Global features of sea-level pressure distribution in April and July associated with contrasting situations of Indian summer monsoon

Global sea-level pressure distribution has been analysed for the months of April and July for 5 years of contrasting situations of Indian summer monsoon, comprising of two drought years (1972 and 1974), a flood year (1975) and two normal monsoon years (1970 and 1973). Mean monthly sea-level pressure data at about 400 stations have been used in the study. Prominent features of pressure departures from long-term normals have also been noted. It is observed that the month of April shows more prominent contrasting features than July. In April, the high pressure centres over USSR and the North Pacific move considerably eastward during poor monsoon years, while a breakaway cell of Icelandic Low goes deep south. Both the high pressure areas over south Indian Ocean and Australia are stronger in good monsoon years. In July, the subtropical high pressure zone over the southern Indian Ocean is stronger and the Australian high is more eastward, in good monsoon years

Zonal winds and temperature structure at the upper levels during poor and good monsoon

Global analyses of zonal wind field and thermal field structure at standard pressure levels of 200,150 and 100 mb have been carried out in India during July 1979-a poor monsoon year and July 1975-a good monsoon year. More than 250 stations in the belt 60°N and 60°S were selected. Contrasting features of the zonal wind field structure and thermal field are brought out, and it is shown that monsoon activity is reflected in the upper level and is controlled by planetary scale

Global features of upper-tropospheric zonal wind and thermal fields during anomalous monsoon situations

Global analyses of mean monthly zonal wind component and temperature at 200, 150 and 100 mb levels have been made for the region between 60°N and 60°S, for the months May through September during two poor monsoon years (1972 and 1979) and a good monsoon year (1975). Prominent and consistent contrasting features of the zonal wind and thermal fields have been identified, with reference to the monsoon performance over India. It has been noticed that the areal spreading of easterlies over the tropics and extratropics is significantly more during a good monsoon year. Shifting of the axis of the tropical easterly jet stream to a higher level and generally stronger easterlies also characterize good monsoon activity. The upper troposphere has been found to be considerably cooler during poor monsoon years

Effect of increasing CO2 on the stratospheric level of CO and O3

Production and destruction processes of carbon monoxide (CO) and ozone (O3) are examined in the light of increasing amount of atmospheric carbon dioxide (CO2). It is found that doubling of CO2 will increase the stratospheric concentration of CO and will have positive effect on O3 concentration

Aeronomic reactions of ozone in the trophosphere and stratosphere

Daytime rates of about 60 chemical and photochemical reactions, which can affect the concentration of ozone (03) in the troposphere and stratosphere, have been computed to examine the role of each of them in the production and destruction mechanisms of O3. Efficiency of various catalytic cycles causing O3 loss have also been studied. The behaviour of atomic oxygen, which is a key element in regulating O3 concentration in the atmosphere has been studied in detail. Results obtained show that, during daytime, the loss of O3 due to various chemical reactions can be neglected when compared to its loss due to photodissociation in different bands. Catalytic chains of NO, OH, HO2 and ClO are not much effective in sunlight

Aeronomic reactions of ozone in the troposphere and stratosphere

Daytime rates of about 60 chemical and photochemical reactions, which can affect the concentration of ozone (03) in the troposphere and stratosphere, have been computed to examine the role of each of them in the production and destruction mechanisms of O3. Efficiency of various catalytic cycles causing O3 loss have also been studied. The behaviour of atomic oxygen, which is a key element in regulating O3 concentration in the atmosphere has been studied in detail. Results obtained show that, during daytime, the loss of O3 due to various chemical reactions can be neglected when compared to its loss due to photodissociation in different bands. Catalytic chains of NO, OH, HO2 and ClO are not much effective in sunlight

Some aspects of carbion dioxide exchange between atmosphere and Indian plant biota

A study has been undertaken to understand some of the aspects of carbon-dioxide exchange between the atmosphere and Indian plant biota. The net primary production and the total pool of carbon in forests, cultivated land, and grassland during 1980 is estimated. The flux of carbon dioxide due to deforestation and the consumption of firewood is also estimated. The total pool of carbon in a forest ecosystem shows a very low value when compared with the size and climate of the country. On the other hand, carbon-dioxide emission due to firewood combustion shows a very high value

Ozone in the mesosphere and lower thermosphere

One-dimensional photochemical diffusive model has been used to obtain the altitude and temporal variation of O3 in the range of 50 to 150km height. More than 60 chemical reactions and photo-dissociatons of oxygen-hydrogen atmosphere are incorporated. Their contribution in the formation or distribution directly or indirectly, is critically examined. In the altitude profile of O3 concentration, it is observed that there is slight increase in concentration around 85km which is due to the increase in production rate at that height through the following reaction as: O+O2+M→O3+M (M=total atmospheric concentration) and the sharp decrease above 90km is also through the same reaction. Two altitude profiles of ozone concentration, one from photochemical equilibrium and other from non-equilibrium model are obtained. It is seen that in the mesosphere these two profiles are comparable. Further it is also seen that the average night time concentration is more than that in the day. Results obtained are compared with experimental value

Role of ozone in the sodium and hydroxyl nightglow

One-dimensional photochemical diffusion model which includes oxygen-hydrogen-sodium atmosphere has been used to examine the relation between sodium and hydroxyl nightglow and the role of ozone in it. It is found that both emissions can be obtained on the basis of photochemistry. The following reactions Na + O3→ NaO + O2 and H + O3→ OH +O2 play key role in sodium and hydroxyl emission respectively. Further it is found that variations in both emissions are controlled by the variation in the concentration of ozon