Monitoring of the MU radar antenna pattern by Satellite Ohzora (EXOS-C)

As the first attempt among MST (mesosphere stratosphere troposphere) type radars, the MU (middle and upper atmosphere) radar features an active phased array system. Unlike the conventional large VHF radars, in which output power of a large vacuum tube is distributed to individual antenna elements, each of 475 solid state power amplifier feeds each antenna element. This system configuration enables very fast beam steering as well as various flexible operations by dividing the antenna into independent subarrays, because phase shift and signal division/combination are performed at a low signal level using electronic devices under control of a computer network. The antenna beam can be switched within 10 microsec to any direction within the zenith angle of 30 deg. Since a precise phase alignment of each element is crucial to realize the excellent performance of this system, careful calibration of the output phase of each power amplifier and antenna element was carried out. Among various aircraft which may be used for this purpose artificial satellites have an advantage of being able to make a long term monitoring with the same system. An antenna pattern monitoring system for the MU radar was developed using the scientific satellite OHZORA (EXOS-C). A receiver named MUM (MU radar antenna Monitor) on board the satellite measures a CW signal of 100 to 400 watts transmitted from the MU radar. The principle of the measurement and results are discussed

Wind and waves in the middle atmosphere observed with the MU radar

The VHF band MU radar at Shigaraki, Japan, has been in full operation successfully since April 1985. Dynamical features found primarily in the data obtained by the radar during a one year period from December 1985 to November 1986 are examined. These include: basic wind observations, quasi-monochromatic gravity waves generated by the jet stream or through a geostrophic adjustment process, seasonal variation of the mesoscale wind variability, the momentum flux due to gravity wave motions, and saturated gravity wave spectrum. A short discussion is added to the relationship between turbulent layers and ambient wind field in the mesosphere

A transceiver module of the Mu radar

The transceiver (TR) module of a middle and upper atmospheric radar is described. The TR module used in the radar is mainly composed of two units: a mixer (MIX unit) and a power amplifier (PA unit). The former generates the RF wave for transmission and converts the received echo to the IF signal. A 41.5-MHz local signal fed to mixers passes through a digitally controlled 8-bit phase shifter which can change its value up to 1,000 times in a second, so that the MU radar has the ability to steer its antenna direction quickly and flexibly. The MIX unit also contains a buffer amplifier and a gate for the transmitting signal and preamplifier for the received one whose noise figure is less than 5 dB. The PA unit amplifies the RF signal supplied from the MIX unit up to 63.7 dBm (2350 W), and feeds it to the crossed Yagi antenna

Spectral analysis of temperature and Brunt-Vaisala frequency fluctuations observed by radiosondes

Recent studies have revealed that vertical wave number spectra of wind velocity and temperture fluctuations in the troposphere and the lower stratosphere are fairly well explained by a saturated gravity wave spectrum. But N(2) (N:Brunt-Vaisala (BV) frequency) spectra seem to be better for testing the scaling of the vertical wave number spectra in layers with different stratifications, beause its energy density is proportional only to the background value of N(2), while that for temperature depends on both the BV frequency and the potential temperature. From temperature profiles observed in June to August 1987 over the MU Observatory, Japan, by using a radiosonde with 30 m height resolution, N(2) spectra are determined in the 2 to 8.5 km (troposphere) and 18.5 to 25 km (lower stratosphere) ranges. Although individual spectra show fairly large day-by-day variability, the slope of the median of 34 spectra agrees reasonably with the theoretical value of -1 in the wave number range of 6 x 10(-4) similar to 3 x 10(-3) (c/m). The ratio of the spectral energy between these two height regions is about equal to the ratio of N(2), consistent with the prediction of saturated gravity wave theory

Observations of gravity waves in the mesosphere with the MU radar

Wind motions were observed at 60 to 90 km altitudes with the MU radar during daylight hours (0800 to 1600 LT) from 13 to 31 October 1986. Quasi-monochromatic gravity waves were evident on 16 of the 19 days of observations. They were characterized by typical vertical wavelength of 5 to 15 km and intrinsic periods centered at about 9 hours. The propagation direction of the gravity waves, determined by the gravity wave dispersion relation, was mostly equatorward. The vertical wave number spectra of the horizontal components of the mesoscale wind fluctuations are explained well by saturated gravity wave theory. The frequency spectrum of vertical wind component has a slope of + 1/3, while the oblique spectra have a slope of -5/3 up to 4 x 10(-3) (c/s); these agree fairly well with model gravity wave spectra. Doppler shift effects on the frequency spectra are recognized at higher frequencies. Upward flux was determined of horizontal momentum flux induced by waves with periods from 10 min to 8 hours, and westward and northward body forces of 5.1 and 4.0 m/s/day, were estimated respectively

Variance of wind estimates using spaced antenna techniques with the MU radar

International audienceVariance of horizontal wind estimates in conditions of anisotropic scattering are obtained for the Spaced Antenna (SA) Full Correlation Analysis (FCA) method of Holloway et al. (1997b) and Doviak et al. (1996), but are equally applicable to the Briggs method of FCA. Variance and covariance of cross-correlation magnitudes are theoretically estimated, and the standard theory of error propagation is used to estimate the variance of the wind components for the infinite SNR case. The effect of baseline orientation is investigated, and experimental data from the MU radar in Japan is presented

Gravity wave intensity and momentum fluxes in the mesosphere over Shigaraki, Japan (35°N, 136°E) during 1986-1997

International audienceAveraged seasonal variations of wind perturbation intensities and vertical flux of horizontal momentum produced by internal gravity waves (IGWs) with periods 0.2-1 h and 1-6 h are studied at the altitudes 65-80 km using the MU radar measurement data from the middle and upper atmosphere during 1986-1997 at Shigaraki, Japan (35° N, 136° E). IGW intensity has maxima in winter and summer, winter values having substantial interannual variations. Mean wave momentum flux is directed to the west in winter and to the east in summer, opposite to the mean wind in the middle atmosphere. Major IGW momentum fluxes come to the mesosphere over Shigaraki from the Pacific direction in winter and continental Asia in summer

A perspective of Middle-Atmosphere Dynamics (MAD) studies at the New International Equatorial Observatory (NIEO)

The equatorial region has attracted many MAD studies mainly based on data of limited locations and resolutions. Established at NIEO are: (1) Climatology of the equatorial middle atmosphere (all of the mean zonal flow, the meridional and/or east-west circulations and the planetary/gravity waves are described based on massive, reliable data statistics); (2) Troposphere-stratosphere coupling at the equator (the candidate location of NIEO is just at the stratospheric fountain area where the tracers and waves are pumped up into the middle atmosphere); and (3) Mesosphere-thermosphere coupling at the equator; thermospheric superrotation, which may be caused either by ion drag or by tidal breaking, is examined in detail by observations covering a wide altitude range from the mesosphere through the thermosphere

Possible Evidence of Gravity Wave Coupling into the Mid-latitude F Region Ionosphere During the SEEK Campaign

On five of eight observation nights during the 1996 SEEK (Sporadic E Experiment over Kyushu) campaign, Japan, unusual “wave‐like” structures were imaged in the 630 nm thermospheric nightglow emission. Four of these events were observed to travel towards the southwest, providing new evidence in support of recent theories describing the coupling of medium‐scale gravity waves into the mid‐latitude F region ionosphere. Available ionosonde data and the visual characteristics of the wave structures indicate no association with the occurrence of mid‐latitude spread F or F region upwellings. Instead, the data support the novel concept of feedback from the ionosphere into the gravity wave, via the Perkins instability, to enhance its visibility

Glass transition and alpha-relaxation dynamics of thin films of labeled polystyrene

The glass transition temperature and relaxation dynamics of the segmental motions of thin films of polystyrene labeled with a dye, 4-[N-ethyl-N-(hydroxyethyl)]amino-4-nitraozobenzene (Disperse Red 1, DR1) are investigated using dielectric measurements. The dielectric relaxation strength of the DR1-labeled polystyrene is approximately 65 times larger than that of the unlabeled polystyrene above the glass transition, while there is almost no difference between them below the glass transition. The glass transition temperature of the DR1-labeled polystyrene can be determined as a crossover temperature at which the temperature coefficient of the electric capacitance changes from the value of the glassy state to that of the liquid state. The glass transition temperature of the DR1-labeled polystyrene decreases with decreasing film thickness in a reasonably similar manner to that of the unlabeled polystyrene thin films. The dielectric relaxation spectrum of the DR1-labeled polystyrene is also investigated. As thickness decreases, the $\alpha$-relaxation time becomes smaller and the distribution of the $\alpha$-relaxation times becomes broader. These results show that thin films of DR1-labeled polystyrene are a suitable system for investigating confinement effects of the glass transition dynamics using dielectric relaxation spectroscopy.Comment: 10 pages, 11 figures, 2 Table