Evaporation processes in marine boundary layer downdrafts inferred from stable water vapor isotopes

• Main Author: Quiñones Meléndez, Estefanía
• Other Authors: de Szoeke, Simon P., College of Earth, Ocean, and Atmospheric Sciences
• Format: Doctoral or Postdoctoral Thesis
• Language: English; unknown
• Published: Oregon State University
• Subjects: North Atlantic
• Online Access: https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/9593v370m

The RV Ronald H. Brown traveled a section of tropical Atlantic waters northeast of Barbados during January-February 2020 in an international collaboration effort known as Elucidating the Role of Clouds Circulation Coupling in Climate Campaign (EUREC4A). ATOMIC (Atlantic Trade-wind Ocean–Atmosphere Mesoscale Interaction Campaign) was the US contribution to EUREC4A focused on determining the vertical water and energy exchanges important to marine trade cumulus (Cu) clouds. The campaign’s sounding network documented the vertical and temporal structure of the trade Cu atmosphere in the North Atlantic trade wind region. The present study describes the vertical structure of stability and humidity in the marine boundary layer, and how it responds to events that affect the trade Cu cloud layer, such as dry intrusions descending from the free troposphere. Surface observations constrain the surface flux of temperature and humidity into the sub-cloud boundary layer (SCL), which serves as a reservoir of moisture for trade Cu cloud development. Observations of stable water isotopes are a novel component of EUREC4A/ATOMIC. The water vapor dataset included near-surface observations along with vertical profiles from the WP-3D Orion (P-3) aircraft. During 13 days of continuous isotopic measurements, 14 cold pools were identified from the decrease of air temperature. In a majority (64 %) of the cold pools, deuterium concentration in the water vapor (δD) increased (from –72 to –66 ‰) as the temperature decreased. Events with higher maximum δD correspond to events with larger temperature differences, and often to precipitation observed at the ship. Air and water vapor sources in the tropical trade wind SCL are analyzed using temperature, specific humidity, and stable water isotopologues (HDO and H218O). Case studies presented here describe cold pools and the isotopes measured in rainwater samples. Isotopic composition, potential temperature and specific humidity suggest that vapor at the downdraft front is isotopically enriched ...