Biogeochemical aspects of atmospheric methane
Abstract
Short lived climate forcers (SLCFs) alter the Earth’s radiative balance and perturb other components of the climate system (cryosphere, clouds, water cycle). SLCFs like black carbon aerosols and CH4 arethe leading contributors to climate change, after CO2. To the total CH4 emissions during 2008-17 (576 Tg/y, top-down), wetlands and biomass burning have contributed nearly 32% and 5%, respectively. Modelling studies predict the increase in microbial activity in wetlands with increasing temperatures thus increased CH4 emissions. Further, biomass burning emissions are projected to increase with land-use change. This emphasizes a need for a coherent understanding of interactions and feedback processes in atmosphere-land-ocean. Role of biogeochemical cycles involving methane and tools to study them will be discussed.
Importance of air-sea exchange of reactive trace gases over the northern Indian Ocean
Abstract
Reactive trace gases play an important role in atmospheric chemistry and climate change in the Earth's atmosphere. One such category of reactive trace gases is volatile organic compounds (VOCs). In addition to terrestrial sources, the emission from global oceans is a significant source of many reactive trace gases via exchange across the air-sea interface. Ocean water is an important source of light non-methane hydrocarbons (NMHCs), oxygenated VOCs, dimethylsulfide (DMS), and halogenated VOCs in remote marine atmosphere. The transfer of trace gases from both the water- and air- sides is driven by several physical processes that can modulate the kinetics of flux across the interface. Along with physical processes, the exchange is also controlled by a concentration gradient at the interface driven by chemical and biological processes. In most studies, the air-sea fluxes of trace gases have been estimated using a diffusive sublayer model. The production of reactive trace gases in seawater is dependent on both biotic and abiotic mechanisms. However, major biogenic VOCs (isoprene and DMS) are predominantly produced by phytoplankton and microbial activity. The high biological activity of the northern Indian Ocean makes it an important region to be investigated for the production and emission of reactive trace gases. I will discuss the processes controlling air-sea exchange and their importance, along with the methodology of identification and quantification of NMHCs and DMS in the marine atmosphere.
Recent works on suprathermal populations and calibration data analysis of STEPS-ASPEX
Abstract
Using 22 years’ of suprathermal particle measurements from the L1 point by the ACE satellite, we have recently brought out the differences in the variations of different (particularly helium and iron) suprathermal populations in solar cycle 23 and 24. Although these results throw light on the possible roles of First Ionization Potential (FIP) and mass to charge ratio (M/Q) dependences of the energization processes, it is also realized that directionally resolved suprathermal particle measurements can be very helpful in understanding these processes. Suprathermal and Energetic Particle Spectrometer (STEPS), a sub-system of the Aditya Solar wind Particle Experiment (ASPEX), on board the upcoming Aditya-L1 satellite will measure suprathermal particles from six directions. These unique, directional measurements might provide important insights on these energization processes that have been elusive so far to the scientific community. STEPS has gone through various test, evaluation and calibration processes. In this talk, I will discuss how the calibration data are being analyzed and incorporated in the data pipelining software to get the desired science data.
Enhancements in Helium abundance in Interplanetary Coronal Mass Ejections
Abstract
The relative abundance of alpha particles with respect to protons (AHe=(nα/np) *100) is 8-8.5% in the photosphere. However, AHe varies from 2-5% in the solar wind depending on the solar activity level and solar wind velocity. Interestingly, AHe can increase significantly and reach above 8% in the interplanetary coronal mass ejections (ICME) passing through the first Lagrangian point (L1) of the Sun-Earth system. To understand the AHe enhancement in ICMEs, we have carried out a detailed investigation using database spanning over two solar cycles. We show that there is a solar activity variation of ICME averaged AHe values. Further, we evaluate the role of various factors like the first ionization potential (FIP) effect, localized coronal heating, chromospheric evaporation, gravitational settling etc. for the variation of AHe beyond 8% in ICMEs. The insights obtained from these investigations will be presented.
Atmospheric chemistry over India: Integrating measurements with photochemical box model
Abstract
Atmospheric chemistry over the Indian region significantly influences the air composition and climate over regional to global scale. Nevertheless, studies on detailed air chemistry particularly related with biogenic emissions, radicals, and halogens remain lacking. In this regard, we included state-of-the-art in situ measurements and satellite data into photochemical box model to study the chemical evolution of air downwind of Ahmedabad. The model simulation shows a large build up in O3 (∼115 ppbv) and numerous secondary inorganics (e.g., nitric acid ∼17 ppbv) and organics (e.g., ketones ∼11 ppbv). The noontime maximum levels of hydroxyl (OH) and hydroperoxyl (HO2) radicals are simulated to be 0.3 and 44 pptv, respectively. Volatile Organic Compounds are the major OH sink initially but contribution of CO is greater on the further days. Model output infused into air trajectories shows outflow of ozone-rich air towards the Arabian Sea, in agreement with measurements and a global model. An observational curve between isoprene and air temperature was included in the model to assess the possible effect of warming on ozone. Further, satellite-derived trend in leaf area and chemistry of key halogens are being included in model to unravel their impact on the oxidation capacity of atmosphere.