FAMOUS

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Ozone

update: Aug’11
use of Rayleigh friction (rayleigh_fric.mod) in the top layer of the model improves the vertical structure and allows the use of higher, more realistic ozone concentrations. We’ve kept this basic scheme however, so that we’re not tied to modern ozone distributions in eg. paleoclimate runs.


Use of climatological ozone fields on the low vertical resolution FAMOUS grid was found to result in odd heating at the tropopause in some cases - a result of ending up specifiying stratospheric O3 amounts in a region the model considered below the tropopause and a resultant water vapour feedback. Original ADTAN FAMOUS thus threw out the climatological data and set O3 to one of three global constants depending on whether the tropopause diagnostic thought it was below (2E-8 kg/kg O3), at (2E-7) or above (1.5E-6) the tropopause.

After much experimentation, we’ve ended up with only a minor tweak on this original 3level ozone mod:

1) The tropopause-finding diagnostic TROPIN is relaxed so as to find the tropopause lower (at a lapse rate of 0.3K/km rather than the WMO standard 0.2K/km)

2) The “above tropopause” value of O3 is now slightly lower (1.0E-6 kg/kg)

3) Slightly higher O3 concentrations are placed in the top model layer everywhere (1.5E-6 kg/kg)

This results in a much improved “stratospheric” temperature profile at low latitudes, and provides for at least some kind of temperature inversion at high latitudes, although significant cold bias still remains near the poles.

Everything else tried, along the lines of realistic climatologies or more layers, looked no better aloft than this mod, and frequently had detrimental impacts on the surface temperature. Ozone concentrations are thus still lower than those observed, but this seems to be required to get a sensible longwave response in FAMOUS.

mods: ozone_mod-3levcustom, tropin11.mod. Replace standard modsets ozone_mod and tropin11

Vertical Temperature
(y-axis is pressure)

Attach:VTEMP_Summer08.png Δ

Ozone profiles
(y-axis is pressure)

Attach:O3_Summer08.png Δ

Black:HadCM3, Red:xbyvs FAMOUS (like adtan), Green:xbyva FAMOUS (with new ozone)
(bottom left, green line covers red exactly)
Page last modified on August 16, 2011, at 10:41 AM by robin