Makoto Abo

Ground‐based network observation of Asian dust events of April 1998 in east Asia

We coordinated a ground-based network that has been in use since 1997 to observe Asian dust during springtime. Huge Asian dust events that occurred in the middle of April 1998 were captured by this network. In this paper we present the organization of the network; a description of the instruments, including the lidar, sky radiometer, and optical particle counter; and the results of the observation, and offer discussions regarding the transport mechanism of Asian dust in east Asia using an on-line tracer model. We discussed the time series of the surface concentration and the height distribution of the dust. A cutoff cyclone generated during the dust episode was responsible for trapping and sedimentation during the transportation of the Asian dust, particularly in the southern parts of China and Japan. Horizontal dust images derived from NOAA/AVHRR clearly revealed the structure of the vortex. The lidar network observation confirmed the general pattern of dust height distribution in this event; the height of the major dust layer was about 3 km over Japan but was higher (4 to 5 km) in Seoul and Hefei. A thin dust layer in the upper troposphere was also commonly observed in Hefei and Japan. Evidence of the coexistence of dust and cirrus was shown by the polarization lidar. The lidar network observation of Asian dust and satellite remote sensing provide key information for the study of the transport mechanism of Asian dust. Further extension of the lidar network toward the interior of the continent and the Pacific Rim would reveal the greater global mechanism of the transportation.

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

Lidar observations of a lot of sporadic sodium layers in mid-latitude

We have routinely observed mesospheric Na layers since November 1991 with a Na ground-based lidar above Tokyo Metropolitan University (TMU) at Hachioji, Tokyo (35.6°N, 139.4°E) in mid-latitude. In the past, the sporadic Na layers have been observed commonly at low-and high-latitude lidar sites [Kwon et al., 1988; Batista et al., 1989; von Zahn et al., 1987] but rarely observed at mid-latitude sites [Senft et al., 1989]. Contrary to expectations, we could observe more than 100 events of the sporadic Na layers for two years from November 1991 until October 1993 in this mid-latitude lidar site, and the large sporadic Na layers had been observed especially during spring and summer. Most of these events were accompanied by sporadic E layers and the most enhancement of the sporadic E layers preceded that of the sporadic Na layers by 15 to 30 minutes.

Development of a 1.6 μ m differential absorption lidar with a quasi-phase-matching optical parametric oscillator and photon-counting detector for the vertical CO 2 profile

We have developed a 1.6 microm carbon dioxide (CO(2)) differential absorption lidar utilizing a quasi-phase-matching optical parametric oscillator (OPO) and a photon-counting detector. The operating wavelengths were chosen based on their low interference from water vapor and low temperature sensitivity. The online wavelength was in the (30012<--0001) band of CO(2), which was insensitive to atmospheric temperature. The established OPO laser achieved a 10 mJ, 200 Hz repetition rate at the online and offline wavelengths. Our observations confirmed the statistical error of 2% with 5 h of accumulation for the CO(2) density profile less than 5.2 km. Also, the statistical error of 1% at an altitude of 2 km was demonstrated. The results of the vertical CO(2) concentrations acquired using a 1.6 microm wavelength are presented.

Random modulation cw lidar using new random sequence.

New modulation codes are presented for a random modulation cw lidar. One characteristic of these modulation codes is that for very noisy background conditions, the signal-to-noise ratio is improved by using these new sequences, and is better than for the maximum-length sequence (the M-sequence) which is commonly used as the modulation code. Another characteristic of these modulation codes is that there is no correlation between them. This fact will be useful for the simultaneous multitransmitter of the differential absorption lidar. These two characteristics of the new modulation codes were confirmed experimentally.

Simultaneous observations of mesospheric gravity waves with the MU radar and a sodium lidar

Simultaneous observations of mesospheric gravity waves have been carried out using meteor wind measurements with the middle and upper atmosphere (MU) radar at Shigaraki, Japan (34.9°N, 136.1°E), and density perturbations of the sodium lidar at Hachioji, Tokyo, Japan (35.6°N, 139.4°E). The study utilizes 7 hours of data collected on the night of December 15-16, 1993, during a time period when a fairly monochromatic gravity wave was dominant. Using hodograph analysis, the dominant gravity wave was found to exhibit a vertical wavelength of 16 km, an intrinsic period of 9.1 hours, and a horizontal wavelength of about 1900 km. The horizontal propagation direction of the gravity wave was determined from the phase relations between the horizontal wind components and the temperature perturbations at Shigaraki. The wave propagated southward, being almost orthogonal to the baseline between Shigaraki and Hachioji. Employing the dispersion and polarization relations for linear gravity waves, the wave-induced neutral density perturbations from the MU radar observations were estimated. A comparison with the corresponding density perturbations derived from the sodium density measurements showed good agreement. The amplitudes of the neutral density perturbations observed at both locations, which are separated by 310 km, were similar, with a maximum perturbation of ∼7% and a good correlation of phase. Time variations of the hourly variance of the density perturbations also agreed quite well between the two independent determinations, which again supports the view that the radar and the lidar detected the same gravity wave.

Studies of the MLT region using the MU radar and simultaneous observations with OH spectrometer and other optical instruments

Abstract The MU radar (middle and upper atmosphere radar) has been used since 1984 to study the dynamics of the mesosphere and lower thermosphere (MLT) as well as the dynamics of the lower atmosphere and the ionosphere. Gravity waves in the mesosphere have been studied extensively over various time and vertical scales during the daylight hours using backscatter from turbulent irregularities. Scatter from meteor trails can be used during day or night to study the dynamics of the MLT, and techniques to apply the MU radar for meteor scatter observations have been developed and recently improved. The meteor observation mode of the MU radar can detect about 15,000–20,000 echoes/day and 10,000 echoes/day are from underdense trails with arrival angle determination. This high meteor echo rate enables us to determine the wind velocities and molecular diffusion coefficient with the time/height resolutions of 30 min × 1 km at 80–100 km for 24 hours a day. From the horizontal distribution of the meteor echoes, horizontal gradients of the wind fields can also be detected, as well as vertical shears of horizontal winds. These high resolution meteor echo observations were made simultaneously with OH spectrometer observations. These combined observations yielded information on both the horizontal and vertical structure of the gravity waves. Comparisons were made between the temperature variations determined by OH airglow and determined by the diffusion coefficient of the meteor echoes and excellent agreement was found. Cooperative observations with sodium lidars, FPI, airglow imagers, and an MF radar are also being carried out.

Lidar network observation of Asian dust (Kosa) in Japan

We have organized a network campaign for the observation of Asian dust in the spring of 1997 and 1998 in Japan. Through the communication with electric mail, we have successfully observed Kosa events by lidar, sunphotometer, and particle counter, etc. These data must be useful to analyze the transport mechanism of Asian dust and validate the satellite observations.

Observations of mesospheric sporadic sodium layers with the MU radar and sodium lidars

The dynamical structure of the atmosphere around the sporadic sodium layer at mid-latitude (∼35°N) below 100 km was studied by simultaneous observation with the MU radar at Shigaraki (34.9°N, 136.1°E), and two Na lidars at Shigaraki and in Hachioji (35.6°N, 139.4°E). In the lidar data, fifteen Nas (sporadic sodium layer) events were detected. Wind shear, temperature, and stability indices, at around the time and height of Nas were observed with the MU radar. Strong total wind shear correlated well with Nas, especially when sporadic Es did not accompany. However, no other clear correlations, such as correlations with temperature etc., were found. The result is similar to the report of the lidar observations in Hawaii during the ALOHA-93 campaign (Qian et al., 1998), and suggests a similar generation mechanism between 20°N and 35°N.

Stimulated Raman Scattering Laser Oscillation around 1.6 µm Carbon Dioxide Absorption Line

A solid-state stimulated Raman scattering (SRS) laser oscillation around the 1.6 µm carbon dioxide absorption lines is demonstrated. The stokes output of the SRS radiation at 1.57 µm is generated from the frequency conversion of the 1.35 µm laser radiation of Nd3+:KGd(WO4)2 (Nd:KGW) in the cavity. The maximum output energy was 13.8 mJ with a repetition rate of 10 Hz, in response to the incident laser pumped from the laser diode to the Nd:KGW. To our knowledge, this result of a 1.57 µm intracavity SRS oscillation at CO2 absorption lines around 1.6 µm is gained for the first time.