WMOD00263

• Project Name: Journal of Weather Modification Abstract
• Title: Simulations of Snowpack Augmentation in the Colorado Rocky Mountains
• Prepared For: Weather Modification Association
• Prepared By: William Cotton, Colorado State University
• Date: 5/1/2006
• State: CO
• Weather Modification - Doc Type: Scientific Study

60

JOURNAL OF WEATHER MODlF1CA nON

Volume 38

Natural ice activation is simulated using a gener-
alization of the Meyers et al. (1992) fonnula:

Nj= NIFNexp[12.96(SI- 1)];
T<-5C,' r >r.
v SI

supersaturation with respect to ice, and

T<-2C', r >r
v rw

supersaturation with respect to water.

The variable NIFN is a forecast variable in RAMS
which can vary both vertically and horizontally
whenever such data are available. Normally we use
measurements in field campaigns with the CSU con-
tinuous flow diffusion chamber to infer NIFN. In the

"

-
.
'0 ~
N
-
.

. , I I

~
1'tR"rf.'J181t" "",.nIl','. f'l1."<<

.....;r~.. ftttI.
MtII:ra1 Uaft u __ flail CMlUUau
_ .. t-.I J.n
:: .........m_
- ..~....
.. c.ut ...n
== _...ta.lS2~
= ~..... 0

_... D

(" 2l9lI'" ....
.'41 ..,.,,, ... nw
"l~ to J-no<92
6-1-11 6-lf.1I
ftU n.OW a
NAlU..... llWT 0

absence of those measurements N1FN is based on the
estimates reported in Meyers et al. (1992) and al-
lowed to drop off in concentration with height consis-
tent with observed lapse in large aerosol concentra-
tions. Recent measurements at the Stonn Peak Labo-
ratory in the Park Range of Colorado by DeMott
(personal communication) suggest that IFN concen-
trations are probably lower than Meyers original es-
timates. However, sensitivity experiments using these
lower background IFN values did not change the re-
sults appreciably.

Secondary ice particle production by the rime-
splinter mechanism following Mossop (1976) is also
simulated.

A seeding algorithm was added into the model
based on sources of IFN from ground-based seeding
generators. Figure 2 shows the activation data that we
used to simulate IFN production at each generator
site. Agl was then added as another prognostic IFN
field.

. I' .

I
1ft' ..''''

o

IHII t..u __ ~ .n.
G AaI .. l.UI -.& .. "."1: IK'.~ ~

-10 "
(t.OUD ........1\11I& fIItl
- Reviewed -

=

::

==

Figure 2. Calibrated Agl activity for the
generators used by WWC. The dashed line
labeled "1973 max," including the acetone-
induced activation enhancement at wanner
temperatures, is the fit used in the model.
Provided by Larry Hjennstad. (WWC
used a 4% AgI solution with sodium iodide
as a carrier in acetone along with 1 % moth
balls to improve nuclei activation between
-2.5.C and -8.0.C.)

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