Friday September 22 CSL Meeting

The Role of Upper Ocean Heat Content and Sea Surface Temperature on Northeast Pacific Hurricane Evolution during Average and Active Years

Presenter: Victoria Ford
Time: Friday 22 September, 2:00-3:00 p.m.
Location: 805 O&M

Abstract: Upon comparison to typical neutral-ENSO conditions in the Northeast Pacific Ocean, the 2014 hurricane season has been identified as highly anomalous in both tropical cyclone frequency and intensity. This research seeks to investigate the influence of sea surface temperatures (SSTs) and upper ocean heat content (UOHC), defined as the excess of heat present above 26°C, upon the upper ocean thermal structure, mesoscale features, and anomalies that led to an active hurricane season in the Northeast Pacific. The 2012 Northeast Pacific hurricane season was selected as a 'normal' season to fully quantify the anomalous 2014 hurricane season. Oceanic variables were extracted nearest-pixel to the hurricane path and were scrutinized through the use of along-track time series analysis, gridded UOHC fields, and a complex scheme of linear regression models. In order to quantify intensity modulation throughout a tropical cyclone, enthalpy flux was calculated along-track for the duration of a landfalling hurricane with atmospheric model data, as well as from in-situ dropsonde observations. Results suggest that variable SSTs and UOHC were critical in tropical cyclone genesis, duration, and maximum intensity. A minimum requirement of 30 kJ cm^-2 of UOHC was found at genesis for all storms. At least 7 of the major hurricanes interacted with a warm oceanic mesoscale feature either at genesis or along-track that induced rapid intensification periods, including one high-end Category-5 hurricane. Cool wake signatures from deep upwelling along-track were detected within gridded UOHC and were also found to be influential in subsequent hurricane trajectories. Along-track enthalpy fluxes peaked at 1234 W m^-2 as the hurricane attained maximum intensity, while dropsonde-derived enthalpy emphasized stronger enthalpy fluxes within the northeast quadrants of the hurricane.

Dropsonde-derived enthalpy fluxes for 6 August 2014 during Hurricane Iselle on approach to the Hawaiian Islands.