Akihiro Uchiyama

OPTIMIZATION OF THE ADVANCED EARTH OBSERVING SATELLITE II GLOBAL IMAGER CHANNELS BY USE OF RADIATIVE TRANSFER CALCULATIONS

The channel specifications of the Global Imager onboard the Advanced Earth Observing Satellite II have been determined by extensive numerical experiments. The results show that there is an optimum feasible position for each ocean color channel. The bandwidth of the 0.763-microm channel should be less than 10 nm for good sensitivity to the cloud top height and geometric thickness of the cloud layer; a 40-nm bandwidth is suitable for the 1.38-microm channel to have the strongest contrast between cloudy and clear radiance with a sufficient radiant energy; and a 3.7-microm channel is better than a 3.95-microm channel for estimation of the sea surface temperature (SST) and determination of the cloud particle size when the bandwidth of the channel is 0.33 microm. A three-wavelength combination of 6.7, 7.3, and 7.5 microm is an optimized choice for water vapor profiling. The combination of 8.6, 10.8, and 12.0 microm is suitable for cloud microphysics and SST retrievals with the split-window technique.

One-year observation of urban mixed layer characteristics at Tsukuba, Japan using a micro pulse lidar

Abstract One-year characteristics of the urban mixed layer is observed by an eye-safe, compact micro pulse lidar (MPL). Retrieval method of the mixed layer height (MLH) and the encroachment model of the mixed layer growing are presented. Two case studies are carried out using summer and late winter data. Comparisons are made between the aerosol optical thickness, the rawinsonde data and the model calculation. The development of the mixed layer exhibits temporal behavior similar to that of the aerosol optical thickness, but with a time difference of about 1– 2 h . The growth rate of the MLH agrees well with the encroachment model only in the morning, with considerate deviation during the daytime because of the wind effect. One-year growth rate and the maximum MLH are estimated from the MPL measurement between May 1999 and May 2000. The results show that the properties of mixed layer are strongly correlated with the seasonal meteorological conditions. This work also demonstrates that an automated, compact lidar system such as a MPL is quite useful for long-term monitoring of the mixed layer.

Aerosol radiative characteristics at Gosan, Korea, during the Atmospheric Brown Cloud East Asian Regional Experiment 2005

[1] 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/m 2 at the surface, -8.3 ± 5.3 W/m 2 at the top of the atmosphere and 12.6 ± 6.8 W/m 2 in the atmosphere. The ARE efficiency was -81.6 W/m 2 , -32.5 W/m 2 and 49.4 W/m 2 , 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 (a) obtained by sky radiometer observations and shows that the increase in YSI corresponds to the decrease in a and the increase in single scattering albedo of aerosol. However, the YSI is poorly correlated with the ARE efficiency.

Estimation of Cloud Physical Parameters from Airborne Solar Spectral Reflectance Measurements for Stratocumulus Clouds

Abstract A new method is proposed to retrieve various cloud physical parameters of water clouds from the solar-flux reflectances at four wavelengths measured by using the airborne Multi-channel Cloud Pyranometer (MCP) system. The MCP system was designed to measure the spectral reflectances at nine wavelengths in the visible and near-infrared region. The estimation procedure assumes a locally plane-parallel and vertically homogeneous water-cloud layer with monomodal particle size distributions of a fixed width. The cloud optical thickness τ500 and the effective particle radius re, of the water-cloud layer can be simultaneously retrieved from the MCP reflectances measured at the visible channel of λ=500 nm and at the near-infrared channel of λ=1650 nm. Under the assumption that cloud pressure height is known, the cloud liquid water content (LWC) can then be retrieved from the MCP reflectance at the oxygen absorption-band channel cantered at λ=760 nm. Finally, the in-cloud water vapor amount uH2O can be esti...

Seasonal Variation of Aerosol Direct Radiative Forcing and Optical Properties Estimated from Ground-Based Solar Radiation Measurements

The surface direct radiative forcing and optical properties of aerosols have been analyzed from a groundbased solar radiation measurement, which was made under clear-sky conditions in Tsukuba, Japan, over two years from April 1997 to March 1999. The global and diffuse irradiances in the total and near-infrared (NIR) solar spectral regions were simultaneously measured by using two sets of the total-band and NIR-band pyranometers, respectively. The visible (VIS)-band irradiances were estimated by taking differences between the totalband and NIR-band irradiances. Spectral aerosol optical thicknesses (AOTs) in the air column were also measured, using a sun photometer. By combining the spectral AOTs and the surface diffuse irradiances, a retrieval algorithm for simultaneously estimating the effective aerosol size distribution and imaginary index of refraction ( mi) was developed. Seasonal variations of the broadband surface radiative forcings and retrieved optical properties of the columnar aerosols have been studied. A close correlation was found among these parameters with similar features of seasonal variations. In winter the columnar aerosols exhibit the minimum surface radiative forcing and a minimum AOT, but the maximum mi value of 0.04. The opposite is true in summer, when the minimum mi value of 0.02 was estimated. The surface radiative forcing in the VIS band was estimated to be almost 4 times larger than in the NIR band. The total-band aerosol forcing efficiency is defined as the change in the surface radiative forcing in the total band due to a unit increase of AOT at 500 nm. This has its largest magnitude of 2 219 Wm 22 in winter and its smallest magnitude of 2 150 Wm 22 in summer. The results suggest that the correlated seasonal variations between the aerosol radiative forcing and the optical properties may result from seasonal changes in the dominant aerosol components.

No evidence for solar absorption anomaly by marine water clouds through collocated aircraft radiation measurements

No observational evidence was found for the so-called anomalous solar absorption by maritime water clouds through collocated aircraft measurements taken during the Japanese Cloud-Climate Study (JACCS) program. The aircraft experiment has been carried out by using two aircraft equipped with various instruments for wintertime stratocumulus clouds over an area centered at (29°N, 129°E) in the East China Sea. Here we have carefully analyzed solar absorption by the water stratocumulus clouds observed on February 2, 1998. The visible-band net fluxes measured above and below the cloud layer were almost the same within measurement accuracy; this means no substantial absorption in the visible spectral region. On the other hand, there were significant differences as much as 50–80 W m−2 between the near-infrared-band net fluxes measured above and below the cloud layer; this difference corresponds to absorptance of 6–10% of the total-band solar irradiance above the cloud layer. Without cloud particles, water vapor absorption was estimated to be about 4% of the total-band irradiance for the layer. Distributions along the flight legs of the measured visible-band and near-infrared-band absorptance were in phase in their positions with zero mean visible-band absorptance. The measured radiation budget averaged over long distances along the flight legs for the inhomogeneous cloud layers agreed well with theoretical counterparts calculated for plane-parallel, homogeneous cloud models based on the observed microphysical parameters.

Application of an extended ESFT method to calculation of solar heating rates by water vapor absorption

Abstract A new method for the exponential-sum fitting of transmissions (ESFT) is developed. We determine a set of equivalent absorption coefficients by a successive correction technique with a set of weights preselected empirically or absorptions coefficients by a successive correction technique with a set of applied to transmission functions of water vapor bands in the near i.r. region deduced from the AFGL absorption-line parameters. Numerical values of the ESFT parameters are presented for each of the water vapor bands and for the one-band parameterization for total absorption. Solar radiative heating rates computed from the present ESFT parameters are compared with those in the literature, as well as with the exact values of Chou [J. Chim. Appl. Met. 25, 1532 (1986)]. The accuracy and utility of our method are demonstrated.

Line-by-line computation of the atmospheric absorption spectrum using the decomposed Voigt line shape

Abstract A new line-by-line method has been developed to calculate the spectral absorption coefficients of absorption lines with a Voigt line shape in the terrestrial atmosphere. This method has also been applied to several problems in the field of atmospheric radiation. In the present method, the Voigt line shape is decomposed into several sub-functions, with even quadratic functions used as sub-functions. This functional form allows for easy estimation of the half-width of the sub-function. The final spectral absorption is obtained by the superposition of independent spectral absorption coefficients. The finer details of the absorption spectrum have then been examined to determine if they are zero or not at every grid point. This procedure eliminates the need for unnecessary calculations in interpolations of absorption coefficients from coarser to finer resolution and also saves storage capacity.

An Application of the Discrete Ordinate Method to Terrestrial Radiation in Climate Models

Abstract Thermal infrared radiation is so incorporated into the discrete ordinate method as to be usable in climate models. A source term for thermal infrared radiation contains up to the second derivative, set to be a constant, of the Planck function with respect to optical thickness, and this treatment (quadratic approximation) is indispensable for ensuring reasonable accuracy in climate models. This is because the models prognostically yield not a continuous temperature profile but a discontinuous layer-mean temperature, from which temperatures at full level and half level are diagnostically determined. Then, the temperature profile presumed from these temperatures comes to show curvature (nonlinearity) within one layer where the layer-mean temperature is minimum or maximum. Assuming that the temperature profile between adjacent full levels is linearly represented with pressure, radiative–convective equilibrium temperatures are calculated with a four-stream approximation in order to examine the accurac...

Retrieval of Asian dust amount over land using ADEOS-II/GLI near UV data

We propose a retrieval method of Asian dust (Yellow sand or Kosa aerosol) columnar amount around source regions using a near ultraviolet radiometry observation from space. The method simultaneously retrieves an optical thickness and mode radius of Kosa aerosol, and then derives its columnar amount. The method was applied to ADEOS-II / GLI data in the spring of 2003 around Taklimakan desert source region, inland China. The retrieved optical thickness and mode radius were about 0.34 and 1.75 μm, respectively, at a validation site. They are comparable to the in situ observations conducted within the framework of ADEC project. The estimated columnar amount around a validation site is about 2.77 g m-2, which seems reasonable under a relatively calm situation. The method should be further validated with a regional model simulation study, and then it is useful to monitor Asian dust around source regions from space in the future.