On Sensitivity of Spectral Radiative Fluxes to Atmospheric Water Vapor in the 940 nm Region (Numerical Simulation) Page: 2 of 10
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Fifteenth ARM Science Team Meeting Proceedings, Daytona Beach, Florida, March 14-18, 2005
development of new methods of retrieval of the total column water vapor content (WVC) in the
atmosphere from data of radiation observations (e.g., Kiedron et al. 2001).
Comparison of simulated and measured downward spectral
fluxes
For calculation of spectral solar fluxes we used algorithms developed by ourselves earlier (Zhuravleva
and Firsov 2004). The effective molecular absorption coefficients were calculated for simplified
(Gaussian) instrumentation functions of RSS (512 channels)
(ftp://oink.asrc.cestm.albany.edu/pub/RSS102) and spectral solar constant of Kurutz (1992) using the
database of spectral lines HITRAN-2004 (http://www.hitran.com) and modern models of the continuum
absorption (http://rtweb.aer.com/continuum code.html). The concentrations of absorbing gases (except
for H20) were chosen in accordance with Air Force Geophysics Laboratory (AFGL) model (Anderson
et al. 1986). The vertical stratification of the aerosol optical properties corresponded to the WCP aerosol
model (WCP 1986). In calculations of extinction coefficient and single scattering albedo of clouds we
used the cloud microstructure model corresponding to the "wide particle size distribution"
(Feigelson 1981).
The simulated spectral fluxes of solar radiation were compared with observations obtained for cases of
single-layer low-level overcast cloudiness during Atmospheric Radiation Measurement (ARM)
campaign of 1997-1998 at Southern Great Plains (SGP) site (Li et al. 2000). The data of the spectral
fluxes were obtained with RSS, which measures the direct, diffuse, and total radiation in 512/1024
channels within spectral region 350-1075 nm (Harrison et al. 1999). The vertical profiles of pressure,
temperature, and water vapor were retrieved from radiosonde data, while the liquid water path of clouds
was retrieved from microwave sensing. The information about total ozone content was taken from Total
Ozone Mapping Spectrometer (TOMS) archive. The top and bottom boundaries of the cloud layer were
determined with the aid of ground-based radars. The calculations accounted for the spectral behavior of
the surface albedo as derived from multi-filter rotating shadowband radiometer (muti-filter rotating
shadowband radiometer MFRSR, Li et al. 2001). The cloud extinction coefficient was chosen so that
the calculated and measured spectral fluxes coincided in the 500-550 nm band.
Comparisons have shown that the results of numerical modeling and spectral irradiance measurements
are in good agreement with each other (Figure 1), and, hence, the algorithms we proposed can be used
for description of the solar radiation transfer in the real atmosphere. Here, also, we present spectral flux
calculations, performed using MODTRAN4 (Li et al. 2000).
The Effect of Variations of Column Water Vapor Content on
Radiative Characteristics
Water vapor measurements. To estimate the variations of the spectral radiative characteristics when
water vapor changes in the atmosphere, we used the radiosonde measurements obtained in summer in
Novosibirsk, Russia (54 N, 83 E) in 1961-1970: profiles of temperature extend up to 30 km, and
humidity profiles up to 7 km. As a rule, radiosonde measurements were performed twice a day (00.00
and 16.00 LT), with total number of profiles being 360. Profiles of temperature and humidity outside2
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Zhuravleva, T.B. & Firsov, K.M. On Sensitivity of Spectral Radiative Fluxes to Atmospheric Water Vapor in the 940 nm Region (Numerical Simulation), article, March 18, 2005; United States. (https://digital.library.unt.edu/ark:/67531/metadc785479/m1/2/: accessed April 18, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.