Hironori Iwai

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...

2-um Coherent Lidar Technology Developed at NICT: Past, Current, and Future

We present a development and research of the 2-µm coherent lidar with a conductively-cooled laser-diode-pumped single-frequency Q-switched Tm,Ho:YLF pulse laser developed at the NICT.

Development of coherent 2-μm differential absorption and wind lidar with laser frequency offset locking technique

We developed a coherent 2-μm differential absorption and wind lidar to measure CO2 concentration and line-of-sight wind speed. The wavelength of on-line laser was set at the R30 absorption line center of CO2 and the atmospheric transmission for the on-line backscattered signal caused by CO2 is large. Measurable range of CO2 measurement was limited. A laser frequency offset locking system was installed into the laser system to improved measurable range of CO2 measurement. Two single-frequency continuous wave lasers are used for the laser frequency offset locking. One laser (center, λCenter) of the two continuous lasers is directly locked to the R30 absorption line center of CO2 and the other (on-line, λOn) is frequency-shifted to λCenter laser. Although long-range CO2 measurement depends on the laser frequency offset, the installation of the laser frequency offset realized vertical CO2 measurement in a range of up to the upper troposphere.

Measurements of Rainfall Velocity and Raindrop Size Distribution Using Coherent Doppler Lidar

AbstractRainfall velocity, raindrop size distribution (DSD), and vertical wind velocity were simultaneously observed with 2.05- and 1.54-μm coherent Doppler lidars during convective and stratiform rain events. A retrieval method is based on identifying two separate spectra from the convolution of the aerosol and precipitation Doppler lidar spectra. The vertical wind velocity was retrieved from the aerosol spectrum peak and then the terminal rainfall velocity corrected by the vertical air motion from the precipitation spectrum peak was obtained. The DSD was derived from the precipitation spectrum using the relationship between the raindrop size and the terminal rainfall velocity. A comparison of the 1-min-averaged rainfall velocity from Doppler lidar measurements at a minimum range and that from a collocated ground-based optical disdrometer revealed high correlation coefficients of over 0.89 for both convective and stratiform rain events. The 1-min-averaged DSDs retrieved from the Doppler lidar spectrum us...

Water vapor estimation using digital terrestrial broadcasting waves: WATER VAPOR ESTIMATION USING DTB WAVES

近年都市部で頻発する局地的大雨(通称ゲリラ豪雨) などの時空間スケールの小さな気象現象は、孤立した 積乱雲の急激な生成・発達により引き起こされる。従 来のレーダー観測ではとらえることが困難だったこの ような現象が、フェーズドアレイ気象レーダー (PAWR)の登場により可視化できるようになってき た。PAWR は半径 60 km の範囲の雨を 30 秒ごとに 三次元観測することができる。さらに、2018 年 3 月 から埼玉大学で観測が開始されたマルチパラメータ・ フェーズドアレイ気象レーダー(MP-PAWR)は、観 測の高速性を保ちつつ偏波の情報を使ってより定量的 な降雨観測を実現している。このようなフェーズドア レイ気象レーダーを用いることで、上空で急発達した 降水粒子が落下に要する 5 ~ 10 分後には地上のどの あたりにどの程度の降水をもたらすか、といった短時 間の予測が可能になってきた。 しかし、防災・減災のための対応が可能となるよう な長いリードタイムを取った予測(20 分~数時間先の 予測)の精度はいまだ十分とは言えない。このような 長い予測の精度向上には数値予報モデルが重要であり、 その予測精度向上にはモデルそのものの改良に加えて、 より多くの観測データを取り込む(データ同化する) ことが必要となってくる。その中でも特に近年期待さ れているのが水蒸気量のデータ同化である。水蒸気は 雨の元となる気体としての水であり、この水蒸気の動 きを早い段階から連続して監視することで、より精度 の高い降雨予測につながると期待されている。本稿で は、NICT が開発し、現在首都圏を中心に実証実験を 実施している地上デジタル放送波(地デジ放送波)を 用いた水蒸気量推定技術を紹介する。