Version 1.3 AIM SOFIE measured methane (CH4): Validation and seasonal climatology

The V1.3 methane (CH4) measured by the Aeronomy of Ice in the Mesosphere (AIM) Solar Occultation for Ice Experiment (SOFIE) instrument is validated in the vertical range of similar to 25-70 km. The random error for SOFIE CH4 is similar to 0.1-1% up to similar to 50 km and degrades to similar to 9% at similar to 70 km. The systematic error remains at similar to 4% throughout the stratosphere and lower mesosphere. Comparisons with CH4 data taken by the SCISAT Atmospheric Chemistry Experiment-Fourier Transform Spectrometer (ACE-FTS) and the Envisat Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) show an agreement within similar to 15% in the altitude range similar to 30-60 km. Below similar to 25 km SOFIE CH4 is systematically higher (>= 20%), while above similar to 65 km it is lower by a similar percentage. The sign change from the positive to negative bias occurs between similar to 55 km and similar to 60 km (or similar to 40 km and similar to 45 km) in the Northern (or Southern) Hemisphere. Methane, H2O, and 2CH(4) + H2O yearly differences from their values in 2009 are examined using SOFIE and MIPAS CH4 and the Aura Microwave Limb Sounder (MLS) measured H2O. It is concluded that 2CH(4) + H2O is conserved with altitude up to an upper limit between similar to 35 km and similar to 50 km depending on the season. In summer this altitude is higher. In the Northern Hemisphere the difference relative to 2009 is the largest in late spring and the established difference prevails throughout summer and fall, suggesting that summer and fall are dynamically quiet. In both hemispheres during winter there are disturbances (with a period of similar to 1 month) that travel downward throughout the stratosphere with a speed similar to the winter descent.