Patrice Rannou

Origin and role of water ice clouds in the Martian water cycle as inferred from a general circulation model

In this paper, we present the results obtained by the general circulation model developed at the Laboratoire de Meteorologie Dynamique which has been used to simulate the Martian hydrological cycle. Our model, which employs a simplified cloud scheme, reproduces the observed Martian water cycle with unprecedented agreement. The modeled seasonal evolution of cloudiness, which also compares well with data, is described in terms of the meteorological phenomena that control the Martian cloud distribution. Whereas cloud formation in the tropical region results from seasonal changes in the overturning circulation, Polar Hood clouds are mostly driven by variations of atmospheric wave activity. A sensitivity study allows us to quantify the effects of the transport of water ice clouds on the seasonal evolution of the water cycle. The residence time of cloud particles is long enough to allow cloud advection over great distances (typically thousands of kilometers). Despite the relatively low proportion of clouds (

A warm layer in Venus' cryosphere and high-altitude measurements of HF, HCl, H2O and HDO

10%) in the total atmospheric inventory of water, their ability to be transported over large distances generally acts at the expense of the north polar cap and generates a water cycle globally wetter by a factor of 2 than a cycle produced by a model neglecting cloud transport. Around aphelion season, clouds modulate the north to south migration of water in a significant fashion and participate just as much as vapor in the cross-equatorial transport of total water. Most of the year, atmospheric waves generate an equatorward motion of water ice clouds near the polar vortex boundaries, partially balancing the opposite poleward flux of water vapor. The combination of both effects delays the return of water to the north polar cap and allows water to build up in the Martian tropics.

SPICAM on Mars Express: Observing modes and overview of UV spectrometer data and scientific results

Venus has thick clouds of H2SO4 aerosol particles extending from altitudes of 40 to 60u2009km. The 60–100u2009km region (the mesosphere) is a transition region between the 4u2009day retrograde superrotation at the top of the thick clouds and the solar–antisolar circulation in the thermosphere (above 100u2009km), which has upwelling over the subsolar point and transport to the nightside. The mesosphere has a light haze of variable optical thickness, with CO, SO2, HCl, HF, H2O and HDO as the most important minor gaseous constituents, but the vertical distribution of the haze and molecules is poorly known because previous descent probes began their measurements at or below 60u2009km. Here we report the detection of an extensive layer of warm air at altitudes 90–120u2009km on the night side that we interpret as the result of adiabatic heating during air subsidence. Such a strong temperature inversion was not expected, because the night side of Venus was otherwise so cold that it was named the ‘cryosphere’ above 100u2009km. We also measured the mesospheric distributions of HF, HCl, H2O and HDO. HCl is less abundant than reported 40u2009years ago. HDO/H2O is enhanced by a factor of ∼2.5 with respect to the lower atmosphere, and there is a general depletion of H2O around 80–90u2009km for which we have no explanation.

The study of the martian atmosphere from top to bottom with SPICAM light on mars express

[1]xa0This paper is intended as an introduction to several companion papers describing the results obtained by the SPICAM instrument on board Mars Express orbiter. SPICAM is a lightweight (4.7 kg) UV-IR dual spectrometer dedicated primarily to the study of the atmosphere of Mars. The SPICAM IR spectrometer and its results are described in another companion paper. SPICAM is the first instrument to perform stellar occultations at Mars, and its UV imaging spectrometer (118–320 nm, resolution ∼1.5 nm, intensified CCD detector) was designed primarily to obtain atmospheric vertical profiles by stellar occultation. The wavelength range was dictated by the strong UV absorption of CO2 (λ < 200 nm) and the strong Hartley ozone absorption (220–280 nm). The UV spectrometer is described in some detail. The capacity to orient the spacecraft allows a great versatility of observation modes: nadir and limb viewing (both day and night) and solar and stellar occultations, which are briefly described. The absolute calibration is derived from the observation of UV-rich stars. An overview of a number of scientific results is presented, already published or found in more detail as companion papers in this special section. SPICAM UV findings are relevant to CO2, ozone, dust, cloud vertical profiles, the ozone column, dayglow, and nightglow. This paper is particularly intended to provide the incentive for SPICAM data exploitation, available to the whole scientific community in the ESA data archive, and to help the SPICAM data users to better understand the instrument and the various data collection modes, for an optimized scientific return.

Global structure and composition of the martian atmosphere with SPICAM on Mars express

Abstract SPICAM Light is a small UV-IR instrument selected for Mars Express to recover most of the science that was lost with the demise of Mars 96, where the SPICAM set of sensors was dedicated to the study of the atmosphere of Mars (Spectroscopy for the investigation of the characteristics of the atmosphere of mars). The new configuration of SPICAM Light includes optical sensors and an electronics block. A UV spectrometer (118–320 nm, resolution 0.8 nm) is dedicated to Nadir viewing, limb viewing and vertical profiling by stellar occultation (3.8 kg). It addresses key issues about ozone, its coupling with H2O, aerosols, atmospheric vertical temperature structure and ionospheric studies. An IR spectrometer (1.2– 4.8 μm , resolution 0.4–1 nm) is dedicated to vertical profiling during solar occultation of H2O, CO2, CO, aerosols and exploration of carbon compounds (3.5 kg). A nadir looking sensor for H2O abundances (1.0– 1.7 μm , resolution 0.8 nm) is recently included in the package (0.8 kg). A simple data processing unit (DPU, 0.9 kg) provides the interface of these sensors with the spacecraft. In nadir orientation, SPICAM UV is essentially an ozone detector, measuring the strongest O3 absorption band at 250 nm in the spectrum of the solar light scattered back from the ground. In the stellar occultation mode the UV Sensor will measure the vertical profiles of CO2, temperature, O3, clouds and aerosols. The density/temperature profiles obtained with SPICAM Light will constrain and aid in the development of the meteorological and dynamical atmospheric models, from the surface to 160 km in the atmosphere. This is essential for future missions that will rely on aerocapture and aerobraking. UV observations of the upper atmosphere will allow study of the ionosphere through the emissions of CO, CO+, and CO2+, and its direct interaction with the solar wind. Also, it will allow a better understanding of escape mechanisms and estimates of their magnitude, crucial for insight into the long-term evolution of the atmosphere. The SPICAM Light IR sensor is inherited from the IR solar part of the SPICAM solar occultation instrument of Mars 96. Its main scientific objective is the global mapping of the vertical structure of H2O, CO2, CO, HDO, aerosols, atmospheric density, and temperature by the solar occultation. The wide spectral range of the IR spectrometer and its high spectral resolution allow an exploratory investigation addressing fundamental question of the possible presence of carbon compounds in the Martian atmosphere. Because of severe mass constraints this channel is still optional. An additional nadir near IR channel that employs a pioneering technology acousto-optical tuneable filter (AOTF) is dedicated to the measurement of water vapour column abundance in the IR simultaneously with ozone measured in the UV. It will be done at much lower telemetry budget compared to the other instrument of the mission, planetary fourier spectrometer (PFS).