Validation of the MIPAS CO2 volume mixing ratio in the mesosphere and lower thermosphere and comparison with WACCM simulations

At 90-105km, MIPAS is generally smaller than SABER by 10-30% in the polar summers. At 100-120km, MIPAS and SABER CO2 agree within approximate to 10% during equinox but, for solstice, MIPAS is larger by 10-25%, except near the polar summer. Whole Atmosphere Community Climate Model (WACCM) CO2 shows the major MIPAS features.

At 75-100km, the agreement is very good (approximate to 5%), with maximum differences of approximate to 10%. At 95-115km MIPAS CO2 is larger than WACCM by 20-30% in the winter hemisphere but smaller (20-40%) in the summer. Above 95-100km WACCM generally overestimates MIPAS CO2 by about 20-80% except in the polar summer where underestimates it by 20-40%.

MIPAS CO2 favors a large eddy diffusion below 100km and suggests that the meridional circulation of the lower thermosphere is stronger than in WACCM. The three instruments and WACCM show a clear increase of CO2 with time, more markedly at 90-100km.