2026-09-19T22:58:46Zhttps://dspace.mit.edu/server/oai/requestoai:dspace.mit.edu:1721.1/1217582026-06-17T14:45:12Zcom_1721.1_7582com_1721.1_7581col_1721.1_131022
Timothy Cronin and Kerry Emanuel.
Beucler, Tom(Tom George)
Massachusetts Institute of Technology. Department of Earth, Atmospheric, and Planetary Sciences.
Massachusetts Institute of Technology. Department of Earth, Atmospheric, and Planetary Sciences
w------
2019-07-17T21:01:34Z
2019-07-17T21:01:34Z
2019
2019
https://hdl.handle.net/1721.1/121758
1102054503
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2019
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 227-251).
The spatiotemporal variability of water vapor near the Equator remains poorly understood because convective organization simultaneously spans the cloud scale (~ 10km) and the planetary scale (~ 10, 000km). Spatiotemporal variability of tropical water vapor may result from internal instabilities of the atmosphere, arising from the interaction between water vapor, radiation and convection. The present work leverages the instability of radiative-convective equilibrium, the most fundamental state of the tropical atmosphere, to connect convective organization in cloud-permitting models with the observed variability of water vapor through common physical mechanisms. First, we propose a simple theory that explains when instability of radiative-convective equilibrium may occur: If the total atmospheric cooling decreases with column water vapor, then radiative-convective equilibrium may be unstable to the growth of moist and dry perturbations.
Secondly, we combine a linear response framework with the weak temperature gradient approximation to analyze the interaction between convection, radiation and water vapor at each level of the atmosphere. We find that convection may interact with radiation to trigger the growth of mid-tropospheric water vapor anomalies by transporting water vapor to the upper troposphere, where it can prevent lower-tropospheric water vapor from radiatively cooling to space. Thirdly, we turn to the spatial organization of water vapor anomalies and relate the evolution of the size of moist and dry regions to diabatic fluxes in twenty cloud-permitting simulations on large domains. Longwave radiation from ice clouds aggregates convection at larger scales, shortwave radiation aggregates convection at smaller scales, and surface enthalpy fluxes smooth out water vapor anomalies through their enthalpy disequilibrium component.
Finally, we relate the transient zonal variability of precipitable water to convective-aggregation mechanisms in realistic models and observations of the atmosphere. Radiative fluxes generate transient water vapor structures of planetary scales, while surface enthalpy fluxes and horizontal energy transport act to smooth out these structures, suggesting parallels between observations and idealized simulations of aggregated convection.
by Tom Beucler.
Ph.D.
Ph.D. Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences
251 pages
eng
Massachusetts Institute of Technology
MIT theses are protected by copyright. They may be viewed, downloaded, or printed from this source but further reproduction or distribution in any format is prohibited without written permission.
http://dspace.mit.edu/handle/1721.1/7582
Earth, Atmospheric, and Planetary Sciences.
Interaction between water vapor, radiation and convection in the tropics
Thesis
application/pdf
2019-07-17T21:01:33Z
Publication
Doctoral
EAPS
unknown
unknown
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<Abstract>The spatiotemporal variability of water vapor near the Equator remains poorly understood because convective organization simultaneously spans the cloud scale (~ 10km) and the planetary scale (~ 10, 000km). Spatiotemporal variability of tropical water vapor may result from internal instabilities of the atmosphere, arising from the interaction between water vapor, radiation and convection. The present work leverages the instability of radiative-convective equilibrium, the most fundamental state of the tropical atmosphere, to connect convective organization in cloud-permitting models with the observed variability of water vapor through common physical mechanisms. First, we propose a simple theory that explains when instability of radiative-convective equilibrium may occur: If the total atmospheric cooling decreases with column water vapor, then radiative-convective equilibrium may be unstable to the growth of moist and dry perturbations.</Abstract>
<Abstract>Secondly, we combine a linear response framework with the weak temperature gradient approximation to analyze the interaction between convection, radiation and water vapor at each level of the atmosphere. We find that convection may interact with radiation to trigger the growth of mid-tropospheric water vapor anomalies by transporting water vapor to the upper troposphere, where it can prevent lower-tropospheric water vapor from radiatively cooling to space. Thirdly, we turn to the spatial organization of water vapor anomalies and relate the evolution of the size of moist and dry regions to diabatic fluxes in twenty cloud-permitting simulations on large domains. Longwave radiation from ice clouds aggregates convection at larger scales, shortwave radiation aggregates convection at smaller scales, and surface enthalpy fluxes smooth out water vapor anomalies through their enthalpy disequilibrium component.</Abstract>
<Abstract>Finally, we relate the transient zonal variability of precipitable water to convective-aggregation mechanisms in realistic models and observations of the atmosphere. Radiative fluxes generate transient water vapor structures of planetary scales, while surface enthalpy fluxes and horizontal energy transport act to smooth out these structures, suggesting parallels between observations and idealized simulations of aggregated convection.</Abstract>
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