the surface. South Asia is the dominant contributor to sulfate
aerosols over the INDOEX region and accounts for 60–70%
of the AOD by sulfate (Reddy et al. 2004).
5.2.5 Impact of Absorbing Aerosols
on Himalayan Snow/Ice Cover
Aerosols also impact the snow albedo in the high mountains
in the north of India. During the pre-monsoon season,
long-range transport and advection of desert dust over the
Himalaya (Duchi et al. 2014) leads to its deposition on
Himalayan snow, particularly over western Himalaya, and
results in long-term reduction in snow albedo (Gautam et al.
2013). This snow darkening leads to accelerated snowmelt
(Lau and Kim 2010). Similarly, dust above clean snow can
also lead to the absorption of solar radiation at shorter
wavelengths, but the warming is instantaneous and reduces
when the dust layer is advected away or deposited (Gautam
et al. 2013). Along with dust, light-absorbing BC and
organic carbon aerosols from biomass burning get transported and lifted to the third pole from neighboring areas.
The impact of BC on snow is similar to that of dust aerosols.
On the deposition of BC on snow, it reduces surface albedo
leading to increased absorption of shortwave radiation
affecting the surface snowmelt.
Kopacz et al. (2011) found that emissions from northern
India and central China contribute to the majority of BC in
the Himalayas, although the precise source location varies
with season. The Tibetan Plateau receives most BC from
western and central China, as well as from India, Nepal, the
Middle East, Pakistan, and other countries. The magnitude
of contribution from each region also varies with season.
The effect on this part of the cryosphere is highest in
pre-monsoon and lowest during monsoon season (Gertler
et al. 2016). Some studies (Xu et al. 2009) have analyzed ice
cores for long-term trends of BC deposition on Himalayan
glaciers. Xu et al. (2009) reported results from five ice core
samples at various locations across Himalaya. Most of the
locations show high concentrations in the 1950s–1960s and
lower values in 1970–1980s. The authors attributed this
temporal variation to the differential long-range transport of
European emissions. The cryospheric soot concentrations
over southern Himalaya show an increasing trend from the
1990s, which reflects an increase in present-day emissions
(Xu et al. 2009). Jacobi et al. (2015) found a 4–5% reduction
of albedo from BC over Himalaya. Kaspari et al. (2014)
computed the change in albedo due to BC and dust over the
Mera glacier and reported a 6–10% albedo reduction during
the winter–spring season. The annual snow albedo surface
forcing has been found in the range of 3–6 W m
−2 (Jacobi
et al. 2015). The radiative forcing in the snow-covered
regions due to the BC-induced snow albedo effect can vary
from 5 to 15 W m
−2 , an order of magnitude larger than
radiative forcing due to the direct effect, and with significant
seasonal variation in the northern Tibetan Plateau (Kopacz
et al. 2011).
5.2.6 Aerosol-Cloud Interaction: Indirect Effect
of Aerosols
Aerosols alter clouds changing the precipitation patterns and
intensity over India. Initial attempts in the AIE in the
monsoon environment were largely based on the satellite
data. Panicker et al. (2010) reported positive (negative) AIE
values during drought (excess monsoon) years for four
consecutive years from 2001 to 2004 using satellite data
demonstrating an inverse relationship between AIE and
ISMR. Quantitative estimates of AIE using two different
methodologies have given two close values of 0.13 and 0.07
over India, and the difference is attributed to the aerosol
effect on the dispersion of cloud drop size distribution
(Pandithurai et al. 2012). During monsoon season over
India, AIE increases from 0.01 to 0.23, with an increase in
liquid water path (Harikishan et al. 2016). Further, AIE
derived from cloud drop number concentration and effective
radius at different liquid water contents recorded at a
high-altitude cloud physical laboratory in the Western Ghats
provides a better understanding of the role of aerosol effect
on cloud drop dispersion (Anil Kumar et al. 2016).
The Cloud-Aerosol Interaction and Precipitation
Enhancement Experiment [CAIPEEX; (Kulkarni et al.
2012)] over India, mainly focusing on continental clouds,
documented the precipitation process and associated
aerosol-cloud interaction over the region. CAIPEEX in situ
observations showed a significant increase in the cloud
droplet number concentration with aerosol, as compared to
the INDOEX study and several other reported results from
around the world (Fig. 5.6). High aerosol loading into the
atmosphere enhances the CCN, increasing the number concentration and decreasing the size of cloud droplets and a
narrow droplet spectrum. This may further suppress collision
coalescence and warm rain may form at an elevated layer
(Konwar et al. 2012).
CAIPEEX observations revealed dilution in cumulus
clouds over India (Nair et al. 2012) with pre-monsoon clouds
in the high aerosol environment having more adiabatic cores
than the monsoon clouds (Bera et al. 2019). Also, the clouds
have a large amount of supercooled liquid water (>3 gm
−3
)
with mixed phase (Prabha et al. 2012). The cloud drop
effective radius increases with the height from the cloud base
(Prabha et al. 2012) and, the depth of warm rain was having a
direct relationship with the subcloud aerosol. A decrease in
the droplet spectral width of pre-monsoon cloud droplet sizes
due to aerosol was reported by Prabha et al. (2012), and the
102
S. Fadnavis et al.
aerosols over the INDOEX region and accounts for 60–70%
of the AOD by sulfate (Reddy et al. 2004).
5.2.5 Impact of Absorbing Aerosols
on Himalayan Snow/Ice Cover
Aerosols also impact the snow albedo in the high mountains
in the north of India. During the pre-monsoon season,
long-range transport and advection of desert dust over the
Himalaya (Duchi et al. 2014) leads to its deposition on
Himalayan snow, particularly over western Himalaya, and
results in long-term reduction in snow albedo (Gautam et al.
2013). This snow darkening leads to accelerated snowmelt
(Lau and Kim 2010). Similarly, dust above clean snow can
also lead to the absorption of solar radiation at shorter
wavelengths, but the warming is instantaneous and reduces
when the dust layer is advected away or deposited (Gautam
et al. 2013). Along with dust, light-absorbing BC and
organic carbon aerosols from biomass burning get transported and lifted to the third pole from neighboring areas.
The impact of BC on snow is similar to that of dust aerosols.
On the deposition of BC on snow, it reduces surface albedo
leading to increased absorption of shortwave radiation
affecting the surface snowmelt.
Kopacz et al. (2011) found that emissions from northern
India and central China contribute to the majority of BC in
the Himalayas, although the precise source location varies
with season. The Tibetan Plateau receives most BC from
western and central China, as well as from India, Nepal, the
Middle East, Pakistan, and other countries. The magnitude
of contribution from each region also varies with season.
The effect on this part of the cryosphere is highest in
pre-monsoon and lowest during monsoon season (Gertler
et al. 2016). Some studies (Xu et al. 2009) have analyzed ice
cores for long-term trends of BC deposition on Himalayan
glaciers. Xu et al. (2009) reported results from five ice core
samples at various locations across Himalaya. Most of the
locations show high concentrations in the 1950s–1960s and
lower values in 1970–1980s. The authors attributed this
temporal variation to the differential long-range transport of
European emissions. The cryospheric soot concentrations
over southern Himalaya show an increasing trend from the
1990s, which reflects an increase in present-day emissions
(Xu et al. 2009). Jacobi et al. (2015) found a 4–5% reduction
of albedo from BC over Himalaya. Kaspari et al. (2014)
computed the change in albedo due to BC and dust over the
Mera glacier and reported a 6–10% albedo reduction during
the winter–spring season. The annual snow albedo surface
forcing has been found in the range of 3–6 W m
−2 (Jacobi
et al. 2015). The radiative forcing in the snow-covered
regions due to the BC-induced snow albedo effect can vary
from 5 to 15 W m
−2 , an order of magnitude larger than
radiative forcing due to the direct effect, and with significant
seasonal variation in the northern Tibetan Plateau (Kopacz
et al. 2011).
5.2.6 Aerosol-Cloud Interaction: Indirect Effect
of Aerosols
Aerosols alter clouds changing the precipitation patterns and
intensity over India. Initial attempts in the AIE in the
monsoon environment were largely based on the satellite
data. Panicker et al. (2010) reported positive (negative) AIE
values during drought (excess monsoon) years for four
consecutive years from 2001 to 2004 using satellite data
demonstrating an inverse relationship between AIE and
ISMR. Quantitative estimates of AIE using two different
methodologies have given two close values of 0.13 and 0.07
over India, and the difference is attributed to the aerosol
effect on the dispersion of cloud drop size distribution
(Pandithurai et al. 2012). During monsoon season over
India, AIE increases from 0.01 to 0.23, with an increase in
liquid water path (Harikishan et al. 2016). Further, AIE
derived from cloud drop number concentration and effective
radius at different liquid water contents recorded at a
high-altitude cloud physical laboratory in the Western Ghats
provides a better understanding of the role of aerosol effect
on cloud drop dispersion (Anil Kumar et al. 2016).
The Cloud-Aerosol Interaction and Precipitation
Enhancement Experiment [CAIPEEX; (Kulkarni et al.
2012)] over India, mainly focusing on continental clouds,
documented the precipitation process and associated
aerosol-cloud interaction over the region. CAIPEEX in situ
observations showed a significant increase in the cloud
droplet number concentration with aerosol, as compared to
the INDOEX study and several other reported results from
around the world (Fig. 5.6). High aerosol loading into the
atmosphere enhances the CCN, increasing the number concentration and decreasing the size of cloud droplets and a
narrow droplet spectrum. This may further suppress collision
coalescence and warm rain may form at an elevated layer
(Konwar et al. 2012).
CAIPEEX observations revealed dilution in cumulus
clouds over India (Nair et al. 2012) with pre-monsoon clouds
in the high aerosol environment having more adiabatic cores
than the monsoon clouds (Bera et al. 2019). Also, the clouds
have a large amount of supercooled liquid water (>3 gm
−3
)
with mixed phase (Prabha et al. 2012). The cloud drop
effective radius increases with the height from the cloud base
(Prabha et al. 2012) and, the depth of warm rain was having a
direct relationship with the subcloud aerosol. A decrease in
the droplet spectral width of pre-monsoon cloud droplet sizes
due to aerosol was reported by Prabha et al. (2012), and the
102
S. Fadnavis et al.