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Leah Johnson

Senior Oceanographer



Department Affiliation

Ocean Physics


2000-present and while at APL-UW

Northern Ocean Rapid Surface Evolution (NORSE): Science and Experiment Plan

Ballard, M., and 35 others including L. Rainville, L. Johnson, C. Lee, J. Shapiro, J. Thomson, and K. Zeiden, "Northern Ocean Rapid Surface Evolution (NORSE): Science and Experiment Plan," Technical Report, APL-UW TR 2102. Applied Physics Laboratory, University of Washington, January 2022, 40 pp.

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13 Jan 2022

The NORSE DRI focuses on characterizing the key physical parameters and processes that govern the predictability of upper-ocean rapid evolution events occurring in the ice-free high latitudes. The goal is to identify which observable parameters are most influential in improving model predictability through inclusion by assimilation, and to field an autonomous observing network that optimizes sampling of high-priority fields. The overall goal is to demonstrate improvements in the predictability of the upper ocean physical fields associated with acoustic propagation over the course of the study. This Science Plan describes the specific objectives and implementation plan.

Global estimate of lateral springtime restratification

Johnson, L., C.M. Lee, and E.A. D'Asaro, "Global estimate of lateral springtime restratification," J. Phys. Oceanogr., 46, 1555–1573, doi:10.1175/JPO-D-15-0163.1, 2016.

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1 May 2016

Submesoscale frontal dynamics are thought to be of leading-order importance for stratifying the upper ocean by slumping horizontal density gradients to produce vertical stratification. Presented here is an investigation of submesoscale instabilities in the mixed layer—mixed layer eddies (MLEs)—as a potential mechanism of frontal slumping that stratifies the upper ocean during the transition from winter to spring, when wintertime forcings weaken but prior to the onset of net solar warming. Observations from the global Argo float program are compared to predictions from a one-dimensional mixed layer model to assess where in the world’s oceans lateral processes influence mixed layer evolution. The model underestimates spring stratification for ~75% ± 25% of the world’s oceans. Relationships between vertical and horizontal temperature and salinity gradients are used to suggest that in 30% ± 20% of the oceans this excess stratification can be attributed to the slumping of horizontal density fronts. Finally, 60% ± 10% of the frontal enhanced stratification is consistent with MLE theory, suggesting that MLEs may be responsible for enhanced stratification in 25% ± 15% of the world’s oceans. Enhanced stratification from frontal tilting occurs in regions of strong horizontal density gradients (e.g., midlatitude subtropical gyres), with a small fraction occurring in regions of deep mixed layers (e.g., high latitudes). Stratification driven by MLEs appears to constrain the coexistence of sharp lateral gradients and deep wintertime mixed layers, limiting mixed layer depths in regions of large lateral density gradients, with an estimated wintertime restratification flux of order 100 W m−2.

Acoustics Air-Sea Interaction & Remote Sensing Center for Environmental & Information Systems Center for Industrial & Medical Ultrasound Electronic & Photonic Systems Ocean Engineering Ocean Physics Polar Science Center