FAT or FiTT: Are Anvil Clouds or the Tropopause Temperature-Invariant?

TitleFAT or FiTT: Are Anvil Clouds or the Tropopause Temperature-Invariant?
Publication TypeJournal Article
Year of Publication2019
AuthorsSeeley, Jacob T., Jeevanjee Nadir, and Romps David M.
JournalGeophysical Research Letters
Volume46
Number3
Pages1842 - 1850
Abstract / Summary

The Fixed Anvil Temperature (FAT) hypothesis proposes that upper‐tropospheric cloud fraction peaks at a special isotherm that is independent of surface temperature. It has been argued that a FAT should result from simple ingredients: Clausius‐Clapeyron, longwave emission from water vapor, and tropospheric energy and mass balance. Here, the first cloud‐resolving simulations of radiative‐convective equilibrium (RCE) designed to contain only these basic ingredients are presented. This setup does not produce a FAT: the anvil temperature varies by about 40% of the surface temperature range. However, the tropopause temperature varies by only 4% of the surface temperature range, which supports the existence of a Fixed Tropopause Temperature (FiTT). In full‐complexity RCE simulations, the spread in anvil temperature is smaller by about a factor of two, but the tropopause temperature remains more invariant than the anvil temperature by an order of magnitude. In other words, our simulations have a FiTT, not a FAT.

URLhttp://doi.wiley.com/10.1029/2018GL080096
DOI10.1029/2018GL080096
Journal: Geophysical Research Letters
Year of Publication: 2019
Volume: 46
Number: 3
Pages: 1842 - 1850

The Fixed Anvil Temperature (FAT) hypothesis proposes that upper‐tropospheric cloud fraction peaks at a special isotherm that is independent of surface temperature. It has been argued that a FAT should result from simple ingredients: Clausius‐Clapeyron, longwave emission from water vapor, and tropospheric energy and mass balance. Here, the first cloud‐resolving simulations of radiative‐convective equilibrium (RCE) designed to contain only these basic ingredients are presented. This setup does not produce a FAT: the anvil temperature varies by about 40% of the surface temperature range. However, the tropopause temperature varies by only 4% of the surface temperature range, which supports the existence of a Fixed Tropopause Temperature (FiTT). In full‐complexity RCE simulations, the spread in anvil temperature is smaller by about a factor of two, but the tropopause temperature remains more invariant than the anvil temperature by an order of magnitude. In other words, our simulations have a FiTT, not a FAT.

DOI: 10.1029/2018GL080096
Citation:
Seeley, JT, N Jeevanjee, and DM Romps.  2019.  "FAT or FiTT: Are Anvil Clouds or the Tropopause Temperature-Invariant?"  Geophysical Research Letters 46(3): 1842 - 1850, pp. 1842 - 1850.  https://doi.org/10.1029/2018GL080096.