[Eoas-seminar] REMINDER: Meteorology MS Defense for Jacob Carstens, Monday, April 1, 2019, 4:00 PM, LOV353

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Mon Mar 25 10:06:55 EDT 2019

Meteorology Seminar

Jacob Carstens

M.S. Meteorology Candidate

Title:  Tropical cyclogenesis from self-aggregated convection in numerical simulations of rotating radiative-convective equilibrium

Major Professor:  Dr. Allison Wing

Date: April 01, 2019                                 Time: 4:00-5:30 PM

Location: Werner A. Baum Seminar Room (353 Love Building)
(Please join us for refreshments served outside room 353 Love @ 3:30 PM)


Organized convection is of critical importance in the tropical atmosphere. Recent advances in numerical modeling have revealed that moist convection can interact with its environment to transition from a quasi-random to organized state. This phenomenon, known as convective self-aggregation, is aided by feedbacks involving clouds, water vapor, and radiation that increase the spatial variance of column-integrated frozen moist static energy. Prior studies have shown self-aggregation to take several different forms, including that of spontaneous tropical cyclogenesis in an environment of rotating radiative-convective equilibrium (RCE). This study expands upon previous work to address the processes leading to tropical cyclogenesis in this rotating RCE framework. More specifically, a 3-D, cloud-permitting numerical model is used to examine the self-aggregation of convection and potential cyclogenesis, and the background planetary vorticity is varied on an f-plane across simulations to represent a range of deep tropical and near-equatorial environments. Convection is initialized randomly in an otherwise homogeneous environment, with no background wind, precursor disturbance, or other synoptic-scale forcing.
All simulations with planetary vorticity corresponding to latitudes from 10° poleward generate intense tropical cyclones, with maximum wind speeds of 80 ms-1 or above. Time to genesis and to hurricane intensity varies widely, even within a 5-member ensemble of 20° simulations, reflecting a potential degree of stochastic variability based in part on the initial random distribution of convection. Shared across this so-called "high-f" group is the emergence of a midlevel vortex in the days leading to genesis, which has dynamic and thermodynamic implications on its environment that facilitates the spinup of a low-level vortex. Tropical cyclogenesis is possible in this model even at very low values of Coriolis parameter, as far equatorward as 1°. In these experiments, convection self-aggregates into a quasi-circular cluster, which then begins to rotate and gradually strengthens into a tropical storm, aided by near-surface inflow and elevated overturning radial circulations within the aggregated cluster. Other experiments at these lower Coriolis parameters instead self-aggregate into an elongated band and fail to undergo cyclogenesis over the 100-day simulation. A large portion of this study is devoted to examining in greater detail the dynamic and thermodynamic evolution of cyclogenesis in these experiments and comparing the physical mechanisms to current theories.

Shel McGuire
Florida State University
Academic Program Specialist
Department of Earth, Ocean, & Atmospheric Science
1017 Academic Way, 410 Love Building (Meteorology)
Tallahassee, FL 32306

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