AMTAtmospheric Measurement TechniquesAMTAtmos. Meas. Tech.1867-8548Copernicus GmbHGöttingen, Germany10.5194/amt-8-2901-2015Diurnal aerosol variations do affect daily averaged radiative
forcing under heavy aerosol loading observed in Hefei, ChinaWangZ.zzwang@aiofm.ac.cnhttps://orcid.org/0000-0002-3648-6124LiuD.dliu@aiofm.ac.cnWangY.WangZ.zzwang@aiofm.ac.cnShiG.Key Laboratory of Atmospheric Composition and Optical Radiation,
Anhui Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Hefei, ChinaUniversity of Science and Technology of China, Hefei, ChinaDepartment of Atmospheric Science, University of Wyoming, Laramie, Wyoming, USAInstitute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, ChinaZ. Wang (zzwang@aiofm.ac.cn) and D. Liu (dliu@aiofm.ac.cn)20July2015872901290727January201523February201501July201502July2015This work is licensed under a Creative Commons Attribution 3.0 Unported License. To view a copy of this license, visit http://creativecommons.org/licenses/by/3.0/This article is available from https://amt.copernicus.org/articles/8/2901/2015/amt-8-2901-2015.htmlThe full text article is available as a PDF file from https://amt.copernicus.org/articles/8/2901/2015/amt-8-2901-2015.pdf
A strong diurnal variation of aerosol has been observed in many heavily polluted
regions in China. This variation could affect the direct aerosol radiative
forcing (DARF) evaluation if the daily averaged value is used as normal
rather than the time-resolved values. To quantify the effect of using the
daily averaged DARF, 196 days of high temporal resolution ground-based data
collected in SKYNET Hefei site during the period from 2007 to 2013 is used
to perform an assessment. We demonstrate that strong diurnal changes of
heavy aerosol loading have an impact on the 24-h averaged DARF when daily
averaged optical properties are used to retrieve this quantity. The DARF
errors varying from -7.6 to 15.6 W m-2 absolutely and from
0.1 to 28.5 % relatively were found between the calculations using
daily average aerosol properties, and those using time-resolved aerosol
observations. These errors increase with increasing daily aerosol optical
depth (AOD) and decreasing daily single-scattering albedo (SSA), indicating
that the high temporal resolution DARF data set should be used in the model
instead of the normal daily-averaged one, especially under heavy aerosol
loading conditions for regional campaign studies. We also found that statistical
errors (0.3 W m-2 absolutely and 11.8 % relatively) will be less,
which means that the effect of using the daily averaged DARF can be weakened
by using a long-term observational data set.
Introduction
The direct aerosol radiative effect (DARF) is defined as the change in
radiative flux caused by the combined scattering and absorption of radiation
by a variety of aerosols. The DARF can be well estimated through the
well-developed model and inputs from the observations regionally, such as
daily estimates of aerosol optical properties (AOP), i.e., aerosol optical
depth (AOD), single-scattering albedo (SSA), and asymmetry factor (ASY).
These AOP could be obtained from ground-based observations, such as the
Aerosol Robotic Network (AERONET) (Holben et al., 1998), Sky Radiometer
Network (SKYNET) (Nakajima et al., 2003), China Aerosol Remote Sensing
Network (CARSNET) (Che et al., 2009) . In the assessment report of IPCC (2013),
the scientific understanding of DARF has been designated as
High. However, DARF can reach tens of W m-2 locally. Estimates of
DARF regionally still contain significant uncertainties due to complex
aerosol sources, strong diurnal variability, and poorly known morphology.
Strong diurnal variations of AOP have been observed in many regions,
especially in some heavily polluted regions, such as in Xianghe (Li et al.,
2007), Taihu (Xia et al., 2007), Beijing (Che et al., 2014), and Hefei (Wang
et al., 2014) China. The diurnal variations of AOP could dramatically affect
aerosol radiative forcing calculations (Christopher et al., 2003) and result
in significant biases especially in regional ADRF estimations (Arola et al.,
2013). However, the uneven high temporal sampling of aerosol properties from
the surface may be unable to faithfully recover the diurnal changes of aerosol
optical properties due to cloudy cover or invalid retrievals. Therefore, it
has been commonly assumed that the aerosol optical properties are constant
and daily averaged values are normally used to calculate 24-h averaged DARF
on regional scales. The influence should be investigated in detail
especially for some polluted regions with heavy aerosol loading and strong
diurnal variations of AOP.
Data and methods
To investigate this problem, the aerosol data observed at the SKYNET Hefei
super site (Nakajima et al., 2007; Zhou et al., 2002) was used, where a
sky-radiometer, a microwave radiometer, and a set of broadband radiometers
have been operated continuously for aerosol-radiation measurements since the end
of 1997. The site is influenced by local urban or rural aerosols depending
on wind direction with high aerosol loading throughout the year. The annual
mean 500 nm AOD at this site is as high as 0.84 (Wang et al., 2014).
Therefore, a strong diurnal variability of AOP is expected at the site. The
Prede POM-02 sky-radiometer measures the direct and diffuse solar radiations
every 10 min in the daytime, which is an advantage with high temporal
resolution measurement to cover all variations of AOP throughout day. This
sky-radiometer has seven aerosol channels with wavelengths of 340, 380, 400, 500,
675, 870, and 1020 nm, which are used to retrieve
AOP with the SKYRAD retrieval package (Nakajima et al., 1996). This
sky-radiometer can be calibrated on-site to derive the calibration constant
(F0) using the improved Langley method (Campanelli et al., 2004). After cloud
screening using the algorithm of Khatri et al. (2009), the spectral values
of AOD (τ), SSA (ω) and ASY (g) are determined during the period from 2007 to 2013. There are
196 completely cloud-free days with high temporal measurements and
retrievals, comprising the data set used in this study. The derived aerosol
properties (τ, ω and g) are used as key input parameters to calculate surface
solar radiations based on the Santa Barbara Discrete-ordinate Atmospheric
Radiative Transfer (SBDART) model (Ricchiazzi et al., 1998), which was
verified with surface broadband spectrum irradiance observations (Halthore
et al., 2005). The complementary parameters (columnar water vapor content,
total ozone amount, and spectral surface albedo) used to run the model are
retrieved from the surface microwave radiometer (Model WVR-1100,
Radiometrics Corporation, USA) (Westwater et al., 1978; Ulaby et al., 1986),
the Ozone Monitoring Instrument (OMI) data sets (McPeters et al., 2008), and
the Moderate Resolution Imaging Spectroradiometer (MODIS) products (Schaaf
et al., 2011), respectively.
Daily variations of retrieved 500 nm AOD (red), SSA
(green) and ASY (blue) on 14 April 2013. This represents a typical
light polluted case (mean AOD of 0.57) with moderate diurnal changes of AOP.
(t]
To estimate the sensitivity of 24-h averaged DARF to the diurnal changes of
aerosol optical properties, we perform the DARF (named, F) at the surface
(named, SFC) calculations with different conditions on the daily AOP (τ,
ω and g) variation in two ways: (1) diurnally varying AOP
according to entire time-dependent observations, AOP = actual changes of
AOP; (2) no diurnally AOP variation but measurement-based, AOP = corresponding
daily averaged AOP. Then we use these two sets of the AOP (the
original high temporal resolution data set, which covers the complete
diurnal variation, plus the additional synthetic set) and the other
complementary parameters as input for the SBDART model to calculate the
diurnal changes of the DARF (named, <Forg> related to time-resolved data set and
<Fave> related to averaged data set). These DARF values at the surface
are given in half hour intervals, from which we calculate the
corresponding 24-h averaged DARF (<F>). Thus, we obtain two sets of values of
<F>, which represent radiative forcings obtained from the original and daily
averaged AOP. Furthermore, the absolute and relative errors of 24-h averaged
DARF will be found as <δF> (i.e., <Fave>-<Forg>) and absδF<Forg>, respectively. These errors are used to
assess quantitatively the effect of aerosol daily averaged radiative forcing
due to diurnal variation.
Results and discussion
We applied our method to two typical kinds of cloud free cases observed at
the SKYNET Hefei site on 14 April 2013 (CASE-I) and 12 February 2008 (CASE-II). The first case is a lightly polluted day, when
diurnal changes of aerosol loading are moderate ranging from -12 to
19 % on AOD as shown in Fig. 1. The daily averaged AOD value of CASE-I
is 0.57 with a maximum 0.68 and a minimum 0.50. On the contrary, the SSA and
ASY are not changing so much with 0.90 (varying from 0.88 to 0.96) and 0.69
(varying from 0.67 to 0.71) on average, respectively. Thus, we will strongly
consider AOD variability in the following discussions.
The corresponding instantaneous DARF values using the
original (red) and daily averaged (black) AOP in Fig. 1, the 24-h average
F values with the absolute (blue) and relative biases (magenta) are
included as well in the inset.
Comparisons between the SBDART simulated and the measured
fluxes of downward shortwave radiations at the surface in Hefei site on
14 April 2013.
Using the original and daily averaged AOP for CASE-I as input parameter, the
corresponding instantaneous DARF values are calculated with large
differences as indicated in Fig. 2. For example, large overestimation
(23 W m-2 in absolute value and 21 % in relative value) at 10:00 and large
underestimation (15 W m-2 in absolute value and 20 % in relative value) at
16:00 of instantaneous DARF (Fave versus Forg) are produced by AOP
variability. It is noted that this overestimation and/or underestimation of
instantaneous DARF may be compensated partially by each other when being used for
estimating 24-h averaged F. The 24-h average F values are -38.1 W m-2
(<Fave>) and -42.1 W m-2 (<Forg>) with the absolute
(4.0 W m-2) and relative (9.5 %) biases
are shown as well in the inset of Fig. 2. As a result of CASE-I, the
impact of the daily averaged aerosol properties on the 24-h average DARF may
not be negligible after integration of instantaneous DARF values over all
daytime hours.
Note that we did not have AOP measurements to cover low solar zenith angles
for calculation of Forg, where real measured flux (with aerosol) and
calculated flux (without aerosol) are used to fill up data before the
sunrise and after the sunset. Figure 3 has performed excellent shortwave
radiative closure experiment using the accurate input parameters from SKYNET
AOP measurements and high precision surface radiation fluxes by Kipp &
Zonen CM21.
Another case is chosen during a highly polluted day, when diurnal changes of
aerosol loading are large ranging from -18 to 32 % on AOD as shown in
Fig. 4. The daily averaged AOD value of CASE-II is 1.08, which is almost
two times that of CASE-I with a maximum of 1.43 and a minimum of 0.89. Meanwhile, the SSA and ASY are 0.96 (varying from 0.94 to 0.97) and
0.69 (varying from 0.68 to 0.72) on average, respectively, with a slight
changing as CASE-I. So, we will also consider AOD variability. Figure 5
shows the corresponding instantaneous DARF values using the original and
daily averaged AOP in Fig. 4, which also produces large biases. The
largest overestimation part of instantaneous DARF (Fave versus
Forg) is 24 W m-2 in absolute value and 17 % in relative value and the
largest underestimation counterpart is 16 W m-2 in absolute value and 15 %
in relative value due to AOD variability. But the 24-h average F values are
-41.9 W m-2 (<Fave>) and -49.5 W m-2
(<Forg>) with the absolute (7.5 W m-2) and relative (15.2 %)
biases, which are larger than those in CASE-I.
The same as Fig. 1 but for a day with large diurnal
changes of aerosol loading under highly polluted (AOD equals to 1.08 in
average) weather conditions on 12 February 2008.
The same as Fig. 2 but using the AOP in Fig. 4.
The same as Fig. 3 but in 12 February 2008.
Figure 6 shows a comparison between the SBDART simulated and the measured
fluxes of downward shortwave radiations at the surface in Hefei site on
12 February 2008, which indicates a good agreement with a high
correlation coefficient 0.9945. So, we can use measured data to fill up
Forg values during the missing periods, which are also examined in
Fig. 3.
Thus, an important result related to aerosol loading issue can be drawn from
the two cases. The strong diurnal changes of heavy aerosol loading in SKYNET
Hefei site have a considerable impact on the 24-h averaged F value if daily
averaged AOP is used to retrieve this quantity.
Let us consider the impact of daily averaged AOP on F value for all selected
196 days, where high temporal resolution AOP is obtained throughout the day.
Figure 7 shows the frequency distributions of daily mean AOD, SSA, and ASY
at 500 nm, the corresponding absolute and relative biases for 24-h average
F calculation in SKYNET Hefei site from 2007 to 2013. From these 196 cloud-free days, the aerosol loading covers clean clear day and heavily polluted day
with daily averaged AOD ranging from 0.14 to 1.88. Large day-to-day
variability of AOD is also found from Fig. 7a with an averaged AOD
0.63±0.29 except for the large diurnal difference discussed before.
In Fig. 7b and 7c, the daily averaged SSA and ASY are also shown with
light variations ranging from 0.85 to 0.99 and from 0.61 to 0.73,
respectively. As a sequence, the absolute and relative biases for 24-h
average F calculation are 0.3±4.2 W m-2 (varying from -7.6 to
15.6 W m-2) and 11.8 % ± 6.6 % (varying from 0.1 to
28.5 %), respectively. That means the impact is significant and cannot be
neglected for each day considered here. However, this kind of impact can be
weakened through long-term high temporal resolution measurements. These
findings are different from the others in some regions, where the observed
conditions without heavy aerosol loading (AOD less than 0.4) are prevalent
from other studies (Kassianov et al., 2013).
The frequency distributions of τave,
ωave, gave,
δF, and 100⋅absδFForg selected in SKYNET Hefei site from 2007 to 2013.
Correlations between aerosol forcing at the surface and
AOD at 500 nm (Fave: black; Forg: red;
δF: blue) with linear fitting equations.
The same as the Fig. 8 but for SSA at 500 nm.
The same as the Fig. 8 but for ASY at 500 nm.
The relationship between DARF at SFC and AOD is examined and high
correlation (0.82 and 0.71) has been found between AOD and 24-h average
Fave and Forg, respectively. At the same time, there is an
increasing trend of absolute biases (δF) for 24-h average F calculation with
increasing daily mean AOD (τ) at 500 nm, and a large scattering in data points is related to high
AOD as well (Fig. 8). Then Figs. 9 and 10 give the relationship
between DARF at SFC and the other two parameters (i.e., SSA and ASY). Only
to find that there is also an increase trend of δF for 24-h average F
calculation with decreasing daily mean SSA (ω) at
500 nm, which means the more absorption of aerosol, the more contribution to
the absolute biases. The phenomena in Figs. 8–10 indicate as follows: (1) the
AOD with strong diurnal variation is more contributed to the
corresponding 24-h averaged F than SSA and ASY with weak temporal changes;
(2) the well-established fact that the instantaneous DARF at SFC is linearly
proportional to AOD (McComiskey et al., 2008) is also related to the highly
polluted area (Li et al., 2010); (3) the extremely high biases for 24-h
averaged F are produced by a strong diurnal variation of AOD, variation of
aerosol absorption property and/or high aerosol loading. Because the
observed conditions mentioned in this study are prevalent in many
climatologically important regions with frequent heavy aerosol loadings,
such as Xianghe (Li et al., 2007), Taihu (Xia et al., 2007), and Beijing
(Che et al., 2014), the daily average radiative forcing calculation requires
not only daily averaged optical properties, but also diurnal changes. Thus,
in order to obtain accurate radiative transfer calculations in a high pollution
region, the observation-based long-term high temporal aerosol data must be
considered.
Summary
We assess the impact of the strong diurnal changes of aerosol on the 24-h
average DARF at the surface using ground-based high temporal resolution
sky-radiometer data in SKYNET Hefei site, China, during 196 cloud-free days
from 2007 to 2013. The assessment evaluates the temporal variability of AOP,
such as AOD, SSA, and ASY, and estimates the errors of this variability in
determining DARF averaged over 24-h. To perform such an assessment, we retrieve
observed high temporal resolution optical properties and their daily
averaged ones as input for the SBDART model, and compare the 24-h average
DARF calculated for these inputs.
The impact of the daily averaged aerosol properties on the 24-h average DARF
can be up to 7.5 W m-2 absolutely and 15.2 % relatively for cases, which may
not negligible. The strong diurnal changes of heavy aerosol loading in
SKYNET Hefei site appear frequently, considerable attention has to be
paid to the impact on the 24-h averaged F value calculation when using daily
averaged AOP.
Using all selected 196 days' data set, there is an increase trend of absolute
biases for 24-h average F calculation with increasing daily mean AOD and
decreasing daily mean SSA at 500 nm. The statistical absolute and relative
biases for 24-h average F calculation are 0.3 ± 4.2 W m-2 and
11.8 % ± 6.6 %, respectively. Thus, care must be taken when aiming
to obtain accurate radiative transfer calculations in a high pollution region based
on measured-retrieved long-term high temporal aerosol data.
Acknowledgements
This research is supported by the Ministry of Science and Technology of
China (No. 2013CB955802), the Anhui Provincial Natural Science Foundation
(No. 1308085MD53), the National Natural Science Foundation of China (No.
41305022), and the Strategic Priority Research Program of the Chinese
Academy of Sciences (XDA05100302). We thank P. Khatri and T. Takamura
from Chiba University for their kind help. We appreciate the
MODIS (http://modis-land.gsfc.nasa.gov/) and
OMI (http://disc.sci.gsfc.nasa.gov/Aura/data-holdings/OMI) teams for supplying
the free satellite products over SKYNET Hefei site. We would also like to
thank all anonymous reviewers for their constructive and insightful
comments.
Edited by: O. Torres
ReferencesArola, A., Eck, T. F., Huttunen, J., Lehtinen, K. E. J.,
Lindfors, A. V., Myhre, G., Smirnov, A., Tripathi, S. N., and Yu, H.:
Influence of observed diurnal cycles of aerosol optical depth on
aerosol direct radiative effect, Atmos. Chem. Phys., 13, 7895–7901,
10.5194/acp-13-7895-2013, 2013.
Campanelli, M., Nakajima, T., and Olivieri, B.: Determination of the solar calibration constant
for a sun-sky radiometer: proposal of an in-situ procedure, Appl. Optics,
43, 651–659, 2004.Che, H., Zhang, X., Chen, H., Damiri, B., Goloub, P., Li, Z., Zhang, X., Wei, Y.,
Zhou, H., Dong, F., Li, D., and Zhou, T.: Instrument calibration and aerosol
optical depth validation of the China Aerosol Remote Sensing Network, J. Geophys. Res., 114,
D03206, 10.1029/2008JD011030, 2009.Che, H., Xia, X., Zhu, J., Li, Z., Dubovik, O., Holben, B.,
Goloub, P., Chen, H., Estelles, V., Cuevas-Agulló, E., Blarel, L., Wang, H.,
Zhao, H., Zhang, X., Wang, Y., Sun, J., Tao, R., Zhang, X., and Shi, G.: Column
aerosol optical properties and aerosol radiative forcing during
a serious haze-fog month over North China Plain in 2013 based on
ground-based sunphotometer measurements, Atmos. Chem. Phys., 14,
2125–2138, 10.5194/acp-14-2125-2014, 2014.Christopher, S. A., Wang, J., Ji, Q., and Tsay, S. C.:
Estimation of diurnal shortwave dust aerosol radiative forcing during
PRIDE, J. Geophys. Res., 108, 8596,
10.1029/2002JD002787, 2003.Halthore, R. N., Crisp, D., Schwartz, S. E., Anderson, G. P., Berk, A., Bonnel, B.,
Boucher, O., Chang, F. L., Chou, M. D., Clothiaux, E. E., Dubuisson, P., Fomin, B.,
Fouquart, Y., Freidenreich, S., Gautier, C., Kato, S., Laszlo, I., Li, Z., Mather,
J. H., Artemio, P. F., Ramaswamy, V., Ricchiazzi, P., Shiren, Y., Trishchenko, A.,
and Wiscombe W.: Intercomparison of shortwave radiative transfer codes and measurements, J. Geophys. Res., 110, D11206,
10.1029/2004JD005293, 2005.
Holben, B. N., Eck, T. F., Slutsker, I., Tanre, D., Buis, J. P., Setzer, A.,
Vermote, E., Reagan, J. A., Kaufman, Y. J., Nakajima, T., Lavenu, F., Jankowiak, I.,
and Smirnov, A.: AERONET – a federated instrument network and data archive for
aerosol characterization, Remote Sens. Environ., 66, 1–16, 1998.
IPCC: Climate Change 2013: The physical science basis, in:
Contribution of Working Group I to the Fifth Assessment Report of the
Intergovernmental Panel on Climate Change, edited by: Stocker, T. F.,
Qin, D., Plattner, G.-K., Tignor, M., Allen, S. K., Boschung, J.,
Nauels, A., Xia, Y., Bex, V., and Midgley P. M., Cambridge University
Press, Cambridge, UK and New York, USA, 2013.
Khatri, P. and Takamura, T.: An algorithm to screen cloud-affected
data for sky radiometer data analysis, J. Meteorol. Soc. Jpn., 87,
189–204, 2009.Kassianov, E., Barnard, J., Pekour, M., Berg, L. K., Michalsky, J., Lantz, K., and Hodges, G.: Do
diurnal aerosol changes affect daily average radiative forcing?,
Geophys. Res. Lett., 40, 3265–3269, 10.1002/grl.50567, 2013.Li, Z., Xia, X., Cribb, M., Mi, W., Holben, B., Wang, P., Chen, H., Tsay, S. C.,
Eck, T. F., Zhao, F., Dutton, E. G., and Dickerson, R. E.: Aerosol
optical properties and their radiative effects in northern China,
J. Geophys. Res., 112, D22S01, 10.1029/2006JD007382, 2007.Li, Z., Lee, K. H., Wang, Y., Xin, J., and Hao, W.: First
observation-based estimates of cloud-free aerosol radiative forcing
across China, J. Geophys. Res., 115, D00K18, 10.1029/2009JD013306, 2010.McComiskey, A., Schwartz, S. E., Schmid, B., Guan, H., Lewis, E. R., Ricchiazzi,
P., and Ogren, J. A.: Direct aerosol forcing: calculation from observables and sensitivities to
inputs, J. Geophys. Res., 113, D09202, 10.1029/2007JD009170, 2008.McPeters, R., Kroon, M., Labow, G., Brinksma, E., Balis, D., Petropavlovskikh, I.,
Veefkind, J. P., Bhartia, P. K., and Levelt, P. F.: Validation of the Aura Ozone Monitoring
Instrument total column ozone product, J. Geophys. Res., 113, D15S14,
10.1029/2007JD008802, 2008.Nakajima, T., Sekiguchi, M., Takemura, T., Uno, I., Higurashi, A., Kim, D., Sohn,
B. J., Oh, S. N., Nakajima, T. Y., Ohta, S., Okada, I., Takamura, T., and Kawamoto, K.:
Significance of direct and indirect radiative forcings of aerosols in
the East China Sea region, J. Geophys. Res., 108, 8658,
10.1029/2002JD003261, 2003.Nakajima, T., Yoon, S. C., Ramanathan, V., Shi, G., Takemura, T., Higurashi, A.,
Takamura, T., Aoki, K., Sohn, B. J., Kim, S. W., Tsuruta, H., Sugimoto, N.,
Shimizu, A., Tanimoto, H., Sawa, Y., Lin, N. H., Lee, C. T., Goto, D., and Schutgens, N.: Overview
of the ABC EAREX 2005 regional experiment and a study of the aerosol
direct radiative forcing in East Asia, J. Geophys. Res., 112, D24S91,
10.1029/2007JD009009, 2007.Ricchiazzi, P., Yang, S., Gautier, C., and Sowle, D.:
SBDART: a research and teaching software tool for plane-parallel
radiative transfer in the Earth's atmosphere, B. Am. Meteorol. Soc.,
79, 2101–2114, 1998.
Schaaf, C. B., Liu, J., Gao, F., and Strahler, A. H.: MODIS
albedo and reflectance anisotropy products from Aqua and Terra, in:
Land Remote Sensing and Global Environmental Change: NASA's Earth
Observing System and the Science of ASTER and MODIS, Remote Sensing
and Digital Image, Proc. Ser., Vol. 11, edited by: Ramachandran, B.,
Justice, C., and Abrams, M., Springer-Verlag, 873 pp., 2011.
Ulaby, F. T., Moore, R. K., and Fung, A. K.: Fundamentals and
Radiometry, Microwave Remote Sensing: Active and Passive, vol. I,
Artech House, Norwood, Mass., 456 pp., 1986.Wang, Z., Liu, D., Wang, Z., Wang, Y., Khatri, P., Zhou, J., Takamura, T., and Shi, G.: Seasonal
characteristics of aerosol optical properties at the SKYNET Hefei site
(31.90∘ N, 117.17∘ E) from 2007 to 2013, J. Geophys. Res.-Atmos.,
119, 6128–6139, 10.1002/2014JD021500, 2014.
Westwater, R.: The accuracy of water vapor and cloud liquid
determination by dual-frequency ground-based microwave radiometry,
Radio. Sci., 13, 677–685, 1978.Xia, X., Li, Z., Holben, B., Wang, P., Eck, T., Chen, H., Cribb, M., and
Zhao, Y.: Aerosol optical properties and radiative effects in the Yangtze
Delta region of China, J. Geophys. Res., 112, D22S12,
10.1029/2007JD008859, 2007.Zhou, J., Yu, G., Jin, C., Qi, F., Liu, D., Hu, H., Gong, Z., Shi, G.,
Nakajima, T., and Takamura, T.: Lidar observations of Asian dust over Hefei,
China, in spring 2000, J. Geophys. Res., 107, AAC5.1–AAC5.8,
10.1029/2001JD000802, 2002.