Cumulonimbus Anvil in Summer Asia Detected by TRMM PR
Fu Yunfei, Liu Peng, Cao Aiqin, Feng Sha, Liu Xiantong, Liu Qi, Wang Yu
University of Science and Technology of China, Hefei，Anhui 230026, China
Abstract
Cases Analysis
The precipitation type of “others” defined by Tropical Rainfall Measuring
Mission (TRMM) Precipitation Radar in the product 2A25 has been neglected
for a long time. So it’s unknown what their physical significances are. Based on
cases analysis and statistics analysis, the “others” in summer Asia of the last
ten years was investigated. Case analysis indicates that profiles of the “others”
show the shape of cumulonimbus anvil, i.e. profile peak (about 0.6～1.0mm/h)
appearing at 8~10km altitude, together with mean reflectivity over 0.8 and
mean infrared brightness temperature below 215K. Based on the features of
cumulonimbus anvil profiles, statistics on cumulonimbus anvil is made under
the definition of accumulative total rain rate greater than 1 mm/h above 5km
altitude for each “others” profile. Results reveal that cumulonimbus anvil
samples are near 70% in the “others”. Furthermore, the occurring frequency of
cumulonimbus anvil ranges 0.1%～0.4% in summer Asia, which is at least
over a tenth part of convective precipitation frequency in summer Asia. Results
also show that the frequency of cumulonimbus anvil over land is greater than
that over ocean. Generally, the averaged thickness of cumulonimbus anvil is
about 3~4km, its bottom is located at 6km altitude while its top altitude about
10~12km. Statistical calculations point out mean reflectivity from 0.8 to 0.9 and
mean infrared brightness temperature below 220K for cumulonimbus anvil.
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Statistics Analysis
(a)
32
(b)
The figure on the left indicates the ratio
distributions of cumulonimbus anvil samples to
total samples of the “others” in summer Asia
based on our anvil definition. On the whole,
ratio of anvil samples occupies 60~90% (over
land) and 50~80% (over ocean) to total
samples of certain “others”.
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Latitude
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29
30
28
Convective
Other
Stratiform
27
26
115
24
116
117
118
119
120
29
28
109
(c)
110
111
112
113
114
(d)
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Latitude
23
22
33
21
32
Occurring
frequency
distribution
of
cumulonimbus anvil ranges 0.1% ～ 0.4% in
summer Asia of the last ten years , which is at
least over one tenth part of convective
precipitation frequency in summer Asia.
Results also show that the frequency of
cumulonimbus anvil over land is greater than
that over ocean.
20
31
19
Data and Methodology
113
114
115
116
117
Longitude
Fig. 1
Fig.2 Near surface rain rate of the
four
convective
precipitation
systems observed by TRMM PR
marked with time and swath
number.
Table 1 Occurrence time, location
and pixel numbers of the four
convective precipitation systems for
“other”
type,
convective
and
stratiform precipitation detected by
TRMM.
114
116
118
120
122
Longitude
16
Height (km)
14
(a)
12
10
8
6
4
2
.2
.4
.6
.8
1.0
1.2
1.4
16
14
(b)
12
10
8
6
4
2
2
4
6
8
10
12
14
16
14
Height (km)
Samples are between
10 and 200 in most part
of Asia as shown in
Fig.1. There are 70%
and 80% grids with
samples between 50
and 200 over ocean
and land except Tibetan
Plateau, respectively.
Statistics in this study is
significant effect based
on the distribution of
these samples.
118
Above figure shows pixel distribution of convective precipitation, stratiform
precipitation and “other” type precipitation in the four convective systems.
Obviously, “others” occurs in side of the convective systems or convective
precipitation blocks, which implies intuitively that these “others” pixels are
cumulonibmus anvils.
Height (km)
TRMM standard products, 2A25 and 1B01, derived from TRMM PR and VIRS
in ten boreal summers from 1998 to 2007 are used in this study. Collocation of
two data sets is made by merging adjacent VIRS pixels to match one PR pixel
using an appropriate distance-weighted function. In this way, each precipitation
profile observed by PR has corresponding signals of VIRS, which helps to know
the top information of precipitating clouds. Based on vertical pattern of the
profiles (i.e., V-method, Awaka et al., 1997) and on horizontal variability of the
echo (i.e., H-method, Steiner et al., 1995), rain pixels detected by PR are
classified into three types, convective, stratiform, and ‘‘others’’, Among the
three types, “others” is defined as those that do not meet the definition of either
stratiform or convective rain, i.e. the profile of ‘‘others’’ do not have brightband
near the freezing level and radar reflectivity in the beam exceeds a
predetermined value of 39 dBZ. For “others”, only certain kind of “others” that
marked with number 300 in 2A25 dataset is selected as plotted in figure 1.
To identify cumulonimbus anvil from convective precipitation system, firstly,
four convective systems shown in figure 2 and table 1 are investigated. Then,
statistics of cumulonimbus anvil is made in Asia （60°E~160°E，0°~40°N）
statistics on cumulonimbus anvil is made under the definition of accumulative
total rain rate greater than 1 mm/h above 5km altitude for each certain “others”
profile
Lab of Satellite Remote Sensing
& Climate Environment
(c)
Case
Case
Case
Case
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(No.32565)
(No.60407)
(No.60696)
(No.61003)
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Left figure gives Mean
precipitation profiles of the
“others”,
convective
and
stratiform for the four systems
from case 1 to case 4 marked
with swath number of TRMM
observations.
Mean profiles of “others”
show clear differences from
those convective and stratiform.
Profile features of the “others”
are their rain rate peak (about
0.6~1.0 mm/h) appearing at
8~10km altitude, less then
0.3mm/h rain rate below 5km
and
above
11km.
These
features confirm the anvil
represented by the “others” in
the four convective systems.
Right
figure
shows
heightlongitude and height-latitude crosssection of rain rate (unit: mm/h) in
cumulonimbus anvil along 5°N,
15°N, 30°N and along 90 ° E, 115 °
E, 140 ° E in summer Asia.
Generally, the averaged thickness
of cumulonimbus anvil is about
3~4km, its bottom is located at 6km
altitude while its top altitude about
10~12km.
Rain Rate (mm/h)
Distributions of the mean
reflectivity at 0.63μm (left panel)
and mean infrared brightness
temperature at 10.8 μm (right
panel) for anvil (a, d), convective
precipitating clouds (b, e) and
stratiform precipitating clouds (c,
f) in summer from 1998 to 2007
point out mean reflectivity from
0.8 to 0.9 and mean infrared
brightness temperature below
220K for cumulonimbus anvil.
Mean reflectivity and infrared brightness temperature of anvil, convective
precipitation and stratiform precipitation in the four convective systems are
shown in above table. Mean reflectivity and far infrared brightness temperatures
in the Table confirm these anvils ulteriorly in their higher reflectivity and lower
temperature than those of convective and stratiform precipitation.
Acknowledgments
TRMM data sets were provided by TRMM Science Data and Information System at the NASA Goddard
Space Flight Center and JAXA/EORC. This research has been jointly supported by NKBRPC grant
2004CB418304, Special Funds for Public Welfare of China grant GYHY-QX-2007, and NSFC grants
(40730950, 40625014, 40605010,40805008).