## 2 Data and Methods
### Initial Data for Climatic Atlas Maps  
For a production of maps of hydrometeorological parameters (surface air temperature, total precipitation, wind speed at the Earth's surface, soil temperature, soil moisture content, air humidity, and snow cover thickness) presented in the atlas, the authors used the MERRA-2 reanalysis data for the period 1980-2021. MERRA-2 dataset (Modern-Era Retrospective Analysis for Research and Applications, version 2) [14] represents the results of reprocessing of a massive catalog of information on climatic parameters, such as air temperature and humidity, atmospheric pressure, wind speed, precipitation, etc. Generally, the database is a set of global daily data on the state of the atmosphere and the Earth's surface, collected over several decades. This mission was implemented at the Global Modeling and Assimilation Office (GMAO) under the direction of the U.S. National Aeronautics and Space Administration (NASA). MERRA was originally created for integration of satellite measurements into a unified climate catalog to facilitate the description of the global hydrological cycle from the Earth's atmosphere to the surface of the planet. This mission was launched in 1979, but by 2016 it was closed due to certain disadvantages: measurement system errors (e.g., non-physical measurement jumps when the observing system changes), imbalances in some atmospheric and terrestrial hydrological parameters, degraded representation of the upper stratosphere, and system limitations that prevented inclusion of new satellite data sources [14]. The main goal of reprocessing and refining the MERRA mission was to provide continuous near-real-time climate analysis (data are published with delays of a couple of weeks). Accordingly, MERRA-2 was designed as a reanalysis that uses the latest developments in data measurement and processing to address the known limitations and disadvantages of MERRA. The reanalysis provides long-term monitoring and comprehensive analysis of Earth conditions by means of system integration of atmospheric, ocean, land, and physical and chemical information. Other updates include information on ozone monitoring and the use of precipitation observations. On the technical side, the MERRA-2 observing system has been equipped with additional instruments that register the following parameters [15]:  
* Atmospheric motion vectors from AVHRR (Advanced Very High Resolution Radiometer);
* Surface wind speed from SSMIS (Special Sensor Microwave Imager/Sounder);
* Temperature profiles and ozone characteristics from EOS (Earth Observing System) Aura MLS (Microwave Limb Sounder);
* Total amount of ozone in the column from EOS (Earth Observing System) Aura OMI (Ozone Monitoring Instrument);
* Deviation angle from GPSRO (Global Positioning System Radio Occultation);
* Microwave sounding from ATMS (Advanced Technology Microwave Sounder);
* Hyper spectral infrared radiation from IASI (Infrared Atmospheric Sounding Interferometer) on MetOp-A and MetOp-B (Meteorological Operational Satellites) and from CrIS (Cross-Track Infrared Sounder) on SNPP (Suomi National Polar-Orbiting Partnership);
* Geostationary radiation from MSG (Meteosat Second Generation) SEVIRI (Spinning Enhanced Visible Infrared Imager). The rest of the observation system remained unchanged as in the original MERRA mission except for improvements of the sensors for measuring surface wind speed and ozone content. These sensors were changed to more advanced models during the mission development. Today, MERRA-2 is known as one of the most accurate global representations of climatic data for land and ocean [14]. This results from the extensive volume of output data available for processing along with high spatial resolution, which is important for the subsequent modeling of regional weather and climate conditions. For example, [PERSON] [16] demonstrated the high-quality representation of precipitation and temperatures over the American continent derived from MERRA data. [PERSON] et al.