Advection scheme TPCORE

NOTE: The page is in construction.

Overview

Dylan Jones and Hongyu Liu both independently found that the existing TPCORE transport code used to perform the advection for GEOS-4 and GEOS-5 meteorology (tpcore_fvdas_mod.f90, by S-J Lin and Kevin Yeh) causes an overshooting in the polar stratopsheric regions. Claire Carouge has supplied a fix for this issue.

Hongyu Liu wrote:

[Here are] the radon plots for all GEOS series as well as the info on GEOS-Chem version and met field version. This is much less of a problem (or not a problem at all) in GEOS-Chem/GEOS-STRAT and GEOS-Chem/GEOS-3. Actually GEOS-Chem/GEOS-STRAT is very close to GMI/GEOS-STRAT (not shown). Compare plots below. All these simulations use same options for tpcore (IORD=3, JORD=3, KORD=7).

• GEOS-Chem v5-05 (GEOS-STRAT)
• GEOS-Chem v7-04 (GEOS-3)
• GEOS-Chem v7-01-02 (GEOS-4)
• GEOS-Chem v8-01-01 (GEOS-5)

It seems that GMI does not have this problem. You might want to compare the plots on Pages 7 & 10 of this PDF file.

Dylan Jones wrote:

Attached are the PowerPoint slides. We added slide 9 which compares the mixed layer depth for GEOS-Chem (with GEOS-5) and GMI (with GEOS-4); we see the same problem in GEOS-Chem with GEOS-5, but we do not see it in GMI.

All the GEOS-4 GEOS-Chem runs were with version v7-02-04. The GEOS-5 GEOS-Chem runs were with v8-01-01.

Claire Carouge replied:

I think I finally got tpcore to work. You have some plots attached for Radon. So far, I ran 5 months of simulation and each month looks much better: no polar spike and much much lower stratospheric tracer. The concentration of Radon is never null in the stratosphere but I don't think it is in GMI neither, I think the range on the plot was cut off. So I did the plot with the same cut off. Let me know if you see something strange I haven't seen.

I don't know for sure what was the problem but I think it was a problem with the definition of the polar cap. In GEOS-Chem, we only averaged values for cells at the poles on 1 band of latitude. In GMI, they use what they call an enlarged polar cap and thus they average values at the poles on 2 bands of latitude.

The pressure fixer was taken from GMI and thus was written for an enlarged polar cap. The parts of the code that were explicitly labelled for the enlarged polar cap had been removed but not other parts that were not explicitly labelled. So we ended up with a hybrid pressure fixer used with a tpcore with a not enlarged olar cap. I'm guessing this was creating the polar spikes.

But, the tpcore in GEOS-Chem and GMI are not easy to compare. I'm not sure there was not a difference in the transport itself and I can't be totally sure the pressure fixer was well introduced in tpcore. I have some doubts about this.

So as GMI was an example of a working (and clean!) algorithm with the enlarged polar cap, I decided to introduce the enlarged polar cap in GEOS-Chem. For this:

1. I slightly modified the pressure-fixer to return to the exact version from GMI
2. I changed tpcore to the one from GMI as I was sure the pressure fixer was well introduced in (and the algorithm is cleaner).

Dylan Jones wrote:

Claire,

Attached are some comparisons of the CO/O3 correlations in the UTLS with the new tpcore.

• CO_O3_lat36_76_lon0_25_20060301_gmi_geos4.png
• CO_O3_lat36_76_lon0_25_alt4_19_200512_gmi_geos.png
• CO_O3_lat36_76_lon0_25_20051201_gmi_geos4_tpcore.png
• CO_O3_lat36_76_lon0_25_20060301_gmi_geos4_tpcore.png

The files called *.gmi_geos.png are with the old version of tpcore and those called *.gmi_geos4_tpcore are with the corrected tpcore. As you can see, there is much less scatter in the correlations, which suggest less anomalous mixing with the new code. The scatter is more similar to what we see in GMI. There is still an offset in the stratosphere (for high ozone in the plots), but I think this may be due to linoz rather than to the transport scheme. This is a huge improvement for GEOS-Chem. Thanks very much for fixing it.

Hongyu Liu replied:

Thanks Claire! Well done. It's clear that the polar overshooting problem is now fixed.