2015年度 惑星大気・電離圏セミナー



■場所　：A棟5F会議室 (変更の場合は赤字)
■時間　：水曜日15:00-　(変更の場合は赤字)
■連絡先：武藤圭史朗 (k.muto[at]ac.jaxa.jp)


開催日時・場所 発表者 (所属・身分)

03/02 (Wed.) 15:00
5F conference room		 Takumi abe
Preliminary report of "S-310-44" sounding rocket experiment conducted in January, 2016 
Abstract:
Sounding rocket observations in Japan suggest that the electron temperature profile occasionally exhibits the local increase by several hundred K at 100-110 km altitudes at 1100-1200 LT in winter. Detailed study of the temperature profiles indicates that such an increase is closely related to the existence of Sq current focus. In order to understand a general feature and to investigate a generation mechanism of this unusual phenomena, a sounding rocket experiment was carried out. In this experiment, “S-310-44” rocket equipped with a suite of five science instruments was launched from Uchinoura Space Center at 12:00 JST on January 16, 2016 after being convinced that the Sq current was approaching to the planned rocket trajectory. In this presentation, we will focus on the energy distribution of thermal electrons and electron temperature obtained from FLP (Fast Langmuir Probe) instrument onboard. The FLP successfully made its measurement during both upleg and downleg of the rocket flight. Observations of the energy distribution suggest that the electron temperature increased by about 200 K with respect to the background in the altitude range from 100 to 110 km. It is also significant that the observed energy distribution unlikely seems Maxwellian distribution and sometimes exhibits a possible existence of non-Maxwellian component in the high electron temperature region. Power spectrum analysis of the electron current by the fixed bias probe indicates that the amplitude in the frequency range of several hundred Hz increased at the E region altitude. In particular, it is remarkable that the strong electron density perturbation was observed in the broad frequency range at altitudes from 95 to 110 km. In this presentation, a report on the preliminary analysis of the thermal electron measurements will be given.


02/26 (Fri.) 17:00
5F conference room		 Vun Choon Wei
A Search for Sodium Absorptions from Exocomets 
Abstract:
The quest to search for Na I absorption from exocomets was pushed forward with several new enhancements in methods being developed. 1679 spectra were obtained from ESO’s HARPS Archive for the observations to be carried out for the years from 2003 to 2014. In extension to previous exocometary search of β Pictoris’s system, another exocomet on 20/08/2013 was confirmed to possess absorption feature in Na I. The exocomet composite of Ca II and Na I were analysed to exhibit radial velocities of (29.77±0.38)km/s and (28.04±1.14)km/s respectively. From the obtained column density data, the relative abundance of the exocomet was determined to be AR ~ (12.5 ±2.4)*(10)^(-3). Exocomets found previously on 17/03/2008 and 19/03/2008 by Seccull (2015) were also confirmed. Analysis on these exocomets were revised and some discrepancies were found i.e. exocomet on 17/03/2008 shows Ca II and Na I have radial velocities of (27.13±0.08)km/s and (29.21±0.15)km/s respectively, and relative abundance of (5.7±0.5)*(10)^(-3), whereas exocomet on 19/03/2008 shows Ca II and Na I have radial velocities of (25.30±0.08)km/s and (25.50±0.36)km/s respectively, and relative abundance of (5.9±0.9)*(10)^(-3). The acceleration ratio on the components i.e. Ca II and Na I due to radiation pressure of β Pictoris was also evaluated to be (a(NaI))/(a(CaII))=7.98. Finally, a new theory was proposed to explain the peculiar discrepancies found in radial velocities of Ca II and Na I, and relative abundances trend found in each exocomet. Three main factors were identified to suffice the observed behaviours of the exocomets: Acceleration ratio of components due to radiation pressure, radial distance from the star, and optical depth effects. In sum, the measurements obtained in both Ca II and Na I for found exocomets were used to attempt in understanding the behaviours of exocomets orbiting around β Pictoris.


02/17 (Wed.) 15:00
5F conference room		 Hiroki Ando
Vertical structure of the axi-asymmetric feature in the Venusian polar vortex 
Abstract:
A lot of infrared measurements have been performed to observe the axi-asymmetric feature seen in the Venusian polar vortex (e.g. Taylor et al. 1980; Piccioni et al. 2007; Garate-Lopez et al. 2013). There are a lot of observational studies which show its horizontal structure, but its vertical structure is not clarified. Then we clarified the vertical structure by analyzing Venus Express radio occultation measurement, which enables us to retrieve a vertical temperature profile precisely. Furthermore, we reproduced the Venusian polar vortex by using our GCM named AFES for Venus (Sugimoto et al. 2014; Ando et al. 2016) and compared the vertical structure of the axi-asymmetric feature seen in our model with those clarified by our radio occultation measurements. In this presentation, we will show our observational and numerical calculation results, and discuss the generation mechanism of this feature. Furthermore, we will also suggest its spatial structure on the basis of the comparison between radio occultation measurement and numerical model.


01/20 (Wed.) 15:00
5F conference room		 Javier Peralta
WTF (Winds Tend to Fall) in the night of Venus? 
Abstract:
VIRTIS-M was an imaging spectrometer onboard the European spacecraft Venus Express that left a rich legacy of images of the Venus atmosphere. Its infrared channel was able to obtain cubes of images at different wavelengths ranging 1-5 microns at a low spectral resolution and allowing to sense different vertical levels of the day and nightside of the planet. Concretely, the wavelengths at 3.9 and 5.0 microns have been demonstrated to sense the upper clouds at about 65 km above the surface, and were mostly used to study the behaviour of the southern polar vortex, while latitudes lower than 60°S have been rarely studied due the low contrast and the geometry of observations of Venus Express polar orbit. After properly processing those VIRTIS-M cubes favouring the observation of lower latitudes, we report that the cloud features at 3.9 and 5.0 microns unexpectedly move slowly (and even prograde in some cases) for latitudes between 30°S-60°S. This stunning result of zonal winds between -40 and +10 m/s, accompanied by strong poleward/equatorward meridional winds has not ever predicted after decades of general circulation models of Venus. We also report the apparent discovery of two new vertical levels sensed at 4.16 and 4.84 microns, as well as a calculation of their approximate altitudes.


01/13 (Wed.) 15:00
5F conference room		 Shin-ya Murakami
A brief review of two-dimensional turbulence on a beta-plane and on a rotating sphere 
Abstract:
We'll present a brief review of two-dimensional turbulence (2DT) on a beta-plane and on a rotating sphere. Theories and numerical simulations of 2DT on a rotating sphere have been developed motivated by planetary atmoshpere, because their features (energy spectra, alternating zonal jets) are resembled. In 2DT on a beta-plane, there is the characteristic scale called Rhines scale. We'll mention that Rhines scale have two meanings. A simple hypothesis on the connection between two meanings are submitted.


01/06 (Wed.) 15:00
5F conference room		 Hiroki Watanabe
観測ロケットS-520-26号機搭載高速ラングミュアプローブの観測によって得られたロケット周辺の電子密度・温度構造 
Abstract:
観測ロケットS-520-26号機が平成24年1月12日05時51分00秒（JST）に、内之浦宇宙空間観測所より打ち上げられた。観測ロケットS-520-26号機の目的は熱圏下部領域のプラズマ密度とその変動、電場と中性風の観測を実施し、中性大気-電離大気間の運動量輸送の素過程を理解するとともに、伝搬性電離圏擾乱などの熱圏下部に特徴的な現象の発生および発展における輸送過程の役割を解明することであった。 本研究ではロケット周辺で発生するプラズマの現象及びロケットスピンによるウェイク現象を明らかにすることが目的である。そのために観測ロケットS-520-26号機に搭載された高速ラングミュアプローブを用いて電離圏の観測を行った。得られたデータを用いて電離圏の電子温度・密度を求め、それらをもとに各現象について検証を行った。その結果、高度160km付近にて電離中間層の観測に成功した。また高度200km以上の領域から観測ロケットスピンによって発生するウェイク効果を確認することに成功した。


12/09 (Wed.) 15:00
5F conference room		 Takayuki Enomoto
Near Infrared Spectro-Polarimetry of Venus using KANATA/HONIR  
Abstract:
We have revealed that the optical thickness of Venusian polar haze layers (τ_h) are decreasing by using polarimetric data (visible wavelength) obtained at Hida Observatory from 2012. Polarization of reflected sunlight from Venus contains microphysical properties of not only upper haze layers but also lower main cloud deck. In our study we fixed the parameters about main cloud deck to those obtained past studies when estimating τ_h. Now τ_h get as small as we cannot consider contribution of the uncertainty of main cloud deck enough small, so it is difficult to precisely determine τ_h without determining main cloud parameters accurately. One of the characteristics of polarization of the light from Venus is that polarization degrees in infrared wavelength largely depends on the size of cloud particles, so we thought that spectro-polarimetry is useful to solve the problem. We performed spectro-polarimetric observations of Venus in June 2015 with "HONIR" instrument attached to "KANATA" telescope in Higashi-Hiroshima observatory. In this seminar, I will show the quick-look results and possible interpretations deduced from comparisons with simple model calculations.


12/02 (Wed.) 15:00
5F conference room		 Ko-ichiro Sugiyama
A Three-dimensional Numerical Simulation of Venus’ Cloud-level Convection  
Abstract:
Although convection has been suggested to occur in the lower part of Venus’ cloud layer by some observational evidences, its structure remains to be clarified. To date, a few numerical studies try to simulate Venus’ cloud-level convection (Baker et al., 1998, 2000; Imamura et al., 2014), but the model they utilized is two-dimensional. It is difficult to attempt direct comparison between the results of their simulations and the observations. Here we report on the results of our numerical simulations performed in order to investigate a possible three-dimensional structure of Venus’ cloud-level convection. We show characteristics of the obtained convective motion and comparison between our results and some observations.


11/25 (Wed.) 15:00
5F conference room		 Takao Satoh
Mid-infrared imaging and spectroscopy of Venus obtained by Subaru/COMICS  
Abstract:
We have analyzed mid-infrared imaging and spectroscopic data obtained by COMICS mounted on Subaru Telescope in Oct. 2007. After I summarize what we learned from the imaging data, I show the current status of our study with spectroscopic data.


11/18 (Wed.) 15:00
5F conference room		 Takehiko Satoh
IR2, a 2-um camera onboard Akatsuki  
Abstract:
IR2, a near-infrared camera in 2-um region onboard Akatsuki has been developed to primarily study the middle-to-lower atmospheric dynamics of Venus as probed in the 1.74- and 2.3-um "windows" of the CO2 atmosphere. Spatial and temporal variability of CO below clouds will also be studied by differentiating 2.32-um CO-band images from simultaneous 2.26-um images. Images of the night-side disk in these wavelengths will visualize the zonal and meridional winds near the cloud-base altitudes. IR2 also images at 2.02 um, center of a CO2 absorption band. Such images will visualize the variation of cloud-top altitudes as contrast features due to different absorption path lengths of the reflected sunlight. Together with other cameras and the radio science equipment on Akatsuki, IR2 will contribute to understandings of production and maintenance mechanism of the super-rotation in the Venusian atmosphere. Details of the instrument as well as the latest preparative works for the soon-to-come VOI-R in December 2015 will be presented.


11/11 (Wed.) 15:00
5F conference room		 Yeon Joo Lee
Thermal flux calculation below the Venus clouds  
Abstract:
Radiative energy distribution below the Venus clouds are highly uncertain. Solar radiation decreases drastically below 60 km altitudes, mainly due to scattering of the clouds, which results in high albedo (76%), and then about 3% of energy reaches the surface. Therefore, thermal emission from the 735 K surface temperature would ominate radiative energy distribution over the globe below the cloud layer. This emission below the clouds are blocked by its thick atmosphere and the cloud layer, so a remote sensing is impossible to study the thermal energy. In this study, we proceeded a radiative model calculation at a broad spectral range (1.2-200 um). We prepared a proper database on thermal opacity sources using recent database including laboratory experiments. We made a sensitivity study of net thermal flux on opacity sources, such as minor gases and aerosols. Our results show that CO2, SO2, H2O, and OCS are important sources, and not for cloud aerosols, HCl nor CO. Our result suggest that the previous study, such as Bullock and Grinspoon (2001), seems to underestimate the role of SO2, due to improper CO2 database. Our result also shows a good agreement with in-situ measurement data, taken from the Night and North probes of Pioneer Venus. Differently from Revercomb et al (1986), which explained observed net flux with 100-200 ppmv water vapor, our results show that the range of observed minor gases abundance, 20-50 ppmv water vapor, are enough to produce the observed net thermal flux profiles.


11/4 (Wed.) 15:00
5F conference room		 Yumika Sakamoto
スポラディックE層内の電子温度・密度構造に関する研究  
Abstract:
スポラディック E 層の観測・研究には長い歴史があり，その生成メカニズムやそのイオン組成などが議論されてきた．しかし，内部での熱エネルギー収支に関する議論は非常に少ない．その原因としては，過去にはスポラディック E 層での十分に信頼性のある電子温度観測データが数えるほどしか存在しなかったことがあげられる． 下部電離圏に発生するスポラディック E 層の空間構造解明を主目的として平成 26 年 8 月 17 日 19 時 10 分 00 秒 (日本標準時) に宇宙航空開発機構内之浦宇宙空間観測所より観測ロケット S-520-29 号機が打ち上げられた．このロケットには高速サンプリングが可能なラングミュアプローブが搭載されており，且つ新たな解析方法を導入したことによってこれまでの観測よりも細かな時間（空間）間隔で，スポラディック E 層内の電子密度・温度の空間構造の推定が可能になった．その結果として，電子密度が増加するスポラディックE 層内における電子温度の変化がはっきり示され、外部との境界付近から中心に向って温度が次第に減少していく傾向が明らかになった．本発表では，スポラディックE層を含む一次元空間で電子，イオン，中性粒子を与え，エネルギー方程式を使用して密度が変化した場合の電子温度分布についての数値計算的検討の方法，および進展の報告を行う．
Masahiro Shimokawa
Atmospheric Composition, Chemistry, and Clouds (reviewing a text)  
Abstract:
Venus' atmosphere has a rich chemistry involving interactions among sulfur, chlorine, nitrogen, hydrogen, and oxygen radicals. The chemical regimes in the atmosphere range from ion-neutral reactions in the ionosphere to photochemistry in the middle atmosphere to thermal equilibrium chemistry and surface-atmosphere reactions in the lower atmosphere. This variety makes Venus an important planet to understand within the context of terrestrial-like planets, both in our own solar system and outside it. The primary chemical cycles are believed known but surprisingly few details about these cycles have been fully verified by concurrence among observations, experiments, and modeling. Good models have been developed that account for many properties of the cloud layers, but the size distribution, shape, and composition of the majority of the aerosol mass are still open issues. This text reviews the state of knowledge prior to the Venus Express mission for the composition, chemistry, and clouds of the neutral atmosphere on Venus. Observations by instruments on Venus Express, in combination with ground-based observations, laboratory experiments, and numerical modeling, should answer some of the major open questions regarding the composition, chemistry, and clouds of Venus' atmosphere.


10/20 (Wed.) 15:00
5F conference room		 Mayu Miyamoto
電波掩蔽データの電波ホログラフィ解析による金星大気温度構造の研究  
Abstract:
電波掩蔽とは探査機が地上局から見て惑星の背後を通過した際に、探査機から送信された電波が惑星大気を通過し地上局に届くことを利用した観測である。惑星大気の高度方向の温度分布を測定することができ、惑星探査における重要な観測手法のひとつである。例えば、この温度の鉛直分布から波に伴う温度擾乱を抽出し、大気重力波の性質が議論されている。重力波は浮力を復元力とする波動で、運動量やエネルギーを鉛直輸送して大気大循環を駆動すると考えられている。また上方伝搬と共に波の振幅が大きくなると、対流不安定やシアー不安定といった局所的な不安定を介して砕波し、それに伴う乱流は物質やエネルギーや運動量の拡散に重要な役割を果たすと考えられている。地球大気では、ラジオゾンデやレーダーにより鉛直波長が数十m〜数kmの重力波が観測され、小スケールの波の構造まで良く理解されている。しかし、惑星大気の観測では従来の電波掩蔽データの解析において電波を１本の光線として扱う幾何光学解法が用いられているため、屈折率の勾配が大きい領域を通過した電波は、複数経路(マルチパス)の電波と重なり地上で同時に受信されてしまうため、分離できない。また、電波の回折効果により鉛直分解能が1km程度に制限されるため、これでは幅広い重力波スペクトルのうちのごく一部分しかとらえておらず、地球以外の惑星における重力波の伝搬・散逸過程はほとんど理解されていない。 そこで我々は、近年の地球大気におけるGPS掩蔽観測で用いられている電波ホログラフィ法という、受信信号の振幅と位相の時系列全体を同時にスペクトル解析して分解能を上げる解法を金星大気に応用した。このことにより、鉛直波長150m程度という高分解能な金星大気の温度の鉛直分布が得られ、またマルチパスの影響により今まで正しく求めることができなかった金星の中高緯度に見られる局所的な低温域の温度構造が明らかになった。本発表では新たに用いた解析手法について述べる。また、得られた温度の鉛直分布から重力波に伴う温度擾乱を抽出しより高波数側まで求まった鉛直波数スペクトルや、より高分解な大気安定度の鉛直分布を用い重力波の減衰について議論する。さらに金星の中高緯度に見られる局所的な低温域の温度構造から、金星の雲層内における対流層についても議論する。


10/14 (Wed.) 10:00
5F conference room		 Yusuke Nara
Turbulent Features in Venus at Low Latitude  
Abstract:
It is known that Venusian cloud has turbulent structure at low latitude observed in ultraviolet wavelength range, but unknown that it represents absorption of ultraviolet light or cloud feature. On the other hand, because absorber has little influence on cloud features in visible wavelength range, it is possible to track cloud features. In addition, studying Venusian cloud features in visible wavelength range is meaningful because solar irradiance mainly consists of visible wavelength. In this study, we compare cloud observed in ultraviolet, visible and near infrared wavelength by using data obtained by Venus Monitoring Camera on Venus Express spacecraft.
Keishiro Muto
Instantaneous three-dimensional thermal structure of the South Polar Vortex of Venus (a review of a paper)  
Abstract:
The Venus thermal radiation spectrum exhibits the signature of CO2 absorption bands which enable the retrieval of atmospheric temperature profiles. We have analyzed VIRTIS-M-IR night-side data obtaining high-resolution thermal maps of the Venus south polar region between 55 and 85 km altitudes. The cold collar is clearly distinguishable centered at ~62 km altitude level. In the three orbits under investigation the South Polar Vortex appears as a vertically extended hot region close to the pole and squeezed by the cold collar between altitudes 55 and 67 km but spreading equatorward at about 74 km. The cold collar is the most vertically stable structure at polar latitudes, while the vortex and sub-polar latitudes show lower stability values. These results were published by Garate-Lopez et al. (2014)


10/7 (Wed.) 10:30
5F conference room		 Masayuki Omino
Morphology of the cloud tops as observed by the Venus Express Monitoring Camera (a review of a paper)  
Abstract:
Since the discovery of ultraviolet markings on Venus, their observations have been a powerful tool to study the morphology, motions and dynamical state at the cloud top level. The Venus Monitoring Camera (VMC) provided almost continuous monitoring of the planet with high temporal resolution during more than 3 years of the Venus Express mission that allowed one to follow changes in the cloud morphology at various scales. The camera discovered new cloud features like bright "lace clouds" and cloud columns at the low latitudes, dark polar oval and narrow circular and spiral "grooves" in the polar regions, different types of waves at the high latitudes. Here I present the results of investigation of the cloud top morphology performed by VMC. These results were published by Titov et al. (2011).


9/30 (Wed.) 15:00
5F conference room		 Atsushi Yamazaki
Planned observation of interplanetary neutral helium distribution using HISAKI (SPRINT-A) satellite  
Abstract:
Local InterStellar Medium (LISM) is injected to interplanetary space in heliosphere with the interstellar wind. The helium atom which has high ionization energy travels to the 0.5 A.U. neighborhood of the sun,and gravitates by the sun's gravity to form a high density region with a corn-like shape in the downwind side.The velocity of the interstellar wind the density and the temperature of helium atom in LISM are derived by measuring helium distribution in the corn-like region. From such studies carried out from the 1970s it is believed that the LISM gas is not variable,but recently it was reported that the speed direction of the interstellar wind changed for several decades (Frisch+13). Observation plan of helium resonance scattering from the interplanetary space using the Hisaki satellite is introduced and the change of the speed direction of the wind between the star is discussed.


8/7 (Fri.) 16:00
6F conference room		 Mayu Miyamoto
Full Spectrum Inversion (FSI) of radio occultation signals for the Venus atmosphere  
Abstract:
Gravity waves with vertical wavelengths from a few tens of meters to kilometers have been observed in the Earth’s atmosphere by radiosondes and radars. Also in the atmospheres of other planets, gravity waves are observed by various methods including radio occultation. The radio occultation method relies on the measurement of the frequency shift of the received signal caused by the bending of radio waves in the radial gradient of the refractive index in the atmosphere. The geometrical optics method has long been used for the analysis of radio occultation data. However, this method cannot disentangle multipath rays and vertical resolution is limited by the size of the Fresnel zone (~ 1 km). Because of this limitation, only a limited part of the gravity wave spectrum has been covered, and thus the propagation and dissipation mechanisms of the gravity waves in other planets are poorly understood. Radio holographic methods have been proposed for processing of radio occultation signals in multipath regions and obtaining atmospheric profiles with high resolution. One of them is the Full Spectrum Inversion (FSI), which was recently applied to GPS occultation data of the Earth’s atmosphere. By applying this technique to Venus Express radio occultation data, we derived temperature profiles with high vertical resolution. In this presentation, I'll show the vertical wave number spectra and static stability of gravity waves for discussing about propagation and dissipation of the gravity waves.


7/22 (Wed.) 17:00
7F conference room		 Javier Peralta
Tools to classify the Venus atmospheric waves to be found with Akatsuki  
Abstract:
The atmospheric superrotation of Venus is an unique phenomenum in the Solar system and is still considered an open problem in geophysical fluid dynamics. Conversely to the other terrestrial planets where the atmosphere co-rotates with the surface, the Venusian winds can reach velocities 60 times higher than the planet surface. A general agreement exists among numerous works concerning the main role that atmospheric waves should have in the generation and maintenance of the superrotation, although most of them try to study the impact of the waves with complex GCMs or using adapted terrestrial dispersion relations by considering frames fixed to unrealistic profiles of Venus winds. Here I introduce the real dispersion relations for the wide variety of atmospheric waves that are possible on Venus conditions. These have allowed to discover a new type of Rossby wave, to explain most of the characteristics of the Venus "Y" feature and to construct dispersion graphs enabling the classification of waves by measuring their horizontal wavelength and phase velocity (nadir observations), or using the wave amplitude and vertical wavelength (radio-occultation observations) or simply the periods apparent in atmospheric magnitudes.


7/10 (Fri.) 16:00
5F conference room		 Ko-ichiro Sugiyama
Numerical Modeling of Moist Convection in Jovian Planets  
Abstract:
It is now widely accepted that moist convection is a common phenomenon in Jovian planets' atmosphere. The moist convection is thought to play an important role in determining the mean vertical structure of the atmosphere, including condensible species distribution. However, the mean structure of the Jovian planets' atmosphere and its relationship to moist convection remain unclear. In order to investigate the idealized characteristics of the vertical structure of multi-composition clouds and the convective motions associated with them, we developed a numerical fluid dynamical model that treats thermodynamics and microphysics of the three cloud components, and perform a series of long-term numerical simulations of moist convection. In this presentation, I will show the characteristics of moist convection obtained from the Saturn's and Uranus' atmosphere cases in detail.


7/3 (Fri.) 16:00
5F conference room		 Takayuki Enomoto
Indications of decreasing Venusian polar hazes captured with an imaging-polarimetry system “HOPS”  
Abstract:
Venus is wholly covered with thick cloud composed of sulfuric acid droplets, and there are thin layers composed of sub-micron particles “hazes” on both its polar regions over the main cloud deck. Some researchers reported that there were temporal variations of the optical thickness of the polar haze layers (e.g. from 0.3 to 0.05 @365nm, Sato et al. [1996]). Such variation can affect energy deposition and determine the kinds of chemical reactions in Venusian atmosphere, it is important to perform continuous monitoring. To investigate the temporal variation of Venusian polar hazes, we have carried out polarimetry with an imaging-polarimetry system “HOPS” (Hida Optical Polarimetry System) attached to 65cm refractor telescope at Hida Observatory form 2012. The optical thickness of polar haze layers (τ@930nm) during 2012 to 2013 are estimated at 0.09 for northern and 0.05 for southern polar regions. These τ were comparable with “thin period” during about 8 years from 1979. From recent observations, we found indications of further decrease of polar hazes, rather consistent with no polar haze model. In this seminar, I will show quick look results of observed data obtained during 2014 and 2015, because there are still some problems in calibrating polarimetric data.


6/19 (Fri.) 16:00
5F conference room		 Miho Kanao
A study on the atmosphere of Venus with the Hinode observation during the transit of Venus  
Abstract:
Venus atmosphere is covered with the thick cloud layer at an altitude from 45 km to 70 km with the haze layer of up to 100 km altitude. The distribution and dynamics of the cloud and haze particles expected to reflect the transition of the thermal and kinetic energy in the atmosphere as well as the photochemical reactions of the cloud particles. The particles composed of the layers are expected to convect in the meridian plane together with the mean zonal wind. I will present the study for the atmosphere of Venus using the images of SOT onboard HINODE solar observatory, which was launched in 2007 from Kagoshima. From a distance of 0.3 AU, we observed the Venusian limb during the 2012 transit of Venus on the 2048 x 2048 pixels CCD with the highest resolution; 0.3 arcsec. Successfully Venus atmosphere could be captured. We determined the altitude of the constant transmittance level with regards to the latitude after the calibration of the plate scale using the G-band images. The limb altitude defined as the transmittance level of 0.5 is displayed both in the morning (06:00) and the evening (18:00). I will interpret the profile and suggest a possible circulation model of the haze and upper cloud layer in this study.


6/12 (Fri.) 16:00
5F conference room		 Hiroki Ando
Theoretical study about the Venusian gravity waves by the two-dimensional numerical model  
Abstract:
There are a lot of observational studies about gravity waves in the Venus atmosphere. Horizontal structure of the gravity wave is investigated by optical measurements, but that at the specific altitude can be examined. On the other hand, vertical one is mainly investigated by radio occultation measurement. However, horizontal structure of the wave cannot be examined. In addition, it is difficult to investigate the spatial structure of the wave because there are few chances to observe the same gravity waves at the same time by optical and radio occultation measurements. The aim of this study is to investigate the spatial structure and propagation characteristic of the gravity wave in the Venus atmosphere by using a numerical calculation model named deepconv. At the beginning we performed a two-dimensional numerical calculation. In this presentation we are going to talk about the progress situation of our study showing some calculation results.


5/29 (Fri.) 16:00
5F conference room		 Takumi Abe
Sounding rocket experiment to investigate electron heating in the Sq current focus  
Abstract:
We are going to conduct sounding rocket experiment this winter to investigate a heating mechanism of thermal electrons in the center of Sq current focus in the lower ionosphere. In this talk, I will briefly introduce how we are trying to elucidate this problem in this experiment. The electron temperature is one of the basic parameters in the ionosphere that has been most frequently observed by instruments on the space-based platform, and has been frequently measured by Langmuir probe on the sounding rocket launched from Uchinoura Space Center. It was suggested from a comparison of the electron temperature profiles obtained above Uchinoura that some of those profiles have the local increase by several hundreds K at the altitude of 100-105 km with respect to the background temperature only when the measurements are made at 11:00 LT in winter time. Subsequent study indicates that such a temperature increase is closely related to the existence of the Sq current focus in the mid-latitude ionosphere, and therefore the temperature increase becomes most significant when the rocket passes through the center of the current system. In order to elucidate a mechanism to cause the above-mentioned electron temperature increase, which might be resulted from the electron heating, the sounding rocket experiment was conducted in Uchinoura on January 16, 2007. The rocket equipped with a total of eight instruments was launched at 11:20 JST after identifying that the Sq current was approaching to the planned rocket trajectory. As a result of observations by the onboard instruments, the electron temperature was significantly increased by about 500-600 K at the altitude of 97-101 km. Data from the Fixed Bias Probe suggest that a strong perturbation in the electron density is observed to exist above 97 km altitude. It is also noticeable that the electric field data includes unusual variation in the same altitude region as the electron temperature increase was observed, suggesting a possible connection between the thermal electron heating and variation of the electric field. However, some of these instruments had difficulties to proceed to the detailed data analysis because of various problems. A similar kind of rocket experiment is planned to conduct in the winter of 2016 by overcoming the problems we had last time. We are trying to detect an inherent causal relation between the electron heating and the electric field which probably plays an important role in energizing thermal electrons. The detailed information on this coming rocket experiment will be presented.


5/22 (Fri.) 16:00
6F conference room		 Shin-ya Murakami
Time-space spectral analysis of zonal winds in simplifiedVenus-like GCM  
Abstract:
Waves in the planetary atmosphere play an important role in various ways. In the Earth's atmosphere, the equatorial waves are found using the time-space spectral analysis of OLR (outgoing longwave radiation) which is a proxy for cloudiness. We apply the time-space spectral analysis to the outputs of the simplified Venus-like GCM. We cannot obtain OLR in the simplified Venus-like GCM, so we use zonal winds instead. We do the time-space spectral analysis for ERA40 reanalysis data at first as a exercise, then we apply the method to the zonal winds of the simplified Venus-like GCM. We show the obtained spectra in each horizontal plane. The spectra are drawn with dispersion curves for equatorial waves with various equivalent depths. We can observe signals of the equatorial waves in lower layers, however, we cannot distinguish westward inertia-gravity waves and Kelvin waves in almost all levels.


5/15 (Fri.) 16:30
6F conference room		 Takehiko Satoh
MDevelopment of a Dust Imager for Future Mars Landing Missions  
Abstract:
We report progress in developing of a "dust imager" for future Marslanding missions. As Martian dust is a key element of its environment and a major potential hazard for human exploration, it is essentialto know what Martian dust is and how it works. However, to date little is known about the Martian dust due primarily to lack of measurements.Direct imaging would greatly help to increase our knowledge about the Martian dust. The dust imager under development is not a microscope but a "bare"imaging sensor of which pixels are fine pitched (we currently use a 1.4-um pitch CMOS in the experiments). More specifically, the imagerconsists of a single-board computer, Raspberry Pi and its camera module (5M pixels OV5647). After exposing the sensor to the air with suspendeddust for a while, we illuminate the sensor with a parallel beam so that shadows of particles on the sensor can directly be imaged. In this way,the imager does not need a focusing mechanism and is expected to be very light-weighted and robust. We present latest results from laboratory experiments with the BBM that successfully imaged particulate matters down probably to 1-um size.


5/8 (Fri.) 16:00
5F conference room		 Takao Sato
Migrating tides in the Martian lower atmosphere inferred from MEX/PFS temperature data  
Abstract:
Thermal tides play an important role in determining the general circulation, thermal structure, and vertical coupling between the lower and the upper atmospheres of terrestrial planets. They are expected to be stronger on Mars than on Earth, because the Martian atmosphere is only about 0.6% as thick as the Earth's atmosphere. The characteristics of migrating tides in the Martian atmosphere have been investigated mainly by GCM studies. The comprehensive temperature observations by MGS/TES and MRO/MCS have been conducted mainly from the sun-synchronous orbit, which means the characteristics of migrating tides still remain to be investigated. Planetary Fourier Spectrometer (PFS) onboard Mars Express (MEX) has observed atmospheric temperatures in the Martian lower atmosphere since the end of MY26. These data enable us to investigate the migrating tides in the lower atmosphere because the orbit of MEX is non sun-synchronous. In this presentation, I will briefly summarize the current knowledge of migrating tides in the Martian atmosphere and show some preliminary results.


5/1 (Fri.) 16:00
5F conference room		 Lee Yeon Joo
Radiative forcing by the Venus clouds and its effects on atmospheric dynamics in the equatorial region  
Abstract:
Observed Venus cloud top morphology at 〜70 km altitude shows small size convective-like cells in the equatorial region. As this feature has a diurnal variation, appearing from the sub-solar point to evening side, we consider that the solar heating near the cloud top may play an important role in this diurnal variation. However, there is a possible influence from lower level convection near 50 km altitude on the cloud top level morphology. In order to understand the connection between radiative forcing due to the clouds and atmospheric dynamics, we developed an atmospheric model to calculate radiative forcing, from surface to 100 km altitude. This result was employed in a 2-D fluid dynamic model (CReSS). Our result shows separated convective layers, near the cloud bottom (〜50 km) and near the cloud top (〜70 km) with opposite diurnal cycles along local time each other. However, the results show a dependence on cloud models, caused by different vertical distributions of radiative forcing. Further study using a global circulation model is also required to make realistic model study, including Hadley circulation, and also to examine a horizontal convection.


4/15(Wed) 16:30
5F conference room
Self-Introducetion  
Abstract: