arXiv subjects

Tridib Banerjee

Publications and source records attributed to Tridib Banerjee.

5 recordsLinked to original sources

arXiv2026

Elastic Non-Uniform FFT (ENUFFT) spectral reconstruction of irregularly sampled orography on unstructured grids

Subgrid-scale orography remains a leading source of uncertainty in numerical modeling because terrain spectra must be recovered from irregularly sampled elevation data and then reduced to a flow-dependent launch budget for parameterizations. Existing approaches are limited either by assuming regular samples on rectangular grids or by fitting coefficients whose truncation and regularization effects become embedded in the spectrum. None achieves dynamic, flow-dependent truncation. This study introduces an Elastic Non-Uniform Fast Fourier Transform (ENUFFT) framework that computes local Fourier coefficients directly from irregularly sampled orography on unstructured grids, without interpolation or fitting. It combines a type-1 NUFFT with local windowing, quadrature weights, and a new Elastic Mode Selection (EMS) algorithm for retaining a local flow-dependent subset of modes. ENUFFT is compared with the strongest relevant existing method in a monochromatic and a real Alpine terrain test. In both cases, it recovers peak amplitude and direction comparably while significantly compacting the spectra (monochromatic ~25%, Alpine ~60%). It also satisfies the Parseval condition more closely with its spectral variance (energy) deviating from reference by ~14-24% versus ~500-122,000% for the existing method. Its EMS is additionally tested in a mountain-wave test where it reduces the launch spectrum by >=75% while keeping launch-power loss <=7%. Along with better compute scaling, ENUFFT is thus a computationally efficient, physically interpretable framework that can make Fourier-based orographic source descriptions practical for spectral-budget-aware parameterizations.

physics.ao-ph↗

arXiv2025

Modeling Product Ecosystems

This paper develops a dynamical-systems framework for modeling influence propagation in product adoption networks, formulated as a positive linear system with Metzler interaction matrices and utility-based decay. Exact solutions are derived for constant, piecewise-constant, and fully time-varying interaction structures using matrix exponentials and the Peano--Baker series. It establishes five results: (i) positive interactions guarantee nonnegative amplification, (ii) perceived utility saturates after $\approx\!3$ complementary additions (Weber--Fechner), (iii) frequency of comparable introductions dominates incremental quality improvements, (iv) reinforcing interactions yields monotone gains while decay control gives ambiguous effects, and (v) long-run retention under SIS-type dynamics is bounded by the inverse spectral radius of the adoption graph. These results extend epidemic-threshold theory and positive-systems analysis to networked adoption, yielding explicit, calibratable expressions for influence dynamics on networks.

cs.SI↗

arXiv2025

The Impact of Non-Orographic Gravity Waves on Transport and Mixing: Effects of Oblique Propagation and Coupling to Turbulence

Gravity waves (GWs) are a fundamental driver of circulation, tracer transport, and mixing in the middle and upper atmosphere, but their treatment in global circulation models remains incomplete. In particular, standard parameterizations typically restrict propagation to the vertical and treat GW-turbulence interactions in only a rudimentary manner, potentially leading to systematic biases in simulated dynamics and transport. Here, we use the Multi-Scale Gravity-Wave Model (MS-GWaM) implemented in the Community Climate Icosahedral Nonhydrostatic Model UA-ICON, together with a novel theoretical framework, to quantify the impact of (i) oblique GW propagation and (ii) explicit bidirectional coupling between GWs and turbulence. Ensemble simulations reveal that allowing for oblique propagation lowers and cools the summer mesopause by shifting the deposition of momentum and heat to lower altitudes, reduces GW-induced vertical shear in the the middle and lower atmosphere, and enhances turbulent kinetic energy in the upper mesosphere and lower thermosphere. In contrast, coupling GWs to turbulence produces a nearly opposite mesopause response, lifting and warming the mesopause, while maintaining a reduction in wave-induced shear and further enhancing turbulence. Tracer experiments additionally show that turbulent coupling significantly increases mixing, particularly in regions of enhanced TKE, with implications for chemical redistribution. These results demonstrate that both oblique GW propagation and GW-turbulence interactions exert leading-order controls on mesosphere-lower thermosphere circulation, temperature structure, and tracer transport. Neglecting these processes in global models likely contributes to biases in the Brewer-Dobson circulation, energy balance, and constituent distributions, underscoring the need for next-generation GW parameterizations that capture these effects.

physics.ao-ph↗

arXiv2023

Split-explicit external mode solver in finite volume sea ice ocean model FESOM2

A novel split-explicit (SE) external mode solver for the Finite volumE Sea ice-Ocean Model (FESOM2) is presented. It is compared with the semi-implicit (SI) solver currently used in FESOM2. The SE solver utilises a dissipative asynchronous (forward-backward) time-stepping scheme. Its implementation with Arbitrary Lagrangian-Eulerian (ALE) vertical coordinates like Z-star and Z-tilde is explored. The comparisons are performed through multiple test cases involving idealised and realistic global simulations. The SE solver demonstrates lower phase errors and dissipation, but maintain a simulated mean ocean state very similar to the SI solver. The SE solver is also shown to possess better run-time performance and parallel scalability across all tested workloads.

physics.ao-ph↗

arXiv2023

Discrete variance decay analysis of spurious mixing

Expressions for local discrete variance decay (DVD) rates are directly derived from discrete tracer equations without any assumptions on discrete fluxes of the second moment. Spurious mixing (SM) associated with numerical implementations of scalar advection and diffusion is thus estimated. The new framework is shown to avoid the need for second-moment flux definition when solved on finite-volume cell edges but still invoke certain second-moment fluxes when the DVD rates are partitioned to participating cell nodes. These implied discrete fluxes are shown to differ from those proposed in earlier literature (but share the same dissipative part) and thus reveal the non-uniqueness of their nature. They are shown to be ambiguous for high-order advection schemes introducing uncertainty to the locality of any estimates produced by a DVD approach. Additional damping of flux divergence through temporal averaging or some coarse-graining is thus shown to be necessary. Through the application of this technique, SM is found to be correlated with the distribution of eddy kinetic energy. The contribution from vertical advection to SM is found to be relatively small and correlated with the distribution of buoyancy fluxes. The explored high-order schemes are found to demonstrate levels of spurious mixing which may locally exceed background physical mixing.

physics.ao-ph↗