Joint Centre for Mesoscale Meteorology (JCMM)
JCMM INTERNAL REPORT NO.109
A guide to aspects of water vapour imagery interpretation: the significance of dry regions
by Nigel M Roberts
Water vapour (WV) imagery provides us with dynamical insight into the upper troposphere. Of primary importance is the relationship between evolving patterns in the imagery and undulations in the height of the tropopause. Variations in tropopause height, inferred from the imagery, can be related to anomalies in potential vorticity (PV) from which aspects of the flow and temperature structure can be deduced.
This report will discuss the relationship between patterns in WV imagery and key structures in flow, temperature and humidity. The focus is strongly on the dry (warm brightness temperature) regions in the imagery because it is these regions that are often associated with the initiation of strong convection and cyclogenesis. The relationship between WV imagery and thunderstorms is the subject of JCMM report 110. A principle aim of this report is to provide a background for that discussion.