Takeshi Imamura
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View article: Radio Scintillation and Gravity Wave Characteristics in the Venusian Atmosphere: Insights From Akatsuki Radio Occultation
Radio Scintillation and Gravity Wave Characteristics in the Venusian Atmosphere: Insights From Akatsuki Radio Occultation Open
We investigated the relationship between radio scintillations—short‐term fluctuations in radio signal intensity—and temperature fluctuations, both observed in vertical profiles from JAXA's Akatsuki radio occultation. Our results indicate t…
View article: Venusian Planetary‐Scale Waves Observed by Akatsuki Longwave Infrared Camera: Coupled Rossby‐Kelvin Waves and Long‐Term Variation
Venusian Planetary‐Scale Waves Observed by Akatsuki Longwave Infrared Camera: Coupled Rossby‐Kelvin Waves and Long‐Term Variation Open
Planetary‐scale waves are expected to be crucial in driving the Venusian planetary‐scale atmospheric circulation, including the superrotation. To understand the interaction between the waves and the mean flow, we obtained temporal frequenc…
View article: On the estimation of solar wind velocity under varying solar activity conditions using <i>Akatsuki</i> measurements
On the estimation of solar wind velocity under varying solar activity conditions using <i>Akatsuki</i> measurements Open
We present an analysis of solar wind dynamics based on Doppler spectral width measurements of X-band radio signals from the Japanese Akatsuki spacecraft. The data set includes two solar conjunction occultation experiments conducted in 2016…
View article: Correction: Temporal variation in the cloud‑top temperature of Venus revealed by meteorological satellites
Correction: Temporal variation in the cloud‑top temperature of Venus revealed by meteorological satellites Open
View article: The MaCro Instrument Aboard M-MATISSE: Scientific Objectives and Operational Concepts
The MaCro Instrument Aboard M-MATISSE: Scientific Objectives and Operational Concepts Open
The M-MATISSE mission, currently undergoing its Phase A study with the European Space Agency (ESA), is a candidate for the Medium-class (M7) program. Its primary objective is to study the complex interactions between Mars' magnetosphere, i…
View article: The MaCro Instrument Concept for Dual-Frequency Crosslink Occultations at Mars
The MaCro Instrument Concept for Dual-Frequency Crosslink Occultations at Mars Open
The M-MATISSE mission, currently in its Phase A study by the European Space Agency (ESA), is a Medium-class (M7) candidate that aims to explore the complex interactions between Mars' magnetosphere, ionosphere, and thermosphere (MIT couplin…
View article: The Joint ESA-NASA Venus Science Coordination Group (VESCOOR) to support the three Venus Missions
The Joint ESA-NASA Venus Science Coordination Group (VESCOOR) to support the three Venus Missions Open
The selection of three new missions to Venus opens a new era to explore the planet and its evolution: ESA’s EnVision and NASA’s VERITAS and DAVINCI missions plan to observe Venus in the next decade. ESA and NASA established a joint Venus S…
View article: Global wind map on Mars during and after the global dust storm in 2018 measured by ALMA
Global wind map on Mars during and after the global dust storm in 2018 measured by ALMA Open
The wind velocity field plays a fundamental role in understanding atmospheric physics. Gaining insight into the three-dimensional structure of atmospheric circulation leads to a deeper comprehension of the mechanisms governing the transpor…
View article: Vertical propagation of Venusian thermal tides above and below clouds investigated by Akatsuki radio occultation
Vertical propagation of Venusian thermal tides above and below clouds investigated by Akatsuki radio occultation Open
The vertical structure of the thermal tide in the Venusian low-latitude region (0˚-30˚ latitudes) was investigated by the Akatsuki radio occultation measurements. The result shows that the phase of the diurnal tide little varies in the ver…
View article: Venusian planetary-scale waves observed by Akatsuki LIR: Rossby-Kelvin instability and long-term variation
Venusian planetary-scale waves observed by Akatsuki LIR: Rossby-Kelvin instability and long-term variation Open
Planetary-scale waves are expected to be crucial in driving the Venusian planetary-scale atmospheric circulation. To understand the interaction between the waves and the mean flow, we obtained temporal frequency spectra of the cloud-top br…
View article: Long-Term Variability of Mean Winds and Planetary-scale Waves around Venusian Cloud Top Observed with Akatsuki/UVI
Long-Term Variability of Mean Winds and Planetary-scale Waves around Venusian Cloud Top Observed with Akatsuki/UVI Open
The Venus orbiter Akatsuki started its observation in December 2015, and it provided valuable data on the atmosphere of Venus until its signal was lost in April 2024. We published a paper with the same title as this presentation by using t…
View article: Study on the variation of Venusian polar tropopause using Venus Express radio occultation
Study on the variation of Venusian polar tropopause using Venus Express radio occultation Open
In the Venusian atmosphere at 50-70km altitudes, there is a thick cloud layer composed of H₂SO₄ and H₂O liquid. Around the cloud base, the clouds absorb infrared radiation from the lower atmosphere, driving convection in the lower and midd…
View article: Thermal Structure of Venus’s Upper Atmosphere (90–110 km) Derived from Radio Occultation Data
Thermal Structure of Venus’s Upper Atmosphere (90–110 km) Derived from Radio Occultation Data Open
Understanding the dynamics of the Venusian atmosphere in the 90–110 km altitude range is critical for investigating the coupling processes between the neutral atmosphere and the lower ionosphere. Recent studies suggest that near-infrared h…
View article: Integrated Study of Martian Dust: Detection of Local Dust Storms, Estimation of Vertical Distribution, and Surface Pressure Analysis Using OMEGA Observations
Integrated Study of Martian Dust: Detection of Local Dust Storms, Estimation of Vertical Distribution, and Surface Pressure Analysis Using OMEGA Observations Open
Understanding the Martian dust cycle is essential for clarifying the atmospheric circulation and meteorological phenomena. Unlike Earth, Mars has a thin atmosphere primarily composed of CO2, where atmospheric dust plays a dominant role in …
View article: Multiple temporal and spatial scales variation of sulfur dioxide at the Venusian cloud-top
Multiple temporal and spatial scales variation of sulfur dioxide at the Venusian cloud-top Open
BackgroundThe cloud layer of Venus, composed of sulfuric‑acid aerosols, plays a key role in controlling the solar energy input of the atmosphere through its effect on planetary albedo. To clarify the sequence of processes whereby sulfur di…
View article: Temporal variation in the cloud-top temperature of Venus revealed by meteorological satellites
Temporal variation in the cloud-top temperature of Venus revealed by meteorological satellites Open
Temporal variations in the cloud-top temperature of Venus are essential observable for understanding its atmospheric dynamics and related phenomena, such as thermal tides and planetary-scale waves. While multiband monitoring of both phenom…
View article: A novel technique for plasma asymmetry correction in radio occultation profiling
A novel technique for plasma asymmetry correction in radio occultation profiling Open
View article: Akatsuki Radio Science Measurements: Insights into the Solar Cycle Dependence of Inner-Middle Corona Turbulence
Akatsuki Radio Science Measurements: Insights into the Solar Cycle Dependence of Inner-Middle Corona Turbulence Open
View article: Temporal variation in the cloud-top temperature of Venus revealed by meteorological satellites
Temporal variation in the cloud-top temperature of Venus revealed by meteorological satellites Open
Temporal variation in the cloud-top temperature of Venus is an essential observable for understanding its atmospheric dynamics and related phenomena, such as thermal tides and planetary-scale waves. While multiband monitoring of both pheno…
View article: Improved cloud tracking method tolerant to streaky features: application to Venusian cloud images
Improved cloud tracking method tolerant to streaky features: application to Venusian cloud images Open
An improved cloud tracking method applicable to cloud images dominated by streaky features was developed and applied to Venusian ultraviolet images. By accounting for streaky features in 365-nm images obtained by the Ultraviolet Imager (UV…
View article: Density fluctuation in the solar corona and solar wind: A comparative analysis of radio-occultation observations and magnetohydrodynamic simulation
Density fluctuation in the solar corona and solar wind: A comparative analysis of radio-occultation observations and magnetohydrodynamic simulation Open
Context. Recent in situ observations and numerical models indicate that various types of magnetohydrodynamic (MHD) waves contribute to the solar wind acceleration. Among them is an MHD wave decomposition at distances closer than 50 R ⊙ usi…
View article: Density fluctuation in the solar corona and solar wind: A comparative analysis of radio-occultation observations and magnetohydrodynamic simulation
Density fluctuation in the solar corona and solar wind: A comparative analysis of radio-occultation observations and magnetohydrodynamic simulation Open
Recent in-situ observations and numerical models indicated various types of magnetohydrodynamic (MHD) waves contributing to the solar wind acceleration. Among them is an MHD wave decomposition at distances closer than 50 $R_{\odot}$ using …
View article: Probing solar wind velocity from simultaneous superior solar conjunction radio science experiments of BepiColombo and Akatsuki missions
Probing solar wind velocity from simultaneous superior solar conjunction radio science experiments of BepiColombo and Akatsuki missions Open
A radio link directly probing the inner solar corona offers the possibility to characterize solar wind properties, including velocity, density, turbulence, and even the axial ratio. In this study, we leveraged radiometric data obtained dur…
View article: Do Solar Energetic Particle (SEP) Events Influence the Formation of the V<sub>0</sub> Layer in the Venusian Ionosphere?
Do Solar Energetic Particle (SEP) Events Influence the Formation of the V<sub>0</sub> Layer in the Venusian Ionosphere? Open
This study investigates the potential impact of Solar Energetic Particles (SEPs) on the V 0 layer of the Venus ionosphere. Electron density profiles obtained from radio occultation experiments conducted by the Venus Express (VEX) and Akats…
View article: Wave-driven cloud formation on Venus
Wave-driven cloud formation on Venus Open
Venus is surrounded by sulfuric acid clouds essential to the planet's climate system. The upper part of the cloud is thought to be of photochemical origin, while the lower part is highly variable and will be more affected by atmospheric dy…
View article: M-MATISSE MaCro: an intersatellite link in Mars orbit
M-MATISSE MaCro: an intersatellite link in Mars orbit Open
The "Mars Magnetosphere ATmosphere Ionosphere and Space-weather SciencE (M-MATISSE)" mission, currently in Phase A study by the European Space Agency (ESA), is a Medium-class (M7) candidate. M-MATISSE aims to unravel the intricate and dyna…
View article: One-dimensional Microphysics Model of Venusian Clouds from 40 to 100 km: Impact of the Middle-atmosphere Eddy Transport and SOIR Temperature Profile on the Cloud Structure
One-dimensional Microphysics Model of Venusian Clouds from 40 to 100 km: Impact of the Middle-atmosphere Eddy Transport and SOIR Temperature Profile on the Cloud Structure Open
Venus is globally covered by thick hydrated sulfuric acid (H2SO4) aerosols, which play a pivotal role in the Venusian atmospheric system. The condensation and evaporation processes affect the abundance of H2SO4 vapor and H2O vapor and the …
View article: Long-term variations of temperature and H2SO4 gas mixing ratio in the Venusian atmosphere studied with Venus Express and Akatsuki radio occultation measurements
Long-term variations of temperature and H2SO4 gas mixing ratio in the Venusian atmosphere studied with Venus Express and Akatsuki radio occultation measurements Open
It is well known that planetary atmospheres have a wide range of time-scale variations that have a significant impact on the surface environment of the planet. Taking the Earth as an example, long-term scale atmospheric variations such as …
View article: Mesoscale stationary waves on Venus&#8217; dayside clouds
Mesoscale stationary waves on Venus’ dayside clouds Open
Venus’ atmosphere remains a dynamic and enigmatic engine which not only completely covers the surface of the planet but is believed to have had a dramatic impact on how the planet evolved. The current mechanisms that d…
View article: Distribution and Variation of the Venusian Cloud-top Sulfur Dioxide Derived from Akatsuki UV Images
Distribution and Variation of the Venusian Cloud-top Sulfur Dioxide Derived from Akatsuki UV Images Open
IntroductionThe horizontal distribution of sulfuric acid clouds in the Venusian atmosphere is an essential factor that influences the solar energy absorbed by the planet. The cloud layer reflects about 75% of the solar energy [1] and contr…