A Numerical Study of Macro and Micro Structures of Stratus Precipitation Cloud
in Spring of Shanxi Province
Peiren Li (1), Junxia Li (1), Lijun Jin (1), Dongdong Shen (1), Gang Ren (1)
(1)Weather Modification Office of Shanxi Province , Taiyuan ,China, 030032, [email protected]
1
Introduction
The CAMS mesoscale cloud model was
introduced and Started for business operation in 2009
of Shanxi Province, China. The main products of the
CAMS mesoscale cloud model include temperature,
wind field, height field, water vapor field and the
horizontal and vertical distribution of different kinds of
cloud particles. For ice crystals, the model can give the
ice crystals number concentration at a certain height,
and for other hydrometerors, the model can give the
ratio water content. The model use T213 forecast data
as initial data, and the resolution is 10km.
This article chose a spring stratus cloud
precipitation process on May 16th~17th, 2010, in Shanxi
Province as an example for analysis using the output
data from the CAMS mesoscale cloud model. We
focused on the macro and micro Structures of the
stratus cloud, especially the vertical physical structures
of the stratus cloud and the precipitation. And finally, we
summed up the macro and micro structure features of
this stratus cloud and precipitation in spring.
2 Ground accumulated precipitation (From 8:00
am on 16th to 8:00am on 17th, May,2010)
Most areas of Shanxi province had significant
precipitation on May 16th~17th, 2010. Most cities and
counties had the rainfall of 0.1~25 mm in 24 hours. The
maximum precipitation occurred in Jiexiu County, and
the 24 hours accumulated precipitation was up to 60
mm.
Figure 1 is the 24 hours accumulated precipitation
forecast graph and the graph of real accumulated
precipitation on May 16th~17th.(The left is the numerical
forcast product, and the right one is the real situation)
Contrasting the precipitation range and intensity of the
forecast with the real precipitation accumulation on that
day we can see that both are coincided better. Strong
precipitation appeared in the central and southeast
areas of Shanxi Province
3
Numerical simulation analysis
3.1 The horizontal distribution characteristics of
the stratus cloud
(1) The distribution of the vertical integrated cloud
th
water from 16:00pm on May 16 to 08:00am on May
th
17 (Fig.2). We can see from fig.2 that the big range of
stratus clouds moved to Shanxi province from the west
to the east. The most areas of Shanxi province had
been covered with stratus clouds gradually at the time
th
to 8:00am,17 .The areas with rich cloud water were
located in the central and southern, especially in the
southeast of the province.
(2) The distribution of supercooled cloud water at
500hpa height.(Fig.3 is the cloud water distribution at
th
th
500hpa at 18:00pm on 16 and 8:00am on 17 .The
shadow is the ratio water content of the cloud (g/kg),
the red lines are temperature isolines). From fig.3 we
can see, the temperature was about -10℃ at
500hpa.The distribution of the supercooled cloud was
uneven. The cloud water became riched from 18:00pm
on 16th, and the areas with rich supercooled cloud
water mainly located in the south and central part of the
north of the Province. The ratio content of the
supercooled cloud water was about 0.1~0.7g/kg.
(3)The distribution of ice crystals at 500hpa.(Fig.4
is the number concentration distribution of ice crystals
at 500hpa at 18:00pm and 21:00pm on May 16th. And
the shadow is the number concentration distribution of
ice crystals ).Fig.4 showed that there had a small
amount of Ice crystals distributed unevenly at 500hpa
height. Combined with fig.3 we can see that the
supercooled cloud water content was relatively rich and
the ice crystals concentration was relatively lower. This
type of cloud structures were with better potential of
artificial precipitation.
3.2 The vertical structure and
characteristics of the clouds
temperature
Numerical simulation results showed that the
height of the clouds with rich supercooled water was
commonly above 700hpa. The thickness of the
supercooled cloud water layer was about 4000 meters,
and the temperature of the layer was about 0℃～-20 ℃.
The ratio water content of the layer was about
0.4g/kg～0.7g/kg. There had a small amount of ice
crystals distributed unevenly above 500hpa height. The
0℃ layer was at 600hpa, and the snow(or supercooled
water)was very rich above the 0℃ layer. There was
existing a strong vertical updraft airflow in the cloud,
and the content of snow and ice crystal was very big in
the strong updraft airflow areas. In the supercooled
area, a lot of ice crystals could stretch up to the height
of which temperature was below -40 ℃.The rich snow
area appeared above zero layer, and the maximum
snow content could reach to 0.21g/kg. Sleet appeared
mainly between 750~450hpa, the maximum ratio water
content of sleet could reach to 0.35~0.45g/kg. The sleet
melt to raindrops below the 0℃ layer. The rainfall
appeared below 700hpa, and the intensity of the rainfall
was distributed unevenly. There were a part of ice form
particles involved in the precipitation.
3.3 Research of the micro physical structure of the
clouds
According to the distribution of the stratus clouds
and the 24hours ground accumulated precipitation in
Shanxi Province from May 16th to 17th, we chose two
stations of Taiyuan City and Jiexiu County to study the
vertical distribution state of the different kinds of
hydrometerors, and analyzed the physical structures of
the hydrometerors using the numerical simulation
products.
(1) Fig.5 is the numerical simulation results of
vertical distribution of the hydrometerors on May 16th
to 17th of
Taiyuan station(qc—cloud water ，
qr—raindrops，qg—sleet,qs——snow，qi—ice crystals).
We can see from fig.5 that various kinds of
hydrometerors were mostly concentrated between the
650hpa to 400hpa at 18:00～22:00pm on May 16th, and
the amount of the hydrometerors was small. From May
17th, the hydrometerors began to increase gradually.
We can see from the picture of 6:00am on May 17th,
there were two or more than two maximum peaks of the
cloud water distribution, which indicated that the cloud
water was distributed unevenly at the time, and the
cloud displayed as multi-layer, and there may have fault
zones at different height of the clouds. In addition, a
large amount of snow crystals of the clouds appeared
above 600hpa, and the thickness of the snow layer was
very deep, extended from 600hpa to nearly 200hpa,
which indicated that the cold process was strong in the
clouds. And, the distribution of the snow was
continuous，the snow distribution of all the pictures had
one maximum peak between 450hpa and 500hpa.The
maximum ratio water content of snow was about
0.2-0.35g/kg. A small amount of ice crystals and sleet
existed up and below the snow. Ice crystals were
mainly distributed above 350hpa height, and the
content of ice crystals was very few from the graph.
From 12:00am on 17th, the sleet increased gradually
under 400hpa height, and reached to the maximum
peak at 600hpa.Obviously, a small amount of ice
particles were involved in the precipitation. The rain
appeared from 550hpa and increased downward
gradually, and the maximum content of rain appeared
at 850hpa.
Analyzed the disposition of the water content of
rain, cloud water and various kinds of ice particles, we
could get the conclusion that the cold process was
stronger in the cloud, and there were also existed part
of the warm cloud process. It showed that a distinct
"Seeder-feeder" process was existing during the ice
and snow particles dropping from the top to the down in
the cloud. In the high-level, the content of cloud water
was higher, and the cloud water provided superior
"supply" as a good growth conditions for the ice, snow
particles seeding from the top. At the same time, we
can see at the bottom of the cloud water area, there
were a large amount of rain with a small amount of
sleet coexistence. The rain water content was larger,
and rainfall had appeared on the ground.
(2)The maximum accumulated precipitation of 24
hours appeared in Jiexiu station that day. Fig.6 is the
numerical simulation results of vertical distribution of
the hydrometerors from May 16th to 17th of Jiexiu
station.
From fig.6 we can see that a small amount of ice
crystals appeared above 500hpa, and the maximum
content was about 0.005g/kg. A lot of the cloud water
mainly distributed above 850hpa, and the content was
very rich, the deep cloud water layer with too much cold
cloud water extended upward to about 400hpa height.
The distribution of cloud water content was uneven.
there are two or two more peaks, and the maximum
water content was up to 0.7g/kg. Two more peaks in
vertical showed that there may have fault zones at
different height of the clouds. The snow appeared from
600hpa and the content was large. The deep snow
layer extended to the higher altitude, which indicated
that the cold cloud process was very strong, and the
rainfall was mainly composed of the cold cloud
precipitation. The distribution of snow was continuous,
and the peak located at about 400-500hpa, the
maximum content was about 0.35g/kg. And the peak of
the cloud water content was at 650-700hpa height. So,
the snow peak height was higher than the height of
cloud water peak. Sleet appeared below 450hpa and
increased downward obviously. The peak of sleet
content was at about 600-550hpa, and the maximum
content was more than 0.15g/kg. The sleet decreased
to the minimum below 850hpa. The rain began to
appear from 550hpa and increased downward to the
ground. The precipitation accumulation was very big,
which was benefit from the large amount of
hydrometerors resources, and a lot of ice form particles
were also involved in the rainfall. From 11:00am on 17th,
all of the ice, snow, sleet and ice particles already
began to decrease, and the cloud water was still rich.
Later from 13:00pm, the hydrometerors gradually
decreased. From the pictures of 13:00pm and 14:00pm,
except for a small amount of cloud water there was no
other hydrometerors existing. And the distribution of
cloud water was extremely uncontinuous. There were
no rain and sleet, and the precipitation tended to stop,
and later, nearly all hydrometerors were gradually
disappeared.
According to the distribution condition of
hydrometerors in Jiexiu station, the precipitation mainly
composed of cold cloud precipitation process. From the
high and low level structure of snow and cloud water,
the snow melt to supercooled cloud water during the
process of falling down. So, the cloud water content
was increased, and the height of snow content peak
was higher than the height of cloud water content peak.
Sleet was transformed from snow, and grown up
through
the
process
of
collision
and
freezing with supercooled cloud droplets. The rain still
mainly came from the conversion of the melting
process of ice, snow, sleet etc. from high altitude, and
partly from the cloud water transformation.
4 Conclusion
(1) The rainfall on May 16th to 17th ,2010, in Shanxi
Province was mainly came from cold stratus cloud
precipitation. The cloud contained a lot of supercooled
water, and the thickness of the rich supercooled water
layer was about 4000～6000 meters. The temperature
of the supercooled layer was about 0～-20℃, and the
ratio content of the supercooled cloud water was about
0.4 ～ 0.7g/kg, within some ice crystals distributed
unevenly.
(2) The structures of the stratus precipitation cloud
can be roughly divided into three layers. The first
layer(upper layer)was mainly composed of ice crystals
and a little snow, and the snow, sleet, and supercooled
cloud water were mixed in the second layer(middle
layer), and the third layer(lower layer)was mainly of
liquid raindrops.
(3) In the early period of the cloud development,
the boundary of the first layer and the second layer was
located at 350～550hpa height. The second layer was
mainly composed of the deep and large amount of
snow, and mixed with a little sleet. Along with the
growth of the snow and sleet melting and landing, the
raindrops in the third layer(warm layer)were led to
increase gradually. And in the later stages of the
precipitation, snow and sleet content of the second
layer decreased, and the water supply from the cold
cloud was not as enough as early, and the clouds
gradually appeared stratified. So, the precipitation
weakened gradually and stopped finally. The sleet
came from the transformation of the deep snow layer
according to the vertical distribution of rain, cloud water,
snow and sleet. The large amount of ground rainfall
mainly came from the melting of snow, sleet, and some
ice particles of the second layer, and part of the
precipitation was from the cloud water transformation.
Of the whole rainfall process, the supercooled cloud
water, snow and sleet in the second(middle) layer gave
the largest contribution to the precipitation
simulated supercell storms. J. Atmos. Sci. 61: 1596-1609.
2004.
Gilmore, M.S., Straka, J.M., Rasmussen, E.N., Precipitation
and evolution sensitivity in simulated deep convective
storms: comparisons between liquid-Only and simple ice
and liquid phase microphysics. J. Mon. wea. Rev.,
132,1897-1916. 2004.
Mcfarquhar, G.M., Henian Zhang, Gerald Heymsfield,
Robbie Hood, Jimy Dudhia, Halverson, J.B., and Frank
Marks JR., Factors affecting the evolution of Hurricane
Erin (2001) and the distributions of hydrometeors: role of
microphysical processes. J. Atmos. Sci. 127:127-150.
2006.
Locatelli, J. D., and P. V. Hobbs, Fall speeds and masses of
solid precipitation particles. J. Geophys. Res., 79,
2185-2197. 1974.
Mitchell,D. L., Use of mass- and area-dimensional power
laws for determining precipitation particle terminal
velocities. J. Atmos. Sci., 53, 1561-1580. 1996.
Khvorostyanov, V. I., and J. A. Curry, Terminal velocities of
droplets and crystals: Power laws with continuous
parameters over the size spectrum. J. Atmos. Sci., 59,
1872-1884. 2002.
Figuers
Fig.1 The 24 hours accumulated precipitation forecast
graph and the graph of real accumulated precipitation on
th
th
May 16 ~17 .
References
Bennetts, D. A., and F. Rawlins, Parameterization of the ice
phase in a model of midlatitude cumulonimbus convection
and its influence on the simulation of cloud development.
Quart. J. Roy. Meteor. Soc., 107, 477-502. 1981.
Lord, S. J., and J. M. Lord, Vertical velocity structure in an
axisymmetric, nonhydrostatic tropical cyclone model. J.
Atmos. Sci., 45, 1453-1461. 1988.
Mcfarquhar G. M., Black R. A., Observations of particle size
and phase in tropical cyclones: implications for mesoscale
modeling of microphysical process. J. Atmos. Sci., 61:
422-439. 2004.
Van Den Heever, Cotton, W.R., The impact of hail size on
Fig.2 Distribution of the vertical integrated cloud water from
th
th
16:00pm on May 16 to 08:00am on May 17 .
Fig.3 The cloud water distribution at 500hpa at 18:00pm on
th
th
16 and 8:00am on 17 .
Fig.4 The number concentration distribution of ice crystals
th
at 500hpa at 18:00pm and 21:00pm on May 16 .
Fig.6
The numerical simulation results of vertical
th
th
distribution of the hydrometerors from May 16 to 17 of
Jiexiu station.
Fig.5
The numerical simulation results of vertical
th
th
distribution of the hydrometerors on May 16 to 17 of
Taiyuan station.