Hans, Anna Christina (2022) Diurnal cycle of near-surface shear, stratification and mixing in the equatorial Atlantic. (Master thesis), Christian-Albrechts-Universität zu Kiel, Kiel, Germany, 46 pp.

Preview

Text MasterThesis_AnnaCHans.pdf - Published Version Available under License Creative Commons: Attribution 4.0. Download (1MB) | Preview

Abstract

The diurnal behaviour of near-surface shear, stratification and turbulent kinetic energy dissipation is examined in the equatorial Atlantic. These processes are important to consider as they modify the near-surface heat and momentum budgets. In particular, they are relevant for understanding air-sea fluxes and the vertical distribution of shear, and hence, also for improving turbulence parameterisations. In this study the respective parameters are analysed using observational data obtained from the TRATLEQ1 cruise, a glider mission, Argo floats and CARTHE as well as SVP surface drifters in the equatorial Atlantic. The results reveal a diurnal cycle for shear, stratification and turbulent kinetic energy dissipation in the upper 2 m to 6 m of the ocean which is up to one order of magnitude stronger and sets in several hours earlier than the deep diurnal cycle below about 10 m to 20 m depth. This leads, among others, to diurnal differences in the dissipation of wind energy close to the surface. Considering 1 m instead of 15 m velocities also increases the daily mean wind power input into the ocean by 39%. Furthermore, it is shown that the wind speed has an influence on the buildup of the diurnal warm layer and the diurnal jet. A pronounced diurnal warm layer forms for wind speeds below ~ 6 ms-1. The appearance of the diurnal jet changes for low (0 - 3 ms-1), moderate (4 - 6 ms-1) and high (8 - 12 ms-1) wind speeds. Following the seasonality of trade winds at the equator, the near-surface shear and stratification show seasonal patterns. As the presence of shear-instabilities is governed by the ratio of shear and stratification, a seasonality for turbulent kinetic energy dissipation is expected as well.

Actions (login required)

View Item