WMOD00300 ‎(2)‎

• Contract/Permit #: 2-07-81-V0256
• Title: Cloud Physics Studies in SCPP From 1977-87
• Date: 10/1/1987
• Weather Modification - Doc Type: Report

~. T~e scavefiging ar CCN by ice is greater than scavenging

raindrops.

tvn:.cal

sizes

~"""'r
.L v_

rr\'
\....Va'

~""a
~L ~

C.i to 1.0 ;J:n.

This

-~1
size o~

ra::ge

~s within the Greenfield (1957) gap i~ which i~ertial

impaction

. " --
a~i'5~~w~ia~ c~fi~sion a~e both ~inimam. Within the G~eenfield gap the'

20~1~c~~ scave2gi~g process is by phcretic

forces,

i.e.,

the

::::erilicphoret:.c a;:d - d::ffusiophoretic.

Tney arp aiillost always of

---;::.

c~Dosi~e directio~.

For the conditions in the ice cloud (water

sat~re~ion), tje ice crystals are slightly warTIer than tte environment

a:l:::'

her:ce

the

ther~ophoretic force

is

neQct2.ve

while

....
\-ne

d~ffusi8?hcre~ic fo~ce is posi~ive.

Theoretical calcula:ions indicate

~ha: raindrcps i3 a w=ter sat~rated environ~ent (Glover,

et al.
--

1977 )

a~c ice crys:als (~crtin. et ai. 1980) in a water satura=ed environment

_':I
bot~ nave co~lectiG~ e:ficie~cies within the Gree~field gap of ~lO~.

The ~i=fe!"e:lce

"'!r'!!
~i.i.

co~centration between ice crysta~s and

raindrops

1

s~gges~s ~here s~culd be fewer cex in an ice C~OUG. Even so, it is not

~Lear ~necner scavengir:g alone would result in fewer C~ above the OOC

r-

level. The scave~gi~g ~rocess is extremely complex anc ir. need of more

.;

i

s:.~::'!: .

c. '.i.ae cloud droplets are accreted by the ice crystals. The
;:olle~tio!: efEciei:.cy of cloed drcplets b" ice crystals ~s
]

co~~e=~ratiaGs ac~oss the O~C level.

Although accretiop. would result

\
I
I
\
1
I
i
t
i
,
i
!

exponent~ally depe~de~t oa cloud droplet size when t~e drop diameter is

< ~L ~I (?r~?pccher a~G Kle~t, 1980, p. 498). This fact alone does not

r
i_
I
.
I
I
k
! -
i
,
!
I
I
I

aQ~e =8 ex~lai~ tte a??arent distinct cifference i~ clo~d droplet

yerticcl g~c~~ent,

~t wo~ld not resul~ in a

distinct

22