The intense mesoscale cyclones (MCs) with a comma or spiral cloud system are often observed over the ocean in a cold season. Their size is 100-1000 km and they exist from a few hours till three days. Parameters and development conditions of MCs are studied insufficiently in comparison with synoptic scale cyclones. MCs are an extreme navigational and coastal zone hazard because of explosive formation character, strong winds and precipitation. The small sizes and sparse hydrometeorological observations over the ocean complicate their revealing on weather maps and forecasting. The best technique for MC research is satellite multisensory sensing. Visible and infrared (IR) images of cloudiness acquired from Aqua and Terra MODIS and NOAA AVHRR since October 2003 till April 2011 have been used for detection of MCs over the Northern Pacific Ocean. QuikSCAT- and MetOp ASCAT-derived wind fields, ADEOS-II AMSR- and Aqua AMSR-E-retrievals provided quantitative information about the atmospheric and ocean surface parameters important for MC research. Additionally, the weather maps and radiosonde data from island and coastal stations were collected. Envisat Synthetic Aperture Radar (SAR) images have been obtained for some MCs. 150-250 MCs were formed over the Japan, Okhotsk and Western Bering Seas during the cold periods (October-April) 2003-2011. Mesocyclones from 200 to 400 km in extent prevailed. The peak of mesoscale cyclogenesis was observed in December-February. The number of MCs at a definite season depended considerably on the total duration of cold air outbreaks. Spatial and time variability in MCs formation was often connected with trajectories of synoptic scale cyclones. AMSR and AMSR-E original retrieval algorithms were built up with the use of database of the simulated brightness temperatures computed by numerical integration of microwave radiative transfer equation in the atmosphere-ocean system. Ship and island radiosonde data and constructed vertical profiles of cloud liquid water content served as input data. Retrievals include the total water vapor content V, total cloud liquid water content Q and sea surface wind speed W. AMSR and AMSR-E retrievals show a distinct mesoscale signals in the fields of V, Q and W. The V-values changed from 4-6 till 10-15 kg/m2 and Q-values were equal in average 0.1-0.2 kg/m2 but sometimes reached 0.5 kg/m2. Sea surface wind speed was 10-20 m/s. Cyclonic circulation was also detected in scatterometer-derived W fields. The difference between V-values in the MC area and in the continental air mass changed between 2 and 15 kg/m2 and increased with the increase of wind speed. The most pronounced MCs are investigated in detail. The structure of the most intense MCs is depicted by high W values (more 20 m/s), high W and V gradients and a large sea surface wind speed shear. The collocation of AMSR-E-derived V- and W fields with radiosonde (V) and scatterometer (W)-derived parameters shows good agreement.