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Ice Crystal Habits and Growth Processes in Stratiform Clouds with Embedded ConvectionExamined through Aircraft Observation in Northern China
SHICHAO ZHU
Key Laboratory for Cloud Physics, Chinese Academy of Meteorological Sciences, Beijing, and Key Laboratory for
Aerosol-Cloud-Precipitation of China Meteorological Administration, Nanjing University of Information Science
and Technology, Nanjing, and Anhui Weather Modification Office, Hefei, China
XUELIANG GUO, GUANGXIAN LU, AND LIJUN GUO
Key Laboratory for Cloud Physics, Chinese Academy of Meteorological Sciences, Beijing, China
(Manuscript received 8 July 2014, in final form 4 January 2015)
ABSTRACT
Ice crystal habits and growth processes in two cases of stratiform clouds with embedded convection are in-
vestigated using data observed simultaneously from three aircraft on 18 April 2009 and 1May 2009 as part of the
BeijingCloudExperiment (BCE). The results show that themajority of ice crystal habits found in the two cases at
temperatures between 08 and2168C included platelike, needle column, capped column, dendrite, and irregular.
Amixture of several ice crystal habitswas identified in all of the clouds studied.However, the ice crystals recorded
in the embedded convection regions containedmore dendrites and possessed heavier riming degrees, and the ice
crystals identified in the stratiform clouds contained more hexagonal plate crystals. Both riming and aggregation
processes played central roles in the broadening of particle size distributions (PSDs), and these processes were
more active in embedded convection regions than in stratiform regions. However, riming was more prevalent in
the 18 April case than aggregation, though aggregates were evident. In contrast, the 1 May case had a more
dominant aggregation processes, but also riming.With the decrease in height, PSDs broadened in both embedded
convection regions and stratiform regions, but the broadening rates between 4.8 km (T ’ 211.68C) and 4.2 km
(T ’ 288C) were larger than those between 4.2 km (T ’ 288C) and 3.6 km (T ’ 258C). In addition, the
broadening rates of PSDs in the embedded convection regions were larger than those in the stratiform clouds, as
the aggregation and riming processes of ice particles in embedded convection regions were active. High super-
cooled water content is critical to enhancing riming and aggregation processes in embedded convection regions.
1. Introduction
Stratiform clouds with embedded convection consti-
tute an important precipitation system that typically has
a long lifetime and that may bring either continuous or
intermittent precipitation to a large region (Hobbs and
Locatelli 1978; Matejka et al. 1980; Hobbs et al. 1980;
Herzegh and Hobbs 1981; Evans et al. 2005). Because of
the presence of high ice crystal concentrations and su-
percooledwater content in embedded convection regions
(Evans et al. 2005; Hobbs and Rangno 1990; Matejka
et al. 1980), these systems can improve the precipitation
efficiency of stratiform clouds by up to 20%–35%
(Herzegh and Hobbs 1980; Houze et al. 1981; Rutledge
and Hobbs 1983). Although ice crystal habit is central to
understanding the generation and growth processes of
precipitation particles in these clouds, it is difficult to
obtain accurate characteristics of crystals and their con-
tinuous growth processes.
At present, the airborne observation is an important
method used to obtain information on ice crystal habits
and growth mechanisms in natural clouds. In deep
stratiform clouds, the formation and growth processes of
ice particles are complex. Such processes include riming
(Ono 1969), the freezing of large drizzle drops (Korolev
et al. 2004), and the aggregation of ice crystals (Takahashi
and Fukuta 1988). However, the growth processes of ice
crystals in stratiform clouds with embedded convection
are more complex.
Corresponding author address:XueliangGuo, ChineseAcademy
of Meteorological Sciences, No.46, Zhongguancun Street, Haidian
District, Beijing 100081, China.
E-mail: [email protected]
MAY 2015 ZHU ET AL . 2011
DOI: 10.1175/JAS-D-14-0194.1
� 2015 American Meteorological Society
A wide variety of particle habits were observed in both
convection and stratiform regions of clouds at tempera-
tures from 08C to;2208C (Stith et al. 2002). McFarquhar
and Black (2004) analyzed data recorded by Particle
Measuring Systems (PMS) two-dimensional cloud (2DC)
probe placed in tropical cyclones and found that the
composition (i.e., graupel or snow), number, and size of ice
particles can vary substantially in convection and strati-
form regions. In stratiform regions, small ice crystals, col-
umns, and medium-sized graupel were observed, while in
convection regions, medium to large graupel, aggregates,
and raindrops were identified. Stark et al. (2013) collected
solid precipitation habits at ground during two winter
storms in coastal, extratropical cyclones and showed that
convective seeder cells resulted in relatively cold
(,2158C) ice crystal characteristics (side planes, bullets,
and dendrites). Needlelike crystals were prevalent during
the pre-band period when the maximum vertical motion
occurred in the 258 to 2108C layer. Moderately rimed
dendritic crystals were observed at snowband maturity.
Ice crystal habits heavily depend on the cloud tem-
peratures at which the ice crystals form. Hogan et al.
(2003) identified pristine planar crystals in aircraft ob-
servations of a multilayered altocumulus cloud with
a cloud-top temperature (CTT) of2158C and found that
at a CTT of 2248C, crystals formed as complex poly-
crystals. Carey et al. (2008) sampled several altocumulus
cloud layers at temperatures between 2128 and 2268Cand found that pristine planar crystals developed close to
the top of the cloud. Westbrook and Heymsfield (2011)
summarized previous studies and concluded that single
pristine crystals are common in thin, mixed-phase clouds
and that the critical temperature for polycrystal particles
lies in the range of approximately 2208 to 2268C, de-pending on the characteristics of the individual cloud.
The findings of laboratory (Fukuta and Takahashi
1999; Heymsfield et al. 2010; Magono and Iwabuchi
1972; Pruppacher and Klett 1997) and field (Evans et al.
2005; Heymsfield et al. 2002; Stith et al. 2002; Woods
et al. 2008) studies indicate that ice crystals formed
between 08 and 248C are predominantly plates, while
those formed between248 and288C are predominantly
needle columns. Bailey and Hallett (2009) produced
a new ice crystal habit diagram based on field and lab-
oratory datasets while retaining descriptions of ice
crystal habits in temperatures above 2188C from older
diagrams. The authors proposed that the ice crystal
form changes from plate (from 08 to 248C) to column
(from 248 to 288C) and then to platelike (plate or
dendrite, from 288 to 2228C).A wide variety of particle growth processes have also
been observed in convection and stratiform regions of
clouds. Analyzing PMS probe data in midlatitude
cyclones, Herzegh and Hobbs (1980) found that riming
growth was dominant in embedded convection regions
where updrafts reached 60cms21, while deposition and
aggregation growth dominated at lower layers where up-
draft velocities were less than 15cms21. Analyzing 2DC
and two-dimensional precipitation (2DP) probe data from
winter storms on the coast of Newfoundland, Canada,
Lawson et al. (1993, 1998) showed that ice crystals grow
rapidly through aggregation processes in embedded con-
vection regions, and similar ice crystal growth character-
istics were found in Arctic clouds during the summer
(Lawson and Zuidema 2009). Studying 2DC and cloud
imaging particle (CIP) probe data from a strong cyclonic
storm over the northeastern Pacific Ocean, Evans et al.
(2005) showed that above the melting layer, vapor de-
position is the dominant growth process in the rainband.
Ice particle growth via riming was found to be negligible,
while significant ice particle aggregation occurred in the
region just above the melting layer. Therefore, dominant
ice crystal growth processes found in different cloud types
were not consistent with previous studies.
The Beijing Cloud Experiment (BCE), a component
of the National Science and Technology Pillar Program
(2006–11) Key Project, was conducted from April to
May 2009 in the Zhangjiakou area, which is located in
the upstream area of Beijing in northern China.
Throughout the experiment, three aircraft observed
aerosol and cloud features simultaneously at different
cloud levels, generating valuable data on aerosol–cloud
interactions in this area (Lu and Guo 2012). Northern
China is located in the middle latitude and it has
a complex precipitating cloud system including both
convective clouds (e.g., Fu andGuo 2012) and stratiform
clouds with embedded convection. The cloud system in
this region is also heavily affected by aerosols and ur-
banization processes owing to rapid industrialization
and population growth (Guo et al. 2006, 2014).
Ice crystal habits and growth processes in two cases of
stratiform clouds with embedded convection were in-
vestigated on 18 April 2009 and 1 May 2009 through
simultaneous observation from three aircraft during the
BCE. The aircraft tracks were layered with radar echoes
to reveal ice crystal distribution and growth processes in
different cloud regions (convection and stratiform) and
at different temperatures and cloud levels. The broad-
ening rate of vertical particle size distribution (PSD) in
different cloud regions was quantitatively calculated
using data collected through simultaneous observations
from three aircraft at different levels of clouds.
A brief description of the instruments and field ex-
periment are provided in section 2. Section 3 introduces
the synoptic weather conditions and the properties of
the cloud system observed. The ice crystal habits
2012 JOURNAL OF THE ATMOSPHER IC SC IENCES VOLUME 72
observed from the three aircraft are listed in section 4,
and the distribution and growth processes of ice crystal
habits are presented in section 5. Section 6 provides the
calculations and discusses the broadening rate of PSD.
A conclusion and discussion are provided in section 7.
2. Instruments and field experiment
Throughout the BCE field observations, simultaneous
measurements were conducted through ground-based
meteorological stations, radar, and aircraft observation.
A schematic diagram of the study area and the obser-
vational facilities used for the BCE are shown in Fig. 1.
The aircraft employed in this experiment included the
Cheyenne III-A from the Shijiazhuang Weather Modi-
ficationOffice (number 3625), theDatongY-12 from the
ShanxiWeatherModificationOffice (number 3817), and
the Beijing Y-12 from the BeijingWeatherModification
Office (number 3830). The three aircraft departed from
airports in Zhangjiakou, Shijiazhuang, and Taiyuan,
respectively, and simultaneously collected data at dif-
ferent cloud levels within the study area.
During the experiment, two cold-frontal systems
passed through the study area on 18 April 2009 and 1
May 2009, respectively, and the dominant cloud type
over the study area was stratiform clouds with em-
bedded convection. The three aircraft simultaneously
observed aerosol, cloud condensation nuclei (CCN),
and cloud microphysics processes at different cloud
levels and collected valuable data on cloud micro-
physical properties in the area. Table 1 provides a list
of the instruments used aboard the three research
aircraft. All instruments were calibrated by Droplet
Measuring Technologies (DMT) in the United States
before the experiment was conducted (Lu and Guo
2012).
FIG. 1. Schematic of the observational region and facilities (the colors indicate the altitudes of terrain).
MAY 2015 ZHU ET AL . 2013
3. Synoptic weather conditions and properties ofthe cloud system observed
On 18 April 2009, a weak cold-frontal system passed
through the study area and produced stratiform clouds
with embedded convection regions over the study area.
The total rainfall recorded at the Zhangjiakou meteo-
rological station was 6.7mm. The synoptic weather
conditions at 0800 BT (Beijing time) on 18 April 2009
are shown in Fig. 2, and the black box shown in the
image denotes the study area. Figure 2 shows that on 18
April 2009, a weak trough at 500 hPa approached the
study area, and a high pressure center in the East China
Sea blocked the movement of the weak trough to the
southeastern direction. The wind at 500 hPa was domi-
nated by southwesterly winds. Figure 2b shows infrared
cloud images from satellite FY-2C at 1900 BT on 18
April 2009. The figure shows that the cloud band was
dispersed throughout the northeast–southwestern re-
gion, and the main cloud band was located in the
northern area of the Zhangjiakou region. Clouds with
nonuniform top developed over the study area.
The radar composite reflectivity shown in Fig. 3
demonstrates that the strong echo band was located
along the front boundary of the cloud system, which was
produced through low-level airflow convergence. A
stratiform cloud with a weak echo formed behind the
convection region. The entire cloud bandwas positioned
in the northeast–southwestern area and moved from
northwest to southeast. Some obvious strong echo re-
gions were embedded in the cloud band, and the maxi-
mum radar reflectivity of the embedded convection
region was approximately 50 dBZ, which was approxi-
mately 10–20 dBZ higher than reflectivities recorded in
surrounding stratiform clouds. Both aircraft 3817 and
3830 recorded observations from the front edge of the
cloud system, and the flight route of aircraft 3625 fol-
lowed a north–south loop through the cloud band.
On 1 May 2009, a stronger frontal system passed
through the study area and generated 6–10mm of total
rainfall in the study area. The synoptic weather condi-
tions at 0800 BT on 1 May 2009 are shown in Fig. 4. The
figure shows that on 1 May 2009, the 500-hPa level over
the study area was controlled by a trough (Fig. 4a).
Comparing these conditions with those of 18 April 2009,
the trough was more obvious and was not blocked by the
high pressure center located in the East China Sea.
Winds at 500 hPa were dominated by southwesterly
winds. Figure 4b provides a visible cloud image taken
from satellite FY-2C at 0900 BT on 1 May 2009 and
shows that themain cloud system,moving in a northwest
to southeast direction, had already moved out of the
study area. The cloud observed from the aircraft was
mainly located in the postfrontal region.
Figure 5 provides a superimposed image of radar
reflectivity at 0930 BT with flight tracks on 1 May 2009.
The figure shows that the entire cloud band assumed a
northeast–southwest formation and moved from north-
west to southeast. Similar to the case on 18 April 2009,
some obvious strong echo regions were embedded in the
cloud band, and the highest radar reflectivity in the em-
bedded convection region was approximately 40dBZ,
which is approximately 5–10 dBZ higher than the re-
flectivities in the surrounding stratiform cloud. The flight
route of aircraft 3625 was not recorded because the GPS
system in the planemalfunctioned during the experiment.
4. Ice crystal habits observed from three aircraft
Ice crystal habits were observed using theDMTCloud
Imaging Probe (CIP) and PMS 2DC, and larger ice
particles were observed via the DMT Precipitation Im-
aging Probe (PIP) and PMS 2DP. CIP and PIP are ba-
sically modified 2DC and 2DP, respectively (Field et al.
2006). A detailed description of the probe features can
be found in Table 1.
TABLE 1. Instruments and measurements collected aboard three BCE aircraft.
Instrument Variable Size range Resolution Aircraft
PCASP-100X Aerosol particles 15 bins, 0.1–3mm Changes in particle size 3625
SPP-200 Aerosol particles 30 bins, 0.1–3mm Changes in particle size 3830
CCN Counter CCN concentration 0.75–10mm Changes in particle size 3525, 3817, 3830
CAS Aerosol and cloud particles 30 bins, 0.6–50mm Changes in particle size 3830
CDP Cloud particles 30 bins, 2–50mm Changes in particle size 3817
FSSP-ER Cloud particles 15 bins, 2–47mm 3mm 3625
OAP-2D-GA2 Cloud and precipitation particles 62 bins, 25–1550mm 25mm 3625
CIP Cloud and precipitation particles 62 bins, 25–1550mm 25mm 3817, 3830
OAP-2D-GB2 Precipitation particles 62 bins,100–6200mm 100mm 3625
PIP Precipitation particles 62 bins,100–6200mm 100mm 3817, 3830
King-LWC Liquid water content (LWC) 0–5 g/m3 — 3625
Hotwire-LWC Liquid water content 0–5 g/m3 3817, 3830
AIMMS-20 Meteorological parameters — — 3817, 3830
2014 JOURNAL OF THE ATMOSPHER IC SC IENCES VOLUME 72
FIG. 2. Synoptic weather background on 18 Apr 2009: (a) geopotential height (gpm) and wind fields at 500 hPa and 0800 BT, (b) FY-2C
infrared cloud image at 1900 BT. The black square indicates the study area.
MAY 2015 ZHU ET AL . 2015
Typical ice crystal habits identified on 18April 2009 are
shown in Fig. 6. The ice crystal images were classified into
the stratiform clouds and embedded convection regions
according to radar reflectivity and LWC in order to iden-
tify differences of ice crystal habits between two regions.
Theplatelike ice habits in this study included both plate
(Bailey andHallett 2009; Kajikawa andHeymsfield 1989;
Woods et al. 2005) and small spheroid (Connolly et al.
2005). The identification of riming and aggregation
levels of ice crystals may roughly depend on their size
and density. The ice particles with large size and high
density are generally identified as heavily rimed ice
crystals, and those with large size and low density (with
clear structure) are classified as aggregate.
Ice crystal habits identified by three aircraft between
228 and 29.58C were predominantly platelike, needle
column, dendrite, and irregular. But needles and plates
could be identified at all temperatures and the only actual
difference is that of size. It can be seen from Fig. 6 that
most of the ice crystals identified in the stratiform clouds
were platelike and needle column and some dendritic
crystals could be also identified. However, in the em-
bedded convection regions, in addition to platelike and
needle-column crystals, more dendritic crystals existed
between 268 and 29.58C and more aggregate existed be-
tween248 and258C. This phenomenon suggests that the
aggregation process in the embedded convection regions
was active. In addition, it also can be seen from Fig. 6 that
the ice crystal images recorded in embedded convection
regions had higher density than those recorded in the
stratiform regions, suggesting that rimingwere also evident
and larger ice particles such as graupel might occur.
Ice crystal habits observed in this case are generally
consistent with previous laboratory research (Fukuta and
Takahashi 1999; Heymsfield et al. 2010; Magono and
Iwabuchi 1972; Pruppacher and Klett 1997) and field obser-
vations (Evans et al. 2005; Heymsfield et al. 2002; Stith et al.
2002; Woods et al. 2008) as well as with the new ice crystal
habit diagram developed by Bailey and Hallett (2009).
Another case of stratiform clouds with embedded
convection was identified in the study area on 1 May
2009 (Fig. 4). Figure 7 shows the typical ice crystal habits
recorded by three aircraft on 1 May 2009. The temper-
ature ranges identified in the cloud from aircraft 3625,
3817, and 3830 were from 2118 to –168, from 288 to–11.68, and from 08 to –118C, respectively.The ice crystal images recorded by aircraft 3625 at
temperatures between2118 and2168C in Fig. 7a indicate
FIG. 3. Superimposed image of radar reflectivity (shading) at 1900 BT with flight tracks recorded on 18 Apr 2009 (green line represents
3817 path, red line represents 3830 path, blue line represents 3625 path).
2016 JOURNAL OF THE ATMOSPHER IC SC IENCES VOLUME 72
FIG. 4. Synoptic weather background at 0800 BT on 1 May 2009: (a) geopotential height (gpm) and wind fields of 500 hPa, The black
square indicates the study area. (b) FY-2C visible cloud image at 0900 BT. The red square indicates the study area, the pink line indicates
the land boundary of China, and the blue line represents the Yellow River.
MAY 2015 ZHU ET AL . 2017
that the ice crystal habits were predominantly needle col-
umn, platelike, capped column, dendrite, and irregular. The
ice crystal images recorded by aircraft 3817 at temperatures
between 288 and 211.68C shown in Fig. 7b demonstrate
that ice habits in these conditions were predominantly
platelike, needle column, capped column, and dendrite. Ice
crystal images recorded by aircraft 3830 at temperatures
between 08 and 2118C indicate that the majority of ice
crystals were platelike, dendrite, and irregular. Heavily
rimmed ice crystals were common at these layers.
Differences of ice crystal habits recorded between the
stratiform clouds and embedded convection regions
were basically similar to those recorded on 18 April
2009. However, there were still some differences be-
tween two cases. The 18 April case had more heavily
rimed ice particles and 1 May case had more aggregate.
This will be discussed in detail in the following sections.
The ice crystal habits recorded in the embedded con-
vection regions contained more dendritic crystals and
possessed a heavier riming degree. In addition, the ice
crystals recorded in the stratiform clouds contained
more hexagonal plate crystals (shown in Figs. 7a,b).
In summary, the ice crystal habits sampled in the two
cases with stratiform clouds containing embedded con-
vection were complex; the ice crystal habits between
08 and 2168C were predominantly platelike, needle
column, capped column, dendrite, and irregular. This
indicates that although temperature may have an effect
on crystal habit, it may not be the primary factor.
It can be concluded from this comparison of ice crystal
habits in different clouds that a mixture of several ice
crystal habits can always be identified. However, the ice
crystal habits recorded in the embedded convection re-
gions contained more dendritic crystals and heavier
riming degree, and the ice crystals recorded in the strat-
iform clouds contained more hexagonal plate crystals.
Previous studies suggest that the characteristics of ice
crystal habits in different stratiform clouds with embed-
ded convection are different because of different cloud
conditions (e.g., temperatures, cloud layers, cloud tops,
LWC, etc.) (McFarquhar and Black 2004; Evans et al.
2005; Stark et al. 2013). The deep clouds with high cloud
top and low temperature could produce more complex
ice crystal habits such as bullet, dendrite, and aggregate.
5. Distribution and growth processes of ice crystalhabits
a. The 18 April 2009 case
Table 2 lists observation data recorded from the air-
craft on 18 April 2009. The three aircraft flew at differ-
ent cloud levels, and the maximum LWC recorded from
FIG. 5. Superimposed image of radar reflectivity (shading) at 0930BTwith flight tracks on 1May 2009 (green line represents 3817 path, red
line represents 3830 path).
2018 JOURNAL OF THE ATMOSPHER IC SC IENCES VOLUME 72
aircraft 3817 and 3830 both exceeded 1 gm23, suggesting
high LWC in the clouds. To investigate the distribution
and growth processes of ice crystal habits in the clouds,
a detailed description of the procedure through which
the three aircraft penetrated the clouds is discussed in
this section.
A cross section of radar reflectivity in the flight path
and relevant observed data recorded from aircraft 3625
on 18 April 2009 are shown in Fig. 8. Aircraft 3625 pri-
marily flew horizontally at 4.8 km (T ’ 268C) in the
early stage and then at 5.1 km (T ’ 29.58C) in the later
stage, penetrating several embedded convection re-
gions. Pristine ice crystal habits identified from the air-
craft were primarily platelike, needle column, and
dendrite between 268 and 29.58C. The cloud particle
spectra derived from 2DC and 2DP shown in Fig. 8b and
Fig. 8c indicate that high concentrations of large ice
particles were present in the embedded convection re-
gion. The formation and growth of these large particles
are difficult to document, but the properties of the ice
habits sampled from aircraft 3625 demonstrate that both
riming and aggregation processes were obvious in the
embedded convection regions. Figure 8d shows that
LWC was not uniformly distributed in the clouds and
high LWC corresponded well with embedded convec-
tion regions. The ice crystal riming degree was heavy in
the embedded convection region with high LWC, such
as that between 1715 and 1728 BT shown in Fig. 8a,
suggesting that riming growth was an important growth
process in the embedded convection regions. At the
same time, it can be seen from the 2DP images show in
Fig. 8a (such as 1727 BT) that the apparent aggregates
appeared between 268 and 29.58C, suggesting that ag-
gregation growth was also an important growth process
within the embedded convection region. But it can be
seen from the ice particle images shown in Fig. 8a that
riming was more prevalent in this case than aggregation,
though aggregates were evident. In contrast, the 1 May
case discussed later had a more dominant aggregation
processes, but also riming.
FIG. 6. Typical ice crystal images recorded by the three aircraft on 18 Apr 2009 (ice crystal
habits at 5.1 and 4.8 km were recorded by 2DC aboard 3625, those at 4.2 km were recorded by
CIP aboard 3817, those at 3.6 km were recorded by CIP aboard 3830).
MAY 2015 ZHU ET AL . 2019
Aircraft 3817 penetrated the clouds at lower layers in
248 to approximately 258C conditions on 18 April 2009.
As the hotwire-LWC equipment used on aircraft 3817 was
in poor condition, no LWC data are available. Figure 9
shows the radar reflectivity cross section in the flight path
and relevant spectra of cloud particles sampled through
CIP and PIP. Figure 9a shows that aircraft 3817 penetrated
both weak and strong embedded convection regions as
well as the stratiform region. The pristine ice crystals from
248 to approximately 258C were predominantly needle
column; however, a wide variety of ice crystal habits, such
as heavily rimed dendrite and ice aggregate, were also
sampled at these layers. From 1743 to 1745 BT, a weak
embedded convection region with a thickness of less than
2km and a cloud top at less than 5km were sampled. The
corresponding CTT was warmer than 288C and the 08–88C layers are suitable for plate and needle-column
crystal formation (Takahashi et al. 1991, 1986). In addi-
tion, most of the cloud particles were single crystals
similar to those recorded by the PIP probe at 1744 BT,
suggesting that the ice crystal aggregation process was
weak and that the growth process should be dominated
by deposition growth.
At 1748 BT, when the CTT was colder than 2138C,aircraft 3817 sampled lightly rimed dendritic crystals in
the cloud. Laboratory studies (Takahashi et al. 1991,
1986) and field (Bailey andHallett 2009; Heymsfield and
Kajikawa 1987) have shown that the optimal tempera-
ture for dendritic crystal formation is approximately
2158C. However, at 4.2 km, the temperature recorded
from aircraft 3817 was approximately 258C. Therefore,lightly rimed dendritic crystals likely fell from higher,
colder cloud layers.
From 1748 to 1750 BT, the heavily rimed and aggre-
gated crystals (such as the images recorded via CIP
probing at 1749 and 1750 BT) were sampled in the
strong embedded convection region, suggesting that
both riming and aggregation processes were important
in the strong embedded convection region.
Since the maximum reflectivity of this cloud system
reached about 50dBZ and with the cloud base tempera-
ture of 128C, cloud-top temperature of2288C (estimated
from radar data in Fig. 9), and LWC of 1gm23, it is
possible for occurrence of graupel in the lower regions of
the embedded convection. Graupel formation has been
found in several other studies with embedded convection.
Figure 10 shows the penetration data recorded by
aircraft 3830 on 18April 2009. From 1800 to 1805 BT, ice
crystal habits recorded at a layer of 3.6 km (T ’ 228C)was dominated by rimed and aggregated plates and
FIG. 7. Typical ice crystal images recorded by the three aircraft
on 1 May 2009: (a) images recorded by 2DC aboard 3625, (b) im-
ages recorded by CIP aboard 3817, (c) images recorded by CIP
aboard 3830.
TABLE 2. Observed results from aircraft taken on 18 Apr 2009.
Number Time (BT)
Altitude
(m) T (8C)LWCmv
(gm23)
3625 1614–1900 4800–5100 From 268 to –9.58 1.5
3817 1655–1904 4200 258 Data error
3830 1705–1855 2700–3600 From 58 to –38 1.1
2020 JOURNAL OF THE ATMOSPHER IC SC IENCES VOLUME 72
FIG. 8. The penetration data recorded by aircraft 3625 on 18 Apr 2009: (a)
cross-section of radar reflectivity for flight path, ice crystal images recorded
with 2DC (panel top) and 2DP (panel bottom), and T (black line); (b) 2DC
instantaneous spectrum; (c) 2DP instantaneous spectrum; and (d) LWC.
MAY 2015 ZHU ET AL . 2021
FIG. 9. The penetration data recorded by aircraft 3817 on 18 Apr 2009: (a) cross section of radar
reflectivity for flight path, ice crystal images recorded through CIP (panel top)and PIP (panel
bottom), and T (black line); (b) CIP instantaneous spectrum; and (c) PIP instantaneous
spectrum.
2022 JOURNAL OF THE ATMOSPHER IC SC IENCES VOLUME 72
FIG. 10. The cloud penetration data recorded by aircraft 3830 on 18
Apr 2009: (a) cross section of radar reflectivity for flight path and ice
crystal habits recorded through CIP, where black solid line represents
flight track, red dashed line represents the 08C layer; (b) CIP in-
stantaneous spectrum; and (c) PIP instantaneous spectrum, (d) temper-
ature (black) and LWC (blue).
MAY 2015 ZHU ET AL . 2023
needle columns in the embedded convection region
(Fig. 10a). Previous laboratorial studies (Pruppacher and
Klett 1997; Bailey and Hallett 2009) have shown that
temperatures at this layer are suitable for plate formation.
Thus, the aggregated plates recorded at this layer may
have formed locally because of the longevity of the
stratiform region. In addition, Fig. 10a shows that crystals
identified at 1803BT included somepristine columns. This
is an interesting finding given that most previous studies
(Bailey and Hallett 2009; Crosier et al. 2011) show that
this crystal habit typically forms at temperatures lower
than228C. Ice formation at this temperature is very rare.
A more plausible explanation could be a secondary ice
formation event driven by Hallett–Mossop processes.
Both aggregation and riming processes became active
when the aircraft passed from the shallow stratiform
region (1801 BT) to the relatively deep embedded
convection region (1804 BT) with an increase in super-
cooled cloud water (Fig. 10d). The corresponding
spectra recorded by the CIP and PIP probes also
broadened rapidly (Figs. 10b,c). From 1805 to 1811 BT,
the aircraft flew downward and passed through the
melting layer as it descended. A small number of melt-
ing ice crystals were recorded by the CIP probewhile the
aircraft passed through the melting layer. With the
melting of ice particles, the cloud particle spectra grad-
ually narrowed because of changes in particle diameters
in the transition from snow to raindrop form. From 1811
to 1820 BT, the aircraft flew at 2.7 km (T ’ 58C), andparticles at this layer were dominated by cloud and rain
drops. From 1813 to 1815 BT, PSD broadened again
owing likely to larger particles aloft melting into larger
raindrops with the increase of cloud top. Upon traveling
from 1815 to 1817 BT, the aircraft passed through a re-
gion of strong radar echo (.30 dBZ). However, at this
moment, the CIP and PIP probes malfunctioned, and
thus, the PSDs recorded in this region were incorrect,
and the particle images recorded at 1816 BT were
dominated by larger raindrops.
b. The 1 May 2009 case
Table 3 lists observations from the three aircraft re-
corded on 1 May 2009. The three aircraft flew at dif-
ferent cloud levels, and the maximum LWC identified in
this case were lower than those recorded on 18 April
2009, suggesting that the ice crystal riming process was
relatively weaker than the process recorded on 18 April
2009. Therefore, pristine ice crystal habits recorded on 1
May 2009 were much clearer. The flight route of aircraft
3625 was not recorded because the GPS system mal-
functioned during the experiment. Therefore, only the
cloud penetration data recorded by aircraft 3817 and
3830 will be discussed in this section.
Figure 11 shows the cloud penetration data recorded
by aircraft 3817 for 1 May 2009. It indicates that aircraft
3817 penetrated both stratiform and embedded con-
vection regions with temperatures ranging from 278 to211.68C throughout the flight. The CIP images show
that the ice crystal habits sampled in the stratiform cloud
region were predominantly plate and needle column
(Fig. 11a, 0925 BT, 1017 BT), and those observed in the
embedded convection regions were predominantly
dendrites (Fig. 11a, 0937 BT, 1026 BT). The ice crystal
images sampled by CIP and PIP show that both riming
and aggregation processes existed in the embedded
convection regions, but riming was not as strong
a growth process as aggregation.
The particle images recorded by PIP probe (Fig. 11a)
show that aggregates were very common in the em-
bedded convection region over a height range of 4.2 km
(T ’ 288C) to 4.9 km (T ’ 2128C), suggesting that ag-
gregation was also a primary growth process in the em-
bedded convection regions. At the same time, the regions
of stronger reflectivity (.20dBZ) contained larger ag-
gregates. For example, the aggregates recorded at 0937,
0942, and 1005 BT were identifiably larger than those
recorded at 0926, 0948, and 1017 BT, indicating that the
aggregation process was more active in the embedded
convection region than in the stratiform regions.
Riming growth at this layer also showed a nonuniform
distribution. The riming degrees of the ice crystals
identified at 0937 and 1000 BT were clearly heavier than
those recorded at 0934 BT. The LWC detected at 0937
BT were higher than 0.1 gm23, but the LWC at 0934 BT
were lower than 0.02 gm23, suggesting that the non-
uniform riming growth distributions found in the clouds
were caused by variations of LWC in the stratiform and
embedded convection clouds. These results echo those
of the 18 April 2009 case. After 0957 BT was reached,
the Hotwire-LWC malfunctioned, so there are no
available data on cloud LWC. However, the particle
images show that riming growth was still nonuniform,
which is consistent with the results of Stark et al.
(2013), who found that the riming degree of ice crystals
is influenced by cloud updrafts in extratropical cy-
clones. The authors also noted that heavy riming in
high updraft regions was caused by high supercooled
LWC in these areas.
TABLE 3. Observed results from aircraft taken on 1 May 2009.
Number Time (BT) Altitude (m) T (8C)LWCmv
(gm23)
3625 0827–1120 4800–5400 From 2118 to –168 0.16
3817 0846–1105 4200–4800 From 288 to –11.68 0.21
3830 0831–1134 1700–4900 From 48 to –128 1.0
2024 JOURNAL OF THE ATMOSPHER IC SC IENCES VOLUME 72
In embedded convection regions (such as at 0938 BT),
both riming and aggregation processes were active
(shown in Fig. 11a), and the PSDs recorded by PIP
probe broadened in the embedded convection regions
(Fig. 11c). Although both riming and aggregation pro-
cesses contributed to the PSD broadening, the particle
images recorded by PIP probes show that the aggrega-
tion process was more critical to the broadening of PSDs
at this layer. Therefore, comparing with 18 April case,
the 1 May case had a more dominant aggregation pro-
cesses but also riming.
The ice crystal habits at this layer were also strongly
affected by CTT, which varied from 288C at the lowest
cloud top of approximately 4.5 km (such as 0925 BT,
1017 BT) to approximately 227.38C at the highest
cloud top of approximately 7 km (such as 0935 BT,
1008 BT). In addition to plate, needle-column, and den-
dritic crystals, capped-column crystals also appeared as
the CTT was colder than2188C (Fig. 11a, 0934 BT). The
initial columns likely formed over a temperature range
of 2188 to 2258C, and then capped columns formed
as these initial columns fell through the planar-crystal
growth region where temperatures ranged from 2128 to2188C (Heymsfield et al. 2002).
The particle images recorded by PIP probe also show
that the large aggregates typically consisted of dendritic
crystals (Fig. 11a). Higher cloud tops (.6km) with
lower temperatures (2208–278C) are suitable for gen-
erating dendritic and capped-column crystals. Dendritic
aggregate more easily than other crystal habits and can
easily capture supercooled cloud droplets (Hashino and
Tripoli 2011; Hobbs et al. 1974). In addition, Fig. 11b
shows that the embedded convection regions with higher
cloud tops (such as 0933 BT, 1009 BT) often contained
more ice crystals than other regions, and high concen-
trations of ice crystals can facilitate the aggregation pro-
cess (Cooper and Lawson 1984; Dye et al. 1976; Holroyd
and Jiusto 1971). Because the embedded convection re-
gions with higher cloud tops contained more ice crystals,
especially dendritic crystals, PSD broadening should be
apparent and precipitation efficiencies should also be
higher. Hobbs et al. (1980) found that precipitation effi-
ciency in wide, cold-frontal rainbands with generating
cells reaches levels of at least 80%, while levels in warm-
sector and narrow, cold-frontal rainbands reach only
40%–50% and 30%–50%, respectively.
Figure 12 shows the cloud penetration data recorded
by aircraft 3830 on 1 May 2009. Although the crystal
habits recorded by CIP probe varied greatly as the flight
altitude of aircraft 3830 changed considerably, ice crys-
tals in this region were dominated by heavily rimed
dendritic and irregular particles. More dendritic crystals
were found in embedded convection regions (such as
FIG. 11. As in Fig. 9, but on 1May 2009 and with (d) Hotwire-LWC
liquid water content.
MAY 2015 ZHU ET AL . 2025
0938 BT, 0958 BT), which is consistent with the ob-
served results of aircraft 3817.
The particle images recorded via CIP probing show
that most of the ice crystals were heavily rimed, in-
dicating that riming is an important growth process for
ice crystals in clouds in the range of 2.3 km (T’ 08C) to3.6 km (T ’ 258C). Compared to the results observed
from aircraft 3817, the riming process was more active in
the lower cloud layer because of the high supercooled
LWC in this layer. Figure 12d, which shows the LWC
FIG. 12. As in Fig. 11, but by aircraft 3830.
2026 JOURNAL OF THE ATMOSPHER IC SC IENCES VOLUME 72
distribution detected from aircraft 3830, demonstrates
that the maximum LWC in the clouds was more than
1 gm23, and most of regions observed from aircraft 3830
exhibited higher LWC values than the upper layer ob-
served from aircraft 3817. The particle images recorded
by PIP probe (Fig. 12a) suggest that the aggregation was
an important growth process in clouds in the range of
2.3 km (T’ 08C) to 4.9 km (T’2128C) and in stronger
embedded convection regions especially.
In summary, the distribution and growth processes of
ice crystal habits in two cases of stratiform clouds with
embedded convection show that the distribution of ice
crystal habits varied greatly between stratiform cloud
regions and embedded convection regions. Higher
concentrations of large ice particles, such as dendritic
crystals, and higher supercooled water content were
found in the embedded convection regions. Both rim-
ing and aggregation processes were more active in the
embedded convection regions than in the stratiform
clouds.
6. The broadening rate of PSDs
To investigate how the PSDs changed with vertical
distance, the three aircraft flew horizontally at different
cloud levels while maintaining constant longitude and
latitude locations (beginning at 0930 BT, 40.8078N,
114.9828E, and ending at 0940 BT, 40.9848N, 115.2928E).The flight levels of aircraft 3625, 3817, and 3830 were
4.8 km (T ’ 211.68C), 4.2 km (T ’ 288C), and 3.6 km
(T’258C), respectively. Although GPS data were lost,
the flight route of aircraft 3625 was recovered for the
first 10min from the pilot’s flight log.
Figure 13a shows the flight routes of the three aircraft
superimposedwith radar echo distributions from 0930 to
0940 BT. Figure 13a shows that, from 0935 to 0940 BT,
the three aircraft simultaneously passed through an em-
bedded, strong echo region. In this region, the LWC de-
tected from the three aircraft reached its peak value
(Figs. 13b,c,d), and the LWC detected from aircraft 3830
was higher than 1gm23.
The averaged spectra between 0935 and 0940 BT at
convection areas are shown in Fig. 13f. In the embedded
convection region, the Marshall–Palmer (MP) fit of the
PSDs shows that the PSDs broadened from 4.8km (T ’211.68C) to 3.6km (T’258C) but most noticeably from
4.8km (T ’ 211.68C) to 4.2km (T ’ 288C). Figure 13e
provides a comparison of particle mean volume di-
ameters. Figure 13e shows that the particle mean volume
diameters at 4.8 km (T ’ 211.68C), 4.2 km (T ’ 288C),and 3.6km (T ’ 258C) were 1.2mm (Dmv4.8 5 1.2mm),
3mm (Dmv4.2 5 3mm), and 3.2mm (Dmv3.6 5 3.2mm),
respectively. The PSD broadening rate from 4.8 km
(T ’ 211.68C) to 4.2 km (T ’ 288C) can be calculated
as follows:
V4:2-4:8km 5Dmv4:22Dmv4:8
0:6 km5
3mm2 1:2mm
0:6 km
5 3mmkm21 . (1)
From 4.2 km (T ’ 288C) to 3.6 km (T ’ 258C), thePSD broadening rate is
V3:6-4:2km5Dmv3:62Dmv4:2
0:6 km5
3:2mm23mm
0:6 km
’ 0:33mmkm21 . (2)
The three aircraft passed through stratiform clouds
from 0930 to 0935 BT (Fig. 13a), and the averaged
spectra between 0930 and 0935 BT at stratiform region
are shown in Fig. 13g. In the stratiform region, PSDs
broadened from 4.8 km (T ’ 211.68C) to 3.6 km (T ’258C), but most noticeably from 4.8km (T ’ 211.68C)to 4.2 km (T ’ 288C). Figure 13e shows that the par-
ticle mean volume diameters at 4.8 km (T ’ 211.68C),4.2 km (T’288C), and 3.6 km (T’258C) were 1.3mm
(Dmv4.85 1.3mm), 2.8mm (Dmv4.25 2.8mm), and 2.9mm
(Dmv3.6 5 2.9mm), respectively. The PSD broadening
rate from 4.8 km (T ’ 211.68C) to 4.2 km (T ’ 288C)can be calculated as follows:
V4:2-4:8km5Dmv4:22Dmv4:8
0:6 km5
2:8mm2 1:3mm
0:6 km
5 2:5mmkm21 . (3)
From 4.2 km (T ’ 288C) to 3.6 km (T ’ 258C), thePSD broadening rate is
V3:6-4:2km5Dmv3:62Dmv4:2
0:6 km5
2:9mm2 2:8mm
0:6 km
’ 0:17mmkm21 . (4)
The PSD broadening processes in the convection and
stratiform regions demonstrate that with the decrease of
height, the PSDs broadened in both regions. However,
the broadening rates between 4.8km (T’ 211.68C) and4.2km (T ’ 288C) were larger than those between
4.2km (T ’ 288C) and 3.6km (T ’ 258C). This phe-nomenon may be because the temperature range be-
tween 4.8km (T’211.68C) and 4.2km (T’288C) wasmore suitable for dendritic crystal formation. Furthermore,
once aggregates are formed, riming is more effective as
well (Bailey and Hallett 2009; Hashino and Tripoli 2011).
The PSD broadening rate in the convection region
was larger than that in the stratiform region. At the same
MAY 2015 ZHU ET AL . 2027
time, Figs. 13f and 13g show that concentrations of ice
particles of sizes less than 1.2mm (convection region)
and 1mm (stratiform region) decreased with the de-
crease in height owing to collision and collection forces
on larger ice particles. Heymsfield et al. (2002) showed
from TRMMfield campaigns that in deep tropical cirrus
and stratiform precipitating cloud, PSDs broaden from
the cloud top toward the cloud base. The broadening
rate was found to be 1–3mmkm21, and concentrations
of particles less than 1mm in size decreased with de-
creasing height. Our case showed similar characteristics
and results on the vertical evolution of PSDs. Particle
images recorded by PIP probe show that the aggregation
process was the main cause of the broadening phe-
nomenon (Fig. 13a).
The PSD broadening rate in the embedded convec-
tion region was found to be higher in our study. Lawson
and Zuidema (2009) analyzed 2DP data from stratiform
clouds with embedded convection regions at high lati-
tudes and found that in embedded convection regions
(CTT’2278C), the maximum diameter of ice particles
at 4 km (T ’ 2138C) was 15mm, and at 2.2 km (T ’08C), the value was approximately 30mm. The PSD
broadening rate was also approximately 6.25mmkm21.
While the broadening rate was higher in that study, their
results were similar to the results of this study, suggest-
ing that PSD broadening rates are higher in embedded
convection regions.
PSD broadening rates were higher in the embedded
convection than in the stratiform clouds. The reason is
too complicated to clearly clarify by the observations of
this study. Studies have shown that riming does enhance
aggregation (Hallgren and Hosler 1960), but when high
concentrations of dendritic crystals exist, aggregation
occurs rapidly (Hashino and Tripoli 2011; Hobbs et al.
1974), creating larger particles favored for riming
growth. The observations in this paper do not consis-
tently support one over the other. Some of the images
show large aggregates with little riming while others
show heavily rimed particles. The importance of one
process over another probably varies, but both are ac-
tive and lead to PSD broadening. Therefore, in the
higher LWC regions of embedded convection, both
particle growth processes are important and feedback
on one another.
7. Conclusions and discussion
In this study, we investigated ice crystal habits, dis-
tribution, and growth processes in two cases of strati-
form clouds with embedded convection on 18April 2009
and 1 May 2009 in northern China. Three aircraft were
employed to observe clouds simultaneously at different
FIG. 13. (a) The flight tracks of three aircraft 3625 (red line), 3817
(black line), and 3830 (green line) superimposed with the cross
section of radar reflectivity on 1May 2009; (b) RH (green line, %),
LWC (black line, gm23), and temperature (blue line, 8C) recordedfrom aircraft 3625; (c) as in (b), but from aircraft 3630; (d) as in (b),
but from 3630 aircraft; (e) comparison of particle mean volume
diameter; (f), average spectrum between 0935 and 0940 BT in
convection region; and (g) as in (f), but between 0930 and 0935 BT
in stratiform region.
2028 JOURNAL OF THE ATMOSPHER IC SC IENCES VOLUME 72
levels of the clouds while maintaining a constant longi-
tude and latitude position. This flight pattern facilitated
an investigation of PSD change with height in the clouds.
This combination of airborne observations and radar
echo distributions allows us to conduct an accurate
evaluation of ice particle distributions and main growth
processes in stratiformcloudswith embedded convection.
The 18 April 2009 case observed prefrontal clouds,
and the convection embedded in stratiform clouds had
a stronger radar echo with a maximum reflectivity of
FIG. 13. (Continued)
MAY 2015 ZHU ET AL . 2029
approximately 50 dBZ, which was stronger than re-
flectivities in the surrounding stratiform clouds of ap-
proximately 10–20 dBZ. The 1 May 2009 case observed
postfrontal clouds with a maximum reflectivity of ap-
proximately 40 dBZ in the embedded convection region,
which was stronger than reflectivities in the surrounding
stratiform clouds of approximately 5–10 dBZ. Two cases
studied here comprised typical stratiform clouds with
embedded convection.
The ice crystal habits sampled in the two cases of
stratiform clouds with embedded convection were com-
plex, and the ice crystal habits present between 08 and2168C were predominantly platelike, needle column,
capped column, dendrite, and irregular. Aggregates and
heavily rimed ice crystals were common in the clouds.
The ice crystal habits recorded from the aircraft were
strongly affected by CTT and cloud type. First, the plate
and needle-column crystals were predominant in clouds
with CTT warmer than 288C, and dendritic and capped-
column crystals were found only in CTT conditions colder
than 2138 and 2188C, respectively. Second, comparisons
of ice crystal habits in different clouds show that a mixture
of several ice crystal habits can always be found. However,
ice crystal habits identified in embedded convection re-
gions contained more dendrites and possessed a heavier
riming degree, and the ice crystals recorded in stratiform
clouds contained more hexagonal plate crystals.
Our case showed similar results to those of Heymsfield
et al. (2002), who identified ice crystal habits recorded
with a cloud particle imager (CPI) probe in deep tropical
cirrus and stratiform precipitating clouds, and concluded
that small, pristine particles are observable in clouds
formed by more transient convective clouds, with CTT
controlling the habits. Most of larger particles were
aggregates and rimed ice particles that were sampled
near deep convective clouds with sustained convection.
The dominant growth process is different for different
clouds. In shallow stratiform clouds, the growth process
is dominated by deposition growth, but in deep strati-
form clouds or embedded convection, both riming and
aggregation are important. The two cases in this study
show that riming was more prevalent in 18 April case
than aggregation, though aggregates were evident. In
contrast, the 1 May case had a more dominant aggrega-
tion processes but also riming. These results are generally
in agreement with previous studies conducted in other
regions, such asWashington, United States (Herzegh and
Hobbs 1980); Newfoundland, Canada (Lawson et al.
1998); Kwajalein, United States (Heymsfield et al. 2002);
and the Arctic (Lawson and Zuidema 2009; Lawson et al.
1998, 1993).
In addition, with changes of height in deep stratiform
clouds or embedded convection, ice crystal growth
processes were different. Both aggregation and riming
processes constituted main growth processes between
08 and 211.68C, but riming processes were more active
in lower cloud layers because of high supercooled LWC
in the clouds. Hou et al. (2010) analyzed 2DC and 2DP
data of a stratiform cloud with embedded convection
regions in northeastern China and found that ice parti-
cles primarily form and grow at layers between 4.0 and
5.5 km (from 218 to –88C), with depositional growth
dominating this process in addition to aggregation. In
contrast, our study shows that riming was also an im-
portant growth process in embedded clouds owing to
high supercooled LWC in the clouds.
The PSD broadening processes in convection and
stratiform regions show that with a decrease in height,
PSD broadened in both regions, but the broadening
rates between 4.8 km (T ’ 211.68C) and 4.2 km (T ’288C) were larger than those between 4.2 km (T ’288C) and 3.6 km (T ’ 258C). In addition, the PSD
broadening rates in embedded convection regions were
larger than those in stratiform clouds, as the aggregation
and riming processes of ice particles in embedded con-
vection regions were active. The existence and extent of
supercooled liquidwater is critical to enhancing riming and
aggregation processes in embedded convection region.
It should be noted that the quality of the microphys-
ical data due to the relatively low resolution of airborne
instruments and the limited data collections in this study
lead to many difficulties and uncertainties for analyzing
classification of particle habits and their growth pro-
cesses. In many cases, we cannot separate plates from
irregular shapes unless the images appear to be larger
size and identify riming and aggregation processes that
come first. On the one hand, riming comes first and then
enhances aggregation. On the other hand, when high
concentrations of dendritic crystals exist, aggregation
occurs rapidly, creating larger particles favored for
riming growth. The observations in this paper do not
consistently support one over the other. Some of the
images show large aggregates with little riming, and
others show heavily rimed particles. The importance of
one process over another probably varies, but both are
active and lead to PSD broadening. Therefore, in the
higher LWC regions of embedded convection, both
particle growth processes are important and feedback
on one another.
The ice particle shattering problems induced by the
older-technology cloud probes (Field et al. 2006; Korolev
et al. 2013) used in this study are not considered in this
paper, which was likely taking place during observations
in these clouds and influencing the data quality. All
these uncertainties need to be further clarified in future
studies.
2030 JOURNAL OF THE ATMOSPHER IC SC IENCES VOLUME 72
Acknowledgments. The authors are grateful for criti-
cal and constructive comments from three anonymous
reviewers and editor, which greatly improved the quality
of this paper. This research was supported by the Key
Project of National Science and Technology Pillar
Program (Grant 2006BAC12B03), the Research and
Development Special Fund for Public Welfare In-
dustry (Meteorology) (Grants GYHY200806001 and
GYHY201306040), the Third Tibetan Plateau Scientific
Experiment: Observations for Boundary Layer and
Troposphere (GYHY201406001), the Key Project of
Basic Scientific Research and Operation fund of Chinese
Academy of Meteorological Sciences (Grant 2013Z009),
and theOpen Funding fromKeyLaboratory forAerosol-
Cloud-Precipitation of China Meteorological Adminis-
tration (KDW1402).
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