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Critical analysis of experimental surface ozone data and cloud coverage is reported over Kolkata during the period January 2011 to December 2011. Significant relationship between these two parameters is observed. Analysis shows that the trend of surface ozone concentration and cloud coverage follow opposite tendency. Some exceptional observations are also reported. Apart from this, seasonal variation of surface ozone with columnar ozone concentration, NO2 and temperature is also examined in relation with cloud cover to obtain a possible explanation of this type of variation.

Aerosols can modify both short and long term weather patterns by impacting the radiation budget of Earth. Numerical simulations were performed to understand the direct effect of aerosol on radiation during an elevated dust and black carbon (BC) concentration period over south Asia. The impact of the aerosol (dust and BC separately) direct effect on meteorology and air quality (focusing on surface ozone) was assessed using a fully coupled chemical transport model (WRF-Chem). The model simulates the elevated dust and BC concentration plume well qualitatively. Our results show that elevated BC concentration can reduce surface temperature up to 2 K. Incoming short wave flux at the surface and the boundary layer height reduced up to 70% due to the radiative impact of BC. ‘This reduction in boundary layer height further increases the BC concentration at the source region. The radiative impact of dust on meteorological parameters are found to be less compared to BC at the surface level. The model simulates realistic surface ozone concentration using HTAP emission inventory. Results reveal that the presence of biomass burning can increase the surface ozone concentration by up to 40%. The radiative impact of BC can reduce the surface ozone concentration by more than 30% by altering the photolysis frequencies.

Thunderstorm, associated with strong convective activity in the tropics, is one of the most prominent weather phenomena in the atmosphere. A critical analysis is done on the nature of variation of the thunderstorm frequencies over an urban metropolitan location Kolkata (22°32′N, 88°20′E), India with the pre-monsoon and monsoon rainfall amounts during the period 1997–2008. The occurrences of severe thunderstorms are decreasing during the last decade, although the number of ordinary thunderstorms occurring in this period has an increasing trend. A decrease in Convective Available Potential Energy (CAPE), Vertical Wind Shear (VWSH), Deep Layer Shear (0–6 km AGL) and an increase in Lifted Index (LI) may be an indicator for the suppression of the severity of thunderstorms over the urban location. There is also a decreasing trend for the pre-monsoon rainfall and an increasing trend in the monsoon rainfall amounts over the region. A further study indicated a significant positive correlation for all the types of thunderstorm (severe, ordinary and total) events with the pre-monsoon rainfall amount which are mainly associated with the vigorous convective phenomenon. On the other hand, a significant anti-correlation is observed between the severe thunderstorm frequencies with the monsoon rainfall amount for the same period. The decrease in the severity of the thunderstorm events is accompanied by an increase of pre-monsoon cloud Liquid Water Content (LWC) with Integrated Water Vapor (IWV). Hence, there is an expected strong association of the thunderstorm frequency with the pre-monsoon and monsoon rainfall amounts at this tropical location. Possible explanations are presented.

The purpose of the paper is to present the variation of total ozone concentration over Ahmedabad during different seasons. It is concluded that the trend of ozone concentration during different seasons is different. A critical analysis is done and the following results are obtained. (i) The total ozone concentration increases during the pre-monsoon and winter periods. During pre-monsoon period rate of formation of ozone decreases in oscillatory manner with the rise of surface temperature. (ii) Total Column Ozone decreases during the monsoon and post-monsoon periods, throughout the duration of study. During monsoon period, rate of depletion of ozone increases and during post-monsoon period, rate of depletion of ozone decreases with the rise of surface temperature. (iii) The overall ozone concentration over Ahmedabad for the period of our study shows slightly increasing trend. Possible explanations are also presented.

In this paper, a simple relationship is employed to investigate the relative impacts on the movement and landfall of tropical cyclone in the Bay of Bengal region when wet component of atmospheric refractivity of different tropospheric levels is used as an input. Four tropical cyclones during pre-monsoon and post-monsoon season over the Bay of Bengal region were selected for the study. The radiosonde/radiowind data of coastal stations, namely Kolkata (Dumdum), Agartala, Bhubaneswar, Visakhapatnam, Machlipatnam, Chennai and Karaikal, were collected for the period of the cyclones under study. The wet component of atmospheric refractivity of different standard levels was plotted against time for the stations for every cyclone. The study suggests that the cyclone moves towards and crosses near the station having a relatively steeper increase in the wet component of atmospheric refractivity up to mid-tropical level. A possible explanation is also presented.

The paper presents the nature of variation of refractive index of atmospheric medium before the onset of squall over kolkata (22°34′N 88°22′E), India. The variation of the refractive index with surface temperature and relative humidity during squall is also presented. It is concluded that sharp decrease of the refractivity may be taken as a possible method of forecasting squall. This kind of study is very much helpful from the standpoint of aviation hazards and communication. Possible explanation for the observed results is also presented.

The nature of monthly, seasonal and latitudinal short-term variations of tropospheric ozone over different stations in India are presented in this paper. Monthly variations depict that at all stations, the nature of monthly mean tropospheric ozone column was oscillatory and had increasing trends from October, 2004 to June, 2009. At most of the places over India it is observed that tropospheric ozone densities had increased sharply from the month of January, attained the maximum value in the month of May, then decreased steeply achieving the lowest value in the month of August and finally had increased gradually from August to December during this period. Seasonal variations clearly reveal that tropospheric ozone value attained maximum during pre-monsoon time and minimum during monsoon time at all the stations except Simla and Srinagar. Winter, pre-monsoon and post-monsoon tropospheric ozone build up had been observed from 2004 to 2009, whereas monsoon ozone decline had been exhibited for the above period over most of the places in India. Tropospheric monthly mean, pre-monsoon, monsoon and post-monsoon ozone had enhanced with rise in latitude in Indian region. Chemical explanations have been proposed for such variations.

The paper presents the nature of long-term seasonal and yearly variations of tropospheric and stratospheric ozone over Thumba (8.5°N, 77°E) and Bangalore (13°N, 77.5°E), India. Seasonal variations clearly reveal that stratospheric ozone concentration attained comparatively higher value in the months from July to September while lower tropospheric ozone concentration at the same time over the above stations during the period 1979–2005. Yearly variation shows increasing trend in tropospheric ozone but decreasing trend in stratospheric ozone from 1979 to 2005. Undesirable environmental effects due to such tropospheric rise and stratospheric decline in ozone are also mentioned.

The paper presents the nature of annual cycles of tropospheric ozone, cloud occurrences, NO2, rainfall, SO2, SPM, CO, non-methane hydrocarbon and surface solar radiation for the period October 2004 to June 2009 over Alipore (22.52°N, 88.33°E), India. Annual cycle of low-level cloud occurrences depicts that the low-level cloud over Alipore had been noticed to occur for many days and nights, particularly from June to September. The low-level cloud occurrences were found in winter months and post-monsoon period. The effect of cloud occurrences on tropospheric ozone concentration has been critically analysed and explained. It has been observed that the concentration of ozone is oscillatory with cloud occurrences and has a slight linear decreasing trend with the increase of cloud occurrences and vice versa. The concentration of tropospheric ozone attained higher value at moderate cloud occurrences and comparatively lower value at both of the lower and higher cloud occurrences. The related possible chemical and physical explanation for role of cloud occurrences on tropospheric ozone has been offered.

A critical analysis is done on the variation of the rate of change of Total Column Ozone (TCO) over Dum Dum (22° 38 N, 88° 26 E) and Total Monsoon Rainfall over Gangetic West Bengal with the variable component of 10.7 cm solar flux during different seasons for the period 1997- 2005. An anti-correlation is observed between the variable component with the rate of change of TCO during the pre-monsoon and monsoon period and significant positive correlations during the post-monsoon and winter seasons. Quite insignificant positive correlations are observed between the variable component and Total Monsoon Rainfall during different seasons for this period. A co-variation is observed with the increase in the variable component of 10.7 cm solar flux throughout the period of study only during the pre-monsoon season. Possible explanations are also presented.

The paper presents the nature of variations of clouds and total ozone over Kolkata (22°34′N, 88°24′E), India. The low-level cloud over Kolkata has been noticed to occur for many days and nights, particularly in the months from June to September. The low level cloud occurrences were minimum in winter months. The effect of cloud occurrence on ozone concentration has been critically analyzed and explained. It has been observed that the concentration of ozone increased with the increase of cloud occurrence. The related possible chemical explanation for ozone production processes has been offered.

The sharp depletion of attenuation of 22.235 GHz signal before the onset of Nor’wester over Kolkata, India is observed and possible explanation of such type of variation is presented. It is concluded that this may be taken as one possible method of forecasting severe thunderstorm associated with Nor’wester. Physical explanations based on the formation and dissipation mechanisms of thunderstorm are also presented.

A critical analysis has been made of the long-term yearly and seasonal variations of ozone concentration at Ahmedabad (23°N, 72.5°E), India and Halley Bay (76°S, 27°W), a British Antarctic Service Station. The effect of O3 depletion on night airglow emission of Li 6708 A line at Ahmedabad and Halley Bay has been studied. Calculations based on chemical kinetics show that the airglow intensity of Li 6708 A line has also been affected due to the depletion of O3 concentration. The nature of yearly variation and seasonal variation of intensity of Li 6708 A line for the above two stations have been shown and compared. It has been shown that the rate of decrease of intensity of Li 6708 A line was comparatively higher at Halley Bay due to dramatic decrease of Antarctic O3 concentration.

This paper presents an analysis of the effect of flare index (Q) on the stratospheric ozone concentration over Dumdum station, Kolkata for the period 1979-95. As Dumdum is situated in northern hemisphere we have considered the flare index values for the northern hemisphere only.

The paper presents the seasonal variation of 6300 A line intensity at Calcutta with relative sunspot number, solar flare number and variable component of 10.7 cm solar flux. A study has been made and important results have been obtained which are as follows.

The paper presents the effect of solar flare index on Antarctic O3 depletion. Solar flare index is the actual representative of energy output of any flare event. A calibration curve between solar flare index and relative sunspot number is drawn. (A straight line is obtained and correlation coefficient between two variables is 0.95, n = 27, P < 0.01).The equation of straight line from least square principle becomes

The approximate age of O3 in the atmosphere of the Earth is calculated from the equation established by Midya et al. (1995) and a critical study of altitudinal variation of ozone concentration with nitric oxide is also presented. It is concluded that NO concentration achieves its minimum value during Antarctic spring and maximum value during the month of February.

The purpose of this paper is to study the nature of variation of O3 concentration of Antarctic Survey Stations and its correlation with solar ultraviolet radiation. Solar UV data for the period November 1978 to October 1984 are taken from Solar Geophysical Data Book. In absence of solar UV data for long period, a calibration curve between solar UV radiation and solar flare number (S.F.NO.) is drawn. (A straight line is obtained and correlation coefficient between two variables is 80%). The equation of straight line from least square principle becomes, UV flux = 0.2672 + 2.7578 × 10−5 × S.F.NO. From this equation UV flux values for long period are calculated from known values of solar flare numbers. O3 concentration of two Antarctic Survey Stations, Halley Bay (76‡ S, 27‡ W) and McMurdo (78‡ S, 166‡ E) are considered for analysis and following important results are obtained: (i) Yearly variations of O3 concentrations and UV radiations are mainly controlled by their October concentrations. (ii) Correlation coefficient between O3 concentration and UV radiation is 62% for the month of October. For the other months it is poor. (iii) It is concluded that dramatic decrease of O3 concentration at Antarctica is independent of solar UV radiation and chemical processes are responsible for special depletion of O3.

The purpose of this paper is to find correlation between OI 6300 A line intensity with solar and ionospheric parameters. A critical study have been made and the following important results are obtained: (i) Solar flare index plays more important role for the emissions of 6300 A line than other solar parameters. (ii) Intensity of 6300 A line increases linearly with the increase of solar flare index. (iii) Virtual height plays more important role than critical frequency for the emission of 6300 A line-intensity. (iv) Possible explanation of this type of variation is also presented.

The paper presents the relations between different solar and ionospheric parameters. Variation of 5577 A line intensity with the variation of solar and ionospheric parametersis also discussed. A study have been made and following important results are obtained

A critical study of distribution of ozone with altitude of about 91 Km and above has been made and following important results are obtained

The paper presents the effect of O3 depletion on OH (8,3) band. It is shown that Bates-Nicolet theory for the excitation of OH band is predominant excitation process. Calculations based on chemical kinetics show that the intensity of OH (8,3) band will also be effected due to the depletion of O3 concentration. O3 is depleted everywhere specially at Antarctica. Intensity of OH (8,3) band is calculated theoretically for Halley Bay (76° S, 27° W), British Antarctic survey station during the period 1973 to 1984.

The paper presents the seasonal variations of OI 6300 A line night airglow emission at Calcutta and other stations. Their covariations with OI 5577 A line are also offered. Explanation for the variation is also provided.

A critical study on different ozone depletion and formation processes has been made and following important results are obtained

The paper presents the effect of O3 depletion on different night airglow emission lines. Calculations based on chemical kinetics show that the airglow intensity of Na5893A, O5577A and OH band emissions will also be affected due to the depletion of O3 concentration. Intensity of Na5893A is calculated theoretically for Halley Bay (76° S,27° W), British Antarctic Survey Station, during the period 1973 to 1984. It is concluded from the covariation of different emission lines that O5577A and OH emissions also follow the same trend of variation. A study has been made to find the correlation between the depletion of O3 concentration and total solar flare numbers. Important results are as follows