Automated Mie-scattering lidars
have been operated since March 2001 at Beijing,
Nagasaki and Tsukuba to reveal the time and height distribution
of Asian dust and its optical properties.
The lidars detect backscattering light from clouds and aerosols
at 532nm in both parallel and perpendicular polarization channels.
They continuously measure profiles every 15 minutes
regardless of weather conditions.
At first we eliminated clouds using vertical profiles of intensity,
then Asian dust was identified by the depolarization ratio.
In Beijing, close to the source region of the dust,
Asian dust events occurred 15 times in March April, and May 2001.
Each event continued for several days. The aerosol depolarization
ratio (ADR) frequently reached up to 40 %.
In Nagasaki, located western part of the Japan, Asian dust was
confirmed near the surface with a delay of a few days from
events in Beijing.
However, in Tsukuba, there were few surface dust events
and passing dust in the free troposphere was confirmed.
The ADR in Tsukuba were lower than those in other two observatories.
Internal mixing of mineral dust and anthropogenic aeorols,
and changing size distribution
may contribute the differences of ADR among observatories.
In Beijing, ground sampling of mineral dust was simultaneously
Mass concentration by the sampler at the surface and
extinction coefficient near the surface derived from lidar observation
were compared to estimate the conversion factor from extinction
coefficient to mass concentration.
Utilizing this factor we estimated the vertical distribution of the mass
of Asian dust in Beijing.