Observed air-sea interactions in tropical cyclone Isaac over Loop Current mesoscale eddy features

• Published in: Dynamics of atmospheres and oceans 2016-12, Vol.76, p.306-324
• Main Authors: Jaimes, Benjamin, Shay, Lynn K., Brewster, Jodi K.
• Format: Article
• Language: English
• ISSN: 0377-0265; 1872-6879
• DOI: 10.1016/j.dynatmoce.2016.03.001

•Rare direct observations of coupled air-sea interactions during the intensification of a tropical cyclone over Gulf of Mexico’s warm oceanic mesoscale eddy features.•New evidence supporting the hypothesis that enhanced buoyant forcing from the ocean is an important intensification mechanism in tropical cyclones over warm oceanic mesoscale eddy features.•First direct observations of a positive oceanic feedback mechanism on storm intensity via wind-driven horizontal convergence of warm sea surface temperatures over warm oceanic mesoscale eddy features.•New direct measurements of contrasting vertical shear, gradient Richardson number, and vertical mixing in Gulf of Mexico’s mesoscale eddy features during the forced stage in a hurricane.•Direct measurements of the water mass response to a Gulf of Mexico hurricane, including an upper-ocean fresh water anomaly and the formation of a new density class. Air-sea interactions during the intensification of tropical storm Isaac (2012) into a hurricane, over warm oceanic mesoscale eddy features, are investigated using airborne oceanographic and atmospheric profilers. Understanding these complex interactions is critical to correctly evaluating and predicting storm effects on marine and coastal facilities in the Gulf of Mexico, wind-driven mixing and transport of suspended matter throughout the water column, and oceanic feedbacks on storm intensity. Isaac strengthened as it moved over a Loop Current warm-core eddy (WCE) where sea surface warming (positive feedback mechanism) of ∼0.5°C was measured over a 12-h interval. Enhanced bulk enthalpy fluxes were estimated during this intensification stage due to an increase in moisture disequilibrium between the ocean and atmosphere. These results support the hypothesis that enhanced buoyant forcing from the ocean is an important intensification mechanism in tropical cyclones over warm oceanic mesoscale eddy features. Larger values in equivalent potential temperature (θE=365   ∘K) were measured inside the hurricane boundary layer (HBL) over the WCE, where the vertical shear in horizontal currents (δV) remained stable and the ensuing cooling vertical mixing was negligible; smaller values in θE (355   ∘K) were measured over an oceanic frontal cyclone, where vertical mixing and upper-ocean cooling were more intense due to instability development in δV. Thus, correctly representing oceanic mesoscale eddy features in coupled numerical models is important to accurately reproduce ocean