JMSJ, 2014, Vol. 92A (September)
Special Issue on SKYNET
Diémoz et al. (2014)
Diémoz, H., M. Campanelli, and V. Estellés, 2014: One year of measurements with a POM-02 sky radiometer at an Alpine EuroSkyRad station. J. Meteor. Soc. Japan, 92A, 1-16.
http://dx.doi.org/10.2151/jmsj.2014-A01 Graphical Abstract
- Characterization of aerosol properties is performed for the first time at the Alpine site of Saint-Christophe, Aosta (Italy). The AOD at the station is generally very low (0.10 at 500nm), however spikes (up to 0.75) can occur due to the transport of Saharan dust and smoke clouds moving on an intercontinental scale.
- SKYRAD and SUNRAD aerosol optical depths and Ångström exponents are compared, providing consistent results. Spectral variation of the Ångström exponent is also employed to discriminate between different types of particles.
- Influence by local meteorology and anthropogenic emissions is investigated, providing useful information to understand the pollution dynamics in mountainous regions.
Che et al. (2014)
Che, H., G. Shi, H. Zhao, T. Nakajima, P. Khatri, T. Takamura, H. Wang, Y. Wang, J. Sun, and X. Zhang, 2013: Aerosol optical properties retrieved from a Prede sky radiometer over an urban site of Beijing, China. J. Meteor. Soc. Japan, 92A, 17-31.
http://dx.doi.org/10.2151/jmsj.2014-A02 Graphical Abstract
- The AOD decreases depending on wavelength during every season in Beijing. Higher and lower AOD values occur in summer and winter. This seasonal AOD pattern may be related to weather conditions (Fig. 1a). Alpha values are higher in summer and lower in spring. Alpha values in summer are commonly higher than in other seasons, indicating that fine particles predominate during the summer season in Beijing (Fig. 1b). Average SSA values shows that the aerosol scattering ability is stronger in the spring and summer while in autumn and winter there is more absorption component in the atmosphere of Beijing (Fig. 1c).
- The frequency of Alpha > 0.80 and SSA < 0.90 at 400 nm is 53.9% (Fig. 2a) and the frequency of Alpha > 0.80 and SSA > 0.90 at 1020 nm is about 69.2% in Beijing. This means that the absorption of fine particles occurs with a greater intensity at short wavelengths and becomes more scattered over infrared wavelengths in the atmosphere of Beijing (Fig. 2b).
Bi et al. (2014)
Bi, J., J. Shi, Y. Xie, Y. Liu, T. Takamura, and P. Khatri, 2014: Dust aerosol characteristics and shortwave radiative impact at a Gobi Desert of northwest China during the spring of 2012. J. Meteor. Soc. Japan, 92A, 33-56.
http://dx.doi.org/10.2151/jmsj.2014-A03 Graphical Abstract
- High aerosol loading and predominantly coarse particulates were observed in Dunhuang during the spring of 2012 ascribed to the influence of prevalent dust storm (Fig. 1).
- The single scattering albedo at 500 nm (SSA500) varied from 0.91 to 0.97 on dusty days and increased with the increase of aerosol optical depth, indicating that the dust aerosols sourced from northwest China were not strongly absorbing.
- The daily mean aerosol shortwave direct radiative forcing (ARF) were largely negative at the surface (-79.4 to -3.2 W m-2) and moderately positive in the atmosphere (2.2 to 25.1 W m-2), which represents a strong cooling at the surface and moderate warming in the atmosphere. The ARF at TOA was positive value when SSA500 is less than 0.85 or the imaginary part at 500 nm was larger than 0.015 (Fig. 2).
Kitakoga et al. (2014)
Kitakoga, S., Y. Inoue, M. Kuji, T. Hayasaka, 2014: Characteristics of aerosol properties of haze and yellow sand examined from SKYNET measurements over East China Sea. J. Meteor. Soc. Japan, 92A, 57-69.
http://dx.doi.org/10.2151/jmsj.2014-A04 Graphical Abstract
- Characteristics of atmospheric phenomena such as haze and yellow sand (Kosa) events were investigated in terms of aerosols by using sky radiometers, LIDAR, and OPC observations at Fukue-jima and Amami-Oshima Islands from 2003 to 2004.
- Aerosol properties such as loading, light absorptivity, particle size, non-sphericity, and vertical distribution showed specific features both in the atmospheric column (Fig. 1: left) and near the surface (Fig. 1: right), depending on the atmospheric phenomena compared with normal atmospheric conditions.
- It was clearly confirmed that the influence of limited light absorptivity dominated even during a Kosa event (Fig. 1: left).
Uchiyama, A., 2014: Method to retrieve single scattering properties of aerosols using multi-wavelength scattering and absorption coefficient data measured by integrating nephelometer and absorption photometer. J. Meteor. Soc. Japan, 92A, 71-91.
http://dx.doi.org/10.2151/jmsj.2014-A05 Graphical Abstract
- This study developed a method for retrieving the single scattering properties of an aerosol from multiwavelength scattering and absorption data and evaluated its performance and accuracy using simulation data based on Optical Properties of Aerosols and Clouds (OPAC) models.
- Using retrieved values, single scattering properties (scattering, absorption, and extinction coefficients: single scattering albedo (SSA); and the asymmetry factor) are more accurately estimated.
- The RMSE of the SSA calculated directly from the measured values was 0.014–0.021, and that of the SSA calculated from retrieved values was 0.002, corresponding to a relative error of 0.2 %.
- Sensitivity tests of the systematic (bias) error of absorption and scattering coefficients in SSA retrieval demonstrated that, with a 10 % systematic error, the maximum difference between the true value and the retrieved SSA exceeded 0.02 for a small SSA, but with a systematic error of 3 % or 5 %, the maximum difference was small. Therefore, a systematic error of less than 5 % is desirable.
- The retrieved volume size distribution and complex refractive index were qualitatively similar to the original values.
Uchiyama et al. (2014)
Uchiyama, A., A.Yamazaki, R. Kudo, E. Kobayashi, H. Togawa, and D. Uesawa, 2014: Continuous ground-based observation of aerosol optical properties at Tsukuba, Japan: Trend and climatology. J. Meteor. Soc. Japan, 92A, 93-108.
http://dx.doi.org/10.2151/jmsj.2014-A06 Graphical Abstract
- To investigate aerosol optical properties, the Meteorological Research Institute has been continuously measuring scattering and absorption coefficients since January 2002 in dry air conditions at Tsukuba, Japan.
- We used these optical data to investigate trends of aerosol properties and climatology.
- The results showed that most aerosol characteristics had seasonal variation and decreasing or increasing trends significant at the 95 % confidence level.
- From 2002 to 2013, the extinction coefficient at 550 nm and absorption coefficient at 530 nm had statistically significant decreases of –1.5 × 10–6 and –5.4 × 10–7 m–1 year–1, respectively. The single scattering albedo (SSA) at 550 nm had a significant increasing trend of 7.4 × 10–3 year–1.
- The increasing trend of 2.1 × 10–2 year–1 in the absorption Ångström exponent from 2006 to 2013 was significant. This tendency suggests a compositional change of light-absorbing aerosol.
- The analysis using the extinction Ångström exponent showed that aerosol characteristics were dependent on the extinction Ångström exponent.
- The aerosol characteristics estimated from optical data were consistent with those derived from radiometer data.
Saito et al. (2014)
Saito, T., and T. Hayasaka, 2014: Effects of dust aerosols on warm cloud properties over East Asia and the Sahara from satellite data. J. Meteor. Soc. Japan, 92A, 109-123.
http://dx.doi.org/10.2151/jmsj.2014-A07 Graphical Abstract
- Analysis of the satellite observation data showed that effective particle radius (Re) for dust-bearing clouds were smaller than those for dust-free clouds and that number concentration of cloud particle (Nc) for dust-bearing clouds were larger than those for dust-free clouds in East Asia. However, it was found that Re does not decrease with an increase in dust concentration (Fig. 1).
- A decrease in Re value is correlated with sulfate concentration in only dust-bearing clouds in East Asia (Fig. 2). It suggest that suggests saturation of the indirect effect from a large amount of anthropogenic aerosols, causing dust particles to have a greater impact on warm cloud in regions of heavy air pollution.
Yamada et al. (2014)
Yamada, K., T. Hayasaka, and H. Iwabuchi, 2014: Variation in radiative contribution by clouds to downward longwave flux. J. Meteor. Soc. Japan, 92A, 125-140.
http://dx.doi.org/10.2151/jmsj.2014-A08 Graphical Abstract
- The cloud radiative forcing (CRF) increases with increasing of cloud fraction and decreasing of precipitable water and cloud base height (Fig. 1). This study evaluated CRF using with 1-dimentional radiative transfer model (mstrnX) and in-situ observation data at eight sites, which belong to the Baseline Surface Radiation Network (BSRN).
- At Antarctic station, cloud shows negative effect, which appears frequently with a strong temperature inversion layer. Under the presence of temperature inversion, the dry region in which precipitable water is smaller than 10 mm shows smaller cloud effect than no temperature inversion (Fig. 2).
- At Japanese station located on the Pacific Ocean side, cloud effect shows increasing with increasing of cloud base height of low cloud. This correlation is caused of the difference of cloud base height during the summer and winter season.
Hayasaka et al. (2014)
Hayasaka, T., and G.-Y. Shi, 2014: Effects of clouds on surface shortwave irradiance in China: Estimation by surface radiation measurements and satellite data. J. Meteor. Soc. Japan, 92A, 141-156.
http://dx.doi.org/10.2151/jmsj.2014-A09 Graphical Abstract
- The negative correlation between PRF (Potential Radiative Forcing) of cloud amount and cloud optical thickness became stronger with increasing cloud optical thickness up to about 8, and became weaker beyond this optical thickness (Fig. 1). In contrast, the correlation coefficient between cloud optical thickness and its PRF exhibited large variation for small optical thickness and converged to a small negative value with increasing optical thickness; this occurred particularly in the South and East regions (Fig. 2).
- The physical values of the PRF of cloud amount and cloud optical thickness obtained from observed data analysis were consistent with those calculated from ISCCP data, although the PRF of cloud amount in the present study was slightly larger for negative values than the previous calculations. This confirmed that PRFs are useful for evaluation of cloud effects on the surface shortwave irradiance.
Chen et al. (2014)
Chen, B., L. Dong, G. Y. Shi, L. J. Li, and L. F. Chen, 2014: Anthropogenic heat release: Estimation of global distribution and possible climate effect. J. Meteor. Soc. Japan, 92A, 157-165.
http://dx.doi.org/10.2151/jmsj.2014-A10 Graphical Abstract
- Global AHR was geographically concentrated, essentially correlating to economic activities, just as Fig.1 shows. Although the global mean flux of AHR is very small, it can reach a high enough level to affect regional climate in the concentrated urban regions.
- The model results(Figs. 2 and 3) show that AHR has a significant impact on surface temperature and that it is able to affect global atmospheric circulation, leading to a 1-2 K increase in the high-latitude areas of Eurasia and North America. The results show that the AHR is able to affect global climate despite being limited to a region. AHR is an important factor in global climate change that should not be ignored.
Song et al. (2014)
Song, H.-J., B. J. Sohn, H.-W. Chun, Y. Chun, and S.-S. Lee, 2014: Improved cloud screening method for the analysis of sky radiometer measurements and application to Asian dust detection. J. Meteor. Soc. Japan, 92A, 167-183.
http://dx.doi.org/10.2151/jmsj.2014-A11 Graphical Abstract
- A cloud screening method employing two successive procedures of variability test and coarse mode test was developed, aiming at better removal of cloud contaminated data in the sky radiometer retrievals
- The variability test effectively removes data contaminated by relatively thick low-level clouds, while the coarse mode test eliminates data likely contaminated by thin cirrus-type clouds. In particular, the coarse mode test could effectively alleviate problems related to high single scattering albedo (SSA) due to the thin cirrus contamination. Compared to the current cloud screening algorithm for SKYNET (Khatri and Takamura, 2009), the new method appeared to provide better results, and in particular, reduced the overestimated AOT and SSA without the use of co-located solar flux measurements.
- After applying the new cloud screening method, many of the data points located in the high AOT and low Ångström exponent sector were eliminated, whereas dust points were relatively well preserved (Fig. 1), indicating the improvement of dust detectability by enhancing cloud screening performance.
Khatri et al. (2014)
Khatri, P., T. Takamura, A. Yamazaki, and A. Uchiyama, 2014: Use of 315nm channel data of the sky radiometer to estimate the columnar ozone concentration: A preliminary study. J. Meteor. Soc. Japan, 92A, 185-194.
http://dx.doi.org/10.2151/jmsj.2014-A12 Graphical Abstract
- A method and preliminary results related to the estimation of the columnar ozone concentration (U) using the 315nm channel data of the sky radiometer are presented. The proposed method consists in calculating the calibration constant for direct intensity at 315nm wavelength F0 (315nm) using in situ observation data, which is an alternative of the traditional Langley method, and then estimating U.
- The temporal values of U at Chiba, Japan for the period of January - April, 2013 were estimated, and they were compared with values observed by the ozone monitoring instrument (OMI). The agreement was satisfactory during the initial period of observation; however, the values from the sky radiometer were observed to be gradually overestimated with time.
- The study suggests that the temporal change of F0 (315nm) is the important factor to be considered while estimating U values for long-term observation and that F0 (315nm) must be determined periodically.
Uchiyama et al. (2014)
Uchiyama, A., A. Yamazaki, and R. Kudo, 2014: Column water vapor retrievals from sky radiometer (POM-02) 940 nm data. J. Meteor. Soc. Japan, 92A, 195-203.
http://dx.doi.org/10.2151/jmsj.2014-A13 Graphical Abstract
- To retrieve the columnar precipitable water vapor amount from sun-sky radiometers, the POM-02 940-nm channel was calibrated using the Langley method, which accounts for gas absorption.
- The relation between column water vapor and atmospheric transmittance at 940 nm was determined using simulation data, and the results were used to retrieve column water vapor.
- This method was applied to data collected at Tsukuba, Japan, in 2011 and compared with global positioning system receiver (GPS).
- A comparison of POM-02 and GPS results showed a bias error of 0.09 g cm–2; the root mean square error was 0.179 g cm–2; and correlation coefficient r = 0.996.