Temperature Change and Water Vapor Feedback in The Atmosphere. A Comprehensive Assessment Using The Atmospheric InfraRed Sounder Instrument on NASA AQUA Satellite.

Global surface temperature has increased &sim0.2 degree Celsius per decade in the past 30 years [Hansen et al. 2006] . Observational data recorded from 1850 to 2007 indicate that the warmest 11 years have occurred between 1995 and 2006. The 2007 report of the Intergovernmental Panel on Climate Change concluded that there is a very high confidence - 95% confidence - that the global average net effect of human activities since 1750 has been one of warming and that most of the observed increase in global average temperatures since the mid-20th century is very likely - 90% confidence - due to the observed increase in anthropogenic greenhouse gas concentrations. Processes in the climate system that can either amplify or dampen the climate response to an external forcing such as an increase in anthropogenic greenhouse gas concentrations, and directly or indirectly affect the Earth's radiation budget at the top of the atmosphere are normally referred to as climate feedbacks. Among all trace gases, water vapor is the most sensitive to temperature variations. In fact, water vapor absorbs strongly in the vibration-rotation and pure rotation bands at wavelengths in which a large portion of infrared emission occurs at temperature characteristic of the Earth's surface and atmosphere In the present study, we exploit the uniform spatial coverage and high vertical resolution of the Atmospheric InfraRed Sounder database of temperature and water vapor profiles to perform a detailed investigation of the covariance between temperature and water vapor. Unlike previous studies, that only analyzed the overall tropically averaged water vapor and temperature relationship, we make a more comprehensive analysis by investigating this relationship on a local basis. By doing so, we explore the horizontal gradient of this relationship in the tropics, in order to better confine its range of variability and the interplay of the physical processes underneath it. In trying to provide a conclusive assessment on the overall water vapor feedback in the tropical region, correlations between tropically averaged water vapor and temperature are analyzed as well. We observe that the highest and positive correlation values occur in the upper troposphere, where values are seen to approach the thermodynamic equilibrium regime. These results appear to confirm an overall positive water vapor feedback to increased surface temperature in the tropical domain