East Asia and Western Pacific METEOROLOGY AND CLIMATE

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3. METHODOLOGY
The data analysis and reduction procedures were detailed in Lin
et aJ. (1986). We employed the Euler-Lagrange equations and the constraint
equation to derive three variationally adjusted wind components
(u, v, w) at each analysis level. The derived wind field is subject to
both random and nonrandom errors. Following Lin et al. (1986), an
error analysis was conducted. Our finding shows that the combined
errors due to statistical uncertainty in the radial velocity estimates
and geometrical considerations are 1-2 m s for the horizontal derived
winds.
Once the detailed wind field was obtained, fields of deviation
perturbation pressure and temperature were recovered from the derived
three-dimensional wind field via a thermodynamic retrieval method
(Gal-Chen, 1978). The retrieved fields, together with the derived wind
field, were then used to study some structural features of a squall
line.
4. DISCUSSION OF RESULTS
4.1 Horizontal View at 0.73 km
The horizontal storm-relative wind field with radar reflectivity
contours superimposed is shown in Fig. 5a. Distances are in
kilometers from the TOGA radar. At the time of analysis, the leading
edge of the squall line was located about 10-20 km west of TOGA. There
are many cells embedded within the squall line. The leading edge is
almost in a north-south direction and moves from 250 at 16.5 m s
The maximum reflectivity is less than 45 dBZ. Several new cells occur
along the eastern edge of the squall line approximately 5-10 km to the
east of the main cells. The low-level convergence line is evident
especially over the northern portion of the domain. On the east side
of the convergence line, storm-relative winds are mainly from the
southeast. The southeast winds transport high 6 environmental air
toward the leading edge of the squall line. Such air feeds the convective
updrafts, resulting in a broad area of high reflectivities in the
vicinity of the convergence line. Pronounced upward motion (Fig. 5b)
prevails at the leading edge due to the strong low-level convergence.
Conversely, downward motion dominates in a broad area west of the convergence
zone. There are many cells in the squall line with new cells
to their east. Most convective updrafts are accompanied by relatively
weak convective downdrafts on their west side. This finding is consistent
with that reported in Roux (1988) for a tropical squall line.
Using dual-Doppler data obtained in the northern Ivory coast, Roux
(1988) showed that the convective region has many short-lived cells of
intense updrafts and high reflectivities with downdrafts in between and
behind.
Figure 6a displays the retrieved P• ' field at the same level*
Low pressure occurs on the downshear side (east) of.the.updraft (U)
with high pressure on the upshear. Notice that high pressure observed
on the west side of the updraft corresponds to the near-saturated
convective-scale downdraft behind the leading edge. The density of the
downdraft air is increased due to precipitation loading, resulting in a