Modes of natural and forced climate variability in 6 years of AIRS and AMSU data

We use the Atmospheric Infrared Sounder (AIRS) and Advance Microwave Sounding Unit (AMSU) data obtained on Aqua spacecraft to study mid-tropospheric temperature variability in 2002-2008. The AIRS and AMSU deliver accurate, simultaneous measurements of the state of the atmosphere twice per day. We investigate the temperature variability at the surface and in a broad layer centered on 400 hPa in a zonally averaged 0-30°N region over the ocean. Taking into account the nonlinear and non-stationary behavior of the temperature we use the data analysis adaptive to the data, the Empirical Mode Decomposition, to separate the atmosphere response to the CO2 increase from the modes of natural climate variability. Our tentative conclusions are as follows: (1) the AIRS record shows a phase shift relative to CO2 and a trend in accord with the increase of CO 2; (2) the simultaneous AMSU record is in agreement with the cooling of the tropical ocean that may be caused in part by the decline in solar activity.