Hiroshi Kumagai

Vertical cloud structure observed from shipborne radar and lidar: Midlatitude case study during the MR01/K02 cruise of the research vessel Mirai

[1]xa0We observed the vertical distribution of clouds over the Pacific Ocean near Japan in May 2001 using lidar and a 95-GHz radar on the Research Vessel Mirai. Cloud analyses derived from synergy use of radar and lidar observations showed that there were two local maxima of cirrus cloud frequency of occurrence at 7 and 10.5 km and the drizzle frequency of occurrence was about the half compared with that of clouds below 4 km. The number of layers could be also measured using these schemes. Single, double, triple, and quadruple (or more) cloud layers had a 48, 23, 7, and 2% probability of occurrence, respectively. The average number of cloud layers when clouds existed was 1.54. The vertical structure of clouds observed with the radar/lidar system was compared to clouds in the aerosol transport model SPRINTARS, which is based on the CCSR-NIES Atmospheric General Circulation Model. The cloud fraction, radar reflectivity factor, and lidar backscattering coefficient were simulated by the model and compared to those by the observations using height-time cross-sections where the radar sensitivity was taken into account. The overall pattern of cloud fraction was well reproduced, although the model underestimated (overestimated) mean cloud fraction below 8 km (above 8 km). Cloud microphysics in the model could also be validated through comparison of derived model radar and lidar signals in grid mean with observations. The model overestimated ice particle size above 10 km, and simulated particle sizes in water clouds of 10 μm were larger than observed.

Vertical cloud properties in the tropical western Pacific Ocean: Validation of the CCSR/NIES/FRCGC GCM by shipborne radar and lidar

[1]xa0This study examined the vertical cloud structure over the tropical western Pacific Ocean using 95-GHz radar and lidar data observed from September to December 2001 during the MR01-K05 cruise of the research vessel Mirai. The cloud vertical structure was homogeneous between 6 and 10 km, and the maximum cloud occurrence was 20% and located at 12 km. The mean precipitation occurrence was 11.5% at 1 km. The cloud fraction, radar reflectivity factor, and lidar backscattering coefficient were simulated along the Mirai cruise track using the output from the Center for Climate System Research, University of Tokyo; National Institute for Environmental Studies; and Frontier Research Center for Global Change (CCSR/NIES/FRCGC) general circulation model (GCM). The original output showed the maximum cloud fraction at 15 km; however, after considering attenuation and the minimum sensitivity of the radar, the maximum shifted to 12 km. The model overestimated the cloud fraction above 8 km, with the simulated fraction more than twice as large as the observed fraction. The model overpredicted the frequency of deep convection reaching the upper atmosphere above 12 km. Further, it overestimated precipitation frequency. Simulated radar reflectivity was underestimated throughout the entire altitude range, whereas simulated and observed lidar backscattering were in good agreement above 12 km with subgrid-scale treatment. The ice effective radius of 40 μm and ice water content were reasonable in thin clouds, but the radius was underestimated in other regions. The simulated liquid water content was overestimated.

Cloud optical thickness and effective particle radius derived from transmitted solar radiation measurements: Comparison with cloud radar observations

[1]xa0A method is presented for determining the optical thickness and effective particle radius of stratiform clouds containing liquid water drops in the absence of drizzle from transmitted solar radiation measurements. The procedure compares measurements of the cloud transmittance from the ground at water-absorbing and nonabsorbing wavelengths with lookup tables of the transmittance precomputed for plane-parallel, vertically homogeneous clouds. The optical thickness derived from the cloud transmittance may be used to retrieve vertical profiles of cloud microphysics in combination with the radar reflectivity factor. To do this, we also present an algorithm for solving the radar equation with a constraint of the optical thickness at the visible wavelength. Observations of clouds were made in August and September 2003 at Koganei, Tokyo, Japan, using a PREDE i-skyradiometer and a 95-GHz cloud radar Super Polarimetric Ice Crystal Detection and Explication Radar (SPIDER). The optical thickness and effective radius of water clouds were derived from the i-skyradiometer. Then, the vertical profile of the effective radius was retrieved from SPIDER, using the optical thickness determined from the i-skyradiometer. We found that the effective radii derived by using these two instruments were in good agreement.

95-GHz Doppler radar and lidar synergy for simultaneous ice microphysics and in-cloud vertical air motion retrieval

[1]xa0We introduce a combined 95-GHz radar multi-parameter (radar reflectivity Ze, Doppler velocity VD, and/or linear depolarization ratio LDR) and lidar backscatter coefficient βbk algorithm for the simultaneous retrieval of ice cloud microphysics and in-cloud vertical air motion Vair within a single radar volume. Unlike earlier methods, our new approach is not limited to a specific temporal or spatial scale of Vair, which makes it applicable to the interaction between cloud dynamics and ice cloud microphysics on various scales. Full one-to-one validation of the retrieved Vair was performed, for the first time, by collocated VHF Doppler radar measurement (Equatorial Atmospheric Radar) every 3 min for a cloud observed on 14 November 2005, at Kototabang, West Sumatra, Indonesia. The spatial structure of the retrieved up-/downward Vair in cloud agreed closely with direct measurements, with an average difference of −0.009 ± 0.119 ms−1. The frequency distributions for the retrieved and measured Vair also agreed closely, with peaks of similar width observed around 0 ms−1. A large improvement in the microphysical retrieval was achieved due to the accurate estimation of the Ze-weighted particle fall velocity Vtz from VD. The correlation coefficient between ice water content retrieved with the estimated Vair and that retrieved with the Vair measured by the EAR improved to 0.70 from values as low as 0.28 without the Vair retrieval.

Cloud profiling radar for EarthCARE mission

Concept and expected performance of cloud profiling radar (CPR) for EarthCARE are described based on preliminary design study conducted to date. High sensitivity and Doppler capability are two significant new features in this CPR. Particularly, Doppler capability is the first attempt to spaceborne atmospheric radar, which requires great efforts in technical development and feasibility validation. We have developed a new numerical simulation method to assess Doppler velocity accuracy applicable to this application, and results are compared with conventional approximation method. Validity and limitation of the approximation method are indicated from comparison with numerical method. It is shown that requirements to radar sensitivity and Doppler measurements will be satisfied. However, because these requirements to CPR are very tough, further detailed study on both design optimization and assessment technique development are necessary. Under radar operation with very high pulse repetition frequency (PRF) required in this CPR, surface clutter interference caused through antenna sidelobes is an important issue. Analysis on this issue and preliminary requirements to the antenna sidelobes are also discussed.

Observation of particle fall velocity in cirriform cloud by VHF and millimeter‐wave Doppler radars

[1]xa0In this study, it is demonstrated that a combination of VHF and millimeter-wave Doppler radars is a key tool for observing particle fall velocity in cirriform clouds. VHF (47-MHz) and millimeter-wave (95-GHz) Doppler radars observed cirriform clouds at West Sumatra, Indonesia (0.2°S, 100.32°E) from 2000 LT 14 to 0800 LT 15 November 2005. Radar reflectivity factor (Ze) observed by the 95-GHz radar showed that echoes from cloud particles had tops around 12–14 km and bottoms around 8–10 km. Doppler velocity observed by the vertically pointed beam of the 95-GHz radar (Vair+Z) was compared with vertical air velocity (Vair) observed by the 47-MHz radar to confirm that Vair+Z, a sum of Vair and reflectivity-weighted particle fall velocity (VZ), showed consistent changes with Vair and hence VZ is able to be retrieved by subtracting Vair from Vair+Z. The correlation coefficient between VZ and Ze in the middle part of clouds (10.5–12.2 km) was −0.81, which was higher than that (−0.47) in the bottom part (7.2–10.5 km). The change of VZ for Ze in the middle part was larger (Ze = −31.9 VZ − 32.2) than that in the bottom part (Ze = −90.2 VZ − 71.8). These results suggest that particle size was a dominant factor that determined Ze in the middle part. Using VZ, median volume diameter (D0) was estimated to suggest that D0 was larger than ∼70 μm in the bottom part and ranged from ∼40 μm to larger than ∼106 μm in the middle part.

Ionospheric disturbances over Japan due to the 18 May 1980 eruption of Mount St. Helens

The effects of the Mount St. Helens eruption at 1532 UT on 18 May 1980 on the ionosphere over Japan are examined using data on total electron content obtained at three closely-spaced stations and HF (5 and 8 MHz) Doppler recordings together with microbarograph data for the surface pressure perturbation. The results strongly suggest that ionospheric perturbations having a predominant period of about 9 min propagated from north to south approximately along the great circle path with a horizontal velocity of about 300 m s−1. The observed time variations of perturbations can be well explained in terms of Lamb waves propagating through the atmospheric sound channel while launching up-going waves to produce the ionospheric oscillations.

Observation of clouds with the newly developed cloud profiling FM-CW radar at 95 GHz

We developed a low-power and high-sensitivity cloud profiling radar transmitting frequency modulated continuous wave (FM-CW) at 95 GHz for ground-based observations. Millimeter wave at 95 GHz is used to realize much higher sensitivity than lower frequencies to small cloud particles. An FM-CW type radar realizes similar sensitivity with much smaller output power to a pulse type radar. Two 1m-diameter parabolic antennas separated by 1.4m each other are used for transmitting and receiving the wave. The direction of the antennas is fixed at the zenith. The radar is designed to observe clouds between 0.3 and 20 km in height with a resolution of 15 m. Using the developed millimeter-wave FM-CW radar at 95 GHz, we observed clouds in a campaign observation in Amami Island in March 2003, and on a sail on Mirai, a Japanese scientific research vessel, in September 2004 to January 2005 in the Arctic Ocean and the southwest of the Pacific Ocean. The radar provided good and sensitive data in these long-term observations.

95-GHz cloud radar and lidar systems: preliminary results of cloud microphysics

In this paper, we report the preliminary studies of cloud microphysics by using ground-based 95GHz cloud radar and lidar systems. Although the active sensors are expected to increase our knowledge about clouds, e.g., vertical profiles of clouds, the single use of radar or lidar gives limited information and it is difficult to retrieve the ice water content (IWC and effective radius of cloud particles. We develop the new method for the combinational use of radar and lidar signals. The algorithm includes the attenuation corrections on both signals which is a long standing problems especially in the analysis of lidar signals. The system enables to retrieve the vertical profiles of effective radius and IWC in each cloud layer. Since both active sensors have dual polarization capabilities, the system provides a unique opportunity to study cloud microphysics form many aspects, e.g., vertical profiles of the relationship between effective radius, IWC and/or depolarization ratio. This system also has a great potential to study aerosol-cloud interaction studies.

Behavior of mid-latitude F-region irregularities deduced from spaced-receiver VHF scintillation measurements

Abstract Using three closely spaced antennas, mid-latitude night-time scintillations at 136 MHz were observed under geomagnetically quiet conditions during June–July 1982. By means of correlation analysis, characteristics of ionospheric irregularities such as drift velocities, shapes and sizes were investigated for seven scintillation events. In the premidnight hours mostly southward or southwestward drifts were observed, while in the postmidnight hours the percentage of northward drifts increased. Mean northward and southward drift velocities were 25 m s −1 and 23 m s −1 , respectively. Large northward drifts (> 80m s −1 ) were occasionally observed in the postmidnight hours. Peculiar drift reversals from northward to southward occurred abruptly in the midst of strong and high-pitch scintillations. They were accompanied by sharp increases in TEC. The directions of the major axes of the diffraction pattern ellipses are coincident with those of the geomagnetic field lines, which suggests that the irregularities are well field-aligned. The mean axial ratio and mean minor radius are 6.2 and 182 m, respectively. The axial ratio increases and the minor radius decreases with increasing S 4 .