Tsukasa Kitahara

Observations of mesospheric sporadic sodium layers with the MU radar and sodium lidars

The dynamical structure of the atmosphere around the sporadic sodium layer at mid-latitude (∼35°N) below 100 km was studied by simultaneous observation with the MU radar at Shigaraki (34.9°N, 136.1°E), and two Na lidars at Shigaraki and in Hachioji (35.6°N, 139.4°E). In the lidar data, fifteen Nas (sporadic sodium layer) events were detected. Wind shear, temperature, and stability indices, at around the time and height of Nas were observed with the MU radar. Strong total wind shear correlated well with Nas, especially when sporadic Es did not accompany. However, no other clear correlations, such as correlations with temperature etc., were found. The result is similar to the report of the lidar observations in Hawaii during the ALOHA-93 campaign (Qian et al., 1998), and suggests a similar generation mechanism between 20°N and 35°N.

Sodium temperature lidar based on injection seeded Nd:YAG pulse lasers using a sum-frequency generation technique

We report on a sodium (Na) temperature lidar based on two injection seeded Nd:YAG pulse lasers using single-pass sum-frequency generation. The laser power at 589 nm is 400 mW (40 mJ per pulse at a repetition rate of 10 Hz) and the pulse width is 22 nsec FWHM. The narrowband laser tuned to the Doppler broadened Na D2 spectrum enables us to measure the temperature of the mesopause region (80-115 km). This solid-state transportable system demonstrated high performance and capability at Syowa Station in Antarctica for 3 years and at Uji in Japan for an additional year without any major operational troubles.

Simultaneous measurements of dynamical structure in the mesopause region with lidars and MU radar

In order to clarify the horizontal structure of the wavelike oscillation frequently observed in the night time sodium density profile with a small Gaussian half-width in the middle of the night and a broad distribution at dusk, simultaneous observations with two lidars at Shigaraki (34.9°N, 136.1°E) and Hachioji (35.6°N, 139.4°E) and the MU radar at Shigaraki has been carried out. In the campaign of 35 nights, simultaneous observation was successful in four nights. On December 27–28, 1995, a large scale wave motion was observed by two lidars and the MU radar with meteor observation mode. Phase velocities were almost the same at the two sites and there were only slight differences in phase between the two sites. The wave motion was inconsistent with the component of the tidal wave and similar with the results of hodograph analyses. It is possible that the wave observed by lidars on December 27–28, 1995 was a gravity wave. The results of analyses suggest the possibility of gravity waves which were observed at fixed local time.

Sum frequency generation of sodium D2 resonance line for the lidar application of mesopause temperature measurements

Sum frequency generation of sodium D2 resonance radiation (589 nm) based on injection seeded Nd:YAG lasers was applied to a sodium lidar transmitter for temperature measurements of the mesopause region (80-105km). The output energy was 40 mJ / pulse at a repetition rate of 10 Hz and a temporal width of 28 nsec. The laser wavelength at 589 nm (~0.04 pm FWHM) was finely tuned with an accuracy of 0.1pm by seeders. The lidar installed at Syowa station (69°S, 39°E), Antarctica, measured temperature profiles between March and September during 2000 and 2001. Monthly averaged temperature profiles in the mesopause region in wintertime (June, July and August) are nearly 20 K lower than those in the northern hemisphere sites. The measured winter mesopause altitudes (~99 km) are in good agreement with those measured in the northern winter hemisphere. The mesopause temperatures (~175 K) in winter months however are about 20 K lower than those observed from a northern hemisphere conjugate site, Andoya (69°N). The lower winter mesopause temperatures measured at Syowa station, which are consistent with southern hemisphere mesopause temperatures measured by a shipborne lidar, suggest the existence of a hemispheric difference. Possible causes for this difference are discussed.