WMOD00311

• Title: Harold D. Orville Symposium - Forty Years of Modeling Clouds and Weather Modification
• Date: 4/26/2003
• Weather Modification - Doc Type: Report

0)

YL CONVECr!ON CURRENT X; 20.00 KM T= 20.00

1&

m"ITT1Tl"""""""I""""" ""~

14

I.

10

'"
':': 8

. . . . . . . .. .. .t~~. . . . . . . . . . . . .
......... f~' ........

. : : ; : J H1L~tJl1~'mi~~:"~ ~ ~ ~ ~ ~ : : : : ::
. . . . . . ~ . . \ , . \ \ '~J\\ t t \ \ :-:-. . . . ~ . . . . .
.........\"',"\ ~ r. ,I"~.
~:;::::~~:~:):;L:!:!~~~~H>.::: .

~ . . . ~ " . . . . ~ . . . . , ~ . . . . . . . ~ . . . . .
. . . . .. . . . . . . ~ . . . . . . . . . .
..,.......... .

o
8

12

16 20

24

28

b)

Y (K"1) ''':ltllF.'II).
YZ CONDUCTION CURRENT X= 20.00 KM T= 20:'60"'''"
\ t I

......~
6 ::::::'/,;'1
. . . . . .,1.,\;
4 :::::::::~>>
. . . . .. ... ----~.....
...... ..,.....--........../".

t~I.I.I.////;;;:::. "
'llB~'l;////",,: ::.
i1.~7./.~~~;~;;::::::
I'h/~~////. '" . ..
.~hl~////.....
$II~~I~~S~;;;:;; :
f ~~:::::::
; 11.~. ~::::::::

I r . I :--'"-...........
/;1 -/ . . . . .
1// -~....

.~~i::::: :

. .. .....-........

.. ...........
.~~~~::::::=
~~..::;:::::~ : : : : : : : :
'tn~t"..........
I I 11 i ~ : : : : : : : : : :

12

lb

20

2<

28

Y lKHI

",;;"lIClal

seA:..!: VEctOR

Figure 7 - a) convection, and b) conduction
current density vectors in a 20 slice through the
model domain at X = 20 km. Scale is 20 nAlm2 in
a) and 2 nAlm2 in b).

further developed for use in subsequent stucHes.
The final area in which new work has begun
is the use of the SEM to study certain aspects of
atmospheric chemistry. Lightning is a source of
nitricoxides (NOx = NO + N02) in the troposphere.
Lightning directly produces NO through heating
effects and the NO so-produced generates N02 by
reacting with ozone. The presence of NOx in the
troposphere is important because it affects the
tropospheric ozone concentration. Of the several
sources of tropospheric NO (fossil fuel burning,
biomass burning, soil microbial action, lightning,
transport from the stratosphere, and aircraft
production), the lightning source strength is the
least well known. Most global and regional
chemistry models now include a source term for
lightning-produced NOx, but there is an order of
magnitude variation in the value used. Pickering
et al. (1998) parameterized the production of NOx

by lightning in the 20 Goddard Cumulus Ensemble
model to arrive at vertical profiles that can be used
in global models. However, assumptions about
the distribution of lightning activity and the relative
production between intracloud and cloud-to-
ground flashes (intracloud production is assumed
to be one-tenth that of cloud-to-ground flashes) as
well as the fixed production rate per flash are
limiting and strongly bias the results. While this
approach to the problem has considerable merit, it
needs to be checked against a more detailed
calculation. The physics-based lightning scheme
within our SEMs allows the more detailed
calculations to be done. Zhang (2002)
conducted a series of simulations with the 20 and
3D SEMs to test the ability of the models to predict
the production and distribution of Iightning-
produced NOx. The first simulation involved the
20 SEM as a proof-of-concept (Zhang et al.,
2003a) using the 19 July CCOPE storm as a base
and simple suite of 4 chemical reactants (including
NO, N02, and 03) and 6 reactions. Production of
NO by lightning is assumed to be a function of
energy dissipation by the lightning flash with NO
produced at the rate of 9.2 x 1016 molecules/J
(Borucki and Chameides, 1984). The results, with
only intracloud lightning present, were in general
agreement with observations, leading to an
expansion of the chemistry module to include 9
reactants (CO, OH, H02, CH4, and HN03 added)
and 18 reactions within the context of the 3D SEM
(Zhang et al., 2003b). Figure 8 shows the results
of the 3D simulation after 38 min and 18 lightning
flashes. The top left panel is a 3D depiction of the
remaining cloud and' ice water contents forming
the anvil, and to its right a 20 slice through the
cloud. The bottom. two panels show the NO
mixing ratio (left) and the N02 mixing ratio (right).
We note an asymmetric distribution of NO within
the anvil and a plume of N02 to the surface. The
primary concentration of NOx remains within the
core of the cloud. Mixing ratios of up to 2.5 ppbv
of NO in the anvil agree with observations, but this
simulation only produced 18 flashes, while
observed storms typically are more active
electrically.
The final step in the process was a simulation
of the multicell, 10 July 1996 storm from the
Stratospheric-Tropospheric Experiment: Radiation,
Aerosols, and Ozone (STERAO) project using the
same model configuration as in Zhang et al.
(2003b). This storm was chosen for simulation
because there were aircraft observations in the
anvil for comparison with the simulated results
(Stith et al., 1999; Dye, et al., 2000), there was a
detailed analysis of the lightning activity (Defer et

I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I

42