Daniel Chavas

Daniel Chavas
Massachusetts Institute of Technology | MIT · Department of Earth Atmospheric and Planetary Sciences

About

22
Publications
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Publications

Publications (22)
Article
Full-text available
Understanding the mechanisms behind the upper bound on the global tropical cyclone (TC) number is important yet still elusive. Using TC simulations on an aqua‐planet tropical channel, this study shows that the tropical atmosphere possesses a maximum capacity in producing TCs globally, regardless of how ideal the environmental conditions are. In par...
Preprint
This study examines the large-scale factors that govern global tropical cyclone (TC) formation and an upper bound on the annual number of TCs. Using idealized simulations for an aqua-planet tropical channel, it is shown that the tropical atmosphere has a maximum capacity in generating TCs, even under ideal environmental conditions. Regardless of ho...
Data
This data consists of all TC detections from global idealized TC simulations, using the WRF model. The simulations are set up for an aquaplanet tropical channel from 45S-45N. All tracking outputs include the latitude, longitude, maximum surface wind, warm-core anomaly, maximum vorticity, minimum central pressure, and lifetime.
Article
Existing hypotheses for the dynamical dependence of tropical cyclone genesis and size on latitude depend principally on the Coriolis parameter f. These hypotheses are tested via dynamical aquaplanet experiments with uniform thermal forcing in which planetary rotation rate and planetary radius are varied relative to Earth values; the control simulat...
Conference Paper
Full-text available
Despite a strong fluctuation in the number of tropical cyclones (TCs) over all ocean basins, there are on average about 80-100 TCs globally every year. While this number has been long documented, the physical mechanisms underlying such a specific range of the global TC count are however still elusive. Using idealized simulations for a tropical chan...
Article
Full-text available
Part I of this work developed a simple physical model for the complete radial structure of the low-level azimuthal wind field in a tropical cyclone that compared well with observations. However, wind field variability in the model is tied principally to its external parameters given by the maximum wind speed and the radius of maximum wind, the latt...
Conference Paper
Full-text available
Striking advances have occurred in the realm of tropical cyclone (TC) wind observations over the past quarter century. These advances include the advent of highly accurate GPS-based navigation for aircraft-based observing platforms, airborne Doppler radar, GPS dropsondes, improved wind retrievals from satellite scatterometers, and the Stepped Frequ...
Article
Full-text available
This work revisits the statistics of observed tropical cyclone outer size in the context of recent advances in our theoretical understanding of the storm wind field. The authors create a new dataset of the radius of 12 m s-1 winds based on a recently updated version of the QuikSCAT ocean wind vector database and apply an improved analytical outer w...
Article
A major hurricane [96+ knots (kt; 1 kt = 0.51 m s–1) of maximum sustained wind] has not made landfall in the United States since Wilma (2005). Recent elegant stochastic–statistical modeling estimates the return period of a 9-yr streak for this metric as 177 yr, suggesting extraordinary rarity, especially in the context of the length of the record (...
Article
Full-text available
A standard atmospheric general circulation model is run in a uniformly rotating global radiative-convective equilibrium configuration to explore the equilibrium state, including the statistics of its constituent tropical cyclones, and its sensitivity to horizontal resolution. The Community Atmosphere Model 5 (CAM5) is run at the conventional resolu...
Article
Global projections of intense tropical cyclone activity are derived from the Geophysical Fluid Dynamics Laboratory (GFDL) High Resolution Atmospheric Model (HiRAM; 50-km grid) and the GFDL hurricane model using a two-stage downscaling procedure. First, tropical cyclone genesis is simulated globally using HiRAM. Each storm is then downscaled into th...
Article
Full-text available
Part I of this work develops a simple model for the complete radial structure of the low-level tropical cyclone wind field. The model is constructed by mathematically merging existing theoretical solutions for the radial wind structure at the top of the boundary layer in the inner ascending and outer descending regions. The model is then compared w...
Technical Report
Full-text available
This document describes the QuikSCAT Tropical Cyclone Radial Structure Dataset (QSCAT-R), including its parameter and file structure as well as the underlying methodology for its construction. QSCAT-R contains data for the radial structure of near-surface wind and rain rate for tropical cyclones globally during the period 1999-2009. The dataset is...
Conference Paper
Full-text available
This report summarizes the current state of research on tropical cyclone (TC) structure, structure change and the processes associated with those changes. It is not intended to be an exhaustive summary of all knowledge on the subject, but instead a focus on the developments in this area since the last IWTC (IWTC-VII) in La Reunion in 2010. This rep...
Article
Tropical cyclone size remains an unsolved problem in tropical meteorology, yet size plays a significant role in modulating damage. This work employs the Bryan cloud model (CM1) to systematically explore the sensitivity of the structure of an axisymmetric tropical cyclone at statistical equilibrium to the set of relevant model, initial, and environm...
Article
Full-text available
The authors examine daily tornado counts in the United States over the period 1994-2012 and find strong evidence for a power-law relationship in the distribution frequency. The scaling exponent is estimated at 1.64 (0.019 s.e.) giving a per tornado-day probability of 0.014% (return period of 71 years) that a tornado day produces 145 tornadoes as wa...
Article
The historical record of U.S. hurricane damage is analyzed using a peaks-over-threshold approach in which the generalized Pareto distribution (GPD) is applied to model excesses above a specified threshold for a given damage metric. In addition to absolute hurricane damages (total damage), this paper defines a damage index as the ratio of base-year...
Article
Full-text available
This study revisits the parametric modeling of the hurricane surface wind field composed of the storm vortex and the environmental background flow. First, we investigate the parametric representation of the surface background wind by analyzing its empirical relationship with storm movement. A marked deceleration and counter-clockwise rotation of th...
Article
QuikSCAT data of near-surface wind vectors for the years 1999–2008 are used to create a climatology of tropical cyclone (TC) size, defined as the radius of vanishing winds. The azimuthally-averaged radius of 12 ms−1 wind (r12) is calculated for a subset of TCs (N = 2154) whose centers of circulation were clearly identifiable via subjective analysis...
Article
Full-text available
[1] The size of a tropical cyclone is known to vary considerably across storms, though little is understood about the environmental and internal factors that modulate it. Making use of newly available extended tropical cyclone records that include information about storm structure, we examine the size distribution of Atlantic tropical cyclones, usi...
Article
Increasing atmospheric greenhouse gas concentrations are expected to induce significant climate change over the next century and beyond, but the impacts on society remain highly uncertain. This work utilizes high-resolution regional climate model output to assess potential climate change impacts on the productivity of five major crops in eastern Ch...

Questions

Question (1)
Question
This would seem to be physically inconsistent, yet I see it often, and I am trying to understand why (e.g. is there a reason that the reanalysis SSTs are not believable?).
Thanks!
Dan

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Projects

Projects (2)
Project
The goal of this project is to provide a dataset of standardized, research-grade flight level data. This project was conceived in 2008 when I wanted to compute some last-minute results from aircraft flight data for a conference presentation. Despite working very hard for three weeks, I did not obtain results in time for my presentation. I found that the plethora of formats and lack of processing into storm-relative coordinates made the existing aircraft data quite challenging for researchers to quickly pick up and use. I decided to work toward making the aircraft data more research-friendly. The current dataset covers nearly all Atlantic, Eastern Pacific, and Central Pacific tropical cyclones with flight level data during the period from 1997 to 2015. The dataset also includes flights in certain Western Pacific TCs in 2008 and 2010. Flight level data is provided in both earth-relative and storm-relative coordinates at the highest temporal resolution available (e.g. 30-second, 10-second, or 1-second). Additionally, flight level data has been parsed by radial leg and interpolated to a standardized radial grid. Data also include surface wind speeds from the Stepped Frequency Microwave Radiometer. Significant effort has been undertaken to quality control the data. The dataset is improved and extended whenever funding allows. Although no data are ever perfect, this dataset should be suitable for a wide variety of research and industry uses, including process studies of TC intensity and structure change, model evaluation and verification studies, and wind risk applications.
Project
The goal of this project was to build a new historical observations-based database of tropical cyclone (TC) track, intensity, size, and structure parameters optimized for wind risk applications.