Observed Global and Regional Variation in Earth's Water Vapor

As the principal greenhouse gas, water vapor variations are a key factor in climate change and abundant water vapor is a necessary precursor for high impact weather events such as heavy precipitation. A new, observational water vapor dataset is now available for a variety of climate and weather studies. The challenges in creating this multisensor, multidecadal satellite-driven climate data record are illustrative of the challenges for all satellite climate data records.

The NASA Making Earth Science Data Records for Research Environments (MEaSUREs) program supported the development of the NASA Water Vapor Project (NVAP-M) dataset which was released to the science community in 2013 via the NASA Langley Atmospheric Science Data Center. NVAP-M is a 22-year (1988 – 2009) global dataset comprised of atmospheric water vapor retrievals over land and ocean from multiple satellite and surface sources. It is observationally driven, with minimal dependence on numerical model fields, making it useful for comparison to models. Different processing paths are available with a global climate, an ocean-only and a weather event focus. The resulting global gridded fields of total and layered precipitable water vapor are available globally at either daily, 1 degree or 6-hourly, ½ degree resolution.

We will present new science results from NVAP-M, including studies of extreme events and timing of maxima and minima. The effect of the changing satellite observing system and sampling impacts (land / ocean; clear / cloudy) on the results will be examined. Global trends in total precipitable water vapor will be presented in light of the sampling challenges. International connections with the Global Energy and Water Exchanges (GEWEX) Water Vapor Assessment (G-VAP) will be discussed . The challenges – both from an observing system and data fusion standpoint - in creating a consistent, multi-decadal satellite climate record of water vapor are common to the satellite climate data record enterprise.