No abstract

In this paper we present the detailed results of a series of experiments designed to study the coherent backscatter of 50‐MHz radar waves from the mid‐latitude F region. Data were obtained with the active phased‐array MU radar in Japan and include some auxiliary E region coherent echoes as well. As in other turbulent ionospheric phenomena the intense nonthermal scatter comes from irregularities oriented parallel to B. The strongest echoes correspond to irregularities at least 20 dB stronger than thermal backscatter at the same frequency from typical F region densities at the same range. Simultaneous observations with ionosondes show that these echoes occur during strong mid‐latitude spread F. As defined by ionosondes, the latter phenomenon is certainly much more widespread than the turbulent upwelling events described here, but we believe that in some sense these correspond to the most violent mid‐latitude spread F. The strongest echoes occur in large patches which display away Doppler shifts corresponding to irregularity motion upward and northward from the radar. At the edges of these patches there is often a brief period of toward Doppler before the echoing region ceases. On rare occasions comparable patches of strong away and toward Doppler are detected, although in such cases the Doppler width of the toward echoes is much narrower than that of the away echoes. The away patches often are characterized by mean velocities well over 250 m/s and Doppler widths (full width at half maximum) of 50 m/s. The multiple beam capability at MU allowed us to track the patches in the zonal direction on two days. The patches moved east to west in both cases at velocities of 125 m/s and 185 m/s, respectively. There is a distinct tendency for the bottom contour of the scattering region to be modulated at the same period as the patch occurrence frequency as well as at higher frequencies. This higher‐frequency component may correspond to substructures in the large patches and to the E region coherent scatter patches which were detected simultaneously in several multiple beam experiments. In the companion paper (Kelley and Fukao, this issue), we explore a number of possible explanations for this phenomenon in more detail.

A new strategy based on polymerization-induced phase separation (PIPS) techniques was proposed for fabricating palladium nanoparticles (PdNPs) captured in a microporous network polymer. Pd(OAc)(2) was premixed with a monomer having a poly(amidoamine)-based dendrimer ligand, and subsequently this was thermally polymerized with an excess amount of ethylene glycol dimethacrylate under PIPS conditions. In this system, the formation of PdNPs occurred concurrently with the polymer synthesis in a one-pot process, even with no additional reducing reagent. The resultant microporous polymer was found to have a mesoporosity; the nitrogen sorption analysis gave a specific-surface area of 511 m(2) g(-1), an average pore diameter of 9.9 nm, and a total pore volume of 1.01 mL g(-1). The TEM images of the polymer revealed that the created PdNPs were very small with a diameter of mainly ca. 2.0 nm; the high-resolution images were lattice-resolvable, showing the crystalline nature of the PdNPs (Pd(111) facets). Catalytic performances of the PdNP-containing microporous polymers were investigated for a heterogeneous Suzuki-Miyaura reaction of 4'-bromoacetophenone and phenylboronic acid in water. In the presence of 10(-2) molar equiv of the polymer, the reaction efficiently proceeded at 80 degrees C and gave the desired product, 4-acetylbiphenyl, in >90% yield after 2 h. On the basis of the ICP-AES analysis, the Pd content released into the solution phase was estimated to be only 0.27% of the initial charge. Thereby, this polymer was successfully recovered by simple filtration and reused with only a minimal loss of activity (yield >90% even at the eighth run). When the catalytic reaction was examined with a low amount of the polymer catalyst, the turnover number (TON) reached 8.5 x 10(4) while maintaining a good yield. Finally, the dendrimer template effect of the polymer catalyst was discussed by referring to the catalytic performances of a control polymer prepared with nonintegrated ligand monomers.

This paper describes the characteristics of the mean winds, equatorial waves with periods ranging from 4 to 20 days, and diurnal tides determined by analyzing the profiles of wind velocity, temperature, and humidity obtained every 5–7 hours in the height range up to about 35 km with a height resolution of 150 m during an observation campaign conducted February 27 to March 22, 1990, in East Java, Indonesia. The structures of the mean winds in the troposphere and lower stratosphere seemed to be affected by the Australian monsoon and the quasi‐biennial oscillation, respectively. Frequency spectra indicated that the equatorial waves as well as the diurnal tides were dominant below about 25 km, while gravity waves with periods shorter than 4 days became more significant above 25 km. A 7‐day oscillation showing an antiphase relation between the eastward and northward components and exhibiting large amplitudes was observed in the lower troposphere. The time‐height variations of the activity of this 7‐day oscillation were clearly correlated with a region of high relative humidity. Perturbations in the zonal wind and temperature with wave periods varying from 15 to 17 days were also enhanced in the troposphere, while Kelvin waves with periods of about 7 and 20 days were detected in the lower stratosphere, and activity near the tropopause was conspicuously enhanced. We found that the 20‐day Kelvin wave greatly modified the structure of the tropopause, such as the minimum temperature, the tropopause height, and the values of the Brunt‐Väisälä frequency squared N2, which further suggests the effects of Kelvin waves on the transportation of tropospheric water vapor into the stratosphere and on the downward mixing of stratospheric minor constituents into the troposphere. The observed profiles of the diurnal oscillation were compared with those of a numerical model assuming only migrating tides, which reasonably agreed above about 25 km. Below 25 km, however, the observed amplitudes were 1–1.5 m/s, exceeding those of the model about 10 times. Moreover, the phase profiles involved fluctuations with small vertical scales, suggesting interference by many nonmigrating tides with short vertical wavelengths.