Syowa Station Research Articles

Quasi-12 h inertia–gravity waves in the lower mesosphere observed by the PANSY radar at Syowa Station (39.6° E, 69.0° S)

Abstract. The first observations made by a complete PANSY radar system (Program of the Antarctic Syowa MST/IS Radar) installed at Syowa Station (39.6° E, 69.0° S) were successfully performed from 16 to 24 March 2015. Over this period, quasi-half-day period (12 h) disturbances in the lower mesosphere at heights of 70 to 80 km were observed. Estimated vertical wavelengths, wave periods and vertical phase velocities of the disturbances were approximately 13.7 km, 12.3 h and −0.3 m s−1, respectively. Under the working hypothesis that such disturbances are attributable to inertia–gravity waves, wave parameters are estimated using a hodograph analysis. The estimated horizontal wavelengths are longer than 1100 km, and the wavenumber vectors tend to point northeastward or southwestward. Using the nonhydrostatic numerical model with a model top of 87 km, quasi-12 h disturbances in the mesosphere were successfully simulated. We show that quasi-12 h disturbances are due to wave-like disturbances with horizontal wavelengths longer than 1400 km and are not due to semidiurnal migrating tides. Wave parameters, such as horizontal wavelengths, vertical wavelengths and wave periods, simulated by the model agree well with those estimated by the PANSY radar observations under the abovementioned assumption. The parameters of the simulated waves are consistent with the dispersion relationship of the inertia–gravity wave. These results indicate that the quasi-12 h disturbances observed by the PANSY radar are attributable to large-scale inertia–gravity waves. By examining a residual of the nonlinear balance equation, it is inferred that the inertia–gravity waves are likely generated by the spontaneous radiation mechanism of two different jet streams. One is the midlatitude tropospheric jet around the tropopause while the other is the polar night jet. Large vertical fluxes of zonal and meridional momentum associated with large-scale inertia–gravity waves are distributed across a slanted region from the midlatitude lower stratosphere to the polar mesosphere in the meridional cross section. Moreover, the vertical flux of the zonal momentum has a strong negative peak in the mesosphere, suggesting that some large-scale inertia–gravity waves originate in the upper stratosphere.

A new species and the shallowest record of Flabegraviera Salazar-Vallejo, 2012 (Annelida: Flabelligeridae) from Antarctica.

A new species of polychaete, Flabegraviera fujiae sp. nov., is described and the first report of F. mundata (Gravier, 1906) from the shallow water around Syowa Station, Antarctica, is presented. Flabegraviera fujiae sp. nov. resembles F. profunda Salazar-Vallejo, 2012 but is discriminated from the latter by having eyes and an exposed cephalic cage. The specimen of F. mundata was collected from a depth of 8 m, providing the shallowest record of this species to date.

Seismic Tremors and Their Relation to Cryosphere Dynamics in April 2015 around the Lützow-Holm Bay, East Antarctica

Characteristics and statistics of seismic tremors occurring during April 2015 were investigated by using short-period and broadband seismographs deployed at Syowa Station (SYO), in the Lutzow-Holm Bay (LHB), East Antarctica. In order to examine a relationship between surface environments in particular cryosphere variation, the MODIS satellite images were utilized for comparison with the detected tremor events. Since a large volume of sea-ice was discharged during the April, together with several large icebergs passed through from the west to the east at northern edge of the fast sea-ice of LHB, it was expected to detect seismic tremors involving cryospehre dynamics. During the month, a total number of 49 tremor events including short duration ice shocks were identified. Majority of the events (N = 39) had their duration times more than 15 minutes, which were divided into both tremors and ice shocks on the basis of experienced definition at SYO. Cryospheric sources recorded by seismic tremors were classified into several origins (collision, calving, crevassing, crashing, etc.): “crevassing events” along the large cracks inside the fast sea-ice in LHB (04 April), “discharge events” of fast sea-ice from the Bay (07 April), “collision events” between iceberg and the edge of fast sea-ice (14 April), “crashing movement” between fragmentation of fast sea-ice and packed sea-ice (18 April), and other origins. In particular, strong amplitude tremors with harmonic overtones were assumed to be occurred independently from whether condition, because these overtone tremors were identified at less stormy days by comparison with infrasound data at SYO.

Statistics of Seismic Tremors with Harmonic Overtones Recorded at Syowa Station, Antarctica: October 2014-March 2015

During the period from October 2014 to March 2015, a total number of 82 seismic tremors and 66 ice-quakes were identified in both three-component short-period seismographs (HES) and broadband seismographs (STS-1) at Syowa Station (SYO), Antarctica. Statistics of the number of these tremors indicated that many tremors were likely to occur when large increases in temperature and/or wind speed during the period. This implied that the rapid increase in temperature enhanced a melting speed of cryosphere environment with generating seismic energy; the tremors were also excited by stormy conditions, associated with interactive resonance between sea-ices and oceanic swells. The characteristic tremors of harmonic overtones with strong amplitudes were explained by repetitive sources, suggesting inter-glacial asperities such as the collision of icebergs and fast sea-ice, calving of glaciers/ice-streams at the coastal environment of Antarctica. These high amplitude tremors occurred independently from other majority types of events, characterized by non-linear, small amplitude and weak signals at the stormy condition and rapid increase in temperature.

Long-Term Variations in Infrasound Signals Observed at Syowa Station, Antarctica: 2008-2014

Long-term Infrasound data at Syowa Station (SYO; 39E, 69S), in the Lützow-Holm Bay (LHB), East Antarctica was analyzed during the period from 2008 to 2014. Seasonal variations in microbaroms and high-frequency harmonic tremors were especially investigated. Infrasound data were strongly involved in local dynamics of surface environments. The microbaroms have relatively low amplitudes in austral winters by extending area of sea-ice around LHB, with decreasing oceanic swell loading effects. The other reasons of seasonal variations in microbaroms amplitudes were caused by the affections of a number of storms during whole year and snow accumulation over the porous hoses on the infrasound station at SYO. In contrast, non-linear high-frequency harmonic tremors were considered to be caused by the katabatic winds from Antarctic continent flowing in northeast dominant orientation. The high-frequency tremors had characteristics of daily variations in particular in austral summer. It is required to continue more than a few years of observation in order to identify relationships with climate change and global warming effects in the Antarctic. Continuous measurement of infrasound in the coastal margin of Antarctica is a proxy for monitoring multi-sphere interaction between the continent and surrounding Southern Ocean.

Vertical Profiles and Temporal Variations of Greenhouse Gases in the Stratosphere over Syowa Station, Antarctica

Vertical Profiles and Temporal Variations of Greenhouse Gases in the Stratosphere over Syowa Station, Antarctica

南極昭和基地沖における融解期の多年氷のマイクロ波輝度温度特性

衛星搭載マイクロ波放射計による海氷観測は，1978年以降観測を継続しており，海氷面積の変動が明らかになっている．海氷面積の推定には，海氷のマイクロ波輝度温度特性の把握が重要である．融解期の多年氷は，融解の影響により輝度温度特性が変化する．そこで本研究は，融解期の多年氷のマイクロ波輝度温度特性を明らかにすることを目的に観測を行った．観測は，南極昭和基地沖の多年氷上で多年氷表面，積雪内部層，積雪表面の輝度温度を測定し，積雪断面観測を実施した．多年氷表面からのマイクロ波輝度温度は，表面状態によって輝度温度が大きく異なるが，積雪内部層は，湿雪が存在するために輝度温度が一定であった．また，積雪表面の輝度温度は，表面が湿雪の場合は高く，乾雪の場合は乾雪の光学的厚さが増加すると，垂直偏波と水平偏波共に36GHzの方が18GHzより低くなる周波数特性を示した．これらのことから，融解期における昭和基地沖の多年氷のマイクロ波輝度温度は，多年氷上の積雪に湿雪が存在する場合，多年氷の輝度温度は影響せず，海氷上積雪の状態に依存することが明らかになった．

<i>Oncholaimus langhovdensis</i> sp. nov. (Nematoda: Enoplea: Oncholaimida), a New Species of Free-living Marine Nematode from Langhovde, Dronning Maud Land, East Antarctica

A new species of free-living marine nematode, Oncholaimus langhovdensis sp. nov., is described from the intertidal zone of Langhovde (near Syowa Station), Dronning Maud Land, East Antarctica. It closely resembles 11 congeners in the conico-cylindrical tail shape present in males and amphid and excretory pore positions, short spicules, and Demanian system structure present in females. However, it mainly differs from these congeners in body size, de Man's ratios, tail length and shape, and Demanian system structure present in females. Oncholaimus langhovdensis sp. nov. also resembles four congeners known only by females, but it can be distinguished from them based on the tail length and uvette position. In addition to O. langhovdensis sp. nov., two undescribed species (Tripyloididae gen. sp. and Axonolaimidae gen. sp.) and four unidentified species (Sphaerolaimus sp., Oncholaimidae gen. sp., Comesomatidae gen. sp., and Chromadorida fam. gen. sp.) were found from the same locality.

Cystobasidium tubakii and Cystobasidium ongulense, new basidiomycetous yeast species isolated from East Ongul Island, East Antarctica

Two new cold-adapted yeast species, Cystobasidium tubakii sp. nov. and Cystobasidium ongulense sp. nov., were isolated from soil collected from East Ongul Island, East Antarctica, during the 49th Japanese Antarctic Research Expedition (JARE 49). Molecular analysis based on large subunit (LSU) D1/D2 domain and the combined sequences of small subunit (SSU) rDNA, internal transcribed spacer (ITS) region, LSU D1/D2 domain and TEF1 sequences showed that these species are novel. Both species could grow at sub-zero temperatures and in vitamin-free media. These characteristics were likely obtained by the yeasts to survive oligotrophic environments such as that in Antarctica. This is the first report of new fungal species isolated from near the Syowa station in the 60-y history of JARE.

南極昭和基地及びその周辺露岩域 ( 野外研究サイトから(10))

南極昭和基地及びその周辺露岩域 ( 野外研究サイトから(10))

Impact of Living at the Japanese Antarctic Research Expedition Base on Urinary Status

Urinary disorders are generally well understood, but there are few reports on the urinary status of people living in unusual climates such as the polar regions. We studied the impact of living conditions on the urinary status of members of the Japanese Antarctic Research Expedition. This prospective study enrolled 12 consenting members of the wintering party stationed at the Syowa Station in Antarctica between November 2012 and March 2014. The subjects completed questionnaires (the International Prostate Symptom Score [IPSS], Overactive Bladder Syndrome Score [OABSS] and Pittsburgh Sleep Quality Index [PSQI]) and kept daily voiding dairies for 3 days consecutively every 2 months. Compared with baseline values, the mean scores on all the questionnaires decreased during the stay in Antarctica, from 3.42 to 2.31 for the IPSS, 1.25 to 0.986 for the OABSS, and 4.58 to 3.78 on the PSQI. A significant difference was noted in the scores of seven subjects with a 3 point or more decrease in IPSS score and five members with a decrease less than 3 points (-2.22 vs 0.448, P = 0.0416). This is the first survey of the urinary status of people living in a polar environment. The findings obtained by questionnaires and voiding dairies indicated that urination and sleep status did not worsen during the stay in Antarctica.

Properties of inertia-gravity waves in the lowermost stratosphere as observed by the PANSY radar over Syowa Station in the Antarctic

Abstract. Inertia-gravity waves (IGWs) are an important component for the dynamics of the middle atmosphere. However, observational studies needed to constrain their forcing are still insufficient especially in the remote areas of the Antarctic region. One year of observational data (January to December 2013) by the PANSY radar of the wind components (vertical resolution of 150 m and temporal resolution of 30 min) are used to derive statistical analysis of the properties of IGWs with short vertical wavelengths ( ≤ 4 km) and ground-based periods longer than 4 h in the lowermost stratosphere (height range 10 to 12 km) with the help of the hodograph method. The annual change of the IGWs parameters are inspected but no pronounced year cycle is found. The year is divided into two seasons (summer and winter) based on the most prominent difference in the ratio of Coriolis parameter (f) to intrinsic frequency (ω^) distribution. Average of f∕ω^ for the winter season is 0.40 and for the summer season 0.45 and the average horizontal wavelengths are 140 and 160 km respectively. Vertical wavelengths have an average of 1.85 km through the year. For both seasons the properties of IGWs with upward and downward propagation of the energy are also derived and compared. The percentage of downward propagating waves is 10.7 and 18.4 % in the summer and winter season respectively. This seasonal change is more than the one previously reported in the studies from mid-latitudes and model-based studies. It is in agreement with the findings of past radiosonde data-based studies from the Antarctic region. In addition, using the so-called dual-beam technique, vertical momentum flux and the variance of the horizontal perturbation velocities of IGWs are examined. Tropospheric disturbances of synoptic-scale are suggested as a source of episodes of IGWs with large variance of horizontal perturbation velocities, and this is shown in a number of cases.

Five years’ gravity observation with the superconducting gravimeter OSG#058 at Syowa Station, East Antarctica: gravitational effects of accumulated snow mass

Five years’ gravity observation with the superconducting gravimeter OSG#058 at Syowa Station, East Antarctica: gravitational effects of accumulated snow mass

Precise gravity-field modeling in the area of the Japanese Antarctic station Syowa and evaluation of recent EGMs

By combining a Gravity Field and Steady-State Ocean Circulation Explorer (GOCE) Earth Gravity Model (EGM) and in situ gravity data obtained from the Japanese Antarctic Research Expedition (JARE) surveys, we estimated the regional gravity field in the area of Syowa Station, a Japanese research station located in Lützow-Holm Bay, East Antarctica. In situ data sets that were used consisted of land gravity data collected since 1967, shipborne data collected since 1985 and airborne gravity data collected in 2006. The GOCE direct (DIR) solution release 5 (R5) model was used as the long-wavelength reference of the gravity field. Using these data sets, we calculated gravity anomalies and geoid heights at 1-by-1′ grid by means of least-squares collocation.The resulting geoid height at Syowa Station was compared with a local height based on GPS, spirit leveling and tide gauge data. The result suggests that the sea surface height at Syowa Station is −1.57 m, which is consistent with a dynamic ocean topography model. During this investigation, we also evaluated GOCE EGMs and other recent EGMs by comparing them with the airborne gravity data. The results indicate that the GOCE DIR R5 produced the smallest RMS (Root Mean Square) differences and that the newer models performed nearly as well. These comparisons demonstrate the importance of using reliable in situ data when evaluating satellite-only EGMs.

"Sizing" Heterogeneous Chemistry in the Conversion of Gaseous Dimethyl Sulfide to Atmospheric Particles.

The oxidation of biogenic dimethyl sulfide (DMS) emissions is a global source of cloud condensation nuclei. The amounts of the nucleating H2SO4(g) species produced in such process, however, remain uncertain. Hydrophobic DMS is mostly oxidized in the gas phase into H2SO4(g) + DMSO(g) (dimethyl sulfoxide), whereas water-soluble DMSO is oxidized into H2SO4(g) in the gas phase and into SO4(2-) + MeSO3(-) (methanesulfonate) on water surfaces. R = MeSO3(-)/(non-sea-salt SO4(2-)) ratios would therefore gauge both the strength of DMS sources and the extent of DMSO heterogeneous oxidation if Rhet = MeSO3(-)/SO4(2-) for DMSO(aq) + ·OH(g) were known. Here, we report that Rhet = 2.7, a value obtained from online electrospray mass spectra of DMSO(aq) + ·OH(g) reaction products that quantifies the MeSO3(-) produced in DMSO heterogeneous oxidation on aqueous aerosols for the first time. On this basis, the inverse R dependence on particle radius in size-segregated aerosol collected over Syowa station and Southern oceans is shown to be consistent with the competition between DMSO gas-phase oxidation and its mass accommodation followed by oxidation on aqueous droplets. Geographical R variations are thus associated with variable contributions of the heterogeneous pathway to DMSO atmospheric oxidation, which increase with the specific surface area of local aerosols.

Characteristics of Vertical Wind Fluctuations in the Lower Troposphere at Syowa Station in the Antarctic Revealed by the PANSY Radar

Using wind data over three years from July 2012-June 2015 from the PANSY radar, an MST radar, newly installed at Syowa Station (39.59°E, 69.0°S), statistical characteristics of vertical winds and vertical momentum fluxes in the Antarctic lower troposphere are examined. Frequency spectra covering a wide frequency range from (30 d)−1 to (8 min)−1 are divided into three frequency regions obeying power laws with different scaling exponents. The transition frequencies are different between horizontal and vertical wind spectra. Vertical fluxes of horizontal momentum were estimated for two wave period ranges of 8 min–2 h and 2 h–1 d which have almost equal logarithmic scales. The momentum fluxes are larger for longer period components. There are evidences showing that the vertical wind disturbances in the lower troposphere are due to gravity waves forced by topography aligned in the north-south direction. First, the strong disturbances are observed when horizontal winds are strong near the surface. Second, zonal winds tend to almost zero around the top of the disturbances. Third, frequency spectra are large at a wide range of frequency below a critical level, as is consistent with the phase modulation of mountain waves by unsteady mean flow.

Seasonal and Interannual Variation of Mesospheric Gravity Waves Based on MF Radar Observations over 15 Years at Syowa Station in the Antarctic

Seasonal and Interannual Variation of Mesospheric Gravity Waves Based on MF Radar Observations over 15 Years at Syowa Station in the Antarctic

The research of ocean tide loading effects on gravity and ambient noise at Zhongshan and Syowa station in Antarctic

The research of ocean tide loading effects on gravity and ambient noise at Zhongshan and Syowa station in Antarctic

Potential changes in feeding behavior of Antarctic fish, Pseudotrematomus bernacchii (Boulenger, 1902) on the East Ongul Island, Antarctica

The feeding habits of the Antarctic fish Pseudotrematomus bernacchii (Previous name: Trematomus bernacchii) under the fast ice around Japanese Syowa Station were investigated in the summers of 2004/2005 and 2009/2010. The results showed that amphipods and krill were the major prey. However, there was a significant difference in the proportions of larger invertebrates such as squids, octopus and other crustaceans found in the fish stomachs between 2009/2010 and the previous years. Moreover, the percentage of amphipods and krill in fish stomachs declined over the 5-year period in all fish size classes. Several factors including sea ice melting, habitat and environmental changes might have influenced the pattern of feeding behavior.

Balloon-borne observations of lower stratospheric water vapor at Syowa Station, Antarctica in 2013

Balloon-borne observations of lower stratospheric water vapor were conducted with the Cryogenic Frostpoint Hygrometer (CFH) in July, September, and November 2013 at Syowa Station (69.0oS, 39.6oE) in the Antarctic. High-precision and high vertical resolution data of water vapor concentration up to an altitude of about 28 km were obtained successfully except for a contamination in the observation of July 2013. A comparison between the CFH and coincident satellite (i.e., Aura/MLS) observations showed a good agreement within their uncertainty. A position of Syowa Station relative to the stratospheric polar vortex edge varied depending on both the observation date and altitude. Temperature and pressure histories of the observed air parcels were examined by 10-day backward trajectories. These analyses clearly demonstrated that most air parcels observed in the lower stratosphere above Syowa Station experienced final dehydration inside the polar vortex. On the other hand, a clear signature of rehydration or incomplete dehydration was also observed around a 25 hPa pressure level in the observation of July 2013.