Climate Sense

[

] 160

bserving

, P

redicting

and

rOjecting

limate

OnditiOns

balloon payloads. To understand the distribution of chlorofluorocarbons

(CFCs)measurements of vertical distributions weremade using high alti-

tude balloons and cryogenic air samplers. A comparison of surface ozone

levels at Ahmedabad shows an average linear rate of 0.5 per cent y-1

during the period 1954/55 to themid 1990s.

In addition, ozone produc-

tion per molecule of NO

is lower in India than in the USA or Europe.

Simultaneous measurements of surface level CO, NO

and non-methane

hydrocarbons, as well as OC to BC ratio have indicated dominance of

biomass burning over fossil fuel, especially in north India.

These factors

lead to the observed higher ∆CO/∆NOx. Satellite data show increasing

levels of columnar NO

at many Indian sites. These gases, having long

residence time in the free troposphere, are transported long distances.

Vertical distributions of ozone and surface level measurements of various

trace gases over India and the surrounding oceans clearly show the influ-

ence of long-range transport of these pollutants from North Africa and

southern Europe, especially during the winter.

Future directions

Reducing uncertainties in current understanding of the climate impli-

cations of aerosols and trace gases requires progress in all aspects

of aerosol-climate science. New observational systems, field experi-

ments, assimilation methods and regional and global scale synthesis

are essential. The large difference between observed and modelled

aerosol radiative impacts is due to inadequate modelling. This calls

for more realistic simulations of aerosol, clouds, and atmospheric

processes to be incorporated into models, and greater synergy among

different types of measurements, models, as well as

between measurements and models. Incorporation of

the mixing state of aerosols in models is still something

of an enigma.

When smaller aerosols accumulate over

larger ones the radiative impact is significantly different

compared to that of an external mixture.

This is partic-

ularly important over the Asian region, where natural

and anthropogenic aerosols coexist.

The vertical distribution of aerosols with respect to

clouds is important, particularly over the tropics, to further

our understanding of aerosol-cloud interaction and the

consequent impacts on ARF. The surprising observation

of elevated aerosol warming and its northward gradient

over India – as well as possible implications for regional

weather and climate – will be the immediate focus. To

quantify this an ARFI field Regional Aerosol Warming

Experiment (RAWEX) is planned, which will carry out

intense observations over the Himalayas and its foothills.

In the longer-term, future ISRO programmes on aerosol

and radiation will be built on the synergy of ground-based

observational networks (eventually leading to regional

mapping of aerosol radiative forcing), three-dimensional

mapping of physical and chemical composition using

integrated campaigns, satellite missions focusing on space-

time synthesis of aerosols, and accurate assimilation of all

these studies into regional and global models.

Space-time synthesis of AOD

Source: ICARB, I_GBP

Space-time synthesis of the AOD showing the large heterogeneity in AOD (top row) and its wavelength dependency expressed through the Angstrom exponent �

(bottom row). The panels in each row correspond to months of March, April and May, from left to right