Abstract:
The vertical distribution of liquid water content
(LWC) in natural fog and low stratus is a crucial variable in many
applications, e.g. the development of satellite based retrievals of
ground fog. Unfortunately, there is very little data concerning fog
LWC-profiles, mainly due to the lack of suitable operational
instrumentation. A novel ground-based 94 GHz FMCW cloud
radar could fill this gap if radar reflectivity Z could be converted to
LWC by using appropriate Z–LWC relations. However, this relation
strongly depends on drop size distribution (DSD) and is hardly
known for natural fog types. In this sensitivity study, the influence
of the DSD on the Z–LWC relation in different types and life cycle
stages of natural fogs is analyzed using a radiative transfer code
(RTC) and published fog drop size distributions. It could be shown
that there is a direct but nonlinear relationship between LWC and
radar reflectivity. The proportionality factor of the Z–LWC equation
in particular reveals specific ranges for the different life cycle
stages. If a proper classification of fog life cycle in the field is
possible, the results could be used to properly convert Z to LWC.
