Decadal Data Sets and Decadal Trends: Considerations Based on Radio Occultation Observation

Radio occultation using signals transmitted by Global Navigation Satellite Systems (GNSS), such as GPS, has produced atmospheric observations with excellent long-term stability. The continuous record of RO observations dating back to 2001 is a valuable resource for exploring atmospheric trends. However, this 15-year record is too short to detect trends without making assumptions about the so-called "natural variability" of the atmosphere. Often such assumptions are derived using climate models. Climate models are also used to estimate the atmospheric signatures of specific climate forcings, which can be compared to the RO observational record. We will selectively review efforts by the RO community to learn about trends and responses to forcings, including our work on trends in the upper-troposphere/lower-stratosphere and the equatorial tropopause. We will present a new RO data set based on the GPSMET proof-of-concept mission that acquired the first such data in 1995. The value to trend observation of this earlier data set will be discussed. We will adapt the methodology adopted by the CLARREO climate observing mission in this value assessment. Finally, we will describe our efforts to contribute RO derived products as part of the Obs4MIPS effort to rigorously evaluate climate models. Building on past efforts within Obs4MIPS using RO observations, Dr. Ao (PI) is planning to provide new datasets with extended altitude range from the surface to mid-stratosphere, producing an observational dataset that resolves the diurnal cycle in temperature and water vapor. The potential value of such data to climate observation is discussed.