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A Top‐Down Pathway to Secondary Eyewall Formation in Simulated Tropical Cyclones
Author(s) -
Tyner Bryce,
Zhu Ping,
Zhang Jun A.,
Gopalakrishnan Sundararaman,
Marks Frank,
Tallapragada Vijay
Publication year - 2018
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
eISSN - 2169-8996
pISSN - 2169-897X
DOI - 10.1002/2017jd027410
Subject(s) - eye , rainband , tropical cyclone , convection , meteorology , environmental science , precipitation , atmospheric sciences , climatology , boundary layer , weather research and forecasting model , geology , mechanics , physics
Idealized and real‐case simulations conducted using the Hurricane Weather Research and Forecasting (HWRF) model demonstrate a “top‐down” pathway to secondary eyewall formation (SEF) for tropical cyclones (TCs). For the real‐case simulations of Hurricane Rita (2005) and Hurricane Edouard (2014), a comparison to observations reveals the timing and overall characteristics of the simulated SEF appear realistic. An important control of the top‐down pathway to SEF is the amount and radial‐height distribution of hydrometeors at outer radii. Examination into the simulated hydrometeor particle fall speed distribution reveals that the HWRF operational microphysics scheme is not producing the lightest hydrometeors, which are likely present in observed TCs and are most conducive to being advected from the primary eyewall to the outer rainband region of the TC. Triggering of SEF begins with the fallout of hydrometeors at the outer radii from the TC primary eyewall, where penetrative downdrafts resulting from evaporative cooling of precipitation promote the development of local convection. As the convection‐induced radial convergence that is initially located in the midtroposphere extends downward into the boundary layer, it results in the eruption of high entropy air out of the boundary layer. This leads to the rapid development of rainband convection and subsequent SEF via a positive feedback among precipitation, convection, and boundary layer processes.