia cf. delicatissima and P. cf. pseudodelicatissima were the most abundant, followed by P. cf. fraudulenta, P. pungens, P. multistriata and P. cf. galaxiae. P. cf. fraudulenta and P. pungens were indicator taxa of winter. P. cf. delicatissima and P. cf. pseudodelicatissima were spring and summer taxa, respectively. P. galaxiae showed maximum abundances in autumn. DNA sequences revealed the presence of two species belonging to the ’P. seriata group’ (i.e. P. fraudulenta and P. pungens) and four species belonging to the ‘P. delicatissima group’ (P. calliantha and P. mannii within the P. pseudodelicatissima species complex, and P. delicatissima and P. cf. arenysensis within the P. delicatissima species complex). The presence of several cryptic and pseudo-cryptic species highlights the need to combine LM observations with DNA sequence data when the ecology of Pseudo-nitzschia is investigated.

Determination of Aliphatic and Polycyclic Aromatic Hydrocarbons in Marine Core Sediments off Johor, Malaysia

Aliphatic hydrocarbons and polycyclic aromatic hydrocarbons (PAHs) were studied in two sediment cores of southern South China Sea off Johor coastal area. The concentrations of the total identified resolved aliphatic hydrocarbons (TiRAHs) in the coastal station (STC104) ranged from 0.35 to 2.07 µg/g while the offshore station (STC100) varied from 0.05 to 14.7 µg/g. The concentrations of total PAHs were varied from not detected to 33.9 ng/g. The nalkanes distribution in STC104 were predominant in short chain carbons from marine productivity, petroleum mixture and minor higher plant input, while STC100 exhibited a bimodal distribution with mixed input of marine and terrestrial origin. PAHs isomer ratios cross-plot have showed mixed input of pyrogenic and petrogenic inputs while perylene was dominated in STC100 followed by fossil fuels and pyrogenic source. Presence of perylene in both cores suggesting the contribution of biogenic sources. Principal component analysis was used to cluster the relationship of the hydrocarbons at both sediment cores.

Raindrop Size Distributions of North Indian Ocean Tropical Cyclones Observed at the Coastal and Inland Stations in South India

The current study summarizes the raindrop size distributions (RSDs) characteristic of the North Indian Ocean (NIO) tropical cyclones (TCs) measured with ground-based disdrometers installed at the coastal (Thiruvananthapuram, 8.5335°N, 76.9047°E) and inland (Kadapa, 14.4742°N, 78.7098°E) stations in south India. The NIO TCs observed at the coastal station showed more mid- and large-size drops (>1 mm) than the inland station. On the other hand, for both inland and coastal stations, small and mid-size drops (<3 mm) primarily contributed to the total number concentration and rainfall rate. The RSDs of the NIO TCs segregated into precipitation types (stratiform and convective) demonstrated the presence of more mid- and large-size drops at the coastal station. The RSD relations of the NIO TCs, which are used in rain retrieval algorithms of remote sensing (global precipitation measurement) radars, exhibited contrasts between the coastal and inland station. Further, the NIO TCs’ rainfall kinetic energy relations, which are crucial in rainfall erosivity studies, estimated for the coastal station revealed dissimilar characteristics to that of the inland station. The conceivable thermo-dynamical and microphysical processes that are accountable for the disparities in the NIO TC RSDs measured at the coastal and inland stations are also elucidated in this work.