Explaining Surface Layer Theory Departures in Marine Flux Profiles with Data-Driven Discovery

TL;DR

This study reveals frequent deviations from Monin-Obukhov Similarity Theory in coastal marine environments, identified through data-driven discovery, highlighting the need for improved flux parameterizations in these settings.

Contribution

The paper introduces a data-driven approach using the Discovery Engine to identify mechanisms causing departures from MOST assumptions in coastal marine flux profiles.

Findings

Wind speed decreases with height in 20% of observations near shore

Large vertical heat flux gradients occur contrary to MOST predictions

Three mechanisms identified: boundary layers, wave-driven jets, stable boundary layers

Abstract

Monin--Obukhov Similarity Theory (MOST), which underpins nearly all bulk estimates of surface fluxes in the atmospheric surface layer, assumes monotonic wind profiles and vertically uniform momentum and heat fluxes. Here, we show that conditions frequently arise in coastal marine settings where these assumptions do not hold. Using flux measurements from the Coastal Land-Air-Sea Interaction (CLASI) project's Air-Sea Interaction Spar (ASIS) buoys with wind and flux measurements at typically ~3m and ~5m above the sea surface, we find that wind speed decreases with height in nearly 20% of observations, and that large vertical gradients in sensible heat flux occur near the surface, contrary to what would be predicted by MOST. Both anomalies are strongly modulated by coastal proximity and wind direction, with the highest occurrence rates near shore under offshore winds. These patterns were found using the Discovery Engine, a general-purpose automated system for scientific discovery, which identifies complex relationships in data without prior hypotheses. The Discovery Engine uncovered three distinct mechanisms responsible for breakdowns in MOST assumptions: internal boundary layers formed by offshore continental flow, wave-driven wind jets associated with high wave age, and thermally stable boundary layers over cold sea surfaces where warm, moist air overlies cooler water far from shore. These findings highlight the limitations of current flux algorithms and suggest directions for improved parameterisation in coastal and open-ocean conditions.