Monday, 10 February 2003
Analysis of the NVAP water vapor dataset: a tool for monitoring Earth’s water vapor from daily to decadal time scales
The NASA Pathfinder water vapor project (NVAP) is a global, daily, 4-layer, satellite-derived water vapor dataset which currently covers the time period from 1988 – 1999. NVAP is currently being extended into the 21st century with a multitude of infrared and microwave satellite instruments, a project called NVAP – Next Generation. NVAP plays a key role in addressing Earth science questions such as “How are global precipitation, evaporation, and the cycling of water changing?”; “What trends in atmospheric constituents and solar radiation are driving global climate?” and “How well can long-term climatic trends be assessed or predicted?”
We examine the NVAP dataset for long-term global and regional trends in water vapor. NVAP is model-independent and plays the role of an independent check on model predictions. Our work with NVAP to date has shown no discernible trend or increase in total column atmospheric water vapor over the past twelve years, in contrast to some model predictions. However major global and regional interannual variations are detected. A near constant relative humidity is observed in the lower troposphere on a global scale. Climate events such as El Nino and La Nina periods are apparent in the NVAP fields. We examine the relationship of water vapor anomalies to other relevant fields such as global temperature, cloudiness, and outgoing longwave radiation.