Jun Inoue

Atmospheric mineral dust and black carbon (BC) aerosols play important roles in the Earth's climate system, yet direct observations over the Southern Ocean (SO) are scarce. In this study, we present the characteristics of airborne water‐insoluble particles (WIPs) collected during a cruise of the R/V Shirase in the Australian and Indian sectors of the SO from December 2022 to March 2023. Using a complex amplitude sensor, we measured complex scattering amplitude of individual WIPs to classify into dust‐like (0.50–2.5 μm in diameter) and BC‐like (0.15–0.50 μm in diameter) particles. The mass concentrations of dust‐like and BC‐like aerosols were 0.0–6.4 ng m ⁻³ and 0.079–3.8 ng m ⁻³ , respectively. The highest concentrations of both were observed when the R/V Shirase was located in a mid‐latitude region closest to Australia, indicating strong influence of the emission from mid‐latitude sources. The lowest concentration of BC‐like aerosols was observed in a sample collected when the ship was near the Antarctic coast and the air mass would be rarely influenced by mid‐latitude emissions. However, the dust‐like aerosol concentration in the same sample was relatively higher than that collected in the most remote offshore region away from both mid‐latitude and Antarctic continents, suggesting a potential source of dust aerosols. Despite a case study based on a limited number of samples, this study fills an observational gap by providing quantitative data of mineral dust and BC aerosols over the SO, providing new insights into their sources and climate effects.

Low‐level clouds over the Southern Ocean (SO) exert a strong influence on surface radiation, yet their representation in reanalyses and climate models remains uncertain. We evaluated cloud properties and surface radiative fluxes from ERA5, MERRA‐2, and the CAM‐ATRAS model using observations obtained over the SO by Japan's R/V Shirase during December 2022 and March 2023. ERA5 and MERRA‐2 overestimate the frequency of low‐level clouds with a base below 1 km. Although CAM‐ATRAS also overestimates very low clouds, it shows the best overall agreement with observations in cloud occurrence and phase. Despite the high frequency of low‐level clouds, all data sets underestimate downward longwave (DLW) radiation. Cold bias and cloud phase bias likely reduce cloud‐base emissivity and contribute to underestimated DLW radiation. Aerosol sensitivity experiments using CAM‐ATRAS indicate that enhanced cloud condensation nuclei concentrations increase low‐level cloud frequency but have a limited impact on surface radiative fluxes.

Precipitation is key to the water budget of inland Antarctica, with extreme precipitation events strongly influencing snowfall and surface climatology. To investigate the contribution and trends of such events at Dome Fuji station (DF) in inland Antarctica, this study analyzed precipitation variability using the ERA5 product validated against observational data from February 2003 to January 2004. ERA5 more accurately reproduces surface temperature, downward radiation, wind speed, surface pressure, and cloudiness throughout the year compared with the previous reanalysis, ERA‐Interim. Although precipitation in ERA5 is slightly underestimated (by approximately 14%), the peak precipitation amount and rapid temperature increase observed during an extreme precipitation event in early November 2003, caused by high‐pressure blocking with a strong ridge near 45°E, is greatly improved compared with the previous reanalysis. Over a 46‐year period (1979–2024), bias‐corrected ERA5 data show a statistically significant increase in the annual precipitation amount at DF at the 99% confidence level, primarily because of an increase in the number of precipitation event days. Application of k‐means clustering analysis to the 46‐year precipitation distribution revealed that the frequency of occurrence of a blocking ridge near 45°E, which favors precipitation over Dronning Maud Land, increased and deepened southward. The change in blocking was not uniform but exhibited periodic variability. Interannual variability of precipitation at DF shows a strong correlation with that of sea surface temperature in the subtropical South Atlantic Ocean. Therefore, it is suggested that periodic changes in sea surface temperature might affect the synchronized blocking high that brings precipitation to the DF.

Atmospheric rivers (ARs) typically lead to intense precipitation and play an essential role in the Antarctic ice surface mass balance. Their detection in the Antarctic region is challenging, preventing consistent evaluation of their role at a global scale. In this study, we extended a conventional method and developed a new three‐dimensional AR detection algorithm, which we applied over Antarctica. The results showed that the detected ARs at Dome Fuji during the 44th Japanese Antarctic Research Expedition were associated with more than half of the significant precipitation events and contributed to approximately 40% of the total precipitation. Climatologically, from 1979 to 2023, the ARs occurred less than 10% of the time but contributed to 30%–60% of the annual total precipitation. Furthermore, AR‐related precipitation effectively captured the regional variability of long‐term trends in Antarctic precipitation, indicating that ARs exert substantial control over Antarctic precipitation variability.

Atmospheric mineral dust and black carbon (BC) aerosols play important roles in the Earth’s climate system, yet direct observations over the Southern Ocean (SO) are scarce. In this study, we present the characteristics of airborne water-insoluble particles collected during a cruise of the R/V Shirase in the Australian and Indian sectors of the SO from December 2022 to March 2023. Using a complex amplitude sensor, we measured complex scattering amplitude of individual water-insoluble particles. Based on the measured complex scattering amplitude, which depends on particle composition, size, and shape, we classified into dust-like (0.50–5.0 µm in diameter) and BC-like (0.15–0.50 µm in diameter) particles. The number (mass) concentrations of dust-like and BC-like aerosols were 0.013–9.2 L-1 (0.52–32 ng m-3) and 5.4–2.3×102 L-1 (0.065–2.1 ng m-3), respectively. For dust-like aerosols, the highest concentration was observed in a region closest to Australia in this cruise, indicating strong influence of the emission from mid-latitude continents. Furthermore, a sample collected nearest to the Antarctic coast exhibited relatively high dust-like aerosol concentrations than that collected in most offshore regions away from both mid-latitude and Antarctic continents, suggesting that the Antarctic continent might be a potential source of dust aerosols. For BC-like aerosols, their concentration showed a clear latitudinal gradient, decreasing with distance from mid-latitude sources even close to the Antarctic coast.

Melt pond is a common and important feature of the Arctic in the summer season. Melt ponds provide unique microbial habitats with high light availability, which can promote photosynthesis. Therefore, melt ponds play an important role for nutrient cycling at the ice‐ocean interface. However, the changes in nutrient dynamics in and under the sea ice resulting from melt pond formation are poorly understood. To elucidate melt pond nutrient (NO ₃ ⁻ , NO ₂ ⁻ , NH ₄ ⁺ , PO ₄ ³⁻ , and Si(OH) ₄ ) dynamics and their relationship with the melt pond bottom ice, which is sea ice right beneath the floor of a melt pond, in the Central Arctic Ocean during late summer, melt pond water and bottom sea‐ice samples were collected during the MOSAiC Expedition (2019–2020). Comparison with the dilution line based on winter surface seawater, which is a source of sea ice, suggest that nutrients in the melt ponds are consumed by algae or other organisms, and then remineralized at the pond bottom. Nutrients then percolated downward through the porous bottom ice. Melt pond water was completely exchanged with surrounding seawater (lead or under‐ice seawater) and snow derived water. If the surrounding seawater and snow are rich in nutrients, the exchange promotes photosynthesis within the melt pond water and can enhance nutrient accumulation within the pond bottom ice.

Ocean circulation around the Antarctic coastal margins plays a critical role in heat delivery to Antarctica, melting ice shelves. However, until recently, satellite‐based sea‐level observations have been limited by the presence of sea ice. With improved algorithms, it is now possible to monitor sea‐level fluctuations over most of the Southern Ocean, including sea ice‐covered areas. We identified several clockwise gyres along East Antarctic coastal margins in satellite‐derived dynamic ocean topography (DOT). Singular value decomposition analyses revealed that the coastal DOT deepening and anomalous clockwise circulation consistently occur during the positive phase of the southern annular mode (SAM), which is associated with negative wind stress curl anomalies. Shifting of the SAM to a more positive phase since the 20th century and its expected continuation into the coming century could lead to enhanced clockwise gyres along East Antarctica, contributing to increased poleward ocean heat transport.

During the Uncrewed Aircraft Systems Demonstration Campaign (UAS‐DC), led by the World Meteorological Organization (WMO), twice‐daily meteorological profiling was conducted for 2 months at the Meteorological Research Institute in Tsukuba City (Japan), which is identified as a densely inhabited district. This campaign was instigated to assess the feasibility of obtaining continuous daily measurements for the long term (over a period of more than 1 month), to distribute the data in a format designated for numerical weather prediction, and to evaluate data quality compared to conventional meteorological data. Three types of uncrewed aircraft systems were utilized, that is, a meteorological medium‐sized hexacopter and medium‐ and small‐sized commercial drones with meteorological sensors attached. The maximum flight height was limited to 900 m above ground level owing to airspace regulations around the observation site. Compared with routine radiosonde data, the bias of air temperature, relative humidity, and wind speed measurements was less than 0.3 K, 1.5%, and 0.6 m , respectively, thereby meeting WMO requirements. Moreover, data transfer to the WMO‐prepared repository was completed within 30 min after measurement acquisition. Based on user experience, several aspects regarding the UAS‐DC campaign were discussed from the perspective of sustainable operation and atmospheric boundary layer research.

Ocean circulation around the Antarctic coastal margins plays a critical role in heat delivery to Antarctica, melting ice shelves. However, until recently, satellite-based sea-level observations have been limited by the presence of sea ice. With improved algorithms, it is now possible to monitor sea-level fluctuations over most of the Southern Ocean, including sea ice-covered areas. We identified several clockwise gyres along East Antarctic coastal margins in satellite-derived dynamic ocean topography (DOT). Singular value decomposition analyses revealed that the coastal DOT deepening and anomalous clockwise circulation consistently occur during the positive phase of the southern annular mode (SAM), which is associated with negative wind stress curl anomalies. Shifting of the SAM to a more positive phase since the 20th century and its expected continuation into the coming century could lead to enhanced clockwise gyres along East Antarctica, contributing to increased poleward ocean heat transport.