May 10, 2010 / Vol. 8, No. 5 / CHINESE OPTICS LETTERS 439
Atomosphere boundary layer height determination and
observation from ceilometer measurements over Hefei
during the total solar on July 22, 2009 eclipse
Junfeng He (ÛÛÛddd¸¸¸)
1,2∗
, Wenqing Liu (444©©©)
1
, Yunjun Zhang (ÜÜÜ)
1
, Ruifeng Kan (VVVaaa¸¸¸)
1
,
Zhenyi Chen (ûûû)
1
, and Jun Ruan (___ ddd)
1
1
Anhui Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Hefei 230031, China
2
Artillery Academy, Hefei 230031, China
∗
E-mail: hejunfeng@aiofm.ac.cn
Received December 4, 2009
Using an improved inflexion point method (IIPM), we investigate atmosphere boundary layer (ABL) height
evolution over Hefei during the total solar eclipse on July 22, 2009. A lidar ceilometer is used in ground-
based observations. Estimations of ABL heights before, during, and after the solar eclipse are analyzed
using the IIPM. Results indicate that the IIPM, which is less sensitive to background noise, is more suitable
in detecting ABL height and temporal evolution. Data demonstrate that the total solar eclipse resultes in
a decrease in ABL height, indicating a suppression of turbulence activity, similar to that observed during
the sunset hours. Changes in ABL height are associated with a slow change in temperature, indicating a
significant weakening of penetrative convection and a time lag between ABL response and the reduction
in solar radiation.
OCIS codes: 010.0010, 140.0140, 280.0280, 290.0290.
doi: 10.3788/COL20100805.0439.
On July 22, 2009, a solar eclipse covering the Yangzi
River Zone, China, took place. The total eclipse lasted
for more than 6 min, the longest total eclipse to be ob-
served in China from 1814 to 2309. Hefei is located in
the central part of China (latitude 32˚, longitude 117˚),
right within the total eclipse zone. A solar eclipse can
simply be considered as a fast sunset and sunrise. As
an astronomical event, it provides a unique opportunity
to study various atmospheric phenomena, especially as
incoming solar radiation is sharply turned off and on
during such events. A solar eclipse provides natural
experimental conditions in studying the atmosphere’s re-
sponses to solar radiation changes because of the sudden
reduction in solar radiation. The atmosphere boundary
layer (ABL) is part of the convective layer, which is di-
rectly affected by the Earth’s surface. It is where the
transport of mass, energy, and momentum towards other
parts of the atmosphere takes place through a turbulence
process. A change in radiative heating or cooling is first
felt in the ABL before it is felt by the free atmosphere.
The ABL height has a strong impact on local and re-
gional weather, as well as on air quality. Regarding air
quality, ABL height determines the volume available for
pollutant dispersion, including the resulting concentra-
tions. It is therefore one of the fundamental parameters
in many dispersion mo dels. Continuous observations of
the ABL top with high vertical and temporal resolutions
are thus desirable to support weather and air quality
predictions.
ABL responds to surface forcing by frictional drag,
evaporation and transpiration, and sensible heat transfer
with a timescale of an hour or less
[1]
. The ABL has
a clearly outlined structure that differs from daytime
to nighttime. During a normal day, a convective at-
mospheric boundary layer (CABL) develops, reaching a
quasi-steady state in the afternoon. The CABL has a
mixed layer from the ground up to the interfacial layer
with the free atmosphere, where strong thermal inver-
sion transpires. The ABL afternoon/evening transition
is marked before sunset by the development of a surface
inversion related to surface cooling. The CABL, called
the residual layer after sunset, becomes neutral above
that stable layer. After sunrise, the stable layer is de-
stroyed and a new mixing layer (ML) develops. During
a solar eclipse, the two transition situations are repro-
duced, with much shorter time scales than those in the
normal diurnal cycle, providing an excellent chance to
investigate the mechanisms that drive the evolution of
ABL.
Research on ABL evolution during a normal day has
been extensively conducted using various complex in-
struments. There have been several important findings
related to ABL evolution during a solar eclipse. Antonia
et al. found that the surface layer turbulence follows a
continuum of equilibrium states in resp onse to stability
changes brought about by changes in surface heat flux
during the solar eclipse on October 23, 1976, over Delin-
quin, Australia. With a lidar, Amiridis et al. studied
the dynamics of ABL during the solar eclipse on Au-
gust 11, 1999, over Bulgaria and found that the solar
eclipse affected the atmosphere’s meteorological param-
eters, ozone concentration, and mixing layer height
[2]
.
The aim of this work is to study the height response
of ABL to the July 2009 solar eclipse by observing the
range-squared-corrected backscatter signal (RSCS) of
the atmosphere using a lidar ceilometer. An improved
inflexion point method (IIPM) is proposed to analyze
backscatter data and to identify ABL height.
Using the modern ground-based remote sensing tech-
niques to monitor diurnal variations of atmospheric lay-
1671-7694/2010/050439-04
c
° 2010 Chinese Optics Letters