A Moisture-Vorticity Theory for the Boreal Summer Quasi-Biweekly Oscillation

[2608.27665] A Moisture-Vorticity Theory for the Boreal Summer Quasi-Biweekly Oscillation Skip to main content Search Submit Donate Log in Physics > Atmospheric and Oceanic Physics arXiv:2608.27665 (physics) [Submitted on 27 Aug 2026] Title: A Moisture-Vorticity Theory for the Boreal Summer Quasi-Biweekly Oscillation Authors: Shubhrangshu Biswas , Jai Sukhatme , Bishakhdatta Gayen View PDF HTML (experimental) Abstract: We develop a moisture vorticity theory for the boreal summer quasi-biweekly oscillation (QBWO) in the tropics and analyze it with the aid of GPT-5.5. The model is formulated on a weak-temperature-gradient slow manifold, in which moisture anomalies diagnose the divergent circulation while the rotational circulation evolves through Rossby wave dynamics and vortex stretching. The key coupling is controlled by eddy advection of the background moisture gradient, with the projection $(\mathbf{k}\cdot\nabla\bar q)$ modifying propagation and the cross-gradient factor $(\mathbf{k}\times\nabla\bar q)_z$ controlling moisture extraction and growth. In the weak-coupling regime, which is relevant for the real-world situation, the QBWO is a Doppler-shifted Rossby mode whose growth or decay is determined by phase-coherent moisture extraction and subsequent vortex stretching; moisture damping weakens this feedback but does not introduce a sharp threshold in the minimal linear model. In terms of subtropical geographical locations, this renders the QBWO unstable over the Bay of Bengal with an intraseasonal growth rate and co-located vorticity and moisture anomalies, and it decays over relatively drier regions such as Central and West Africa with a quadrature relation between vorticity and moisture anomalies. The equations also admit a strong-coupling regime where the system approaches a moist-vortex limit. The theory interprets the QBWO as a Rossby-moisture-vorticity instability whose regional behavior depends on background moisture-gradient geometry, coupling strength, damping, and mean-flow advection. Comments: 24 pages, 6 figures, submitted to the Quarterly Journal of the Royal Meteorological Society Subjects: Atmospheric and Oceanic Physics (physics.ao-ph) ; Fluid Dynamics (physics.flu-dyn) Cite as: arXiv:2608.27665 [physics.ao-ph] (or arXiv:2608.27665v1 [physics.ao-ph] for this version) https://doi.org/10.48550/arXiv.2608.27665 Focus to learn more arXiv-issued DOI via DataCite Submission history From: Shubhrangshu Biswas [ view email ] [v1] Thu, 27 Aug 2026 19:53:48 UTC (3,536 KB) Full-text links: Access Paper: View PDF HTML (experimental) TeX Source view license Current browse context: physics.ao-ph < prev | next > new | recent | 2026-08 Change to browse by: physics physics.flu-dyn References & Citations SciX Google Scholar Semantic Scholar export BibTeX citation Bookmark Bibliographic Tools Bibliographic and Citation Tools Bibliographic Explorer Toggle Bibliographic Explorer ( What is the Explorer? ) Connected Papers Toggle Connected Papers ( What is Connected Papers? ) Litmaps Toggle Litmaps ( What is Litmaps? ) scite.ai Toggle scite Smart Citations ( What are Smart Citations? ) Code, Data, Media Code, Data and Media Associated with this Article alphaXiv Toggle alphaXiv ( What is alphaXiv? ) Links to Code Toggle CatalyzeX Code Finder for Papers ( What is CatalyzeX? ) DagsHub Toggle DagsHub ( What is DagsHub? ) GotitPub Toggle Gotit.pub ( What is GotitPub? ) Huggingface Toggle Hugging Face ( What is Huggingface? ) ScienceCast Toggle ScienceCast ( What is ScienceCast? ) Demos Demos Replicate Toggle Replicate ( What is Replicate? ) Spaces Toggle Hugging Face Spaces ( What is Spaces? ) Spaces Toggle TXYZ.AI ( What is TXYZ.AI? ) Related Papers Recommenders and Search Tools Link to Influence Flower Influence Flower ( What are Influence Flowers? ) Core recommender toggle CORE Recommender ( What is CORE? ) Author Venue Institution Topic About arXivLabs arXivLabs: experimental projects with community collaborators arXivLabs is a framework that allows collaborators to develop and share new arXiv features directly on our website. Both individuals and organizations that work with arXivLabs have embraced and accepted our values of openness, community, excellence, and user data privacy. arXiv is committed to these values and only works with partners that adhere to them. Have an idea for a project that will add value for arXiv's community? Learn more about arXivLabs . Which authors of this paper are endorsers? | Disable MathJax ( What is MathJax? ) We gratefully acknowledge support from our major funders , member institutions , and all contributors. About · Help · Contact · Subscribe · Copyright · Privacy · Accessibility · Operational Status (opens in new tab) Major funding support from (opens in new tab) (opens in new tab) (opens in new tab)

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