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Chromophoric dissolved organic matter (CDOM) variability over the continental shelf of the northern Bay of Bengal

Das S., Das I., Giri S., Chanda A., Maity S., Lotliker A. A., Kumar T. S., Akhand A., Hazra S.

Oceanologia

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2017

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No. 59 (3)

271--282

EN

The present paper dealt with the annual dynamics of the absorption coefficient of chromophoric dissolved organic matter at 440 nm {aCDOM(440)} during February 2015 to January 2016 in the continental shelf of northern Bay of Bengal (nBoB) for the first time. Sea surface salinity (SSS), chlorophyll-a (Chl-a), total suspended matter (TSM) were also analyzed. It was hypothesized that CDOM should exhibit significant spatial and temporal variability in this region. aCDOM (440) and spectral slope ranged between 0.1002 m−1 – 0.6631 m−1 and 0.0071 nm−1 – 0.0229 nm−1 respectively during the entire study period. Higher values of aCDOM (440) were observed in the near shore stations and gradually decreased towards the offshore. Significant seasonal variability of aCDOM (440) was observed between the monsoon and non-monsoon seasons (p < 0.05). Thus the framed hypothesis was successfully accepted by means of the present study. The CDOM was mainly found to be of allochthonous character in this region. aCDOM (440) portrayed a significant negative linear relationship with SSS (R2 = 0.80; p < 0.05) implying conservative mixing of marine and terrestrial end members. However, examining the spatial variability of the relationship, it was observed that this relationship was significant only in the nearshore stations. While examining the seasonal variability of this relationship, it was found to be most significant during the monsoon (R2 = 0.81; p < 0.05). Thus it was inferred that whenever the SSS gradient was higher, the relationship between aCDOM (440) and SSS was found to be most significant.

2

Measures of complexity in wind direction

Chanda A., Das J.

Journal of Technical Physics

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2003

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Vol. 44, no 2

207-214

EN

In the present paper an attempt has been made to utilise two different forms of complexity measures in directional change of wind. Two types of complexity measures are average mutual information and multifractal dimensions. Four sets of data have been studied. For each set, all the three measures have been calculated. From the results, a comparative study of the properties of the two measures of complexity vis-a-vis understanding the nature of complexity has been done.

3

Self-similarity in the decay of homogeneous and isotropic turbulence

Chanda A., Das P., De A., Das J.

Journal of Technical Physics

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2000

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Vol. 41, no 1

43-47

EN

Decay of turbulent energy in isotropic and homogeneous conditions has been discussed from the point of view of geometrical and statistical self similarity. Assuming the presence of self-similar eddies in the inertial subrange, a model of the inertial transfer of turbulent energy in the sense of fractal has been built. A method to extend the model to multifractal formalism has been also suggested.

4

On geometric and statistical selfsimilarity in wind direction in turbulent atmosphere

Chanda A.

Journal of Technical Physics

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1998

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Vol. 39, no 2

237-243

EN

Direction of wind, the horizontal component of air velocity is assumed to form a fractal set. Higher above ground, wind becomes stronger are more unidirectional and hence the direction data are less random, what leads to lowering of its fractal dimension (FD). FD of wind direction data, measured a meteorological tower at different altitudes have been estimated. The conjecture as above has been tested by means of the estimated FD and the mean wind of the given data. In addition, intermittency behaviour of the data set and its depedence upon the distance from ground have been examined by calculating the correlation dimension. Is has been observed that intermittency is more near the ground. This observation is inconformity with the findings of Chilla et al. [1] in a laboratory experiment, and also with the recent findings of Chanda et al. [2] in a meteorological experiment.