Geoscience Reference
In-Depth Information
ANTHROPOGENIC AEROSOL RADIATIVE
FORCING IN THE INDO-GANGETIC BASIN
SAGNIK DEY
∗
andS.N.TRIPATHI
†
Department of Civil Engineering, Indian Institute of Technology,
Kanpur 208016, India
∗
sagnik@iitk.ac.in
†
snt@iitk.ac.in
Long-term (2001-2005) estimation of anthropogenic contribution to aerosol
direct radiative forcing, and its spatial variability over Indo-Gangetic Basin
(IGB) is presented. An optically equivalent model has been formulated based on
the surface measurements of aerosol properties, and the optical properties are
used to estimate the direct radiative forcing at the top-of-atmosphere (TOA),
surface, and atmosphere. Anthropogenic aerosols contribute more than 80%
to the composite aerosol optical depth (at 0.5
m) in the winter, whereas the
natural dusts contribute more than 55% in the summer. Mean annual clear-
sky TOA, surface, and atmospheric forcing due to anthropogenic aerosols in
the IGB are +0
µ
9Wm
−
2
, respectively.
Anthropogenic contribution is persistently found to be high in the eastern
IGB (
±
6
.
8,
−
12
.
6
±
6
.
7, and +12
.
6
±
6
.
SD)
annual heating rate of 0
.
64
±
0
.
19 K day
−
1
over IGB; the heating rate even
goes up to more than 0.9 K day
−
1
in many places seasonally. Persistently,
large reduction of net surface radiation would affect the regional hydrological
cycle through decrease in evaporation and sensible heat flux. The variable
spatial heterogeneity in the atmospheric heating would affect the atmospheric
circulation in this region.
>
70%). Anthropogenic aerosols contribute 55% to the mean (
±
1. Introduction
Aerosols perturb the Earth's radiation budget directly through scattering
and absorption of sunlight,
1
and indirectly through interaction with
clouds.
2
The change in the radiative fluxes at the top-of-the-atmosphere
(TOA) and at the surface due to the aerosols (natural + anthropogenic) is
termed as aerosol radiative forcing. One major uncertainty in aerosol direct
radiative forcing (ADRF) arises from limited knowledge of the relative
proportion of the anthropogenic and natural components and their mixing
state.
3
,
4
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