Study of Sulfuric Acid Clouds using Venus General Circulation Model

Credit by ESA

Credit by ESA

Venusian sulfuric acid cloud deck exists in the altitude of 50km-70km. It is considered that this cloud affects atmospheric general circulation by reflecting and absorbing solar radiation and emitting heat. It is known that this cloud varies temporaly and spatially. I study the production/extinction system and distributions of  sulfuric acid clouds on general circulation of Venus’ atmosphere using Venus General Circulation Model (VGCM). Presently, I try to reproduce variations of sulfric acid vapor, and I want to reproduce radiation from sulfuric acid cloud and reveal the effect eventually.

(Kazunari Itoh)

Flux ropes in the Venusian upper atmosphere

Planetary upper atmosphere is partially ionized and in the plasma state. In general, plasma motion is strongly affected by the surrounding magnet field. Thus, it is important to understand magnet field of the planet for understanding its upper atmosphere.
Although Venus has no intrinsic magnetic field, the magnetic field exists in the Venusian upper atmosphere originated from the interaction with the solar wind. In the dayside ionosphere of Venus, magnetic rope-like fine structures, called ‘flux ropes’ have been often observed. So far some models have been proposed by previous studies, but the generation mechanism of the flux ropes has not yet been understood. We propose a new model to generate flux ropes, focusing on ‘magnetic reconnection’. Our model is validated using MHD simulation. Our study contributes for a further understanding magnetic field of Venus and its upper atmosphere.
(Hitoshi Sakamoto)

Atmospheric escape simulation of the terrestrial planets


Planetary upper atmospheres are subject to Sun’s ultraviolet radiation and solar wind interaction, which strip away some of the planetary atmospheres. We have developed a global hybrid (particle ions/fluid electrons) model of the solar wind interaction with the upper atmosphere of unmagnetized planets as well as an MHD model, and investigated the escape processes and escape channels of the ions of planetary origin. Collaborating with satellite/ground-based observations, we are investigating the escape and long-term evolution of the atmospheres of Mars, Venus, and exoplanets, and trying to better understand the conditions needed to form a habitable planet.

Water cycle on Mars


Water cycle on Mars is one of the big issues because recently it is suggested that a large amount of ice exists under the soil. We investigate the map of isotopic ratio in water vapor by Subaru telescope and compare with the GCM model for understanding of water cycle on Mars. Also, we attempt to derive vertical profile of the water vapor. Very recent study shows super saturation of water vapor and it needs further research of its vertical profile. In future, we plan to do continuous observation of the trace gases with our developing infrared heterodyne spectrometer at our Hawaii Haleakala telescope.

Trace gases in the Martian atmosphere

Credit by ESA

Credit by ESA

We investigate methane(CH4), hydrogen peroxide(H2O2), and water vapor in the Martian atmosphere by the Planetary Fourier Spectrometer (PFS) onboard Mars Express spacecraft. Recently, methane is discovered in the Martian atmosphere. It is remarkable because its sources are potentially a geological and a biological activity on Mars. We observed Mars for constraint of the source of methane and the data analysis is on-going now. We attempt to derive vertical profile of methane with the PFS limb-geometry observation data. Hydrogen peroxide is one of the best tracers of oxidizer in the Martian atmosphere. We detected it by the PFS onboard MarsExpress. It was first time to detect hydrogen peroxide with an instrument onboard Mars explorer. The derived amount was very small (~40ppb), which is not enough to destroy methane in weeks or months. Since the observed lifetime of methane is weeks or months, is needs further research of the sink of methane.

Development of the instrument onboard the spacecraft

Credit by NASA

Credit by NASA

Staffs work for long-term, which do not always provide products soon. Now, we are running following projects, in which we take the responsibility for electric / radio / digital integratation instruments.
– Small-sized EUV explorer ‘Exceed’ (Launch: 2013?)
– Mercury mission ‘BepiColombo’ (Launch: 2014)
– Small-sized radiation belt explorer ‘ERG’ (Launch: 2014)
We also join the base investigations of the multi-spacecraft magnetospheric ‘SCOPE’, future Mars, and future Jupiter missions, which will be in the end of next decade. Let’s enjoy with the short-term ‘ground-based and orbiter observations’, ‘numerical studies’, and ‘base development of og sensor technologies’.

Numerical simulation of the Martian atmospheric escape


The present day Martian climate is cold and dry, but a number of observations show surface features recording a history of running water. The amount of water that once existed was estimated as about 500 to 1000 m of the equivalent water layer. The presence of liquid water in substantial amounts at early times seems to imply a massive atmosphere with a heavy content of greenhouse gases. Where have the Martian water and greenhouse gases gone? The atmospheric escape to space is potentially important for the evolution of the Martian atmosphere. Understanding the way escape processes work in the Martian atmosphere at times in the past as well as at present is a fundamental issue when the evolution of the Martian atmosphere is studied.

CO2 cloud on Mars

Credit by ESA

Credit by ESA

In martian mesosphere, not only water-cloud, but also CO2-cloud exists. CO2-cloud was first observed by a spectroscopy onboard Mars Express. Until today, It is found that CO2-cloud have spatial and seasonal dependence , but detail of cloud itself is not clear. We use infrared fourier spectrometer PFS which have high-spectral resolution , and it could make cloud feature clear.

Mars General Circulation Model

Credit by NASA

Credit by NASA

Mars has colder environment in comparison with Earth, with dry and thin atmosphere, rough topography, seasonal CO2 ice cap, and dust storms which sometimes expand to planet-encircling. On the other hand, there are many topographic evidences which indicate the existence of rich liquid water on the surface of old Mars. Most of the water is thought to be escaped into space by interactions with the solar wind, while not a little water has been found in the north polar cap and underground. We have developed a Mars General Circulation Model named DRAMATIC (Dynamics, RAdiation, MAterial Transport and their mutual InteraCtions), based on the terrestrial atmospheric model developed in the Univ. of Tokyo, NIES and JAMSTEC, by introducing some physical schemes specific on Mars such as the radiative effects of CO2 and dust and the phase changes of CO2. The model well reproduces the seasonal changes of temperature field, surface pressure and CO2 polar ice distribution, and has been used for the investigations of atmospheric dynamics such as the change of atmospheric circulation in different dust opacity. Moreover, we are starting the implementation of the material transport schemes such as water and CO2 ice clouds, and have reproduced consistent distributions of water vapor column density and hygropause with observations. We have also reproduced consistent seasonal and latitudinal distributions of CO2 ice clouds in middle atmosphere (higher than ~50 km) with observations. We have also implemented the HDO cycle for the future observations of the water isotopic ratios on Mars, and have reproduced consistent seasonal and latitudinal changes of HDO/H2O ratio distributions with the previous theoretical studies.

Atmospheric trace species

Credit by JAXA

Credit by JAXA

“Atmospheric trace species” is the component which mixing ratio is less than 1%, like O3, CO2, CH4 etc. Despite of their small amount, they affect a lot to temperature and circulation of the atmosphere. It also affects human health in the case of air pollution by NOx etc. We have observed the variation of these species mainly by spectroscopic methods such as FTIR and high-altitude balloon observations.

IR heterodyne spectroscopy


The laser heterodyne spectroscopy is the most sensitive and highest resolution spectroscopy (1E7-8) in the middle infrared region, and has been expected to be a powerful method for atmospheric studies. Fully resolved molecular features provided by applying heterodyne techniques are possible allowing retrieval of many physical parameters from single lines. Our group in Tohoku University has developed since 1985, and the terrestrial minor constituents and their vertical profiles have been investigated. From 2009, our infrared laser heterodyne spectroscopy has been developed with quantum cascade lasers (QCLs) which offer sufficient optical output power of several to hundreds milliwatts to guarantee an efficient heterodyne process and high system sensitivity for planetary study. This instrument will be onboard the dedicated PLANETS telescope and Tohoku-60cm  (T60) telescope at the top of Mt. Haleakala, Hawaii, in order to perform continuous monitoring of planetary atmospheres. Our equipment and T60 has been successfully moved to the summit on August 2014, thanks to the great collaboration with University of Hawaii (Jeff Kuhn, Joe Ritter, and their colleagues). T60 itself has been carefully setup by an excellent works of Mitaka-Koki. Our heterodyne is also almost ready to go. Thanks to many people, we are just in front of the first light of T60 and heterodyne instrument. (August 28 2014, Hiromu Nakagawa)

Magnetic and ionospheric electric fields


The Earth has the region dominated by its magnetic field, called magnetosphere. In the magnetosphere, large-scale magnetic disturbance phenomena such as storms and substorms are observed by the input of energy from solar wind. These phenomena are triggered by convection electric fields that cause the transport and acceleration of charged particles and electromagnetic energies in the magnetosphere. Therefore, investigating evolution of convection electric fields is essential to understand the energy transport associated with solar wind disturbance in the magnetosphere-ionosphere coupled system. Currently, we are trying to clarify evolution of convection electric fields and the energy transport associated with magnetic disturbance phenomena by the in-situ multiple observations of magnetic and ionospheric electric fields – using by THEMIS, RBSP, SuperDARN, and etc.