Analysis of Atmospheric Infrared Sounder (AIRS) and Advanced Microwave Sounding Unit (AMSU) data between 2002 and 2007 reveal a cycle in the mid-troposphere (500 mbar) temperature with a 400 mK peak-to-peak modulation and three pronounced minima spaced about 1.8 years apart. The anomaly for the tropical oceans is well correlated with the AVN surface temperature in the Atlantic, Pacific and Indian tropical oceans, but less well with the ENSO index. The anomaly of the mid tropospheric moisture and cloud data from AIRS show no significant features. The currently available five year time series of AIRS data is not adequate to identify this feature as a quasi-biannual-oscillation. However, the presence of a multi-annual global mid-tropospheric temperature variability at the 400 mK level imposes significant limitations on the ability to reliably measure mid-tropospheric global warming related trends, since the variability far exceed the 100 mK/decade magnitude of expected climate changes.

The data used for this study are based on the AIRS Climate Data Subset (ACDS), which is available from the GSFC/DACC. AIRS and AMSU were launched on the EOS Aqua spacecraft in May 2002 into a 705 km polar sun-synchronous orbit. Essentially un-interrupted data are available since September 2002.