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The discontinuity/disruption is a recurrent atmospheric wave observed to propagate during decades at the deeper clouds of Venus (47-56 km above the surface), while its absence at the top of the clouds (~70 km) suggests that it might dissipate at the upper clouds and contribute to the puzzling atmospheric superrotation through wave-mean flow interaction.Thanks to a campaign of ground-based observations performed in coordination with JAXA's Akatsuki mission since December 2021 until July 2022, we aimed to undertake the longest uninterrupted monitoring of the cloud discontinuity up to date to obtain a pioneering long-term characterization of its main properties and better constrain its recurrence and lifetime. The dayside upper, middle and nightside lower clouds were studied with images taken with suitable filters acquired by Akatsuki/UVI, amateur observers and NASA's IRTF/SpeX, respectively. Hundreds of images were inspected in search of discontinuity events and to measure properties like its dimensions, orientation or rotation period.We succeeded in tracking the discontinuity at the middle clouds during 109 days without interruption. The discontinuity exhibited properties nearly identical to measurements in 2016 and 2020, with an orientation of 91º±8º, length of 4100±800, width of 500±100 km and a rotation period of 5.11±0.09 days. Ultraviolet images during 13-14 June 2022 suggest that we have witnessed for the first time a manifestation of the discontinuity at the top of the clouds during ~21 hours, facilitated by an altitude change in the critical level for this wave due to slower zonal winds.

We present PlAnetaRy SciencE Collaboration tool (PARSEC), a service for coordinating the Solar System observations for observers and researchers. Parsec contains observational campaign coordination tool with alert system and email notifications. The service can be found at www.parsec-europlanet.eu. In the framework of the Europlanet-2024-RI project we are developping a generalized Alert System for observations, which will notify and allow participating observatories to select appropriate targets across the diverse range of planetary science topics. This will provide both regular monitoring of targets and alerts for events requiring time-critical and/or spatially distributed observations (e.g. stellar occultations by asteroids). The service will be based on the existing alert system software created to coordinate amateur observations of asteroids in support of the ESA Gaia mission (Gaia-GOSA, www.gaiagosa.eu, Santana-Ros et al., 2016). We have chosen a toolset for the service development: PARSEC (PlAnetaRy SciencE Collaboration tool) which is a webapp created in Python, Flask and bootstrap frameworks with additional C++ code and postgresql database. The main features were programmed, thereby enabling request views on the main page, request filtering by observation date, target category, ownership, campaign view, and a notification system. The user can also establish preferences for notifications and follow requests/campaigns. In the „Requests” view there is the possibility of adding, editing, deleting, commenting the observational needs. Similarly, in „Campaigns” the user can start and coordinate observing campaigns of objects or events. In addition, observational alerts on topics related to planetary atmospheres are announced at the PVOL database (http://pvol2.ehu.eus/pvol2/) including in some cases detailed observation ephemeris and links to relevant campaigns around each alert. The service is currently under developmend, and testing by users is strongly recommended. The service can be found at www.parsec-europlanet.eu.Santana-Ros T., Marciniak A., Bartczak P., 2016, “Gaia-GOSA: A Collaborative Service for Asteroid Observers”,MPBull, 43, 205

Non-professional astronomers can significantly contribute to key research projects in Astronomy. The collaboration between professional and amateur astronomers is known as ProAm collaboration. Since 2009 the Spanish Astronomy Association (SEA) has housed a specific working group promoting the relationship between professional and amateur astronomers: the ProAm Commission. The SEA ProAm Commission has just published a report analyzing the status of the ProAm collaboration in Spain. It is the first time that such analysis has been performed in Spain. Data were collected using the information provided in recent amateur astronomy conferences. An exhaustive search of scientific publications in which amateur astronomers had participated was also carried out. And a survey to both amateur and professional astronomers was conducted to compile key information. This report confirms that Spanish amateur astronomers collaborate significantly with professional astrophysicists, with around a 100 of them being regularly included in science publications and astronomical circulars. The number of ProAm collaborations is steadily increasing with time. More than 200 peer-reviewed publications and almost 5000 astronomical circulars including Spanish amateur astronomers have been published to date. However the fraction of women involved in ProAm collaborations is low: 4% and 7% for the professional and amateur astronomers, respectively. This significant gender gap needs to be addressed. Both amateur and professional astronomers requested to improve communication channels in both directions. The SEA ProAm Commission is addressing this issue with the development of a specific webpage, https://proam.sea-astronomia.es . In addition, since 2021 the SEA ProAm Commission organizes informative sessions on a monthly basis with the aim of promoting the visibility of the ProAm collaboration in Spain. The SEA ProAm Commission is also coordinating several training courses to increase the observing and data processing skills of amateur astronomers. So far two courses have been held: 'Python Course for amateur astronomers' and the 'Astronomical Calculation Course'. All the training courses (material and recordings of the sessions) and the dissemination sessions of the ProAm projects are publically available in the SEA ProAm Commission webpage. Finally, we have defined a code of good conduct applicable to ProAm collaborations and relationships in astronomy, where the rules and good practices to be followed are brought together to guarantee the well-being of all the people who participate in ProAm projects.

One of Venus’ unsolved mysteries is the dynamics of its polar vortices: what makes them so changeable? Where do they get the energy to survive for at least 8 years without disappearing once? How, if at all, do they affect the general circulation of the atmosphere (the so-called superrotation)? Here, we will show new measurements of wind, air temperature, and Ertel’s potential vorticity to try to clarify these points. The VIRTIS imaging spectrometer on board the Venus Express spacecraft constantly observed the south polar vortex from 2006 to 2014. Using the data provided by this instrument in the 1.0 – 5.1 microns wavelength range, we have analysed 11 different dates and morphologies of the vortex, which added to those analysed in our previous studies [1, 2, 3] sum up to 35 in total for the wind analysis, 8 for the thermal analysis and 8 for the potential vorticity analysis. Wind speed has been measured by tracking clouds in more than a couple of images per date. Radiative transport and inversion techniques have been used to obtain the three-dimensional spatial distribution of the air temperature [4]. In this way, we have produced wind maps at two heights (for the lower cloud and the upper cloud, that is, ~42 km and ~62 km above the surface at polar latitudes) and air temperature maps for several atmospheric layers between 55 and 85 km altitude. The aim is to improve our understanding of the dynamics governing these vortices by confirming or refuting previously observed trends [3]. For example, the annular shape of the potential vorticity in the upper level of the clouds or the anti-correlation between the visible structures in the thermal infrared (the most characteristic structures of the Venus polar vortex) and the peaks of the potential vorticity. References [1] I. Garate-Lopez, R. Hueso, A. Sánchez-Lavega, J. Peralta, G. Piccioni, P. Drossart. A chaotic long-lived vortex in Venus’ southern pole. Nature Geoscience 6, 254-257 (2013). https://doi.org/10.1038/ngeo1764 [2] I. Garate-Lopez, A. García Muñoz, R. Hueso, A. Sánchez-Lavega. Instantaneous three-dimensional thermal structure of the South Polar Vortex of Venus. Icarus 245, 16-31 (2015). https://doi.org/10.1016/j.icarus.2014.09.030 [3] I. Garate-Lopez, R. Hueso, A. Sánchez-Lavega, A. García Muñoz. Potential Vorticity of the South Polar Vortex of Venus. Journal of Geophysical Research: Planets 121, 574-593 (2016). https://doi.org/10.1002/2015JE004885 [4] D. Grassi, P. Drossart, G. Piccioni, N. I. Ignatiev, L. V. Zasova, A. Adriani, M. L. Moriconi, P. G. J. Irwin, A. Negrao, A. Migliorini (2008). Retrieval of air temperature profiles in the venusian mesosphere from VIRTIS-M data: Description and validation of algorithms. Journal of Geophysical Research: Planets 113, 1–12. https://doi.org/10.1029/2008JE003075

The Europlanet 2024 Research Infrastructure (RI) provides free access to the world’s largest collection of planetary simulation and analysis facilities, data services and tools, a ground-based observational network and programme of community support activities (https://www.europlanet-society.org/europlanet-2024-ri/). A new collaboration between telescopes around the world has been launched in 2020 to provide coordinated observations and rapid responses in support of planetary research from space missions and in follow-ups of new events. The Europlanet Telescope Network (EPN-TN) is providing professional and trained amateur observers with access to small and medium-sized telescopes located around the globe (https://www.europlanet-society.org/europlanet-2024-ri/telescope-network/). The EPN-TN currently comprises 16 observatories with 46 telescopes ranging from 40 cm to 2 m in size. The network can be accessed free of charge to carry out projects on a wide variety of scientific studies about the Solar System and exoplanets, as well as related astronomical investigations. The network is open for new infrastructures. The first scientific results achieved with EPN-TN were presented at the Europlanet Telescope Network Science Meeting held on the 6-11 February, 2022. Among 210 participants from 43 countries, there were 80 amateur astronomers participating (http://mao.tfai.vu.lt/europlanet2022/). The network aims to strengthen collaborations between professional and amateur astronomers, who are playing an increasingly important role in planetary research. Observing time applicants from amateur astronomers are very welcome. We will overview the EPN-TN and its potential in fostering the collaboration between professional and amateur astronomers. Acknowledgements Europlanet 2024 RI has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 871149.

The Planetary Virtual Observatory & Laboratory database (PVOL, http://pvol2.ehu.eus/pvol2/) contains a large set of amateur observations of solar system planets and is a tool that has been widely used in pro-am collaborations. PVOL is integrated in the Virtual European Solar and Planetary Access (VESPA, http://vespa.obspm.fr/planetary/data/) set of services developed through Europlanet 2020 RI and Europlanet 2024 RI, further increasing its visibility in the professional astronomy landscape. The essential content of PVOL is images of the planets obtained by amateur astronomers. This content is continuously updated by registered users, and a web manager who uploads submissions from not registered users sent by email to pvol@ehu.eus. Close to planetary oppositions, daily observations of Mars, Jupiter and Saturn allow detailed surveys of their atmospheric activity. Near maximum elongation of Venus, amateur images unveil large-scale structures in the clouds. Amateur observations of Uranus and Neptune are not so common, but amateurs obtain very valuable observations of these atmospheres in special cases when alerts of new large atmospheric features are sent. The potential for science of these data sets is very large, and PVOL contains a list of >40 scientific publications led by researchers from several independent teams using data from PVOL in different domains. Further observations of Galilean moons and even our Moon can be submitted to PVOL where the data can serve different purposes, including educational ones. Thus, PVOL is increasing is role as a general service to the planetary sciences community and the amateur astronomers collaborating with different research groups. Figure 1 shows a set of various images of planets available in the database. Figure1: Set of amateur images in the PVOL database obtained by different observers and covering different scientific domains. In recent years, new data types have been added including: (i) Maps of Junocam images of Jupiter (see Figure 2), (ii) photometry and spectroscopic data. The system also keeps track of publications using PVOL data and supports specific campaigns, like the Venus BepiColombo flyby, or the search for Jovian Impacts in collaboration with the DeTeCt project at http://www.astrosurf.com/planetessaf/doc/project_detect.php. In addition, PVOL contains an alert section where observational alerts are updated regularly besides submissions by email to specific e-mail lists of amateur astronomers. In this contribution we review the status of the data in PVOL (see Figure 3) and additional services and we indicate future plans for PVOL including a better handling of photometric and spectroscopic data submitted by amateur astronomers. Figure 2: One of the many Junocam maps of Jupiter in the PVOL database. Figure 3: Number of observations per target currently stored in PVOL. Jupiter numbers include maps of Jupiter obtained by the Junocam instrument on the Juno mission. Acknowledgements We are very grateful to the large community of amateur astronomers submitting their observations to PVOL. We are also grateful to C. Hansen and G. S. Orton for their generous collaboration in helping us with data from the Junocam instrument, and also from their continuous support of pro-am activities around Juno. Europlanet 2024 RI has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 871149.

Europlanet 2024 RI is a Research Infrastructure funded by the European Commission from Feb. 2020 to Feb. 2024 to enhance collaborations among planetary scientists through Europe by providing networking activities, virtual services and access to research facilities. One of the activities of the RI is the Europlanet Telescope Network (ETN), a program to fund access and costs of use to a network of telescopes for observations of Solar System objects and exoplanets. One of the goals of the network is to widen the participation of amateur astronomers in professional and amateur (pro-am) collaborations accepting proposals from amateur astronomers that are evaluated by a scientific committee on the scientific merit only. Many amateur astronomers have a long-standing experience in astronomical observations and data analysis, can extract very valuable observations from the telescopes of the network and are part of large pro-am projects. However amateur astronomers have little to no experience in the subtleties of writing proposals. To counteract this disadvantage the project decided to organize a workshop on proposals writing that could inspire amateur astronomers and result in future successful proposals. The first of such workshops was organized as a virtual meeting on May 15, 2021 (Saturday) [1], in collaboration with the Spanish-Portuguese hub of the Europlanet Society [2], the Pro-Am Commission of the Spanish Society of Astronomy [3], and the Federation of Amateur Astronomical Associations of Spain [4]. Although the workshop was conducted in Spanish there were participants from France and Portugal, and some participants from South America. Here we will show how we structured the workshop, the first one developed to publicise the ETN among amateurs and facilitate access for them in a practical way. We will also detail the positive results so far and the lessons learnt from this experience. The workshop was structured in three main sessions: (1) A morning session with full details of the ETN and examples of pro-am collaborations (2 hours long); (2) An afternoon session dedicated to the ETN call and the proposal writing (4 hours); (3) A night-time session dedicated to remote observation that started at 9 p.m. and was extended from 1 a.m. (official closing time of the workshop) to 6 a.m. In the first session, the Europlanet project and the telescope network were described, with emphasis on the closest telescopes most likely to be used by the Spanish amateur community. Several Pro-Am projects in which they could collaborate with their observations were also detailed. Special emphasis was given to projects embedded in Europlanet2024RI such as Gaia-GOSA [5] or ExoClock [6], and VESPA [7] and associated databases (such as PVOL [8]). Finally, several activities undertaken by the Pro-Am Commission of the Spanish Society of Astronomy were presented. In the second session, the process of accessing the network was explained with the conditions to be fulfilled and the steps to be followed. Public information on the proposals granted so far were analysed and examples of studies that amateurs can perform with the telescopes of the network were shown, emphasising the scientific contribution of these observations. The open call and funding application form were explained in detail in a writing workshop. The scientific approach to be given to the whole funding proposal was highlighted and examples were given in all sections. This session ended with a demonstration of remote use of one of the telescopes of the network: the 1.23m of the Calar Alto Observatory. The night session was organized around observations of objects previously proposed by the participants. These were the comets C2021A1 and C2017K2 (figure 1), the transiting exoplanet WASP-14b (figure 2), and we ended up with an observation of Saturn and 6 of its moons (figure 3). The number of active participants was about 70 in all sessions and 15 of them stayed on until 6 a. m. They all said they like the initiative, the project, and being able to use these telescopes. For many amateurs the main drawback to prepare an application is the bureaucratic steps associated to the proposal. For others, a drawback is the perceived difficulties in using a large telescope and its instrument from the available documentation resulting in stiff learning curves. For most of them, the direct experience of using a 1-m class size telescope resulted in a very positive experience and some observers declared the workshop motivated them to prepare proposals to the network in the near future. We recommend to the rest of the Europlanet hubs to reproduce similar workshops in their regions which can boost not only the use of the ETN, but also the participation of amateur astronomers in varied pro-am projects. Acknowledgements Europlanet 2024 RI has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 871149. We are very grateful to the Calar Alto Observatory for their good disposal and technical support. References [1] https://www.europlanet-society.org/virtual-workshop-on-the-use-of-the-europlanet-telescope-network-for-amateur-astronomers/ [2] https://spainportugal-eps.org/index.php/en/ [3] https://www.sea-astronomia.es/colaboracion-pro-am [4] https://federacionastronomica.es/ [5] http://www.gaiagosa.eu [6] https://www.exoclock.space/ [7] http://www.europlanet-vespa.eu/ [8] http://pvol2.ehu.eus/pvol2/ Figure 1: Comets C/2017K2 (left) and C/2021A1 (right). Data analyzed by Ramón Navès. Images are stacks of 25 (left) and 21 (right) exposures of 2 minutes in both panels. Brightness isolines are represented in the insets in color. Figure 2: Lightcurve of exoplanet WASP-14b based on 2 seconds exposures. Data analyzed by Mercè Correa with the Hops program of the ExoClock project. Figure 3: Saturn and moons. Single shot of 0.01 s near dawn.

Venus has one of today’s most unknown atmospheres with one of the unsolved mysteries being the origin and maintenance of its polar vortices. Although the current orbiting espacecraft, the Japanese Akatsuki, cannot adequately observe the planet's poles, the previous European Space Agency’s Venus Express mission studied the south polar vortex for more than 7 years. The VIRTIS-M imaging spectrometer observed this peculiar atmospheric structure and its constantly changing shape day after day from 2006 to 2014. This translates into an immense amount of data, which is still not fully exploited today. Some time ago we obtained preliminary maps of the Ertel potential vorticity [1], a characteristic magnitude in the study of fluid dynamics as it is conserved following the full three-dimensional motions of an air parcel. However, the number of data-cubes we were able to analyse did not allow us to draw statistically strong conclusions. We now aim to improve these statistics in order to confirm or disprove previously observed trends, such as the annular shape of the potential vorticity at the upper cloud level or the anti-correlation between the structures visible in thermal infrared (the most characteristic structures of the Venus’ polar vortex) and the potential vorticity’s peaks [1]. To this end, here we will present new measurements of the wind field at two atmospheric levels (~42 km above the surface and ~62 km) using images at 1.74 microns and at 3.8 or 5.1 microns obtained by the VIRTIS instrument for about 10 different dates and morphologiess. We measured the wind velocity by cloud tracking in more than one pair of images per date. We will also present new measurements of three-dimensional distribution of the air temperature. The VIRTIS instrument provides us with spectra for each pixel of the image in the range 1.0 - 5.1 microns. Using radiative transport and inversion techniques [2], we know how to calculate the spatial distribution of the temperature field for several atmospheric layers between 55 and 85 km height [3]. We intend to obtain temperature maps for the lower and upper cloud layers in as many pairs of images as possible, thus studying both the short and long term evolution. And finally, with wind and temperature fields’ distribution at both cloud layers in our hands, we will try to construct and exhibit Ertel’s potential vorticity maps. References [1] I. Garate-Lopez, R. Hueso, A. Sánchez-Lavega, A. García Muñoz. Potential Vorticity of the South Polar Vortex of Venus. Journal of Geophysical Research: Planets 121, 574-593 (2016). https://doi.org/10.1002/2015JE004885 [2] D. Grassi, et al., 2008. Retrieval of air temperature profiles in the venusian mesosphere from VIRTIS-M data: Description and validation of algorithms. Journal of Geophysical Research: Planets 113, 1–12. https://doi.org/10.1029/2008JE003075 [3] I. Garate-Lopez, A. García Muñoz, R. Hueso, A. Sánchez-Lavega. Instantaneous three- dimensional thermal structure of the South Polar Vortex of Venus. Icarus 245, 16-31 (2015). https://doi.org/10.1016/j.icarus.2014.09.030

Since February 2020, the Horizon 2020 research infrastructure project Europlanet 2024 (EPN 2024 RI; website: bit.ly/2Z1XA8u) is serving the planetary sciences community with diverse schemes and funding opportunities. As part of this project, the Europlanet Telescope Network (website: bit.ly/37SCiyj), a collaboration between small telescope facilities in Europe and beyond, kick-started in June of the same year with the goal to provide coordinated observations, support for space missions, and to better integrate amateur astronomers into planetary sciences. Since then, the network is providing access for professional and citizen scientists to 16 different observatories ranging from 40cm to 2m in size (see figure and list below). While the network plans to draw in additional facilities and to build new collaborations, scientists and amateurs can apply through a rolling Call for Observations (website: bit.ly/2Br5LDt) to visit those facilities that are already participating in the network and have their expenses reimbursed for the time needed to make their observations. This also comprises the possibility of remote observations since the network includes 14 robotic or remotely operated facilities. Any of the short applications to the call (2 to 3 pages in size) will be reviewed anonymously by the Science Advisory Panel on a bi-monthly basis which should assure a relatively fast reaction to potential observational alerts. Even though the focus of the network is on planetary sciences and exoplanets, the project does also accept applications covering other scientific areas. The first proposals granted, therefore, cover a diverse scientific field, ranging from asteroids to exoplanets, and the observation of variable nebulae. This presentation will review the Europlanet Telescope Network and the facilities involved, how researchers and amateur astronomers can apply, and will also give examples on the first observations performed at the network. Besides coordinated observations at the Europlanet Telescope Network, this project also supports the integration of amateur astronomers into planetary sciences through the organization of dedicated workshops and the provision of a newly developed web platform for the issuing of observational alerts and the organization of coordinated campaigns. While we will overview these activities in the second part of our presentation, we will also give an outlook onto the upcoming years and on the support that we are yet planning to provide for amateur astronomers and the planetary sciences community. The telescopes in the network: 1. Pic du Midi Observatory, France: 1.06-m telescope2. Moletai Astronomical Observatory, Lithuania: 1.65-m and 35/51-cm telescopes3. Kryoneri Observatory, Greece: 1.2-m telescope4. Skalnate Pleso Observatory, Slovakia: 1.3-m and 61-cm telescopes5. Faulkes Telescope Project: two 2-m, nine 1-m, and ten 40-cm robotic telescopes6. Tartu Observatory, Estonia: 1.5-m and 60-cm telescopes, and 30-cm robotic telescope7. Danish 1.54-m telescope at La Silla Observatory, Chile: 1.54-m telescope8. Beacon Observatory, UK: 42-cm telescope9. Observatorie del Teide, Spain: 82-cm and 45-cm telescopes10. Calar Alto Observatory, Spain: 1.23-m telescope11. Lisnyky Observation Station, Ukraine: 70-cm telescope12. Chuguev Observatory, Ukraine: 70-cm telescope13. Terskol Peak Observatory, Ukraine: 2-m and 60-cm telescopes14. Konkoly Observatory, Hungary: 1-m and 80-cm telescopes15. Ussuriysk Astrophysical Observatory, Russia: 25-cm and 50-cm telescopes16. Rozhen Observatory, Bulgaria: 2-m, 60-cm, and 50/70-cm telescopes Further information on the different facilities can be found at bit.ly/2Br5LDt. Acknowledgements. Europlanet 2024 RI has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 871149.

Feasibility of radio occultation measurement (RO) among small satellites is investigated by observing system simulation experiment (OSSE) of the Venus data assimilation system in two test cases introducing real orbits. One observes cold collar in polar region. The other observes thermal tides in equatorial region. The reproducibility of the cold collar or thermal tides is investigated by several types of orbits. Results suggests that the cold collar is successfully reproduced with two or three satellites. In addition, zonal wind can be improved by temperature assimilation of the thermal tides with two satellites. Therefore, RO among small satellites would be promising to reproduce global phenomena in the Venus atmosphere. 1. Introduction Venus atmosphere has a global, thick cloud cover at about 48–70 km altitude. Therefore, it is very difficult to observe under the cloud by the images. One of the most useful methods to obtain vertical temperature profiles is RO. For Earth, daily observations have been performed by GNSS (Global Navigation Satellite System). However, Venus has been observed only between one satellite, e.g., Venus Express or Akatsuki [1], and Earth. For multiple satellites, by transmitting and receiving radio waves between them, more observations, multiple points and better time resolution, could be obtained. In the previous study, we have shown that RO among small satellites can reproduce the cold collar with fixed observational points [2]. In order to check feasibility, however, we have to consider realistic orbits of flying multiple satellites around Venus. So far, we have developed Venus atmospheric general circulation model (AGCM) named AFES-Venus (AGCM for the Earth Simulator for Venus) [3]. Recently, using the local ensemble transform Kalman filter (LETKF) [4], we have succeeded in developing the AFES LETKF data assimilation system for Venus (ALEDAS-V) [5]. In this study, we performed OSSE assuming RO among small satellites in two test cases with real orbits targeting the cold collar and thermal tides. 2. Experimental setting AFES-Venus solves dry 3-D Primitive equation on sphere. The physical parameters are based on Venus. The latitude-longitude grids (128 times 64) with 60 vertical layers are used. The simulation starts from idealized super rotation and spin up for 4 Earth years. Reproduced zonal wind is in good agreement with observations [6]. ALEDAS-V uses the LETKF [4] to produce an improved estimate (called analysis) by combining observations and short time ensemble forecasts of AFES-Venus. The number of ensemble members is 31. Assimilation cycle is 6 hourly interval. Observational errors and inflation are set to 3.0 K and 10%, respectively. Details are described in [2, 5]. Two experiments are conducted; one is evaluated by the cold collar (experiment 1), and the other is evaluated by the thermal tides (experiment 2). Idealized temperature observations at 40-90 km are prepared by the GCMs assuming RO among small satellites. Experiment 1 uses data from IPSL VGCM because the cold collar is more realistically reproduced [7]. Note that temperature bias between IPSL VGCM and AFES-Venus is corrected. Experiment 2 uses data from AFES-Venus itself but experimental settings are different. Observation points are based on real orbits; Experiment 1 covers polar region and experiment 2 does equatorial region. They are assimilated to AFES-Venus by ALEDAS-V and results are compared with frf (free run forecast). The reproducibility of the cold collar or thermal tides is investigated by several orbits. 3. Results Figure 1 shows the temperature distributions at 30-90°N at ~66 km in experiment 1. Four situations are considered: (a) frf and (b,c,d) has different orbits. p1, p2 and p3 indicate each pair of satellites. Cold collar is most clearly reproduced for (d) in which all 3 satellites proceed RO. Figure 1: Temperature distributions at ~66 km (at 30-90°N seen from the north pole): (a) frf, (b) 1 pair of satellites (p1), (c) 2 pairs (p1 and p3), and (d) 3 pairs (p1, p2 and p3). Figure 2 shows latitude-height cross sections of zonal wind (contour) and difference of zonal wind between frf and the Qt8 cases (color) in which the solar heating is reduced to 80% compared with that used in frf. The 4 types of orbits are considered. The zonal wind above the cloud top (~80 km) is significantly decelerated in (d). It is suggested that temperature observations of the thermal tides can improve zonal wind. Figure 2: Latitude-height cross sections of zonal wind (contour) and difference of zonal wind between frf and the Qt8 cases (color). 4 types of orbits are shown: a2 (a), b1 (b), b2 (c), and c2 (d). c2 has most observations, following b2, b1 and a2. Summary and Conclusions In the present study, we have checked feasibility of the Venus future mission of RO among small satellites by introducing real orbits. In experiment 1, the cold collar is reproduced with 2 or 3 satellites observing polar region. In experiment 2, zonal wind is improved by the temperature observations of the thermal tides in equatorial region. Results suggest that RO with two or three small satellites would be promising to reproduce global phenomena. Furthermore, it is also suggested that this kind of observing system simulation experiment would be very useful to design future missions. Acknowledgements This study and supported by the Japan Science and Technology Agency (JST). References [1] Ando, H. et al.: Thermal structure of Venus atmosphere from sub-cloud region to the mesosphere observed by radio occultation, Scientific Rep., 2020. [2] Sugimoto, N. et al.: Observing system simulation experiment for radio occultation measurements of the Venus atmosphere among small satellites, Journal of JSCE A2: Applied Mechanics, 2019. [3] Sugimoto, N. et al.: Baroclinic instability in the Venus atmosphere simulated by GCM, J. Geophys. Res., Planets, 2014. [4] Miyoshi, T. and S. Yamane: Local ensemble transform Kalman filtering with an AGCM at a T159/L48 resolution. Mon. Wea. Rev. 135, 2007. [5] Sugimoto, N. et al.: Development of an ensemble Kalman filter data assimilation system for the Venusian atmosphere, Scientific Rep., 2017. [6] Sugimoto, N. et al.: Waves in a Venus general circulation model, Geophys. Res. Lett., 2014. [7] Garate-Lopez, I and S. Lebonnois: Latitudinal variation of clouds’ structure responsible for Venus’ cold collar, Icarus, 2018.

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 +/&minus, 55&deg, 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 102 Pa pressure level and at high-latitudes, while semidiurnal tide dominates between 102 and 104 Pa, from low to mid-latitudes. The main difference revealed by our analysis is located poleward of 50&deg, where the model is affected by a second temperature inversion arising at 103 Pa. This second inversion, possibly related to the adopted aerosols distribution, is not observed in data.

International audience; Global Climate Models (GCM) are very useful tools to study theoretically the general dynamics and specific phenomena in planetary atmospheres. In the case of Venus, several GCMs succeeded in reproducing the atmosphere’s superrotation and the global temperature field. However, the highly variable polar temperature and the permanent cold collar present at latitude have not been reproduced satisfactorily yet.

International audience; Based on our experience of Earth and Mars Global Climate Models, a model for Venus's climate system has been developed within Institute Pierre Simon Laplace (LMD, LATMOS) for twelve years. Thermal radiation scheme is based on Net-Exchange Rate (NER) matrices, with look-up tables for solar heating rate forcing.