Influences of Cloud-Radiative Forcing and Boundary Layer Mixing on Tropical Cyclones

Numerous studies have focused on the radiatively-forced diurnal cycle on tropical cyclones (TCs), as it appears in observations (e.g., Kossin 2002; Dunion et al. 2014) and in models (e.g., Melhauser and Zhang 2014; Navarro and Hakim 2016). Our prior work (e.g., Fovell and Su 2007, Fovell et al. 2009) demonstrated that cloud microphysical assumptions can dramatically influence TC track and structure, and sometimes intensity, and this resulted principally through cloud-radiative forcing (CRF), the interaction of radiation with hydrometeors (Fovell et al. 2010; Fovell et al. 2016). Absorption of longwave radiation, in particular, produces weak but persistent ascent through a large volume, encouraging greater convective activity at larger radii and leading to a broader wind field (Bu et al. 2014). In this fashion, CRF can act as a positive feedback on storm size (Fovell et al. 2016).

More recently, we have been investigating how other model physics, notably the planetary boundary layer (PBL) scheme, influences storm structure, using the Hurricane WRF and WRF-ARW models (Bu et al. 2017). Significant differences in storm size result with different PBL schemes, owing to the combined influence of CRF and PBL mixing. We will demonstrate how and why this occurs, using special simulations in which mixing and CRF components are controlled and manipulated.

References:

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Fovell, R. G., and H. Su, 2007: Impact of cloud microphysics on hurricane track forecasts. Geophys. Res. Lett., 34, L24810.

Fovell, R. G., K. L. Corbosiero, and H.-C. Kuo, 2009: Cloud microphysics impact on hurricane track as revealed in idealized experiments. J. Atmos. Sci., 66, 1764-1778.

Fovell, R. G., K. L. Corbosiero, A. Seifert, and K.-N. Liou, 2010: Impact of cloud-radiative feedback on hurricane track. Geophys. Res. Lett., 37, L07808.

Bu, Y. P., R. G. Fovell, and K. L. Corbosiero, 2014: Influence of cloud-radiative forcing on tropical cyclone structure. Journal of the Atmospheric Sciences, 71, 1644-1662.

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Fovell, R. G., and coauthors, 2016: Influence of cloud microphysics and radiation on tropical cyclone structure and motion. In “Multiscale Convection-Coupled Systems in the Tropics”, Meteor. Monog., 56, 11.1-11.27, doi: 10.1175/AMSMONOGRAPHS-D-15-0006.1.

Navarro, E. L., and G. J. Hakim, 2016: Idealized numerical modeling of the diurnal cycle of tropical cyclones. J. Atmos. Sci., 73, 4189-4201.

Bu, Y. P., R. G. Fovell, and K. L. Corbosiero, 2017: The influences of boundary layer mixing and cloud-radiative forcing on tropical cyclone size. J. Atmos. Sci., in press. doi:10.1175/JAS-D-16-0231.1