[Eoas-seminar] Meteorology PhD Defense for Jonathan Christophersen, Thursday, March 26, 2020, 3:30 PM, Zoom meeting ID: https://fsu.zoom.us/j/6234926316

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Thu Mar 26 09:37:41 EDT 2020

Zoom Meeting ID: https://fsu.zoom.us/j/6234926316<https://urldefense.com/v3/__https:/fsu.zoom.us/j/6234926316__;!!PhOWcWs!ntfOrep-8rtYp2jv7sPFDzC-_1sXWsteFFrhpVaw2nRZkEh6V2m7ujr6f-jm1q0$>

Meteorology Seminar

Jonathan Christophersen

PhD Meteorology Candidate

Title:  Observational analysis of atmospheric and oceanic diurnal cycles in the tropical Atlantic

Major Professor:  Dr. Philip Sura

Date: Thursday March 26, 2020                                   Time: 3:30 PM

Location: Zoom Meeting ID: https://fsu.zoom.us/j/6234926316<https://urldefense.com/v3/__https:/fsu.zoom.us/j/6234926316__;!!PhOWcWs!ntfOrep-8rtYp2jv7sPFDzC-_1sXWsteFFrhpVaw2nRZkEh6V2m7ujr6f-jm1q0$>

Interactions between the lower atmosphere and upper ocean on diurnal time scales are assessed in the tropical Atlantic Ocean by combining over 20 years of observations from the Prediction and Research Moored Array in the Tropical Atlantic (PIRATA) with reanalysis, satellite, and model data. In the first section of this study, analysis of surface winds and pressure from PIRATA moorings along 23oW reveals semi-diurnal patterns in the 10-meter zonal wind anomalies and a diurnal pattern in the 10-meter meridional wind anomalies. Past research on the diurnal and semi-diurnal wind patterns observed in the tropical Pacific concluded that the zonal semi-diurnal wind patterns are consistent with migrating atmospheric thermal tidal (ATT) forcing. However, causes of the diurnal cycle in the meridional winds remains elusive. This work extends the past analysis in the tropical Pacific to show how the nonmigrating ATT drives the diurnal cycle of the meridional winds and how that leads to an offshore early morning precipitation maximum during the boreal summer in the tropical Atlantic basin.

Secondly, data from the Tropical Atlantic Current Observation Study (TACOS) at 4oN, 23oW is analyzed to better understand air-sea coupling in the equatorial Atlantic Ocean on short time scales. This particular PIRATA mooring offers high-temporal resolution (10 minute - 1 hour) wind, current, temperature, and salinity data from 2017 to the present. Equipped with 11 current sensors, this site uniquely resolves the diurnal cycle of vertical shear. Throughout the first deployment of the TACOS mooring (March 2017 - March 2018), the presence of a shear-variance layer was observed. Spectral analysis confirms that significant oscillations in the seasonal thermocline, due to the passage of internal tides, modulate the velocity field, altering the shear. During those times that experienced high diurnal SST amplitudes, the deepening nocturnal mixed layer interacts with the shear-variance reservoir, thereby enhancing marginal instability.

Upper-ocean processes are then compared between the PIRATA/TACOS observations and the Nucleus for European Modelling of the Ocean (NEMO) model in the last part of this study. Similarities and discrepancies in mixing processes, static stability, upper-ocean currents as a response to wind forcing, and other air-sea components are discussed. Discrepancies between the dynamic and thermohaline fields persist throughout the record of the analysis time period, thereby contributing to differences in the stratification and shear, resulting in the model being "over mixed".

Shel McGuire
Florida State University
Academic Program Specialist
Department of Earth, Ocean, & Atmospheric Science
1011 Academic Way, 2019 EOA Building
Tallahassee, FL 32306

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