4.5A Which of internal dynamics or radiation effect dominates diurnal variability of mature Hurricane Edouard (2014)?

Monday, 3 August 2015: 5:15 PM
Republic Ballroom AB (Sheraton Boston )
Xiaodong Tang, Nanjing University, Nanjing, China; and F. Zhang, E. B. Munsell, C. Melhauser, and Y. Weng

Handout (3.9 MB)

This work explores a quasi-diurnal variation of Hurricane Edouard (2014) at its mature stage through convection-permitting simulations using the WRF model motivated by apparent diurnal variations of cloud canopy from satellite observations of the event as well as a recent composite study of Dunion et al. (2014). From the WRF simulations, it is found that the peak-to-peak intensity amplitude variations near the diurnal frequency are as much 5 hPa for minimum sea level pressure and 5 m/s for maximum 10-m surface wind speed at the mature stage, with peak (nadir) intensity occurring around midnight (noon). In the outer core region, the peak (nadir) value of outgoing longwave radiation (OLR) occurs with inner-core peak (nadir) intensity simultaneously, which is related inversely to column-total cloud fraction.

Preliminary analysis suggests that the shortwave solar radiation may be responsible for heating the cloud top of inner edge of eyewall, hence reduces convective instability, which consequently suppresses the convective activities and weakens intensity during day time. During nighttime the above process appears to undergo a reversal. Outward propagation of convectively driven gravity waves may be responsible for the cloud canopy variation in the outer core region.

However, it remains to be further explored by ongoing analysis and sensitivity experiments to determine whether this quasi-diurnal variation of Edouard's intensity and cloud canopy can be attributable to the diurnal variation in the solar radiative forcing. It remains possible that the variation may be fully or partially driven by internal dynamics of the storm without radiation, since the observed hurricane is situated around 30N during its mature which will have an inertial oscillation period near diurnal frequency that is independent of diurnal radiative forcing, and given a recent study of Li and Wang (2012) who simulated quasi-diurnal variation of an idealized tropical cyclone without radiation process.

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