Physics
Scientific paper
May 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agusmsa34a..04e&link_type=abstract
American Geophysical Union, Spring Meeting 2009, abstract #SA34A-04
Physics
0342 Middle Atmosphere: Energy Deposition (3334), 3332 Mesospheric Dynamics, 3334 Middle Atmosphere Dynamics (0341, 0342), 3384 Acoustic-Gravity Waves, 3389 Tides And Planetary Waves
Scientific paper
Recent observation and model studies show not only latitudinal variation but also large longitudinal variations of density, temperature, and dynamics in the middle atmosphere and ionosphere. Long-term observations by sodium temperature lidar at the mid-latitude were mainly in the US longitude [e.g., She et al., 2000; Chu et al., 2005]. In the Western Pacific longitude, occurrence rate of sporadic sodium (Nas) layer were reported by statistical analysis of sodium density profiles [Nagasawa and Abo, 1995; Gong et al., 2002]. However, vertical distributions of temperature in the mesosphere and lower-thermosphere (MLT) region were not measured well. We have observed the temperature and sodium density profiles since August, 2007 at Uji (34.9oN, 135.8oE) located ˜25 km west from Shigaraki Middle and Upper Atmosphere (MU) observatory by a sodium temperature lidar, which was developed by Shinshu University and National Institute for Polar Research (NIPR) and was operated at Syowa in Antarctica, in order to reveal these variations in the Western Pacific longitude. These profiles for 147 nights (more than 1300 hours) have been obtained. Comparisons of seasonal variations of these profiles between Japan and the US longitudes showed some similarities and differences. Sodium density in Japan showed similar seasonal variation to that in the US, except for an enhancement (90-100 km) in June-July caused by Nas in Japan. Temperatures below 98 km showed semi-annual variation in both longitudes, but months of temperature maximum were slightly different. Because the long-term observation periods are different between Japan and the US, the differences between two longitudes include longitudinal variation and also year-to-year variation. An estimate for the vertical motion associated with long-period waves such as the tides can be determined from the temperature perturbations assuming long-period wave motions are adiabatic. A remarkable increase of sodium column density of 70-120 km and OI (557.7 nm) emission were observed on December 9, 2007, simultaneously. The sodium lidar temperature profiles showed long-period wave with a downward phase propagation, and vertical displacement of atomic oxygen, oxygen, and nitrogen estimated from the temperature profiles could explain the OI enhancement. The long-period wave was probably a part of tides, which had unusual large amplitude shown by TIMED/SABER temperature measurements. Further studies of detailed comparison with the Na lidar results in the US, as well as investigation of atmospheric stability characteristics and its longitudinal dependencies are being carried out under collaboration between Japan, the US and China.
Ejiri Mitsumu K.
Kawahara Takuya D.
Nakamura Takashi
Oberheide J. D.
Shepherd Gordon G.
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