arXiv subjects

Itziar Garate-Lopez

Publications and source records attributed to Itziar Garate-Lopez.

4 recordsLinked to original sources

arXiv2026

Information content on Venusian aerosols in VIRTIS-M infrared data

Venus presents a complex cloud structure with aerosol particles of different sizes located mainly between 48 km and 70 km in altitude. However, the number of free parameters that can describe such a cloud structure is usually overwhelming, and a number of simplified parameterizations are commonly assumed. In this work, we re-analyze the information content on aerosol vertical distribution provided by the nightside infrared data collected by VIRTIS instrument onboard Venus Express. Starting from Haus et al. (2013) aerosol vertical distribution description, we use the archNEMESIS radiative transfer code and retrieval suite together with the Bayesian inference tool Multinest to compute the evidence supporting different models based on alternative choices of model parameters. This study analyzes locations at three different regions: mid-latitudes, the so-called cold collar, and the South Polar Vortex. We use a data cube that covers all of these regions simultaneously and additional observations distributed throughout the Venus Express mission. We find that these observations provide significant information about the peak particle number density, base altitude and layer thickness of aerosol modes 2, 2' and 3 when individual parameters are retrieved - a more informative description than the scaling `mode factors' often used in similar retrievals. Including mode 1 in our models, however, does not provide a significant increase of Bayesian evidence. Our retrieved cloud and temperature profiles are in general agreement with previous studies, although we find higher cloud tops in the South Polar Vortex locations. This initial computing effort provides an optimal parameterization that will allow us to study in greater detail the instantaneous horizontal cloud and temperature structure from the entire VIRTIS-M infrared database, which we will discuss in a forthcoming paper.

astro-ph.EP↗

arXiv2025

Evaluation of new radio occultation observations among small satellites at Venus by data assimilation

We conducted observing system simulation experiments (OSSEs) for radio occultation measurements (RO) among small satellites, which are expected to be useful for future Venus missions. The effectiveness of the observations based on realistic orbit calculations was evaluated by reproduction of the "cold collar", a unique thermal structure in the polar atmosphere of Venus. Pseudo-temperature observations for the OSSEs were provided from the Venus atmospheric GCM in which the cold collar was reproduced by the thermal forcing. The vertical temperature distributions between 40 and 90 km altitudes at observation points were assimilated. The result showed that the cold collar was most clearly reproduced in the case where the temperature field in high-latitudes was observed twice a day, suggesting that the proposed observation is quite effective to improve the polar atmospheric structure at least. Although the cold collar was also reproduced in the OSSEs for Longwave Infrared Camera (LIR) observations, the result seemed unrealistic and inefficient compared to that obtained in the RO OSSEs. The present study shows that the OSSEs can be used to evaluate observation plans and instruments in terms of reproducibility of specific atmospheric phenomena, and applied to future missions targeting planetary atmospheres.

astro-ph.EP↗

arXiv2024

Validation of the IPSL Venus GCM Thermal Structure with Venus Express Data

General circulation models (GCMs) are valuable instruments to understand the most peculiar features in the atmospheres of planets and the mechanisms behind their dynamics. Venus makes no exception and it has been extensively studied thanks to GCMs. Here we validate the current version of the Institut Pierre Simon Laplace (IPSL) Venus GCM, by means of a comparison between the modelled temperature field and that obtained from data by the Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) and the Venus Express Radio Science Experiment (VeRa) onboard Venus Express. The modelled thermal structure displays an overall good agreement with data, and the cold collar is successfully reproduced at latitudes higher than +/-55°, with an extent and a behavior close to the observed ones. Thermal tides developing in the model appear to be consistent in phase and amplitude with data: diurnal tide dominates at altitudes above 10^2 Pa pressure level and at high-latitudes, while semidiurnal tide dominates between 10^2 and 10^4 Pa, from low to mid-latitudes. The main difference revealed by our analysis is located poleward of 50°, where the model is affected by a second temperature inversion arising at 10^3 Pa. This second inversion, possibly related to the adopted aerosols distribution, is not observed in data.

astro-ph.EP↗

arXiv2024

Six years of Venus winds at the upper cloud level from UV, visible and near infrared observations from VIRTIS on Venus Express

Venus Express provided a long-term monitoring of Venus atmosphere. Several works focused on the dynamics of the upper cloud visible on the day-side in ultraviolet images sensitive to the 65-70 km altitude and in the lower cloud level (50 km height) observable in the night-side of the planet in 1.74 microns. Here we use VIRTIS-M spectral images to study the upper cloud layer in ultraviolet (360-400 nm), visible (570-680 nm) and near infrared (900-955 nm) extending in time previous analysis of VIRTIS-M data. UV images show relatively well contrasted cloud features at the cloud top. Cloud features in the visible and near infrared images lie a few kilometers below the upper cloud top, have low contrast and are distinct to the features observed in the uv. Wind measurements were obtained over a six-year period using a semi-automatic cloud correlation algorithm. Results for the upper cloud confirm analysis based on images obtained by the Venus Monitoring Camera (Khatuntsev et al. 2013). At the cloud top the mean zonal and meridional winds vary with local time accelerating towards the local afternoon. The upper branch of the Hadley cell reaches maximum velocities at 45deg latitude and local times of 14-16h. The mean zonal winds in the uv cloud accelerated in the course of the 2006-2012 period 15 ms-1. The near infrared and visible images show a more constant circulation without time variability or longitudinal variations. The meridional circulation is absent in near infrared and visible images indicating thatthe Hadley-cell circulation in Venus atmosphere is shallow or the returning branch of the meridional circulation extends to levels below levels sensed in near infrared images. At the clod tops observed in UV images there are signatures of a long-term acceleration of the zonal winds when comparing winds from 2006-2008 to 2009-2012 with a mean acceleration of 17 ms-1 between both time periods

astro-ph.EP↗