Upper Oceanic Energy Response to Tropical Cyclone Passage

Abstract

The upper oceanic temporal response to tropical cyclone (TC) passage is investigated using a 6-yr daily record of data-driven analyses of two measures of upper ocean energy content based on the U.S. Navy's Coupled Ocean Data Assimilation System and TC best-track records. Composite analyses of these data at points along the TC track are used to investigate the type, magnitude, and persistence of upper ocean response to TC passage, and to infer relationships between routinely available TC information and the upper ocean response. Upper oceanic energy decreases in these metrics are shown to persist for at least 30 days-long enough to possibly affect future TCs. Results also indicate that TC kinetic energy (KE) should be considered when assessing TC impacts on the upper ocean, and that existing TC best-track structure information, which is used here to estimate KE, is sufficient for such endeavors. Analyses also lead to recommendations concerning metrics of upper ocean energy. Finally, parameterizations for the lagged, along-track, upper ocean response to TC passage are developed. These show that the sea surface temperature (SST) is best related to the KE and the latitude whereas the upper ocean energy is a function of KE, initial upper ocean energy conditions, and translation speed. These parameterizations imply that the 10-day lagged SST cooling is approximately 0.78C for a ''typical'' TC at 308 latitude, whereas the same storm results in 10-day (30-day) lagged decreases of upper oceanic energy by about 12 (7) kJ cm 22 and a 0.58C (0.38C) cooling of the top 100 m of ocean.

Dynamical system properties of an axisymmetric convective tropical cyclone model

“…Note, the SST represents a lower boundary condition in HURMOD. Hence the ocean is considered as an unlimited energy reservoir, whereas the airÁsea interaction associated with real TCs results in a cooling of surface waters beneath the TC due to enhanced vertical turbulent entropy fluxes into the atmosphere, vertical turbulent mixing within the ocean mixed layer and upwelling (Knaff et al, 2013;Mei and Pasquero, 2013). In case I, we also run simulations with different values for the tropopause temperature to test the sensitivity to vertical temperature stratification and outflow temperature.…”

The Evolution and Role of the Saharan Air Layer during Hurricane Helene (2006)

“…Between 16 and 19 September, the storm motion decreased from 5.6 to 3.2 m s 21 , suggesting the potential for increased impact of storm-induced cooling of the underlying ocean. Observationally, Brand (1971), Price (1981), Lin et al (2009), Dare and McBride (2011), and Knaff et al (2013) have shown that slower storm motions tend to produce greater reductions in SST. Simulations by Khain and Ginis (1991), Bender et al (1993), and Bender and Ginis (2000) have yielded similar results and have shown that such cooling can have a significant impact in reducing storm intensity.…”

Improving Tropical Cyclone Intensity Forecasting With Theoretically-Based Statistical Models, Year 3

“…All six OHC parameters are being used for investigation of potential intensity and they will also be considered as potential input for LGEM. Knaff et al (2012) investigated a number of questions about ocean responses to TCs using the NCODA based OHC26C and T100M in conjunction with the historical TC records. The investigation focused on composite analyses that show the type, magnitude, and persistence of upper ocean response to TC passage as a function of initial ocean conditions, latitude, translation speed, intensity, and a simplified (from TC wind radii) Kinetic Energy (KE) and then discussed possible relationships between these factors and the upper ocean response.…”