Middle And Upper Radar Research Articles

Intercomparison of various SA techniques on wind estimation using multi-receiver phased array radar

In this paper we have applied various spaced antenna (SA) techniques to derive horizontal winds with Middle and Upper (MU) atmospheric radar observations. SA techniques comprise different analysis methods like Full Correlation Analysis (FCA), Cross Correlation Ratio (CCR), Slope at Zero lag (SZL) and Intersection (INT) methods etc. Among these methods, FCA is considered one of the classical approaches. In the present study, the MU radar antenna array is regrouped (in software) into three different antenna segments, each segment consists of 8 channels and forming an equilateral triangle. Grouping of antenna has been done with 4 different orientations by interchanging the channels. FCA wind has been estimated with an equilateral triangle grouping of antenna array in all orientations. With the same grouping in different orientations, winds are estimated with CCR, SZL and INT methods. Winds estimated with different orientation are averaged to obtain the mean winds component. In most of studies reported earlier using CCR, SZL and INT methods, winds have been estimated with pair of antenna having baseline parallel to the antenna array plane. We have retrieved the zonal wind with a pair of antennas having baseline parallel to the antenna array plane in east–west direction and meridional wind is estimated with a pair of antennas having baseline parallel to the antenna array plane in north–south direction. The mean winds obtained with various SA techniques are compared with that observed by the Doppler Beam swinging (DBS) technique and GPS-sonde. It is observed that mean winds obtained with the approach adopted using different spatially distributed array grouping has yielded higher height coverage up to ~20km and in good agreement with the results obtained using DBS observations even with a temporal resolution of ~1.3min in clear air condition. Various statistical analyses like correlation analysis, standard deviation, root mean square error (RMSE) and error analysis have been performed to understand the performance of other techniques in comparison with FCA. The analysis is carried out for an observation of 6h for two different observation periods.

Characteristics of atmospheric gravity waves observed using the MU (Middle and Upper atmosphere) radar and GPS (Global Positioning System) radio occultation

The wind velocity and temperature profiles observed in the middle atmosphere (altitude: 10–100 km) show perturbations resulting from superposition of various atmospheric waves, including atmospheric gravity waves. Atmospheric gravity waves are known to play an important role in determining the general circulation in the middle atmosphere by dynamical stresses caused by gravity wave breaking. In this paper, we summarize the characteristics of atmospheric gravity waves observed using the middle and upper atmosphere (MU) radar in Japan, as well as novel satellite data obtained from global positioning system radio occultation (GPS RO) measurements. In particular, we focus on the behavior of gravity waves in the mesosphere (50–90 km), where considerable gravity wave attenuation occurs. We also report on the global distribution of gravity wave activity in the stratosphere (10–50 km), highlighting various excitation mechanisms such as orographic effects, convection in the tropics, meteorological disturbances, the subtropical jet and the polar night jet.

Motion of echo structures observed with volume imaging atmospheric radar

Volume imaging radar often shows echo patterns on horizontal scale ∼ 100 – 1000 m , moving across the radar. The echoes could be from convection, and moving at near the background wind velocity; other explanations are clouds or regions of turbulence. This paper studies the motion of echoes, with a two-dimensional correlation method widely used for cloud motion winds and tracking weather radar echoes, but not applied before to wind profiling radar. Data are from the MU (middle and upper atmosphere) radar, Japan. Several factors causing an underreading of echo speed are removed; however, remaining data still show echoes moving a few m s - 1 slower than the background wind, with similar direction. This could be explained by convection, consistent also with some increased vertical-beam spectral width showing turbulence. Motion of convective echoes slower than the background wind could bias other radar wind measurements.

Estimation of Humidity Profiles by Combining Co-Located VHF and UHF Wind-Profiling Radar Observation

The turbulence echo intensity observed by a wind-profiling radar is closely related to the vertical gradient of refractive index squared (M 2 ), which largely depends on the vertical humidity gradient in a moist atmosphere. We have developed a radar remote-sensing technique for determining humidity profiles by using the turbulence echo characteristics. The sign of M is determined so that the precipitable water vapor determined by the radar agrees with that derived from the GPS measurements. In this study we have combined the results collected with two co-located radars; the MU (Middle and Upper atmosphere) and Lower Troposphere Radar (LTR) operating at 46.5 MHz and 1.3 GHz frequencies, respectively, and humidity profiles determined at 0.3-7.5 km. The echo power profiles (signal-to-noise ratio, SNR) with the two radars are connected smoothly in a height range between 1.5 and 1.95 km, by considering reduction of the receiver sensitivity for the MU radar due to leakage of the transmission signal. The retrieved humidity profiles show detailed time-height variations, which agree well with the simultaneous Raman lidar and radiosonde measurements.

High-resolution vertical imaging of the troposphere and lower stratosphere using the new MU radar system

Abstract. In the present paper, a new application of the range imaging technique called Frequency Interferometry Imaging (FII) or Range Imaging (RIM), performed in April 2005, is shown using the new 46.5-MHz Middle and Upper (MU) atmosphere radar system (Shigaraki, Japan). Height-time images of brightness distribution have been computed at the highest resolution ever obtained for imaging with VHF radars in the troposphere and, for the very first time, in the lower stratosphere, up to about 22 km. The images were produced by processing signals obtained with an initial range-resolution of Δr=150 m and five equally-spaced frequencies within Δf=1.0 MHz, with the adaptive Capon method. These values represent an improvement of a factor 2 over all the previous published experiments at VHF, which were performed with Δr=300 m and Δf=0.5 MHz. The Capon images present realistic and self-consistent features, and reveal many more organized structures than the height-time SNR plots at the initial range-resolution. For example, the Capon images show persistent enhanced brightness layers significantly thinner than 150 m in the stratosphere, which are impossible to track with the standard single-frequency mode owing to a lack of range resolution. These observations thus support the idea of strong stratification even at vertical scales much smaller than 100 m, as suggested by recent high-resolution temperature observations by balloons (Dalaudier et al., 1994). We also present comparisons of Capon images with patterns obtained from the dual-FDI technique and two parametric methods (the MUSIC algorithm and the newly-introduced Maximum Entropy Method based on an auto-regressive (AR) model). The comparisons confirm the insufficiencies of the dual-FDI technique and indicate that parametric methods such as MEM and the MUSIC algorithm can help to validate the Capon images when the parametric methods provide similar patterns.

Combined MU radar and ozonesonde measurements of turbulence and ozone fluxes in the tropo‐stratosphere over Shigaraki, Japan

Turbulent diffusivity and turbulent ozone fluxes in the tropo‐stratosphere are studied employing simultaneous observations with the Middle and Upper (MU) Atmosphere radar and ozonesondes in Shigaraki, Japan during April 16–24, 1998. A broad region around the tropopause was dynamically active. Maxima of turbulent diffusivity were observed at 8–14 km altitude. Such maxima may produce vertical turbulent ozone fluxes across the tropopause with magnitudes comparable to those required for the global ozone budget. Meso‐meteorological ozone intrusions may enhance the fluxes.

地球大気のレーダーリモートセンシング(PD-1 基調講演)

Atmospheric radar techniques are developed for sensing the Earth's atmospheric dynamics. Winds and other parameters aloft are deduced from echoes reflected back from the atmosphere. The MU (Middle and Upper atmosphere) radar established by Kyoto University in 1984 has resolved numerous mysteries of the atmosphere, especially above 10km in altitude. The region used to be thought so quiet that no significant meteorological phenomena occurred there. However, the MU radar has revealed that various atmospheric waves are raging there, and even the seasonal change of global-scale winds around 60-90km is controlled by these waves propagating upward from near the surface. The atmospheric radar techniques have been employed for the operational weather forecast in Japan. Also, it is expected that a number of the mysteries of the equatorial atmosphere will be enlightened with the MU-like radar called the Equatorial Atmosphere Radar established at the equator in Sumatra, Indonesia.

A Lower Troposphere Radar: 1.3-GHz Active Phased-Array Type Wind Profiler with RASS

We have developed an atmospheric radar (wind profiler) for lower tropospheric observations (Lower Troposphere Radar: LTR), based on the 1357.5-MHz boundary layer radar (BLR), which we previously developed mainly for observations of the atmospheric boundary layer. System gain of this radar is improved due to newly developed large-sized active phased-array antenna, active transmitting modules with higher output power, and pulse compression technique. It has the following functions: an antenna gain of 33 dBi is obtained with a 4 m × 4 m active phased array antenna which has 96 antenna subelements, a peak output power of 2 kW is obtained by 24 active transmitting modules, and maximum S/N is improved 8 times by using a pulse compression technique which uses 8-bit optimized coding developed by Spano and Ghebrebrhan (1996c). The LTR is the first active phased-array 1.3 GHz-band wind profiler radar. It is possible to vary the beam direction by electronically steering the zenith angle within 45°. Atmospheric winds in the lower troposphere, including the atmospheric boundary layer, are obtained with high time and height resolutions in real time. Observations of atmospheric temperature are also possible using the radio acoustic sounding system (RASS) technique with speaker horns. We have confirmed LTR’s potential as a reliable tool for atmospheric observations, using simultaneous observation results with the MU (Middle and Upper atmosphere) radar, a Doppler sodar, and a radiosonde.

Meso-.ALPHA.-Scale Wind Field and Precipitating Clouds in Typhoon 9426 (Orchid) Observed by the MU Radar

A general structure of Typhoon 9426 (Orchid) up to the lower stratosphere including the inner core region was observed by the MU (middle and upper atmosphere) radar on 29-30 September 1994. In this paper, a meso-α-scale wind field and meso-β and -y scale features of precipitating clouds in the typhoon were investigated. The kinematic structure in the front and rear of the typhoon was quite different because of its transition from mature to decaying stages and an asymmetric distribution of cloud and precipitation. In front of the typhoon, the meso-α-scale wind field was characterized by a cyclonic rotation with the maximum at low level, outflow regions tilted outward with height, and vertical motions affected by convection and topography. In the vicinity of the typhoon center, the tangential wind had a vertical spiral structure for the center, considered to be the result from deformation of the center of the decaying typhoon. In the rear of the typhoon without precipitating clouds, the cyclonic wind became weak, and the outflows and vertical motions as seen in the front were not detected. In front of the typhoon, an eyewall and wide rainband were observed. In the eyewall, a meso-γ-scale remarkable updraft associated with an outflow region, considered to be a part of vertical circulation, was found in the upper troposhere. The outflow region tilted outward was originated from the area of maximum radial shear of the low-level cyclonic wind. It was extended to an updraft region within an upper-level band-shaped cloud, located far from the typhoon center. The wide rainband (50-70 km width) was located at the outer edge of the band-shaped cloud, and it lasted in the development of the upper-level cloud. It was accompanied by the tilted outflow region to 6 km altitude, the bottom of which was located at the maximum of the cyclonic wind. A narrow rainband (20-40 km width), that a lifetime was quite short (1.5 hours), was also observed by the boundary layer radar (BLR) at another site. An outflow region with the tilted structure was present in the outer part (convective portion) of the rainband, and its bottom was not associated with strong cyclonic wind as seen in the wide rainband.

Development of a Transportable 3-GHz Wind Profiler for Wind and Precipitation Studies.

A transportable 3-GHz wind profiler has been developed for convenient observations of wind and precipitation. It consists of a phased array antenna with a diameter of 1 m, a transmitter with peak output power of 500 W, a receiver, a radar controller, a DSP (Digital Signal Processor) unit, and a workstation. The whole system is loaded onto a small truck for easy transportability. To verify the validity of wind velocity data obtained by the 3-GHz wind profiler, we conducted simultaneous observations with the MU (Middle and Upper atmosphere) radar at the Shigaraki MU Observatory on January 15, 1998. It showed that the 3-GHz wind profiler has sufficient reliability for wind velocity observations. We investigated the ability of observational height coverage of the 3-GHz wind profiler using height profiles of wind velocities obtained at the Shigaraki MU Observatory during May 25, 1998-November 2, 2000. It showed that the pulse compression is very effective, and the 3-GHz wind profiler has good performance to provide wind velocities in the lower troposphere, especially in precipitation. We also present preliminary results of observation of the front on May 4, 1999 to show the performance of the 3-GHz wind profiler.

Implications of meteor observations by the MU Radar

We report high resolution meteor echo observations using the Kyoto University Middle and Upper (MU) Atmosphere 46.5 MHz Radar. When the MU radar was pointed perpendicular to the geomagnetic field lines (B), numerous long‐lived range spread trail echoes were observed which were largely absent when the beam was pointed in the vertical and parallel‐to‐B directions. This shows that this type of trail echo is largely due to scattering structures aligned along B. Additionally, nearly all the head echoes displaying an along‐the‐beam velocity component were followed by range spread echoes in the perpendicular‐to‐B pointing geometry. This demonstrates that meteoric field aligned irregularity is present in essentially all meteors up to the detection limit of the MU radar. Practically all the spectra are limited within a bandwidth corresponding to a Doppler shift of 320 m/s, suggesting that the two stream instability is absent most of the time. Meteoric field aligned structures can be a potential error source for aeronomical applications if they are not appropriately considered.

A Global Morphology of Gravity Wave Activity in the Stratosphere Revealed by the GPS Occultation Data (GPS/MET)

Using temperature profiles obtained by the GPS/MET (GPS Meteorology) experiment from April 1995 to February 1997, we have extracted mesoscale temperature perturbations with vertical wavelengths ranging from 2 to 10 km and background Brunt‐Väisälä frequency squared, N2. For each occultation event, we can evaluate a potential energy Ep which is assumed to be caused by atmospheric gravity waves. The monthly mean values of Ep at 15–20 km around Japan showed an annual variation with an enhancement in winter, which is consistent with the climatological behavior of the kinetic energy of gravity waves observed with the MU (middle and upper atmosphere) radar (34.9°N, 136.0°E) from 1985 to 1989. We have then derived the global distribution of Ep at 20–30 km during Northern Hemisphere winter (from November to February). Our analysis shows that the largest Ep values are generally centered around the equator between 25°N and 25°S with considerable longitude variations. Longitudinal variations of Ep at 20–30 km in a latitude range of 30°–60°N are also analyzed, resulting in larger Ep values over the continents than over the Pacific Ocean. Using GPS/MET data without antispoofing, latitudinal variations of Ep are determined in 15–45 km. Although large Ep values are concentrated near the equator at 20–30 km, Ep tends to become larger at midlatitudes at 30–40 km and higher‐altitude regions. At midlatitudes, Ep is found to be larger in winter months in both hemispheres. Height variations of Ep indicate a decrease at 25–30 km and a monotonic increase above 30 km.

MUレーダーと気象レーダーによって観測された梅雨前線近傍の降水雲に伴うメソβ-γスケール循環

During the Baiu season (17 June-8 July 1991) we carried out simultaneous tropospheric observation by using the MU (Middle and Upper atmosphere) radar (VHF band, Kyoto University) and meteorological radars (C band of Osaka Meteorological Observatory, X band of Hokkaido University and C/Ku band of Kyoto University). Vertical distributions of three components of wind field and precipitation particles were observed by the MU and C/Ku-band radars, respectively. The C- and X-band radars were used to investigate horizontal distributions of precipitating clouds in the meso-α and -β scales, respectively. Several meso-β and -γ-scale cloud systems were observed around a meso-α-scale cyclone center during 4-5 July when rainfall was the strongest in the whole observational period. They were divided into two groups of convective clouds i) near a surface warm front and ii) near a surface cold front, and iii) one group of stratiform clouds on the north-western side of the surface cold front. In i), a remarkable updraft inside a precipitating cloud extending up to an altitude of 14km was produced by a convergence (inflows coming from the front and rear of the precipitating cloud) at an altitude of 4-5km and by strong southerly wind in the middle troposphere. In ii), a narrow rainband with gust front was seen at the leading edge of the surface cold front.Two meso-γ-scale rotor circulations were found in front of and inside the rainband, respectively. In iii), south-easterly (north-westerly) ascent (descent) flows were observed above (inside/under) the cold frontal surface extending up to an altitude of about 9km. Below the cold frontal surface, there was a dry region without precipitation, and a part of the descending westerly flow returned to the back of the precipitating cloud. In this study, vertical structures of meso-β and -γ-scale cloud systems with characteristic wind flows as mentioned above were revealed by the detailed three components of wind field in both clear and precipitating atmosphere. They were presented as smaller cloud systems in the hierarchical structure of cloud clusters near the meso-α-scale cyclone in the central region of the Japan Islands.

Estimation of turbulence energy dissipation rate and vertical eddy diffusivity with the MU radar RASS

We have conducted RASS (Radio Acoustic Sounding System) observations with the MU (Middle and Upper atmosphere) radar on 28–31 July 1994 at Shigaraki, Japan (34°51′ N, 136°06′ E) and determined the characteristics of turbulence energy dissipation rate ( ε) and vertical eddy diffusivity ( K) in the troposphere and lower stratosphere. We have first examined the accuracy of the Brunt Väisälä frequency squared ( N 2) derived from RASS temperature profiles. Then, ε and K are determined by using N 2 and the Doppler spectral width of turbulence echoes ( σ 2 turb). We found that the structures of ε and K are sometimes affected by the local variations of N 2. We found that sometimes ε became small, even though σ 2 turb was large, because N 2 was small. On the contrary, K was enhanced due to small N 2, although σ 2 turb was small.

The MU radar measurements and modeling of the gravity wave climatology and sources in the atmosphere

A statistical analysis of the data of 10 year observations with the Middle and Upper (MU) atmosphere radar gives information about seasonal variations of the intensity of irregular wind disturbances, which are different in the troposphere and mesosphere. A comparison of seasonal variations of internal gravity wave intensity observed by the MU radar with a numerical model of wave spectrum propagation explains the differences of the seasonal variations and gives information about vertical distribution of the intensity of hydrodynamic wave sources. Discussed are the MU radar measurements of nonlinear advective accelerations in the tropo-stratosphere, which reflect the activity of nonlinear wave generation.

Analysis on Vertical Profile of DSD and Building up an Algorithm for Estimating Ground Rainfall Using Radar

To improve the accuracy of the radar-estimated rainfall, we observe and analyze the vertical profile of the rain drop size distribution (DSD), then create a new formulation of vertical profile of DSD related to rainfall type and build up an algorithm for estimating ground rainfall using radar. Observation of the vertical profile of DSD is carried out by a vertical pointing VHF Doppler radar named the MU (Middle and Upper) Radar, which can detect vertical profiles of Doppler spectrum that composed of bothrain drop itself and air movements.

Wind velocity and temperature fluctuations due to a 2‐day wave observed with radio meteor echoes

We study in this paper characteristics of both wind velocity and temperature fluctuations due to a 2‐day wave near the mesopause, by means of meteor echo measurements with the MU (middle and upper atmosphere) radar in Shigaraki, Japan (35°N, 136°E) and a meteor wind radar, newly constructed near Jakarta, Indonesia (6°S, 107°E). A 2‐day wave was conspicuously enhanced on July 12–19, 1993, at both Shigaraki and Jakarta. Fluctuations of temperature and northward wind were inphase in Shigaraki, and they became antiphase in Jakarta, consistent with a prediction assuming a Rossby‐gravity wave. The phase lag of the fluctuations between the two sites suggested that this wave propagated westward with a zonal wavenumber of 3. Seasonal variations of the 2‐day wave in Jakarta were examined by using a frequency spectrum and complex demodulation technique for temperature and wind fields, finding clear enhancements during periods corresponding to summer months in each hemisphere, especially in January 1993. The dominant wave period was fairly stable and was confined in a narrow range centered around 47 and 49 hours during summer months of the southern and northern hemispheres, respectively. The phase variations of temperature preceded those for the northward wind by 180°–225° when an enhanced 2‐day wave was seen in the northward component, indicating their antiphase relation in the southern hemisphere. These results strongly support the interpretation of the 2‐day wave near the mesopause as the (3,0) mode of a Rossby‐gravity wave with zonal wavenumber of 3.

Phase calibration of VHF spatial interferometry radars using stellar sources

This work describes a method for phase calibration of spatial interferometry (SI) systems, which have recently seen increasing use in the wind profiling community. The various available techniques are inherently dependent on any phase imbalance in the system. The imbalance is caused by a path length difference between the multiple receivers, which is typically corrected at the time of construction. Aging of the system and other environmental changes can cause a modification in the path lengths, however. An obvious method for calibrating an SI system involves examining the phase differences between the receivers for a signal produced by a source with known location. For physically small systems, this can be accomplished by pointing the antenna beam toward a man‐made source, such as a simple transmitter with the same center frequency as the radar. For large MST (mesosphere/stratosphere/troposphere) radar systems, such as the Middle and Upper (MU) Atmosphere radar, this method is impractical. The present work describes the calibration of the MU radar using the radio star Cygnus A as a source of known location. As the radio star traverses the beam, the MU radar passively tracks it by measuring the phase differences of the cosmic noise signal received on spatially separated receivers. Since the location of Cygnus A is known from astronomical calculations, any phase imbalance can be compensated. Data from May 1992 show the usefulness of the method.

Observations of Tropospheric Temperature Fluctuations with the MU Radar-RASS

Abstract Applying the RASS (radio acoustic sounding system) technique to the MU (middle and upper atmosphere) radar, profiles of both temperature and wind velocity were observed every 90 s in the height range of about 1.5–7.0 km, with a height resolution of 300 m, for about 40 h on 6–8 August 1990. The temperature profiles obtained with RASS agreed well with the virtual temperature derived from radiosonde sounding, where the mean difference between the temperature values was approximately 0.3°C. The observed frequency spectra above about 2.5-km altitude, having an asymptotic slope of −5/3 and approximately 0 for temperature and vertical wind velocity fluctuations, respectively, were reasonably consistent with a model spectrum of gravity waves. But, below 2.5 km, low-frequency components were conspicuously enhanced, especially for vertical wind velocity, presumably affected by convection. Wavelike temperature fluctuations with a dominant period of 6–8 h clearly showed downward phase progression and a π/2 p...

ＭＵレーダによる下部成層圏風速の観測 成層圏無線中継システムのための環境評価

Height, seasonal, and short-period variations of lower stratospheric winds around 20km altitude, where aircraft for the stratospheric radio link system will fly, are analyzed based on the wind data obtained by the MU (middle and upper atmosphere) radar for three years. While the stratospheric jet stream was found to be weak enough in summer, it turned to be fairly strong in winter even at the so-called ‘zero-wind’ height of around 20km, sometime exceeding 40m/s over a period of two days. Random wind fluctuations of the order of 1m/s was found to exist in thin turbulent layers of 50-100m thickness.