L. Montabone

Eight-year climatology of dust optical depth on Mars

Abstract We have produced a multiannual climatology of airborne dust from martian year 24–31 using multiple datasets of retrieved or estimated column optical depths. The datasets are based on observations of the martian atmosphere from April 1999 to July 2013 made by different orbiting instruments: the Thermal Emission Spectrometer (TES) aboard Mars Global Surveyor, the Thermal Emission Imaging System (THEMIS) aboard Mars Odyssey, and the Mars Climate Sounder (MCS) aboard Mars Reconnaissance Orbiter (MRO). The procedure we have adopted consists of gridding the available retrievals of column dust optical depth (CDOD) from TES and THEMIS nadir observations, as well as the estimates of this quantity from MCS limb observations. Our gridding method calculates averages and uncertainties on a regularly spaced spatio-temporal grid, using an iterative procedure that is weighted in space, time, and retrieval quality. The lack of observations at certain times and locations introduces missing grid points in the maps, which therefore may result in irregularly gridded (i.e. incomplete) fields. In order to evaluate the strengths and weaknesses of the resulting gridded maps, we compare with independent observations of CDOD by PanCam cameras and Mini-TES spectrometers aboard the Mars Exploration Rovers “Spirit” and “Opportunity”, by the Surface Stereo Imager aboard the Phoenix lander, and by the Compact Reconnaissance Imaging Spectrometer for Mars aboard MRO. We have statistically analyzed the irregularly gridded maps to provide an overview of the dust climatology on Mars over eight years, specifically in relation to its interseasonal and interannual variability, in addition to provide a basis for instrument intercomparison. Finally, we have produced regularly gridded maps of CDOD by spatially interpolating the irregularly gridded maps using a kriging method. These complete maps are used as dust scenarios in the Mars Climate Database (MCD) version 5, and are useful in many modeling applications. The two datasets for the eight available martian years are publicly available and distributed with open access on the MCD website.

Influence of water ice clouds on Martian tropical atmospheric temperatures

The Reanalysis derived from the UK Mars general circulation model assimilation of Thermal Emission Spectrometer temperature and dust opacity retrievals at present provides the best estimate of the evolving state of the Martian atmosphere over the course of the Mars Global Surveyor mapping mission. A Control simulation has also been carried out using the same evolving dust distribution as the Reanalysis, but without the temperature assimilation. Differences in zonal mean temperatures between these two simulations reflect possible biases in the representation of dynamical and radiative forcing in the assimilating model. We have identified a cold bias in the Control simulation of tropical temperature which develops in the northern hemisphere summer solstice season. We attribute this bias to the absence of radiatively active water ice clouds in the model and show that clouds likely play a prominent role in shaping the vertical thermal structure of the tropical atmosphere during this season.

The Venus nighttime atmosphere as observed by the VIRTIS‐M instrument. Average fields from the complete infrared data set

We present and discuss here the average fields of the Venus atmosphere derived from the nighttime observations in the 1960–2350 cm−1 spectral range by the VIRTIS-M instrument on board the Venus Express satellite. These fields include: (a) the air temperatures in the 1–100 mbar pressure range (~85–65 km above the surface), (b) the altitude of the clouds top, and (c) the average CO mixing ratio. A new retrieval code based on the Bayesian formalism has been developed and validated on simulated observations, to statistically assess the retrieval capabilities of the scheme once applied to the VIRTIS data. The same code has then been used to process the entire VIRTIS-M data set. Resulting individual retrievals have been binned on the basis of local time and latitude, to create average fields. Air temperature fields confirm the general trends previously reported in Grassi et al. (2010), using a simplified retrieval scheme and a more limited data set. At the lowest altitudes probed by VIRTIS (~65 km), air temperatures are strongly asymmetric around midnight, with a pronounced minima at 3LT, 70°S. Moving to higher levels, the air temperatures first become more uniform in local time (~75 km), then display a colder region on the evening side at the upper boundary of VIRTIS sensitivity range (~80 km). As already shown by Ignatiev et al. (2008) for the dayside, the cloud effective altitude increases monotonically from the south pole to the equator. However, the variations observed in night data are consistent with an overall variation of just 1 km, much smaller than the 4 km reported for the dayside. The cloud altitudes appear slightly higher on the evening side. Both observations are consistent with a less vigorous meridional circulation on the nightside of the planet. Carbon monoxide is not strongly constrained by the VIRTIS-M data. However, average fields present a clear maximum of 80 ppm around 60°S, well above the retrieval uncertainty. Once the intrinsic low sensitivity of VIRTIS data in the region of cold collar is kept in mind, this datum is consistent with a [CO] enrichment toward the poles driven by meridional circulation.

Polar vortices on Earth and Mars: A comparative study of the climatology and variability from reanalyses

Polar vortices on Mars provide case-studies to aid understanding of geophysical vortex dynamics and may help to resolve long-standing issues regarding polar vortices on Earth. Due to the recent development of the first publicly available Martian reanalysis dataset (MACDA), for the first time we are able to characterise thoroughly the structure and evolution of the Martian polar vortices, and hence perform a systematic comparison with the polar vortices on Earth. The winter atmospheric circulations of the two planets are compared, with a specific focus on the structure and evolution of the polar vortices. The Martian residual meridional overturning circulation is found to be very similar to the stratospheric residual circulation on Earth during winter. While on Earth this residual circulation is very different from the Eulerian circulation, on Mars it is found to be very similar. Unlike on Earth, it is found that the Martian polar vortices are annular, and that the Northern Hemisphere vortex is far stronger than its southern counterpart. While winter hemisphere differences in vortex strength are also reported on Earth, the contrast is not as large. Distinctions between the two planets are also apparent in terms of the climatological vertical structure of the vortices, in that the Martian polar vortices are observed to decrease in size at higher altitudes, whereas on Earth the opposite is observed. Finally, it is found that the Martian vortices are less variable through the winter than on Earth, especially in terms of the vortex geometry. During one particular major regional dust storm on Mars (Martian year 26), an equatorward displacement of the vortex is observed, sharing some qualitative characteristics of sudden stratospheric warmings on Earth.

Variability of the Martian thermosphere during eight Martian years as simulated by a ground‐to‐exosphere global circulation model

F.G.G. was partly funded by a CSIC JAE-Doc grant financed by the European Social Fund. F.G.G., M.-A.L.V., and M.G.C. thank the Spanish MICINN for funding support through the CONSOLIDER program ASTROMOLCSD2009-00038 and through projects AYA2011-23552/ESP and AYA2012-39691-C02-01. This work has also been partially funded by the ESA-CNES project Mars Climate Database and Physical Models.

Reconstructing the weather on Mars at the time of the MERs and Beagle 2 landings

We reconstruct the temperature, wind and density structure of the atmosphere on Mars from the surface to 120 km altitude at the time of the landing of the two NASA Mars Exploration Rovers (MER), and ESA’s “Beagle 2”. This reconstruction is based on an assimilation of temperature and dust opacity observations from the Thermal Emission Spectrometer aboard the Mars Global Surveyor spacecraft into a general circulation model of the Martian atmosphere and, for the case of the MERs, on retrievals of temperature and density profiles from accelerometer data. For all landers, the reconstruction of the atmospheric state is compared with the climatological state predicted by the European Mars Climate Database (EMCD) for two different prescribed dust scenarios, with added large and small scale variability. This comparison exhibits good agreement for all three landers within the modeled variability, confirming a posteriori the accuracy of the climate forecasts by the EMCD.

A Lorenz/Boer energy budget for the atmosphere of Mars from a “reanalysis” of spacecraft observations

We calculate a Lorenz energy budget for the Martian atmosphere from reanalysis derived from Mars Global Surveyor data for Mars years 24–27. We present global, annual mean energy and conversion rates per unit area and per unit mass and compare these to Earth data. The directions of the energy conversion terms for Mars are similar to Earth, with the exception of the barotropic conversion between zonal and eddy kinetic energy reservoirs. Further, seasonal and hemispheric decomposition reveals a strong conversion between zonal energy reservoirs over the year, but these balance each other out in global and annual mean. On separating the diurnal timescale, the contribution to the conversion terms and eddy kinetic energy for diurnal and shorter timescales in many cases (especially during planet-encircling dust storms) exceeds the contribution of longer timescales. This suggests that thermal tides have a significant effect on the generation of eddy kinetic energy.

Mars Analysis Correction Data Assimilation (MACDA): MGS/TES v1.0

This dataset contains basic gridded atmospheric and surface variables for the planet Mars over three martian years (a martian year is 1.88 terrestrial years), as produced by data assimilation of spacecraft observations. Each file in the dataset spans 30 martian mean solar days (sols) during the science mapping phase of the National Aeronautics and Space Administrationss (NASA) Mars Global Surveyor (MGS) spacecraft, between May 1999 and August 2004. The dataset is produced by the re-analysis of Thermal Emission Spectrometer (TES) retrievals of nadir thermal profiles and total dust opacities, using the Mars Analysis Correction Data Assimilation (MACDA) scheme in a Mars global circulation model (MGCM). The MGCM used is the UK spectral version of the model developed by the Laboratoire de Meteorologie Dynamique in Paris, France. MACDA is a collaboration between the University of Oxford and The Open University in the UK.

The Mars Climate Database (version 4.3)

THE MARS CLIMATE DATABASE (VERSION 5.3) E. Millour, F. Forget, A. Spiga, M. Vals, V. Zakharov, L. Montabone, F. Lefèvre, F. Montmessin, J.-Y. Chaufray, M. A. López-Valverde, F. González-Galindo, S. R. Lewis, P. L. Read, M.-C. Desjean, F. Cipriani and the MCD development team Laboratoire de Météorologie Dynamique (LMD), IPSL, UPMC, Paris, France, millour@lmd.jussieu.fr, Space Science Institute, Boulder, USA, Laboratoire Atmosphères, Milieux, Observations Spatiales (LATMOS), IPSL, Paris, France, Instituto de Astrofisica de Andalucia (IAA-CSIC), Granada, Spain, Department of Physical Sciences, The Open University, Milton Keynes, UK, Atmospheric, Oceanic and Planetary Physics (AOPP), Oxford, UK, Centre National D’Etudes Spatiales (CNES), Toulouse, France, European Space Research and Technology Center (ESTEC), Noordwijk, The Netherlands

Assimilating and Modeling Dust Transport in the Martian Climate System

A meteorological data assimilation system has been developed recently for analyzing measurements of temperature and dust opacity on Mars and has been successfully applied in several studies (e.g. Montabone et al. 2005, Lewis et al. 2007) to study various atmospheric phenomena. A more sophisticated data assimilation system, now with full dust transport incorporated, is becoming available to represent more accurately and realistically the physical transport of dust.