Geoscience Reference
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(b)
(a)
60 km
15 km
30 km
30 km
Imposed surface heterogeneity
Atmospheric response
(c)
Vertical ascent (m s
−
1
) in RAMS model
GOES-8 Visible Image
−
0.25
0
0.25
0.5
1.5
0.75
1
1.25
Uniform fluxes
(average of observed)
Heterogeneous fluxes
(observed)
Figure 25.10
(a) Patterns of imposed heterogeneity of dry and wet surfaces imposed in the Regional Atmospheric
Modeling System (RAMS) during a 12 hour simulation beginning at 06:00 local time on July 28, 1989 and (b) accumulated
precipitation in millimeters calculated by RAMS between 06:00 and 18:00 on this day with these patterns of surface
wetness. (Redrawn from Avissar and Liu, 1996, published with permission.) (c) Simulated horizontal distribution in vertical
wind speed at 1117 m across the ARM-CART site calculated by RAMS at 15:30 on July 13, 1995 when surface sensible and
latent heat fluxes are set to the average values across the site (left figure), and when these are set to the measured
distribution of surface sensible and latent heat fluxes (center figure), and the cloud cover shown in the
GOES-8
satellite
visible image at 15:15 on this day. (Redrawn from Weaver and Avissar, 2001, published with permission.)
cloud generation and potentially precipitation. Sometimes (over flat regions) the
effect of organized circulations linked to patterns in surface vegetation becomes
visible in the form of boundary layer cloud cover, thus confirming that such a
mechanism does indeed exist. However, most of the evidence for the existence
of mesoscale circulation stimulated by heterogeneity in surface cover is derived
from mesoscale modeling studies. Early numerical studies (e.g., Avissar and Liu, 1996)
