WMOD00536

• Title: Release of Potential Instability by Mesoscale Triggering - An Obective Model Simulation
• Weather Modification - Doc Type: Report

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conditions characteristic of organized
Mesoscale triggering of convection and random
Isolated convection. Model results indicated
that ul'lder conditions of observed mesoscale
organized convection and random isolated
convection on the High Plains, the atmosphere
was indeed sensitive to mesoscale lifting.
Considerable deep convection was diagnosed In
both conditions ~en liftln~ was applied, and
relatively little development was diagnosed
When surface heating and eddy mixing were the
only sources of destabilization. That result
leads directly to this important conclusion:
some tonn of organized Hftlng is required to
initiate deep convection and release the
available potential instability on the
High Plains.

Cohen (1971) noted that, during the summer
months, Goodland nearly always had high
instability; however, clear skies often
persisted in spite of the large instability.
Results presented in figures 2 and 3 also
clearly support this hypothesis by showing
that very few cases have any convective
development unless mesoscale lifting is
applied to the atmosphere. Studies by
Achtemeler (see Chang non et al. ,1918) at the
Illinois State Water Survey using a dif-
ferent version of the MESOCU model support
the conclusion that significant available
potential instability ellists on the Plains.

4. CONCLUSIONS

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The results of this research suggest three
conclusions:

a. lifting is a key factor in the release
of available potential instability (API) on
the High Plains. Nearly all days appear to
have sufficient API to produce deep convec-
tion provided lifting or IIlE!chanical forcing
15 applied.

b. The MESOCU model 15 a useful tool in
asseSSing the effects of lifting on the
release of API.

c. Better IIlE!thods are required to determine
when and where mesoscale triggering will
occur. Once this has been dete~ined, the
HESOCU MOdel can be used to diagnose the
effect of lifting on the release of API.

5. FUTURE STUDIES

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One ~thod to solve the probl~ of recognizing
the location and strength of ~esoscale trig-
gering is to perform an optilllllll analysis of
~esoscale organization and structure of clouds
observed in satellite lmagery. This analysis
should be combined with informatlon from MeSO-
scale rawfnsonde and surface networks which
describe the detailed structure of convergence
and determine the vertical profile of lifting.
Thh vertlcal profile of lifting can then be
used to initialize the MESOCU IIIOdel to deter-
~lne the effect of mesoscale triggerlng on the
release of API.

Ultimately. a multivariate discriminant function
would be used to select the appropriate vertical
profiles of lifting associated with mesoscale
triggers observed in satellite lmagery when no
mesoscale rawinsonde data are available. Then,
initialization of the MESOCU model with a
representative rawtnsonde and lifting function
could lead to an objective operational analysis
and forecasting tool.

Thh mesoscale forecasting tool could be applied
to the analysis and forecasting of flash-flood
events. The Big Thompson, Johnstown, and Kansas
City floods have been assoclated with strong
mesoscale forcing (Maddoll, 1918).

An lmportant factor in any study of meteorolog-
leal phenomena is climatic national variability
of moisture and stability. The results presented
here refer a relatively small sample observed
during two summers. These results suggest that
~re general conclusions may be drawn from
further study of larger more homogeneous
samples drawn from many more years.

1. ACKNOWLEOGlENTS

Many thanks go to Ors. Carl Kre1 tzberg and Don
Perkey, whO developed the original MESOCU model
as part of their three-di:nensional mesoscale
mOdeling effort under sponsorShip of the Air
Force Geophysics Laboratory, National Sclence
Foundatlon, and National Aeronautics and Space
Administration. I sincerely appreciate their
pe~itt1ng my use of the lIIodel and their
stimulating conversations regarding its applica-
tion. Messrs. Fran Politte and Douglas Hale
developed the Environmental Data Network soft-
ware which made all HIPL(X and NWS rawlnsondes
readily accessible for model ellperiments.
Discussions with the HIPLEX field ~teorologist
at Goodland, Kansas, Or. Steven Cohen, aided in
interpretation of model results from th15 site.
Sincere appreciation is given to Mr. RiChard
Eddy for careful review of this paper and many
helpful suggestions.

8. REFERENCES

Changnon, S. A., and P. T. Schickendanz. B.
Ackennan, G. Achtemeier, et 011.,1978: Design
of the High Plains Cooperative Pilot Project.
Final Report, l111nois State Water Survey.
Urbana, I1l1no15

Cohen, S., 1977: Verification and Refinement
of Forecast Sounding Techniques for the HIPLEX
Kansas Program, Preprints, 6th Conference on
Planned and Inadvertent Weather Modification.
pp.244-241

Corbell, P., and C. J. Callahan and W. J. Kotsch,
1916: The GOES/SMS Users Guide. NOAA, NESS,
World Weather Building, Camp Sprln9, Maryland

Haltiner, G. J., and F. l. Martin, 1957:
Oynamical and Physical Meteorology, McGraw-
Hl11 Book Company, Inc., 63 pp.