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Asian dust is transported over a long range via the mid-latitude westerlies when dust is lifted to the free troposphere over the source regions, whereas dust remaining in the atmospheric boundary layer is not transported far. In the Gobi Desert, a major source region of Asian dust, a ceilometer (compact lidar) monitors the vertical distribution of dust at Dalanzadgad, Mongolia. On 29-30 April 2015, the ceilometer observed a developed dust storm over the ground, followed by a dust layer within a height of 1.2-1.8 km. The dust storm had already developed in the upwind region before reaching Dalanzadgad. This feature was also shown in the ceilometer observation data. The dust layer remained at almost the same height for 12 h, because the dust became trapped within an inversion layer at a height of 1.2-1.5 km over cold air. This result suggests that the inversion layer prevented the dust from reaching the free troposphere, thereby restraining the long-range transport of the dust via the westerlies. This is the first paper that reports this type of vertical distribution of dust in the source region based on observation data.

Ulaanbaatar, the capital of Mongolia, is subject to high levels of atmospheric pollution during winter, which severely threatens the health of the population. By analyzing surface meteorological data, ground-based LIDAR data, and radiosonde data collected from 2008 to 2016, we studied seasonal variations in particulate matter (PM) concentration, visibility, relative humidity, temperature inversion layer thickness, and temperature inversion intensity. PM concentrations started to exceed the 24-h average standard (50 μg/m3) in mid-October and peaked from December to January. Visibility showed a significant negative correlation with PM concentration. Relative humidity was within the range of 60-80% when there were high PM concentrations. Both temperature inversion layer thickness and intensity reached maxima in January and showed similar seasonal variations with respect to PM concentration. The monthly average temperature inversion intensity showed a strong positive correlation with the monthly average PM2.5 concentration. Furthermore, the temperature inversion layer thickness exceeded 500 m in midwinter and overlaid the weak mixed layer during daytime. Radiative cooling enhanced by the basin-like terrain led to a stable urban atmosphere, which strengthened particulate air pollution.

Aerosol particles, including airborne microorganisms, are transported through the free troposphere from the Asian continental area to the downwind area in East Asia and can influence climate changes, ecosystem dynamics, and human health. However, the variations present in airborne bacterial communities in the free troposphere over downwind areas are poorly understood, and there are few studies that provide an in-depth examination of the effects of long-range transport of aerosols (natural and anthropogenic particles) on bacterial variations. In this study, the vertical distributions of airborne bacterial communities at high altitudes were investigated and the bacterial variations were compared between dust events and non-dust events.Aerosols were collected at three altitudes from ground level to the free troposphere (upper level: 3000 or 2500 m; middle level: 1200 or 500 m; and low level: 10 m) during Asian dust events and non-dust events over the Noto Peninsula, Japan, where westerly winds carry aerosols from the Asian continental areas. During Asian dust events, air masses at high altitudes were transported from the Asian continental area by westerly winds, and laser imaging detection and ranging (lidar) data indicated high concentrations of non-spherical particles, suggesting that dust-sand particles were transported from the central desert regions of Asia. The air samples collected during the dust events contained 10–100 times higher concentrations of microscopic fluorescent particles and optical particle counter (OPC) measured particles than in non-dust events. The air masses of non-dust events contained lower amounts of dust-sand particles. Additionally, some air samples showed relatively high levels of black carbon, which were likely transported from the Asian continental coasts. Moreover, during the dust events, microbial particles at altitudes of > 1200 m increased to the concentrations ranging from 1. 2 × 106 to 6. 6 × 106 particles m−3. In contrast, when dust events disappeared, the microbial particles at > 1200 m decreased slightly to microbial-particle concentrations ranging from 6. 4 × 104 to 8. 9 × 105 particles m−3.High-throughput sequencing technology targeting 16S rRNA genes (16S rDNA) revealed that the bacterial communities collected at high altitudes (from 500 to 3000 m) during dust events exhibited higher diversities and were predominantly composed of natural-sand/terrestrial bacteria, such as Bacillus members. During non-dust periods, airborne bacteria at high altitudes were mainly composed of anthropogenic/terrestrial bacteria (Actinobacteria), marine bacteria (Cyanobacteria and Alphaproteobacteria), and plant-associated bacteria (Gammaproteobacteria), which shifted in composition in correspondence with the origins of the air masses and the meteorological conditions. The airborne bacterial structures at high altitudes suggested remarkable changes in response to air mass sources, which contributed to the increases in community richness and to the domination of a few bacterial taxa.

There is increasing interest in finding the relation between solar activity and climate change. In general, fractal properties may be observed in the time series of the dynamics of complex systems, such as solar activity and climate. This study investigates the relations among solar activity, geomagnetic activity, and climatic regime shift by performing a multifractal analysis. To investigate the change in multifractality, we apply a wavelet transform to time series. The change in fractality of the sunspot number (SSN) correlates closely with that of the solar polar field strength. For the SSN and solar polar field strength, a weak multifractality or monofractality is present at the maximum SSN, minimum SSN, and maximum solar polar field strength. A strong multifractality is present two years before the maximum SSN. The climatic regime shift occurs when the SSN increases and the disturbance of the geomagnetic activity is large. At the climatic regime shift, the changes in the fractality of the Pacific Decadal Oscillation (PDO) index and changes in that of the solar activity indices corresponded with each other. From the fractals point of view, we clarify the relations among solar activity, geomagnetic activity, and climatic regime shift. The formation of the magnetic field of the sunspots is correlated with the solar polar field strength. The solar activity seems to influence the climatic regime shift. These findings will contribute to investigating the relation between solar activity and climate change.

The distribution and transport of windblown dust that occurred in Northeast Asia from 28 March to 2 April 2012 was investigated. Data of particulate matter less than 10 micrometers (PM10) near the surface and light detection and ranging (LiDAR) measurements from the ground up to 18 km were used in the study. A severe dust event originated over southern Mongolia and northern China on 28 March 2012, and the widespread dust moved from the source area southeastward toward Japan over several days. Windblown dust reached Japan after two days from the originating area. LiDAR measurements of the vertical distribution of the dust were one to two km thick in the lower layer of the atmosphere, and increased with the increasing distance from the source area.

Airborne microorganisms transported by dust events from Asian Deserts influence climate changes, ecosystem dynamics and human health in the westerly-wind blowing areas of East Asia. However, the vertical transport of airborne microorganisms was not understood in detail. We collected aerosols at high altitudes (800 m and 500 m) and ground levels (5 m and 10 m) at Asian dust-source area, such as the Taklimakan and Gobi Deserts, for analyzing compositions and abundances of the airborne microorganisms that are distributed vertically over desert area. Assessment of the dust particles using an optical particle counter and microscopic observation counts demonstrated that the mineral and microbial particles remained suspended at altitudes of over 300 m and decreased to half to one-tenth of concentrations compared to those at the ground level. High-throughput sequencing of 16S rRNA genes (bacterial taxonomic marker) revealed that the airborne bacterial communities were mixed vertically at the altitudes of some hundreds of meters over both the sites and were predominantly composed of the phyla Actinobacteria, Firmicutes, Bacteroidetes, and Proteobacteria. In contrast, using sequencing analysis of internally transcribed spacer regions (fungal taxonomic markers), the fungal community structures over both the sites were different at high altitudes and ground levels. Sequences belonging to the phylum Ascomycota increased at high altitudes and comprised those of a commonly detected mold that includes the genera Cladosporium and Alternaria and is thought to be resistant to atmospheric stressors. Our results indicate that airborne bacterial communities are easily mixed vertically over dust-source desert, while stressor-tolerant fungi of airborne Ascomycota remain at high altitudes of desert atmosphere.

Climate change can be interpreted from the perspective of fractals. This study uses the wavelet transform to analyze the multifractal behavior of the monthly El Nino/Southern Oscillation index (NINO3.4), the monthly Indian Ocean Dipole Mode Index (DMI), and the monthly North Atlantic Oscillation (NAO) index. Strong multifractality was observed when NINO3.4 and DMI had high coherency. Changes from multifractal to monofractal behavior were observed at the 1976/77 regime shift for NINO3.4 and DMI, and at the 1988/89 regime shift for NAO index. We found that a regime shift occurs when the fluctuation is large and multifractality is strong.

In April 2002, a severe dust storm occurred in the Taklimakan Desert. A large amount of the dust was lifted up by the dust storm and gradually removed in the following few days. The whole event of the dust storm was observed by the Mie-scattering depolarization lidar at Aksu, Xinjiang, China (40.62°N, 80.83°E, 1028 m above mean sea level). This paper describes the dust event and the removal process that was observed by the lidar. During the dust storm (April 13-16), a dense dust layer developed from the ground up to 5.5 km. The backscattering ratio was 20 or more, and the depolarization ratio was 15-25%. Due to the absorption of the laser beam by the heavy dust, a normal lidar observation was impossible for several hours. In this study, we estimated the backscattering ratio at the lowest height during the dust storm by solving the lidar equation directly. After the dust storm (April 17-20), a clear diurnal variation of the top of the dust layer was found by the lidar. An investigation of the lidar signals at different heights shows that there were two types of the removal process of the dust. The lidar signals at lower heights (less than the 2 km) gradually decreased during the post-dust storm period. This result indicates that the gravitational settling of the relatively large sized dust (coarse particles with a diameter of 10 μm or more) occurs near the ground. On the other hand, lidar signals at 2-4 km had a clear diurnal variation with spike-like peaks from evening to midnight. These peaks suggest that the advection of the relatively small sized dust picked up in other location is due to the local circulation that occurs in the Tianshan Mountains and Tarim Basin.

From the evening of 25 March 2003 until 27 March an Asian dust event (Kosa) was observed at a total of 37 routine meteorological observatories in Japan, although no significant dust storms had been observed in the arid regions of China and Mongolia. A numerical simulation with a three-dimensional global aerosol transport model and meteorological observations reveal that the observed mineral dust particles were generated through dust storms in North Africa and the Middle East on 19 March. The simulation predicted that dust particles generated in the Sahara Desert and Arabian Peninsula on 19 March would be transported north of the Tien Shan Mountains in China and arrive over Japan in about 6–7 days. It also indicated that over 50% of the dust particles in Japan on 26–27 March came from North Africa, about 30% from the Middle East, and only about 10% from China in the boundary layer. The simulated result is consistent with polarization lidar and sky radiometer observations, indicating that the simulation is realistic. The simulation indicates that the Kosa phenomenon was caused by a mixture of transported dust and anthropogenic pollutants. The simulation of this dust event suggests the possible importance of dust transport from the Sahara and the Arabian Peninsula to East Asia.

In order to elucidate the variation and characterization of dust particles that originate in the arid and semi-arid regions of inland Asia and are transported to Japan, we established a sampling network system in east China and Japan and collected aeolian dust under the Japan-China joint project "ADEC". Monitoring of the total suspended particle (TSP) and size-segregated dust concentrations were carried out in Beijing, Qingdao and Hefei in China, and Fukuoka, Nagoya, Tsukuba and Naha in Japan. The seasonal variations showed the general trend that the aerosol concentration was high in spring and low in summer, though it sometimes became high in winter in Qingdao. The aerosol size distribution was bimodal. One peak at around 0.5 μm diameter corresponds to particles of anthropogenic origin, in which the main components are black carbon, NH4 + and SO 4 2 - , and some elements such as Pb, Cd, Sn, Sb and Bi are abundant. The other peak at around 4-5 μm diameter corresponds to mineral dust of soil origin, in which the main soluble components are Na + , Ca 2 + , NO 3 - and Cl - . The coarser particles increased when a dust event occurred. The IOP program was conducted in the spring of 2002 (IOP-1) and 2003 (IOP-2). The dust concentration during IOP-1 was high in China, particularly in Beijing. The average dust concentration during a dust event decreased in the order of Beijing > Qingdao > Hefei and Beijing > Fukuoka > Nagoya > Tsukuba > Naha. However, there were few observable dust events during IOP-2. From the results of continuous monitoring, the dust concentration during periods without dust events seemed to be almost equal at all monitoring locations in Japan. This suggests that the segregation of dust occurs in China and fine dust particles are transported to Japan. Seasonal variations of TSP, Pm 1 1 (particulate size is less than 11 μm), PM 2 . 1 (less than 2.1 μm) and mineral matter (larger than 2.1 you) contents were studied. It was shown that these values decrease with distance from the source area.

Aerosol particles were collected in the situation of the widespread dust suspension on 21 February 1991 at Qira in the southern edge of the Taklamakan Desert, western China. The collected particles were examined by a transmission electron microscope equipped with an energy-dispersive X-ray (EDX) analyzer in order to obtain the size and elemental composition of individual mineral particles. On the basis of EDX analyses for 386 particles, mineral particles were present in high number fractions (>99%) of particles in the radius range of 0.1–4 μm. Particles mainly composed of silicates comprised 76% of mineral particles. “Ca-rich” particles were detected in 7% of all the particles. Ca in the particles would be present not only as CaCO3 but also as an internal mixture of CaCO3 and CaSO4. Particles containing halite (NaCl) were detected in number proportions of about 10% and were mainly present in the radius range of ⩾0.5 μm. Some halite particles would be modified by chemical reactions with sulfuric acid.

The present study investigates the relationship between surface wind convergence and clouds by performing statistical analyses of time variations in surface wind field, its horizontal divergence, cloud distribution, and appearance frequency of radar echoes in the Nobi Plain in the daytime on summer sunny days using various observation data from 1990 to 1999. The 99 summer sunny days when general wind was weak were selected objectively in advance of the analyses. The results of analyses show that a westerly wind from the Biwa Lake direction and a sea breeze from Ise Bay converge in the north of Nagoya after 1300 JST on summer sunny days. In addition, clouds (cumulus) tend to be formed all over the Nobi Plain from late in the morning to about noon by thermal convections, and the formation of clouds continues near strong surface wind convergence zones until around 1500 JST on summer sunny days, although clouds are hardly formed in the afternoon in almost all parts of the plain due to the decline of the thermal convections. The continuation of the cloud formation is especially remarkable at the northeast of Nagoya. Thus, in the Nobi Plain on summer sunny days, the conditions where clouds are easily formed continue at the northeast of Nagoya until around 1500 JST, because of a strong surface wind convergence between a westerly wind from the Biwa Lake direction and a sea breeze from Ise Bay. The analysis of radar echoes observed around 1500 JST shows that the echoes occasionally appear near the northeast of Nagoya on summer sunny days. These results indicate that the strong surface wind convergence plays an important role in the formation of clouds, after thermal convection has weakened, on summer sunny days.

In the spring of 1991, individual aerosol particles were collected on electron microscopic grids in Beijing (China) and Nagasaki (Japan). In order to study the change in the chemical composition of Asian dust-storm particles during transport, the dust particles were examined using an electron microscope equipped with an energy-dispersive X-ray (EDX) analyzer. An isentropic backward-trajectory analysis was carried out in order to obtain the transport path of the dust-storm particles. Spatial distributions of clouds by the Geostationary Meteorological Satellite (GMS) were also used in order to examine the presence of clouds along the transport path. Asian dust-storm particles mixed internally with sea salt (mixed particles) ranged from 16 to 100 % among the dust particles in the air over Nagasaki. For the two cases that the same dust-storm events were observed in Beijing and Nagasaki, dust-storm particles containing sea salt were present abundantly in Nagasaki in a case that the air would have been influenced largely by clouds in the maritime atmosphere during the transport. It is suggested that these mixed dust-storm particles were formed by cloud processes.

The surface energy balance at the Zhangye Oasis during June 1991 was calculated from the fundamental observation period (FOP) data of the Heihe River Basin Field Experiment (HEIFE). Typical phenomena induced by the oasis effect were observed during the afternoons on fair weather days in June. An inversion layer over the oasis developed from the surface to 8 m height in the afternoon when the wind speed was strong. The temperature difference between 1-8 m heights was about 2°C. The specific humidity exhibited a steep vertical gradient over the oasis. The latent heat flux was the dominant term in the surface energy balance. The sensible heat flux was small and upward during the morning hours, but was directed downward in the afternoon due to large evaporative heat loss. On the contrary, the sensible heat flux was the dominant term at the desert station. The net radiation in the daytime was small and only 63 % of that at the oasis. A model of the observed oasis effect is proposed in the present note.

The atmospheric boundary layer over the central area of Tokyo was studied by a Mie-scattering polarization lidar. Negative correlation of the depolarization ratio with relative humidity was observed in the lower atmosphere throughout the year. Contributions of hygroscopic or water-soluble and deliquescent aerosol particles, especially sea-salt particles to the depolarization ratio are discussed in the light of the chemical compositions of the surface aerosol in Tokyo.

Aerosol particles were collected at China and Japan in the same spring Asian dust-storm event of 1991 in order to study the change in composition of mineral aerosol particles during long range transport. It was found on the basis of a microchemical analysis that dust particles containing Mg, Al, Si, K, Ca and Fe were a major fraction of the aerosol particles collected at Hohhot and Beijing, China, and Nagasaki, Japan. A large fraction of the mineral aerosol particles was internally mixed with sea salt in Nagasaki. Present study suggests that the internal mixed particles were mainly produced by cloud processes through droplet coalescence.

Aerosol particles were collected in the spring of 1990 and 1991 and in the summer of 1990 at Zhangye and its surrounding areas in northwestern China and analyzed with an electron microscope equipped with an energy-dispersive X-ray (EDX) analyzer. The weight percentages of elements with atomic numbers larger than 11 (sodium) in individual particles were obtained using EDX spectra. Three samples collected in spring and one sample in summer were analyzed and particle type classifications were given. In spring, mineral particles were present in high number fractions (97-98 %) of particles in the radius range of 0.1-6 μm. Particles mainly composed of aluminosilicate comprised 60-70 % of mineral particles. The samples were characterized by the presence of Ca-rich particles. The Ca-rich particles were present in number proportions (10-20 %) of mineral particles and often contained S, suggesting the presence of CaSO 4 .2H 2 O (gypsum). However, most of the mineral particles had the weight ratios of S/Ca less than 0.1. The analysis showed that Ca-dominant particles, which would be mainly composed of CaCO 3 (calcite), were present mainly in the sub-micrometer radius range. In summer, particles were collected under the atmospheric condition of strong wind (8 ms −1 ). The sample also showed that mineral particles were dominant (98 % by number) in particles of 0.1-5 μm radius. This result suggests the importance of mineral particles, even in the summertime atmosphere.

[1] Extensive dust outbreaks occurred on the late morning of 26 March 2004 in the Taklimakan Desert. An image by the satellite AQUA shows the dust outbreaks as an enormous dust storm extending as far as 1000 km in the direction of east and west across the desert. A ground-based lidar was successful in observing the dust storm. Values of the backscattering ratio from near the ground surface to an altitude of 6 km above sea level rapidly increased as soon as the dust storm covered the lidar observation site. Numerical experiments including a diffusion experiment revealed that strong westerly winds appeared at the surface level following the morning inversion breakup and then induced the dust outbreaks. The nocturnal inversion layer prevented the strong westerly winds from spreading to the surface level until the breakup. Notable nocturnal inversion is considered to be easily formed in the Taklimakan Desert because of its deep basin topography which can accumulate cold air masses. These results show the stability of the planetary boundary layer to be an extremely important factor in dust outbreaks especially in basin deserts, in addition to the intensity of surface winds. This implies that the occurrence frequency of dust storms in the desert has a diurnal cycle.

Etude des variations regionales du spectre des vents de surface au Japon: l'analyse a ete effectuee sur des spectres pour des periodes allant de 2 h a plusieurs annees (jusqu'a 3,7 ans), apres enregistrement dans 206 stations, a l'aide de 5 annees de donnees horaires, moyennees sur 10 minutes

ライダーの基本的な問題の1つとしてレーザー送信部と受信望遠鏡との光軸合わせがある。ここでは、光軸合わせに便利なライダー後方散乱信号を、よく使用されているルビーレーザー、ヤグレーザーのそれぞれの基本波、高調波に対し、エーロゾル・オゾンを含めた大気モデルを用いて計算している。 次に光軸合わせにミスアライメントがあった場合、後方散乱信号はどうなるか、また成層圏エーロゾル観測にどのような影響を及ぼすかを調べている。ライダーのレーザー送信部と受信望遠鏡の光軸が完全なアライメントから、互いに外向きにはずれた場合は、高度10～30km間で、上向きに大きくなるような見かけ上の後方散乱比RB′が、例えエーロゾルが存在しなくとも現れ、互いに光軸が交差した時には下向きに大きくなるようなRB′が観測されることになる。このような場合のRB′を補正する1方法について述べているが、言うまでもなく、このようなミスアライメントが起こらないようにライダーシステム設計することが重要である。