NVAP and Reanalysis-2 Global Precipitable Water Products : Intercomparison and Variability Studies

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In this study similarities and differences between NASA's Water Vapor Project (NVAP) and NCEP–NCAR's reanalysis-2 total precipitable water (TPW) datasets are investigated, along with an assessment of its space–time variability, using simple statistical techniques. Global and hemispheric, as well as annual and seasonal differences between the two datasets are analyzed in detail. It is found that, in general, both datasets show very similar spatial and temporal patterns of variability, and there is a good correlation between them. The spatial TPW variability is closely related to latitudinal and altitudinal variations, and temporal TPW variability is strongly related to monsoon and ENSO events. In spite of the similarity in the patterns, there are significant differences in the magnitudes of TPW amount and variability between the two datasets. At the global scale it is found that the NCEP–NCAR reanalyis-2 product shows a more moist atmosphere than NVAP. On the other hand, variability analyses show that NVAP has higher spatial and temporal variability than the NCEP–NCAR reanalysis-2 data. Further, we found out that the TPW anomalies are driven by the global surface temperature anomalies, but with a lag.

Environmental Hydrology and Hydraulic Engineering, Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois

CORRESPONDING AUTHOR: Dr. Praveen Kumar, Environmental Hydrology and Hydraulic Engineering, Department of Civil and Environmental Engineering, University of Illinois at Urbana–Champaign, Urbana, IL 61801, E-mail: kumarl@uiuc.edu

In this study similarities and differences between NASA's Water Vapor Project (NVAP) and NCEP–NCAR's reanalysis-2 total precipitable water (TPW) datasets are investigated, along with an assessment of its space–time variability, using simple statistical techniques. Global and hemispheric, as well as annual and seasonal differences between the two datasets are analyzed in detail. It is found that, in general, both datasets show very similar spatial and temporal patterns of variability, and there is a good correlation between them. The spatial TPW variability is closely related to latitudinal and altitudinal variations, and temporal TPW variability is strongly related to monsoon and ENSO events. In spite of the similarity in the patterns, there are significant differences in the magnitudes of TPW amount and variability between the two datasets. At the global scale it is found that the NCEP–NCAR reanalyis-2 product shows a more moist atmosphere than NVAP. On the other hand, variability analyses show that NVAP has higher spatial and temporal variability than the NCEP–NCAR reanalysis-2 data. Further, we found out that the TPW anomalies are driven by the global surface temperature anomalies, but with a lag.

Environmental Hydrology and Hydraulic Engineering, Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois

CORRESPONDING AUTHOR: Dr. Praveen Kumar, Environmental Hydrology and Hydraulic Engineering, Department of Civil and Environmental Engineering, University of Illinois at Urbana–Champaign, Urbana, IL 61801, E-mail: kumarl@uiuc.edu
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