A New Reprocessing Scheme to Improve the Aqua AIRS Global Temperature and Water Vapor Retrievals in the Lower Troposphere and Stratosphere using GPS Radio Occultation Measurements

Water vapor is the major greenhouse gas in the atmosphere. It plays an important role in all the climate change processes. Its transports and phase changes also play a significant role in cloud and precipitation processes, which directly influence the hydrological cycle and the energy balance of the earth. It is very critical to have accurate water vapor measurements from space to ensure a more complete spatial, temporal and vertical coverage. NASA Terra and Aqua satellites, launched in 1999 and 2002, respectively, are the first two major EOS observatories. Although Terra and Aqua data provide very close temporally and spatially collocated measurements to reveal the interrelationships among atmospheric, land, and oceanic processes, due to the limitation of resolving power in terms of weighting functions and signal to noise ratio of these instruments, and most measurements from Terra/Aqua instruments cannot penetrate clouds, accurate water vapor estimates i) in the lower troposphere (LT), ii) in the upper Troposphere and lower Stratosphere (UT/LS), and iii) within and below clouds are still not available. Recently, the Global Positioning System (GPS) radio occultation (RO) limb sounding technique, which can provide high vertical resolution all-weather refractivity profiles, has emerged as a robust global observing system. In this study, we will demonstrate the usage of GPS RO data combined with Atmospheric Infrared Sounder (AIRS) measurements from the Aqua satellite to derive i) accurate water vapor retrievals, especially in the LT under clear conditions for both land and oceans, ii) to improve the water vapor retrievals within and below clouds, and iii) to improve the moisture retrievals in the UT/LS whenever Aqua AIRS data are collocated with GPS RO data. These derived water vapor products will be made available to the scientific community.