Application of numerical cloud model in hail suppression of cold clouds
Javanmard, Sohaila1; Karimpirhayati, Mahla2; BodaghJamali, Javad3; Abedini, Yusefali2
Atmospheric Science and Meteorological Research Center (ASMERC), Pajuhesh Blvd., Tehran-Karaj
Highway, Tehran, I. R. of Iran, [email protected], [email protected]
2
Department of Physics, Zanjan University, Zanjan, I. R. of Iran, [email protected], [email protected]
3
University of Environment, standard Squar, Karaj, I. R. of Iran, [email protected], [email protected]
1
1.
Introduction
Hail induces many damages to agriculture,
transportation, economical affairs in hail prone area
over Iran annually (Jamali et al., 2010). In order to
achieve hail risk management to decrease eht
induced destruction in Iran, application of hail
suppression methods is necessary. In order to asses
the performance of operational cloud seeding
operations and achieve desirable results, application
of numerical cloud model is one of the most
important tools to assess the seeding effect on hail
suppression. In this paper, effects of Silver Iodide
(AgI) cloud seeding in order to hail suppression have
been examined using one dimensional time
dependent numerical cloud model.
2.
Hail suppression model
The governing dynamical equations of model
is based on Ogura and Takahashi (1971),
microphysical
parameterization
of
natural
precipitation process is based on Lin et al., (1983),
and cloud seeding parameterization is based on
Zhen and Heng-Chi (2010).
Ogura and Takahashi model is a time
dependent and one dimensional model with bulk
parameterization. In this model, the cloud is modelled
as a circular air column with a time dependent radius
in an environment at rest. All dynamical equations
have been formulated in a one dimensional space
based on Asai and Kasahara(1967). In Ogura and
Takahashi model, nine microphysical processes has
been parameterized with four water substances
including water vapor, cloud droplet, raindrop and
hail.
Lin et al. model (1983) is a two dimensional,
time dependent cloud model which it has been used
to simulate a moderate intensity thunderstorm. In this
model, six forms of water substance (water vapor,
cloud water, cloud ice, rain, snow and hail/graupel)
are simulated and 32 microphysical processes are
considered as shown in Fig .1.
In hail suppression model, dynamic and
thermodynamic equations are based on Ogura and
Takahashi model (1971) that cloud ice and snow are
added and microphysics of natural precipitation is
based on Lin et al. model (1983). Three
microphysical processes for seeding are added to
model that is based on Zhen and Heng-Chi (2010).
When AgI is inserted to the cloud base, it affects on
six cloud hydrometeors including cloud droplet,
raindrop, snow and hail mixing ratios via contact and
deposition nucleation, transportation from rain drop to
snow and droplet to cloud ice due to seeding.
The equation of the vertical component of
velocity in a cylindrical coordinate may be written as:
2
∂w
∂w 2α
~ )+
−
= −w
w w + u~a ( w − w
a
∂t
∂z
a
a
T − Tν 0
g ν
− g (Qc + Qr + Qi + Qs + QG + X s )(1)
ν0
The first term in the right-hand side of Eq. (1)
represents the vertical advection, the second term
the lateral eddy exchange, the third term the dynamic
entertainment that is required to satisfy the mass
continuity between the cloud and the environment,
the fourth term the buoyancy, and the last term the
drag force that is assumed to be provided by the
weight of cloud droplets, raindrops, cloud ice, hail,
snow, and AgI.
In this research, dynamical equations with 32
microphysical processes have been coded by Fortran
programming according to Javanmard et al. (2010),
then three seeding microphysical parameterization
have been added to cloud model. Finally, results
have been compared before and after seeding.
Water Vapor
PIMLT
Cloud Droplet
PIDW
PIHOM
PSFW
PSAUT
PSACI
PSACW
PREVP
PGACW
Cloud
Ice
PSFI
PRACI
PSSUB
PSDEP
Snow
PRACW
PGSUB
PSACR
PSACW
PRAUT
PGAUT
PIACR
PGACS
PRACI
PRACS
PSMLT
PGACR
Rain
Water
PGACR
PIACR
PGMLT
PGFR
PSACR
Hail/Graupel
Precipitation at Ground
Fig. 1. Microphysical processes in Lin et al. model (1983).
3.
Results and conclusion
In this paper, effects of cloud seeding by AgI
have been simulated in one dimensional cloud
model. It is concluded that as AgI introduced into the
cloud at height about 6.5 km above the surface
(temperature less than -20 degree Celsius) within 30
minutes after cloud formation, and with mixing ratio
about 2.5*10-9 gg-1 resulting in rainfall intensity
enhancement about %20. Moreover, heterogeneous
nucleation of AgI enhanced the cloud ice, so snow
increased and rainfall enhanced by melting of snow
and cloud ice. On the other hand, cloud ice
consumed to produce snow and they did not grow up
to reach hail size, so the processes that related to
growth of hail decreased strongly.
(dry growth of
hail) before seeding and they are
(wet growth of graupel/hail)
graupel/hail) and
after seeding. From Figs. 6 and 7, it has been
concluded that the most effective sink terms is
(melting of hail to form rain) before seeding and it is
(sublimation of hail) after seeding.
HIAL MIXING RATIO (gr/kg) BEFORE SEEDING
14
7.09685
5.67748
4.73123
4.25811
3.31186
2.83874
2.36562
1.41937
0.473123
12
2.37
8
1.42
6
6
3.3
1
4.2
HEIGHT(km)
0.47
10
4.73 2.84
4
Fig. 4. Hail sources terms (
0.47
) before seeding
2
20
40
60
80
TIME(min)
Fig. 2. Hail mixing ratio versus height and time before
seeding
HAIL MIXING RATIO (gr/kg) AFTER SEEDING
14
3.33154
2.88733
2.44313
1.99892
1.55472
1.11051
0.666308
0.222103
0.22
1
1.1
10
1.55
0.67
6
Fig. 5. Hail sources terms (
9
2.44
2.8
8
3
3.3
0 7
2.0 0.6
HEIGHT(km)
12
) after seeding
4
0.2
2
20
2
40
60
80
TIME(min)
Fig. 3. Hail mixing ratio versus height and time after
seeding
The contours of hail mixing ratio versus
height and time have been shown in Figs. 2 and 3,
which the maximum values of hail mixing ratio are7.1
and 3.3
before and after seeding,
respectively. Hail mixing ratio has been reduced
about %53. From Figs. 4 and 5, the most effective
(accretion of rain by cloud
source terms are
(accretion of rain by snow;
ice; produces hail),
(freezing of rain to form
produces hail), and
Fig. 6. Hail sinks terms (
) before seeding
Fig. 7. Hail sinks terms (
) after seeding
References
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th
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