Impact of Cloud Condensation Nuclei Reduction on Cloud Characteristics and Solar Radiation during COVID-19 Lockdown 2020 in Moscow

We used MODIS observations to retrieve number concentration of cloud droplets (N-d) at cloud lower boundary during spring 2018-2020 for the Moscow region. Looking through the similar synoptic situations of the northern clear air advection, we obtained N-d within the limits of 200-300 cm(-3). During the lockdown period, with similar northern advection conditions, the reduction of N-d on 40-50 cm(-3) (or 14-16%), with the increase in droplet effective radius by 8 +/- 1% and cloud optical thickness reduction by 5 +/- 2%, was observed in contrast to the values in typical conditions in 2018-2019. We used these values for setting up corresponding parameters in numerical simulations with the COSMO-Ru model. According to the numerical experiments, we showed that the observed reduction in cloud droplet concentration by 50 cm(-3) provides a 5-9 W/m(2) (or 9-11%) increase in global irradiance at ground in overcast cloud conditions with LWP = 200-400 g/m(2).

Automated summary

This study used MODIS observations to study the changes in cloud droplet concentration in the Moscow region during the spring of 2018-2020. The results showed that during the lockdown period, there was a decrease in cloud droplet concentration by 40-50 cm(-3), an increase in droplet effective radius by 8 +/- 1%, and a reduction in cloud optical thickness by 5 +/- 2%.