## 1 Introduction  
Polar lows (PLs) are convective mesocyclones with a spiraliform or \"comma cloud\" signature and nearly cloud-free central area (eye), which are formed in the cold air masses over the open water of mid-high-latitudes poleward from the main tropospheric front (polar or arctic). Due to the explosive cyclogenesis, intense PLs are often called Arctic hurricanes or \"Arctic bombs\" [1]. These mesoscale systems--with lifetime ranging from several hours to 3 days and horizontal sizes up to 1000 km (with predominant sizes of 200-600 km)--are often accompanied by storm and hurricane-force winds, high waves, heavy precipitations and vessel icing. Because of the small size and short lifecycle, the PLs are not always resolved by weather charts and numerical weather prediction models [1]. However, their cloud signatures are clearly identified on satellite visible and infrared (IR) images. Satellite observations that began in the 1960s gave a start to the systematic study of marine mesoscale weather systems.  
One of the trigger mechanisms for convective and mesocyclonic activity is the intensification of air-sea interaction during cold air outbreaks (CAO) at the rear of synoptic-scale cyclones when dry cold air mass moves over the relatively warm sea surface. As the air-sea interaction intensifies, deep convection, cloud cells and mesovortices are developed [1]. The main regions of mesoscale cyclogenesis in the Northern Hemisphere are the North Atlantic/Nordic Seas [2; 3; 4; 5] and the North Pacific [6; 7; 8; 9; 10; 11]. In the Pacific Arctic (PA) region, the PL formation conditions were previously considered unfavorable because of a predominance of non-seasonal sea ice cover and the absence of warm ocean currents. Therefore, there is a lack of systematic studies of mesoscale cyclogenesis in this area. Only a few works [1; 12] have reported the development of mesocyclones with storm winds over the Beaufort Sea which can be classified as PLs. In addition, [PERSON] [13] detected \"local mesocyclones\" (with a diameter of 100 km) over the Eurasian Arctic and Bering Sea coastal zones, which developed under the influence of orography on the oncoming airflow.  
Since the 21 st century, the rapid Arctic sea ice retreat has led to a more variable seasonality of ice cover and a stronger meridionality of the atmospheric circulation [14; 15; 16]. It resulted in the earlier onset of sea ice melting [17] or its later autumn freeze-up [18] and, consequently, the intensification of mesocyclonic activity in the PA [19; 20; 21]. However, without systematic studies and sufficient PL statistics, we cannot conclude whether climate change in the Arctic affects the frequency of severe PLs in the PA. Meanwhile, such studies are encouraged by the intensified exploitation of the Northern Sea Route, the development of offshore platforms on the Arctic shelf and the expansion of new fishery areas.  
In this work, we examine unusually strong PLs observed over the Chukchi and Beaufort seas on 18-22 October 2017 combining multi-sensor satellite measurements, ERA5, MERRA-2 and CFSv2 reanalysis datasets. The study addresses the following questions:  
* Can a multi-sensor approach provide insights into the development of strong PLs?
* How accurately do the ERA5, MERRA-2 and CFSv2 reanalysis datasets capture the development of the PLs in comparison with satellite observations?
* What are reanalyzes strengths and weaknesses in the PLs identification, tracking and representation of its intensity?  
Section 2 describes the satellite measurements, MERRA-2, CFSv2 and ERA5 reanalysis datasets used in the study and the methods applied. Section 3 gives a synoptic review and analysis of the PLs evolution and presents a comparative analysis of near sea surface wind speed. Finally, a summary and conclusions are given in Section 4.