Mars low albedo regions: Possible map of near-surface

2001

In the 1970s, Mariner and Viking spacecraft observations of the north polar region of Mars revealed polar brightness temperatures that were significantly below the expected kinetic temperatures for CO2 sublimation. For the past few decades, the scientific community has speculated as to the nature of these Martian polar cold spots. Thermal Emission Spectrometer (TES) thermal spectral data have shown these cold spots to result largely from fine-grained CO2 and have constrained most of these cold spots to the surface (or near-surface). Cold spot formation is strongly dependent on topography, forming preferentially near craters and on polar slopes. TES data, combined with Mars Orbiter Laser Altimeter (MOLA) cloud data, suggest atmospheric condensates form a small fraction of the observed cold spots. TES observations of spectra close to a blackbody indicate that another major component of the polar cap is slab CO2 ice; these spectrally bland regions commonly have a low albedo. The cause is uncertain but may result from most of the light being reflected toward the specular direction, from the slab ice being intrinsically dark, or from it being transparent. Regions of the cap where the difference between the brightness temperatures at 18 /•m (T•8) and 25 /•m (T25) is less than 5 ø are taken to indicate deposits of slab ice. Slab ice is the dominant component of the polar cap at latitudes outside of the polar night. 1. Introduction Nearly one-third of the Martian atmosphere is cycled through the polar caps each year, condensing out of the atmosphere in the fall and winter and sublimating from the cap in the spring and summer. This CO2 cycle is the dominant factor in the global climate of Mars. Changes in the polar cap albedo or emissivity modify the polar cap energy budget and the amount of CO2 condensation, consequently affecting the global Martian climate. In the 1970s, spacecraft observations of the polar regions of Mars revealed polar brightness temperatures that were significantly below the expected kinetic temperatures (140-148 K) for CO2 sublimation [Kieffer et al., 1976]. These locations were typically a few hundred kilometers in diameter, with 20 /•m brightness temperatures (T20) as low as 130 K and had characteristic durations of a few days [Kieffer et al., 1976]. For historical reasons, we will refer to these regions as Copyright 2001 by the American Geophysical Union. Paper number 2000JE001284. 0148-022 7 / 01 / 2000JE001284509.00 cold spots even though their kinetic temperatures may actually be the same as the rest of the polar cap. Three early hypotheses suggested that these cold spots are (1) high-altitude CO2 clouds [Hunt, 1980], (2) surface CO2 with low emissivity [Ditteon and Kieffer, 1979], and (3) low-kinetic surface temperatures due to lower-than-expected CO2 partial pressures [Kieffer et al., 1977]. More recently, Forget et al. [1995] have combined hypothesizes I and 2, suggesting the cold spots may be CO2 condensates and freshly fallen CO2 snow. The exact nature of the cold spots is important because they locally modify the energy budget, and therefore, place constraints on current Global Circulation Models (GCMs). Observations from Viking revealed that the cold spots are more common in the Northern Hemisphere than in the Southern Hemisphere [Forget and Pollack, 1996]. An understanding of the underlying phenomenon of the cold spots also may relate to other apparent asymmetries that exist between the Northern and Southern Hemispheres (e.g., the composition of the residual caps). In this paper, we present Thermal Emission Spectrometer (TES) observations from the aerobaking phase of the Mars Global Surveyor (MGS) mission. Our put-23,181

Mars Atmosphere: …, 2011

This paper reports on ana. lyses of the surface pressure, surface wind, and seasonality of temperature and precipitation in the central parts of Greenland a, nd Antarctica. a.s simulated by different general circulation models (GCMs) for the present and for the Last Glacial Maximum (LGM) climates. These parameters, in addition to the mean surface temperature, influence the air content of the ice either directly or through their influence on the pore volume. To correctly interpret the air content of the ice in terms of past ice sheet elevation changes, the wria, tions of these parameters must therefore be known. Most of the simulaUons discussed here have been ca. rried out within the framework of the Paleoclimate Modeling Intercomparison Project. Moreover, a stretched grid GCM has been used with a. high resolution over the ice sheets. We show that not [aking into account changes of surface pressure at constant altitude between the LGM a. nd today leads to an overestimation of pa, st ice sheet elevation up to 150 m, while wind speed changes are too weak to have a significant influence on ice core air content. The results concerning changes of the amplitude or phase of the seasonal variations of precipitation and tempera. ture are somewhat a. mbiguous. Most, but not all, of the models suggest an intensification of the seasonal cycle of surface temperatures over central Greenla. nd, and, to a lesser extent, over central East Antarctica. Neglecting these changes might lead to an underestimation of past eleva. tion by up to 140 m for the Greenland ice sheet, but this number is subject to large uncerta. inties. come isolated) [Raynaud and Lebel, 1979; Martinerie et al., 1992]. Because of the strong dependence on at-•nospheric pressure it has been proposed to use t, he air content A as an indicator of past ice sheet surface elevation [Lorius et al., 1968]. Nevertheless, the use of such a "paleobarometer" requires knowledge of the past. evolution of the at. mospheric pressure fields at. the surface of the ice sheet.. Moreover, past wind speed as well as temperature and precipitation seasonality must. be known because these surface climate parameters influence the ice porosity [Martinerie et al., 1994; Ra!tnaud et al., 1997]. The air content A (in cm 3 g-l) of ice is a function of the atmospheric pressure Pi, of the temperature of the site at, the close-off time interval, and of the porous volume 2Now at. Program for Climat. e Model Diagnosis and Inter-of the ice • at. close off. If the close-off pore volume and comparison, Lawrence Livermore National Laboratory, air temperature are known, one can thus theoretically Livermore, California. retrieve the paleosurface pressure Pi by measuring the air content of old ice [e.g., Martinerie et al., 1992]'

In the 1970s, Mariner and Viking spacecraft observations of the north polar region of Mars revealed polar brightness temperatures that were significantly below the expected kinetic temperatures for CO2 sublimation. For the past few decades, the scientific community has speculated as to the nature of these Martian polar cold spots. Thermal Emission Spectrometer (TES) thermal spectral data have shown these cold spots to result largely from fine-grained CO2 and have constrained most of these cold spots to the surface (or near-surface). Cold spot formation is strongly dependent on topography, forming preferentially near craters and on polar slopes. TES data, combined with Mars Orbiter Laser Altimeter (MOLA) cloud data, suggest atmospheric condensates form a small fraction of the observed cold spots. TES observations of spectra close to a blackbody indicate that another major component of the polar cap is slab CO2 ice; these spectrally bland regions commonly have a low albedo. The cause is uncertain but may result from most of the light being reflected toward the specular direction, from the slab ice being intrinsically dark, or from it being transparent. Regions of the cap where the difference between the brightness temperatures at 18 /•m (T•8) and 25 /•m (T25) is less than 5 ø are taken to indicate deposits of slab ice. Slab ice is the dominant component of the polar cap at latitudes outside of the polar night. In the 1970s, spacecraft observations of the polar regions of Mars revealed polar brightness temperatures that were significantly below the expected kinetic temperatures (140-148 K) for CO2 sublimation [Kieffer et al., 1976]. These locations were typically a few hundred kilometers in diameter, with 20 /•m brightness temperatures (T20) as low as 130 K and had characteristic durations of a few days [Kieffer et al., 1976]. For historical reasons, we will refer to these regions as Copyright 2001 by the American Geophysical Union. Paper number 2000JE001284. 0148-022 7 / 01 / 2000JE001284509.00 cold spots even though their kinetic temperatures may actually be the same as the rest of the polar cap. Three early hypotheses suggested that these cold spots are (1) high-altitude CO2 clouds [Hunt, 1980], (2) surface CO2 with low emissivity [Ditteon and Kieffer, 1979], and (3) low-kinetic surface temperatures due to lower-than-expected CO2 partial pressures [Kieffer et al., 1977]. More recently, Forget et al. [1995] have combined hypothesizes I and 2, suggesting the cold spots may be CO2 condensates and freshly fallen CO2 snow. The exact nature of the cold spots is important because they locally modify the energy budget, and therefore, place constraints on current Global Circulation Models (GCMs). Observations from Viking revealed that the cold spots are more common in the Northern Hemisphere than in the Southern Hemisphere [Forget and Pollack, 1996]. An understanding of the underlying phenomenon of the cold spots also may relate to other apparent asymmetries that exist between the Northern and Southern Hemispheres (e.g., the composition of the residual caps). In this paper, we present Thermal Emission Spectrometer (TES) observations from the aerobaking phase of the Mars Global Surveyor (MGS) mission. Our put-23,181

Science, 2009

The light detection and ranging instrument on the Phoenix mission observed water-ice clouds in the atmosphere of Mars that were similar to cirrus clouds on Earth. Fall streaks in the cloud structure traced the precipitation of ice crystals toward the ground. Measurements of atmospheric dust indicated that the planetary boundary layer (PBL) on Mars was well mixed, up to heights of around 4 kilometers, by the summer daytime turbulence and convection. The water-ice clouds were detected at the top of the PBL and near the ground each night in late summer after the air temperature started decreasing. The interpretation is that water vapor mixed upward by daytime turbulence and convection forms ice crystal clouds at night that precipitate back toward the surface.

Journal of Geophysical Research: Planets, 2019

We report observations by the Mars Climate Sounder showing strong diurnal variations in temperature and the vertical dust distribution during the 2018 (Mars Year 34) global dust event. The temperature field shows weak diurnal tidal activity at equatorial latitudes but a strong diurnal tide in middle to high latitudes with a maximum amplitude of 29 K in the lower atmosphere of the south polar region. The diurnal variability of dust is small in the equatorial region and increases toward higher latitudes. At middle and low latitudes, comparable dust amounts are found about 5-10 km higher in the atmosphere on the dayside than on the nightside. The dust reaches the highest altitudes in the late afternoon and is found at the lowest altitudes in the late night. In the southern high latitudes a persistent cold air mass with low dust content is identified on the nightside of the planet centered at 3-6 a.m. local time. The observed variations are well represented by model simulations with the Laboratoire de Météorologie Dynamique General Circulation Model. Comparisons between data and model results suggest that the diurnal variations in the dust are largely driven by the meridional circulation exhibiting diurnal tidal variations. The model results show that the compact air mass in the south polar region has a high potential vorticity, supporting its interpretation as a remnant of the southern polar vortex, which is forced toward the nightside of the planet due to the enhanced diurnal tide during the global dust event. Plain Language Summary One of the most distinctive features of the Martian atmosphere are global dust storms, one of which occurred in 2018. We report on observations of the vertical structure of atmospheric temperature and dust by the Mars Climate Sounder onboard Mars Reconnaissance Orbiter. Strong differences between day and night are found in both temperature and dust vertical structure. The strongest temperature variations are observed in the south polar atmosphere, with temperature differences up to 58 • C/136 • F between day and night. Comparable dust amounts are found 5-10 km (3-6 miles) higher in the atmosphere on the dayside than on the nightside at central and equatorial latitudes. In the southern polar region a persistent cold body of air with low dust is identified on the nightside of the planet. The observations are compared with the results from a global atmospheric computer model. The observed temperature and dust distribution and their variations over the Martian day are well represented by the model. The diurnal variations in the dust are largely driven by diurnal changes in the large-scale atmospheric circulation. The compact body of air in the south polar region is forced to the nightside by this altered circulation but does not dissipate for several months.

Journal of Geophysical Research, 2010

In the 1970s, Viking and Mariner observed areas in the polar regions of Mars with winter brightness temperatures below the expected kinetic temperatures for CO 2 ice sublimation. These areas have since been termed "cold spots" and have been identified as surface deposits of CO 2 atmospheric condensates and, occasionally, active CO 2 storms. Three Mars years of data from the Mars Global Surveyor Thermal Emission Spectrometer were used to observe autumn and winter cold spot activity. In this study, cold spots that occur near and on the southern perennial cap were compared to those found near or on the northern perennial cap. On the southern perennial cap, cold spots associated with topographic features (induced by orographic lifting) were less common than cold spots independent of topography, similar to the north. However, the cold spots in the south lasted longer than those observed in the north. There is also evidence that cold spot formation in the south was affected by the global dust storm of 2001, even though the dust storm occurred during the southern spring and summer seasons. Prior to the dust storm, the amount of overall cold spot activity closer to the perennial cap increased and the average CO 2 grain size for most of the cold spots increased as well. Following the dust storm, the majority of cold spots in the south increased in size and duration but they did not form north of 62°S latitude, whereas, in other years, cold spots formed as far north as 48°S.

Geophysical Research Letters, 2014

Key Points: • Simulations of recent ice ages are performed using an improved climate model • Cloud radiative effect and coupling to the dust cycle control snow deposition • The location of predicted ice deposits is consistent with geologic evidence Correspondence to: (2014), Recent ice ages on Mars: The role of radiatively active clouds and cloud microphysics, Geophys.

2017

Icarus, 2005

2005). The atmospheric circulation and dust activity in different orbital epochs on Mars. Icarus, 174(1), pp. 135-160. For guidance on citations see FAQs. c [not recorded] Version: [not recorded] Link(s) to article on publisher's website: http://dx.doi.org/Newman et al., Icarus, 174 (1) 135-160, 2005 2