FAMOUS

Interestingly, tuning the gravity wave drag param doesn’t do very much. Ramping it up pretty high slightly improves the overestimation of the northern hemisphere midlatitude jet, maybe. Ozone though: my current best results, resulting in a tropopause without degrading the surface climate involve:

These look almost identical, and not too bad in the tropics (slight warm bias below the tropopause, slightly cold above c.f HadCM3). Significant cold biases remain at higher latitudes, above ~300mb, but both do have a jolly good go at a temperature inversion, which is more than can be said for the old 3level results.

I’m going to go forward with fine-tuning these two versions of O3, and trying to find some justification for using what amount to pretty low column O3 amounts better than “otherwise we screw the longwave budget up worse than it already is”. Fine tuning involves combining it with the other cold-bias fixes - see that section for more details.

have started looking at this again. My current thinking, comparing FAMOUS and HadCM3 forced by the “same” O3 climatology is that the problem still lies in FAMOUS ending up with stratospheric O3 levels where there’s tropospheric water vapour. The thickness of the topmost level in FAMOUS means that, in the tropics where the tropopause is highest, there’s still some water vapour in the top layer, so even confining ozone to the topmost layer still results in the anomalous warming. I’m not exactly 100% convinced, but it’s my best idea right now - and it would explain why climatological O3 has never been used in FAMOUS (a tropopause-following mod should only really be necessary for global warming experiments where the tropopause is likely to move) and why none of my various O3 mods make very much difference - they all have to have significant O3 in the top layer at the end of the day. Am experimenting with an extra layer, or raising the top layer of the model, so I can keep stratopsheric O3 well out of troposphere and match the shortwave heating profiles in HadCM3 and FAMOUS better.

Nope, having removed some extraneous bugs, that doesn’t actually help. I can do various things in the stratosphere, but the troposphere response is remarkably similar in all cases.

What does help everywhere, is just reducing climatological values. Using o3=(climatology/5.) gives a rather good-looking temperature profile, although o3 plots obviously now look too small, especially in the stratosphere. Interestingly, this puts o3 levels back to around the 3level o3 numbers. I think the problem with the 3level stuff may be mainly to do with the tropopause diagnostic not behaving appropriately for it, not the o3 concs. it specifies, which now look more appropriate for creating the right heating rates in FAMOUS.

I’ve also just been reminded of the influence of gravity wave drag on vertical temperature profiles - Manoj has pointed out that the tunable params in there are set for HadCM3 and may be too weak for the lower resolution FAMOUS. Looking at it, the “low level” boundary is almost certainly too high in std. FAMOUS. Maybe if I can tune this better, the vertical T gradient will improve, making the tropopause diagnostic work better and setting the O3 concentrations (in both 3-level and climatological regimes) better, and all will be well! Next week, I’ll work on the parameterisation of flying pigs, which is sadly lacking in FAMOUS.

Using a spatially fixed ozone climatology had previously caused problems in low resolution versions of the UM, where warming raised the physical tropopause above the fixed climatological ozone tropopause, leading to unphysical ozone warming in the troposphere (enhanced by the associated water-vapour feedbacks). The original ozone_mod, used in the Jones et al. etc. (i.e. adtan) runs, located the physical tropopause using a simple diagnostic (tropin.f) and then specified one of three values for each level in the column (below-, at-, and above- the tropopause values). This is not only a very crude approximation to the spatial variation in ozone concentration, we found that the tropopause diagnostic was not performing well at the vertical resolution used in FAMOUS (often failing to find a tropopause at all) and the ozone values specified were too low - the combined effect was that the model hardly had any ozone, leading to the large temperature errors at altitude seen in the Jones et al. runs

Climatological ozone concentrations are once again read in, and an ozone tropopause diagnosed. The physical tropopause diagnostic can be relaxed to produce better results, and the ozone climatology is then shifted up/down in each column so that the two tropopauses match. Ozone concentrations are modified so that the new above-tropopause and below-tropopause integrated concentrations match those in the original climatology. This hugely improves temperatures aloft, but also causes anomalous warming throughout the whole atmosphere and exacerbates the pre-existing warm bias in the low latitudes at the surface. Preliminary re-tuning of the cloud variables tuned in Jones et al. doesn’t seem to help, and the biases are clearly seen in the clear-sky fluxes anyway. Until this is fixed, the new ozone mods will not included in the standard FAMOUS. Currently I’m hoping an improvement in high-latitude coldness may result in the transport some of the excess tropical warmth away…

notes

base mods tropin11 and ozone_mod need to be disabled. The new diagnostics are at 2,314 (level index) and 2,315 (level found=1)