Variability of Atmospheric Aerosols Over India
S.K. Satheesh, S. Suresh Babu, B. Padmakumari, G. Pandithurai and V.K. Soni
The effect of aerosols on climate through various radiative interactions (involving the atmosphere, clouds, and the cryosphere) is well recognized by the international community (e.g., Andreae et al. 2005; Satheesh and Moorthy 2005; Bollasina et al. 2011; IPCC 2013). Atmospheric aerosols play a significant role in climate change due to their ability to scatter and absorb the incoming and outgoing radiation (direct effect). In addition to this, aerosols can also impact climate through modifying cloud properties, such as droplet size distribution and cloud lifetime, a process known as “indirect effect” (Twomey 1974; Kaufman et al. 2005; Rosenfeld et al. 2014). In addition, absorption of solar radiation by aerosols can lead to changes in cloud properties known as semi-direct effect (Lohmann et al. 2001). Of late, several reports focus on the impact of carbon-containing aerosols on monsoon, even though there have been contradictions and the processes are not understood well. Further, there have been reports that aerosols might impact crop yields, stimulate tropical cyclones, cause droughts and floods, and so on, most of these not validated yet (Chameides et al. 1999; Chung and Ramanathan 2006). Carbon-containing aerosols
S.K. Satheesh (H)
S. Suresh Babu
Space Physics Laboratory, Indian Space Research Organization, Thiruvananthapuram, India
B. Padmakumari • G. Pandithurai
Indian Institute of Tropical Meteorology, Earth System Science Organization, Pune, India
India Meteorological Department, Earth System Science Organization,
New Delhi, India © Springer Science+Business Media Singapore 2017
M.N. Rajeevan and S. Nayak (eds.), Observed Climate Variability and Change Over the Indian Region, Springer Geology, DOI 10.1007/978-981-10-2531-0_13
are composed of black carbon (BC) and organic carbon (OC); however, they have different climate forcing. Major sources of both BC and OC are biomass and fossil fuel burning. While OC is of light-scattering type, the most important light-absorbing aerosol species is BC. The OC through its cloud condensation nuclei (CCN) activity also contributes to indirect forcing while BC can contribute to evaporation of clouds known as “cloud burn off” (Ackerman et al. 2000). The fact that atmospheric aerosols exhibit high degree of spatial and temporal heterogeneity which makes their role in cloud microphysics very complex. Consequently, the aerosol-cloud interactions have been a subject matter of great interest to the climate science community, and efforts are being made by making use of a wide variety of experiments onboard ground-based, airborne, and space-borne platforms (Koren et al. 2004, 2008, 2014). Thus, it is imperative that relevant aerosol quantities are being measured from ground, aircraft, and space and used to carefully answer the fundamental questions related to the aerosol-climate problem.
Systematic studies on aerosols, clouds, and radiation budget were virtually nonexisting in India till the 1980s, except a few studies based on the atmospheric turbidity measurements using Volz Sun photometers by the India Meteorological Department (IMD) (Mani 1968; Mani and Huddar 1972; Mani and Chacko 1980; Rangarajan and Mani 1982). Even though aerosol research in India dates back to 1950s, systematic studies of the aerosols commenced only in the 1980s under the Indian Middle Atmosphere Programme (I-MAP) (Murthy 1988; Moorthy et al. 1988, 1999, 2009). During the I-MAP, a project to monitor the aerosol characteristics was initiated by utilizing multi-wavelength radiometers over a few selected locations (Murthy et al. 1988; Moorthy et al. 1988, 1989, 1991, 1993), following common instrumentation, data and analysis protocols, based on a network concept involving multi-institutional collaboration. This project became operational in the mid-eighties. Realizing its scientific potential and success, this project has been continued after IMAP under ISRO’s Geosphere Biosphere Programme (ISRO-GBP) as Aerosol Climatology and Effects (ACE) having long-term objectives. With this modest beginning, networking at several geographically distinct locations, a few selected sites were equipped with a regional focus under ISRO-GBP since the 1990s (Moorthy et al. 1993, 1994, 1996; Moorthy and Satheesh 2011). Around the same time, vertical profiles of aerosols have been obtained using rocket-borne and balloon-borne payloads and Lidars (Parameswaran et al. 1984; Devara et al. 1994). These activities have enabled the increased recognition of the important role aerosols may have on climate forcing, and the ACE activity was converted to a national project namely the Aerosol Radiative Forcing over India (ARFI) project (Moorthy et al. 2009; Moorthy and Satheesh 2011) with the regional network of observatories known as ARFINET. This currently comprises of 41 aerosol observatories spread across India covering urban, remote, island, coastal, inland, semiarid, arid, and remote mountain regions over the mainland and the adjoining oceanic regions (Babu et al. 2013) (Fig. 1 for ARFINET locations). Around the same time, the global network of aerosols such as AErosol RObotic NETwork (AERONET) also established surface-based sites in India (Holben et al. 2001). In addition, recent years witnessed the expansion of several other regional networks also in India such as SKYNET (Kim et al. 2005).
In this chapter, long-term changes and variability of aerosol concentration and its spatial vertical distribution over the Indian region are discussed, based on the results from several experiments conducted over the Indian region. Aerosol observations carried out during various experiments/campaigns are discussed, and analysis was
Fig. 1 Locations of ARFINET sites marked on a digital elevation map of India, where each circle represents the ARFINET observatories, identified by its short name. The red circles denotes the stations which are operational and yellow circles denotes which are not operational. The triangle symbols indicate AERONET stations made on different types of aerosols with special emphasis to black carbon aerosols. Potential linkages between the changes in aerosol, radiation and clouds are also discussed.