Masanori Yabuki

An intercomparison of lidar-derived aerosol optical properties with airborne measurements near Tokyo during ACE-Asia

[1] During the ACE-Asia intensive observation period (IOP), an intercomparison experiment with ground-based lidars and aircraft observations was conducted near Tokyo. On 23 April 2001, four Mie backscatter lidars were simultaneously operated in the Tokyo region, while the National Center for Atmospheric Research C-130 aircraft flew a steppedascent profile between the surface and 6 km over Sagami Bay southwest of Tokyo. The C-130 observation package included a tracking Sun photometer and in situ packages measuring aerosol optical properties, aerosol size distribution, aerosol ionic composition, and SO2 concentration. The three polarization lidars suggested that the observed modest concentrations of Asian dust in the free troposphere extended up to an altitude of 8 km. We found a good agreement in the backscattering coefficient at 532 nm among lidars and in situ 180� backscatter nephelometer observations. The intercomparison indicated that the aerosol layer between 1.6 and 3.5 km was a remarkably stable and homogenous in mesoscale. We also found reasonable agreement between the aerosol extinction coefficients (sa � 0.03 km � 1 ) derived from the airborne tracking Sun photometer, in situ optical instruments, and those estimated from the lidars above the planetary boundary layer (PBL). We also found considerable vertical variation of the aerosol depolarization ratio (da) and a negative correlation between da and the backscattering coefficient (da) below 3.5 km. Airborne measurements of size-dependent optical parameters (e.g., the fine mode fraction of scattering) and of aerosol ionic compositions suggests that the mixing ratio of the accumulation-mode and coarse-mode (dust) aerosols was primarily responsible for the observed variation of da. Aerosol observations during the intercomparison period captured the following three types of layers in the atmosphere: a PBL (surface to 1.2–1.5 km) where fine (mainly sulfate) particles with a low da (<10%) dominated; an intermediate layer (between the top of the PBL and 3.5 km) where fine particles and dust particles were moderately externally mixed, giving moderate da; and an upper layer (above � 3.5 km) where dust dominated, giving a high da (30%). A substantial dust layer between 4.5 and 6.5 km was observed just west of Japan by the airborne instruments and found to have a lidar ratio of 50.4 ± 9.4 sr. This agrees well with nighttime Raman lidar measurements made later on this same dust layer as it passed over Tokyo, which found a lidar ratio of 46.5 ± 10.5 sr. INDEX TERMS: 0305 Atmospheric Composition and Structure: Aerosols and particles

Arctic Study of Tropospheric Aerosol and Radiation (ASTAR) 2000: Arctic haze case study

The ASTAR 2000 (Arctic Study of Tropospheric Aerosol and Radiation) campaign ran from 12 March until 25 April 2000 with extensive flight operations in the vicinity of Svalbard (Norway) from Longyearbyen airport (78.25°N, 15.49°E). It was a joint Japanese (NIPR Tokyo)–German (AWI Bremerhaven/Potsdam) airborne measurement campaign using AWI aircraft POLAR 4 (Dornier 228-101). Simultaneous ground-based measurements were done at the international research site Ny-Ålesund (78.95°N, 11.93°E) in Svalbard, at the German Koldewey station, at the Japanese Rabben station and at the Scandinavian station at Zeppelin Mountain (475 m above sea level). During the campaign 19 profiles of various aerosol properties were measured. In general, the Arctic spring aerosol in the vicinity of Svalbard had significant temporal and vertical variability. A strong haze event occurred between 21 and 25 March in which the optical depth from ground-based observation was 0.18, which was significantly greater than the background value of 0.06. Airborne measurements on 23 March during this haze event showed a high aerosol layer with an extinction coefficient of 0.03 km−1 or more up to 3 km and a scattering coefficient from 0.02 in the same altitude range. From the chemical analyses of airborne measurements, sulfate, soot and sea salt particles were dominant, and there was a high mixing ratio of external soot particles in some layers during the haze event, whereas internal mixing of soot in sulfate was noticeable in some layers for the background condition. We argue that the high aerosol loading is due to direct transport from anthropogenic source regions. In this paper we focus on the course of the haze event in detail through analyses of the airborne and ground-based results.

Antarctic polar stratospheric clouds under temperature perturbation by nonorographic inertia gravity waves observed by micropulse lidar at Syowa Station

[1] Type II polar stratospheric clouds (PSCs) were observed by micropulse lidar (MPL) at Syowa Station in the Antarctic on 30 June and on 1 July 2001. The vertical profiles of the PSCs had a wavy structure that was synchronized with the temperature fluctuations. A wave analysis using radiosonde data shows that the wavy fluctuations were associated with an inertia gravity wave that was not forced by ground topography, but probably by a spontaneous adjustment in association with synoptic-scale wave-breaking processes in the upper troposphere. It is suggested that the observed PSCs were generated under the low-temperature conditions induced by these waves and that such gravity waves generated by spontaneous adjustment of large-scale fields can be more important to the formation of PSC particles, in both the Antarctic and Arctic stratosphere, than topographically forced gravity waves, because the former are not fixed to the ground topography. INDEX TERMS: 0305 Atmospheric Composition and Structure: Aerosols and particles (0345, 4801); 0320 Atmospheric Composition and Structure: Cloud physics and chemistry; 0340 Atmospheric Composition and Structure: Middle atmosphere—composition and chemistry; 3334 Meteorology and Atmospheric Dynamics: Middle atmosphere dynamics (0341, 0342); KEYWORDS: polar stratospheric clouds, inertia gravity waves, micropulse lidar

Determination of Vertical Distributions of Aerosol Optical Parameters by Use of Multi-Wavelength Lidar Data

A lookup table (LUT) method is proposed to derive vertical distributions of aerosol optical parameters in the troposphere from multi-wavelength observations using a Mie-scattering lidar. A LUT is constructed by means of Mie-scattering calculations. For aerosol size distributions, we assume eleven models including the urban and maritime models as two extreme cases. For the aerosol refractive index, the imaginary part is changed between 0.0 and 0.03 in steps of 1.0×10-4, and the real part between 1.40 and 1.60 in steps of 0.01. The observed wavelength dependence of the lidar signal is compared with that of the LUT to determine the aerosol extinction coefficient, size distribution, refractive index, and the extinction-to-backscattering ratio (S1 parameter) for each altitude. We apply the method to analyze data obtained with a four-wavelength lidar (355, 532, 756, and 1064 nm) operated at Chiba University. Compared with the conventional analysis with the Fernald method, the LUT approach has the advantage that it is capable of giving detailed optical parameters simultaneously with the extinction coefficient. Besides, since the analysis starts at the near-end boundary, the effect of detection noise becomes less influential.

Determination of Aerosol Extinction-to-Backscattering Ratio from Multiwavelength Lidar Observation

We propose a method to determine the extinction-to-backscattering ratio (S1 parameter) in the troposphere from multiwavelength (355, 532, 756, and 1064 nm) lidar data. In our approach, reference profiles are prepared by using the wavelength dependence of the extinction coefficient as derived either from the sun photometer data or from the Mie calculation. By comparing these reference profiles with the profiles calculated using the conventional Fernald inversion method, the S1 parameter is determined for each wavelength. When a reasonable range is covered at 532 nm, this method makes it possible to determine the S1 parameters for shorter or longer wavelengths for which full range observation cannot be attained, due presumably to small laser power or limited detector efficiency. In addition, information about the vertical uniformity of aerosol properties can be derived from the S1 dependence of the difference between the reference and retrieved profiles.

Determination of vertical distributions of aerosol optical parameters by use of multiwavelength lidar data

We propose a lookup table method to derive vertical distributions of aerosol optical parameters in the troposphere from multiwavelength observations using a Mie-scattering lidar. The method is characterized by the capability of treating generalized aerosol size distributions, as well as by rapid convergence of the iteration procedure. The methodology and numerical simulation are described.

Retrieval of aerosol optical thickness from NOAA/AVHRR data and its application to the derivation over land area in Chiba

We present the retrieval algorithm of aerosol optical thickness over the land area. The algorithm is based on the dark-target approach combined with the texture analysis. In the first part of the algorithm, we employ the 6S code to calculate the relevant radiance components. The aerosol optical thickness is retrieved over the sea surface assuming a surface reflectance of 0.02. Two-dimensional linear interpolation is applied to tentatively determine the optical thickness over the land area that is surrounded by the sea area. In the second part, a difference image is calculated between an actual satellite image (turbid image, NOAA AVHRR channel 1 on December 1, 1997) and a clear image that is obtained by applying the atmospheric correction to a satellite image (December 15, 1997). The atmospheric feature included in the difference image is then analyzed by the texture analysis. For each area that includes both land and sea surfaces, and is categorized into a texel (i.e. its atmospheric feature is considered to be uniform), the optical thickness of the land area is assumed to be the same with that over the sea area. In addition, we present a Taerosol model on the basis of the ground measurements conducted at 11 sites on the Kanto plain during December 22 to approximately 24, 1997. In this model, chemical composition data are used to derive the single scattering albedo and the asymmetry parameter. These optical parameters are useful to improve the accuracy of the radiation calculation with the 6S code.

Important contributions of sea-salt aerosols to atmospheric bromine cycle in the Antarctic coasts

Polar sunrise activates reactive bromine (BrOx) cycle on the Antarctic coasts. BrOx chemistry relates to depletion of O3 and Hg in polar regions. Earlier studies have indicated “blowing snow” as a source of atmospheric BrOx. However, surface O3 depletion and BrO enhancement occurs rarely under blowing snow conditions at Syowa Station, Antarctica. Therefore, trigger processes for BrOx activation other than the heterogeneous reactions on blowing snow particles must be considered. Results of this study show that enhancement of sea-salt aerosols (SSA) and heterogeneous reactions on SSA are the main key processes for atmospheric BrOx cycle activation. Blowing snow had Br− enrichment, in contrast to strong Br− depletion in SSA. In-situ aerosol measurements and satellite BrO measurements demonstrated clearly that a BrO plume appeared simultaneously in SSA enhancement near the surface. Results show that surface O3 depletion at Syowa Station occurred in aerosol enhancement because of SSA dispersion during the polar sunrise. Amounts of depleted Br− from SSA were matched well to the tropospheric vertical column density of BrO and BrOx concentrations found in earlier work. Our results indicate that SSA enhancement by strong winds engenders activation of atmospheric BrOx cycles via heterogeneous reactions on SSA.

Correction to: Shigaraki UAV-Radar Experiment (ShUREX): overview of the campaign with some preliminary results

An error in computing the spectral level from time series data from UAV-borne sensors was discovered after this article (Kantha et al. 2017) was published.

Special issue “GNSS and SAR Technologies for Atmospheric Sensing”

Recent advances in the field of atmospheric and ionospheric sensing by GNSS and SAR technologies were discussed during two workshops held in February 2016 and October 2016 in Italy, hosted by GEOlab of Politecnico di Milano under partial support of the JSPS Bilateral Open Partnership Joint Research Projects. Another symposium was held in March 2017 at the Research Institute for Sustainable Humanosphere of Kyoto University, to discuss (1) the water vapor and ionospheric maps retrieval from space-borne and airborne SAR, (2) ionosphere and troposphere monitoring by the ground-based GNSS network and radio occultation, (3) mesoscale numerical weather prediction models and data assimilation, and (4) ground-based remote-sensing techniques, such as a wind profiling radar. This special issue collects high-quality papers that describe the findings reported during these three meetings, not limited to GNSS and SAR, but also including ground-based atmospheric sensing systems and numerical weather prediction models.