Thursday, 7 August 2003: 4:00 PM
Can't see the forest for the trees: Methods for the analysis and visualization of large radar datasets
In the case study approach of a precipitation event
two dimensional images (PPIs, RHIs, etc.) of radar data
are often examined frame by frame (as a function of time) in
order to understand the evolution and dynamics of the event.
When dealing with several weeks, months or even years of data,
however, such approaches often end in frustration and little
understanding is gained from the massive amounts of radar images.
If we are to study the precipitation cycle and understand its relationship
to forcing mechanisms (synoptic, density currents, undular bores, diurnal
heating, etc.) for a long time series, other approaches that reduce the
volume of data to a manageable level can provide more insight.
One approach is to reduce the dimensions of the dataset by averaging
in one spatial dimension (latitude or longitude) and plotting the data
in the remaining spatial dimension as a function of time (time-longitude or time-latitude).
Such plots are often referred to as Hovmoller diagrams and have been used in the
climatology community for many years. In the Hovmoller diagrams
coherent precipitation episodes travelling across the continent
appear as streaks, and patterns associated with different types of forcing
are revealed. From the streaks, statistics on the propagation
speed, span (km) and duration (h) of the precipitation event are easily
obtained. Several examples of precipitation episodes forced by various
mechanisms will be shown as well as methods for displaying data averaged
over several years. This approach is not limited to radar data and when
combined with satellite, model analysis and lightning data becomes
even more powerful.
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