Cloud types frequency over Poland in satellite-based (MODIS) and surface-based (SYNOP) observations

Clouds significantly affect Earth's energy budget by absorbing, reflecting and transmitting short- and long-wave radiation. They can either intensify, or weaken the greenhouse effect. The overall impact of cloudiness on radiating transfer depends on macro- and micro-physical properties of clouds (e.g., optical thickness, altitude, water content, cloud drop effective radius) and still remains one of the greatest uncertainties in global climate predictions.

Recent studies based on traditional, synoptic (surface) data have shown several statistically significant trends in cloud types (genera) frequency over Poland. Those changes included an increase in high and convective clouds, along with a decrease in Stratus, Altostratus and Nimbostratus. As the ability to observe mid and high-level clouds from the ground is limited due to clouds overlapping, in this research we aim to explore whether these trends can be confirmed by satellite records.

We use Moderate Resolution Imaging Spectroradiometer (MODIS) data, restricted to the area of Poland, as well as surface (SYNOP) observations of cloud genera from the country's 27 ground-based stations for the period 2003–2021. In order to define cloud types from MODIS records, we analyze cloud optical thickness (COT) and cloud top pressure (CTP) parameters and use International Satellite Cloud Climatology Project (ISCCP) COT–CTP classification.

We found that while for some cloud types (Cirrus, Altostratus + Nimbostratus and Cumulus) MODIS and SYNOP show the similar trends over the last two decades, for other cloud types (Cumulonimbus, Altocumulus, Stratocumulus) the two sources of data are not consistent. Hence, we conclude that they should be treated as independent rather than complementary. Additionally, we demonstrated that the increase in high-level clouds over Poland, which has been observed by other authors who based their research on synoptic data, is not due to a decrease in the frequency of low- and mid-level clouds, but can be confirmed by satellite records.

This research was funded by the University of Warsaw.