Introducing Potential Radiative Forcing (PRF) for quantifying the Earth radiation budget

In order to investigate the contributions of atmospheric factors to variability in surface shortwave irradiance (S) under both cloud-free and cloudy sky conditions, we defined the sensitivity of S to differential increases from given values of cloud, aerosol, and water vapor as potential radiative forcing (PRF). The expected change in S due to one factor would be the product of the PRF and the change in that factor. We formulated the PRF from a simple equation and described the geographical features of the PRF over China in January and July. We noted some shortcomings, but confirmed the usefulness of the PRF for determining the relative contributions. In particular, we suggested that accurate knowledge of aerosol absorption properties was critical for quantitative radiation budget estimates.CURRENT PROBLEMS IN ATMOSPHERIC RADIATION (IRS 2008): Proceedings of the International Radiation Symposium (IRC?IAMAS) : Foz do Iguacu (Brazil), 3?8 August 200

Cloud and aerosol contributions to variation in shortwave surface irradiance over East Asia in July during 2001 and 2007

It is important to clarify the contributions of clouds and aerosols to the variation of surface shortwave irradiance (S) for climatological studies. This study examined the contributions of clouds and aerosols to the variation in S over East Asia (75-135°E, 20-55°N) in July during 2001 and 2007 using the index of potential radiative forcing (PRF) to characterize the temporal and geographical variations. After confirming the validity of PRF for multiyear analyses, we performed several temporal analyses of clouds and aerosols over the whole research domain. Changes in the geographical distribution, contribution histograms, and averaged values were studied. In agreement with previous studies that treated single-year cases, we confirmed that the magnitudes of the temporal changes in S variations due to clouds and aerosols were highly variable geographically. As for domain-averaged S variations, we did not observe defined trends for the research period. It was also found that the temporal variation between one parameter and its S variation was negatively correlated, from the point analyses at two locations. Based on these results, we concluded that PRF is a promising tool for research into long-term S variations. This kind of information will be quite valuable as basic data for use in climate modeling

Stratospheric aerosol increase after eruption of Pinatubo observed with lidar and aureolemeter

An increase in the amount of stratospheric aerosol due to the Pinatubo eruption (June 12-15, 1991, 15.14 deg N, 120.35 deg E) was observed from the end of June, 1991 by a lidar in NIES (National Institute for Environmental Studies), Tsukuba (36.0 deg N, 140.1 deg E). After large fluctuations in summer of 1991, the amount of the aerosols increased in mid-September as a result of enhanced transportation from the subtropical region. In autumn and winter of 1991, dense aerosol layers were continuously observed. Aureolemeter (scanning spectral radiometer) measurements were also carried out with lidar measurements and columnar size distribution of stratospheric aerosols was estimated for some cases. Collaborative measurements with the lidar and aureolemeter provided some information on height distribution of the surface area of aerosols in late 1991

Aerosol climatology over Japan site measured by ground-based sky radiometer

Aerosol and cloud optical properties are studied using data from ground-based and ship-borne sky radiometer measurements in the world. We are seeking in this data information on the aerosol optical characteristics with respect to their temporal and spatial variability and validation of Satellite and numerical models. The aerosol optical thickness has clear temporal and spatial variability at six sites in Japan. Comparisons between aerosol optical thickness at 0.5 μm retrieved with a sky radiometer and SPRINTAS at six Japan sites. Model of all sky AOT500 is good correlation. But, model of clear sky AOT500C is not good correlation. We will confirm the trends of aerosol climatology and help explain the reason.International Radiation Symposium: Radiation Processes in the Atmosphere and Ocean, IRS 2012; Berlin; Germany; 6 August 2012 ～ 10 August 201

Increased Aerosols Can Reverse Twomey Effect in Water Clouds Through Radiative Pathway

Aerosols play important roles in modulations of cloud properties and hydrological cycle by decreasing the size of cloud droplets with the increase of aerosols under the condition of fixed liquid water path, which is known as the first aerosol indirect effect or Twomey-effect or microphysical effect. Using high-quality aerosol data from surface observations and statistically decoupling the influence of meteorological factors, we show that highly loaded aerosols can counter this microphysical effect through the radiative effect to result both the decrease and increase of cloud droplet size depending on liquid water path in water clouds. The radiative effect due to increased aerosols reduces the moisture content, but increases the atmospheric stability at higher altitudes, generating conditions favorable for cloud top entrainment and cloud droplet coalescence. Such radiatively driven cloud droplet coalescence process is relatively stronger in thicker clouds to counter relatively weaker microphysical effect, resulting the increase of cloud droplet size with the increase of aerosol loading; and vice-versa in thinner clouds. Overall, the study suggests the prevalence of both negative and positive relationships between cloud droplet size and aerosol loading in highly polluted regions

Atmospheric Turbid Conditions due to Fine Particles in Recent Years at Nagasaki, Japan

Atmospheric turbid conditions caused by fine particles, which are defined as the particles in the size range between 0.3 and 1.0μμm in diameter, are occasionally significant in recent years over the Nagasaki area in Japan. These conditions make the horizontal visibility very low as 4-5 km despite of fair weather. We studied two significantly turbid cases rich with fine particles, which took place during 25-27 March 2003 and on 23 May 2005, from the viewpoint of a detailed understanding of their influences to visibility and the properties of fine aerosols. As a result of this study, the noticeably low visibility conditions due to fine particles are closely connected with the high concentration of sulfur which transported from the Asian continent. Fine particles sometimes make very turbid conditions in spring without the influence of yellow sand dust particles. This peculiarity should be paid further attention from the viewpoint of air quality conservation over East Asia

Comparison of Cloud Properties between SGLI Aboard GCOM-C Satellite and MODIS Aboard Terra Satellite

This study presents a comprehensive comparison of Level 2.0 cloud properties between a Second-generation Global Imager (SGLI) aboard the GCOM-C satellite and a Moderate Resolution Imaging Spectroradiometer (MODIS) aboard the Terra satellite, to better understand the qualities of cloud properties obtained from SGLI/GCOM-C launched on 23 December 2017. The cloud pixels identified as water phase by both satellite sensors are highly consistent to each other by more than 90%, although the consistency is only ~60% for ice phase cloud pixels. A comparison of cloud properties—cloud optical thickness (COT) and cloud particle effective radius (CER)—between these two satellite sensors reveals that water and ice cloud properties can have different degrees of agreement depending on underlying surface. The relative difference (RD) values of 22% (18%) and 37% (24%) for water cloud COT (CER) comparison over ocean and land surfaces and respective values of 35% (42%) and 35% (62%) for comparisons of ice cloud properties, and also other comparison metrics, suggest better agreements for water cloud properties than for ice cloud properties, and for ocean surface than for land surface. Though cloud properties differences between MODIS and SGLI can arise from inherent features of cloud retrieval algorithms, such as differences in ancillary data, surface reflectance, cloud droplet size distribution function, model for ice particle habit, etc., this study further identifies the important roles of cloud thickness and Sun and satellite positions for differences in cloud properties between SGLI and MODIS: the differences in cloud properties are found to increase for thinner clouds, higher solar zenith angle, and higher differences in viewing zenith and azimuth angles between these satellite sensors, and such differences are more distinct for water cloud properties than for ice cloud properties

The coarse particle aerosols in the free troposphere around Japan

Airborne measurements of solar aureole intensities were carried out around Japan with a spectral scanning radiometer. Horizontal and vertical stratifications and volume spectra of tropospheric aerosols were retrieved from the measured solar aureole intensities. The results show that bimodal volume spectra of aerosols with a saddle point radius around 0.5 μm are generally observed in the troposphere, both within and above the planetary boundary layer. A submicrometer particle mode of the spectra, known as the accumulation mode, dominates the coarse particle mode within the planetary boundary layer, especially in summer, whereas coarse particles were observed frequently in the free troposphere. Synoptic analyses with air mass trajectories, isentropic surfaces, and weather charts suggest that the windblown dust particles injected into the atmosphere in arid regions of eastern Asia are the origin of the coarse particles observed in the free troposphere around Japan. Windblown dust particles are elevated to the free troposphere by ascending air motion in a warm front and then transported by the westerlies. The arid regions to the east of the Tibetan Plateau, where disturbances due to the frontogenesis occur frequently, are capable of supplying coarse particles to the free troposphere over the northwestern Pacific Ocean throughout the year. ©American Geophysical Union 199