Polar lows (PLs) are intense mesoscale weather systems that often cause severe storm winds in the Nordic Seas but were considered as being exceedingly rare in the Pacific Arctic region before sea ice decline. Here, we explore four PLs observed on 18–22 October 2017 in the Chukchi and Beaufort Seas—an area with an exceptionally sparse observation network. The study is based on the combined use of the satellite microwave measurements, as well as infrared imagery, the ERA5, MERRA-2 and NCEP-CFSv2 reanalysis data sets. An unusually strong PLs pair developed near the marginal ice zone during a marine-cold air outbreak in anomalously low sea ice extent conditions. PLs pair moved southward as a mesocyclonic system called the “merry-go-round”, under the upper-level tropospheric vortex with a cold core. Multi-sensor satellite measurements show that, in the mature stage, a PL pair had near-surface wind speeds (W) close to hurricane force—over 30 m/s. Comparison analysis of W distributions within the strongest PL showed that all reanalysis data sets reasonably reproduce the PL median wind speed but underestimate its extreme values by 15–23%. The reanalysis data sets detected only two PLs with horizontal scales of over 220 km. Tracks of identified PLs for all data sets are in good agreement with the ones obtained from satellite images capturing the main features of the mesoscale weather system propagation. For the track of the strongest PL event, ERA5 exhibited the most accordance with satellite observations with a tracking error of 50–60 km.

In the present article, cold-air outbreak (CAO) and polar low (PL) events were examined over the Chukchi Sea during low sea ice extent of the basin in the November-December period, 2015. An analysis of weather events was performed using multisensor satellite measurements, the NCEP Climate Forecast System, version 2 (CFSv2), and Arctic System Reanalysis, version 2 (ASR2). The CFSv2 data showed that the most intense cold advection occurred at the 1000-900 hPa boundary layer. It was shown that CAO had been developing from November 30 to December 6 and was accompanied by the sea surface wind speed exceeding 20 m/s and rapid formation and drift of sea ice. Analysis of the sea ice response to the CAO showed fast freezing of the Chukchi Sea for seven days indicating excessive heat loss of the water basin. In addition, significant increase in the open and very open ice areas was observed. These areas could be exposed to excessive cold atmosphere, releasing heat into the atmosphere. PL events have been identified during intensive mesocyclogenesis over the sea during 15-17 November. Weather conditions were characterized by the values of wind speed reaching 15-17 m/s and dry air with total water vapor content (5-7 kg/m²). Analysis of the synthetic aperture radar image revealed the position and horizontal size of the meso-α-cyclone, the fine structure of the mesoscale frontal system of the PL forming meso-γ-vortices, and the wave-like line of the horizontal wind shear in the local convergence zone. The representation of PL events in sea level pressure and near-surface wind speed fields from the ASR2 and CFSv2 datasets was ambiguous. However, the satellite-based and CFSv2 wind speeds better agreed for high-wind conditions.

Here, we examine extreme ocean winds associated with intense wintertime extratropical windstorms over the North Pacific. The study was mainly based on NASA Soil Moisture Active Passive (SMAP) L-band radiometer observations allowing the retrieval of ocean wind speeds up to 70 m/s regardless of precipitation intensity. Additionally, we assessed the ability of atmospheric reanalysis ERA5 and the Climate Forecast System Version 2 (CFSv2) to reproduce high-wind features within severe windstorms, particularly those associated with “explosive” cyclogenesis. The analysis identified 145 windstorm events with hurricane-force (HF) wind zones within the SMAP L-band radiometer swath from 2015 to 2023. These windstorms develop most frequently over two areas: southeast of Kamchatka and south of Alaska, spanning 40–47°N latitudes. Both reanalysis datasets significantly underestimated HF wind speeds compared to SMAP measurements, but CFSv2 tends to reproduce more-intense windstorms than ERA5. Among the notable new findings is that the SMAP data revealed two distinct groups in maximum wind speed distribution, indicating the existence of a separate class of severe windstorm events with a distinct mechanism for extreme wind formation related probably to a Shapiro–Keyser cyclogenesis and the presence of sting jet (SJ) feature. The study highlights the potential of SMAP measurements to study wind extremes and underscores the need for improvements in operational predictive models to better reproduce the formation of SJ windstorms.

Freezing precipitation and the resultant ice glaze can have catastrophic impacts on urban infrastructure, the environment, forests, and various industries, including transportation, energy, and agriculture. In this study, we develop and evaluate regional algorithms for detecting freezing precipitations in the Far East, utilizing the ERA5 reanalysis dataset from the European Centre for Medium-Range Weather Forecasts, along with standard meteorological observations for 20 cold seasons (September–May) from 2004 to 2024. We propose modified diagnostic algorithms based on vertical atmospheric temperature and humidity profiles, as well as near-surface characteristics. Additionally, we apply a majority voting ensemble (MVE) technique to integrate outputs from multiple algorithms, thereby enhancing classification accuracy. Evaluation of detection skills shows significant improvements over the original method developed at the Finnish Meteorological Institute and the ERA5 precipitation-type product. The MVE-based method demonstrates optimal verification statistics. Furthermore, the modified algorithms validly reproduce the spatially averaged inter-annual variability of freezing precipitation activity in both continental (mean correlation of 0.93) and island (correlation of 0.54) regions. Overall, our findings offer a more effective and valuable tool for operational activities and climatological assessments in the Far East.

В этой работе продемонстрированы возможности оптических наблюдений со спутников Sentinel-2, 3 для изучения связанных физических и биологических процессов в поверхностном слое океане во время интенсивного осеннего цветения фитопланктона у юго-восточного побережья Камчатки в сентябре 2020 г. В Авачинском заливе цветение водорослей проявлялось в виде областей с высокой концентрацией хлорофилла-а, придавая морской поверхности соответствующий темно-зеленый оттенок. На композитном изображении с разрешением 10 м из-за выраженных спектральных различий на морской поверхности выделялись скопления водорослей, организованные в сложные системы мезомасштабных и субмезомасштабных взаимодействующих вихревых структур. По данным реанализа ERA5 установлено, что среднемесячная температура поверхности океана (ТПО) акватории Авачинского залива в сентябре 2020 г. показала положительную аномалию с максимумом ТПО (12.0°С) за последние 42 года при климатической норме 10.4°С. Мы допускаем, что при сохранении тенденции роста в ближайшие годы этот максимум будет превышен. The paper demonstrates the possibilities of optical observations from the satellites Sentinel-2, 3 for studying linked physical and biological processes in the ocean's surface layer. The specific example of using an observation system for surveillance over intense autumn-flowering of phytoplankton near Kamchatka's southeast shore in September 2020 is considered. In Avachinsky Bay, the microalgae flowering manifested as areas with high chlorophyll-a concentration, coloring the sea surface into the corresponding dark green shade. On a composite image with a resolution of 10 m, significant spectral differences on the sea surface highlighted conglomerates of algae organized in complex systems of mesoscale and submesoscale interacting vortex structures. According to ERA5 reanalysis, it was found that the average monthly sea-surface temperature in Avachinsky Bay in September 2020 demonstrated a positive anomaly with a maximum (12,0° C) over the past 42 years with a climate normal of 10,4° C. It is assumed that this maximum will be surpassed if the current trends continue.