The figure to the right illustrates how the Water Vapor Transport Index (WVTI) has been used to obtain seasonal mean maps of vapor transport. The WVTI vectors represent the wind velocity times the specific humidity (q x V) and in this figure are overlaid on the mean layer pressure height (hPa). By clicking on the image, you can view 18 months (6 seasons) of WVTI-pressure maps spanning part of the 1987-1988 El-Nino Southern Oscillation (ENSO) period.
   Several features become quite apparent in this image. Towards the midlatitudes WVTI vectors are significantly stronger than in the tropics as the wind speeds during this season are quite strong. The pressure heights generally are much higher in the troposphere in the tropics where there exists more water vapor at these altitudes. The darkest red regions coincide with the mean position of large-scale high pressure regions where the upper troposphere is relatively dry. Upper tropospheric vapor transport over the tropical East Pacific is from the east but backs to become westerly over the southern Pacific Ocean.

Last updated on: November 2, 1999