Masanori Yabuki

Long-term polarization-sensitive micro-pulse lidar (PMPL) observations provide valuable information on aerosol transport over coastal Antarctica. Still, the interpretation of aerosolenhanced layers has largely relied on manual inspection of quick-look images. Here we propose an objective image-based framework for identifying aerosol transport regimes from PMPL observations at Syowa Station, East Antarctica, during 2016–2022. Aerosol-enhanced layers were first detected using the backscatter ratio, its temporal variability, and the particle depolarization ratio. Image features were then extracted from PMPL quick-look images using a pre-trained ResNet50 convolutional neural network, standardized, reduced in dimensionality by principal component analysis, and classified by k-means clustering. A total of 254 aerosol events were identified and classified into two transport regimes with distinct vertical structures: one characterized by vertically extensive aerosol layers and the other by shallow, near-surface layers. Independent composite analyses of ERA5 500-hPa geopotential height anomalies indicate that the two regimes occur under different synoptic environments. These results suggest that PMPL observations alone contain sufficient information to objectively identify physically meaningful aerosol transport regimes without using meteorological information in the classification. The framework provides a reproducible tool for long-term analyses of Antarctic aerosol transport.

TKE dissipation rate can be estimated from VHF/UHF Doppler radars. The currently used model for stably stratified conditions seems to be challenged by comparisons with UAV measurements. An alternative model derived for weakly stable conditions (Basu and Holtslag, EFM, 21, 1273, 2021) provides better agreements for shear-generated turbulent layers.

Black carbon (BC) aerosol deposited in and onto Arctic snow increases the snow's absorption of solar radiation and accelerates snowmelt. Concentrations of BC in the Arctic atmosphere and snow are controlled by wet deposition; however, details of this process are poorly understood owing to the scarcity of time‐resolved measurements of BC in hydrometeors. We measured mass concentrations of BC in hydrometeors (C_MBC) and in air (M_BC) with 16% and 15% accuracies, respectively, at Ny‐Ålesund, Svalbard during 2012–2019. Median monthly M_BC and C_MBC values showed similar seasonal variations, being high in winter‐spring and low in summer. Median monthly BC wet deposition mass flux (F_MBC) was highest in winter and lowest in summer, associated with seasonal patterns of C_MBC and precipitation. Seasonally averaged BC size distributions in hydrometeors were similar except for summer. Measurements of M_BC and C_MBC in spring 2017 showed a size‐independent removal efficiency, indicating that BC‐containing particles were efficiently activated into cloud droplets. These observations at Ny‐Ålesund were compared with observations at Barrow, Alaska, during 2013–2017. The near‐surface M_BC at Ny‐Ålesund and Barrow had similar seasonal patterns; however, the two sites differed in C_MBC and F_MBC. In summer, C_MBC was low at Ny‐Ålesund but moderate at Barrow, likely reflecting differences in M_BC in the lower troposphere. Seasonally averaged BC size distributions in hydrometeors were similar at both sites, suggesting that average BC size distributions are similar in the Arctic lower troposphere. The efficiency of BC removal tends to be size‐independent during transport, leading to the observed similarity.

Atmospheric sea-salt and halogen cycles play important roles in atmospheric science and chemistry including cloud processes and oxidation capacity in the Antarctic troposphere.

A Raman lidar with a deep ultraviolet laser was constructed to continuously monitor water vapor distributions in the atmospheric boundary layer for twenty-four hours. We employ a laser at a wavelength of 266 nm and detects the light separated into an elastic backscatter signal and vibrational Raman signals of oxygen, nitrogen, and water vapor. The lidar was encased in a temperature-controlled and vibration-isolated compact container, resistant to a variety of environmental conditions. Water vapor profile observations were made for twelve months from November 24, 2017, to November 29, 2018. These observations were compared with collocated radiosonde measurements for daytime and nighttime conditions.

Under stably stratified conditions, the dissipation rate ε of turbulence kinetic energy (TKE) is related to the structure function parameter for temperature , through the buoyancy frequency and the so-called mixing efficiency. A similar relationship does not exist for convective turbulence. In this paper, we propose an analytical expression relating ε and in the convective boundary layer (CBL), by taking into account the effects of nonlocal heat transport under convective conditions using the Deardorff countergradient model. Measurements using unmanned aerial vehicles (UAVs) equipped with high-frequency response sensors to measure velocity and temperature fluctuations obtained during the two field campaigns conducted at Shigaraki MU observatory in June 2016 and 2017 are used to test this relationship between ε and in the CBL. The selection of CBL cases for analysis was aided by auxiliary measurements from additional sensors (mainly radars), and these are described. Comparison with earlier results in the literature suggests that the proposed relationship works, if the countergradient term γ _D in the Deardorff model, which is proportional to the ratio of the variances of potential temperature θ and vertical velocity w, is evaluated from in situ (airplane and UAV) observational data, but fails if evaluated from large-eddy simulation (LES) results. This appears to be caused by the tendency of the variance of θ in the upper part of the CBL and at the bottom of the entrainment zone to be underestimated by LES relative to in situ measurements from UAVs and aircraft. We discuss this anomaly and explore reasons for it.