COVID-19 is an emerging infectious disease and highly contagious in nature.• Temperature, dew point, and absolute humidity showed positive significant associations with SARS-CoV-2 transmission. • SARS-CoV-2 displayed negative associations with wind speed and ventilation coefficient.

We describe and show results from a series of field campaigns that used balloonborne instruments launched from India and Saudi Arabia during the summers 2014–17 to study the nature, formation, and impacts of the Asian Tropopause Aerosol Layer (ATAL). The campaign goals were to i) characterize the optical, physical, and chemical properties of the ATAL; ii) assess its impacts on water vapor and ozone; and iii) understand the role of convection in its formation. To address these objectives, we launched 68 balloons from four locations, one in Saudi Arabia and three in India, with payload weights ranging from 1.5 to 50 kg. We measured meteorological parameters; ozone; water vapor; and aerosol backscatter, concentration, volatility, and composition in the upper troposphere and lower stratosphere (UTLS) region. We found peaks in aerosol concentrations of up to 25 cm–3 for radii > 94 nm, associated with a scattering ratio at 940 nm of ∼1.9 near the cold-point tropopause. During medium-duration balloon flights near the tropopause, we collected aerosols and found, after offline ion chromatography analysis, the dominant presence of nitrate ions with a concentration of about 100 ng m–3. Deep convection was found to influence aerosol loadings 1 km above the cold-point tropopause. The Balloon Measurements of the Asian Tropopause Aerosol Layer (BATAL) project will continue for the next 3–4 years, and the results gathered will be used to formulate a future National Aeronautics and Space Administration–Indian Space Research Organisation (NASA–ISRO) airborne campaign with NASA high-altitude aircraft.

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Abstract. Tropical cyclones play an important role in modifying the tropopause structure and dynamics as well as stratosphere-troposphere exchange (STE) processes in the upper troposphere and lower stratosphere (UTLS) region. In the present study, the impact of cyclones that occurred over the north Indian Ocean during 2007-2013 on the STE processes is quantified using satellite observations. Tropopause characteristics during cyclones are obtained from the Global Positioning System (GPS) radio occultation (RO) measurements, and ozone and water vapour concentrations in the UTLS region are obtained from Aura Microwave Limb Sounder (MLS) satellite observations. The effect of cyclones on the tropopause parameters is observed to be more prominent within 500 km of the centre of the tropical cyclone. In our earlier study, we observed a decrease (increase) in the tropopause altitude (temperature) up to 0.6 km (3 K), and the convective outflow level increased up to 2 km. This change leads to a total increase in the tropical tropopause layer (TTL) thickness of 3 km within 500 km of the centre of cyclone. Interestingly, an enhancement in the ozone mixing ratio in the upper troposphere is clearly noticed within 500 km from the cyclone centre, whereas the enhancement in the water vapour in the lower stratosphere is more significant on the south-east side, extending from 500 to 1000 km away from the cyclone centre. The cross-tropopause mass flux for different intensities of cyclones is estimated and it is found that the mean flux from the stratosphere to the troposphere for cyclonic storms is 0.05 ± 0.29 × 10 −3 kg m −2 , and for very severe cyclonic storms it is 0.5 ± 1.07 × 10 −3 kg m −2 . More downward flux is noticed on the north-west and south-west side of the cyclone centre. These results indicate that the cyclones have significant impact in effecting the tropopause structure, ozone and water vapour budget, and consequentially the STE in the UTLS region.

The role of environmental factors in the transmission of COVID-19 still needs to be determined. The main objective of the present study is to explore the relationship between environmental factors (both meteorological and air pollution parameters) and the daily confirmed COVID-19 cases over Delhi, India. This study employed a secondary data analysis of COVID-19 (from 1 March to 30 June, 2020) from the Delhi State Health Bulletin and the environmental factors from the Indian Meteorological Department (IMD) and Central Pollution Control Board (CPCB) of India. Pearson's correlation coefficients were assessed to show the correlation between environmental factors and daily confirmed COVID-19 cases. The temperature (maximum, minimum, average, and dew point) and wind speed exhibited a significant positive correlation with daily COVID-19 cases. However, diurnal temperature range, rainfall, and relative humidity showed non-significant correlations. Air pollutants were found to be weakly associated with daily COVID-19 cases. However, O 3 exhibited a significant positive correlation with daily COVID-19 cases in Delhi. The probability distribution analysis reveals that approximately 80% of the total confirmed cases were registered when the average temperature was higher than 30°C. The present study finds a prominent relationship between different environmental factors and COVID-19 transmission in Delhi. However, further detailed analysis over different parts of entire India is required to get a complete picture and solid conclusion.