One of the areas of the world with higher Aerosol
concentration is South Asia, due to the recent rapid urbanization and
population growth. Ramanathan et al., (2005) suggests the aerosol forcing in
over populated regions at the surface and in the atmosphere can be an order of
magnitude greater than those of anthropogenic greenhouse gases, as in the case
for the Indo-Asian haze. Subsequently concerns have been raised that
anthropogenic aerosols are impacting monsoon rainfall and mechanisms. Bollasina and Nigam (2008) have produced some observational research indicating the
impacts. Their work is aligned with the vast quantity of other observed research
linked to aerosols and the Indian monsoon.
The authors statistically analysed the relationship between
distribution and variability of aerosols (derived from Total Ozone Mapping
Spectrometer) with cloud cover, surface heating, surface shortwave and longwave
radiation and monthly precipitation. The
research produced two important conclusions:
1.
Increased anthropogenic aerosols present in May
leads to reduced cloud cover and precipitation, increased surface wave
radiation, and land surface warming. These changes are attributed to the
evaporation of the cloud layer from the absorption of solar radiation by
aerosols and subsequent heating of the air – also known as the “semi direct”
effect.
2.
As the monsoon progresses, the monsoon
intensifies leading to increased rainfall in June and July over India. The
authors argue that the enhancement of the monsoon results from the increased
thermal contrast (originated in May).
Fundamentally the authors identify that large-scale
anthropogenic aerosol influence on monsoon circulation and hydroclimate is
mediated by the heating of the land surface, pursuant to reduced cloudiness and
precipitation in may.
The following post shall look summate the relationship
between aerosols and the Indian monsoon based on models.
No comments:
Post a Comment