[show abstract][hide abstract] ABSTRACT:  We analyzed data observed at Fukue-jima (32.752°N, 128.682°E), the downwind of the East Asian desert and urban areas, during the spring season (March, April, and May) of 2008 - 2011 aiming to understand the light-absorption capacity of Asian dust aerosols, which is a topic of controversy. The observational data showed the decreasing tendency of single scattering albedo, SSA (the ratio of scattering to extinction) with the decrease of Ångström exponent, ALPHA (a parameter describing the wavelength dependence of aerosol optical thickness; larger the sizes of dominant aerosols, smaller the ALPHA and vice versa) and the increase of yellow sand index, YSI (the ratio of dust aerosol optical thickness to total aerosol optical thickness), suggesting the important role of coarse-mode dust aerosols on observed low SSA values. The observational data further indicated that the low values of SSA during strong dust events were less likely due to the effect of only strong light-absorbing carbonaceous aerosols, such as black carbon (BC), indicating the association of aerosol size distribution on modulating SSA. Such observational results are justified by numerical calculations showing that aerosol size distribution can be the key factor on modulating SSA even without any change in relative amount of light-absorbing aerosol as well as total aerosol optical thickness. Therefore, the observed low SSAs in the downwind regions during dust events could be partially due to the dominance of coarse-mode aerosols over fine-mode aerosols, which are usual in dust events, along with the effect of mixed light-absorbing aerosols. The study further suggests that such effect of aerosol size distribution on SSA can be one of the important reasons for the low SSAs of dust aerosols in the source region as reported by some studies, if coarse-mode aerosols dominate fine- mode aerosols.
Journal of Geophysical Research: Atmospheres. 12/2013;
[show abstract][hide abstract] ABSTRACT: Potential improvements of aerosols algorithms for future climate-oriented satellites such as the coming Global Change Observation Mission Climate/Second generation Global Imager (GCOM-C/SGLI) are discussed based on a validation study of three years’ (2008–2010) daily aerosols properties, that is, the aerosol optical thickness (AOT) and the Ångström exponent (AE) retrieved from two MODIS algorithms. The ground-truth data used for this validation study are aerosols measurements from 3 SKYNET ground sites. The results obtained show a good agreement between the ground-truth data AOT and that of one of the satellites’ algorithms, then a systematic overestimation (around 0.2) by the other satellites’ algorithm. The examination of the AE shows a clear underestimation (by around 0.2–0.3) by both satellites’ algorithms. The uncertainties explaining these ground-satellites’ algorithms discrepancies are examined: the cloud contamination affects differently the aerosols properties (AOT and AE) of both satellites’ algorithms due to the retrieval scale differences between these algorithms. The deviation of the real part of the refractive index values assumed by the satellites’ algorithms from that of the ground tends to decrease the accuracy of the AOT of both satellites’ algorithms. The asymmetry factor (AF) of the ground tends to increase the AE ground-satellites discrepancies as well.
Advances in Meteorology 08/2013; 2013. · 1.24 Impact Factor
[show abstract][hide abstract] ABSTRACT: Concentrations of atmospheric CO2 and aerosol were measured in a field campaign conducted in winter 2006 around Mt. Tsukuba, Japan using ground-based CO2 analyzers, a lidar, and sky radiometers as well as CO2 analyzers onboard an aircraft. Vertical measurements revealed occasional similarity between the profiles of CO2 and aerosol concentrations, though their temporal variations are not always coordinated because of the effects of local sources or sinks. A sudden increase of downward winds, due to the approach of an anticyclonic synoptic flow, resulted in a rapid decrease in both the CO2 and aerosol concentrations in the boundary layer. These observation results have demonstrated that simultaneous measurements with airborne and ground-based instruments set on the summit/foot of a mountain are useful for the study of variability of CO2 concentration in the boundary layer.
Geophysical Research Letters - GEOPHYS RES LETT. 01/2009; 36(7).
[show abstract][hide abstract] ABSTRACT: We developed a cloud profiling radar, named FALCON-I, transmitting frequency modulated continuous wave (FM-CW) at 95GHz. The radar can observe vertical radar reflectivity factor of clouds with high sensitivity and high spatial resolution. The observation of Doppler velocity is more necessary to know the inside structure of clouds and interaction with aerosol. Doppler velocities of clouds can be obtained from the phase shift of the signal by using double-FFT method. As a result of the observations at Chiba University, Doppler velocities of thin clouds were successfully obtained as well as of bright band, and rainfall.
IEEJ Transactions on Fundamentals and Materials 01/2009; 129(4):177-182.
[show abstract][hide abstract] ABSTRACT: We developed a cloud profiling radar, named FALCON-I, transmitting frequency-modulated continuous wave (FM-CW) at 95 GHz for high sensitivity and high spatial resolution ground-based observations. Millimeter wave at 95 GHz is used to realize high sensitivity to small cloud particles. An FM-CW type radar realizes similar sensitivity with much smaller output power to a pulse type radar. Two 1m-diameter parabolic antennas separated by 1.4m each other are used for transmitting and receiving the wave. The direction of the antennas is fixed at the zenith at this moment. The radar can observe clouds up to 20 km in height with a resolution of 9 m. Beam size of the antenna is as small as 0.2 degree of arc, which corresponds to 15 m at the range of 5 km. Observation results showed that the sensitivity of -34 dBZ is realized at 5 km in range, and good spatial resolutions.
IEEJ Transactions on Fundamentals and Materials 01/2008; 128(4):257-262.
[show abstract][hide abstract] ABSTRACT: We have developed a low-power and high-sensitivity cloud profiling radar, named FALCON-I, transmitting frequency modulated continuous wave (FM-CW) at 95 GHz for ground-based observations. Millimeter wave at 95 GHz is used to realize much higher sensitivity than lower frequencies to small cloud particles. An FM-CW type radar realizes similar sensitivity with much smaller output power to a pulse type radar. Two 1m-diameter parabolic antennas separated by 1.4m each other are used for transmitting and receiving the wave. The direction of the antennas is fixed at the zenith at this moment. The radar can observe clouds up to 20 km in height with the range resolution of 15 m and the angular resolution of 0.2 degree. Simultaneous observations of FALCON-I and a pulse type radar, SPIDER, show good performance of FALCON-I. Sensitivity of FALCON-I is -32 dBZ in radar reflectivity factor at 5 km, which is only 3dB worse than that of SPIDER although its output power is 1/3000 to SPIDER. Ranging resolution of 15m is realized for FALCON-I, which is 1/10 of that of SPIDER. Using developed FALCON-I, we observed clouds in various regions and oceans in the last three years.
Physics and Engineering of Microwaves, Millimeter and Submillimeter Waves and Workshop on Terahertz Technologies, 2007. MSMW '07. The Sixth International Kharkov Symposium on; 07/2007
[show abstract][hide abstract] ABSTRACT: The ABC (Atmospheric Brown Cloud project) Gosan campaign 2005 (EAREX2005) was carried out at Gosan on Cheju Island, Korea, in March 2005. The objective of the campaign was to clarify aerosol characteristics as well as to compare each instrument for radiation and chemical observation. From these observations, eleven clear sky cases were selected and analyzed to estimate the aerosol radiative effect (ARE). As a result, the mean ARE during the campaign was −20.8 ± 9.0 W/m2 at the surface, −8.3 ± 5.3 W/m2 at the top of the atmosphere and 12.6 ± 6.8 W/m2 in the atmosphere. The ARE efficiency was −81.6 W/m2, −32.5 W/m2 and 49.4 W/m2, respectively. These results suggest that the aerosols during the campaign might consist of more or less yellow sand in comparison with the results simulated using typical aerosol models. On the basis of simultaneous observation of the depolarization ratio by lidar, a common feature of yellow sand is also found in a daily trend of aerosols through the period. A yellow sand index (YSI) is introduced using a column integration of extinction coefficients for spherical and nonspherical particles, separated empirically by the depolarization ratio. This index is equivalent to the fraction of yellow sand (nonspherical) aerosol in the observed aerosol optical thickness. The YSI has a good correlation with the Angstrom index (α) obtained by sky radiometer observations and shows that the increase in YSI corresponds to the decrease in α and the increase in single scattering albedo of aerosol. However, the YSI is poorly correlated with the ARE efficiency.
Journal of Geophysical Research 01/2007; 112. · 3.17 Impact Factor
[show abstract][hide abstract] ABSTRACT: Seasonal variations of tropospheric aerosol properties in Chiba, Japan, are investigated by means of optical monitoring (1999–2005), ground sampling (1998–2004), and wind data. The observation site at Chiba University is located in the urban Chiba area, about 30 km southeast of Tokyo. The aerosol optical thickness (AOT) and Angstrom exponent are derived from the data taken with a sun photometer. The value of AOT at the wavelength of 500 nm exhibits a seasonal variation, showing small values (<0.2) in fall and winter, and large values (∼0.5) in spring and summer. The variation of Angstrom exponent is in the range 0.5–1.8, showing negative correlation with the wind speed. This indicates that the influence of anthropogenic particles from local sources becomes relatively important when the wind is weak near the ground level. The influence of Asian dust particles is also detected during March and April. The seasonal variation is remarkable also in the chemical analysis data. For fine particles with diameters less than 2 μm, elemental carbon dominates in fall and winter, while (NH4)2SO4 is prominent in spring and summer. For coarse particles, the fraction of sea salt particles increases in spring and summer.
[show abstract][hide abstract] ABSTRACT: We developed a low-power and high-sensitivity cloud profiling radar transmitting frequency modulated continuous wave (FM-CW) at 95 GHz for ground-based observations. Millimeter wave at 95 GHz is used to realize much higher sensitivity than lower frequencies to small cloud particles. An FM-CW type radar realizes similar sensitivity with much smaller output power to a pulse type radar. Two 1m-diameter parabolic antennas separated by 1.4m each other are used for transmitting and receiving the wave. The direction of the antennas is fixed at the zenith. The radar is designed to observe clouds between 0.3 and 20 km in height with a resolution of 15 m. Using the developed millimeter-wave FM-CW radar at 95 GHz, we observed clouds in a campaign observation in Amami Island in March 2003, and on a sail on Mirai, a Japanese scientific research vessel, in September 2004 to January 2005 in the Arctic Ocean and the southwest of the Pacific Ocean. The radar provided good and sensitive data in these long-term observations.
[show abstract][hide abstract] ABSTRACT: A Mie lidar was used to make observation of Asian dust over Hefei (31.90° N, 117.16° E) in the every spring from 1998 through 2004. This paper presents main features of vertical distribution and temporal variation of Asian dust extinction coefficient at 532 nm wavelength during the seven years. There were two kinds of vertical distributions of Asian dust extinction coefficients. One indicated that the Asian dust particles intruded into the local boundary layer, causing the very thick dust layer with depth of about 3-4 km. The other showed that the Asian dust passed over Hefei area just above the boundary layer. The aerosol extinction coefficients in the elevated dust layer within the middle troposphere from 3 to 6 km were unusual large. Seasonal average aerosol extinction coefficient profiles showed that larger aerosol extinction coefficients from 1 km to 10 km altitude range were observed in the springtime rather than in any other season.
[show abstract][hide abstract] ABSTRACT: The data analyses of the ADEOS-II (Midori-II) GLI data have started. The optical and microphysical properties of warm water and cold ice clouds were retrieved by use of originally developed GLI data analysis algorithms. On the one-month mean results of warm water cloud in April 2003, very thick cloud optical thickness appeared in the east coast of the North America, the East Europe, and the South-East Asia. The moderately optically thick area spread over the Atlantic Ocean and West to Middle Pacific oceans. The effective radius was smaller on the continents and coastal area than ocean area. Especially, the South-East Asia to the middle pacific area where often covered with aerosols coming from continent in April, is the region of the smaller cloud effective particles. For the cirrus clouds, the smaller effective radii and larger effective radii can be obtained in low-to-mid and mid-to-high latitude area, respectively. Very low cloud top temperatures around 210K were often observed in the tropics. Warmer cloud top temperatures ranging from 220 to 240K were widely seen both over continental and oceanic area in mid-to-high latitude area.
[show abstract][hide abstract] ABSTRACT: Cloud is an important factor for the radiation budget through reflection of solar radiation and absorption of terrestrial radiation. Climate change is dependent on these two effects and focusing on an aerosol-cloud interaction. In East Asian region, consumption of fossil fuels is increasing and emits many kinds of gas and particles in addition of natural sources. The indirect effect of aerosol depends on the aerosol characteristics and weather conditions. The particle size and chemical features of aerosols affect cloud formation and particle size. Therefore, it is interesting to understand cloud properties such as a liquid water path (LWP) and cloud effective radius (Reff). This study is to estimate these two parameters with ground-based observations. In the paper a method to estimate a cloud effective radius and optical thickness is proposed using a combination of corrected LWP and the downward solar radiation. It is useful for continuous observation, especially LWP can be estimated for all day.
[show abstract][hide abstract] ABSTRACT: 1] Aerosol optical properties (aerosol optical thickness, Å ngström exponent, size distribution, and single scattering albedo) over east Asia were examined using long-term measurements of sky radiation at Mandalgovi, Dunhuang, Yinchuan, and Sri-Samrong sites of the Skyradiometer Network (SKYNET). Also included were sky radiation measurements at Anmyon, Gosan in Korea, and Amami-Oshima in Japan during April for examining optical properties of Asian dust. Results show that the seasonal average of aerosol optical thickness (AOT) generally exhibits a maximum in spring and a minimum in autumn over east Asia. At Sri-Samrong and Yinchuan, relatively distinct seasonal cycles are noted, in comparison to the arid desert regions of Dunhuang and Mandalgovi. In general, aerosol size distributions are characterized by a bimodal pattern, with a fine mode around 0.2 mm and a coarse mode around 2À5 mm. Similar to AOT and a, volume spectra are also much dependent on geographical location and season. Dunhuang mostly shows coarse mode particles in all seasons, while Mandalgovi and Sri-Samrong show large seasonal variations in the total volume of fine mode particles. The single scattering albedos of dust particles over east Asia are around 0.9 at 0.5 mm, which are larger than the previously known values of 0.63–0.89 but similar to those found in the Aerosol Robotic Network (AERONET) analysis. It is noted that the optical properties of Asian dust around Korea and Japan are quite similar to those found in dust source regions such as Dunhuang and Mandalgovi. However, the single scattering albedo appears to be smaller than those observed in Dunhuang and Mandalgovi. Furthermore, single scattering albedo tends to become smaller during the dust outbreak period. Considering that aerosols in Korean and Japanese areas are much influenced by anthropogenic aerosols emitted in China particularly under the westerly conditions, the mixing processes between different aerosol species may be the cause of the different optical properties of Asian dust.
Journal of Geophysical Research 01/2004; 109. · 3.17 Impact Factor
[show abstract][hide abstract] ABSTRACT: A cloud profiling radar transmitting frequency-modulated continuous wave (FM-CW) at 95 GHz is developed for ground-based observations. Millimeter wave at 95 GHz is used to realize high sensitivity to small cloud particles. Two 1m-diameter parabolic antennas separated by 1.4m each other are used for transmitting and receiving the wave. The direction of the antennas is fixed at the zenith. The radar is designed to observe clouds between 0.3 and 15 km in height with a resolution of 15 m. The system was integrated and sensitivities and stabilities have been measured. Results of test measurements of clouds show that the system is sensitive and stable enough to observe various clouds.
[show abstract][hide abstract] ABSTRACT: Radiative forcings of aerosols and clouds in the East China Sea region are studied using data from surface radiation measurements, satellite remote sensing, and model simulation conducted in April 2001 as a study of Asian Atmospheric Particle Environmental Change Studies (APEX) cooperating with International Global Atmospheric Chemistry (IGAC)/ACE-Asia project. The monthly mean whole sky radiative forcing of the aerosol direct effect is derived from various methods as −5 to −8 W/m2 at the top of atmosphere (TOA) and −10 to −23 W/m2 at Earth's surface of Gosan (33.28N, 127.17E) and Amami-Oshima (28.15N, 129.30E) sites, though there is a large regional difference caused by changes in the aerosol optical thickness and single scattering albedo. The cloud forcing is estimated as −20 to −40 W/m2, so that the aerosol direct forcing can be comparable to the cloud radiative forcing at surface. However, the estimate of the aerosol direct forcing thus obtained strongly depends on the estimation method of the aerosol properties, especially on the single scattering albedo, generating a method difference about 40%. The radiative forcing of the aerosol indirect effect is roughly estimated from satellite method and SPRINTARS model as −1 to −3 W/m2 at both TOA and surface.
Journal of Geophysical Research 01/2003; 108. · 3.17 Impact Factor