In this study, the Precipitation Water (PW) was compared against the
actual Precipitation (P) obtained through field stations and satellite
images to achieve a reliable cloud seeding threshold model. Gao and Goetz
(1990) studied the PW through remote instrument. In the convective cloud
seeding projects (PACE), the P augmentation for crops experiments, carried
out successfully by Czys and Scott (1993). The PW and buoyancy potential
in 500 millibar were determined as suitable factors in cloud seeding and
the PW for 26 mm was found to be the optimal p threshold in conducting
convective cloud seeding activities. Costa et al. (2001) calculated
the instability indices for tornado, hail storm and heavy rainfall in
northern Italy and introduced the suitable indices to identify the rainfalls.
Simoenov and Georgiev (2003) computed the instability indices through
studying sever wind/hail storm over Sofia, Bulgaria to obtain the cloud
seeding threshold and hail suppression. In this study the CAPE was found
to be 3785 J kg-1, the vertical wind velocity of 21.9 m sec-1
and PW of 12.9 J kg-1. Manzato and Morgan (2003) studies the
regional thunderstorms over Venice, Italy during a 7 year period whereby
they found the most suitable forecast indices of thunderstorms and their
strength to be the vertical wind velocity, PW, CAPE and KI (K Index).
Platnich et al. (2003) studied the clouds` temperature qualities,
microphysical parameters and PW through the 5 min data obtained from the
MODIS satellite over South American coast.
Gao and Kaufman (2003) reviewing the methods used in finding the PW through
MODIS satellite, came to the conclusion that the MODIS is capable of providing
global coverage. MODIS is the first space device used for recovering general
P. The quality control is also performed for both geographical and climatological
studies, as well as statistical analysis. King and Bock (2003) while emphasizing
the importance of satellite in research, introduced the band limits of
129 for studying the atmospheric characteristics like cloudage, the vertical
profile of atmosphere, aerosol and the general PW and managed to find
two different patterns of PW in polar clouds. Krauss and Santos (2004)
obtained some instability indices through performing hail suppression
activities over Alberta, Canada, employing the cloud seeding operations
on hailstorms for 82 days in the summers of 2001 and 2002. The indices
were as follows: the average PW (18.8 mm), Shulter index (-1.3 ° C),
set of sets index (TT) (54 ° C), vertical index (-3) and convective
available potential energy (781 J kg-1). Sajjadi (2008) studied
on calculating PW with thermodynamic graphs and MODIS satellite and calculated
PW with thermodynamic graphs and MODIS satellite in Tabriz and compared
two method with together.
The study was performed within 4 years (2000-2003) where the PW, as registered
by P stations, were determined and through MODIS satellite over Kermanshah
and selecting the fittest variables, ground P and PW, the suitable threshold
for cloud seeding was estimated.
MATERIALS AND METHODS
The areas under study (Kermanshah) the amount of PW with Eq.
1 on rainy days in 2000-2003. The increase in convectional movements
and heat transfer follows the increase in age and thickness of clouds.
The upward movements of the cloud drops by the base are slower than, but
they take more speed due to increase in instability produced by the release
of the latent heat of drops condensation as the cloud thickness increases
and so does the PW, Rogers and Yau (1996). The upward movements and drops
growth, as shown in Fig. 1 and 2,
reach the maximum in 3/4 of the cloud base. The drops, around the peak
and brims of cloud, then vaporize as the surrounding dry and cold air
intermingle, in other words, the process causes the temperature decrease
rapidly and consequently, the floating forces and upward movement speed
decrease as well. Moreover, the amount of water in clouds decreases as
the drops vaporize and the air gets cold in the cloud peak when the dry
and cold airs intermingle.
In case it happens, the cloud temperature decreases sharply and the upward
movement, too, become downward gradually. To determine the cloud seeding
threshold. The information in the Fig. 1 and
2 shows the cloud seeding threshold of the region where the P recorded
by the stations remains stable while the PW are increased, also, as shown
in the Fig. 5, the clouds` age and thickness are not
suitable for seeding. At this stage, any attempt for cloud seeding would
result in decrease of P potential, but if the indices exceed the threshold,
the P increases, which can be claimed to be the right index for cloud seeding.
||Differences in density and size of droplets by altitude
and their spectrums in each altitude (Rogers and Yau, 1996)
Maximum differences in upward and downward movements
and the average amount of square root of vertical velocity and the
turbulent energy differences based on the altitude from the cloud
base (Rogers and Yau, 1996)
||Cloud coverage of the zone under the study obtained
in Jan the 11th, 2003
By definition, the condensed water in a humid air column
is referred to as PW, as shown on centimeter or millimeter scale. Manzato
(2003) has used the following simple relation to calculate the PW as an
index for the P of conversion activity, the Eq. 1:
where, r is the average amount of mixing between the pressure levels
of the cloud base and peak.
To calculate the PW through the Skew-T the following is done.
MODIS is one of the five instruments in TERA satellite. Water vapor (W)
in atmosphere has different absorption proportion on the MODIS channels
passages in the vicinity of 0.935, 0.94 and 0.905 μm consequently,
these three channels have different sensitivities to the water vapor in
similar atmospheric conditions. The average W is obtained by the Eq.
|w1, w2 and w3
||The amounts of water
vapor in channels 0.935, 0.94 and 0.915 μm
|F1, F2 and F3
||Functions of weight
The satellite pictures of MODIS evaluator in the region and the dates
stated and the information related to the PW was obtained. The data of
PW by the MODIS included the vertical profile of water vapor present in
the atmosphere through using the infrared algorithm during the day. Its
position dissociation power is one kilometer during the day which is obtained
after receiving the temperature bands data and applying it to the estimation
model of output PW. A model of the pictures related to the cloud coverage
and PW obtained from the region under the study is presented. The required
output was obtained as Fig. 3 ([W of Iran] where the
weather condition is simply indicative of the presence of cirrus clouds
and a jet from the southwest). In the west of the country and within the
zone [W of Iran], the clouds are a combination of high, middle and low
levels. Then the temperature band enter the estimation model of PW. The
obtained output in pictorial mode is grey in context. In case a color
picture is needed in distance evaluation software the favorite color codes
are defined for it. As an example the average amount of precipitation
in ranking (Fig. 4) based on centimeter and geographical
region is clarified from which the average PW for example was obtained
in the present pixels in 2002/1/11.
The output of PW is in centimeter and in the calculations is in millimeter.
Date; 2002/1/11 code; 34.9857 47.1867 PW; 1.65
Date; 2002/1/11 code; 34.9781 47.2428 PW; 1.98
Date; 2002/1/11 code; 34.9705 47.2539 PW; 1.47
Date; 2002/1/11 code; 34.9705 47.2988 PW; 2.05
And finally the average of PW for all points in 2002/1/11 is 2 mm.
Precipitable Water (PW) obtained of the zone under the
study by MODIS in Jan the 11th, 2003
||Precipitable water (PW) fitting obtained by MODIS on
average precipitation (p) in Kermanshah, curve (R2 = 0.51)
is the best PW fitting by MODIS
RESULTS AND DISCUSSION
Czys and Scott (1993) determined the threshold of cloud seeding
with p and instability indices, also Gao and Goetz (1990), Costa et
al. (2001), Simoenov and Georgiev (2003), Manzato and Morgan (2003)
and Krauss and Santos (2004) studied on instability indices (CAPE, KI,
SI,TT, PW), Platnich et al. (2003), Gao and Kaufman (2003) and
King and Bock (2003) have studied on MODIS data and Sajjadi (2008) introduced
the suitable factor (PW) for cloud seeding.
In this study after obtaining the amounts of PW by MODIS in the rainy
days (17 cases) and the amount of ground P on these days by PW fitting
index on the average of P, the appropriate threshold of cloud seeding
was obtained in each case. The amounts for PW and the average of P were
calculated as 25, 50 and 75%.
||The amount of precipitable water (PW, mm) by MODIS and
the average precipitation (P, mm) in Kermanshah of specific percentages
Using these amounts, it can be calculated
that the index amount is indicative of how much the downpour of the different regions are.
The best PW fitting obtained by MODIS on P average in Kermanshah (17 cases
of study) is shown in Fig. 5. The appropriate threshold
for cloud seeding of the index of PW measured by the MODIS in Kermanshah
based on the curve, the best fitting in Fig. 5 is almost
12 mm. Based on Table 1 the amount of first quarter
of PW and average P are 16 and 9 mm. As it is clear from Table
2 when the PW is 32 mm, the amount of expected P is 25 mm although
Data by MODIS is related to the water vapor absorption in thick clouds.
||The relationship between the precipitation water (PW,
mm) by MODIS and probability of different precipitations (P, mm) in
The greatest source of error is due to the uncertainty of the spectrum
of reflections on the surface targets and the unclear amount of fog Fraser
and Kaufman (1985).
The amounts of PW in Kermanshah was obtained by MODIS 12 mm.
The proportion of P obtained from the PW in Kermanshah: 20 by MODIS.
MODIS itself shows a 5 to 15% of error, in the amounts obtained is due
to some reasons: Information by the PW in MODIS were obtained while passing
the region and in limited dates when the cloud may not have enough thickness
for the droplets to grow or have passed that stage, also in foggy weather
there may be more errors. The information on water vapor absorption by
MODIS in thick clouds is valid.