Shoken Ishii

Coherent 2 μm differential absorption and wind lidar with conductively cooled laser and two-axis scanning device

A coherent 2 microm differential absorption and wind lidar (Co2DiaWiL) was developed to measure CO(2) concentration and line-of-sight wind speed. We conductively cooled a pumping laser head to -80 degrees C and diode arrays to approximately 20 degrees C. A Q-switched laser outputs an energy of 80 mJ (pulse width 150 ns (FWHM), pulse repetition frequency up to 30 Hz). CO(2) measurements made over a column range (487-1986 m) for 5 min accumulation time pairs achieved 0.7% precision. Line-of-sight wind speeds for ranges up to approximately 20 km and returns from a mountainside located 24 km away from the Co2DiaWiL were obtained.

Dual‐Doppler lidar observation of horizontal convective rolls and near‐surface streaks

Received 4 May 2008; revised 9 June 2008; accepted 18 June 2008; published 23 July 2008. [1] Dual-Doppler lidar and heliborne sensors were used to investigate the three-dimensional (3D) structure of the wind field over Sendai Airport in June 2007. The 3D structures of several-hundred-meter-scale horizontal convective rolls (HCRs) in the sea-breeze layer were observed by the dual-Doppler lidar. The scale of the HCRs determined by the heliborne sensors roughly agreed with that determined by the dual-Doppler lidar. Analysis of the dual-Doppler lidar data showed that the region of upward flow in the HCRs originated in near-surface low-speed streaks. This structure is consistent with the results of large-eddy simulations of the atmospheric boundary layer. The aspect ratios of the HCRs were close to those predicted by linear theories. Citation: Iwai, H., et al. (2008), Dual-Doppler lidar observation of horizontal convective rolls and near-surface streaks, Geophys. Res. Lett., 35, L14808, doi:10.1029/ 2008GL034571.

Cloud-Resolving 4D-Var Assimilation of Doppler Wind Lidar Data on a Meso-Gamma-Scale Convective System

AbstractThe authors evaluated the effects of assimilating three-dimensional Doppler wind lidar (DWL) data on the forecast of the heavy rainfall event of 5 July 2010 in Japan, produced by an isolated mesoscale convective system (MCS) at a meso-gamma scale in a system consisting of only warm rain clouds. Several impact experiments using the nonhydrostatic four-dimensional variational data assimilation system (NHM-4DVAR) and the Japan Meteorological Agency nonhydrostatic model with a 2-km horizontal grid spacing were conducted in which 1) no observations were assimilated (NODA), 2) radar reflectivity and radial velocity determined by Doppler radar and precipitable water vapor determined by GPS satellite observations were assimilated (CTL), and 3) radial velocity determined by DWL were added to the CTL experiment (LDR) and five data denial and two observational error sensitivity experiments. Although both NODA and CTL simulated an MCS, only LDR captured the intensity, location, and horizontal scale of the obs...

Performance and Technique of Coherent 2-μm Differential Absorption and Wind Lidar for Wind Measurement

AbstractA coherent 2-μm differential absorption and wind lidar (Co2DiaWiL) has been built with a high-power Q-switched Tm,Hm:YLF laser to measure CO2 concentration and radial wind speed. The performance of the Co2DiaWiL is described and analyzed, with a view to demonstrating system capabilities for remote measurements of wind velocities in the atmospheric boundary layer and free troposphere. Bias in the velocity measurements was estimated at −0.0069 m s−1 using measurements from a stationary hard target. The Co2DiaWiL achieved a velocity precision of 0.12 m s−1, derived from the magnitude of random error in radial wind velocity measurements. These measurements were made for ranges out to 20–25 km by using a horizontally fixed beam mode for average times of 1 min. Quantitative intercomparisons of 1-min averages between the Co2DiaWiL and a sonic anemometer revealed a correlation coefficient of 0.99. This study demonstrated measurements of horizontal wind profiles, by making radial wind velocity measurements...

Partial CO2 Column-Averaged Dry-Air Mixing Ratio from Measurements by Coherent 2-μm Differential Absorption and Wind Lidar with Laser Frequency Offset Locking

AbstractA coherent 2-μm differential absorption and wind lidar (Co2DiaWiL) with a 2-μm single-frequency Q-switched laser with laser frequency offset locking was used for long-range CO2 measurement. The frequency stabilization of the single-frequency λ on pulsed laser was 1.0 MHz. Experimental horizontal CO2 measurement over a column range of 2.6–5.6 km and 900 shot pairs (1-min integration time) was conducted on 22 October 2009 to examine the detection sensitivity of the Co2DiaWiL. The achieved precision was less than 2.1%. The root-mean-square of the differences between the 30-min CO2 averages measured by the Co2DiaWiL and a ground-based in situ instrument was 0.9% (3.5 ppm). Experimental vertical CO2 measurements were conducted in February 2010 and January and February 2011. The partial CO2 column-averaged dry-air mixing ratios (XCO2) for an altitude between 0.4 and 1.0 km in 2010 and 2011 were 403.2 ± 4.2 and 405.6 ± 3.4 ppm, respectively. In the paper, the Co2DiaWiL results were well validated careful...

Toward Improved Forecasts of Sea-Breeze Horizontal Convective Rolls at Super High Resolutions. Part I: Configuration and Verification of a Down-Scaling Simulation System (DS3)

AbstractHorizontal convective rolls (HCRs) that develop in sea breezes greatly influence local weather in coastal areas. In this study, the authors present a realistic simulation of sea-breeze HCRs over an urban-scale area at a resolution of a few meters. An advanced Down-Scaling Simulation System (DS3) is built to derive the analyzed data using a nonhydrostatic model and data assimilation scheme that drive a building-resolving computational fluid dynamics (CFD) model. The mesoscale-analyzed data well capture the inland penetration of the sea breeze in northeastern Japan. The CFD model reproduces the HCRs over Sendai Airport in terms of their coastal initiation, inland growth, streamwise orientation, specific locations, roll wavelength, secondary flows, and regional differences due to complex surfaces. The simulated HCRs agree fairly well with those observed by dual-Doppler lidar and heliborne sensors. Both the simulation and observation analyses suggest that roll updrafts typically originate in the narro...

Toward Improved Forecasts of Sea-Breeze Horizontal Convective Rolls at Super High Resolutions. Part II: The Impacts of Land Use and Buildings

AbstractHorizontal convective rolls form in coastal areas around Sendai Airport during sea-breeze events. Using a building-resolving computational fluid dynamics model nested in an advanced forecast system with a data assimilation scheme, the authors perform a series of sensitivity experiments to investigate the impacts of land use and buildings on these rolls. The results show that the roll positions, intensities, and structures are significantly affected by variations in land use and the presence of buildings. Land-use heterogeneity is responsible for generating rolls with evident regional features. Major rolls tend to develop downwind of warm surfaces, and they dominate over neighboring rolls; thus, a heterogeneity-scale mode is imposed on the inherent roll wavelength. The roll’s rapid growth is attributable to warm surfaces that initiate a strong coupling among turbulent thermals, convective updrafts, pressure perturbations, and secondary flows in sea breezes. The heterogeneity-induced features differ...

A design strategy for a high-energy Tm,Ho: YLF laser transmitter

We report on a design strategy for a Tm,Ho:YLF laser transmitter capable of 125 mJ pulse energy at 30 Hz. Using the results of simulations and experiments, total efficiencies were compared for two different configurations. One is the oscillator operating at 193 K, and the other is the master oscillator and power amplifier operating at 233 K. In the latter case, an extensive cooling system is not required, while the laser efficiency becomes lower. Numerical simulations were performed by using a simple rate equation model. In order to validate the results of simulations, the laser experiments were made with a conductively cooled, side-pumped Tm,Ho:YLF laser in the temperature range of 195-228 K. Based on these results, an optimum configuration to achieve the 125-mJ pulse energy are discussed.

Conductive-cooled 2micron laser for CO2 and wind observations

We have developed 2micron Q-switched lasers with conductive-cooled side pumped laser head. Q-switched output of 100mJ at 20Hz has been achieved in a Tm,Ho:YLF laser oscillator with a composite rod. The experiments showed that very good thermal conduction is held between rod and heat sink. This laser head may be used for laser amplifier of 500mJ output. Another type of Tm,Ho:YLF laser head has been developed for the oscillator of 50-100mJ output at 20-40Hz. These 2micron lasers are applied to coherent lidar systems, which will be used to measure atmospheric CO2 and wind profiling.

7.28-W, High-Energy, Conductively Cooled, Q-Switched Tm,Ho:YLF Laser

A diode-side-pumped laser oscillator with a Tm,Ho:YLF rod conductively cooled to -80 °C was developed. A Q-switched pulse energy of 104 mJ was achieved at a pulse repetition frequency of 70 Hz, corresponding to an average output power of 7.28 W. In addition, the maximum Q-switched pulse energy of 125 mJ was obtained at 50 Hz. Even at the maximum output level, the beam quality factor M2 was measured to be ≤ 1.5. To the best of our knowledge, this is the highest average output power reported for a 100-mJ-class Q-switched 2-μm laser oscillator using a conductively cooled laser head.