Simultaneous observations of the middle atmosphere and lower thermosphere by Na Wind/Temperature (W/T) and Rayleigh/Raman lidar and other ground‐based measurements were conducted the night of October 21, during the ALOHA‐93 campaign. Rayleigh/Raman lidar measurements provide density from 25 to 90 km and temperature from 25 to 85 km. From the same location, Na W/T lidar measurements were also obtained between ∼83 and 103 km. The combined data provides continuous temperature from 25 to 103 km. Strong perturbations which may be associated with the diurnal tide are observed in the temperature and wind profiles.

Oxidized metal clusters (NaxO and KxO for 2≤x≤4) were formed in a gas phase reaction between metal clusters and an oxidizing gas using a double expansion technique. Their appearance potentials were measured using a molecular beam-photoionization mass spectrometer system. These first photoionization data for oxidized clusters provide information on trends of ionization potentials as a function of the degree of aggregation. The ionization potentials do not differ greatly from the analogous metallic species, but in the case of the sodium tetramer the value does fall below that of the bare metal cluster. This finding is in accord with what has been observed as an influence of impurities on the work function of the bulk sodium. The results are also of interest concerning questions of octet rule violations and hypervalency.

Ammonia clusters, produced via supersonic expansion, are subjected to multiphoton ionization using a tunable pulsed laser. The products of ionization and subsequent dissociation processes are investigated using a time-of-flight mass spectrometer equipped with a reflectron (reflecting electric field). Cluster ions containing more than 65 ammonia molecules were formed via internal ion molecule reactions taking place within the initially ionized aggregate. The proton transfer reaction which ensues leads to substantial excess internal energy and subsequent cluster decomposition. Dissociation due to both collisional and unimolecular processes was identified in the field-free region. Studies of the dynamics of dissociation were made for species up to the protonated 16-mer; the loss of up to at least five monomer units following cluster ion formation was observed. Results of an investigation of the influence of laser fluence and the energy of the ionizing photons are also presented.

Abstract. Observations made during the Airborne Lidar and Observations of HawaiianAirglow (ALOHA-93) campaign during October 1993 revealed the presence of persistent large perturbations of the temperature and density in the 80 to 100 km mesopause region. These perturbations, seen both by passive airglow and active lidar techniques, were identified as due to the presence of diurnal and semidiurnal tides. These results were compared with the predictions of the thermosphere/ionosphere/mesosphere electrodynamics general circulation model (TIME-GCM). This model was recently tuned to agree with the observations from the Upper Atmosphere Research Satellite (UARS) with respect to mesosphere/lower thermosphere winds (60-200 km). It is found that although the TIME-GCM agrees with UARS winds, it underpredicts the diurnal, and possibly the semidiurnal, tidal temperature perturbations seen during ALOHA-93. Since the TIME-GCM only includes migrating tides, this comparison suggests that nonmigrating tides may have had a significant amplitude during the ALOHA-93 campaign period. UARS observations of the major nonmigrating diurnal mode were made just before and after the ALOHA-93 period. It is found that the zonally symmetric nonmigrating tide can account for the discrepancy between the ALOHA-93 results and the TIME-GCM predictions only for a few periods and only at an altitude around 88 km. If the zonally symmetric nonmigrating tide is to account for the discrepancies between the model and the data, than it has to be highly variable.

Ground‐based observations of atmospheric density profiles to 92 km were obtained for four successive seasons between summer 1989 and spring 1990. These results were obtained with a powerful Rayleigh lidar facility located at Wright Patterson Air Force Base (Dayton, Ohio). This instrument combined a 14‐W XeF laser transmitter with a 2.54‐m receiver mirror to observe returns from altitudes between 40 and 95 km. Analysis of the scale height dependence of the density profiles produced temperatures with a measurement error of about 5 K (∼2.5%) at 90 km when the lidar data was averaged for 20 min. and smoothed in height over 2.7 km. Examination of these profiles for the total of 18 nights showed that there often existed in the mesophere a layer of enhanced temperatures when compared with the U.S. standard profile. The layer centroid height was about 85 km for summer and 70 to 75 km for winter. Data obtained for the equinoctial periods showed the amplitude of these layers to be weak. The winter temperature profiles showed evidence forlong‐period waves passing through the region of the thermal anomaly while the equinox profiles revealed more sporadic wave activity with shorter vertical wavelengths. Both the winter and summer temperature data displayed regions where the observed lapse rate approached the adiabatic lapse rate. In the summer the wave activity near the inversion layer was weak.