A study of forecast sensitivity to observations in the Bay of Bengal using LETKF

IntroductionAssimilating all available observations in numerical models may lead to deterioration of the analysis. Ensemble Forecast Sensitivity to Observations (EFSO) is a method that helps to identify all such observations which benefit the analyses. EFSO has never been tested in an ocean data assimilation system because of a lack of robust formulation of a squared norm against which beneficiality of observations can be estimated.MethodsHere, we explore the efficacy of EFSO in the ocean data assimilation system that comprises the ocean model, Regional Ocean Modeling System (ROMS), coupled to the assimilation system Local Ensemble Transform Kalman Filter (LETKF), collectively called LETKF- ROMS, in the Bay of Bengal by envisaging a novel squared norm. The Bay of Bengal is known for its higher stratification and shallow mixed layer depth. In view of baroclinicity representing the stratification of the ocean, we use the modulus of the baroclinic vector as the squared norm to evaluate forecast errors in EFSO.ResultsUsing this approach, we identify beneficial observations. Assimilating only the beneficial observations greatly improves the ocean state. We also show that the improvements are more pronounced in the head of the Bay of Bengal where stratification is much higher compared to the rest of the basin.DiscussionThough this approach doesn’t degrade the ocean state in other regions of the Indian Ocean, a universal squared norm is needed that can be extended beyond the Bay of Bengal basin

Direct measurement of VOCs diffusivities in tree tissues: Impacts on tree-based phytoremediation

Recent discoveries regarding volatile organic compounds’ (VOCs) fate in phytoremediation have confirmed that diffusion and subsequent volatilization from trees comprise a fundamental transport processes. Diffusion of VOCs through woody plant tissues has direct impact on contaminant fate in phytoremediation. Diffusion studies experiments were conducted to investigate the transport rates of VOCs in wood tissues. Compounds investigated were chlorinated compounds such as trichloroethylene (TCE), perchloroethene (PCE), and tetrachloroethane (TeCA), and aromatic hydrocarbons such as benzene, toluene, and methyl tert-butyl ether (MTBE). Direct measurement of diffusion rates was carried out on hybrid poplar tree cores (P delotoides X P nigra, clone DN34). Diffusivities were determined by modeling the diffusive transport using one dimensional diffusive flux with appropriate initial and boundary conditions. Diffusivities found to be inversely related to molecular weight of the compounds. The determined diffusivities compare favorably with theory-based predictions, considering wood as a three phase media. Confirming and enhancing the theoretical model, this study opens the door to projecting the potential fate of many volatile and semi volatile compounds that have not been studied explicitly and will increase the understanding and potentially the acceptance of VOC phytoremediation efforts --Abstract, page iv