Abstract:
[Source: NASA/GISS,
http://data.giss.nasa.gov/stormtracks/ ]
Extratropical storms directly effect the environment and economy
throughout the mid-latitudes, greatly impacting the lives of billions
of people on a daily basis. This on-line atlas provides fundamental
information about extratropical storm systems, including maps of storm
frequency and intensity as well as plots of individual storms
... paths. In addition to storm intensity being presented as time average
the "most severe" storms are also plotted. Maps are available as
monthly and seasonal means for the years 1961 through 1999. Together,
the images presented in this atlas describe the state of the
mid-latitude storm tracks during the last half of the 20th century.
There are many methods used to define the position of the
extratropical storm tracks, probably the most common being to plot the
variance of the 500-mb geopotential height field. That technique,
however, does not yield information on the transient position of
individual storms. Here we have employed a different technique in
which we track the position of each low pressure center within a
series of gridded sea level pressure (SLP) fields. The technique was
originally developed to examine the storm tracks produced by
atmospheric general circulation models (GCMs), but it is directly
applicable to other gridded SLP datasets, such as those derived in
weather forecasts or reanalysis projects. The SLP fields used in this
atlas are derived from the 12-hourly (0Z and 12Z) 500 HPa and 1000 HPa
geopotential heights generated by the NCEP Reanalysis project.
It is important to note that neither the SLP data nor our storm
products represent raw meteorological observations. Rather, they are a
data assimilation product, based on both observations and computer
modeling techniques. The advantage is that we are able to produce
storm data sets that are global in extent. However, users should be
aware that the input data, and thus the results, are not of equal
quality at all locations (e.g. over remote ocean regions) due to the
nonuniform distribution of observations used in the data assimilation
process.
The Extratropical Storm Tracks Atlas is updated periodically, as the
annual NCEP/NCAR Reanalysis CD-ROM series is updated.
See: http://data.giss.nasa.gov/stormtracks/ 
