[Show abstract][Hide abstract] ABSTRACT: The 1.27-μm O2(a1Δg) dayglow on Mars is a product of the ozone photolysis by solar UV radiation. The intensity of the O2(a1Δg) emission rate depends on ozone concentration, atmospheric density and kinetic parameters of involved photochemical reactions. In turn, the distribution of ozone is sensitive to the vertical and spatial distribution of water vapor, which is an effective destructor of O3. SPICAM IR on the Mars-Express mission measures the O2(1Δg) dayglow with spectral resolving power of 2200. The results of 147 limb observations from 2004 to 2013 are reported. Limb resolution of the instrument is variable and exceeds the scale height of the atmosphere. The slant emission rate reaches a maximum at the high Northern latitudes at northern and southern springs Ls = 0–50° and 160–190°, respectively and a minimum in middle and low latitudes at southern summer Ls = 200–300°. We have compared the SPIVAM O2(a1Δg) limb profiles with the General Circulation Model simulation by the Laboratoire de Meteorologie Dynamique (LMD GCM, Lefèvre, F., Lebonnois, S., Montmessin, F., Forget, F. . J. Geophys. Res. 109, E07004. http://dx.doi.org/10.1029/2004JE002268; Lefèvre, F., et al. . Nature 454(7207), 971–975) reduced to the vertical resolution of the instrument. The GCM includes the radiative effect of the water clouds and an interactive dust scheme, and well reproduces Martian Climate Sounder (MCS) temperature profiles (Clancy, R. Todd et al. . J. Geophys. Res. 117, 10. http://dx.doi.org/10.1029/2011JE004018). The model underestimates the emission for Ls = 0–50°, Ls = 160–180° and overestimates it from Ls = 60° to Ls = 150° at high Northern latitudes. In the Southern hemisphere the model underestimates the emission for Ls = 170–200° and overestimates it for Ls = 200–230° at high Southern latitudes. The disagreement could be related to the water vapor distribution as the model reproduces it. The most recent version of the LMD GCM including microphysical representation of cloud formation taking into account the effect of dust scavenging by water ice clouds (Navarro, T., Madeleine, J.-B., Montmessin, F., Forget, F., Spiga, A., Millour, E. . Modeling of the martian water cycle with an improved representation of water ice clouds. European Planetary Science Congress 2013, EPSC Abstracts, vol. 8, EPSC2013-203) gives much better agreement with SPICAM O2(a1Δg) dayglow limb observations. Characterization of the Mars water cycle by GCMs continues to improve, and the observations of the O2(a1Δg) dayglow offer a powerful tool for its validation.
[Show abstract][Hide abstract] ABSTRACT: Mesospheric CO2 ice clouds on Mars are simulated with a 1D microphysical model, which includes a crystal growth rate adapted to high supersaturations encountered in the martian mesosphere. Observational constraints (crystal radius and opacity) exist for these clouds observed during the day around the equator at ∼60–80 km altitude. Nighttime mesospheric clouds interpreted as CO2 ice clouds have also been characterized at low southern latitudes, at ∼90–100 km altitude. From modeling and observational evidence, it is believed that mesospheric clouds are formed within temperature minima created by thermal tides, where gravity wave propagation allows for the creation of supersaturated layers (cold pockets). Thus, temperature profiles perturbed by gravity waves are used in the model to initiate nucleation and maintain growth of CO2 ice crystals. We show that it is possible to reproduce the observed effective radii for daytime and nighttime clouds. Crystal sizes are mainly governed by the altitude where the cloud forms, and by the amplitude of supersaturation. The temporal and spatial behavior of the cloud is controlled by the extent and lifetime of the cold pocket. The cloud evaporates fast after the cold pocket has vanished, implying a strong correlation between gravity wave activity and CO2 cloud formation. Simulated opacities remain far below the observed ones as long as typical dust conditions are used. In the case of the lower daytime clouds, the enhanced mesospheric dust loading typically reached during dust storm conditions, allows for greater cloud opacities, close to observed values, by supplying the atmosphere with condensation nuclei. However, CO2 ice clouds are not detected during the dust storm season, and, because of fast sedimentation of dust particles, an exogenous supply (meteoritic flux) appears necessary to explain opacities of both daytime and nighttime mesospheric CO2 ice clouds along their whole period of observation.
[Show abstract][Hide abstract] ABSTRACT: The Mars Color Imager (MARCI) onboard the Mars Reconnaissance Orbiter
(MRO) employs ultraviolet imaging bands within (260nm) and longward (320
nm) of Hartley band ozone absorption, in support of daily global mapping
retrievals for Mars atmospheric ozone columns. We present the first
release of this unique global atmospheric mapping data set, consisting
of 1010 ozone column retrievals spanning MY29-31 on a daily global grid
of 8x8 km spatial resolution. Coincident 320nm cloud optical depth
retrievals are obtained in conjunction with the MARCI ozone columns
(Wolff et al, 2011). The MARCI ozone column detection limit 1
μm-atm) is appropriate to mapping elevated ozone abundances at low
latitudes around Mars aphelion, and over mid-to-high latitudes during
fall/winter/spring seasons. MARCI ozone maps for these regions reveal
the detailed spatial and temporal behaviors of water vapor saturation
conditions that force large variations in water vapor photolysis
products (HOx) responsible for the catalytic destruction of ozone in the
Mars atmosphere. In the context of full temporal/spatial resolution, we
present aphelion increases in low latitude ozone and potential cloud and
topographic correlations, high latitude ozone maxima associated with
planetary waves and weather fronts during northern early spring, and
surprising (yet to be explained) winter season ozone variations within
the Hellas basin. Comparisons are provided for MARCI ozone measurements
to ozone simulations from the Laboratory of Meteorology and Dynamics
General Circulation Model (LMDGCM; Lefevre et al., 2006) and ozone
measurements by the SPICAM ultraviolet spectrometer on Mars Express
(Perrier et al, 2006).
[Show abstract][Hide abstract] ABSTRACT: A new approach is presented to model the condensational growth of carbon dioxide (CO2) ice crystals on Mars. These condensates form in very particular conditions. First, ∼95% of the atmosphere is composed of CO2 so that near‐pure vapor condensation takes place. Second, the atmosphere is rarefied, having dramatic consequences on the crystal growth. Indeed, the subsequently reduced efficiency of heat transport helps maintain a high temperature difference between the crystal surface and the environment, inhibiting the growth. Besides, the Stefan flow which would have been expected to increase the growth rate of the crystal, because of the near‐pure vapor condensation, is negligible. We show that the heritage of the convenient and explicit linearized crystal growth rate formula used for Earth clouds, initially derived for a trace gas, has to be reconsidered in the case of near‐pure vapor condensation for high saturation ratios that appear to be common in the Martian mesosphere. Nevertheless, by comparing our approach with a more complex condensation model, valid for all atmospheric conditions and all vapor abundances, we show that a very simple set of equations can still be used to efficiently reproduce the CO2 ice crystal growth rate. Our model, referred to as the CLASSIC model here, provides similar crystal growth rates than the traditionally used linearized growth rate models at low supersaturations but predicts lower crystal growth rates at high supersaturations. It can thus be used to model the condensational growth of CO2 ice crystals in the mesosphere where high supersaturations are observed.
Journal of Geophysical Research: Planets. 10/2013; 118(10).
[Show abstract][Hide abstract] ABSTRACT: Since the seasonal and spatial distribution of ozone on Mars was detected 1 by the ultraviolet spectrometer onboard the spacecraft Mariner 7, our understanding has evolved consider-ably thanks to parallel efforts in observations and modelling 2–7 . At low-to-mid latitudes, martian ozone is distributed vertically in two main layers, a near-surface layer and a layer at an alti-tude between 30 and 60 km (ref. 5). Here we report evidence from the SPICAM UV spectrometer onboard the Mars Express orbiter for the existence of a previously overlooked ozone layer that emerges in the southern polar night at 40–60 km in altitude, with no counterpart observed at the north pole. Comparisons with global climate simulations for Mars indicate that this layer forms as a result of the large-scale transport of oxygen-rich air from sunlit latitudes to the poles, where the oxygen atoms recombine to form ozone during the polar night. However, transport-driven ozone formation is counteracted in our simulations by the destruction of ozone by reactions with hydrogen radicals, whose concentrations vary seasonally on Mars, reflecting seasonal variations of water vapour. We conclude that the observed dichotomy between the ozone layers of the two poles, with a significantly richer layer in the southern hemisphere, can be explained by the interplay of these mechanisms. The ozone layer on Mars is typically 3,000 times thinner than on Earth, but exhibits orders of magnitude variations in space and time as a consequence of photolysis, atmospheric dynamics and of the catalytic destruction cycles induced by the hydrogen radicals (HO x) released by water molecule dissociation. An anti-correlation between O 3 and H 2 O is therefore suspected to take place in the atmosphere of Mars, a prediction that has been confirmed by ozone observations performed from the Earth 2,3 and from satellites in orbit around Mars 4 . A compilation of night-time ozone profiles was made with the SPICAM UV spectrometer on Mars Express 5 that covers the northern spring equinox (solar longitude L s = 8 •) to northern winter solstice (L s = 270 •) time frame. These observations along with theoretical studies 5–7 have allowed characterization of the night-time ozone vertical distribution at mid-to-low latitudes, allowing the clear distinction between the near-surface layer, the top of which is perceptible below 30 km, and the elevated layer, which is present only around aphelion. The near-surface layer existence is promoted by ultraviolet screening by CO 2 molecules, which inhibits HO x production through H 2 O photolysis. The elevated layer of ozone appears essentially at night as O 3 is rapidly photolysed after sunrise. Its magnitude is controlled by HO x concentration above 25 km. For this reason, seasonal variations of the water saturation level exert a strong modulation of the elevated layer of ozone in the tropics, forcing O 3 to maximize around the northern summer solstice (that is, the aphelion season) when temperatures are lowest and to vanish soon after L s ∼ 130 • . In the polar regions, H 2 O is LATMOS – CNRS/UVSQ/UPMC, 11 bd d'Alembert, 78280 Guyancourt, France. *e-mail: email@example.com Latitude 70° S¬80° S 10 7 10 8 10 9 10 10 O 3 density (molecules per cm 3) 0 20 40 60 80 a b L s (°) 40¬60 60¬80 80¬100 L s 60¬80° 0.01 0.10 1.00 10.00 O 3 volume mixing ratio (ppmv) 0 20 40 60 80 Latitude 10° S 30° S 50° S 75° S Altitude (km) Altitude (km) Figure 1 | A synthesis of SPICAM data showing the prominent southern polar ozone layer around 50 km. a, A series of ozone profiles observed from 2004 to 2011 by SPICAM between 70 • S and 80 • S and covering solar longitude (L s) 40 • –100 • . The colour coding distinguishes three periods to highlight the seasonal peak at L s ∼ 70 • (red curves). b, Profiles of O 3 given in volume mixing ratio (O 3 number density ratioed to the atmospheric number density of the GCM, in ppmv) at the time of the seasonal peak and averaged within four latitudinal intervals from the south pole to the equator. minimum in autumn and winter. The O 3 column is in turn found to be maximum, and large concentrations are found in the first 25 km above the surface 5 . The results reported here concern the identification from the SPICAM night-time data set of a previously overlooked ozone layer
[Show abstract][Hide abstract] ABSTRACT: The international research project RECONCILE has addressed central questions regarding polar ozone depletion, with the objective to quantify some of the most relevant yet still uncertain physical and chemical processes and thereby improve prognostic modelling capabilities to realistically predict the response of the ozone layer to climate change. This overview paper outlines the scope and the general approach of RECONCILE, and it provides a summary of observations and modelling in 2010 and 2011 that have generated an in many respects unprecedented dataset to study processes in the Arctic winter stratosphere. Principally, it summarises important outcomes of RECONCILE including (i) better constraints and enhanced consistency on the set of parameters governing catalytic ozone destruction cycles, (ii) a better understanding of the role of cold binary aerosols in heterogeneous chlorine activation, (iii) an improved scheme of polar stratospheric cloud (PSC) processes that includes heterogeneous nucleation of nitric acid trihydrate (NAT) and ice on non-volatile background aerosol leading to better model parameterisations with respect to denitrification, and (iv) long transient simulations with a chemistry-climate model (CCM) updated based on the results of RECONCILE that better reproduce past ozone trends in Antarctica and are deemed to produce more reliable predictions of future ozone trends. The process studies and the global simulations conducted in RECONCILE show that in the Arctic, ozone depletion uncertainties in the chemical and microphysical processes are now clearly smaller than the sensitivity to dynamic variability.
ATMOSPHERIC CHEMISTRY AND PHYSICS 09/2013; · 5.30 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Visible and near-IR Meinel band emissions originate from excited OH in the terrestrial upper atmosphere (Meinel, I.A.B. . Astrophys. J. 111, 555. http://dx.doi.org/10.1086/145296), and have recently been detected in the Venus nightside upper mesosphere (Piccioni, G. et al. . Astron. Astrophys. 483, L29–L33. http://dx.doi.org/10.1051/0004-6361:200809761). Meinel band observations support key studies of transport and photochemistry in both of these atmospheres. In the case of Mars, OH regulates the basic stability of the CO2 atmosphere to photolytic decomposition (to CO and O2, e.g. Parkinson, T.D., Hunten, D.M. . J. Atmos. Sci. 29, 1380–1390. http://dx.doi.org/10.1175/1520-0469(1972)029<1380:SAAOOO>2.0.CO;2), and yet has never been measured. We present the first detection of Mars atmospheric OH, associated with CRISM near-IR spectral limb observations of polar night Meinel band emissions centered at 1.45 and 2.9 μm. Meinel band (1–0), (2–1), and (2–0) average limb intensities of 990 ± 280, 1060 ± 480, and 200 ± 100 kiloRayleighs (kR), respectively, are determined for 70–90 NS polar winter latitudes over altitudes of 40–56 km. Additional OH bands, such as (3–2), (3–1), and (4–2), present ⩽1σ measurements. Uncertainty in the (4–2) band emission rate contributes to increased uncertainty in the determination of the O2(1Δg) (0–0)/(0–1) band emission ratio A00/A01=47-12+26. An average profile retrieval for Mars OH polar nightglow indicates 45–55 km altitude levels for volume emission rates (VER) of 0.4 (2–0) to 2 (1–0, 2–1) × 104 photons/(cm3 s). Similar to polar night O2(1Δg) emission (e.g. Clancy, R.T. et al. . J. Geophys. Res. (Planets) 117, E00J10. http://dx.doi.org/10.1029/2011JE004018), Meinel OH band emission is supported by upper level, winter poleward transport of O and H in the deep Hadley solsticial circulations of Mars. The retrieved OH emission rates are compared to polar winter OH nightglow simulated by the LMD (Laboratoire de Météorologie Dynamique) photochemical GCM (global climate model), employing detailed photochemistry (e.g. Lefèvre, F., Lebonnois, S., Montmessin, F., Forget, F. . J. Geophys. Res. (Planets) 109, E07004. http://dx.doi.org/10.1029/2004JE002268) and energy transfer processes (excitation and quenching) developed for Mars Meinel OH band nightglow by García Muñoz et al. (García Muñoz, A., McConnell, J.C., McDade, I.C., Melo, S.M.L. . Icarus 176, 75–95). Modeled versus observed OH emission behavior agrees within measurement uncertainties with the assumptions of a Bates–Nicolet (H + O3) source for excited OH production, and ‘collisional-cascade’ quenching of the OH vibrational population by CO2. ‘Sudden-death’ quenching of excited OH by CO2 leads to 100× less OH emission than observed. The combined agreement between LMD GCM simulated and CRISM observed O2(1Δg) and Meinel OH polar nightglow behaviors represents a significant demonstration of the LMD model capability to couple odd oxygen and hydrogen photochemistry and transport by the Mars global circulation in a realistic fashion.
[Show abstract][Hide abstract] ABSTRACT: Observations of ozone, a trace gas on Mars, have the potential to
constrain atmospheric dynamical and physical processes. Current Mars
Global Circulation Models (MGCMs) [1, 2, 3] are able to represent the
photochemistry occuring in the atmosphere, with comparisons to
observations used to confine particular species. However, a long term
comparison using data assimilation provides a more robust constraint on
the model. We have assimilated total-ozone observations from SPICAM into
an MGCM to study the Martian ozone cycle. Ozone has never before been
assimilated for an extraterrestrial planet. Our aim is to use ozone to
provide a preliminary technique for trace gas data assimilation for the
analysis of observations from current and future satellite missions
(such as ExoMars) which observe the spatial and temporal distribution of
trace gases on Mars.
[Show abstract][Hide abstract] ABSTRACT: An unprecedented ozone loss occurred in the Arctic in spring 2011. The
details of the event are re-visited from the twice-daily total ozone and
NO2 columns measurements of the eight SAOZ/NDACC
(Système d'Analyse par Observation Zénitale/Network for
Detection of Atmospheric Composition Changes) stations in the Arctic. It
is shown that the total ozone depletion in the polar vortex reached 38%
(approx. 170 DU) by the end of March that is larger than the 30% of the
previous record in 1996. Asides from the long extension of the cold
stratospheric NAT PSC period, the amplitude of the event is shown to be
resulting from a record daily total ozone loss rate of 0.7%
day-1 after mid-February, never seen before in the Arctic but
similar to that observed in the Antarctic over the last 20 yr. This high
loss rate is attributed to the absence of NOx in the vortex
until the final warming, in contrast to all previous winters where, as
shown by the early increase of NO2 diurnal increase, partial
renoxification is occurring by import of NOx or
HNO3 from the outside after minor warming episodes, leading
to partial chlorine deactivation. The cause of the absence
of renoxification and thus of high loss rate, is attributed to a vortex
strength similar to that of the Antarctic but never seen before in the
Arctic. The total ozone reduction on 20 March was identical to that of
the 2002 Antarctic winter, which ended around 20 September, and a 15-day
extension of the cold period would have been enough to reach the mean
yearly amplitude of the Antarctic ozone hole. However there is no sign
of trend since 1994, neither in PSC volume, early winter
denitrification, late vortex renoxification, and vortex strength nor in
total ozone loss. The unprecedented large Arctic ozone loss in 2011
appears to resulting from an extreme meteorological event and there is
no indication of possible strengthening related to climate change.
[Show abstract][Hide abstract] ABSTRACT: Ozone is a tracer of photochemistry in the atmosphere of Mars and an observable used to test predictions of photochemical models. We present a comparison of retrieved ozone abundances on Mars using ground-based infrared heterodyne measurements by NASA Goddard Space Flight Center’s Heterodyne Instrument for Planetary Wind And Composition (HIPWAC) and space-based Mars Express Spectroscopy for the Investigation of the Characteristics of the Atmosphere of Mars (SPICAM) ultraviolet measurements. Ozone retrievals from simultaneous measurements in February 2008 were very consistent (0.8 μm-atm), as were measurements made close in time (ranging from <1 to >8 μm-atm) during this period and during opportunities in October 2006 and February 2007. The consistency of retrievals from the two different observational techniques supports combining the measurements for testing photochemistry-coupled general circulation models and for investigating variability over the long-term between spacecraft missions. Quantitative comparison with ground-based measurements by NASA/GSFC’s Infrared Heterodyne Spectrometer (IRHS) in 1993 reveals 2–4 times more ozone at low latitudes than in 2008 at the same season, and such variability was not evident over the shorter period of the Mars Express mission. This variability may be due to cloud activity.
[Show abstract][Hide abstract] ABSTRACT: stratospheric ozone depletion has acted to cool the Earth's surface. As
the result of the phase-out of anthropogenic halogenated compounds
emissions, stratospheric ozone is projected to recover and its radiative
forcing (RF-O3 ~ -0.05 W/m2 presently) might
therefore be expected to decay in line with ozone recovery itself. Using
results from chemistry-climate models, we find that, although model
projections using a standard greenhouse gas scenario broadly agree on
the future evolution of global ozone, they strongly disagree on
RF-O3 because of a large model spread in ozone changes in a
narrow (several km thick) layer, in the northern lowermost stratosphere.
Clearly, future changes in global stratospheric ozone cannot be
considered an indicator of its overall RF. The multi-model mean
RF-O3 estimate for 2100 is +0.06 W/m2 but with a
range such that it could remain negative throughout this century or
change sign and reach up to ~0.25 W/m2.
Geophysical Research Letters 06/2013; 40(11):2796-2800. · 4.46 Impact Factor