Geoscience Reference
In-Depth Information
Table 23.1 The total number
of cyclones as well as those
counted as deepening or
decaying, or coming from the
north, northwest, west,
southwest, or south in this
study
Cyclone characteristic
Number
Deepening
37
Decaying
87
From the north
4
From the northwest
19
From the west
37
From the southwest
48
From the south
16
All cyclones
198
have forecast runs early in its lifetime when it deepens and forecast runs later in
its lifetime when it decays. In the subsequent discussion, we will use 'storms' to
refer to unique cyclones (i.e. the 27 storms) and 'cyclones' to refer to the individual
forecast runs (i.e. one of the 200 samples).
The observation targeting calculations indicate the estimated variance reduction
to the response function due to the assimilation of hypothetical temperature, wind,
and pressure observations at analysis time beyond the assimilated routine data. In
turn, the largest variance reduction values reveal the locations where an initial-time
observation would reduce the uncertainty of the 24-h response function the most.
23.3.3
Characteristics of Observation Targeting
for a Single Cyclone
Figure 23.2 shows the 00-h, 12-h, 18-h, and 24-h ensemble mean forecast initialized
at 0600 UTC November 9, 2009 that depicts one particular cyclone that made
landfall on the west coast of North America. This cyclone decays from 986-hPa
central pressure in the analysis to 993-hPa central pressure when it makes landfall
on the Canadian coast at 24-h forecast time. The targeting regions for winds,
temperature, and pressure valid at analysis time are shown in Fig. 23.3 ,andare
plotted at the level where the maximum value of estimated variance reduction was
found. The targeting regions based on temperature and winds are localized and
mesoscale in nature, which is generally the case for most land-falling cyclones
during the 2009/2010 winter season (not shown). The targeting regions based on
pressure are more typically characterized by synoptic-scale features, which is the
case in Fig. 23.3 . The largest targeting regions based on winds and pressure for this
specific cyclone are found in the lower troposphere (from roughly 880 to 750 hPa
for winds, 930 hPa for pressure), and near the tropopause (roughly 380 hPa) for
temperature. Targeting regions based on all four observation types reveal areas in
the immediate vicinity of the incipient system at analysis time, with wind and
temperature targets aloft flanking the central position of the 500-hPa geopotential
height minimum, and the primary pressure targets positioned just over the cyclone
center at the surface. Dynamically, the primary zonal and meridional wind targets
exist north and south (for zonal wind) and east and west (for meridional wind) of the
cyclone center aloft, suggesting the effects of observations there would beneficially
 
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