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EARLY ONLINE RELEASE
This is a PDF of a manuscript that has been peer-reviewed
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formatted, copy edited or proofread, the final published
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This pre-publication manuscript may be downloaded,
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Commons Attribution 4.0 International (CC BY 4.0) license.
It may be cited using the DOI below.
The DOI for this manuscript is
DOI:10.2151/jmsj. 2018-023
J-STAGE Advance published date: January 26, 2018
The final manuscript after publication will replace the
preliminary version at the above DOI once it is available.
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1
Lidar Network Observation of Dust Layer Development 2
over the Gobi Desert in Association with a Cold Frontal 3
System on 22–23 May 2013 4
5
Kei KAWAI1, Kenji KAI 6
7
Graduate School of Environmental Studies 8
Nagoya University, Nagoya, Japan 9
10
Yoshitaka JIN, Nobuo SUGIMOTO 11
12
National Institute for Environmental Studies 13
Tsukuba, Japan 14
15
and 16
17
Dashdondog BATDORJ 18
National Agency for Meteorology and Environmental Monitoring 19
Ulaanbaatar, Mongolia 20
21
22
23
January 16, 2018 24
25
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1
------------------------------------ 27
1) Corresponding author: Kei Kawai, Graduate School of Environmental Studies, Nagoya 28
University, Furo-cho, Chikusa-ku, Nagoya 464-8601, Japan. 29
Email: [email protected] 30
Tel: +81-52-788-6045 31
Fax: +81-52-789-4257 32
33
Abstract 34
35
The Gobi Desert is one of the major sources of Asian dust, which influences the 36
climate system both directly and indirectly through its long-range transport by the 37
westerlies. In this desert, three ground-based lidars are operated in Dalanzadgad, 38
Sainshand, and Zamyn-Uud, Mongolia. This study firstly combined these lidars into a 39
lidar network and shows the spatial development of a dust layer over the desert and the 40
long-range transport of the dust during 22–23 May 2013 via the lidar network. During this 41
dust event, a cold front accompanying an extratropical cyclone moved southeastward 42
across the desert and sequentially passed through Dalanzadgad, Sainshand, and 43
Zamyn-Uud. In Dalanzadgad, in the central part of the desert, a dust storm occurred 44
owing to the strong wind (6–10 m s-1) associated with the cold front and reached a top 45
height of 1.6 km. Some of the dust floated at a height of 0.9–1.6 km along the cold frontal 46
surface. In Sainshand and Zamyn-Uud, in the eastern part of the desert, the dust layer 47
extended from the atmospheric boundary layer (ABL) to the free troposphere in the 48
updraft region of warm air in the cold frontal system. Overall, while the dust layer was 49
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2
moving across the desert with the cold frontal system, it was developing up to the free 50
troposphere. The mechanism of this development can be explained by the combination 51
of two processes as follows: (1) continuous emission of dust from the desert surface to 52
the ABL by the strong wind around the cold front and (2) continuous transport of the dust 53
from the ABL to the free troposphere by the updraft of the warm air in the cold frontal 54
system. This mechanism can contribute to the long-range transport of dust by the 55
westerlies in the free troposphere. 56
57
Keywords Asian dust; cold front; the Gobi Desert; lidar network observation; 58
long-range transport 59
60
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3
1. Introduction 61
Asian dust originates in arid and semi-arid regions of East Asia such as the Gobi Desert, 62
Taklimakan Desert, and Loess Plateau (Sun et al. 2001; Kurosaki and Mikami 2005; Wu et 63
al. 2016). In the source regions, dust is emitted from the ground surface to the atmospheric 64
boundary layer (ABL) by strong wind. If the dust ascends from the ABL to the free 65
troposphere, it is transported over a long range toward the North Pacific by the 66
middle-latitude westerlies (Kai et al. 1988; Husar et al. 2001; Hara et al. 2009; Uno et al. 67
2009; Yumimoto et al. 2009). This transported dust influences the climate system both 68
directly and indirectly (Huang et al. 2014). Therefore, the spatial distribution of dust over the 69
source regions is a key factor in the long-range transport of dust. 70
A ground-based lidar is effective for observing vertical distribution of dust continuously. In 71
the Taklimakan Desert, a depolarization lidar was installed in 2002 (Tsunematsu et al. 2005; 72
Kai et al. 2008) through the Japan–China Joint Studies on Origin and Transport of Aeolian 73
Dust and its Impact on Climate (ADEC) (e.g., Mikami et al. 2005; Takemi 2005). In the 74
Loess Plateau, a group from Lanzhou University, China, conducts a lidar observation and 75
many other measurements (Huang et al. 2008). In the Gobi Desert, there are two lidars in 76
the eastern part (Sugimoto et al. 2008) and one in the central part (Kawai et al. 2015). 77
In the Gobi Desert, almost all dust events arise from cold frontal activity (Shao and Wang 78
2003; Takemi and Seino 2005). A cold front often passes through the desert in spring 79
(Hayasaki et al. 2006). This is related to frequent cyclogenesis in the lee of the 80
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Altai-Hangayn-Sayan Mountains (Fig. 1) in spring (Chen et al. 1991; Adachi and Kimura 81
2007; Wang et al. 2009). Therefore, it is important to understand the relationship between 82
dust events and cold fronts. In previous studies, dust events associated with cold fronts 83
were analyzed via satellite images and numerical models (Husar et al. 2001; Adachi et al. 84
2007; Hara et al. 2009). However, the spatial relationship between dust events and cold 85
fronts, which involves the long-range transport of dust, is not yet shown in detail based on 86
the lidar observations in the source region. 87
A dust event occurred in the Gobi Desert during the passage of a cold front on 22–23 88
May 2013. Our previous study showed the dust transport from the ABL to the free 89
troposphere by the cold frontal system during the dust event, based on the lidar in the 90
central part of the desert (Kawai et al. 2015). In the present study, we firstly combined the 91
three lidars in the desert into a lidar network and analyzed the spatial distribution of dust. 92
The purpose of the present study is to show the spatial development of a dust layer and the 93
long-range transport of the dust during the dust event by using the lidar network. 94
95
2. Observations and data 96
2.1 Gobi Desert lidar network 97
The lidar network in the Gobi Desert consists of three lidars: a ceilometer in the central 98
part and two AD-Net lidars in the eastern part. A ceilometer is a compact backscatter lidar 99
that is easy to operate and maintain. AD-Net is short for the Asian Dust and Aerosol Lidar 100
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Observation Network, which is a widespread lidar network in East Asia (Sugimoto et al. 101
2008). 102
103
a. Ceilometer observation 104
The ceilometer is located in Dalanzadgad (43.58°N, 104.42°E, 1470 m above sea level 105
(ASL)) in southern Mongolia (Fig. 1). The ceilometer observation has been conducted since 106
the end of April 2013. It is part of the collaborative research between Nagoya University, 107
Japan, and the Information and Research Institute of Meteorology, Hydrology and 108
Environment (IRIMHE), Mongolia. The ceilometer is a Vaisala CL51. The laser wavelength 109
is 910 nm, the pulse repetition rate is 6.5 kHz, and the pulse energy is 3.0 μJ. A preliminary 110
ceilometer observation was carried out in Tsukuba, Japan, and the observational 111
performance of the ceilometer was verified via a sophisticated lidar (Jin et al. 2015). 112
The ceilometer outputs a vertical profile of attenuated backscatter coefficients up to a 113
height of 15.4 km with a height resolution of 10 m every 6 seconds. An attenuated 114
backscatter coefficient is a backscatter coefficient considering the attenuation of an emitted 115
laser pulse and the backscatter light in the atmosphere. The influence of water vapor on the 116
attenuated backscatter coefficients obtained from the ceilometer is probably small because 117
of low relative humidity in the Gobi Desert as discussed in Jin et al. (2015). The average of 118
the data for one minute was used in this study. 119
The major scatterers over the Gobi Desert in spring are dust, clouds, and precipitation. 120
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Their detection and distinction are based on the magnitude, height, and distribution of 121
attenuated backscatter coefficients. During this dust event, the threshold of attenuated 122
backscatter coefficient for distinguishing dust and the others was about 9 × 10-3 km-1 sr-1. In 123
addition, relative humidity in a region of large attenuated backscatter coefficients supports 124
their distinction. Natsagdorj et al. (2003) showed that relative humidity was low in most dust 125
storms. 126
127
b. AD-Net lidar observations 128
The AD-Net lidars are located in Sainshand (44.87°N, 110.12°E, 937 m ASL) and 129
Zamyn-Uud (43.72°N, 111.90°E, 962 m ASL) in southeastern Mongolia (Fig. 1). These 130
lidars are operated by the National Institute for Environmental Studies (NIES), Japan, and 131
the National Agency for Meteorology and Environmental Monitoring (NAMEM), Mongolia. 132
The lidars are dual-wavelength polarization-sensitive backscatter lidars. The laser 133
wavelengths are 532 and 1064 nm, the pulse repetition rate is 10 Hz, and the pulse energy 134
is 50 mJ. The polarization of backscatter light is measured at a wavelength of 532 nm. 135
The observational data includes the vertical profiles of attenuated backscatter 136
coefficients at both wavelengths and volume depolarization ratio at a wavelength of 532 nm. 137
The time and height resolutions are 15 minutes and 30 m, respectively. The volume 138
depolarization ratio is an index of particle sphericity. This value is zero for a spherical 139
particle and increases with non-sphericity. We calculated volume color ratio, a relative index 140
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of particle size, by dividing the 1064-nm attenuated backscatter coefficient by the 532-nm 141
one. This value increases as particle size increases. The 532-nm attenuated backscatter 142
coefficient near the ground in Zamyn-Uud was calibrated for an incomplete overlap function 143
by using data on 24 May 2013, when the atmosphere was clean following the dust event. 144
145
2.2 Meteorological data 146
Surface weather charts produced by the Japan Meteorological Agency (JMA) were used. 147
Surface meteorological observational data were obtained from 3-hourly SYNOP reports 148
acquired from the Integrated Surface Database produced by the National Oceanic and 149
Atmospheric Administration (NOAA), USA (Smith et al. 2011). Three-dimensional gridded 150
meteorological data produced by the National Centers for Environmental Prediction (NCEP) 151
of NOAA were used. The data are NCEP FNL (Final) Operational Global Analysis data of 1º 152
1º grids. This product is generated from the global meteorological data of the Global Data 153
Assimilation System (GDAS) using the same model as the NCEP global forecast system. In 154
addition, trajectory analyses were performed using the Hybrid Single-Particle Lagrangian 155
Integrated Trajectory (HYSPLIT) model provided by the NOAA Air Resources Laboratory 156
(Stein et al. 2015). The GDAS data of 1º 1º grids were selected as the input 157
meteorological data of the trajectory analyses. The local standard time (LST) of Mongolia, 158
which is 8 hours ahead of the coordinated universal time (UTC), is used in this paper. 159
160
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3. Results 161
3.1 Meteorological conditions in Mongolia 162
Surface weather charts for Mongolia on 22–23 May 2013 are shown in Fig. 2. An 163
extratropical cyclone covered central Mongolia at 14 LST on 22 May (Fig. 2a) and moved 164
northeastward for the next 18 hours. The center pressure of the cyclone was almost 165
constant at 988 hPa during this period. Warm and cold fronts accompanied the cyclone 166
from 20 LST on 22 May (Figs. 2b–2d). The cold front extended from the cyclone center to 167
southern Mongolia across the Gobi Desert at 20 LST on 22 May (Fig. 2b) and then moved 168
southeastward through the desert at a speed of about 30 km h-1. During the movement, it 169
passed through Dalanzadgad between 14 and 20 LST on 22 May, Sainshand between 20 170
LST on 22 May and 02 LST on 23 May, and Zamyn-Uud between 02 and 08 LST on 23 171
May. 172
Figure 3 shows the meteorological fields observed around Mongolia at the same time as 173
the second and third weather charts (Figs. 2b and 2c) obtained from the SYNOP report. At 174
20 LST on 22 May, the cold air behind the cold front covered central Mongolia (including 175
Dalanzadgad), and the warm air in front of the cold front covered eastern Mongolia (Fig. 3a). 176
At 02 LST on 23 May, the cold air expanded to eastern Mongolia (including Sainshand) 177
while the cold front moved southeastward (Fig. 3b). At both these times, the wind directions 178
were between north and northwest in the cold air and between south and west in the warm 179
air. These wind conditions show cold and warm air advections. The cold and warm airflows 180
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converged along the cold front. 181
Figure 4 presents meteorological fields at 700 hPa at the same times as in Fig. 3 182
obtained from the NCEP FNL data. The height at 700 hPa is about 1.5–2.0 km above the 183
ground in Mongolia. At both times in Fig. 4, updrafts spread the warm air in along the 184
surface cold front. These updrafts were caused by the convergence of the cold and warm 185
air on the ground (Fig. 3). Therefore, the warm air on the ground ascended onto the cold air, 186
as shown in the general cold frontal system (e.g., Simpson 1997; Wallace and Hobbs 187
2006). 188
189
3.2 Results in Dalanzadgad, located in the central part of the desert 190
Figure 5 indicates the temporal variations in surface meteorological elements observed in 191
Dalanzadgad from 12 LST on 22 May to 09 LST on 23 May 2013. Figure 6 shows the 192
time-height cross sections of a ceilometer observation result and meteorological conditions 193
obtained from the NCEP FNL data in Dalanzadgad during the same period as in Fig. 5. In 194
Fig. 6, four characteristic regions were discerned and are indicated by the letters A–D. They 195
are discussed as follows. 196
Region A of medium to large attenuated backscatter coefficients (>1.0 × 10-3 km-1 sr-1, 197
light blue to red) shows a dust storm between the ground and a height of 1.6 km from 14 198
LST on 22 May to 02 LST on 23 May (Fig. 6a). Near the ground during the dust storm, the 199
relative humidity was 11–14% (Fig. 5c), and the wind speed was 6–10 m s-1 (Fig. 5d). Thus, 200
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the strong wind raised the dust from the desert surface. In the dust storm at 20 LST on 22 201
May, the potential temperature was constant at 312 K with height, and the wind speed was 202
12–14 m s-1 (region A in Fig. 6b). The atmospheric neutral stability and the strong wind 203
show that vertical and horizontal mixing was active because of turbulence in the dust storm. 204
The sea level pressure increased by 23.3 hPa from 17 LST on 22 May to 08 LST on 23 205
May (Fig. 5a). The temperature decreased from 28.9 °C at 17 LST on 22 May to 9.4 °C at 206
08 LST on 23 May (Fig. 5b). Hence, the cold front (Fig. 2) passed between 17 and 20 LST 207
on 22 May, and the cold air (Fig. 3) started to advect on the ground during the dust storm. 208
Judging from the potential temperature and wind conditions, the vertical structure of the 209
cold air is shown by region B under the dotted line in Fig. 6b. The sloping top height 210
between 20 LST on 22 May and 01 LST on 23 May was the cold frontal surface. The top 211
height of the cold air is assumed to be about 1.4 km at 02 and 08 LST on 23 May. In 212
particular, the top height at 08 LST corresponds to the cloud base height observed by the 213
ceilometer (Fig. 6a). The potential temperature was 301 K at 02 LST and 294–298 K at 08 214
LST on 23 May (Fig. 6b). The wind directions in and above the cold air were northeast and 215
west, respectively. Most of the cold air indicates small attenuated backscatter coefficients 216
(<0.5 × 10-3 km-1 sr-1, light purple) from 2230 LST on 22 May (Fig. 6a), where little dust was 217
floating. The leading edge of the cold air was occupied by the dust storm. 218
Region C of medium to large attenuated backscatter coefficients (>1.0 × 10-3 km-1 sr-1, 219
red) shows clouds over a height of 1.6 km between 02 and 07 LST on 23 May (Fig. 6a). It is 220
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likely that the clouds were generated by the updraft of the warm air (Fig. 4), as a general 221
cold frontal system (e.g., Simpson 1997; Wallace and Hobbs 2006). Precipitation is shown 222
by the region of middle to large attenuated backscatter coefficients (>1.0 × 10-3 km-1 sr-1, 223
light blue to red) under the clouds between 05 and 07 LST on 23 May. The precipitation led 224
to the increase in relative humidity at 08 LST on 23 May (Fig. 5c). 225
Region D, which is indicated by medium attenuated backscatter coefficients (1.0–1.4 × 226
10-3 km-1 sr-1, light blue) at a height of 0.9−1.6 km between 22 LST on 22 May and 00 LST 227
on 23 May, shows a dust layer (Fig. 6a). The thickness of the dust layer ranged from 0.2 to 228
0.5 km. Because it was located over the cold frontal surface, the dust was probably 229
transported from the dust storm by the updraft of the warm air (Fig. 4). The subsequent 230
movement of the dust layer will be discussed in Section 4 by using trajectory analysis. 231
232
3.3 Results in Sainshand, located in the eastern part of the desert 233
Figure 7 presents the temporal fluctuations in surface meteorological elements observed 234
in Sainshand in the eastern part of the Gobi Desert from 18 LST on 22 May to 15 LST on 23 235
May 2013. Figures 8 and 9 show the time-height cross sections of lidar observation results 236
and meteorological conditions obtained from the NCEP FNL data, respectively, for 237
Sainshand during the same period as in Fig. 7. 238
Between 22 LST on 22 May and 01 LST on 23 May, a dust storm is shown by region E of 239
large attenuated backscatter coefficients (>5.5 × 10-3 km-1 sr-1, yellow to red) on the ground 240
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(Fig. 8a). At 23 LST on 22 May, during the dust storm, the wind speed was 11 m s-1 (Fig. 7d), 241
and the relative humidity was 19% (Fig. 7c). In the dust storm, the volume depolarization 242
ratio was 0.2–0.3 (Fig. 8b), and the volume color ratio was about 2.0 (Fig. 8c). 243
The sea level pressure increased by 21.3 hPa from 20 LST on 22 May to 08 LST on 23 244
May (Fig. 7a). The temperature dropped from 35.4 °C at 17 LST on 22 May to 13.3 °C at 08 245
LST on 23 May (Fig. 7b). Between 20 and 23 LST on 22 May, the wind direction changed 246
from south to northwest, and the wind speed increased from 6 to 11 m s-1 (Fig. 7d). 247
According to these features, the cold front shown in Fig. 2 passed through between 20 and 248
23 LST on 22 May, and the cold air replaced the warm air, as shown in Fig. 3. 249
Judging from the potential temperature and wind conditions, the vertical structure of the 250
cold air is indicated in region F below the dotted line in Fig. 9a. The top height was 1.1 km 251
at 02 LST and 1.3 km at 08 and 14 LST on 23 May. The potential temperature was 303–307 252
K at 02 LST and 295 K at 08 and 14 LST on 23 May. At 08 and 14 LST on 23 May, there 253
was an inversion layer between 1.1 and 1.5 km in height. The wind directions in and above 254
the cold air were north and west, respectively. The attenuated backscatter coefficients were 255
small (<2.0 × 10-3 km-1 sr-1, blue) in the cold air after the dust storm (region F in Fig. 8a), 256
indicating little floating dust. 257
Region G of medium to large attenuated backscatter coefficients (>2.0 × 10-3 km-1 sr-1, 258
red) shows clouds, which were located around a height of 2–5 km (Fig. 8a). Most of the 259
clouds indicate volume depolarization ratios of more than 0.2 (Fig. 8b), indicating the 260
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presence of ice crystals (Shimizu et al. 2004). The temperatures around the clouds were 261
between 0 and -10 °C according to the NCEP FNL data (not shown). Therefore, it is likely 262
that the dust particles mentioned later worked as ice nuclei, as suggested by Sakai et al. 263
(2003). The volume color ratio in the clouds was 2.0–2.4 (Fig. 8c). The region of medium 264
attenuated backscatter coefficients (2.0–6.0 × 10-3 km-1 sr-1, light blue to yellow) under the 265
clouds around 11 LST on 23 May shows precipitation (Fig. 8a). In the precipitation, the 266
volume depolarization ratio was about 0.1 (Fig. 8b), which is consistent with that reported 267
by Sassen (2006). The volume color ratio of the precipitation was 2.0–3.0 (Fig. 8c). 268
A dust layer is shown by the medium attenuated backscatter coefficients (2.0–6.0 × 10-3 269
km-1 sr-1, light blue to yellow) in region H (Fig. 8a). It extended from the dust layer (region E) 270
to the clouds (region G) over the cold air (region F). It seems that the dust layer was mixed 271
with the clouds. The top height of the dust layer increased from 1.6 km at 22 LST on 22 May 272
to at least 4.0 km at 04 LST on 23 May. The presence of the dust layer above a height of 273
4.0 km was unclear because of the clouds. The thickness of the dust layer was between 1.6 274
and 2.5 km. In the dust layer, the volume depolarization ratio was 0.1–0.3 (Fig. 8b), and the 275
volume color ratio was 1.0–2.0 (Fig. 8c). According to the volume color ratio, the dust 276
particles were smaller than the precipitation particles and the ice crystals of the clouds. 277
Vertical velocity represents updraft in the dust layer at 02 LST on 23 May (region H in Fig. 278
9b). Therefore, the dust layer was distributed in the updraft region of the warm air in the 279
cold frontal system. 280
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281
3.4 Results in Zamyn-Uud, located in the eastern part of the desert 282
The time series of surface meteorological elements observed in Zamyn-Uud on 22–23 283
May 2013 are indicated in Fig. 10. Figures 11 and 12 show the time-height cross sections of 284
the lidar observation results and meteorological conditions obtained from the NCEP FNL 285
data, respectively, for Zamyn-Uud during the same period as in Fig. 10. Three characteristic 286
regions were found and are denoted with the letters I–K. As with Sainshand, a dust layer 287
(region I) was located over the cold air (region J) and probably mixed with a cloud (region 288
K). 289
The dust layer over the cold air is shown by medium attenuated backscatter coefficients 290
(1.6–4.0 × 10-3 km-1 sr-1, light blue to green) up to a height of about 4 km until 17 LST on 23 291
May (region I in Fig. 11a). The top height increased from 1.4 km at 03 LST to 3.8 km at 15 292
LST on 23 May. The thickness ranged from 0.3 to 1.7 km. In the dust layer, the volume 293
depolarization ratio was 0.2–0.3 (Fig. 11b), and the volume color ratio was 1.0–2.4 (Fig. 294
11c). As with Sainshand, the dust layer was located in the updraft region (region I in Fig. 295
12b). 296
The sea level pressure increased by 13.4 hPa from 17 LST on 22 May to 11 LST on 23 297
May (Fig. 10a). The temperature decreased from 32.5 °C at 17 LST on 22 May to 18.4 °C at 298
05 LST on 23 May (Fig. 10b). The wind direction changed from southwest to northwest 299
between 02 and 05 LST on 23 May (Fig. 10d). These characteristics show that the cold 300
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front (Fig. 2) passed through between 02 and 05 LST on 23 May, and the cold air replaced 301
the warm air (Fig. 3). 302
Judging from the potential temperature and wind conditions, the cold air is indicated by 303
region J below the dotted line in Fig. 12a. The top height of the cold air was about 1.0 km at 304
08 LST and 1.3 km at 14 and 20 LST on 23 May. The potential temperature in the cold air 305
was 297–306 K. The wind directions rotated from north in the cold air to west above the 306
cold air. This counterclockwise rotation is consistent with the cold air advection. The 307
attenuated backscatter coefficients were small (<1.6 × 10-3 km-1 sr-1, blue) in the upper part 308
of the cold air (region J in Fig. 11a). 309
Region K, which is indicated by medium to large attenuated backscatter coefficients 310
(>1.6 × 10-3 km-1 sr-1, red) over a height of 2.2 km between 1700 and 1930 LST on 23 May, 311
shows a cloud (Fig. 11a). It seems that the cloud was mixed with the dust layer. In the cloud, 312
the volume depolarization ratio was mostly greater than 0.3 (Fig. 11b), and the volume color 313
ratio was more than 3.0 (Fig. 11c). As with Sainshand, it is likely that the dust particles 314
worked as ice nuclei. The ice crystals of the cloud were larger than the dust particles based 315
on their color ratios. 316
317
4. Discussion 318
4.1 Dust layer development 319
Figure 13 illustrates the observational models at the lidar observation sites during the 320
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dust event. The characteristics of the dust layers over the cold air are summarized in Table 321
1. In Dalanzadgad, a dust storm occurred around the cold front and reached a top height of 322
1.6 km (Fig. 13a). A dust layer was distributed at a height of 0.9–1.6 km over the cold air, 323
with a thickness that ranged from 0.2 to 0.5 km. Forward trajectories for the dust layer are 324
presented in Fig. 14. The trajectories extended eastward, reaching the eastern part of the 325
Gobi Desert (Fig. 14a), and ascended to a height of more than 2.0 km for the first 13–15 326
hours (Fig. 14b). The relative humidity along the trajectories was about 50% until 08 LST on 327
23 May (Fig. 14c). In contrast, the dust layers observed in Sainshand and Zamyn-Uud 328
reached a height of about 4 km (Figs. 13b and 13c) and were 1.6–2.5 and 0.3–1.7 km thick, 329
respectively. Therefore, the dust layer produced during this dust event was developing 330
upward from the ABL to the free troposphere while moving eastward through the Gobi 331
Desert with the cold frontal system. 332
It is suggested that the development of the dust layer was based on the combination of 333
the following two processes: (1) the continuous emission of dust from the desert surface to 334
the ABL and (2) the continuous transport of the dust from the ABL up to the free 335
troposphere. 336
Process (1): Dust was raised from the ground to the ABL over the Gobi Desert by the 337
strong wind around the cold front. It is likely that the dust layer was supplied continuously 338
with new dust from the desert surface while moving through the desert. 339
Process (2): The dust in the ABL was transported to the free troposphere by the updraft 340
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of the warm air in the cold frontal system, as suggested by Kawai et al. (2015). The updraft 341
is shown in Figs. 9b, 12b, and 14b. This transport must have continued while the dust layer 342
was moving through the desert with the cold frontal system. 343
In conclusion, the cold frontal system induced the dust layer development from the ABL 344
up to the free troposphere by the combination of the two processes. This mechanism 345
should have contributed to the long-range transport of the dust by the middle-latitude 346
westerlies. It will be discussed below (Section 4.2) through trajectory analyses. 347
348
4.2 Long-range transport of the dust 349
Forward trajectories for the dust layers observed in Sainshand and Zamyn-Uud are 350
shown in Figs. 15 and 16, respectively. The trajectories extended northeastward or 351
eastward and reached northeastern China and Russian Far East (Figs. 15a and 16a). 352
These directions are consistent with the westerly winds over the cold air (Figs. 9a and 12a). 353
Most of the trajectories extended upward and exceeded a height of 4 km (Figs. 15b and 354
16b). They were located in the free troposphere, where the middle-latitude westerlies 355
prevail. The height increase of these trajectories agrees with the updrafts in the dust layers 356
(Figs. 9b and 12b). Hence, it was caused by the updraft of warm air in the cold frontal 357
system. The relative humidity along the trajectories increased and, at times, exceeded 80% 358
(Figs. 15c and 16c). The high relative humidity indicates the presence of clouds. It is likely 359
that the clouds were generated by the updraft of warm air in the cold frontal system. In 360
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conclusion, it is suggested that the dust produced during this dust event was transported 361
over a long range by the westerlies, as reported in previous studies (e.g., Kai et al. 1988; 362
Husar et al. 2001; Hara et al. 2009; Uno et al. 2009; Yumimoto et al. 2009). 363
364
5. Conclusions 365
The Gobi Desert lidar network observed the spatial distributions of dust during the dust 366
event that occurred over the desert on 22–23 May 2013. In this study, the dust event was 367
analyzed by using the lidar network and various meteorological data. The main findings are 368
summarized below. 369
(1) During the dust event, a cold front moved southeastward across the desert. 370
(2) In Dalanzadgad, in the central part of the desert, a dust storm was observed around 371
the cold front from the ground to a height of 1.6 km. A dust layer was distributed at a height 372
of 0.9–1.6 km over the cold frontal surface. The updraft of warm air in the cold frontal 373
system should have transported the dust emitted from the dust storm. 374
(3) In Sainshand and Zamyn-Uud, in the eastern part of the desert, a dust layer ascended 375
from the ABL to the free troposphere over the cold air and reached a top height of about 4 376
km. The dust layer was located in the updraft region of warm air. 377
(4) The overall dust layer was developing from the ABL up to the free troposphere while 378
moving across the desert with the cold front. It is suggested that this development was 379
caused by the combination of the continuous emission and transport of dust by the cold 380
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frontal system. 381
This is the first study showing the spatial development of a dust layer in association with 382
a cold frontal system by using the Gobi Desert lidar network. It is important to maintain and 383
expand the lidar network and analyze many dust events. This effort will help us better 384
understand the mechanisms of the emission and transport of Asian dust. 385
386
Acknowledgments 387
The authors gratefully acknowledge the Dalanzadgad Meteorological Observatory for 388
supporting the ceilometer observation, Dr. Atsushi Shimizu of NIES for teaching the 389
calibration method of the AD-Net lidar data, JMA for the provision of weather charts 390
(http://www.jma.go.jp/jma/), NOAA’s National Climatic Data Center for the provision of ISD 391
data (https://www.ncei.noaa.gov/isd), NCEP for the provision of FNL data 392
(https://rda.ucar.edu/datasets/ds083.2/), and NOAA’s Air Resources Laboratory for the 393
provision of the HYSPLIT transport and dispersion model and the READY website 394
(http://www.ready.noaa.gov). This study was supported by Grants-in-Aid for Scientific 395
Research from JSPS (Nos. 24340111 and 16H02703) and by the JSPS Core-to-Core 396
Program (B. Asia-Africa Science Platforms). 397
398
References 399
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Adachi, S., and F. Kimura, 2007: A 36-year climatology of surface cyclogenesis in East Asia 401
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northern East Asia. Adv. Atmos. Sci., 26, 471–479. 482
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occurrence and its controlling factors in East Asia. Sci. Online Lett. Atmos., 12, 187–191. 484
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An elevated large-scale dust veil from the Taklimakan Desert: Intercontinental transport 486
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models. Atmos. Chem. Phys., 9, 8545–8558. 488
489
List of Figures 490
491
Fig. 1 Topographic map of Mongolia and surrounding areas. 492
493
Fig. 2 Surface weather charts for Mongolia at (a) 14 LST and (b) 20 LST on 22 May and at 494
(c) 02 LST and (d) 08 LST on 23 May 2013 provided by JMA. The red dots show the 495
locations of Dalanzadgad (D), Sainshand (S), and Zamyn-Uud (Z). The sparse and 496
dense red-shaded areas indicate altitudes of more than 1500 and 3000 m above sea 497
level, respectively. 498
499
Fig. 3 Potential temperature (red contours; every 3 K) and wind (barbs) observed at (a) 20 500
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LST on 22 May and (b) 02 LST on 23 May 2013 obtained from the SYNOP report. The 501
half and full barbs represent the wind speeds of 2 and 4 m s-1, respectively. The blue 502
lines indicate the cold fronts transcribed from the weather charts (Figs. 2b and 2c). The 503
blue circles with the letters D, S, and Z show the locations of Dalanzadgad, Sainshand, 504
and Zamyn-Uud, respectively. 505
506
Fig. 4 Temperature (contours; every 3 K) and vertical velocity (color) at 700 hPa at (a) 20 507
LST on 22 May and (b) 02 LST on 23 May 2013 obtained from the NCEP FNL data. For 508
the vertical velocity, a negative value (red) indicates an updraft, whereas a positive value 509
(blue) indicates a downdraft. The green lines indicate the surface cold fronts transcribed 510
from the weather charts (Figs. 2b and 2c). The black dots with D, S, and Z show the 511
locations of Dalanzadgad, Sainshand, and Zamyn-Uud, respectively. 512
513
Fig. 5 Time series of the (a) sea level pressure (SLP), (b) temperature (T), (c) relative 514
humidity (RH), and (d) wind observed in Dalanzadgad from 12 LST on 22 May to 09 LST 515
on 23 May 2013 (after Kawai et al. 2015). The half and full barbs and the pennants 516
represent the wind speeds of 1, 2, and 10 m s-1, respectively. 517
518
Fig. 6 Time-height cross sections of the (a) 910-nm attenuated backscatter coefficient 519
(ABC) observed by the ceilometer (after Kawai et al. 2015) and (b) potential temperature 520
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(PT) and horizontal wind obtained from the NCEP FNL data for Dalanzadgad during the 521
same period as in Fig. 5. The half and full barbs and pennants represent the wind speeds 522
of 2, 4, and 20 m s-1, respectively. Regions A–D correspond to a dust storm, cold air, 523
clouds, and a dust layer, respectively. The dotted line represents the top of the cold air. 524
525
Fig. 7 Same as Fig. 5, except that the location is Sainshand, and the period is from 18 526
LST on 22 May to 15 LST on 23 May 2013. 527
528
Fig. 8 Time-height cross sections of the (a) 532-nm attenuated backscatter coefficient 529
(ABC), (b) 532-nm volume depolarization ratio (VDR), and (c) 1064/532-nm volume color 530
ratio (VCR) at a height of 0–5 km observed by the AD-Net lidar in Sainshand during the 531
same period as in Fig. 7. Regions E–H correspond to a dust storm, cold air, clouds, and a 532
dust layer, respectively. 533
534
Fig. 9 Time-height cross sections of the (a) potential temperature (PT) and horizontal wind 535
and (b) vertical velocity (VV) and horizontal wind obtained from the NCEP FNL data for 536
Sainshand during the same period as in Figs. 7 and 8. The half and full barbs and 537
pennants represent wind speeds of 2, 4, and 20 m s-1, respectively. Regions F and H are 538
the same as in Fig. 8. 539
540
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Fig. 10 Same as Fig. 5, except that the location is Zamyn-Uud, and the period is from 00 541
to 21 LST on 23 May 2013. 542
543
Fig. 11 Same as Fig. 8, except that the location is Zamyn-Uud, the height range is 0–4 km, 544
and the period is from 00 to 21 LST on 23 May 2013 (same as in Fig. 10). Regions I–K 545
correspond to a dust layer, cold air, and a cloud, respectively. 546
547
Fig. 12 Same as Fig. 9, except that the location is Zamyn-Uud, and the period is from 00 548
to 21 LST on 23 May 2013 (same as Fig. 10). Regions I and J are the same as in Fig. 11. 549
550
Fig. 13 Observational models for (a) Dalanzadgad, (b) Sainshand, and (c) Zamyn-Uud at 551
a height of 0–4 km during the dust event. The distance was calculated by using the 552
moving speed of the cold front (30 km h-1). The distance of 0 km indicates the leading 553
edge of the cold air (i.e., the cold front on the ground) at each observation site. The right 554
side is the moving direction of the cold front (southeast). The letter P means precipitation. 555
556
Fig. 14 (a) The locations, (b) the height above ground level (AGL), and (c) the relative 557
humidity (RH) of 24-hour forward trajectories of air parcels corresponding to the dust 558
layer that was observed over cold air in Dalanzadgad on 22–23 May 2013. In panel (a), 559
the dots on the trajectories indicate their location every 6 hours, and the numerical values 560
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of 00 and 12 near the trajectories represent the hours of 00 and 12 LST, respectively. 561
562
Fig. 15 Same as Fig. 14, except that the location is Sainshand. 563
564
Fig. 16 Same as Fig. 14, except that the location is Zamyn-Uud, and the initial time of the 565
forward trajectories is 23 May 2013. 566
567
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568
569
570
Fig. 1 Topographic map of Mongolia and surrounding areas. 571
572
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30
573
574
575
Fig. 2 Surface weather charts for Mongolia at (a) 14 LST and (b) 20 LST on 22 May and at 576
(c) 02 LST and (d) 08 LST on 23 May 2013 provided by JMA. The red dots show the 577
locations of Dalanzadgad (D), Sainshand (S), and Zamyn-Uud (Z). The sparse and 578
dense red-shaded areas indicate altitudes of more than 1500 and 3000 m above sea 579
level, respectively. 580
581
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31
582
583
584
Fig. 3 Potential temperature (red contours; every 3 K) and wind (barbs) observed at (a) 20 585
LST on 22 May and (b) 02 LST on 23 May 2013 obtained from the SYNOP report. The 586
half and full barbs represent the wind speeds of 2 and 4 m s-1, respectively. The blue 587
lines indicate the cold fronts transcribed from the weather charts (Figs. 2b and 2c). The 588
blue circles with the letters D, S, and Z show the locations of Dalanzadgad, Sainshand, 589
and Zamyn-Uud, respectively. 590
591
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32
592
593
594
Fig. 4 Temperature (contours; every 3 K) and vertical velocity (color) at 700 hPa at (a) 20 595
LST on 22 May and (b) 02 LST on 23 May 2013 obtained from the NCEP FNL data. For 596
the vertical velocity, a negative value (red) indicates an updraft, whereas a positive value 597
(blue) indicates a downdraft. The green lines indicate the surface cold fronts transcribed 598
from the weather charts (Figs. 2b and 2c). The black dots with D, S, and Z show the 599
locations of Dalanzadgad, Sainshand, and Zamyn-Uud, respectively. 600
601
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33
602
603
604
Fig. 5 Time series of the (a) sea level pressure (SLP), (b) temperature (T), (c) relative 605
humidity (RH), and (d) wind observed in Dalanzadgad from 12 LST on 22 May to 09 LST 606
on 23 May 2013 (after Kawai et al. 2015). The half and full barbs and the pennants 607
represent the wind speeds of 1, 2, and 10 m s-1, respectively. 608
609
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34
610
611
612
Fig. 6 Time-height cross sections of the (a) 910-nm attenuated backscatter coefficient 613
(ABC) observed by the ceilometer (after Kawai et al. 2015) and (b) potential temperature 614
(PT) and horizontal wind obtained from the NCEP FNL data for Dalanzadgad during the 615
same period as in Fig. 5. The half and full barbs and pennants represent the wind speeds 616
of 2, 4, and 20 m s-1, respectively. Regions A–D correspond to a dust storm, cold air, 617
clouds, and a dust layer, respectively. The dotted line represents the top of the cold air. 618
619
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35
620
621
622
Fig. 7 Same as Fig. 5, except that the location is Sainshand, and the period is from 18 623
LST on 22 May to 15 LST on 23 May 2013. 624
625
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36
626
627
628
Fig. 8 Time-height cross sections of the (a) 532-nm attenuated backscatter coefficient 629
(ABC), (b) 532-nm volume depolarization ratio (VDR), and (c) 1064/532-nm volume color 630
ratio (VCR) at a height of 0–5 km observed by the AD-Net lidar in Sainshand during the 631
same period as in Fig. 7. Regions E–H correspond to a dust storm, cold air, clouds, and a 632
dust layer, respectively. 633
634
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37
635
636
637
Fig. 9 Time-height cross sections of the (a) potential temperature (PT) and horizontal wind 638
and (b) vertical velocity (VV) and horizontal wind obtained from the NCEP FNL data for 639
Sainshand during the same period as in Figs. 7 and 8. The half and full barbs and 640
pennants represent wind speeds of 2, 4, and 20 m s-1, respectively. Regions F and H are 641
the same as in Fig. 8. 642
643
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38
644
645
646
Fig. 10 Same as Fig. 5, except that the location is Zamyn-Uud, and the period is from 00 647
to 21 LST on 23 May 2013. 648
649
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39
650
651
652
Fig. 11 Same as Fig. 8, except that the location is Zamyn-Uud, the height range is 0–4 km, 653
and the period is from 00 to 21 LST on 23 May 2013 (same as in Fig. 10). Regions I–K 654
correspond to a dust layer, cold air, and a cloud, respectively. 655
656
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40
657
658
659
Fig. 12 Same as Fig. 9, except that the location is Zamyn-Uud, and the period is from 00 660
to 21 LST on 23 May 2013 (same as Fig. 10). Regions I and J are the same as in Fig. 11. 661
662
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41
663
664
665
Fig. 13 Observational models for (a) Dalanzadgad, (b) Sainshand, and (c) Zamyn-Uud at 666
a height of 0–4 km during the dust event. The distance was calculated by using the 667
moving speed of the cold front (30 km h-1). The distance of 0 km indicates the leading 668
edge of the cold air (i.e., the cold front on the ground) at each observation site. The right 669
side is the moving direction of the cold front (southeast). The letter P means precipitation. 670
671
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42
672
673
674
Fig. 14 (a) The locations, (b) the height above ground level (AGL), and (c) the relative 675
humidity (RH) of 24-hour forward trajectories of air parcels corresponding to the dust 676
layer that was observed over cold air in Dalanzadgad on 22–23 May 2013. In panel (a), 677
the dots on the trajectories indicate their location every 6 hours, and the numerical values 678
of 00 and 12 near the trajectories represent the hours of 00 and 12 LST, respectively. 679
680
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681
682
683
Fig. 15 Same as Fig. 14, except that the location is Sainshand. 684
685
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44
686
687
688
Fig. 16 Same as Fig. 14, except that the location is Zamyn-Uud, and the initial time of the 689
forward trajectories is 23 May 2013. 690
691
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45
692
List of Tables 693
694
Table 1 Summary of the maximum top height and thickness range of the dust layer over 695
cold air observed in each site on 22–23 May 2013. In Sainshand, the presence of the 696
dust layer above a height of 4.0 km was unclear because of clouds. 697
698
699
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46
Table 1 Summary of the maximum top height and thickness range of the dust layer over 700
cold air observed in each site on 22–23 May 2013. In Sainshand, the presence of the 701
dust layer above a height of 4.0 km was unclear because of clouds. 702
703
Dust layer Dalanzadgad Sainshand Zamyn-Uud
Maximum top height 1.6 km (4.0 km) 3.8 km
Minimum thickness 0.2 km 1.6 km 0.3 km
Maximum thickness 0.5 km 2.5 km 1.7 km
704