East Asia and Western Pacific METEOROLOGY AND CLIMATE

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Stauffer and Warner (1987) used the MM4 to simulate the development and maintenance of
an episode of cold-air damming that occurred during 13-14 January 1980, and was associated with
a moderate ice storm during this period. Fig. 3 shows a west-east vertical cross section across the
Appalachians and the coast at 12 h of the simulation. The section shows the shallow dome of cold
air trapped between the Appalachians and the coast. Low-level east and northeast How
maintaining this cold air is overrun by southwest winds aloft. A strong baroclinic zone inland
from the coast depicts the coastal front The simulation also showed realistic vertical profiles of
temperature and wind, including a mountain-parallel jet which is commonly observed along
mountain ridges during episodes of cold air damming,
a
600
CRW BKW
ROA RMT
HAT
CD
Fig. 3: West-east
isentropic cross
section and winds
(m/s) from 12~h
simulation
verifying at 0000
UTC 14 January
1980. One full
barb represents 5
m/s. The caret
denotes the
location of the
coast. (Stauffer
and Warner,
1987).
HTS
DAN
2.8 Urban Heat Island Effects
EWN
Although the MM4 is a hydrostatic model, it has been used at horizontal resolutions as
high as a few km under conditions when nonhydrostatic effects are assumed to be small. In
simulations of the flow over St. Louis, Missouri, Seaman eliL (1989) used a two-way interactive
nested grid version of MM4 with 7.5 km resolution on the outer grid and 2.5 km resolution on the
inner mesh. Realistic ihree-dimensionaliy variable initial and lateral boundary conditions were
specified from observations in order that numerical simulations could be used for quantitative
evaluation of urban effects on the atmosphere. After it was demonstrated that the model could
accurately simulate the observed heat-island effects in a control simulation, the importance of a
number of processes in the urban PBL were investigated. These PBL effects were isolated in
different simulations by using the present surface parameters associated with St. Louis as well as
parameters appropriate to the pre-urban environment and hypothetical parameters associated
with a possible future enhanced urban environment.
2,9 Use Of MM4 To Drive Regional Acid Deposition Model
It is well-known that the three-dimensional synoptic and mesoscale variations in wind
flow, humidity, temperature, clouds and precipitation are important in regional-scale transport,
transformation, and deposition of chemical species in the atmosphere. However, because
atmospheric chemistry has only a small effect on the atmospheric dynamics over periods as short
as a few days, it is possible to use output from a meteorological model as input into a model that
calculates the evolution of chemical trace species. This strategy has been followed in the
development of a three-dimensional Eulerian regional acid deposition model to calculate episodic
chemical concentrations and dry and wet deposition of acidic material over North America (Chang
1987).