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Sample records for polar ice caps

  1. North Polar Ice Cap

    NASA Technical Reports Server (NTRS)

    1997-01-01

    North polar ice cap of Mars, as seen during mid summer in the northern hemisphere. The reddish areas consist of eolian dust, bright white areas consist of a mixture of water ice and dust, and the dark blue areas consist of sand dunes forming a huge 'collar' around the polar ice cap. (The colors have been enhanced with a decorrelation stretch to better show the color variability.) Shown here is an oblique view of the polar region, as seen with the Viking 1 spacecraft orbiting Mars over latitude 39 degrees north. The spiral bands consist of valleys which form by a combination of the Coriolis forces, wind erosion, and differential sublimation and condensation. In high-resolution images the polar caps are seen to consist of thick sequences of layered deposits, suggesting that cyclical climate changes have occurred on Mars. Cyclical climate changes are readily explained by quasi-periodic changes in the amount and distribution of solar heating resulting from perturbations in orbital and axial elements. Variations in the Earth's orbit have also been linked to the terrestrial climate changes during the ice ages.

  2. South Polar Ice Cap

    NASA Technical Reports Server (NTRS)

    2003-01-01

    MGS MOC Release No. MOC2-337, 21 April 2003

    This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows the 'swiss cheese' pattern of frozen carbon dioxide on the south polar residual cap. Observation of these materials over two Mars years has revealed that the scarps that bound the mesas and small buttes are retreating-the carbon dioxide ice is subliming away-at a rate of about 3 meters (3 yards) per Mars year in some places. The picture covers an area about 900 m (about 900 yards) wide near 87.1oS, 93.7oW. Sunlight illuminates the scene from the upper left.

  3. Textures in south polar ice cap #2

    NASA Technical Reports Server (NTRS)

    1998-01-01

    Textures of the south polar permanent residual ice cap and polar layered terrains. This 15 x 14 km area image (frame 7306) is centered near 87 degrees south, 341 degrees west.

    Figure caption from Science Magazine

  4. Textures in south polar ice cap #1

    NASA Technical Reports Server (NTRS)

    1998-01-01

    Textures of the south polar permanent residual ice cap and polar layered terrains. This 30 x 29 km area image (frame 7709) is centered near 87 degrees south, 77 degrees west.

    Figure caption from Science Magazine

  5. Morphology of Mars North Polar Ice Cap

    NASA Astrophysics Data System (ADS)

    Zwally, H. J.; Fountain, A.; Kargel, J.; Kouvaris, L.; Lewis, K.; MacAyeal, D.; Pfeffer, T.; Saba, J. L.

    2000-08-01

    The northern ice cap of Mars consists of a parabolic dome centered within 13 km of the pole, plus an arm-like ridge extending from the dome between about 135 and 225 east. Chasma Boreale lies between the dome and the extended ridge. The base of the dome is approximately elliptical with a major axis of 1100 km along the 90 east to 270 east direction and minor axis of 700 km along zero east to 180 deg. The heights of the dome and the extended ridge are respectively 2900 inches and 1700 inches above the surrounding basin. Least-squares fitting of a parabola through height profiles of the dome along longitudes 90 deg to 270 deg and zero deg to 180 deg gives an elliptic-paraboloid equation for the dome: Z(m) = 2800 - [(X-x)2/113.6] - [(Y-y)2/50.3], where X is the 90 deg to 270 deg axis, x = 9.90 km, y = 13.32 km, and the slightly-different fitted heights for the two axes are averaged. The center of the dome is shifted 13.32 km from the pole along zero deg longitude and 9.90 km along 90 deg longitude. Typical mean surface slopes on the ice cap are the order of 1/100 (0.6 deg), A small central portion of the cap, about 100 km by 200 km, extends in elevation about 200 inches above the parabolic shape of the cap. Additional information is contained in the original extended abstract.

  6. Formation of the Carbon Dioxide Ice Seasonal Polar Caps

    NASA Astrophysics Data System (ADS)

    Forget, F.

    1998-01-01

    One of the key processes controlling the geology of the martian polar regions is the seasonal condensation of the atmosphere into CO2 ice caps. These polar caps mostly condense during the polar night, when surface and atmospheric temperature become cold enough to reach the frost point of CO2. Thus, almost all that is known about the formation of the polar caps has come from the Mariner 9 and Viking infrared measurements. These observations showed that the physical processes controlling the condensation are complex, because of the unique radiative and microphysical properties Of CO2 ice condensing in a CO2 atmosphere. For instance, the Infrared Thermal Mapper (IRTM). One of the key processes controlling the geology of the martian polar regions is the seasonal condensation of the atmosphere into CO2 ice caps. These polar caps mostly condense during the polar night, when surface and atmospheric temperature become cold enough to reach the frost point of CO2. Thus, almost all that is known about the formation of the polar caps has come from the Mariner 9 and Viking infrared measurements. These observations showed that the physical processes controlling the condensation are complex, because of the unique radiative and microphysical properties Of CO2 ice condensing in a CO2 atmosphere. For instance, the IRTM instrument observed variable structures exhibiting brightness temperatures far below the physical temperature appropriate for condensed CO, in vapor pressure equilibrium at the expected atmospheric pressure. A detailed analysis of the data suggests that these low brightness temperatures result from the radiative properties of the SMO CO2 ice particles that condense in the atmosphere rather than directly on the surface New observations are being transmitted by Mars Global Surveyor. TES and MOLA data should greatly improve our understand- ing of what is really going on during the cap formation. instrument observed variable structures exhibiting brightness temperatures

  7. Water Ice Albedo Variations on the Martian Northern Polar Cap

    NASA Technical Reports Server (NTRS)

    Hale, A. S.; Bass, D. S.; Tamppari, L. K.

    2003-01-01

    The Viking Orbiters determined that the surface of Mars northern residual cap is water ice. Many researchers have related observed atmospheric water vapor abundances to seasonal exchange between reservoirs such as the polar caps, but the extent to which the exchange between the surface and the atmosphere remains uncertain. Early studies of the ice coverage and albedo of the northern residual Martian polar cap using Mariner 9 and Viking images reported that there were substantial internannual differences in ice deposition on the polar cap, a result which suggested a highly variable Martian climate. However, some of the data used in these studies were obtained at differing values of heliocentric solar longitude (L(sub s)). Reevaluation of this dataset indicated that the residual cap undergoes seasonal brightening throughout the summer, and indicated that this process repeats from year to year. In this study we continue to compare Mariner 9 and Viking Orbiter imaging observations and thermal data of the north residual polar cap to data acquired with Mars Global Surveyor s Mars Orbiter Camera (MOC) instrument. In the current study, our goal is to examine all released data from MGS MOC in the northern summer season, along with applicable TES data in order to better understand the albedo variations in the northern summer and their implications on water transport. To date, work has focused primarily on the MOC dataset. In 1999, data acquisition of the northern polar regions began at L(sub s) = 107, although there was little north polar data acquired from L(sub s)= 107 to L(sub s) = 109. We examined a total of 409 images from L(sub s) = 107 to L(sub s)=148. We have also examined data from 2000 from L(sub s)= 93 to L(sub s)= 110; additional progress is ongoing. Here we present a progress report of our observations, and continue to determine their implications for the Martian water cycle.

  8. Seasonal Changes in Mars' North Polar Ice Cap

    NASA Technical Reports Server (NTRS)

    1997-01-01

    These images, which seem to have been taken while NASA's Hubble Space Telescope (HST) was looking directly down on the Martian North Pole, were actually created by assembling mosaics of three sets of images taken by HST in October, 1996 and in January and March, 1997 and projecting them to appear as they would if seen from above the pole. This first mosaic is a view which could not actually be seen in nature because at this season a portion of the pole would have actually been in shadow; the last view, taken near the summer solstice, would correspond to the Midnight Sun on Earth with the pole fully illuminated all day. The resulting polar maps begin at 50 degrees N latitude and are oriented with 0 degrees longitude at the 12 o'clock position. This series of pictures captures the seasonal retreat of Mars' north polar cap.

    October 1996 (early spring in the Northern hemisphere): In this map, assembled from images obtained between Oct. 8 and 15, the cap extends down to 60 degrees N latitude, nearly it's maximum winter extent. (The notches are areas where Hubble data were not available). A thin, comma-shaped cloud of dust can be seen as a salmon-colored crescent at the 7 o'clock position. The cap is actually fairly circular about the geographic pole at this season; the bluish 'knobs' where the cap seems to extend further are actually clouds that occurred near the edges of the three separate sets of images used to make the mosaic.

    January 1997 (mid-spring): Increased warming as spring progresses in the northern hemisphere has sublimated the carbon dioxide ice and frost below 70 degrees north latitude. The faint darker circle inside the cap boundary marks the location of circumpolar sand dunes (see March '97 map); these dark dunes are warmed more by solar heating than are the brighter surroundings, so the surface frost sublimates from the dunes earlier than from the neighboring areas. Particularly evident is the marked hexagonal shape of the polar cap at this season

  9. Formation of the Carbon Dioxide Ice Seasonal Polar Caps

    NASA Astrophysics Data System (ADS)

    Foster, J.; Chang, A.; Hall, D.; Tait, A.; Klein, A.

    1998-01-01

    One of the key processes controlling the geology of the martian polar regions is the seasonal condensation of the atmosphere into CO, ice caps. These polar caps mostly condense during the polar night, when surface and atmospheric temperature become cold enough to reach the frost point of CO2. Thus, almost all that is known about the formation of the polar caps has come from the Mariner 9 and Viking infrared measurements. These observations showed that the physical processes controlling the condensation are complex, because of the unique radiative and microphysical properties of CO2 ice condensing in a CO2 atmosphere. For instance, the Infrared Thermal Mapper (IRTM) instrument observed variable structures exhibiting brightness temperatures far below the physical temperature appropriate for condensed CO2 in vapor pressure equilibrium at the expected atmospheric pressure. A detailed analysis of the data suggests that these low brightness temperatures result from the radiative properties of the small CO2 ice particles that condense in the atmosphere rather than directly on the surface. Indeed, simulations performed with General Circulation Models have shown that a fraction of the total CO2 condensation can take place in the atmosphere. Atmospheric condensation can result from radiative cooling on the one hand (especially when the atmosphere is dust laden) and from adiabatic cooling in upward motions on the other . The resulting CO2 snowfalls could create the observed features, because the CO2 ice particles that condense in the atmosphere can be efficient scatterers at infrared wavelengths (whether they are airborne or have just fallen to the ground) carbon dioxide ice deposits composed of nonporous solid ice, however, having directly condensed on the ground or having undergone frost metamorphism should behave almost like blackbody emitters, or, more likely, be transparent in the infrared so that the ground beneath can radiate through. In fact, by simply parametrizing

  10. Driving Stresses in Mars Polar Ice Caps and Conditions for Ice Flow

    NASA Technical Reports Server (NTRS)

    Zwally, H. Jay; Saba, Jack L.

    1999-01-01

    Measurements of the topography of the North polar ice cap by the Mars Orbiter Laser Altimeter (MOLA) show that the ice cap is 2950 +/- 200 meters thick. The volume of the cap is about 1.2 x 10(exp 6) cu km covering an area of 1.04 x 10(exp 6) sq km, which is about 40 percent of the Greenland ice sheet in volume and 62 percent in area. The composition of the Northern cap was previously concluded to be predominately H2O, rather than CO2 ice, based on thermodynamic considerations of the insustainablity of CO2 during summer. Principal questions about the cap are: does the ice move and at what rate, is the cap currently growing or depleting in volume, and how and when was the cap formed? Recent research on terrestrial ice sheets indicates that rates of ice deformation at the low stress values characteristic of ice sheets are significantly higher than the rates given by the classic viscous-plastic flow laws commonly used.

  11. Diurnal Albedo Variations of the Martian North Polar Water Ice Cap

    NASA Technical Reports Server (NTRS)

    Troy, R. F.; Bass, D.

    2002-01-01

    Presentation of findings regarding diurnal variations in the north polar water ice cap of Mars as part of a larger study of the interannual and seasonal variations of the Martian north polar water ice cap. Additional information is contained in the original extended abstract.

  12. Perennial water ice identified in the south polar cap of Mars.

    PubMed

    Bibring, Jean-Pierre; Langevin, Yves; Poulet, François; Gendrin, Aline; Gondet, Brigitte; Berthé, Michel; Soufflot, Alain; Drossart, Pierre; Combes, Michel; Bellucci, Giancarlo; Moroz, Vassili; Mangold, Nicolas; Schmitt, Bernard

    2004-04-01

    The inventory of water and carbon dioxide reservoirs on Mars are important clues for understanding the geological, climatic and potentially exobiological evolution of the planet. From the early mapping observation of the permanent ice caps on the martian poles, the northern cap was believed to be mainly composed of water ice, whereas the southern cap was thought to be constituted of carbon dioxide ice. However, recent missions (NASA missions Mars Global Surveyor and Odyssey) have revealed surface structures, altimetry profiles, underlying buried hydrogen, and temperatures of the south polar regions that are thermodynamically consistent with a mixture of surface water ice and carbon dioxide. Here we present the first direct identification and mapping of both carbon dioxide and water ice in the martian high southern latitudes, at a resolution of 2 km, during the local summer, when the extent of the polar ice is at its minimum. We observe that this south polar cap contains perennial water ice in extended areas: as a small admixture to carbon dioxide in the bright regions; associated with dust, without carbon dioxide, at the edges of this bright cap; and, unexpectedly, in large areas tens of kilometres away from the bright cap. PMID:15024393

  13. Interannual observations and quantification of summertime H2O ice deposition on the Martian CO2 ice south polar cap

    NASA Astrophysics Data System (ADS)

    Brown, Adrian J.; Piqueux, Sylvain; Titus, Timothy N.

    2014-11-01

    The spectral signature of water ice was observed on Martian south polar cap in 2004 by the Observatoire pour l'Mineralogie, l'Eau les Glaces et l'Activite (OMEGA) (Bibring et al., 2004). Three years later, the OMEGA instrument was used to discover water ice deposited during southern summer on the polar cap (Langevin et al., 2007). However, temporal and spatial variations of these water ice signatures have remained unexplored, and the origins of these water deposits remains an important scientific question. To investigate this question, we have used observations from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) instrument on the Mars Reconnaissance Orbiter (MRO) spacecraft of the southern cap during austral summer over four Martian years to search for variations in the amount of water ice. We report below that for each year we have observed the cap, the magnitude of the H2O ice signature on the southern cap has risen steadily throughout summer, particularly on the west end of the cap. The spatial extent of deposition is in disagreement with the current best simulations of deposition of water ice on the south polar cap (Montmessin et al., 2007). This increase in water ice signatures is most likely caused by deposition of atmospheric H2O ice and a set of unusual conditions makes the quantification of this transport flux using CRISM close to ideal. We calculate a 'minimum apparent' amount of deposition corresponding to a thin H2O ice layer of 0.2 mm (with 70% porosity). This amount of H2O ice deposition is 0.6-6% of the total Martian atmospheric water budget. We compare our 'minimum apparent' quantification with previous estimates. This deposition process may also have implications for the formation and stability of the southern CO2 ice cap, and therefore play a significant role in the climate budget of modern day Mars.

  14. Martian Polar Caps: Folding, Faulting, Flowing Glaciers of Multiple Interbedded Ices

    NASA Astrophysics Data System (ADS)

    Kargel, J. S.

    2001-12-01

    The Martian south polar cap (permanent CO2 cap and polar layered deposits), exhibit abundant, varied, and widespread deformational phenomena. Folding and boudinage are very common. Strike-slip or normal faults are rarer. Common in the vicinity of major troughs and scarps are signs of convergent flow tectonics manifested as wrinkle-ridge-like surface folds, thrust faults, and viscous forebulges with thin-skinned extensional crevasses and wrinkle-ridge folds. Such flow convergence is predicted by theory. Boudinage and folding at the 300-m wavelength scale, indicating rheologically contrasting materials, is widely exposed at deep levels along erosional scarps. Independent morphologic evidence indicates south polar materials of contrasting volatility. Hence, the south polar cap appears to be a multiphase structure of interbedded ices. The north polar cap locally also exhibits flow indicators, though they are neither as common nor as varied as in the south. The large-scale quasi-spiral structure of the polar caps could be a manifestation of large-scale boudinage. According to this scenario, deep-level boudinage continuously originates under the glacial divide (the polar cap summit). Rod-like boudin structures are oriented transverse to flow and migrate outward with the large-scale flow field. Troughs develop over areas between major boudins. A dynamic competition, and possibly a rough balance, develops between the local flow field in the vicinity of a trough (which tends to close the trough by lateral closure and upwelling flow) and sublimation erosion (which tends to widen and deepen them). Over time, the troughs flow to the margins of the polar cap where they, along with other polar structures, are destroyed by sublimation. Major ice types contributing to rheological and volatility layering may include, in order of highest to lowest mechanical strength, CO2 clathrate hydrate, water ice containing inert/insoluble dust, pure water ice, water ice containing traces of

  15. Tracking the Martian CO2 Polar Ice Caps in Infrared Images

    NASA Technical Reports Server (NTRS)

    Wagstaff, Kiri L.; Castano, Rebecca; Chien, Steve

    2006-01-01

    Researchers at NASA s Jet Propulsion Laboratory have developed a method for automatically tracking the polar caps on Mars as they advance and recede each year (see figure). The seasonal Mars polar caps are composed mainly of CO2 ice and are therefore cold enough to stand out clearly in infrared data collected by the Thermal Emission Imaging System (THEMIS) onboard the Mars Odyssey spacecraft. The Bimodal Image Temperature (BIT) histogram analysis algorithm analyzes raw, uncalibrated data to identify images that contain both "cold" ("polar cap") and "warm" ("not polar cap") pixels. The algorithm dynamically identifies the temperature that separates these two regions. This flexibility is critical, because in the absence of any calibration, the threshold temperature can vary significantly from image to image. Using the identified threshold, the algorithm classifies each pixel in the image as "polar cap" or "not polar cap," then identifies the image row that contains the spatial transition from "polar cap" to "not polar cap." While this method is useful for analyzing data that has already been returned by THEMIS, it has even more significance with respect to data that has not yet been collected. Instead of seeking the polar cap only in specific, targeted images, the simplicity and efficiency of this method makes it feasible for direct, onboard use. That is, THEMIS could continuously monitor its observations for any detections of the polar-cap edge, producing detections over a wide range of spatial and temporal conditions. This effort can greatly contribute to our understanding of long-term climatic change on Mars.

  16. Black carbon aerosols and the third polar ice cap

    SciTech Connect

    Menon, Surabi; Koch, Dorothy; Beig, Gufran; Sahu, Saroj; Fasullo, John; Orlikowski, Daniel

    2010-04-15

    Recent thinning of glaciers over the Himalayas (sometimes referred to as the third polar region) have raised concern on future water supplies since these glaciers supply water to large river systems that support millions of people inhabiting the surrounding areas. Black carbon (BC) aerosols, released from incomplete combustion, have been increasingly implicated as causing large changes in the hydrology and radiative forcing over Asia and its deposition on snow is thought to increase snow melt. In India BC emissions from biofuel combustion is highly prevalent and compared to other regions, BC aerosol amounts are high. Here, we quantify the impact of BC aerosols on snow cover and precipitation from 1990 to 2010 over the Indian subcontinental region using two different BC emission inventories. New estimates indicate that Indian BC emissions from coal and biofuel are large and transport is expected to expand rapidly in coming years. We show that over the Himalayas, from 1990 to 2000, simulated snow/ice cover decreases by {approx}0.9% due to aerosols. The contribution of the enhanced Indian BC to this decline is {approx}36%, similar to that simulated for 2000 to 2010. Spatial patterns of modeled changes in snow cover and precipitation are similar to observations (from 1990 to 2000), and are mainly obtained with the newer BC estimates.

  17. CO2 jets formed by sublimation beneath translucent slab ice in Mars' seasonal south polar ice cap

    USGS Publications Warehouse

    Kieffer, H.H.; Christensen, P.R.; Titus, T.N.

    2006-01-01

    The martian polar caps are among the most dynamic regions on Mars, growing substantially in winter as a significant fraction of the atmosphere freezes out in the form of CO2 ice. Unusual dark spots, fans and blotches form as the south-polar seasonal CO2 ice cap retreats during spring and summer. Small radial channel networks are often associated with the location of spots once the ice disappears. The spots have been proposed to be simply bare, defrosted ground; the formation of the channels has remained uncertain. Here we report infrared and visible observations that show that the spots and fans remain at CO2 ice temperatures well into summer, and must be granular materials that have been brought up to the surface of the ice, requiring a complex suite of processes to get them there. We propose that the seasonal ice cap forms an impermeable, translucent slab of CO2 ice that sublimates from the base, building up high-pressure gas beneath the slab. This gas levitates the ice, which eventually ruptures, producing high-velocity CO 2 vents that erupt sand-sized grains in jets to form the spots and erode the channels. These processes are unlike any observed on Earth. ?? 2006 Nature Publishing Group.

  18. CO2 jets formed by sublimation beneath translucent slab ice in Mars' seasonal south polar ice cap.

    PubMed

    Kieffer, Hugh H; Christensen, Philip R; Titus, Timothy N

    2006-08-17

    The martian polar caps are among the most dynamic regions on Mars, growing substantially in winter as a significant fraction of the atmosphere freezes out in the form of CO2 ice. Unusual dark spots, fans and blotches form as the south-polar seasonal CO2 ice cap retreats during spring and summer. Small radial channel networks are often associated with the location of spots once the ice disappears. The spots have been proposed to be simply bare, defrosted ground; the formation of the channels has remained uncertain. Here we report infrared and visible observations that show that the spots and fans remain at CO2 ice temperatures well into summer, and must be granular materials that have been brought up to the surface of the ice, requiring a complex suite of processes to get them there. We propose that the seasonal ice cap forms an impermeable, translucent slab of CO2 ice that sublimates from the base, building up high-pressure gas beneath the slab. This gas levitates the ice, which eventually ruptures, producing high-velocity CO2 vents that erupt sand-sized grains in jets to form the spots and erode the channels. These processes are unlike any observed on Earth. PMID:16915284

  19. A Case for Microorganisms on Comets, Europa and the Polar Ice Caps of Mars

    NASA Technical Reports Server (NTRS)

    Hoover, Richard B.; Pikuta, Elena V.

    2003-01-01

    Microbial extremophiles live on Earth wherever there is liquid water and a source of energy. Observations by ground-based observatories, space missions, and satellites have provided strong evidence that water ice exists today on comets, Europa, Callisto, and Ganymede and in the snow, permafrost, glaciers and polar ice caps of Mars. Studies of the cryoconite pools and ice bubble systems of Antarctica suggest that solar heating of dark rocks entrained in ice can cause localized melting of ice providing ideal conditions for the growth of microbial communities with the creation of micro-environments where trapped metabolic gasses produce entrained isolated atmospheres as in the Antarctic ice-bubble systems. It is suggested that these considerations indicate that several groups of microorganisms should be capable of episodic growth within liquid water envelopes surrounding dark rocks in cometary ices and the permafrost and polar caps of Mars. We discuss some of the types of microorganisms we have encountered within the permafrost and snow of Siberia, the cryoconite pools of Alaska, and frozen deep within the Antarctic ice sheet above Lake Vostok.

  20. IR spectral properties of dust and ice at the Mars south polar cap

    NASA Astrophysics Data System (ADS)

    Titus, T. N.; Kieffer, H. H.

    2001-11-01

    Removal of atmospheric dust effects is required to derive surface IR spectral emissivity. Commonly, the atmospheric-surface separation is based on radiative transfer (RT) spectral inversion methods using nadir-pointing observations. This methodology depends on a priori knowledge of the spectral shape of each atmospheric aerosol (e.g. dust or water ice) and a large thermal contrast between the surface and atmosphere. RT methods fail over the polar caps due to low thermal contrast between the atmosphere and the surface. We have used multi-angle Emission Phase Function (EPF) observations to estimate the opacity spectrum of dust over the springtime south polar cap and the underlying surface radiance, and thus, the surface emissivity. We include a few EPFs from Hellas Basin as a basis for comparisons between the spectral shape of polar and non-polar dust. Surface spectral emissivities over the seasonal cap are compared to CO2 models. Our results show that the spectral shape of the polar dust opacity is not constant, but is a two-parameter family that can be characterized by the 9 um and 20 um opacities. The 9 um opacity varies from 0.15 to 0.45 and characterizes the overall atmospheric conditions. The 9 um to 20 um opacity ratio varies from 2.0 to 5.1, suggesting changes in dust size distribution over the polar caps. Derived surface temperatures from the EPFs confirm that the slightly elevated temperatures (relative to CO2 frost temperature) observed in ``cryptic'' regions are a surface effect, not atmospheric. Comparison of broad-band reflectivity and surface emissivities to model spectra suggest the bright regions (e.g. perennial cap, Mountains of Mitchell) have higher albedos due to a thin surface layer of fine-grain CO2 (perhaps either frost or fractured ice) with an underlying layer of either coarse grain or slab CO2 ice.

  1. Mapping the Martian Polar Ice Caps: Applications of Terrestrial Optical Remote Sensing Methods

    NASA Astrophysics Data System (ADS)

    Nolin, A. W.

    1998-01-01

    With improvements in both instrumentation and algorithms, methods for mapping terrestrial snow cover using optical remote sensing data have progressed significantly over the past decade. Multispectral data can now be used to determine not only the presence or absence of snow but the fraction of snow cover in a pixel. Radiative transfer models have been used to quantify the nonlinear relationship between surface reflectance and grain size, thereby providing the basis for mapping snow grain size from surface reflectance images Because subpixel mixtures of snow and other land cover types create erroneous estimates of snow grain-size, the snow fraction information can be used in tandem with the grain size algorithm to limit its use to only those pixels that have complete snow cover. Model-derived characterization of the bidirectional reflectance distribution function (BRDF) provides the means for converting measured bidirectional reflectance to directional-hemispherical albedo. In recent work, this approach has allowed climatologists to examine the large-scale seasonal variability of albedo on the Greenland ice sheet. This seasonal albedo variability results from increases in snow grain size and exposure of the underlying ice cap as the seasonal snow cover ablates away. it will soon be possible to apply some of these terrestrial mapping methods to learn more about martian polar caps. What is most needed for this purpose is multispectral optical imagery. The extent and variability of the ice caps and their seasonal CO2 frost covering can be mapped with only a few spectral bands distributed through the visible and near-infrared wavelengths. Imaging spectrometer data would provide the ability to quantify mineral-ice mixtures and to better characterize the martian atmosphere. These are both needed for albedo determinations while only the former is required for subpixel frost/ice mapping. Perhaps the most significant terrestrial mapping application is the potential use of

  2. Mars Water Ice and Carbon Dioxide Seasonal Polar Caps: GCM Modeling and Comparison with Mars Express Omega Observations

    NASA Technical Reports Server (NTRS)

    Forget, F.; Levrard, B.; Montmessin, F.; Schmitt, B.; Doute, S.; Langevin, Y.; Bibring, J. P.

    2005-01-01

    To better understand the behavior of the Mars CO2 ice seasonal polar caps, and in particular interpret the the Mars Express Omega observations of the recession of the northern seasonal cap, we present some simulations of the Martian Climate/CO2 cycle/ water cycle as modeled by the Laboratoire de Meteorologie Dynamique (LMD) global climate model.

  3. Science goals for a Mars Polar Cap subsurface mission : optical approaches for investigations of inclusions in ice

    NASA Technical Reports Server (NTRS)

    Carsey, Frank; Mogensen, Claus T.; Behar, Alberto; Engelhardt, Hermann; Lane, Arthur L.

    2002-01-01

    The Mars Polar Caps are highly interesting features of Mars and have received much recent attention with new and exciting data on morphology, basal units, and layered outcroppings. We have examined the climatological, glaciological, and geological issues associated with a subsurface exploration of the Mars North Polar Cap and have determined that a finescale optical examination of ice in a borehole, to examine the stratigraphy, geochemistry and geochronology of the ice, is feasible. This information will enable reconstruction of the development of the cap as well as prediction of the properties of its ice. We present visible imagery taken of dust inclusions in archived Greenland ice cores as well as in-situ images of accreted lithologic inclusions in West Antarctica, and we argue for use of this kind of data in Mars climate reconstruction as has been successful with Greenland and Antarctic ice core analysis. .

  4. Science goals for a Mars Polar Cap subsurface mission : optical approaches for investiagations of inclusions in ice

    NASA Technical Reports Server (NTRS)

    Mogensen, Claus T.; Carsey, Frank D.; Behar, Alberto; Engelhardt, Hermann; Lane, Arthur L.

    2002-01-01

    The Mars Polar Caps are highly interesting features of Mars and have received much recent attention with new and exciting data on morphology, basal units, and layered outcroppings. We have examined the climatological, glaciological, and geological issues associated with a subsurface exploration of the Mars North Polar Cap and have determined that a finescale optical examination of ice in a borehole, to examine the stratigraphy, geochemistry and geochronology of the ice, is feasible. This information will enable reconstruction of the development of the cap as well as predication of the properties of its ice. We present visible imagery taken of dust inclusions in archived Greenland ice cores as well as in-situ images of accreted lithologic inclusions in West Antarctica, and we argue for use of this kind of data in Mars climate reconstruction as has been successful with Greenland and Antarctic ice core anlaysis.

  5. Azimuthal Structure of the Sand Erg that Encircles the North Polar Water-Ice Cap

    NASA Astrophysics Data System (ADS)

    Teodoro, L. A.; Elphic, R. C.; Eke, V. R.; Feldman, W. C.; Maurice, S.; Pathare, A.

    2011-12-01

    The sand erg that completely encircles the perennial water-ice cap that covers the Martian north geographic pole displays considerable azimuthal structure as seen in visible and near-IR images. Much of this structure is associated with the terminations of the many steep troughs that cut spiral the approximately 3 km thick polar ice cap. Other contributions come from the katabatic winds that spill over steep-sided edges of the cap, such as what bounds the largest set of dunes that comprise Olympia Undae. During the spring and summer months when these winds initiate from the higher altitudes that contain sublimating CO2 ice, which is very cold and dry, heat adiabatically when they compress as they lose altitude. These winds should then remove H2O moisture from the uppermost layer of the sand dunes that are directly in their path. Two likely locations where this desiccation may occur preferentially is at the termination of Chasma Boreale and the ice cap at Olympia Undae. We will search for this effect by sharpening the spatial structure of the epithermal neutron counting rates measured at northern high latitudes using the Mars Odyssey Neutron Spectrometer (MONS). The epithermal range of neutron energies is nearly uniquely sensitive to the hydrogen content of surface soils, which should likely be in the form of H2O/OH molecules/radicals. We therefore convert epithermal counting rates in terms of Water-Equivalent-Hydrogen, WEH. However, MONS counting-rate data have a FWHM of ~550 km., which is sufficiently broad to prevent a close association of WEH variability with images of geological features. In this study, we reduce spurious features in the instrument smeared neutron counting rates through deconvolution. We choose the PIXON numerical deconvolution technique for this purpose. This technique uses a statistical approach (Pina 2001, Eke 2001), which is capable of removing spurious features in the data in the presence of noise. We have previously carried out a detailed

  6. Variability of Mars' North Polar Water Ice Cap: I. Analysis of Mariner 9 and Viking Orbiter Imaging Data

    USGS Publications Warehouse

    Bass, D.S.; Herkenhoff, K. E.; Paige, D.A.

    2000-01-01

    Previous studies interpreted differences in ice coverage between Mariner 9 and Viking Orbiter observations of Mars' north residual polar cap as evidence of interannual variability of ice deposition on the cap. However, these investigators did not consider the possibility that there could be significant changes in the ice coverage within the northern residual cap over the course of the summer season. Our more comprehensive analysis of Mariner 9 and Viking Orbiter imaging data shows that the appearance of the residual cap does not show large-scale variance on an interannual basis. Rather we find evidence that regions that were dark at the beginning of summer look bright by the end of summer and that this seasonal variation of the cap repeats from year to year. Our results suggest that this brightening was due to the deposition of newly formed water ice on the surface. We find that newly formed ice deposits in the summer season have the same red-to-violet band image ratios as permanently bright deposits within the residual cap. We believe the newly formed ice accumulates in a continuous layer. To constrain the minimum amount of deposited ice, we used observed albedo data in conjunction with calculations using Mie theory for single scattering and a delta-Eddington approximation of radiative transfer for multiple scattering. The brightening could have been produced by a minimum of (1) a ???35-??m-thick layer of 50-??m-sized ice particles with 10% dust or (2) a ???14-??m-thick layer of 10-??m-sized ice particles with 50% dust. ?? 2000 Academic Press.

  7. Influence of ice rheology and dust content on the dynamics of the north-polar cap of Mars

    NASA Astrophysics Data System (ADS)

    Greve, Ralf; Mahajan, Rupali A.

    2005-04-01

    The evolution and dynamics of the north-polar cap (residual-ice-cap/layered-deposits complex) of Mars is simulated with a thermomechanical ice-sheet model. We consider a scenario with ice-free initial conditions at 5 Ma before present due to the large obliquities which prevailed prior to this time. The north-polar cap is then built up to its present shape, driven by a parameterized climate forcing (surface temperature, surface mass balance) based on the obliquity and eccentricity history. The effects of different ice rheologies and different dust contents are investigated. It is found that the build-up scenarios require an accumulation rate of approximately 0.15-0.2 mm a -1 at present. The topography evolution is essentially independent of the ice dynamics due to the slow ice flow. Owing to the uncertainties associated with the ice rheology and the dust content, flow velocities can only be predicted within a range of two orders of magnitude. Likely present values are of the order of 0.1-1 mm a -1, and a strong variation over the climatic cycles is found. For all cases, computed basal temperatures are far below pressure melting.

  8. Polar Cap Formation on Ganymede

    NASA Technical Reports Server (NTRS)

    Pilcher, C. B.; Shaya, E. J.

    1985-01-01

    Since thermal migration is not an effective mechanism for water transport in the polar regions at the Galilean satellites, some other process must be responsible for the formation of Ganymede's polar caps. It is proposed that Ganymede's polar caps are the optical manifestation of a process that began with the distribution of an ice sheet over the surface of Ganymede. The combined processes of impact gardening and thermal migration led, in regions at latitudes less than 40 to 45 deg., to the burial of some fraction of this ice, the migration of some to the polar caps margins, and a depletion of free ice in the optical surface. At higher latitudes, no process was effective in removing ice from the optical surface, so the remanants of the sheet are visible today.

  9. The role of sublimation and condensation on the development of ice sedimentation waves on the North Polar Cap of Mars

    NASA Astrophysics Data System (ADS)

    Herny, C.; Carpy, S.; Bourgeois, O.; Masse, M.; Spiga, A.; Le Mouélic, S.; Perret, L.; Smith, I. B.; Rodriguez, S.

    2015-10-01

    Mass and energy balance of ice sheets are driven by complex interactions between the atmosphere and the cryosphere. For instance, it has been demonstrated that feedbacks between katabatic winds and the cryosphere lead to the formation of sedimentation waves at the surface of Martian and terrestrial ice sheets [1, 2, 3 and 4]. Here we explore the role of sublimation and condensation of water vapor in the development of these sedimentation waves. We conduct this study by complementary observational and numerical investigations on the North Polar Cap of Mars.

  10. Polar cap formation on Ganymede

    NASA Technical Reports Server (NTRS)

    Shaya, E. J.; Pilcher, C. B.

    1984-01-01

    It is argued that Ganymede's polar caps are the remnants of a more extensive covering of water ice that formed during a period in which the satellite was geologically active. It is inferred that the initial thickness of this covering was a significant fraction of the gardening depth since the covering formed. This suggests an initial thickness of at least a few meters over heavily cratered regions such as the south polar grooved terrain. The absence of similar polar caps on Callisto apparently reflects the absence of comparable geologic activity in the history of this satellite.

  11. Why is the north polar cap on Mars different than the south polar cap?

    NASA Technical Reports Server (NTRS)

    Lindner, Bernhard Lee

    1994-01-01

    One of the most puzzling mysteries about the planet Mars is the hemispherical asymmetry in the polar caps. Every spring the seasonal polar cap of CO2 recedes until the end of summer, when only a small part, the residual polar cap, remains. During the year that Viking observed Mars, the residual polar cap was composed of water ice in the northern hemisphere but was primarily carbon dioxide ice in the southern hemisphere. Scientists have sought to explain this asymmetry by modeling observations of the latitudinal recession of the polar cap and seasonal variations in atmospheric pressure (since the seasonal polar caps are primarily frozen atmosphere, they are directly related to changes in atmospheric mass). These models reproduce most aspects of the observed annual variation in atmospheric pressure fairly accurately. Furthermore, the predicted latitudinal recession of the northern polar cap in the spring agrees well with observations, including the fact that the CO2 ice is predicted to completely sublime away. However, these models all predict that the carbon dioxide ice will also sublime away during the summer in the southern hemisphere, unlike what is observed. This paper will show how the radiative effects of ozone, clouds, airborne dust, light penetration into and through the polar cap, and the dependence of albedo on solar zenith angle affect CO2 ice formation and sublimation, and how they help explain the hemispherical asymmetry in the residual polar caps. These effects have not been studied with prior polar cap models.

  12. Analysis of vanillic acid in polar ice cores as a biomass burning proxy - preliminary results from the Akademii Nauk Ice Cap in Siberia

    NASA Astrophysics Data System (ADS)

    Grieman, M. M.; Jimenez, R.; McConnell, J. R.; Fritzsche, D.; Saltzman, E. S.

    2013-12-01

    Biomass burning influences global climate change and the composition of the atmosphere. The drivers, effects, and climate feedbacks related to fire are poorly understood. Many different proxies have been used to reconstruct past fire frequency from lake sediments and polar ice cores. Reconstruction of historical trends in biomass burning is challenging because of regional variability and the qualitative nature of various proxies. Vanillic acid (4-hydroxy-3-methoxybenzoic acid) is a product of the combustion of conifer lignin that is known to occur in biomass burning aerosols. Biomass burning is likely the only significant source of vanillic acid in polar ice. In this study we describe an analytical method for quantifying vanillic acid in polar ice using HPLC with electrospray ionization and tandem mass spectrometric detection. The method has a detection limit of 100 pM and a precision of × 10% at the 100 pM level for analysis of 100 μl of ice melt water. The method was used to analyze more than 1000 discrete samples from the Akademii Nauk ice cap on Severnaya Zemlya in the high Russia Arctic (79°30'N, 97°45'E) (Fritzsche et al., 2002; Fritzsche et al., 2005; Weiler et al., 2005). The samples range in age over the past 2,000 years. The results show a mean vanillic acid concentration of 440 × 710 pM (1σ), with elevated levels during the periods from 300-600 and 1450-1550 C.E.

  13. Mars residual north polar cap - Earth-based spectroscopic confirmation of water ice as a major constituent and evidence for hydrated minerals

    NASA Technical Reports Server (NTRS)

    Clark, R. N.; Mccord, T. B.

    1982-01-01

    A description is presented of new earth-based reflectance spectra of the Martian north residual polar cap. The spectra indicate that the composition is at least mostly water ice plus another component with a 'gray' reflectance. The other minerals in the ice cap appear to be hydrated. The data were obtained with a cooled circular variable filter spectrometer on February 20, 1978, using the 2.2-m telescope on Mauna Kea, Hawaii. It is pointed out that the identification of water ice in the north polar cap alone does not indicate that water makes up all or even most of the bulk of the cap. Kieffer (1970) has shown that a small amount of water will mask the spectral features of CO2.

  14. Measurements of the north polar cap of Mars and the earth's Northern Hemisphere ice and snow cover

    NASA Technical Reports Server (NTRS)

    Foster, J.; Owe, M.; Capen, C.

    1986-01-01

    The boundaries of the polar caps of Mars have been measured on more than 3000 photographs since 1905 from the plate collection at the Lowell Observatory. For the earth, the polar caps have been accurately mapped only since the mid 1960s when satellites were first available to synoptically view the polar regions. The polar caps of both planets wax and wane in response to changes in the seasons, and interannual differences in polar cap behavior on Mars as well as earth are intimately linked to global energy balance. Data on the year to year variations in the extent of the north polar caps of Mars and earth have been assembled and compared, although only 6 years of concurrent data were available for comparison.

  15. North Polar Cap

    NASA Technical Reports Server (NTRS)

    2004-01-01

    [figure removed for brevity, see original site]

    This week we will be looking at five examples of laminar wind flow on the north polar cap. On Earth, gravity-driven south polar cap winds are termed 'catabatic' winds. Catabatic winds begin over the smooth expanse of the cap interior due to temperature differences between the atmosphere and the surface. Once begun, the winds sweep outward along the surface of the polar cap toward the sea. As the polar surface slopes down toward sealevel, the wind speeds increase. Catabatic wind speeds in the Antartic can reach several hundreds of miles per hour.

    In the images of the Martian north polar cap we can see these same type of winds. Notice the streamers of dust moving downslope over the darker trough sides, these streamers show the laminar flow regime coming off the cap. Within the trough we see turbulent clouds of dust, kicked up at the trough base as the winds slow down and enter a chaotic flow regime.

    The horizontal lines in these images are due to framelet overlap and lighting conditions over the bright polar cap.

    Image information: VIS instrument. Latitude 86.5, Longitude 64.5 East (295.5 West). 40 meter/pixel resolution.

    Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

    NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation

  16. North Polar Cap

    NASA Technical Reports Server (NTRS)

    2004-01-01

    [figure removed for brevity, see original site]

    This week we will be looking at five examples of laminar wind flow on the north polar cap. On Earth, gravity-driven south polar cap winds are termed 'catabatic' winds. Catabatic winds begin over the smooth expanse of the cap interior due to temperature differences between the atmosphere and the surface. Once begun, the winds sweep outward along the surface of the polar cap toward the sea. As the polar surface slopes down toward sealevel, the wind speeds increase. Catabatic wind speeds in the Antartic can reach several hundreds of miles per hour.

    In the images of the Martian north polar cap we can see these same type of winds. Notice the streamers of dust moving downslope over the darker trough sides, these streamers show the laminar flow regime coming off the cap. Within the trough we see turbulent clouds of dust, kicked up at the trough base as the winds slow down and enter a chaotic flow regime.

    The horizontal lines in these images are due to framelet overlap and lighting conditions over the bright polar cap.

    Image information:VIS instrument. Latitude 86.5, longitude 57.4 East (302.6 West). 40 meter/pixel resolution.

    Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

    NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is

  17. North Polar Cap

    NASA Technical Reports Server (NTRS)

    2004-01-01

    [figure removed for brevity, see original site]

    This week we will be looking at five examples of laminar wind flow on the north polar cap. On Earth, gravity-driven south polar cap winds are termed 'catabatic' winds. Catabatic winds begin over the smooth expanse of the cap interior due to temperature differences between the atmosphere and the surface. Once begun, the winds sweep outward along the surface of the polar cap toward the sea. As the polar surface slopes down toward sealevel, the wind speeds increase. Catabatic wind speeds in the Antartic can reach several hundreds of miles per hour.

    In the images of the Martian north polar cap we can see these same type of winds. Notice the streamers of dust moving downslope over the darker trough sides, these streamers show the laminar flow regime coming off the cap. Within the trough we see turbulent clouds of dust, kicked up at the trough base as the winds slow down and enter a chaotic flow regime.

    The horizontal lines in these images are due to framelet overlap and lighting conditions over the bright polar cap.

    Image information: VIS instrument. Latitude 84.3, Longitude 314.4 East (45.6 West). 40 meter/pixel resolution.

    Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

    NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation

  18. North Polar Cap

    NASA Technical Reports Server (NTRS)

    2004-01-01

    [figure removed for brevity, see original site]

    This week we will be looking at five examples of laminar wind flow on the north polar cap. On Earth, gravity-driven south polar cap winds are termed 'catabatic' winds. Catabatic winds begin over the smooth expanse of the cap interior due to temperature differences between the atmosphere and the surface. Once begun, the winds sweep outward along the surface of the polar cap toward the sea. As the polar surface slopes down toward sealevel, the wind speeds increase. Catabatic wind speeds in the Antartic can reach several hundreds of miles per hour.

    In the images of the Martian north polar cap we can see these same type of winds. Notice the streamers of dust moving downslope over the darker trough sides, these streamers show the laminar flow regime coming off the cap. Within the trough we see turbulent clouds of dust, kicked up at the trough base as the winds slow down and enter a chaotic flow regime.

    The horizontal lines in these images are due to framelet overlap and lighting conditions over the bright polar cap.

    Image information: VIS instrument. Latitude 84.2, Longitude 57.4 East (302.6 West). 40 meter/pixel resolution.

    Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

    NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation

  19. Melting probes as a means to access the subsurface of Mars' polar caps and Jupiter's ice moons

    NASA Astrophysics Data System (ADS)

    Biele, J.; Ulamec, S.; Funke, O.; Engelhardt, M.

    There is a high scientific interest in exploring certain planetary icy environments in the solar system (Mars' polar caps, Europa and other icy satellites) motivated by the search for traces of life in these extreme environments as well as interest in planetary climate history as in the case of Mars. A promising technique to penetrate thick ice layers with small and reliable probes which do not require the heavy, complex and expensive equipment of a drilling rig is by melting. Contamination avoidance with respect to planetary protection requirements can be fulfilled using melting probes, since the melting channel refreezes behind the probe and shuts off the contact to the surface; also, in-situ decontamination of the probe is possible. Melting probes can be equipped with a suite of scientific instruments that are capable e.g. of determining the chemical and isotopic composition of the embedded or dissolved materials, of the ices themselves, of the dust content and possible traces of indigenous biological activity. Due to the still rather high energy demand to overcome the melting enthalpy, in case of extraterrestrial application (e.g. Europa or polar caps of Mars), only heating with radioactive isotopes seems feasible for reaching greater depths. The necessary power is driven by the desired penetration velocity (linearly) and the dimensions of the probe (proportional to the cross section). On Mars, however, solar cells could be used to power small tethered melting probes in polar summer. While such probes have successfully been used for terrestrial applications, e.g., in Antarctica in the 1990ies, the technology is not yet mature for space applications; for example, the behaviour in vacuum (below the triple point pressure of water, i.e., 611 Pa) needs to be assessed. We will report briefly on our laboratory tests with melting probes in vacuum and under very low temperatures to this end. Practical issues (impact of dust on the performance, gravity dependence

  20. Analog experiments on the formation of spiral troughs on the North Polar Ice cap of Mars : Layered deposits emplaced by cyclic steps on ice

    NASA Astrophysics Data System (ADS)

    Yokokawa, M.; Izumi, N.; Naito, K.; Shimizu, H.; Yamada, T.; Greve, R.

    2012-12-01

    The spiral troughs observed on the Mars' North Polar Layered Deposits (NPLD) show intriguing features that contain a detailed stratigraphic record of surface processes in Mars' recent polar history. SHARAD radar data showed that the troughs have migrated as much as 65 km towards the north during the accumulation of the uppermost ~ 600 m of NPLD (Smith and Holt, 2010). Though they are suspected to have some relation with katabatic wind blowing on the ice cap, it has not been known how the spiral troughs are formed in detail. From their features, the spiral troughs may possibly be cyclic steps formed by a density current created by cooling of the atmosphere due to ice (Smith and Holt, 2010). Cyclic steps are spatially periodic bedforms where each wavelength is delineated by an upstream and downstream hydraulic jump. They migrate upstream keeping the same wavelength. Recently cyclic steps have been reported from various environments on the Earth, such as fluvial and deep-sea settings, and in various bed materials, such as bedrock, non-cohesive sediments, and cohesive sediments (e.g., Kostic et al., 2010). Smith et al (2011) have demonstrated that numerical simulation with a cyclic step model can show reasonable consistency with an observed migration rate. In this study, we have performed a series of physical experiments analogous to the formation of cyclic steps on ice by density currents. The experiments were conducted using the cold laboratory of the Institute of Low Temperature Science, Hokkaido University. In the case of Mars, sublimation by katabatic winds results in erosion in some places and in the other places, water included in the atmosphere blowing on ice is sublimated to become ice and deposited on the bed covered with ice. In order to model this process, we used a hydrophobic liquid that include water but do not freeze even below the ice point, i.e., mixture of silicon oil (20cS) and water (0.5 - 30 volume % of water) whose freezing point is -0.7 degrees

  1. Martian north polar water ice clouds

    NASA Technical Reports Server (NTRS)

    Tamppari, L. K.; Bass, D.

    2000-01-01

    The Viking Orbiter determined that the surface of Mars' northern residual cap consists of water ice. An examination of north polar water-ice clouds could lend insight into the fate of the water vapor during this time period.

  2. What Lies Below a Martian Ice Cap

    NASA Technical Reports Server (NTRS)

    2008-01-01

    [figure removed for brevity, see original site] Click on image for larger annotated version

    This image (top) taken by the Shallow Radar instrument on NASA's Mars Reconnaissance Orbiter reveals the layers of ice, sand and dust that make up the north polar ice cap on Mars. It is the most detailed look to date at the insides of this ice cap. The colored map below the radar picture shows the topography of the corresponding Martian terrain (red and white represent higher ground, and green and yellow lower).

    The radar image reveals four never-before-seen thick layers of ice and dust separated by layers of nearly pure ice. According to scientists, these thick ice-free layers represent approximately one-million-year-long cycles of climate change on Mars caused by variations in the planet's tilted axis and its eccentric orbit around the sun. Adding up the entire stack of ice gives an estimated age for the north polar ice cap of about 4 million years a finding that agrees with previous theoretical estimates. The ice cap is about 2 kilometers (1.2 miles) thick.

    The radar picture also shows that the boundary between the ice layers and the surface of Mars underneath is relatively flat (bottom white line on the right). This implies that the surface of Mars is not sagging, or bending, under the weight of the ice cap and this, in turn, suggests that the planet's lithosphere, a combination of the crust and the strong parts of the upper mantle, is thicker than previously thought.

    A thicker lithosphere on Mars means that temperatures increase more gradually with depth toward the interior. Temperatures warm enough for water to be liquid are therefore deeper than previously thought. Likewise, if liquid water does exist in aquifers below the surface of Mars, and if there are any organisms living in that water, they would have to be located deeper in the planet.

    The topography data are from Mars Orbiter Laser Altimeter, which was flown on NASA's Mars Global

  3. Evaporites on Ice: Experimental Assessment of Evaporites Formation on Antarctica (and on Martian North Polar Residual Cap)

    NASA Astrophysics Data System (ADS)

    Losiak, Anna; Derkowski, Arkadiusz; Skala, Aleksander; Trzcinski, Jerzy

    2016-04-01

    Evaporites are highly water soluble minerals, formed as a result of the evaporation or freezing of bodies of water. They are common weathering minerals found on rocks (including meteorites) on Antarctic ice sheet [1,2,3,4]. The water necessary for the reaction is produced by melting of ice below the dark-colored meteorites which can heat up to a few degrees above 0 °C due to insolation heating during wind-free summer days [5,6]. The Martian North Polar Residual Cap is surrounded by a young [7] dune field that is rich in evaporitic mineral: gypsum [8]. Its existence implies that relatively recently in the Martian history (in late Amazonian, when surface conditions were comparable to the current ones) there was a significant amount of liquid water present on the Mars surface. One of the proposed solutions to this problem is that gypsum is formed by weathering on/in ice [9,10,11,12,13], similarly to the process occurring on the Antarctic ice sheet. Recently, Losiak et al. 2015 showed that that during the warmest days of the Martian summer, solar irradiation may be sufficient to melt pure water ice located below a layer of dark dust particles lying on the steepest sections of the equator-facing slopes of the spiral troughs within Martian NPRC. Under the current irradiation conditions, melting is possible in very restricted areas of the NPRC and it lasts for up to couple of hours, but during the times of high irradiance at the north pole [15] this process could have been much more pronounced. Liquid water can be metastable at the NPRC because the pressure during the summer season is ~760-650 Pa [16] which is above the triple point of water. The rate of free-surface "clean" liquid water evaporation under average Martian conditions determined experimentally by [17] is comparable to the rate of melting determined by [21] (if there is no wind at the surface). In the current study we attempt to determine experimentally how many melting-freezing cycles are required to form

  4. Polar Cap Pits

    NASA Technical Reports Server (NTRS)

    2005-01-01

    17 August 2005 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows kidney bean-shaped pits, and other pits, formed by erosion in a landscape of frozen carbon dioxide. This images shows one of about a dozen different patterns that are common in various locations across the martian south polar residual cap, an area that has been receiving intense scrutiny by the MGS MOC this year, because it is visible on every orbit and in daylight for most of 2005.

    Location near: 86.9oS, 6.9oW Image width: width: 3 km (1.9 mi) Illumination from: upper left Season: Southern Spring

  5. Volatile-rich Crater Interior Deposits in the Polar Regions of Mars: Evidence for Ice Cap Advance and Retreat

    NASA Technical Reports Server (NTRS)

    Russell, Patrick S.; Head, James W.; Hecht, Michael H.

    2003-01-01

    Many craters on Mars are partially filled by distinctive material emplaced by post-impact processes. This crater fill material is an interior mound which is generally separated from the walls of the crater by a trough that may be continuous along the crater circumference (i.e. a ring-shaped trough), or which may only partially contact the crater walls (i.e. a crescent-shaped trough). The fill deposit is frequently offset from the crater center and may be asymmetric in plan view. Populations of such craters include those in the circum-south polar cap region, in Arabia Terra, associated with the Medusae Fossae Formation, and in the northern lowlands proximal to the north polar cap. We focus on those craters in circumpolar regions and assess their relationship to polar cap advance and retreat, especially the possibility that fill material represents remnants of a formerly larger contiguous cap. Volatile-rich deposits have the property of being modifiable by the local stability of the solid volatile, which is governed by local energy balance. Here we test the hypothesis that asymmetries in volatile fill shape, profile, and center-location within a crater result from asymmetries in local energy balance within the crater, due mainly to variation of solar insolation and radiative effects of the crater walls over the crater interior. Model profiles of crater fill are compared with MOLA topographic profiles to assess this hypothesis. If asymmetry in morphology and location of crater fill are consistent with radiative-dominated asymmetries in energy budget within the crater, then 1) the volatile-rich composition of the fill is supported (this process should not be effective at shaping volcanic or sedimentary deposits), and 2) the dominant factor determining the observed shape of volatile-rich crater fill is the local radiative energy budget (and erosive processes such as eolian deflation are secondary or unnecessary). We also use a geographic and energy model approach to

  6. Northern Polar Cap

    NASA Technical Reports Server (NTRS)

    2004-01-01

    [figure removed for brevity, see original site]

    Released 13 May 2004 This nighttime visible color image was collected on November 26, 2002 during the Northern Summer season near the North Polar Cap Edge.

    The THEMIS VIS camera is capable of capturing color images of the martian surface using its five different color filters. In this mode of operation, the spatial resolution and coverage of the image must be reduced to accommodate the additional data volume produced from the use of multiple filters. To make a color image, three of the five filter images (each in grayscale) are selected. Each is contrast enhanced and then converted to a red, green, or blue intensity image. These three images are then combined to produce a full color, single image. Because the THEMIS color filters don't span the full range of colors seen by the human eye, a color THEMIS image does not represent true color. Also, because each single-filter image is contrast enhanced before inclusion in the three-color image, the apparent color variation of the scene is exaggerated. Nevertheless, the color variation that does appear is representative of some change in color, however subtle, in the actual scene. Note that the long edges of THEMIS color images typically contain color artifacts that do not represent surface variation.

    Image information: VIS instrument. Latitude 80, Longitude 43.2 East (316.8 West). 38 meter/pixel resolution.

    Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

    NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for

  7. Polar Cap Colors

    NASA Technical Reports Server (NTRS)

    2004-01-01

    [figure removed for brevity, see original site]

    Released 12 May 2004 This daytime visible color image was collected on June 6, 2003 during the Southern Spring season near the South Polar Cap Edge.

    The THEMIS VIS camera is capable of capturing color images of the martian surface using its five different color filters. In this mode of operation, the spatial resolution and coverage of the image must be reduced to accommodate the additional data volume produced from the use of multiple filters. To make a color image, three of the five filter images (each in grayscale) are selected. Each is contrast enhanced and then converted to a red, green, or blue intensity image. These three images are then combined to produce a full color, single image. Because the THEMIS color filters don't span the full range of colors seen by the human eye, a color THEMIS image does not represent true color. Also, because each single-filter image is contrast enhanced before inclusion in the three-color image, the apparent color variation of the scene is exaggerated. Nevertheless, the color variation that does appear is representative of some change in color, however subtle, in the actual scene. Note that the long edges of THEMIS color images typically contain color artifacts that do not represent surface variation.

    Image information: VIS instrument. Latitude -77.8, Longitude 195 East (165 West). 38 meter/pixel resolution.

    Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

    NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA

  8. Creation of polar cap patches

    NASA Astrophysics Data System (ADS)

    Hosokawa, K.; Taguchi, S.; Ogawa, Y.

    2014-12-01

    Polar cap patches, which are islands of enhanced plasma density drifting anti-sunward, are one of the outstanding phenomena in the polar cap F region ionosphere. In the last decade, data from all-sky airglow imagers have been extensively used for better understanding the propagation of patches in the central polar cap region. But still, it has been rather difficult to capture the birth of patches in their generation region near the dayside cusp, because, in most places, the dayside part of the polar cap ionosphere is sunlit even in winter. In Longyearbyen (78.1N, 15.5E), Norway, however, optical observations are possible near the dayside cusp region in a limited period around the winter solstice. This enables us to directly image how polar cap patches are born in the cusp. In this paper, we present a few intervals of daytime optical observations, during which polar cap patches were generated within the field-of-view of an all-sky imager in Longyearbyen. During all the intervals studied here, we identified several signatures of poleward moving auroral forms (PMAF) in the equatorward half of the field-of-view, which are known as ionospheric manifestations of dayside reconnection. Interestingly, patches were directly produced from such poleward moving auroral signatures and propagated poleward along the anti-sunward convection near the cusp. In the literature, Lorentzen et al. (2012) first reported such a direct production of patches from PMAFs. During the current observations, however, we succeeded in tracking the propagation of patches until they reached the poleward edge of the field-of-view of the imager. This confirms that the faint airglow structures produced from PMAFs were actually transported for a long distance towards the central polar cap area; thus, polar cap patches were produced. From this set of observations, we suggest that polar cap patches during moderately disturbed conditions (i.e, non-storm time conditions) can be directly produced by the

  9. South Polar Cap, Summer 2000

    NASA Technical Reports Server (NTRS)

    2000-01-01

    This is the south polar cap of Mars as it appeared to the Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) on April 17, 2000. In winter and early spring, this entire scene would be covered by frost. In summer, the cap shrinks to its minimum size, as shown here. Even though it is summer, observations made by the Viking orbiters in the 1970s showed that the south polar cap remains cold enough that the polar frost (seen here as white) consists of carbon dioxide. Carbon dioxide freezes at temperatures around -125o C (-193o F). Mid-summer afternoon sunlight illuminates this scene from the upper left from about 11.2o above the horizon. Soon the cap will experience sunsets; by June 2000, this pole will be in autumn, and the area covered by frost will begin to grow. Winter will return to the south polar region in December 2000. The polar cap from left to right is about 420 km (260 mi) across.

  10. Mountain Glaciers and Ice Caps

    USGS Publications Warehouse

    Ananichheva, Maria; Arendt, Anthony; Hagen, Jon-Ove; Hock, Regine; Josberger, Edward G.; Moore, R. Dan; Pfeffer, William Tad; Wolken, Gabriel J.

    2011-01-01

    Projections of future rates of mass loss from mountain glaciers and ice caps in the Arctic focus primarily on projections of changes in the surface mass balance. Current models are not yet capable of making realistic forecasts of changes in losses by calving. Surface mass balance models are forced with downscaled output from climate models driven by forcing scenarios that make assumptions about the future rate of growth of atmospheric greenhouse gas concentrations. Thus, mass loss projections vary considerably, depending on the forcing scenario used and the climate model from which climate projections are derived. A new study in which a surface mass balance model is driven by output from ten general circulation models (GCMs) forced by the IPCC (Intergovernmental Panel on Climate Change) A1B emissions scenario yields estimates of total mass loss of between 51 and 136 mm sea-level equivalent (SLE) (or 13% to 36% of current glacier volume) by 2100. This implies that there will still be substantial glacier mass in the Arctic in 2100 and that Arctic mountain glaciers and ice caps will continue to influence global sea-level change well into the 22nd century.

  11. The Enigmatic Martian Polar Caps

    SciTech Connect

    James, Philip

    2005-08-17

    The Martian polar caps have puzzled astronomers for over a century. Extensive study by many instruments on various spacecraft has resolved many questions but has at the same time created a new generation of puzzles. The polar caps are intimately coupled to the current Martian climate and volatile cycles. They also hold clues to climate variations on a variety of longer time scales. The results of recent missions will be reviewed, and the potential outlook for resolution of the outstanding questions will be examined.

  12. North Polar Water-ice Clouds

    NASA Astrophysics Data System (ADS)

    Tamppari, L. K.; Smith, M. D.; Bass, DS

    2002-09-01

    Mars Global Surveyor (MGS) Thermal Emission Spectrometer (TES) limb sounding and nadir pointed data in the north polar region of Mars have been analyzed during northern spring and summer to find water-ice clouds. There has been uncertainty about the amount of water cycling in and out of the polar region, as evidenced by visible brightness changes in the residual polar cap from year to year which were originally though to be interannual variations (James and Martin, 1995; Kieffer, 1990). Bass et al. (2000) re-examined Viking data and found that 14-35 pr microns of water -ice appeared to be deposited on the cap later in the summer season. This deposition could be due to adsorption directly onto the cap surface or due to snowfall. In addition, Viking IRTM albedo and MAWD water vapor data were examined throughout this season (Bass and Paige, 2000), and water vapor was observed to increase in the cap area as the residual cap brightened. The possibility that some of the water is seasonally sequestered in water-ice clouds and may allow later precipitation had not been previously considered. Water-ice clouds, in the north polar region, have previously been tentatively identified in the Viking data (Tamppari and Bass, 2000), and some water-ice cloud identifications have been made in the north polar region during the MGS era (M. Smith, pers. comm., 2001). The detection of water-ice clouds over a cold surface is difficult (Tamppari et al., 2000) and during northern spring, the CO2 cap is retreating. Therefore, it is advantageous to examine TES limb-pointed observations over the seasonal polar cap regions and to combine those data with nadir-pointed data over the non-frost covered areas. We are examining these two data sets together to identify and track water-ice clouds and current results will be presented.

  13. South Polar Cap

    NASA Technical Reports Server (NTRS)

    2004-01-01

    [figure removed for brevity, see original site]

    Released 28 May 2004 This image was collected February 29, 2004 during the end of southern summer season. The local time at the location of the image was about 2 pm. The image shows an area in the South Polar region.

    The THEMIS VIS camera is capable of capturing color images of the martian surface using its five different color filters. In this mode of operation, the spatial resolution and coverage of the image must be reduced to accommodate the additional data volume produced from the use of multiple filters. To make a color image, three of the five filter images (each in grayscale) are selected. Each is contrast enhanced and then converted to a red, green, or blue intensity image. These three images are then combined to produce a full color, single image. Because the THEMIS color filters don't span the full range of colors seen by the human eye, a color THEMIS image does not represent true color. Also, because each single-filter image is contrast enhanced before inclusion in the three-color image, the apparent color variation of the scene is exaggerated. Nevertheless, the color variation that does appear is representative of some change in color, however subtle, in the actual scene. Note that the long edges of THEMIS color images typically contain color artifacts that do not represent surface variation.

    Image information: VIS instrument. Latitude -84.7, Longitude 9.3 East (350.7 West). 38 meter/pixel resolution.

    Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

    NASA's Jet

  14. Mars South Polar Cap 'Fingerprint' Terrain

    NASA Technical Reports Server (NTRS)

    2000-01-01

    This picture is illuminated by sunlight from the upper left.

    Some portions of the martian south polar residual cap have long, somewhat curved troughs instead of circular pits. These appear to form in a layer of material that may be different than that in which 'swiss cheese' circles and pits form, and none of these features has any analog in the north polar cap or elsewhere on Mars. This picture shows the 'fingerprint' terrain as a series of long, narrow depressions considered to have formed by collapse and widening by sublimation of ice. Unlike the north polar cap, the south polar region stays cold enough in summer to retain frozen carbon dioxide. Viking Orbiter observations during the late 1970s showed that very little water vapor comes off the south polar cap during summer, indicating that any frozen water that might be there remains solid throughout the year.

    This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image was obtained in early southern spring on August 4, 1999. It shows an area 3 x 5 kilometers (1.9 x 3.1 miles) at a resolution of about 7.3 meters (24 ft) per pixel. Located near 86.0oS, 53.9oW.

    Malin Space Science Systems and the California Institute of Technology built the MOC using spare hardware from the Mars Observer mission. MSSS operates the camera from its facilities in San Diego, CA. The Jet Propulsion Laboratory's Mars Surveyor Operations Project operates the Mars Global Surveyor spacecraft with its industrial partner, Lockheed Martin Astronautics, from facilities in Pasadena, CA and Denver, CO.

  15. High-Resolution South Polar Cap Mosaics

    NASA Technical Reports Server (NTRS)

    2000-01-01

    The layered terrains of the polar regions of Mars are among the most exotic planetary landscapes in our Solar System. The layers exposed in the south polar residual cap, vividly shown in the top view, are thought to contain detailed records of Mars' climate history over the last 100 million years or so. The materials that comprise the south polar layers may include frozen carbon dioxide, water ice, and fine dust. The bottom picture shows complex erosional patterns that have developed on the south polar cap, perhaps by a combination of sublimation, wind erosion, and ground-collapse. Because the south polar terrains are so strange and new to human eyes, no one (yet) has entirely adequate explanations as to what is being seen.

    These images were acquired by the Mars Orbiter Camera aboard the Mars Global Surveyor spacecraft during the southern spring season in October 1999. Each of these two pictures is a mosaic of many individual MOC images acquired at about 12 m/pixel scale that completely cover the highest latitude (87oS) visible to MOC on each orbital pass over the polar region. Both mosaics cover areas of about 10 x 4 kilometers (6.2 x 2.5 miles) near 87oS, 10oW in the central region of the permanent--or residual--south polar cap. They show features at the scale of a small house. Sunlight illuminates each scene from the left.'Gaps' at the upper and lower right of the second mosaic, above, are areas that were not covered by MOC in October 1999.

  16. Mapping of the water ice content within the Martian surficial soil on the periphery of the retreating seasonal northern polar cap based on the TES and the OMEGA data

    NASA Astrophysics Data System (ADS)

    Kuzmin, R. O.; Zabalueva, E. V.; Evdokimova, N. A.; Christensen, P. R.

    2012-11-01

    Analysis of seasonal data from the Mars Global Surveyor Thermal Emission Spectrometer (TES) shows a significant increase in thermal inertia during autumn, winter and spring in the middle and high latitudes of Mars. At each stage of the northern seasonal polar cap's recession in spring a distinct high thermal inertia (HTI) annulus arises around the cap's edge. Within this annulus, we estimated and mapped the springtime water ice content in the daily thermal skin depth layer using spring and summer values of the thermal inertia in TES surface footprints. The results show that the average water content in the surface soil within the HTI annulus varies from ˜5 vol % at the early stages of the seasonal polar cap retreating (Ls = 340°-360°) to ˜1 vol % at later stages (Ls = 60°-70°). Maximum values of water ice content within the HTI annulus occur at Ls = 0°-20° (2-6 vol %) and Ls = 20°-40° (4-10 vol %). We analyzed the temporal and spatial relationship between the HTI annuli and the water ice (WI) annuli at the edge of the northern seasonal polar cap. The water ice within the WI annuli was mapped using a water ice spectral index (the absorption band depth at the 1.5 μm wavelength) derived from the OMEGA (Observatoire pour la Minéralogie, l'Eau, les Glaces et l'Activité) imaging spectrometer aboard the Mars Express spacecraft. Recent OMEGA observations show that the WI annuli formation arises only around the retreating northern seasonal polar cap, never around the retreating southern seasonal cap. For this reason our study is confined only to the northern hemisphere. The observed relationship between the HTI and WI annuli in the northern hemisphere of Mars indicates a close physical interdependence between these two phenomena. Our results confirm that the seasonal permafrost exposed by the retreating northern polar cap (within the HTI annuli) is actively involved today in the condensation and sublimation processes in the modern water cycle on Mars. The water

  17. South Polar Cap Erosion and Aprons

    NASA Technical Reports Server (NTRS)

    2000-01-01

    This scene is illuminated by sunlight from the upper left.

    While Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) images have shown that the north and south polar cap surfaces are very different from each other, one thing that the two have in common is that they both seem to have been eroded. Erosion in the north appears mostly to come in the form of pits from which ice probably sublimed to vapor and was transported away from the polar cap by wind. Erosion in the south takes on a wider range of possible processes that include collapse, slumping and mass-movement on slopes, and probably sublimation. Among the landforms created by these process on the south polar cap are the 'aprons' that surround mesas and buttes of remnant layers such as the two almost triangular features in the lower quarter of this image. The upper slopes of the two triangular features show a stair-stepped pattern that suggest these hills are layered.

    This image shows part of the south polar residual cap near 86.9oS, 78.5oW, and covers an area approximately 1.2 by 1.0 kilometers (0.7 x 0.6 miles) in size. The image has a resolution of 2.2 meters per pixel. The picture was taken on September 11, 1999.

    Malin Space Science Systems and the California Institute of Technology built the MOC using spare hardware from the Mars Observer mission. MSSS operates the camera from its facilities in San Diego, CA. The Jet Propulsion Laboratory's Mars Surveyor Operations Project operates the Mars Global Surveyor spacecraft with its industrial partner, Lockheed Martin Astronautics, from facilities in Pasadena, CA and Denver, CO.

  18. Martian polar and circum-polar sulfate-bearing deposits: Sublimation tills derived from the North Polar Cap

    NASA Astrophysics Data System (ADS)

    Massé, M.; Bourgeois, O.; Le Mouélic, S.; Verpoorter, C.; Le Deit, L.; Bibring, J. P.

    2010-10-01

    Previous spectroscopic studies have shown the presence of hydrated minerals in various kinds of sedimentary accumulations covering and encircling the martian North Polar Cap. More specifically, gypsum, a hydrated calcium sulfate, has been detected on Olympia Planum, a restricted part of the Circum-Polar Dune Field. To further constrain the geographical distribution and the process of formation and accumulation of these hydrated minerals, we performed an integrated morphological, structural and compositional analysis of a key area where hydrated minerals were detected and where the main polar landforms are present. By the development of a spectral processing method based on spectral derivation and by the acquisition of laboratory spectra of gypsum-ice mixtures we find that gypsum-bearing sediment is not restricted to the Olympia Planum dunes but is also present in all kinds of superficial sediment covering the surface of the North Polar Cap and the Circum-Polar Dune Field. Spectral signatures consistent with perchlorates are also detected on these deposits. The interpretation of landforms reveals that this gypsum-bearing sediment was released from the ice cap by sublimation. We thus infer that gypsum crystals that are now present in the Circum-Polar Dune Field derive from the interior of the North Polar Cap. Gypsum crystals that were initially trapped in the ice cap have been released by sublimation of the ice and have accumulated in the form of ablation tills at the surface of the ice cap. These gypsum-bearing sublimation tills are reworked by winds and are transported towards the Circum-Polar Dune Field. Comparison with sulfates found in terrestrial glaciers suggests that gypsum crystals in the martian North Polar Cap have formed by weathering of dust particles, either in the atmosphere prior to their deposition during the formation of the ice cap, and/or in the ice cap after their deposition.

  19. The hemispherical asymmetry of the residual polar caps on Mars

    NASA Technical Reports Server (NTRS)

    Lindner, Bernhard Lee

    1991-01-01

    A model of the polar caps of Mars was created which allows: (1) for light penetration into the cap; (2) ice albedo to vary with age, latitude, hemisphere, dust content, and solar zenith angle; and (3) for diurnal variability. The model includes the radiative effects of clouds and dust, and heat transport as represented by a thermal wind. The model reproduces polar cap regression data very well, including the survival of CO2 frost at the south pole and reproduces the general trend in the Viking Lander pressure data.

  20. Effects of Atmospheric Dust on Residual South Polar Cap Stability

    NASA Technical Reports Server (NTRS)

    Bonrv, B. P.; Bjorkman, J. E.; Hansen, G. B.; James, P. B.; Wolff, M. J.

    2005-01-01

    The Martian polar caps have been studied from the time of Herschel. Neither polar cap normally disappears in summer. The Residual North Polar Cap (portion that remains through summer) is composed of a mixture of water ice and dust, and its interannual stability is due to its low sublimation rate at the summer temperatures in the North Polar Region. The Residual South Polar Cap (RSPC) is more enigmatic, surviving the relatively hot perihelic summer season despite being composed of much more volatile CO2. It is able to do so because of its unusually high albedo, which is larger than that of other bright regions in the seasonal cap (e.g. Mountains of Mitchel). The proximity of the albedo of the RSPC to the critical albedo for stability raises the question of whether the RSPC exists in every Martian year. The ground based record is somewhat ambivalent. Douglass and Lowell reported that RSPC suddenly vanished at Ls=297deg in 1894 and did not reappear until Ls=0deg [1], and Kuiper reported that it disappeared in 1956 [2]; but both observations were questioned by contemporaries, who tended to attribute them to obscuring dust. Barker [3] reported a large amount of water vapor over the south polar cap in 1969 that could be attributed to exposure of near surface water ice during partial removal of the CO2 in the RSPC in 1969.

  1. Periodicities of polar cap patches

    NASA Astrophysics Data System (ADS)

    Hosokawa, K.; Taguchi, S.; Ogawa, Y.; Aoki, T.

    2013-01-01

    A highly sensitive all-sky electron multiplier charge-coupled device airglow imager has been operative in Longyearbyen, Norway since October 2011. The imager captures 630.0 nm all-sky images with an exposure time of 4 s, which is about 10 times shorter than that achieved by conventional cooled CCD imagers. This allows us to visualize the structure of polar cap patches without blurring effects and better estimate their periodicities. We present, as one of the first results from the imager, an event of successive appearance of patches on the night of 21 December 2011. A time series of the optical intensity at zenith showed modulations having two distinguished periods, one at 40 min and the other at 5-12 min. One possible explanation is that such a coexistence of two different periodicities is a manifestation of simultaneous occurrence of patch generation processes on the 40 min periodicity was created by large-scale reconfiguration of the dayside convection pattern while the 5-12 min modulations were closely associated with mechanisms driven by pulsed reconnection on the dayside magnetopause. Such a combined effect of multiple patch generation processes may play a role in structuring patches; thus, it would be of particular importance for evaluating the space weather effects in the trans-ionospheric communications environment in the polar cap.

  2. Multi-Year Monitoring of Ices, Frost and Dust in Mars Polar Caps from VIS-NIR Imaging Spectrometry

    NASA Astrophysics Data System (ADS)

    Langevin, Y.; Appéré, T.; Schmidt, F.; Douté, S.; Pilorget, C.; Vincendon, M.; Bibring, J.-P.; Schmitt, B.; Brown, A. J.; Herkenhoff, K. E.; Russell, P.; Titus, T. N.; Pommerol, A.; Gondet, B.; Seelos, K. D.

    2014-07-01

    Mex/OMEGA and MRO/CRISM, operating since 01/2004 and 11/2006, have played a major role in revealing the complexity and strong spatial variegation of polar processes on Mars, in relationship with seasonal and long term atmospheric evolution.

  3. Martian circumpolar sulfate-rich deposits: sublimation tills derived from the North Polar Cap

    NASA Astrophysics Data System (ADS)

    Masse, M.; Bourgeois, O.; Le Mouélic, S.; Verpoorter, C.; Le Deit, L.

    2009-12-01

    The North Polar Cap of Mars is an accumulation of ice layers with various amounts of interstratified dust particles. A dune field surrounds this polar cap. On one of the densest part of this dune field, Olympia Undae, Langevin et al. (Science, 2005) have detected calcium-rich sulfates (gypsum). To constrain the origin of these gypsum deposits, we performed an integrated morphological, structural and compositional analyses of a key area where it is possible to see the circum-polar dune field, the surface of the ice cap and a cross-section through the ice cap. The mineralogical composition of this area is investigated by applying a spectral derivative method to data acquired by OMEGA and CRISM hyperspectral imaging spectrometers. These are compared to laboratory spectra of ice-gypsum mixtures in simulated martian pressure and temperature conditions. We find that dunes of the circumpolar field and dust interstratified in the ice cap have the same composition. Both contain gypsum. Landforms produced by sublimation of ice are also visible on dust-rich layers of the ice cap. We therefore infer that the superficial circumpolar dust deposits correspond to a sublimation till produced by the ice cap. Circumpolar gypsum-rich deposits thus derive directly from the ice cap. Gypsum crystals are released at the surface of the cap as the ice sublimes. This material is then reworked by winds and forms the circumpolar dunes. There are two hypotheses for the ultimate origin of the gypsum crystals. (1) Pre-existing gypsum crystals might have been deposited together with ice crystals during the formation of the ice cap. (2) Authigenic gypsum crystals might have grown within the ice cap by weathering of dust trapped in the ice. The second hypothesis is consistent with the existence of authigenic sulfate inclusions in terrestrial polar ice (Ohno et al., GRL, 2006) and with the formation process suggested by Niles et al. (Nature, 2009) for martian equatorial sulfates.

  4. Edge of polar cap patches

    NASA Astrophysics Data System (ADS)

    Hosokawa, K.; Taguchi, S.; Ogawa, Y.

    2016-04-01

    On the night of 4 December 2013, a sequence of polar cap patches was captured by an all-sky airglow imager (ASI) in Longyearbyen, Norway (78.1°N, 15.5°E). The 630.0 nm airglow images from the ASI of 4 second exposure time, oversampled the emission of natural lifetime (with quenching) of at least ˜30 sec, introduce no observational blurring effects. By using such high-quality ASI images, we succeeded in visualizing an asymmetry in the gradients between the leading/trailing edges of the patches in a 2-D fashion. The gradient in the leading edge was found to be 2-3 times steeper than that in the trailing edge. We also identified fingerlike structures, appearing only along the trailing edge of the patches, whose horizontal scale size ranged from 55 to 210 km. These fingers are considered to be manifestations of plasma structuring through the gradient-drift instability (GDI), which is known to occur only along the trailing edge of patches. That is, the current 2-D observations visualized, for the first time, how GDI stirs the patch plasma and such a mixing process makes the trailing edge more gradual. This result strongly implies a close connection between the GDI-driven plasma stirring and the asymmetry in the large-scale shape of patches and then suggests that the fingerlike structures can be used as markers to estimate the fine-scale structure in the plasma flow within patches.

  5. A Warmer Atmosphere on Mars Near the Noachian-Hesperian Boundary: Evidence from Basal Melting of the South Polar Ice Cap (Dorsa Argentea Formation)

    NASA Astrophysics Data System (ADS)

    Fastook, J. L.; Head, J. W.; Marchant, D. R.; Forget, F.; Madeleine, J.-B.

    2011-03-01

    Dorsa Argentea Formation (Noachian-Hesperian) eskers are evidence for basal melting. Ice-flow models show that the mean annual south polar temperature must be raised to -50° to -75°C, providing an independent estimate of elevated lower latitude surface temperature.

  6. Thermal cracking of CO2 slab ice as the main driving force for albedo increase of the martian seasonal polar caps

    NASA Astrophysics Data System (ADS)

    Philippe, S.; Schmitt, B.; Beck, P.; Brissaud, O.

    2015-10-01

    Understanding the microphysical processes occuring on the Martian seasonal cap is critical since their radiative properties can affect the martian climate. A well documented phenomenom is the albedo increase of the Martian seasonal caps during spring, Fig.1. There are a lot of hypotheses that have been proposed as an explanation for this observation : the decrease of the CO2 grain size [2], a cleaning process of the CO2 slab that would imply either the sinking or the ejection of the dust contained in its volume ([1], [2], [5]), a water-layer accumulation on the top of the slab [5], the role played by aerosols [2] etc ... So far, no experimental simulations have been realized to discriminate between these processes. We designed an experiment to investigate the hypothesis of CO2 ice grain size decrease through thermal cracking as well as that of dust segregation as the possible reasons for albedo increase.

  7. The effect of polar caps on obliquity

    NASA Technical Reports Server (NTRS)

    Lindner, B. L.

    1993-01-01

    Rubincam has shown that the Martian obliquity is dependent on the seasonal polar caps. In particular, Rubincam analytically derived this dependence and showed that the change in obliquity is directly proportional to the seasonal polar cap mass. Rubincam concludes that seasonal friction does not appear to have changed Mars' climate significantly. Using a computer model for the evolution of the Martian atmosphere, Haberle et al. have made a convincing case for the possibility of huge polar caps, about 10 times the mass of the current polar caps, that exist for a significant fraction of the planet's history. Since Rubincam showed that the effect of seasonal friction on obliquity is directly proportional to polar cap mass, a scenario with a ten-fold increase in polar cap mass over a significant fraction of the planet's history would result in a secular increase in Mars' obliquity of perhaps 10 degrees. Hence, the Rubincam conclusion of an insignificant contribution to Mars' climate by seasonal friction may be incorrect. Furthermore, if seasonal friction is an important consideration in the obliquity of Mars, this would significantly alter the predictions of past obliquity.

  8. Acoustic Monitoring of the Arctic Ice Cap

    NASA Astrophysics Data System (ADS)

    Porter, D. L.; Goemmer, S. A.; Chayes, D. N.

    2012-12-01

    Introduction The monitoring of the Arctic Ice Cap is important economically, tactically, and strategically. In the scenario of ice cap retreat, new paths of commerce open, e.g. waterways from Northern Europe to the Far East. Where ship-going commerce is conducted, the U.S. Navy and U.S. Coast Guard have always stood guard and been prepared to assist from acts of nature and of man. It is imperative that in addition to measuring the ice from satellites, e.g. Icesat, that we have an ability to measure the ice extent, its thickness, and roughness. These parameters play an important part in the modeling of the ice and the processes that control its growth or shrinking and its thickness. The proposed system consists of three subsystems. The first subsystem is an acoustic source, the second is an array of geophones and the third is a system to supply energy and transmit the results back to the analysis laboratory. The subsystems are described below. We conclude with a plan on how to tackle this project and the payoff to the ice cap modeler and hence the users, i.e. commerce and defense. System Two historically tested methods to generate a large amplitude multi-frequency sound source include explosives and air guns. A new method developed and tested by the University of Texas, ARL is a combustive Sound Source [Wilson, et al., 1995]. The combustive sound source is a submerged combustion chamber that is filled with the byproducts of the electrolysis of sea water, i.e. Hydrogen and Oxygen, an explosive mixture which is ignited via a spark. Thus, no additional compressors, gases, or explosives need to be transported to the Arctic to generate an acoustic pulse capable of the sediment and the ice. The second subsystem would be geophones capable of listening in the O(10 Hz) range and transmitting that data back to the laboratory. Thus two single arrays of geophones arranged orthogonal to each other with a range of 1000's of kilometers and a combustive sound source where the two

  9. O+ transport across the polar cap

    NASA Astrophysics Data System (ADS)

    Elliott, H. A.; Jahn, J.; Pollock, C. J.; Moore, T. E.; Horwitz, J. L.

    2006-12-01

    The plasma sheet, inner magnetosphere, and high latitude magnetosphere all contain significant amounts of O+ ions during active times. Singly charged oxygen ions unambiguously come from the ionosphere making them an excellent tracer species. As the solar wind dynamic pressure increases, the O+ density in the in the cleft, high altitude polar cap, and plasma sheet also increases. We test the "cleft ion fountain" model, which asserts that O+ ions escape from the cleft, cross the polar cap, and then enter the plasma sheet against a mo of outflows originating from the entire polar cap. We use observations of O+ transport across the polar cap from TIDE polar cap ion outflow measurements. The Tsyganenko magnetic field model, driven with ACE solar wind parameters is used to provide magnetic mapping and organization of the observations. We calculate the distance between the cleft and the foot-points of magnetic field lines mapped from the Polar spacecraft along the noon-midnight meridian. Using the observed outflow speed and magnetic field line length we calculate travel time for the ions. We then plot the distance from the cleft versus the travel time for an entire pass. For O+ this plot is quite linear, and the slope of the line is the average convection speed of the magnetic field lines across the polar cap. The convection speed we determined is consistent with the convection speed measured in the ionosphere. We conclude that O+ ions emanating principally from the cleft are transported across the polar cap, and these O+ ions have access to the ring current and plasma sheet.

  10. Polar gypsum on Mars : wind-driven exhumation from the North Polar Cap and redistribution in the Circumpolar Dune Field

    NASA Astrophysics Data System (ADS)

    Masse, M.; Bourgeois, O.; Le Mouélic, S.; Verpoorter, C.; Le Deit, L.; Mercier, E.; Bibring, J.

    2010-12-01

    The North Polar Cap of Mars is associated with different kinds of superficial sediments, including the Circumpolar Dune Field and sedimentary veneers scattered over the ice cap. In order to resolve the mineralogical composition of these sediments, we processed OMEGA and CRISM hyperspectral data with an original method based on spectral derivation (Huguenin and Jones, 1986). We find that gypsum is present in all areas where undefined hydrated minerals had been previously detected (Poulet et al., 2008; Horgan et al., 2009; Calvin et al., 2010), including the superficial sedimentary veneers found on the North Polar Cap and the whole Circumpolar Dune Field. Integrated morphological and structural analyses reveal that these gypsum crystals derive directly from the interior of the ice cap (Massé et al., 2010). The source of sedimentary veneers is the dust that was previously contained in the upper part of the ice cap, the ice-rich North Polar Layered Deposits (NPLD). This gypsum-bearing dust was exhumed, on south-facing slopes of spiral troughs and arcuate scarps, by ice ablation induced by katabatic winds. By the analysis of all associations of erosional scarps and dune fields over the North Polar Cap, we also demonstrate that the source of the polar dunes are sand-sized particles that were previously contained in the sediment-rich BU (Basal Unit), corresponding to the lower part of the ice cap. These particles were exhumed from the BU, by regressive ablation of the ice at marginal scarps that border the North Polar Cap, or by vertical ablation of the ice on Olympia Planum. From a reconstruction of wind flow lines over and around the ice cap, we infer that katabatic winds descending from the polar high and rotating around the North Polar Cap are responsible for the exhumation of this gypsum-bearing sand and for its redistribution in the Circumpolar Dune Field. The intensity of gypsum diagnostic spectral absorption bands decreases along wind flow lines in the

  11. Devon island ice cap: core stratigraphy and paleoclimate.

    PubMed

    Koerner, R M

    1977-04-01

    Valuable paleoclimatic information can be gained by studying the distribution of melt layers in deep ice cores. A profile representing the percentage of ice in melt layers in a core drilled from the Devon Island ice cap plotted against both time and depth shows that the ice cap has experienced a period of very warm summers since 1925, following a period of colder summers between about 1600 and 1925. The earlier period was coldest between 1680 and 1730. There is a high correlation between the melt-layer ice percentage and the mass balance of the ice cap. The relation between them suggests that the ice cap mass balance was zero (accumulation equaled ablation) during the colder period but is negative in the present warmer one. There is no firm evidence of a present cooling trend in the summer conditions on the ice cap. A comparison with the melt-layer ice percentage in cores from the other major Canadian Arctic ice caps shows that the variation of summer conditions found for the Devon Island ice cap is representative for all the large ice caps for about 90 percent of the time. There is also a good correlation between melt-layer percentage and summer sea-ice conditions in the archipelago. This suggests that the search for the northwest passage was influenced by changing climate, with the 19th-century peak of the often tragic exploration coinciding with a period of very cold summers. PMID:17733504

  12. Polar cap precursor of nightside auroral oval intensifications using polar cap arcs

    NASA Astrophysics Data System (ADS)

    Zou, Ying; Nishimura, Yukitoshi; Lyons, Larry R.; Donovan, Eric F.; Shiokawa, Kazuo; Ruohoniemi, J. Michael; McWilliams, Kathryn A.; Nishitani, Nozomu

    2015-12-01

    Recent radar and optical observations suggested that localized fast flows in the polar cap precede disturbances within the nightside auroral oval. However, how commonly this connection occurs has been difficult to examine due to limited coverage of radar flow measurements and diffuse and dim nature of airglow patches. Polar cap arcs are also associated with fast flows in the polar cap and appear much brighter than patches, allowing evaluation of the interaction between polar cap structures and nightside aurora more definitively. We have surveyed data during six winter seasons and selected quasi-steady polar cap arcs lasting >1 h. Thirty-four arcs are found, and for the majority (~85%) of them, as they extend equatorward from high latitude, their contact with the nightside auroral poleward boundary is associated with new and substantial intensifications within the oval. These intensifications are localized (< ~1 h magnetic local time (MLT)) and statistically occur within 10 min and ±1 h MLT from the contact. They appear as poleward boundary intensifications in a thick auroral oval or an intensification of the only resolvable arc within a thin oval, and the latter can also exhibit substantial poleward expansion. When radar echoes are available, they corroborate the association of polar cap arcs with localized enhanced antisunward flows. That the observed oval intensifications are major disturbances that only occur after the impingement of polar cap arcs and near the contact longitude suggest that they are triggered by localized fast flows coming from deep in the polar cap.

  13. Determining surface elevation change of small ice caps on Greenland

    NASA Astrophysics Data System (ADS)

    Hess, D. P.; Schenk, A.; Csatho, B. M.; Nagarajan, S.; Briner, J. P.

    2010-12-01

    Among the hundreds of small ice caps that dot the periphery of the Greenland ice sheet, several (such as Sukkertoppen, North Ice Cap, and Flade Isbrink) have been flown multiple times by the NASA Airborne Topographic Mapper (ATM). Although highly resolved, these flights cover only a small portion of each ice cap surface. In this work we introduce ICESat as a complementary sensor to estimate surface elevation change over a larger area. Surface Elevation Reconstruction and Change detection (SERAC) is a method that has been successfully applied to several cases where fusion of multisensory data is required to reconstruct surface topography. The method is based on fitting analytical functions to laser points within repeat tracks or cross-over areas and provides high resolution, precise changes in surface topography along with a rigorous error estimate of the reconstructed elevation changes. In this study we apply SERAC to precisely reconstruct surface change for multiple ice caps using ATM and ICESat data through multiple time epochs. Small ice caps that surround the Greenland ice sheet reside at relatively low elevation and respond quickly to climate forcing. Moreover, dynamic thinning processes are comparatively limited in the ice caps when compared to the ice sheet proper. Small ice caps and alpine glaciers and expected to provide the largest contribution to eustatic sea-level rise over the coming century. There is therefore an urgent need to develop and maintain an inventory of small ice cap mass balance, especially those that surround the large ice sheets.

  14. Eddy intrustion of hot plasma into the polar cap and formation of polar-cap arcs

    NASA Technical Reports Server (NTRS)

    Chiu, Y. T.; Gorney, D. J.

    1983-01-01

    Under the simple postulate that multiple large scale detachable magnetospheric convection eddies can exist in the vicinity of the convection reversal boundary and in the polar cap, by Kelvin-Helmholtz instability or otherwise, it is shown that a number of seemingly disconnected plasma and electric field observations in the polar cap can be organized into a theory of magnetosheath and plasmasheet plasma intrusion into the polar cap. Current theory of inverted V structures then predicts existence of similar, but weaker, structures at the eddy convection reversal boundaries in the polar cap. A possible consequence is that the polar cap auroras are natural offshoots from discrete oval arcs and evidently are formed by similar processes. The two arc systems can occassionally produce an optical image in the form of the theta aurora.

  15. INFLUENCE OF THE POLAR CAP CURRENT ON PULSAR POLARIZATION

    SciTech Connect

    Kumar, D.; Gangadhara, R. T. E-mail: ganga@iiap.res.in

    2012-07-20

    We have developed a model for the polarization of curvature radiation by taking into account the polar-cap-current-induced perturbation on the dipolar magnetic field. We present the effects of the polar cap current on the pulsar radio emission in an artificial case when the rotation effects, such as aberration and retardation, are absent. Our model indicates that the intensity components and the polarization angle inflection point can be shifted to either the leading or the trailing side depending upon the prevailing conditions in the viewing geometry, the non-uniformity in source distribution (modulation), and the polar-cap-current-induced perturbation. Also, we find evidence for the origin of symmetric-type circular polarization in addition to the antisymmetric type. Our model predicts a stronger trailing component compared to that on the leading side of a given cone under some specific conditions.

  16. Spatial variability in the seasonal south polar CAP of Mars

    NASA Astrophysics Data System (ADS)

    Calvin, Wendy M.; Martin, Terry Z.

    1994-10-01

    The first comprehensive discussion of the south seasonal polar cap spectra obtained by the Mariner 7 infrared spectrometer in the short-wavelength region (2-4 microns) is presented. The infrared spectra is correlated with images acquired by the wide-angle camera. Significant spectral variation is noted in the cap interior and regions of varying water frost abundance, CO2 ice/frost cover, and CO2-ice path length can be distinguished. Many of these spectral variations correlate with heterogeneity noted in the camera images, but certain significant infrared spectral variations are not discernible in the visible. Simple reflectance models are used to classify the observed spectral variations into four regions. Region I is at the cap edge, where there is enhanced absorption beyond 3 microns inferred to be caused by an increased abundance of water frost. The increase in water abundance over that in the interior is on the level of a few parts per thousand or less. Region II is the typical cap interior characterized by spectral features of CO2 ice at grain sizes of several millimeters to centimeters. These spectra also indicate the presence of water frost at the parts per thousand level. A third, unusual region (III), is defined by three spectra in which weak CO2 absorption features are as much as twice as strong as in the average cap spectra and are assumed to be caused by an increased path length in the CO2. Such large paths are inconsistent with the high reflectance in the visible and at 2.2 microns and suggest layered structures or deposition conditions that are not accounted for in current reflectance models. The final region (IV) is an area of thinning frost coverage or transparent ice well in the interior of the seasonal cap. These spectra are a combination of CO2 and ground signatures.

  17. Grain metamorphism in polar nitrogen ice on Triton

    NASA Technical Reports Server (NTRS)

    Zent, Aaron P.; Mckay, Christopher P.; Pollack, James B.; Cruikshank, Dale P.

    1989-01-01

    The rate of nitrogen grain growth on putative N2-rich polar caps on Triton is calculated. For most plausible assumptions of independent variables, mean grain sizes in polar N2 are meter-scale. Triton's polar caps should constitute the definitive solar-system test bed for the process of ice grain metamorphism. Interpretation of data already in hand may require long path length through condensed N2, possibly due to grain growth. Upcoming Voyager data may clarify the situation, although possible complications in detecting a glaze of N2 ice exist.

  18. Energetic particles over Io's polar caps

    NASA Astrophysics Data System (ADS)

    Williams, D. J.; Thorne, R. M.

    2003-11-01

    We present results obtained from the Galileo satellite's Energetic Particles Detector during its final two encounters in 2001 with Jupiter's moon Io. These encounters returned the first data from just above Io's polar caps. They complement previous low-latitude data and provide a new perspective of Io's interaction with Jupiter's magnetosphere and ionosphere. The evolution of electron and ion distributions was measured from the upstream region throughout the polar cap traversals. From the time of initial field contact with Io and continuing throughout the encounter these distributions evolve in a manner consistent with adiabatic motion along the Io-Jupiter field line. At encounter all particles develop narrow trapped-like distributions indicative of the creation of a near-Io magnetic bottle caused by an enhancement of field at Io's upstream surface. The measured pitch angle distributions indicate a field enhancement of up to 10%-15% higher than the field observed at Galileo's position. Distribution evolution times agree roughly with particle bounce times on the Io-Jupiter field line. The ion distribution evolution times provide an estimate of ˜3-7 km/s for the field line convection speed across Io's polar caps, a value small (˜10%) compared with the upstream convection speed. Along with these trapped distributions, beams of ions and electrons are observed streaming into Io's polar caps throughout the encounters. The continued observation of ion beams across the polar cap is consistent with their half-bounce times. The data further indicate that the convection speed may vary as the polar cap is traversed. The one exception to the adiabatic particle behavior discussed above is the observation of intense electron beams streaming into Io's polar caps. The polar cap electron beams are similar to those previously measured in Io's wake [, 1996] and apparently originate from the same source. The source has been located at low (˜0.5 RJ) altitudes on the Io-Jupiter field

  19. The Mars water cycle at other epochs - Recent history of the polar caps and layered terrain

    NASA Technical Reports Server (NTRS)

    Jakosky, Bruce M.; Henderson, Bradley G.; Mellon, Michael T.

    1993-01-01

    A numerical model is presented of the integrated role of seasonal water cycle on the evolution of polar deposits on Mars over the last 10 million years. From the model, it is concluded that the only major difference between the polar caps which affects their long-term behavior is ultimately the difference in their elevations. Because of that difference, there is a preference for CO2 frost to stay longer on the northern polar cap. The average difference in sublimation at the caps results in a net south-to-north transport of water ice over long time scales. Superimposed on any long-term behavior is a transfer of water ice between the caps on the 10 exp 5 - 10 exp 6 yr time scales. The amount of water exchanged is small compared to the total ice content of the polar deposits.

  20. Plasma structuring in the polar cap

    SciTech Connect

    Basu, S.; Basu, S.; Weber, E.J.; Bishop, G.J.

    1990-01-01

    Propagation experiments providing scintillation, total electron content and drift data in the field of view of an all-sky imager near the magnetic polar in Greenland are utilized to investigate the manner in which ionospheric plasma becomes structured within the polar cap. It is found that under IMF Bz southward conditions, large scale ionization patches which are convected through the dayside cusp into the polar cap get continually structured. The structuring occurs through the ExB gradient drift instability process which operates through an interaction between the antisunward plasma convection in the neutral rest frame and large scale plasma density gradients that exist at the edges of the ionization patches. It is shown that with the increase of solar activity the strength of the irregularities integrated through the ionosphere is greatly increased. Under the IMF Bz northward conditions, the plasma structuring occurs around the polar cap arcs in the presence of inhomogeneous electric field or disordered plasma convection. In that case, the irregularity generation is caused by the competing processes of non-linear Kelvin-Helmholtz instability driven by sheared plasma flows and the gradient drift instability process which operates in the presence of dawn-dusk motion of arc structures. The integrated strength of this class of irregularities also exhibits marked increase with increasing solar activity presumably because the ambient plasma density over the polar cap is enhanced.

  1. Polar Rain Gradients and Field-Aligned Polar Cap Potentials

    NASA Technical Reports Server (NTRS)

    Fairfield, D. H.; Wing, S.; Newell, P. T.; Ruohoniemi, J. M.; Gosling, J. T.; Skoug, R. M.

    2008-01-01

    ACE SWEPAM measurements of solar wind field-aligned electrons have been compared with simultaneous measurements of polar rain electrons precipitating over the polar cap and detected by DMSP spacecraft. Such comparisons allow investigation of cross-polarcap gradients in the intensity of otherwise-steady polar rain. The generally good agreement of the distribution functions, f, from the two data sources confirms that direct entry of solar electrons along open field lines is indeed the cause of polar rain. The agreement between the data sets is typically best on the side of the polar cap with most intense polar rain but the DMSP f's in less intense regions can be brought into agreement with ACE measurements by shifting all energies by a fixed amounts that range from tens to several hundred eV. In most cases these shifts are positive which implies that field-aligned potentials of these amounts exist on polar cap field lines which tend to retard the entry of electrons and produce the observed gradients. These retarding potentials undoubtedly appear in order to prevent the entry of low-energy electrons and maintain charge quasi-neutrality that would otherwise be violated since most tailward flowing magnetosheath ions are unable to follow polar rain electrons down to the polar cap. In more limited regions near the boundary of the polar cap there is sometimes evidence for field-aligned potentials of the opposite sign that accelerate polar rain electrons. A solar electron burst is also studied and it is concluded that electrons from such bursts can enter the magnetotail and precipitate in the same manner as polar rain.

  2. The polar cap environment of outflowing O(+)

    NASA Technical Reports Server (NTRS)

    Horwitz, J. L.; Pollock, C. J.; Moore, T. E.; Peterson, W. K.; Burch, J. L.; Winningham, J. D.; Craven, J. D.; Frank, L. A.; Persoon, A.

    1992-01-01

    The properties of the core (0-50 eV) and 'energetic' (0-1 keV) ions, plasma waves, and auroral images obtained from Dynamics Explorer 1 (DE-1) and those of electrons, obtained from DE-2, are examined in the context of the polar cap environment. Results indicate the presence of two populations: high-speed (10-30 eV, or higher, streaming energies) polar beams and low-speed (generally less than 10-eV streaming energies) streams. The high-speed polar beams show an auroral connection (i.e., they are observed on or near the field lines threading auroral arcs), while the low-speed streams are on or near the field lines threading the dark polar cap and may be converted from the cleft ion fountain. Compared to the high-speed streams, the low-speed streams are significantly more stable with respect to energy and flux.

  3. The Residual South Polar Cap of Mars: Stable or Transitory?

    NASA Astrophysics Data System (ADS)

    Glenar, David A.; Bonev, B. P.; Hansen, G. B.; James, P. B.; Bjorkman, J. E.

    2006-09-01

    It remains uncertain whether the CO2 residual south polar cap (RSPC) is a permanent feature of the present Mars climate, or whether it occasionally sublimes completely during years marked by dramatic dust storm activity. While there is no firm evidence for complete disappearance of the cap in the past, observations show that the residual cap lost significant CO2 material in the spring / summer season prior to the Mariner 9 encounter. On the other hand, little interannual change has been observed in the RSPC during the MGS mission [1], despite the massive early-spring dust storm which occurred in 2001. We discuss whether a global dust storm beginning near perihelion could enhance the net CO2 sublimation sufficiently to completely remove the RSPC. We utilize a surface-plus-aerosol radiative transfer model under conditions of both modest and heavy atmospheric dust loading. The sublimination behavior depends critically on the extended (visible to thermal IR) albedo spectrum of the polar CO2 ice, which we have strongly constrained [2] from a combination of HST photometric imaging, ground based near-IR imaging spectroscopy and spectroscopic measurements by the Mars Express PFS. The extension of the cap spectrum to thermal IR wavelengths was accomplished by forward modeling using a semi-infinite grid of scattering grains. Results of this analysis depend on the strength of possible feedback mechanisms (increased surface dust content; exposure of water ice) as well as on the possibility of dust confinement by the polar vortex; but the general conclusion is that it would require multiple, intense dust storms in a given year in order to completely remove the CO2 ice veneer layer. This work has been supported by the NASA Planetary Astronomy and Mars Data Analysis Programs. [1] Benson and James, Icarus 174, 513, 2005; [2] Bonev et al., Planet Space Sci. 2006 (accepted).

  4. Seasonal aldedo variations on the Martian north polar cap as seen by MGS

    NASA Technical Reports Server (NTRS)

    Hale, Amy S.; Bass, Deborah S; Tamppari, Leslie K.

    2003-01-01

    The Viking Orbiters determined that the surface of Mars' northern redisual cap is water ice. Many researchers have related observed atmospheric water vapor abundances to seasonal exchange between reservoirs such as the polar caps, but the extent to which the exchange between the surface and the atmosphere remains uncertain.

  5. Sunlight penetration through the Martian polar caps: Effects on the thermal and frost budgets

    NASA Technical Reports Server (NTRS)

    Lindner, Bernhard Lee

    1992-01-01

    An energy balance model of the seasonal polar caps on Mars is modified to include penetration of solar radiation into and through the ice. Penetration of solar radiation has no effect on subsurface temperature or total frost sublimation if seasonal ice overlies a dust surface. An effect is noted for seasonal ice which overlies the residual polar caps. For the case of an exposed water-ice residual polar cap, the temperature at depth is calculated to be up to several degrees warmer and the calculated lifetime of seasonal CO2 frost is slightly lower when penetration of sunlight is properly treated in the model. For the case of a residual polar cap which is perennially covered by CO2 frost, the calculated lifetime of seasonal CO2 frost is very slightly increased as a result of sunlight penetration through the ice. Hence, penetration of sunlight into the ice helps to stabilize the observed dichotomy in the residual polar caps on Mars, although it is a small effect.

  6. Sunlight penetration through the Martian polar caps - Effects on the thermal and frost budgets

    NASA Technical Reports Server (NTRS)

    Lindner, Bernhard L.

    1992-01-01

    An energy balance model of the seasonal polar caps on Mars is modified to include penetration of solar radiation into and through the ice. Penetration of solar radiation has no effect on subsurface temperature or total frost sublimation if seasonal ice overlies a dust surface. An effect is noted for seasonal ice which overlies the residual polar caps. For the case of an exposed water-ice residual polar cap, the temperature at depth is calculated to be up to several degrees warmer, and the calculated lifetime of seasonal CO2 frost is slightly lower when penetration of sunlight is properly treated in the model. For the case of a residual polar cap which is perennially covered by CO2 frost, the calculated lifetime of seasonal CO2 frost is very slightly increased as a result of sunlight penetration through the ice. Hence, penetration of sunlight into the ice helps to stabilize the observed dichotomy in the residual polar caps on Mars, although it is a small effect.

  7. Lobe cell convection and polar cap precipitation

    NASA Astrophysics Data System (ADS)

    Eriksson, S.; Peria, W. J.; Bonnell, J. W.; Su, Y.-J.; Ergun, R. E.; Tung, Y.-K.; Parks, G. K.; Carlson, C. W.

    2003-05-01

    The characteristic electric and magnetic field signature of lobe cells as observed by the low-altitude FAST satellite in 55 dawn-dusk passes are compared with Polar ultraviolet images of polar cap auroral activity. Initial results from 34 events of UV image coverage suggest that there is an intimate coupling between the sunward convection flow of the lobe cell and transpolar auroral arcs or diffuse polar cap precipitation in ˜62% of these cases. However, in some cases where the field signatures are suggestive of lobe cell convection, there is no detectable particle precipitation either in Polar UVI or the FAST data sets. Moreover, the presence of lobe cells coincide with UV data intensifications in the premidnight 2000-2400 MLT sector and/or the postnoon 1500 MLT region in ˜59% of all cases with UVI coverage. The magnetic local time dependence of the lobe cells and polar cap precipitation on the interplanetary magnetic field (IMF) are examined using the upstream Wind monitor. The relative importance of the IMF By and Bz components are investigated and compared with the predictions of the antiparallel merging model and strongly suggests a connection with the magnetospheric sash, as is further implied by the mapping of magnetic field lines using the [2002] (T01) model. It was also noted that a majority of lobe cell events occurred during enhanced AE index substorm-like conditions and that generally stronger AE indices are measured for stronger IMF By magnitudes during these events.

  8. Fourier spectra from exoplanets with polar caps and ocean glint

    NASA Astrophysics Data System (ADS)

    Visser, P. M.; van de Bult, F. J.

    2015-07-01

    Context. The weak orbital-phase dependent reflection signal of an exoplanet contains information on the planet surface, such as the distribution of continents and oceans on terrestrial planets. This light curve is usually studied in the time domain, but because the signal from a stationary surface is (quasi)periodic, analysis of the Fourier series may provide an alternative, complementary approach. Aims: We study Fourier spectra from reflected light curves for geometrically simple configurations. Depending on its atmospheric properties, a rotating planet in the habitable zone could have circular polar ice caps. Tidally locked planets, on the other hand, may have symmetric circular oceans facing the star. These cases are interesting because the high-albedo contrast at the sharp edges of the ice-sheets and the glint from the host star in the ocean may produce recognizable light curves with orbital periodicity, which could also be interpreted in the Fourier domain. Methods: We derive a simple general expression for the Fourier coefficients of a quasiperiodic light curve in terms of the albedo map of a Lambertian planet surface. Analytic expressions for light curves and their spectra are calculated for idealized situations, and dependence of the spectral peaks on the key parameters inclination, obliquity, and cap size is studied. Results: The ice-scattering and ocean glint contributions can be separated out, because the coefficients for glint are all positive, whereas ice sheets lead to even-numbered, higher harmonics. An in-view polar cap on a planet without axial tilt only produces a single peak. The special situation of edge-on observation, which is important for planets in transit, leads to the most pronounced spectral behavior. Then the respective spectra from planets with a circumventing ocean, a circular ocean (eyeball world), polar caps, and rings, have characteristic power-law tails n-2, n-7/2, n-4, and (-1)n + 1n-2. Conclusions: Promising recently discovered

  9. Polar Cap Precursor of Nightside Auroral Oval Intensifications Using Polar Cap Arcs

    NASA Astrophysics Data System (ADS)

    Zou, Y.; Nishimura, T.; Lyons, L. R.; Donovan, E.; Shiokawa, K.; Ruohoniemi, J. M.; McWilliams, K. A.; Nishitani, N.

    2015-12-01

    Recent radar and optical observations have revealed that localized fast flows in the polar cap can closely relate to disturbances within the nightside auroral oval. However, how commonly this connection occurs has been difficult to examine due to limited coverage of radar flow measurements and diffuse and dim nature of airglow patches. This question can now be addressed by using polar cap arcs, which are also associated with fast flows and appear much brighter than patches, allowing evaluation of the interaction between polar cap flows and nightside aurora more definitively. Utilizing an array of high-resolution 630.0 nm all-sky imagers, we have selected quasi-steady polar cap arcs lasting >1 h from six winter seasons. Thirty four arcs are found and for the majority (~85%) of them, as they extend equatorward from magnetic pole, their contact with the nightside auroral poleward boundary is associated with new and substantial intensifications within the oval, in contrast to the otherwise quiet oval. These intensifications are localized (<~1 h MLT) and statistically occur within 10 min and ±1 h MLT from the contact. They appear as poleward boundary intensifications (PBIs) in a thick auroral oval or an intensification of the only resolvable arc in a thin oval, and the latter can also exhibit substantial poleward expansion. When radar echoes are available, they corroborate the association of polar cap arcs with localized enhanced anti-sunward polar cap flows. That the observed oval intensifications are major disturbances that only occur after and initiate near the impingement of polar cap arcs suggest that they are triggered by localized fast flows coming from deep in the polar cap. Such observation suggests that meso-scale fast flows in the lobe can traverse the open-closed field line boundary through enhanced magnetic reconnection and closely couple with disturbances in the plasma sheet.

  10. Lithospheric Loading by the Northern Polar CAP on Mars

    NASA Astrophysics Data System (ADS)

    Johnson, C. L.; Solomon, S. C.; Head, J. W.; Smith, D. E.; Zuber, M. T.

    1999-03-01

    Loading of the martian lithosphere by the northern polar cap is investigated using elastic and viscoelastic models and constraints from MOLA data and geology. Implications for basement topography, polar cap volume and the gravity field are discussed.

  11. Correlation between south polar cap composition from OMEGA/MEX data and geomorphologic units

    NASA Astrophysics Data System (ADS)

    Mangold, N.; Poulet, F.; Forget, F.; Gendrin, A.; Gondet, B.; Langevin, Y.; Schmitt, B.; Bibring, J.-P.; OMEGA, Team

    A series of observations covering the south polar cap and part of the surrounding terrains have been recorded in the first weeks of OMEGA operation. From these first observations nearly pure H2O ice has been discovered in several areas surrounding the bright cap on which CO2 ice is mainly concentrated. A strong correlation exists between these compositional units and geomorphic features observed on MOC images acquired during the summer of the south hemisphere. As postulated by previous studies using MOC and THEMIS data, CO2 ice is strongly correlated with the geomorphic features called swiss-cheese terrains characterized by quasi-circular depressions. H2O ice, devoid of any CO2 ice, is observed with OMEGA in the periphery of these these swiss-cheese terrains. These H2O ice terrains on MOC images are very smooth and only affected by polygonal cracks which likely result of thermal contraction. The CO2 ice is apparently superimposed on these H2O ice layers confirming that the CO2 ice cap is restricted to a thin layer of few meters thick. Outside of the bright cap, patches of H2O ice are observed with OMEGA in correlation with grooved homogeneous surfaces on MOC images. They represent part of an H2O ice cap devoid of any overlying CO2 units which suggests an extension of the cap far beyond the bright polar cap. Preliminary results of the modeling of the sublimation processes of these different ices units will be presented.

  12. Glaciers and ice caps outside Greenland

    USGS Publications Warehouse

    Sharp, Marin; Wolken, G.; Burgess, D.; Cogley, J.G.; Copland, L.; Thomson, L.; Arendt, A.; Wouters, B.; Kohler, J.; Andreassen, L.M.; O'Neel, Shad; Pelto, M.

    2015-01-01

    Mountain glaciers and ice caps cover an area of over 400 000 km2 in the Arctic, and are a major influence on global sea level (Gardner et al. 2011, 2013; Jacob et al. 2012). They gain mass by snow accumulation and lose mass by meltwater runoff. Where they terminate in water (ocean or lake), they also lose mass by iceberg calving. The climatic mass balance (Bclim, the difference between annual snow accumulation and annual meltwater runoff) is a widely used index of how glaciers respond to climate variability and change. The total mass balance (ΔM) is defined as the difference between annual snow accumulation and annual mass losses (by iceberg calving plus runoff).

  13. Recrystallization Diagram for Polar Ice

    NASA Astrophysics Data System (ADS)

    Weikusat, Ilka; Azuma, Nobuhiko; Faria, Sérgio H.

    2014-05-01

    Ice is the most frequent mineral on the Earth's surface, however experiences conditions comparable to silicate minerals at high metamorphic grades. In all natural conditions ice is a hot material with homologous temperatures between 0.9 and 0.7 at least. Under such circumstances recrystallization plays a decisive role in governing the state and thus the behaviour of the material. This has been recognized and interpreted in many ice cores in the last decades (Faria et al. in press a) assigning recrystallization regimes to ice sheet depth ranges. This assignment made use of microstructure observations (mainly grain size) and estimated boundary conditions (temperature and stress/strain amounts) which change systematically with depth. To generalize the use of recrystallization regimes we decouple their occurrence from the ice sheet depth information and connect them directly to the activators and causes: strain rate and temperature (Faria et al. in press b). References: Faria, S. H.; Weikusat, I. & Azuma, N. The Microstructure of Polar Ice. Part I: Highlights from ice core research. Journal of Structural Geology , in press a, DOI: 10.1016/j.jsg.2013.09.010 Faria, S. H.; Weikusat, I. & Azuma, N. The Microstructure of Polar Ice. Part II: State of the Art .Journal of Structural Geology , in press b, DOI: 10.1016/j.jsg.2013.11.003

  14. Lobe Cell Convection and Polar cap Precipitation

    NASA Astrophysics Data System (ADS)

    Eriksson, S.; Peria, W. J.; Su, Y.; Ergun, R. E.; Tung, Y.; Parks, G.; Carlson, C. W.

    2002-12-01

    The characteristic electric and magnetic field signature of lobe cells as observed by the low-altitude FAST satellite are compared with Polar ultraviolet images of polar cap auroral activity. Initial results from 55 events suggest that there is an intimate coupling between the sunward convection flow of the lobe cell and transpolar auroral arcs or diffuse polar cap precipitation. Moreover, the presence of lobe cells coincide with UV data intensifications in the premidnight 2100-2400 MLT sector and/or the postnoon 1500 MLT region in ~54% of all cases with UVI coverage. The magnetic local time dependence of the lobe cells and polar cap precipitation on the interplanetary magnetic field (IMF) are examined using the upstream Wind monitor. The relative importance of the IMF By and Bz components are investigated and compared with the predictions of the antiparallel merging model and strongly suggests a connection with the magnetospheric sash, as is further implied by the mapping of magnetic field lines using the Tsyganenko [2002] (T01) model. It was also noted that a majority of events occurred during enhanced AE index substorm-like conditions and that generally stronger AE indices are measured for stronger IMF By magnitudes.

  15. The Martian North Polar Cap in Summer - One Year Later

    NASA Technical Reports Server (NTRS)

    2001-01-01

    In the middle of January 2001, Mars Global Surveyor (MGS) completed one Mars year in its 380 km-high (236 mi) mapping orbit. The mapping orbit was originally achieved in late February 1999. In March of that year, MGS conducted a series of operations in preparation for full-up mapping, first calibrating its scientific instruments and then operating in a mode in which the high gain antenna was held fixed against the body of the spacecraft. During this Fixed High Gain Antenna period, 'contingency science' observations were made in case the high gain antenna failed to properly deploy. The wide angle view of the martian north polar cap shown on the left was acquired on March 13, 1999, during early northern summer. The image on the right was acquired almost exactly one Mars year later, on January 26, 2001. The light-toned surfaces are residual water ice that remains through the summer season. The nearly circular band of dark material surrounding the cap consists mainly of sand dunes formed and shaped by wind. The north polar cap is roughly 1100 kilometers (680 miles) across. Close inspection will show that there are differences in the frost cover between the two images (for example, in the upper center of each image, and on the left edge center). Although these changes appear small, they are in fact quite large--the change in frost covering is equivalent to the amount of frost that would be evaporated (in the case of areas that are darker) or deposited (in areas where frost is still on the ground) in almost 5 months. What gives rise to such large changes in the heat budget for the polar caps from one year to the next is not known. Changes in the coloration and brightness of the polar cap suggest dust, deposited perhaps by dust storms during critical periods of the year, may play an important role.

  16. Polar cap size metrics study at CCMC

    NASA Astrophysics Data System (ADS)

    Rastaetter, L.; Kuznetsova, M. M.; Hesse, M.; Gombosi, T. I.; Raeder, J.; Weimer, D.

    2005-12-01

    The Community-Coordinated Modeling Center (CCMC) tests space physics models covering space from the Sun's corona to the Earth's ionosphere and makes them available for researchers through a run-on-request capability. The polar cap size and location as observed by global auroral imagers is used as a basis model to study the performance of global MHD simulation models and statistical models of the auroral ionosphere. With good confidence one can assume that auroral emissions are located within the closed magnetic field lines in a narrow region adjacent to the boundary of the open field line region of the polar cap. In this study we are using imager data from POLAR (FUV) for several events from 1997 to 2000 for which reasonable coverage is available. Simulation runs have been performed using the global magnetospheric models BATSRUS (T. Gombosi et al., U. Michigan) and OpenGGCM (J. Raeder, U. New Hampshire) as well as the Weimer (2000,2005) field-aligned current models (D. Weimer, Mission Research Corp.) fed with upstream solar wind data from the ACE or Geotail satellites. In addition to direct field line tracings available from the 3D MHD model outputs, we use field-aligned currents from both MHD models and the Weimer-2K model to determine the polar cap boundary by using the position of the maximum absolute FAC value in 16 local time sectors. We define skill scores that measure the agreement in the polar cap sizes and location between measurements and models as an example of implementations of metrics to track model performance and apply the analysis to a number of storm event days.

  17. North-Polar Martian Cap as Habitat for Elementary Life

    NASA Astrophysics Data System (ADS)

    Wallis, M. K.; Wickramasinghe, J. T.; Wickramasinghe, N. C.

    2008-09-01

    North-polar cap over millenia Atmospheric water in Mars tends currently as for the past millenia to distil onto the polar caps and be buried under dust deposits. Diffusive release from ground-ice (and its excavation in meteorite impacts [1]) replenishes atmospheric water, allowing the gradual build up of polar ice-dust deposits. When sunlit, this warmed and sublimating ice-dust mix has interest as a potential habitat for micro-organisms. Modelling shows precipitable vapour at 10-50μm/yr, varying sensitively with small changes in orbitable obliquity around the present 25° [2]. The modelling applies to a globe with regionally uniform albedo, unlike the steep topography and dark layering of the north polar cap whose upper 300m have accumulated over the last 500 kyr [3]. The cliffs and ravines of the north-polar cap are thought to form through south-facing slopes sublimating and gaining a dirt-encrusted surface, while horizontal surfaces brighten through frost deposits. The two-phase surface derives from the dust and frost feedback on surface albedo [4] and the resulting terrain develops over diurnal cycles of frosting and sublimation, and over annual seasonal cycles. The steep south-facing sides of observed ravines when unshadowed would see for a few hours the full intensity of sunlight at near normal incidence, without the atmospheric dimming at similar inclinations on Earth. As exposed ice sublimates at T > 200K (partial pressure exceeds typical martian 0.1 Pa), a crust of dirt develops to maintain quasi-stability. The dirt crust's main function is to buffer the ice against diurnal temperature fluctuations, but it also slows down vapour diffusion - analogous to south polar ice sublimation [5] and the growth of ground-ice [6]. We envisage 1-10 mm/yr as the net sublimation rate, compatible with the 100 kyr life and scales of the north polar ravines. Modelling of icy-dirt crusts in the polar cap Plane-parallel layers have been used to model the changing temperature

  18. The Phase Composition of Triton's Polar Caps.

    PubMed

    Duxbury, N S; Brown, R H

    1993-08-01

    Triton's polar caps are modeled as permanent nitrogen deposits hundreds of meters thick. Complex temperature variations on Triton's surface induce reversible transitions between the cubic and hexagonal phases of solid nitrogen, often with two coexisting propagating transition fronts. Subsurface temperature distributions are calculated using a two-dimensional thermal model with phase changes. The phase changes fracture the upper nitrogen layer, increasing its reflectivity and thus offering an explanation for the surprisingly high southern polar cap albedo (approximately 0.8) seen during the Voyager 2 flyby. The model has other implications for the phase transition phenomena on Triton, such as a plausible mechanism for the origin of geyser-like plume vent areas and a mechanism of energy transport toward them. PMID:17757213

  19. The phase composition of Triton's polar caps

    NASA Technical Reports Server (NTRS)

    Duxbury, N. S.; Brown, R. H.

    1993-01-01

    Triton's polar caps are modeled as permanent nitrogen deposits hundreds of meters thick. Complex temperature variations on Triton's surface induce reversible transitions between the cubic and hexagonal phases of solid nitrogen, often with two coexisting propagating transition fronts. Subsurface temperature distributions are calculated using a two-dimensional thermal model with phase changes. The phase changes fracture the upper nitrogen layer, increasing its reflectivity and thus offering an explanation for the surprisingly high southern polar cap albedo (approximately 0.8) seen during the Voyager 2 flyby. The model has other implications for the phase transition phenomena on Triton, such as a plausible mechanism for the origin of geyser-like plume vent areas and a mechanism of energy transport toward them.

  20. The phase composition of Triton's polar caps

    NASA Astrophysics Data System (ADS)

    Duxbury, N. S.; Brown, R. H.

    1993-08-01

    Triton's polar caps are modeled as permanent nitrogen deposits hundreds of meters thick. Complex temperature variations on Triton's surface induce reversible transitions between the cubic and hexagonal phases of solid nitrogen, often with two coexisting propagating transition fronts. Subsurface temperature distributions are calculated using a two-dimensional thermal model with phase changes. The phase changes fracture the upper nitrogen layer, increasing its reflectivity and thus offering an explanation for the surprisingly high southern polar cap albedo (approximately 0.8) seen during the Voyager 2 flyby. The model has other implications for the phase transition phenomena on Triton, such as a plausible mechanism for the origin of geyser-like plume vent areas and a mechanism of energy transport toward them.

  1. Geology of the southern hemisphere of Triton: No polar cap

    NASA Technical Reports Server (NTRS)

    Schenk, P.; Moore, J. M.

    1993-01-01

    The bright southern hemisphere, comprising Uhlanga Regio, is perhaps the most poorly understood geologic province on Triton. The entire bright southern hemisphere has been described as a bright polar 'cap', implying a seasonal origin, or as a permanent geologic terrain distinct from the equatorial terrains. Also, thermal models have predicted seasonal migration of frosts and ices from the presently sun-lit south latitudes to the dark northern latitudes. The distribution of frosts and geologic history of this region must be determined observationally. We reexamine the geology of this terrain with the goal of answering these questions.

  2. Slab Ice and Snow Flurries in the Martian Polar Night

    NASA Astrophysics Data System (ADS)

    Titus, T.; Kieffer, H.; Mullins, K.; Christensen, P.

    1999-11-01

    In the 1970s, spacecraft observations of the polar regions of Mars revealed polar brightness temperatures that were significantly below the expected kinetic temperatures for CO_2 sublimation. For the past few decades, we have speculated as to the nature of these Martian polar cold spots. Are the cold spots surface or atmospheric effects? Do the cold spots behave as blackbodies, or do they have emissivities less than unity? Two developments allow us to begin to answer these questions: the measurement of the optical constants of CO_2 by Gary Hansen and direct thermal spectroscopy by the Thermal Infrared Spectrometer (TES). TES thermal data has identified numerous cold spots at the Martian north pole. These areas of the polar cap have a strong absorption feature at 25 microns that is indicative of fine-grained CO_2. Brightness temperatures at 18 microns and 15 microns constrain most of these cold spots to the surface. Cold spot formation is strongly dependent on topography, forming preferentially near craters and on polar slopes. While most cold spots are surface effects, the formation of the fine-grained CO_2 is not restricted to formation on the surface. TES data, combined with MOLA cloud data, atmospheric condensates form a few of the observed cold spots. TES observations seem to indicate that another major component of the north polar cap's composition is slab CO2 ice. Slab ice has near unity spectral emissivity and appears to have a low albedo. Two explanations for the low albedo are that the slab ice is intrinsically dark or the slab ice is transparent and TES is seeing through to the underlying substrate. Regions of the cap where [T_18-T_25] < 5 degrees indicates deposits of slab ice. Slab ice is the dominant endmember of the polar cap at latitudes south of the polar night.

  3. A Warmer Atmosphere on Mars near the Noachian-Hesperian Boundary: Evidence from Basal Melting of the South Polar Ice Cap (Dorsa Argentea Formation)

    NASA Astrophysics Data System (ADS)

    Fastook, J. L.; Head, J. W.; Marchant, D. R.; Forget, F.; Madeleine, J.-B.

    2012-05-01

    Eskers in the Dorsa Argentea Formation imply the presence of an ice sheet with a wet bed. With an ice sheet model, we examine a range of geothermal heat fluxes and warmer climates to determine what conditions could produce such an ice sheet.

  4. Fast-flowing outlet glaciers on Svalbard ice caps

    SciTech Connect

    Dowdeswell, J.A. ); Collin, R.L. )

    1990-08-01

    Four well-defined outlet glaciers are present on the 2510 km{sup 2} cap of Vestfonna in Nordaustlandet, Svalbard. Airborne radio echo sounding and aerial-photograph and satellite-image analysis methods are used to analyze the morphology and dynamics of the ice cap and its component outlet glaciers. The heavily crevassed outlets form linear depressions in the ice-cap surface and flow an order of magnitude faster than the ridges of uncrevassed ice between them. Ice flow on the ridges is accounted for by internal deformation alone, whereas rates of outlet glacier flow require basal motion. One outlet has recently switched into and out of a faster mode of flow. Rapid terminal advance, a change from longitudinal compression to tension, and thinning in the upper basin indicate surge behavior. Observed outlet glacier discharge is significantly greater than current inputs of mass of the ice cap, indicating that present rates of flow cannot be sustained under the contemporary climate.

  5. Estimated bedrock topography and ice thickness of the Renland Ice Cap, East Greenland

    NASA Astrophysics Data System (ADS)

    Koldtoft, Iben; Hvidberg, Christine; Panton, Christian

    2016-04-01

    The Renland Ice Cap in East Greenland (71.30°N, 26.72°W) is a separate ice cap located on a high mountain plateau in the Scoresbysund Fjord, with the highest elevation of 2340 m. In 1988 a 324.35 m long ice core was drilled near summit on the eastern dome of the ice cap. The recovered ice core contains a climate record reaching back to the Eemian. In the spring 2015 a new ice core (584 m) was drilled on Renland during the RECAP project. Knowledge of the basal topography of the Renland Ice Cap is very limited. However, old airborne radar surveys show that the bedrock topography is very mountainous. Knowledge of the bedrock topography and ice thickness was needed to locate the best possible drilling site for the new ice core. An iterative inverse method was used to present a modelled estimate of the subglacial topography and ice thickness of the Renland Ice Cap based on the knowledge of the surface topography and climate forcing. The modelled estimate showed initially twice as large ice thickness as expected, but having improved the surface topography with data from the field work on Renland Ice Cap, the modelled ice thickness are in the same order as radar measurements shows.

  6. Topography of Impact Structures on the Northern Polar Cap of Mars

    NASA Technical Reports Server (NTRS)

    Sakimoto, S. E. H.; Garvin, J. B.

    1998-01-01

    The north polar residual ice deposits of mars are thought to be relatively young, based on the reported lack of any fresh impact craters in Viking Orbiter images. A handful of possible impact features were identified, but available data were inconclusive. Determining the number and current topographic characteristics of any craters on the polar residual ice surface is important in constraining the surface age, relative importance of polar cap resurfacing processes and ice flow dynamics, and the role of the cap deposits in the global volatile and climate cycles. Subsequent image processing advances and new Mars Orbiter Laser Altimeter (MOLA) data in the north polar region are now a considerable aid in impact feature identification. This study reconsiders the abundant Viking high-resolution polar images along with the new altimetry data. We examine possible impact features, compare their topography with known mars high-latitude impact features, and use their morphology as a constraint on crater modification processes.

  7. The nonuniform recession of the south polar cap of Mars

    NASA Technical Reports Server (NTRS)

    Veverka, J.; Goguen, J.

    1973-01-01

    The nature of the irregular springtime recession of the Martian polar caps is investigated, with particular reference to the southern polar cap. Our current knowledge about the composition of the caps is outlined, and the historical record of their springtime recession is reviewed. An attempt is made to correlate the irregularities of the recession pattern of the southern polar cap with the features of the terrain revealed by Mariner 9 photography at a time when the southern cap was at its minimum extent. The results are interpreted in terms of the physical and meteorological processes active in the polar regions.

  8. Water-ice clouds in the Martian North Polar Region

    NASA Astrophysics Data System (ADS)

    Tamppari, L. K.; Qu, Z.; Smith, M. D.; Bass, D. S.; Hale, A. S.

    2004-11-01

    There has been uncertainty about the amount of water cycling in and out of the polar region during the northern spring/summer timeframe, as evidenced by visible brightness changes in the residual polar cap from year to year which were originally though to be interannual variations (James and Martin, 1995; Kieffer, 1990). Subsequently, through comparison of Viking and Mariner 9 data sets, these variations were thought to be late season water deposition (Bass et al., 2000: Bass and Paige, 2000), perhaps in the form of direct condensation or snowfall. More recently, examination of multi-year MGS MOC data (Hale et al., 2004) opens this question again. Water cycling can be assessed using data sets by examination of water vapor, polar cap changes, and water-ice clouds. In this presentation, we examine the Mars Global Surveyor (MGS) Thermal Emission Spectrometer (TES) nadir pointed data in the north polar region of Mars during northern spring and summer to find and map water-ice clouds. Water-ice clouds, in the north polar region, have previously been tentatively identified in the Viking data (Tamppari and Bass, 2000), and some water-ice clouds identifications have been made in the north polar region during the MGS era (M. Smith, pers. comm., 2001). We present our results of water-ice clouds for 3 Mars years' spring and summer times, including opacities, spatial and temporal variations.

  9. Holocene fluctuations of Bregne ice cap, Scoresby Sund, eastern Greenland

    NASA Astrophysics Data System (ADS)

    Levy, L.; Kelly, M. A.; Lowell, T. V.; Hall, B. L.

    2011-12-01

    The Arctic cryosphere is responding rapidly to modern global warming. Documenting past changes in the Arctic cryosphere, particularly during times of warmer than present conditions such as the Holocene Thermal Maximum (HTM; 9,000-5,000 yr BP) provides an important background against which the present response and potential for future changes can be compared. Small ice caps located adjacent to the Greenland Ice Sheet respond sensitively to climate change and their past extents provide a proxy for the climatic conditions that have influenced the ice sheet margin. In order to document cryosphere and climatic changes during warmer conditions, we are constructing records of Holocene fluctuations of small ice caps in the Scoresby Sund region of eastern Greenland (71° N, 25.6° W). We use geomorphic mapping, lake sediment records, radiocarbon, and surface exposure (10Be) dating to reconstruct past ice extents. Lake sediment records are from both glacially fed (i.e., threshold) lakes and lakes with no glacial input during the time of interest (i.e., control). Here we present a record of the Holocene extents of Bregne ice cap, Milne Land, western Scoresby Sund, ~50 km southeast of Renland ice cap. Sediments from Two Move Lake (TML), a threshold lake, register the entire Holocene in a thickness of ~70 cm. Radiocarbon dates of lake sediments indicate that the onset of organic accumulation in the lake following the Last Glacial Maximum occurred 8,890±120 cal yr BP. The mid-Holocene is characterized by organic rich mud that is finely laminated in some sections. The onset of Neoglaciation (cooling after HTM) occurs at 2,810±50 cal yr BP and finely laminated sediments during Neoglaciation may register annual deposition. The sediment record from Last Chance Lake, a control lake located 0.5 km from TML, indicates that there has been no glacial input since deglaciation from the Last Glacial Maximum. Unweathered moraines occur <0.5 km from the modern ice cap margin, inboard from

  10. Seismic explosion sources on an ice cap - Technical considerations

    NASA Astrophysics Data System (ADS)

    Shulgin, Alexey; Thybo, Hans

    2015-03-01

    Controlled source seismic investigation of crustal structure below ice covers is an emerging technique. We have recently conducted an explosive refraction/wide-angle reflection seismic experiment on the ice cap in east-central Greenland. The data-quality is high for all shot points and a full crustal model can be modelled. A crucial challenge for applying the technique is to control the sources. Here, we present data that describe the efficiency of explosive sources in the ice cover. Analysis of the data shows, that the ice cap traps a significant amount of energy, which is observed as a strong ice wave. The ice cap leads to low transmission of energy into the crust such that charges need be larger than in conventional onshore experiments to obtain reliable seismic signals. The strong reflection coefficient at the base of the ice generates strong multiples which may mask for secondary phases. This effect may be crucial for acquisition of reflection seismic profiles on ice caps. Our experience shows that it is essential to use optimum depth for the charges and to seal the boreholes carefully.

  11. Elevation changes of ice caps in the Canadian Arctic Archipelago

    NASA Astrophysics Data System (ADS)

    Abdalati, W.; Krabill, W.; Frederick, E.; Manizade, S.; Martin, C.; Sonntag, J.; Swift, R.; Thomas, R.; Yungel, J.; Koerner, R.

    2004-12-01

    Precise repeat airborne laser surveys were conducted over the major ice caps in the Canadian Arctic Archipelago in the spring of 1995 and 2000 in order to measure elevation changes in the region. Our measurements reveal thinning at lower elevations (below 1600 m) on most of the ice caps and glaciers but either very little change or thickening at higher elevations in the ice cap accumulation zones. Recent increases in precipitation in the area can account for the slight thickening where it was observed but not for the thinning at lower elevations. For the northern ice caps on the Queen Elizabeth Islands, thinning was generally <0.5 m yr-1, which is consistent with what would be expected from the warm temperature anomalies in the region for the 5 year period between surveys, and appears to be a continuation of a trend that began in the mid-1980s. Farther south, however, on the Barnes and Penny ice caps on Baffin Island, this thinning was much more pronounced at over 1 m yr-1 in the lower elevations. Here temperature anomalies were very small, and the thinning at low elevations far exceeds any associated enhanced ablation. The observations on Barnes, and perhaps Penny, are consistent with the idea that the observed thinning is part of a much longer term deglaciation, as has been previously suggested for Barnes ice cap. On the basis of the regional relationships between elevation and elevation change in our data, the 1995-2000 mass balance for the archipelago is estimated to be -25 km3 yr-1 of ice, which corresponds to a sea level increase of 0.064 mm yr-1. This places it among the more significant sources of eustatic sea level rise, though not as substantial as the Greenland ice sheet, Alaskan glaciers, or the Patagonian ice fields.

  12. Elevation Changes of Ice Caps in the Canadian Arctic Archipelago

    NASA Technical Reports Server (NTRS)

    Abdalati, W.; Krabill, W.; Frederick, E.; Manizade, S.; Martin, C.; Sonntag, J.; Swift, R.; Thomas, R.; Yungel, J.; Koerner, R.

    2004-01-01

    Precise repeat airborne laser surveys were conducted over the major ice caps in the Canadian Arctic Archipelago in the spring of 1995 and 2000 in order to measure elevation changes in the region. Our measurements reveal thinning at lower elevations (below 1600 m) on most of the ice caps and glaciers, but either very little change or thickening at higher elevations in the ice cap accumulation zones. Recent increases in precipitation in the area can account for the slight thickening where it was observed, but not for the thinning at lower elevations. For the northern ice caps on the Queen Elizabeth Islands, thinning was generally less than 0.5 m/yr , which is consistent with what would be expected from the warm temperature anomalies in the region for the 5-year period between surveys and appears to be a continuation of a trend that began in the mid 1980s. Further south, however, on the Barnes and Penny ice caps on Baffin Island, this thinning was much more pronounced at over 1 m/yr in the lower elevations. Here temperature anomalies were very small, and the thinning at low elevations far exceeds any associated enhanced ablation. The observations on Barnes, and perhaps Penny are consistent with the idea that the observed thinning is part of a much longer term deglaciation, as has been previously suggested for Barnes Ice Cap. Based on the regional relationships between elevation and elevation-change in our data, the 1995-2000 mass balance for the region is estimated to be 25 cu km/yr of ice, which corresponds to a sea level increase of 0.064 mm/ yr . This places it among the more significant sources of eustatic sea level rise, though not as substantial as Greenland ice sheet, Alaskan glaciers, or the Patagonian ice fields.

  13. Observations of the northern seasonal polar cap on Mars: I. Spring sublimation activity and processes

    USGS Publications Warehouse

    Hansen, C.J.; Byrne, S.; Portyankina, G.; Bourke, M.; Dundas, C.; McEwen, A.; Mellon, M.; Pommerol, A.; Thomas, N.

    2013-01-01

    Spring sublimation of the seasonal CO2 northern polar cap is a dynamic process in the current Mars climate. Phenomena include dark fans of dune material propelled out onto the seasonal ice layer, polygonal cracks in the seasonal ice, sand flow down slipfaces, and outbreaks of gas and sand around the dune margins. These phenomena are concentrated on the north polar erg that encircles the northern residual polar cap. The Mars Reconnaissance Orbiter has been in orbit for three Mars years, allowing us to observe three northern spring seasons. Activity is consistent with and well described by the Kieffer model of basal sublimation of the seasonal layer of ice applied originally in the southern hemisphere. Three typical weak spots have been identified on the dunes for escape of gas sublimed from the bottom of the seasonal ice layer: the crest of the dune, the interface of the dune with the interdune substrate, and through polygonal cracks in the ice. Pressurized gas flows through these vents and carries out material entrained from the dune. Furrows in the dunes channel gas to outbreak points and may be the northern equivalent of southern radially-organized channels (“araneiform” terrain), albeit not permanent. Properties of the seasonal CO2 ice layer are derived from timing of seasonal events such as when final sublimation occurs. Modification of dune morphology shows that landscape evolution is occurring on Mars today, driven by seasonal activity associated with sublimation of the seasonal CO2 polar cap.

  14. Observations of the northern seasonal polar cap on Mars: I. Spring sublimation activity and processes

    NASA Astrophysics Data System (ADS)

    Hansen, C. J.; Byrne, S.; Portyankina, G.; Bourke, M.; Dundas, C.; McEwen, A.; Mellon, M.; Pommerol, A.; Thomas, N.

    2013-08-01

    Spring sublimation of the seasonal CO2 northern polar cap is a dynamic process in the current Mars climate. Phenomena include dark fans of dune material propelled out onto the seasonal ice layer, polygonal cracks in the seasonal ice, sand flow down slipfaces, and outbreaks of gas and sand around the dune margins. These phenomena are concentrated on the north polar erg that encircles the northern residual polar cap. The Mars Reconnaissance Orbiter has been in orbit for three Mars years, allowing us to observe three northern spring seasons. Activity is consistent with and well described by the Kieffer model of basal sublimation of the seasonal layer of ice applied originally in the southern hemisphere. Three typical weak spots have been identified on the dunes for escape of gas sublimed from the bottom of the seasonal ice layer: the crest of the dune, the interface of the dune with the interdune substrate, and through polygonal cracks in the ice. Pressurized gas flows through these vents and carries out material entrained from the dune. Furrows in the dunes channel gas to outbreak points and may be the northern equivalent of southern radially-organized channels ("araneiform" terrain), albeit not permanent. Properties of the seasonal CO2 ice layer are derived from timing of seasonal events such as when final sublimation occurs. Modification of dune morphology shows that landscape evolution is occurring on Mars today, driven by seasonal activity associated with sublimation of the seasonal CO2 polar cap.

  15. Pulsar gamma rays from polar cap regions

    NASA Technical Reports Server (NTRS)

    Chiang, James; Romani, Roger W.

    1992-01-01

    The production is studied of pulsar gamma rays by energetic electrons flowing in the open field region above pulsar polar caps. The propagation was followed of curvature radiation from primary electrons, as well as hard synchrotron radiation generated by secondary pairs, through the pulsar magnetosphere for vacuum dipole open field geometries. Using data from radio and optical observations, models were constructed for the specific geometries and viewing angles appropriate to particular pulsars. These detailed models produce normalized spectra above 10 MeV, pulse profiles, beaming fractions and phase resolved spectra appropriate for direct comparison with COS-B and GRO data. Models are given for the Crab, Vela, and other potentially detectable pulsars; general agreement with existing data is good, although perturbations to the simplified models are needed for close matches. The calculations were extended to the millisecond pulsar range, which allows the production of predictions for the flux and spectra of populations of recycled pulsars and search strategies are pointed out.

  16. Interannual variability of Mars' south polar CAP

    NASA Astrophysics Data System (ADS)

    James, P. B.; Malolepszy, K. M.; Martin, L. J.

    1987-08-01

    Published observational data on the seasonal recession of the south polar cap on Mars (covering the period 1903-1977) are compiled in tables and graphs and analyzed statistically. The basic data set (photographic observations obtained at Lowell Observatory) of Fischbacher et al. (1960) and James and Lumme (1982) and the reduction procedures described by Baum and Martin (1973) are employed, and Viking data from 1977 are used for comparison; the early onset (relative to the mean) of the 1956 recession is characterized in detail. A list of photographically documented large dust storms is provided, and it is suggested that in years with early spring storms, recession may be slower than in years without such storms.

  17. The small ice cap instability in diffusive climate models

    NASA Technical Reports Server (NTRS)

    North, G. R.

    1984-01-01

    Simple climate models which invoke diffusive heat transport and ice cap albedo feedback have equilibrium solutions with no stable ice cap smaller than a radius of about 20 deg on a great circle. Attention is presently given to a solution of this phenomenon which is physically appealing. The ice-free solution has a thermal minimum, and if the minimum temperature is just above the critical value for ice formation, then the artificial addition of a patch of ice leads to a widespread depression of the temperature below the critical freezing temperature. A second stable solution will then exist whose spatial extent is determined by the range of the influence function of a point sink of heat, due to the albedo shift in the patch.

  18. Effects of Snowfall on the Thickness and Stability of Mars' Seasonal Ice Caps

    NASA Astrophysics Data System (ADS)

    Hayne, P. O.; Paige, D. A.; Aharonson, O.; Schofield, J. T.; Kass, D. M.; Kleinboehl, A.; Heavens, N. G.; Shirley, J. H.; McCleese, D. J.

    2012-12-01

    Seasonal exchange of carbon dioxide between the Martian atmosphere and ice caps is responsible for cyclical variations of ~30% in global atmospheric pressure, as well as for the growth and retreat of the seasonal ice caps. Energy balance and general circulation models have had limited success in reproducing the important aspects of this cycle, largely due to uncertainties in the radiative properties (albedo and emissivity) of the ice caps. Evidence from remote sensing by several different orbital investigations suggests that snowfall consisting primarily of solid CO2 contributes substantial material to the growing seasonal caps, strongly affecting their radiative properties. However, the mass of material deposited as snow, its spatial and temporal variation, and its effect on the energy budget, have all remained uncertain. Using data from the Mars Climate Sounder (MCS), we have quantified and mapped snow cloud formation and surface accumulation based on opacity profiles and calculated infrared cooling rates. We then compared the derived snowfall distribution to seasonal cap thicknesses derived from Mars Orbiter Laser Altimeter (MOLA) "crossover" data. Large variations in the occurrence, thickness, and timing of snow clouds are observed, with the most extensive and persistent clouds observed over the south polar residual cap (SPRC). We find a strong correlation between clouds, "cold spots" (regions of suppressed thermal emission), and seasonal cap thickness. Furthermore, some of these regions of high snow cloud activity also exhibit high solar albedo in the spring and summer. Together, these results suggest that granular deposits of CO2 snow: 1) are thicker (probably due to lower density) on average than "slab ice" formed by direct vapor deposition; 2) reduce energy loss by thermal emission during the polar night; and 3) reduce energy gain by reflecting solar radiation during spring and summer. As the snowiest place on Mars, the SPRC exhibits all of these properties

  19. The Martian polar caps: Stability and water transport at low obliquities

    NASA Astrophysics Data System (ADS)

    Henderson, B. G.; Jakosky, B. M.

    1992-12-01

    The seasonal cycle of water on Mars is regulated by the two polar caps. In the winter hemisphere, the seasonal CO2 deposits at a temperature near 150 K acts as a cold trap to remove water vapor from the atmosphere. When summer returns, water is pumped back into the atmosphere by a number of mechanisms, including release from the receding CO2 frost, diffusion from the polar regolith, and sublimation from a water-ice residual cap. These processes drive an exchange of water vapor between the polar caps that helps shape the Martian climate. Thus, understanding the behavior of the polar caps is important for interpreting the Martian climate both now and at other epochs. Mars' obliquity undergoes large variations over large time scales. As the obliquity decreases, the poles receive less solar energy so that more CO2 condenses from the atmosphere onto the poles. It has been suggested that permanent CO2 condenses from the atmosphere onto the poles. It has been suggested that permanent CO2 caps might form at the poles in response to a feedback mechanism existing between the polar cap albedo, the CO2 pressure, and the dust storm frequency. The year-round presence of the CO2 deposits would effectively dry out the atmosphere, while diffusion of water from the regolith would be the only source of water vapor to the atmosphere. We have reviewed the CO2 balance at low obliquity taking into account the asymmetries which make the north and south hemispheres different. Our analysis linked with a numerical model of the polar caps leads us to believe that one summertime cap will always lose its CO2 cover during a Martian year, although we cannot predict which cap this will be. We conclude that significant amounts of water vapor will sublime from the exposed cap during summer, and the Martian atmosphere will support an active water cycle even at low obliquity.

  20. Substorm Bulge/Surge Controlled by Polar Cap Flow Channels

    NASA Astrophysics Data System (ADS)

    Lyons, L. R.; Nishimura, T.; Zou, Y.; Gallardo-Lacourt, B.; Donovan, E.; Shiokawa, K.; Nicolls, M. J.; Chen, S.; Ruohoniemi, J. M.; Nishitani, N.; McWilliams, K. A.

    2015-12-01

    Previous studies have provided evidence that localized channels of enhanced polar cap flow drive plasma sheet/auroral oval flow channels, auroral poleward boundary intensifications and streamers, and substorm onset. Evidence has also indicated that a persistence of such flow channels after substorm onset may enhance post-onset auroral poleward expansion and activity. Here, we combine auroral imager and radar observations to show evidence that polar-cap flow channels can directly feed the substorm bulge westward motion, i.e., the westward traveling surge, and its poleward expansion well into the pre-existing polar cap. By taking advantage of the capability of tracing polar cap arcs and patches over long distances with red line imaging, we are able to trace flow features that strongly affect the substorm bulge across the polar cap for up to ~1-1.5 hr prior to their impacting and affecting the substorm bulge.

  1. Holocene history of North Ice Cap, northwestern Greenland

    NASA Astrophysics Data System (ADS)

    Corbett, L. B.; Kelly, M. A.; Osterberg, E. C.; Axford, Y.; Bigl, M.; Roy, E. P.; Thompson, J. T.

    2013-12-01

    Although much research has focused on the past extents of the Greenland Ice Sheet, less is known about the smaller ice caps on Greenland and how they have evolved over time. These small ice caps respond sensitively to summer temperatures and, to a lesser extent, winter precipitation, and provide valuable information about climatic conditions along the Greenland Ice Sheet margins. Here, we investigate the Holocene history of North Ice Cap (76°55'N 68°00'W), located in the Nunatarssuaq region near Thule, northwest Greenland. Our results are based on glacial geomorphic mapping, 10Be dating, and analyses of sediment cores from a glacially fed lake. Fresh, unweathered and unvegetated boulders comprise moraines and drift that mark an extent of North Ice Cap ~25 m outboard of the present ice margin. It is likely that these deposits were formed during late Holocene time and we are currently employing 10Be surface exposure dating to examine this hypothesis. Just outboard of the fresh moraines and drift, boulders and bedrock show significant weathering and are covered with lichen. Based on glacial geomorphic mapping and detailed site investigations, including stone counts, we suggest that the weathered boulders and bedrock were once covered by erosive Greenland Ice Sheet flow from southeast to northwest over the Nunatarssuaq region. Five 10Be ages from the more weathered landscape only 100-200 m outboard of the modern North Ice Cap margin are 52 and 53 ka (bedrock) and 16, 23, and 31 ka (boulders). These ages indicate that recent ice cover has likely been cold-based and non-erosive, failing to remove inherited cosmogenic nuclides from previous periods of exposure, although the youngest boulder may provide a maximum limiting deglaciation age. Sediment cores collected from Delta Sø, a glacially-fed lake ~1.5 km outside of the modern North Ice Cap margin, contain 130 cm of finely laminated sediments overlying coarse sands and glacial till. Radiocarbon ages from just above

  2. Multi-scale, multi-year investigations of H2O ice deposits observed in late summer, at the time of minimum extent of the Southern polar cap of Mars

    NASA Astrophysics Data System (ADS)

    Langevin, Y.; Seelos, K.; Russell, P.; Bibring, J.-P.; Vincendon, M.; Gondet, B.

    2012-09-01

    Extended regions exhibiting water ice signatures have been observed by OMEGA on Mars Express at the boundary of the CO2 perennial cap during the first months of operation of the mission [1]. This period in late summer (Ls 335°-340°) corresponds to the minimum extent of the ice coverage around the South pole. The retreat of the South seasonal cap, spectrally dominated by CO2 frost [2, 3] ends at Ls 310° - 315° for years which do not present a global dust storm [4], and the first signs of H2O frost recondensation are observed before the fall equinox (Ls 0°). A large outlier had been identified by OMEGA observations at longitudes from 290°E to 10°E. It was shown to extend over an area representing ~ 25% of the surface of the perennial cap by Themis observations [5]. The H2O covered regions at the boundary of the cap and within the outlier have an intermediate albedo (30-35%) between that of the perennial cap (> 60%) and that of surrounding terrains (~ 20%). These southern surface H2O ice deposits constitute a major source of atmospheric H2O at the end of the Southern summer. They are much smaller in extent than the northern perennial cap and they are exposed to sunlight for 2 months in late summer instead of 6 months in the North over the whole summer. This is in line with the highly asymmetric seasonal cycle of atmospheric water [6, 7]. In late 2009, OMEGA observations of the South cap at the time of minimum extent (Ls 340°) showed a much larger extent of H2O ice signatures compared to what had been observed in early 2004 [1]. H2O ice covered regions appeared homogeneous at the km scales corresponding to OMEGA observations. A series of CRISM observations were planned for the next southern fall season (mid-2011), in order to further investigate the time variability of the southern H2O ice deposits within the outlier at the 20 m scale (CRISM high resolution mode). Combining OMEGA and CRISM observations demonstrates that variegation of surface H2O ice is mainly

  3. Albedo Variations on the Martian Northern Polar Cap as Seen by MGS

    NASA Technical Reports Server (NTRS)

    Hale, A. S.; Bass, D. S.; Tamppan, L. K.

    2003-01-01

    The Viking Orbiters determined that the surface of Mars northern residual cap is water ice. Many researchers have related observed atmospheric water vapor abundances to seasonal exchange between reservoirs such as the polar caps, but the extent to which the exchange between the surface and the atmosphere remains uncertain. Early studies of the ice coverage and albedo of the northern residual Martian polar cap using Mariner 9 and Viking images reported that there were substantial internannual differences in ice deposition on the polar cap, a result that suggested a highly variable Martian climate. However, some of the data used in these studies were obtained at differing values of heliocentric solar longitude (Ls). Reevaluation of this dataset in indicated that the residual cap undergoes seasonal brightening throughout the summer, and indicated that this process repeats from year to year. In this study we continue this work with data acquired with Mars Global Surveyor s Mars Orbiter Camera (MOC) and Thermal Emission Spectrometer (TES) instruments. We use MOC Wide Angel (WA) red filter images

  4. Tracking Retreat of the North Seasonal Ice Cap on Mars: Results from the THEMIS Investigation

    NASA Technical Reports Server (NTRS)

    Ivanov, A. B.; Wagstaff, K. L.; Ttus, T. N.

    2005-01-01

    The CO2 ice caps on Mars advance and retreat with the seasons. This phenomenon was first observed by Cassini and then confirmed by numerous ground based observations in 19th and 20th centuries. With the advent of the space age observations of the seasonal ice cap were done by all orbiting spacecraft starting with Mariner 7. Viking Orbiters and more recently the Mars Global Surveyor (particularly Mars Orbiter Camera (MOC) and Thermal Emission Spectrometer (TES) instruments) have accumulated significant data on the retreat of the CO2 seasonal cap. During Mars year 2 of THEMIS operations at Mars, we planned an observational campaign in which the THEMIS instrument (onboard the Mars Odyssey spacecraft) repeatedly observed the north seasonal polar cap from midwinter to late spring. THEMIS allows simultaneous observations in both Thermal IR (12.57 m) and Visible wavelengths (0.65 m). One of the goals for this work is to initiate an interannual program for observations of the seasonal ice caps using the THEMIS instrument. The most efficient way to detect the edge between frost and bare ground is directly onboard of the spacecraft. Prior to onboard software design effort, we have developed two groundbased algorithms for automatically finding the edge of the seasonal polar cap in THEMIS IR data. The first algorithm relies on fully calibrated data and can be used for highly reliable groundbased analyses. The second method was specifically developed for processing raw, uncalibrated data in a highly efficient way. It has the potential to enable automatic, onboard detections of the seasonal cap retreat. We have experimentally confirmed that both methods produce similar results, and we have validated both methods against a model constructed from the MGS TES data from the same season.

  5. Viewing Ice Crystals Using Polarized Light.

    ERIC Educational Resources Information Center

    Kinsman, E. M.

    1992-01-01

    Describes a method for identifying and examining single ice crystals by photographing a thin sheet of ice placed between two inexpensive polarizing filters. Suggests various natural and prepared sources for ice that promote students' insight into crystal structures, and yield colorful optical displays. Includes directions, precautions, and sample…

  6. Variations of the polar cap potential measured during magnetospheric substorms

    SciTech Connect

    Weimer, D.R.; Kan, J.R.; Akasofu, S.I. )

    1992-04-01

    Measurements of the polar cap potential drop and size have been obtained during magnetospheric substorms. Using double-prove electric field measurements on the DE 2 satellite, 148 measurements have been obtained at random times preceding, during, and after 64 substorms. The polar cap potentials are graphed as a function of the difference between the time of the polar cap measurement and the time of the expansion onset of the corresponding substorm. The ratios of the auroral electrojet (AE) indices and the potential are also determined. The results show that on the average the polar cap potential starts to increase at 1.5 hours before onset. However, on a case-by-case basis there are substantial variations from the average, as polar cap potentials over 1,200 kV were measured as early as 1 hour before substorm onset and values as low as 40 kV were observed during the expansion phase. The size of the polar cap ranged from 23{degree} to 38{degree} invariant latitude at the time of onset, and had an average value of 31{degree}. The AE/{Phi}{sub PC} ratio is nearly constant before and after substorms, but decreases slightly during the substorm growth phase and increases greatly during the expansion phase. This increase is most likely due to a higher conductivity and westward electric field within the electrojet during expansion, which causes AE to increase without a corresponding change in the polar cap potential.

  7. Ir Spectral Mapping of the Martian South Polar Residual CAP Using Crism

    NASA Astrophysics Data System (ADS)

    Campbell, Jacqueline; Sidiropoulos, Panagiotis; Muller, Jan-Peter

    2016-06-01

    Polycyclic aromatic hydrocarbons (PAHs) are considered to be important in theories of abiogenesis (Allamandola, 2011) . There is evidence that PAHs have been detected on two icy Saturnian satellites using the Visual and Infrared Mapping Spectrometer (VIMS) on the Cassini spacecraft (Cruikshank et al., 2007). The hypothesised presence of PAHs in Mars south polar cap has not been systematically examined even though the Mars south polar cap may allow the preservation of organic molecules that are typically destroyed at the Martian surface by UV radiation (Dartnell et al. 2012). This hypothesis is supported by recent analyses of South Polar Residual Cap (SPRC) structural evolution (Thomas et al., 2009) that suggest the possibility that seasonal and long term sublimation may excavate dust particles from within the polar ice. Periodic sublimation is believed to be responsible for the formation of so-called "Swiss Cheese Terrain", a unique surface feature found only in the Martian south polar residual cap consisting of flat floored, circular depressions (Byrne, 2009). We show the first examples of work towards the detection of PAHs in Swiss Cheese Terrain, using data from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM), on board NASA's Mars Reconnaissance Orbiter (MRO). CRISM is designed to search for mineralogical indications of past and present water, thus providing extensive coverage of the south polar cap. In this work, we discuss whether CRISM infrared spectra can be used to detect PAHs in Swiss Cheese Terrain and demonstrate a number of maps showing shifts in spectral profiles over the SPRC.

  8. Extending Icelandic volcanological network operations into the ice caps

    NASA Astrophysics Data System (ADS)

    Vogfjord, Kristin; Bean, Chris; Roberts, Matthew; Ofeigsson, Benedikt; Guralp Systems Ltd.

    2013-04-01

    Many of Iceland's most active volcanoes are located under glaciers, with limited access for monitoring equipment. In the warming climate however, a few rock outcrops (nunataks) have emerged from the ice permitting some access improvement, but to properly monitor seismic signals from volcanoes deep inside the ice caps, instruments placed in the ice itself are needed. Continuous, real-time operation of monitoring equipment in harsh climate, heavy snow accumulation and icing conditions on a glacier is a considerable challenge. The FP7 project FUTUREVOLC, which focusses on Icelandic volcanoes, aims for the development of a multiparametric volcano monitoring and early warning system. One of the new developments in the project involves strengthening the existing real-time seismic monitoring and analysis systems by extending the permanent network into the Vatnajökull ice cap. The goal is to improve detection and location of seismic signals, such as microseismicity, LP events, ice-quakes and continuous tremor due to volcanic eruptions at the volcanoes under the ice cap. Real-time processing and discrimination of these signals could give early warnings of an imminent eruption. At subglacial volcanoes however, other processes, such as subglacial floods (jökulhlaup) and subglacial hydrothermal systems - boiling due to sudden drainage -also generate continuous tremor and can therefore lead to false eruption alarms. To minimise the number of false alarms, the network and processing will need to discriminate between the different tremor sources by determining their characteristics and track the temporal evolution and location of the source. For this purpose broad-band instruments will be placed on nunataks as well as in the ice and two short-period arrays will be located at the margin of Vatnajökull, close to subglacial flood paths from the Skaftár ice cauldrons. To record ice movements associated with the jökulhlaups, GPS receivers will be placed on outlet glaciers during

  9. Holocene Activity of the Quelccaya Ice Cap: A Working Model

    NASA Astrophysics Data System (ADS)

    Lowell, T. V.; Smith, C. A.; Kelly, M. A.; Stroup, J. S.

    2012-12-01

    The patterns and magnitudes of past climate change in the topics are still under discussion. We contribute here by reporting on patterns of glacier length changes of the largest glacier in the tropics, Quelccaya Ice Cap (~13.9°S, 70.9°W, summit at 5645 m). This ice cap has several local domes that may have different patterns of length changes because of differing elevations of the domes (high to the north, lower to the south). Prior work (Mark et al. 2003, Abbott et al., 2004; Thompson et al., 2005; Buffen, et al., 2009), new radiocarbon ages, and stratigraphic and geomorphic relationships are used to determine the general pattern of length changes for the outlets from this ice cap. We exploit geomorphic relationships and present new radiocarbon ages on interpreted stratigraphic sections to determine the pattern of length changes for this ice cap. Ice retreated during late glacial times (Rodbell and Seltzer, 2000; Kelly et al., in press). By 11,400 yr BP it had reached a position ~1.2 km beyond its present (2000 AD) extent. While length during the early Holocene is problematic, present evidence permits, but does not prove, extents of 0.5 to 1.0 km down-valley from the present margin. Between 6400 and 4400 yr BP the ice cap was smaller than present, but it advanced multiple times during the late Holocene. Lengths of up to 1 km beyond present were achieved at 3400 yr BP and ~500 yr BP. Additionally, the ice advanced to 0.8 km beyond its present margin at 1600 yr BP. Because these glaciers were temperate, we take these lengths to represent primarily changes in temperature. This may suggest that lowering insolation values in the northern hemisphere during the Holocene provide a first order control on tropical temperatures. Alternatively, it may be that major reorganization of the topical circulation belts about 5000 yr BP yields two configurations of the QIC and hence Holocene temperatures - one at the present ice margin and and the second about 1 km beyond the

  10. Response of northern winter polar cap to auroral substorms

    NASA Astrophysics Data System (ADS)

    Liou, Kan; Sotirelis, Thomas

    2016-05-01

    The three-phase substorm sequence has been generally accepted and is often tied to the Dungey cycle. Although previous studies have mostly agreed on the increase and decrease in the polar cap area during an episode of substorm, there are disparate views on when the polar cap starts to contract relative to substorm onset. Here we address this conflict using high-resolution (~1-3 min) snapshot global auroral images from the ultraviolet imager on board the Polar spacecraft. On the basis of 28 auroral substorm events, all observed in the Northern Hemispheric winter, it is found that the polar cap inflated prior to onset in all events and it attained the largest area ~6 min prior to the substorm expansion phase onset, while the dayside polar cap area remained steady around the onset. The onset of nightside polar cap deflation is found to be attributed to intensifications of aurora on the poleward edge of the nightside oval, mostly in the midnight sector. Although this result supports the loading-unloading and reconnection substorm models, it is not clear if the initial polar cap deflation and the substorm expansion are parts of the same process.

  11. Mars Polar Cap During Transition Phase Instrument Checkout

    NASA Technical Reports Server (NTRS)

    2006-01-01

    During the last week of September and the first week or so of October 2006, scientific instruments on NASA's Mars Reconnaissance Orbiter were turned on to acquire test information during the transition phase leading up to full science operations. The mission's primary science phase will begin the first week of November 2006, following superior conjunction. (Superior conjunction is where a planet goes behind the sun as viewed from Earth.) Since it is very difficult to communicate with a spacecraft when it is close to the sun as seen from Earth, this checkout of the instruments was crucial to being ready for the primary science phase of the mission.

    Throughout the transition-phase testing, the Mars Color Imager (MARCI) acquired terminator (transition between nighttime and daytime) to terminator swaths of color images on every dayside orbit, as the spacecraft moved northward in its orbit. The south polar region was deep in winter shadow, but the north polar region was illuminated the entire Martian day. During the primary mission, such swaths will be assembled into global maps that portray the state of the Martian atmosphere -- its weather -- as seen every day and at every place at about 3 p.m. local solar time. After the transition phase completed, most of the instruments were turned off, but the Mars Climate Sounder and MARCI have been left on. Their data will be recorded and played back to Earth following the communications blackout associated with conjunction.

    Combined with wide-angle image mosaics taken by the Mars Orbiter Camera on NASA's Mars Global Surveyor at 2 p.m. local solar time, the MARCI maps will be used to track motions of clouds.

    This image is a composite mosaic of four polar views of Mars, taken at midnight, 6 a.m., noon, and 6 p.m. local Martian time. This is possible because during summer the sun is always shining in the polar region. It shows the mostly water-ice perennial cap (white area), sitting atop the north polar layered

  12. Recent Changes in High-Latitude Glaciers, Ice Caps, and Ice Sheets

    NASA Technical Reports Server (NTRS)

    Abdalati, Waleed

    2006-01-01

    The glaciers and ice sheets of the world contain enough ice to raise sea level by approximately 70 meters if they were to disappear entirely, and most of this ice is located in the climatically sensitive polar regions. Fortunately changes of this magnitude would probably take many thousands of years to occur, but recent discoveries indicate that these ice masses are responding to changes in today s climate more rapidly than previously thought. These responses are likely to be of great societal significance, primarily in terms of their implications for sea level, but also in terms of how their discharge of freshwater, through melting or calving, may impact ocean circulation. For millions of years, oceans have risen and fallen as the Earth has warmed and cooled, and ice on land has shrunk and grown. Today is no different in that respect, as sea levels have been rising at a rate of nearly 2 m per year during the last century (Miller and Douglas 2004), and 3 mm/yr in the last 12 years (Leuliette et al. 2004). What is different today, however, is that tens - perhaps hundreds - of millions of people live in coastal areas that are vulnerable to changes in sea level. Rising seas erode beaches, increase flood potential, and reduce the ability of barrier islands and coastal wetlands to mitigate the effects of major storms and hurricanes. The costs associated with a one-meter rise in sea level are estimated to be in the hundreds of billions of dollars in the United States alone. The worldwide costs in human terms would be far greater as some vulnerable low-lying coastal regions would become inundated, especially in poorer nations that do not have the resources to deal with such changes. Such considerations are particularly important in light of the fact that a one meter sea level rise is not significantly outside the 0.09 to 0.88 range of predictions for this century (IPCC 2001), and rises of this magnitude have occurred in the past in as little as 20 years (Fairbanks 1989

  13. Polar cap arcs: Sun-aligned or cusp-aligned?

    NASA Astrophysics Data System (ADS)

    Zhang, Y.; Paxton, L. J.; Zhang, Qinghe; Xing, Zanyang

    2016-08-01

    Polar cap arcs are often called sun-aligned arcs. Satellite observations reveal that polar cap arcs join together at the cusp and are actually cusp aligned. Strong ionospheric plasma velocity shears, thus field aligned currents, were associated with polar arcs and they were likely caused by Kelvin-Helmholtz waves around the low-latitude magnetopause under a northward IMF Bz. The magnetic field lines around the magnetopause join together in the cusp region so are the field aligned currents and particle precipitation. This explains why polar arcs are cusp aligned.

  14. Effects of ice-cap unloading on shallow magmatic reservoirs

    NASA Astrophysics Data System (ADS)

    Bakker, Richard; Frehner, Marcel; Lupi, Matteo

    2015-04-01

    One of the effects of global warming is the increase of volcanic activity. Glacial melting has been shown to cause visco-elastic relaxation of the upper mantle, which in turn promotes upwelling of magmas through the crust. To date, the effects of ice-cap melting on shallow (i.e., less than 10 km depth) plumbing systems of volcanoes are still not clear. We investigate the pressure changes due to glacial unloading around a magmatic reservoir by combining laboratory and numerical methods. As a case study we focus on Snæfellsjökull, a volcano in Western Iceland whose ice cap is currently melting 1.25 meters (thickness) per year. Our approach is as follows: we obtain representative rock samples from the field, preform tri-axial deformation tests at relevant pressure and temperature (PT) conditions and feed the results into a numerical model in which the stress fields before and after ice cap removal are compared. A suite of deformation experiments were conducted using a Paterson-type tri-axial deformation apparatus. All experiments were performed at a constant strain rate of 10-5 s-1, while varying the PT conditions. We applied confining pressures between 50 and 150 MPa and temperatures between 200 and 1000 ° C. Between 200 and 800 ° C we observe a localized deformation and a slight decrease of the Young's modulus from 41 to 38 GPa. Experiments at 900 and 1000 ° C exhibit macroscopically ductile behavior and a marked reduction of the Young's modulus down to 4 GPa at 1000 ° C. These results are used to construct a numerical finite-element model in which we approximate the volcanic edifice and basement by a 2D axisymmetric half-space. We first calculate the steady-state temperature field in the volcanic system and assign the laboratory-derived temperature-dependent Young's modulus to every element of the model. Then the pressure in the edifice is calculated for two scenarios: with and without ice cap. The comparison between the two scenarios allows us estimate the

  15. Model-observation comparison study of multiple polar cap arcs

    NASA Astrophysics Data System (ADS)

    Zhu, L.; Valladares, C. E.; Sojka, J. J.; Schunk, R. W.; Crain, D. J.

    1996-01-01

    A quantitative model-observation comparison of multiple polar cap arcs has been conducted by using a time-dependent theoretical model of polar cap arcs. In particular, the electrodynamical features of multiple polar cap arcs with various spacings are simulated and the results are compared with the images obtained from the All-Sky Intensified Photometer at Qaanaaq. The results show that the observed and simulated arcs are quite similar, both spatially and temporally. The results support the theory proposed by Zhu et al. [1993a, 1994b] that the structure of polar cap arcs is mainly determined by the magnetosphere-ionosphere (M-I) coupling processes and that the spacing of multiple polar cap arcs is closely related to the hardness of the primary magnetospheric precipitation. It is found that for the multiple polar cap arcs with both narrow and wide spacings, the associated field-aligned currents are mainly closed by Pedersen currents. It is also found that a hard precipitation can lead to a highly structured secondary arc because of the nonlinear M-I coupling processes.

  16. Possible recent and ancient glacial ice flow in the south polar region of Mars

    NASA Technical Reports Server (NTRS)

    Kargel, J. S.

    1992-01-01

    Martian polar science began almost as soon as small telescopes were trained on the planet. The seasonal expansion and contraction of the polar caps and their high albedoes led most astronomers to think that water ice is the dominant constituent. In 1911 Lowell perceived a bluish band around the retreating edge of the polar caps, and interpreted it as water from melting polar ice and seasonal snow. An alternative idea in his time was that the polar caps consist of frozen carbonic acid. Lowell rejected the carbonic acid hypothesis on account of his blue band. He also pointed out that carbonic acid would sublimate rather than melt at confining pressures near and below one bar, hence, carbonic acid could not account for the blue band. In comparing Lowell's theories with today's knowledge, it is recognized that (1) sublimation is mainly responsible for the growth and contraction of Mars' polar caps, (2) carbon dioxide is a major component of the southern polar cap, and (3) Lowell's blue band was probably seasonal dust and/or clouds. Geomorphic evidence that glacial ice and glacial melt waters once flowed over broad areas of the southern polar region. Two aspects of the south polar region suggest possible glacial processes during two distinct eras in Mars' history.

  17. Stratigraphy and evolution of the buried CO2 deposit in the Martian south polar cap

    NASA Astrophysics Data System (ADS)

    Bierson, C. J.; Phillips, R. J.; Smith, I. B.; Wood, S. E.; Putzig, N. E.; Nunes, D.; Byrne, S.

    2016-05-01

    Observations by the Shallow Radar instrument on Mars Reconnaissance Orbiter reveal several deposits of buried CO2 ice within the south polar layered deposits. Here we present mapping that demonstrates this unit is 18% larger than previously estimated, containing enough mass to double the atmospheric pressure on Mars if sublimated. We find three distinct subunits of CO2 ice, each capped by a thin (10-60 m) bounding layer (BL). Multiple lines of evidence suggest that each BL is dominated by water ice. We model the history of CO2 accumulation at the poles based on obliquity and insolation variability during the last 1 Myr assuming a total mass budget consisting of the current atmosphere and the sequestered ice. Our model predicts that CO2 ice has accumulated over large areas several times during that period, in agreement with the radar findings of multiple periods of accumulation.

  18. Idealized model of polar cap currents, fields, and auroras

    NASA Technical Reports Server (NTRS)

    Cornwall, J. M.

    1985-01-01

    During periods of northward Bz, the electric field applied to the magnetosphere is generally opposite to that occurring during southward Bz and complicated patterns of convection result, showing some features reversed in comparison with the southward Bz case. A study is conducted of a simple generalization of early work on idealized convection models, which allows for coexistence of sunward convection over the central polar cap and antisunward convection elsewhere in the cap. The present model, valid for By approximately 0, has a four-cell convection pattern and is based on the combination of ionospheric current conservation with a relation between parallel auroral currents and parallel potential drops. Global magnetospheric issues involving, e.g., reconnection are not considered. The central result of this paper is an expression giving the parallel potential drop for polar cap auroras (with By approximately 0) in terms of the polar cap convection field profile.

  19. The Effect of CO2 Ice Cap Sublimation on Mars Atmosphere

    NASA Technical Reports Server (NTRS)

    Batterson, Courtney

    2016-01-01

    Sublimation of the polar CO2 ice caps on Mars is an ongoing phenomenon that may be contributing to secular climate change on Mars. The transfer of CO2 between the surface and atmosphere via sublimation and deposition may alter atmospheric mass such that net atmospheric mass is increasing despite seasonal variations in CO2 transfer. My study builds on previous studies by Kahre and Haberle that analyze and compare data from the Phoenix and Viking Landers 1 and 2 to determine whether secular climate change is happening on Mars. In this project, I use two years worth of temperature, pressure, and elevation data from the MSL Curiosity rover to create a program that allows for successful comparison of Curiosity pressure data to Viking Lander pressure data so a conclusion can be drawn regarding whether CO2 ice cap sublimation is causing a net increase in atmospheric mass and is thus contributing to secular climate change on Mars.

  20. Martian North Polar Water-Ice Clouds During the Viking Era

    NASA Technical Reports Server (NTRS)

    Tamppari, L. K.; Bass, D. S.

    2000-01-01

    The Viking Orbiters determined that the surface of Mars' northern residual cap consists of water ice. Observed atmospheric water vapor abundances in the equatorial regions have been related to seasonal exchange between reservoirs such as the polar caps, the regolith and between different phases in the atmosphere. Kahn modeled the physical characteristics of ice hazes seen in Viking Orbiter imaging limb data, hypothesizing that ice hazes provide a method for scavenging water vapor from the atmosphere and accumulating it into ice particles. Given that Jakosky found that these particles had sizes such that fallout times were of order one Martian sol, these water-ice hazes provided a method for returning more water to the regolith than that provided by adsorption alone. These hazes could also explain the rapid hemispheric decrease in atmospheric water in late northern summer as well as the increase during the following early spring. A similar comparison of water vapor abundance versus polar cap brightness has been done for the north polar region. They have shown that water vapor decreases steadily between L(sub s) = 100-150 deg while polar cap albedo increases during the same time frame. As a result, they suggested that late summer water-ice deposition onto the ice cap may be the cause of the cap brightening. This deposition could be due to adsorption directly onto the cap surface or to snowfall. Thus, an examination of north polar waterice clouds could lend insight into the fate of the water vapor during this time period. Additional information is contained in the original extended abstract.

  1. Cassini multi-instrument assessment of Saturn's polar cap boundary

    NASA Astrophysics Data System (ADS)

    Jinks, S. L.; Bunce, E. J.; Cowley, S. W. H.; Provan, G.; Yeoman, T. K.; Arridge, C. S.; Dougherty, M. K.; Gurnett, D. A.; Krupp, N.; Kurth, W. S.; Mitchell, D. G.; Morooka, M.; Wahlund, J.-E.

    2014-10-01

    We present the first systematic investigation of the polar cap boundary in Saturn's high-latitude magnetosphere through a multi-instrument assessment of various Cassini in situ data sets gathered between 2006 and 2009. We identify 48 polar cap crossings where the polar cap boundary can be clearly observed in the step in upper cutoff of auroral hiss emissions from the plasma wave data, a sudden increase in electron density, an anisotropy of energetic electrons along the magnetic field, and an increase in incidence of higher-energy electrons from the low-energy electron spectrometer measurements as we move equatorward from the pole. We determine the average level of coincidence of the polar cap boundary identified in the various in situ data sets to be 0.34° ± 0.05° colatitude. The average location of the boundary in the southern (northern) hemisphere is found to be at 15.6° (13.3°) colatitude. In both hemispheres we identify a consistent equatorward offset between the poleward edge of the auroral upward directed field-aligned current region of ~1.5-1.8° colatitude to the corresponding polar cap boundary. We identify atypical observations in the boundary region, including observations of approximately hourly periodicities in the auroral hiss emissions close to the pole. We suggest that the position of the southern polar cap boundary is somewhat ordered by the southern planetary period oscillation phase but that it cannot account for the boundary's full latitudinal variability. We find no clear evidence of any ordering of the northern polar cap boundary location with the northern planetary period magnetic field oscillation phase.

  2. Polar cap auroral arcs: Observations, theories, and a numerical model

    SciTech Connect

    Berg, G.A.

    1993-12-31

    This thesis reports the results of probably the most completely documented study of auroras near the polar cap boundary performed to date. Three fully instrumented rockets flew into the morning sector of the polar cap, complemented on the ground by a digital all-sky camera and incoherent scatter radar. Additionally, DMSP satellite passes over the polar cap bracketed the launches. We use these data to address two main issues: (1) the relationship between the state of the magnetosphere and the formation of polar cap arcs, and (2) the character of the current systems associated with polar cap arcs. The data indicate that in a decaying magnetosphere sun-aligned arcs erupt into the polar cap at high velocity from regions of enhanced brightness in the auroral oval. Two bright polar cap arcs formed in this manner in the region sampled by the rockets. The most equatorward of the arcs, sampled by two of the rockets during its lifetime, erupted into a region already characterized by strong sunward convection. The most poleward, however, which formed after the rockets had passed, pushed into a region where anti-sunward convection pertained less than two minutes earlier. It is likely that the boundary between sunward and anti-sunward convection shifted poleward so that sunward convection pertained at this arc as well. One of the payloads measured, with high resolution, both E and {delta}B as well as energetic particle flux. This permitted an in-depth study of the current systems flown through. The correlation between {delta}E and {delta}B is classic, both fields indicating upward field-aligned currents in virtually every region of enhanced electron precipitation. However, the currents deduced from the electrons do not agree in magnitude with those deduced from the fields. The conclusion is that for arcs embedded in a region of low {Sigma}{sub P} a current composed of upward thermal electrons flows concurrently with the precipitating electrons.

  3. A study of auroral activity in the nightside polar cap

    SciTech Connect

    Wu, Q.

    1989-01-01

    Using various ground observations at South Pole, Antarctica (invariant magnetic latitude -74{degree}) and its conjugate point, Frobisher Bay, Canada, the author has studied the following aspects of nightside polar cap auroral activity: the appearance and disappearance of polar cap auroras (diffuse and discrete) associated with substorms and interplanetary magnetic field (IMF) variations; auroral optical emission line intensities; and the seasonal variation of auroral conjugacy. The observations show that the polar cap auroras usually fade away before the expansive phase of a substorm and bright auroral arcs reach high latitude (-74{degree}) near the recovery phase. Just before the auroras fade away the discrete polar cap auroral arcs, which are usually on the poleward boundary of the diffuse aurora, intensify for 1 to 2 minutes. The observations also indicate the IMF may have stronger control over polar cap auroral activity than do substorms. A search for energy spectral variation of precipitating electrons using the intensities of 630.0 nm (0) and 427 nm (N{sub 2}{sup +}) auroral emission lines reveals no dramatic changes in the energy spectrum; instead, the data show possible atmospheric scattering and geometric effects on the photometric measurements while the bright auroral arc is moving into the polar cap. The conjugate observations show that the stormtime auroral electrojet current, which is associated with the bright auroral arc, in most cases reaches higher (lower) latitudes in the winter (summer) hemisphere. An asymmetric plasma sheet (with respect to the neutral sheet) is proposed, which expands deeper into the winter lobe, under a tilted geomagnetic dipole. Accordingly, the winter polar cap would have smaller area and the auroral electrojet would be at higher latitude.

  4. Using Coastal Ice Cap Records to Investigate Maritime Climate and Ice Sheet Processes in West Greenland

    NASA Astrophysics Data System (ADS)

    Das, S. B.; Evans, M. J.; Frey, K. E.; Osman, M. B.; Smith, B. E.; Stevens, L. A.; Trusel, L. D.; York, A.; Bingham, M.

    2014-12-01

    Recent changes, including outlet glacier retreat and speedup, and increased rates of surface melting, have dramatically increased the Greenland ice sheet contribution to sea-level rise over the past few decades. Increasingly studies point towards the influence of coupled ocean-ice processes in modulating Greenland ice sheet mass balance and glacier behavior in response to climate change, but many of these studies are limited to the past few years to decades, restricting our ability to understand these ocean-ice relationships over longer time periods. Ice core records have the potential to provide unique, high-resolution records of interest (e.g. accumulation and melt variability, as well as contemporaneous proxy records of regional air temperature and sea surface conditions), but suitable Greenland ice sheet coring regions are often located far inland (>200 km) from many maritime regions of interest. In this study we focus on new records from previously unstudied maritime ice caps (10-30 km from the coast) to reconstruct past environmental conditions in the Disko, Ummannaq and Baffin Bay regions. Here we present results from our recent 2014 field investigation of three high altitude ice caps (1300-2000 m) on Disko Island and the Nuussuaq Peninsula, as well as complementary results from two sites in the western ice sheet accumulation zone. Geophysical observations provide constraints on ice thickness, layering, and ice flow. Physical and chemical stratigraphic observations from snow pits and shallow firn cores are used to reconstruct recent accumulation rate and melt variability, as well as to develop and test environmental proxy relationships over the satellite era. Multi-century records from longer coastal ice cores, to be drilled in 2015, will contribute a key missing component to the existing observational record documenting ice, ocean and atmospheric changes in this region over a time period of dramatic change in Greenland ice sheet behavior (retreat and

  5. Direct Observations of the Evolution of Polar Cap Ionization Patches

    NASA Astrophysics Data System (ADS)

    Zhang, Q.; Zhang, B.; Lockwood, M. M.; Hu, H.; Moen, J. I.; Ruohoniemi, J.; Thomas, E. G.; Zhang, S.; Yang, H.; Liu, R.; McWilliams, K. A.; Baker, J. B.

    2013-12-01

    Patches of ionization are common in the polar ionosphere where their motion and associated density gradients give variable disturbances to High Frequency (HF) radio communications, over-the-horizon radar location errors, and disruption and errors to satellite navigation and communication. Their formation and evolution are poorly understood, particularly under disturbed space weather conditions. We report direct observations of the full evolution of patches during a geomagnetic storm, including formation, polar cap entry, transpolar evolution, polar cap exit, and sunward return flow. Our observations show that modulation of nightside reconnection in the substorm cycle of the magnetosphere helps form the gaps between patches where steady convection would give a 'tongue' of ionization (TOI).

  6. The Mars water cycle at other epochs: Recent history of the polar caps and layered terrain

    NASA Technical Reports Server (NTRS)

    Jakosky, Bruce M.; Henderson, Bradley G.; Mellon, Michael T.

    1992-01-01

    The Martian polar caps and layered terrain presumably evolves by the deposition and removal of small amounts of water and dust each year, the current cap attributes therefore represent the incremental transport during a single year as integrated over long periods of time. The role was studied of condensation and sublimation of water ice in this process by examining the seasonal water cycle during the last 10(exp 7) yr. In the model, axial obliquity, eccentricity, and L sub s of perihelion vary according to dynamical models. At each epoch, the seasonal variations in temperature are calculated at the two poles, keeping track of the seasonal CO2 cap and the summertime sublimation of water vapor into the atmosphere; net exchange of water between the two caps is calculated based on the difference in the summertime sublimation between the two caps (or on the sublimation from one cap if the other is covered with CO2 frost all year). Results from the model can help to explain (1) the apparent inconsistency between the timescales inferred for layer formation and the much older crater retention age of the cap and (2) the difference in sizes of the two residual caps, with the south being smaller than the north.

  7. South Polar Residual Cap Geomorphology and Inferred Environmental Changes

    NASA Astrophysics Data System (ADS)

    Byrne, S.; Ingersoll, A.; Pathare, A.

    2003-12-01

    The CO2 southern residual cap (SRC) both controls circulation patterns regionally and buffers the atmospheric pressure globally. In turn this CO2 deposit is affected by changes in environmental conditions wrought by external forces such as dust storm activity. Mars Global Surveyor data of this area have revealed a rich variety of geomorphic features (1) of which there are several distinct classes. These different classes may be end members of the same basic process of insolation driven ablation. We are currently investigating two types of SRC features. Swiss-cheese features (SCF) are depressions characterized by flat floors and steep walls, which retreat 1-3 meters each Martian year (2). In some regions they have a definite symmetry axis along the north-south direction (3). After the seasonal frost disappears the residual ice exposed in the walls has a lower albedo (4). Previously (5) we modeled the evolution and growth of these depressions as a hole in a layer of CO2 ice underlain by water ice, which best explains their morphologic and thermal properties. The observed thickness of the CO2 slab can be as high as 8 meters but in general is much lower. Larger SCF?s commonly possess a raised central island of CO2 surrounded by a moat that penetrates to the underlying water ice (3). The fast rate of wall retreat observed (2) combined with the small sizes of the SCF?s indicate that all SCF?s visible today were created geologically recently. Within a particular region the size distribution is quite narrow (3): no larger (older) or smaller (younger) features were seen indicating that some relatively abrupt change in environmental conditions initiated the growth of this particular population of features. Fingerprint terrain (1) are areas with evenly spaced parallel ridges, which are steeper on one side. These ridges may have small areas of water ice exposed in the intervening troughs. Their wavelength is on the order of 70-90m with the steep edges facing northeast although

  8. DEAD ZONE IN THE POLAR-CAP ACCELERATOR OF PULSARS

    SciTech Connect

    Chen, Alexander Y.; Beloborodov, Andrei M.

    2013-01-10

    We study plasma flows above pulsar polar caps using time-dependent simulations of plasma particles in the self-consistent electric field. The flow behavior is controlled by the dimensionless parameter {alpha} = j/c{rho}{sub GJ}, where j is the electric current density and {rho}{sub GJ} is the Goldreich-Julian charge density. The region of the polar cap where 0 < {alpha} < 1 is a {sup d}ead zone{sup -}in this zone, particle acceleration is inefficient and pair creation is not expected even for young, rapidly rotating pulsars. Pulsars with polar caps near the rotation axis are predicted to have a hollow-cone structure of radio emission, as the dead zone occupies the central part of the polar cap. Our results apply to charge-separated flows of electrons (j < 0) or ions (j > 0). In the latter case, we consider the possibility of a mixed flow consisting of different ion species, and observe the development of two-stream instability. The dead zone at the polar cap is essential for the development of an outer gap near the null surface {rho}{sub GJ} = 0.

  9. Testing the Expanding-Contracting Polar Cap Paradigm

    NASA Astrophysics Data System (ADS)

    Sotirelis, T.; Keller, M. R.; Smith, D.; Barnes, R. J.; Talaat, E. R.; Newell, P. T.; Baker, J. B.

    2013-12-01

    The expanding-contracting polar cap (ECPC) paradigm is tested. Under the ECPC paradigm ionospheric convection in the polar cap is driven by the combined effects of dayside merging and nightside reconnection, as opposed to being mapped down from higher altitudes. The ECPC paradigm is tested by separately examining convection when the polar cap is expanding versus contracting. The open magnetic flux is estimated from SuperDARN observations of the convection reversal boundary (CRB) made simultaneously at different local times. (Sotirelis et al. [2005] established the CRB as a proxy for the Open-Closed Boundary (OCB).) The correlation of the ionospheric convection potential with solar wind/IMF driving is indeed found to depend on whether the polar cap is expanding or contracting. Specifically, when the polar cap is expanding, ionospheric convection correlates best (0.86) with the most recent 10 minutes of solar wind/IMF driving (versus 0.57 for contracting). When contracting, convection correlates best (0.87) with 90-minute averages of solar wind/IMF driving (versus 0.51 for expanding). This is consistent with ECPC expectations.

  10. Evolution of the Mars Northern Ice Cap and Results From the Mars Orbiter Laser Altimeter (MOLA)

    NASA Astrophysics Data System (ADS)

    Muhleman, D. O.; Ivanov, A. B.

    1998-01-01

    Martian ice caps play an extremely important role in regulating climate of Mars. It is well known that they are acting as a reservoir for CO2 and maybe for water and dust. However, a reliable quantitative estimate of the balance or amount of volatiles inside the ice caps was never possible, because little data were available for this purpose. Here we will present initial results and analysis of topography data over the northern ice cap obtained by the Mars Orbiter Laser Altimeter (MOLA) onboard Mars Global Surveyor (MGS). We interpret the observed shape of the ice caps as created by ablation due to sublimation of water ice.

  11. The Residual Polar Caps of Mars: Geological Differences and Possible Consequences

    NASA Technical Reports Server (NTRS)

    Thomas, P. C.; Sullivan, R.; Ingersoll, A. P.; Murray, B. C.; Danielson, G. E.; Herkenhoff, K. E.; Soderblom, L.; Malin, M. C.; Edgett, K. S.; James, P. B.

    2000-01-01

    The Martian polar regions have been known to have thick layered sequences (presumed to consist of silicates and ice), CO2 seasonal frost, and residual frosts that remain through the summer: H2O in the north, largely CO2 in the south. The relationship of the residual frosts to the underlying layered deposits could not be determined from Viking images. The Mars Orbiter Camera on Mars Global Surveyor has provided a 50-fold increase in resolution that shows more differences between the two poles. The north residual cap surface has rough topography of pits, cracks, and knobs, suggestive of ablational forms. This topography is less than a few meters in height, and grades in to surfaces exposing the layers underneath. In contrast, the south residual cap has distinctive collapse and possibly ablational topography emplaced in four or more layers, each approx. two meters thick. The top surface has polygonal depressions suggestive of thermal contraction cracks. The collapse and erosional forms include circular and cycloidal depressions, long sinuous troughs, and nearly parallel sets of troughs. The distinctive topography occurs throughout the residual cap area, but not outside it. Unconformities exposed in polar layers, or other layered materials, do not approximate the topography seen on the south residual cap. The coincidence of a distinct geologic feature, several layers modified by collapse, ablation, and mass movement with the residual cap indicates a distinct composition and/or climate compared to both the remainder of the south polar layered units and those in the north.

  12. Polar cap auroral electron fluxes observed with Isis 1

    NASA Technical Reports Server (NTRS)

    Winningham, J. D.; Heikkila, W. J.

    1974-01-01

    Three types of auroral particle precipitation have been observed over the polar caps, well inside the auroral oval, by means of the soft particle spectrometer on the Isis 1 satellite. The first type is a uniform, very soft (about 100 eV) electron 'polar rain' over the entire polar cap; this may well be present with very weak intensity at all times, but it is markedly enhanced during worldwide geomagnetic storms. A second type of precipitation is a structured flux of electrons with energies near 1 keV, suggestive of localized 'polar showers'; it seems likely that these are the cause of the sun-aligned auroral arcs that have been observed during moderately quiet conditions. During periods of intense magnetic disturbance this precipitation can become very intense and exhibit a characteristic pattern that we have come to call a 'polar squall'.

  13. Destabilisation of an Arctic ice cap triggered by a hydro-thermodynamic feedback to summer-melt

    NASA Astrophysics Data System (ADS)

    Dunse, T.; Schellenberger, T.; Kääb, A.; Hagen, J. O.; Schuler, T. V.; Reijmer, C. H.

    2014-05-01

    Mass loss from glaciers and ice sheets currently accounts for two-thirds of the observed global sea-level rise and has accelerated since the 1990s, coincident with strong atmospheric warming in the Polar Regions. Here we present continuous GPS measurements and satellite synthetic aperture radar based velocity maps from the Austfonna ice cap, Svalbard, that demonstrate strong links between surface-melt and multiannual ice-flow acceleration. We identify a hydro-thermodynamic feedback that successively mobilizes stagnant ice regions, initially frozen to their bed, thereby facilitating fast basal motion over an expanding area. By autumn 2012, successive destabilization of the marine terminus escalated in a surge of the ice cap's largest drainage basin, Basin-3. The resulting iceberg discharge of 4.2 ± 1.6 Gt a-1 over the period April 2012 to May 2013 triples the calving loss from the entire ice cap. After accounting for the terminus advance, the related sea-level rise contribution of 7.2 ± 2.6 Gt a-1 matches the recent annual ice-mass loss from the entire Svalbard archipelago. Our study highlights the importance of dynamic glacier wastage and illuminates mechanisms that may trigger a sustained increase in dynamic glacier wastage or the disintegration of ice-sheets in response to climate warming, which is acknowledged but not quantified in global projections of sea-level rise.

  14. F-layer polar-cap arcs. Master's thesis

    SciTech Connect

    Fite, D.D.

    1987-09-01

    Two types of ionospheric anomalies were discovered recently in the polar cap: patches and arcs. Polar-cap arcs are the focus of this study, which seeks correlation between arcs and total election content (TEC) enhancements and amplitude scintillation effects. Simultaneous optical and radio-frequency measurements were taken at Thule AFB and Qanaaq, Greenland, using the All-Sky Imaging Photometer (ASIP) and a specially equipped Global Positioning System (GPS) receiver. Arcs were discovered to produce significant, rapidly varying TEC increases, and small but measurable amplitude scintillation.

  15. Landscape Evolution and the Reincarnation of the Southern Residual Ice Cap

    NASA Astrophysics Data System (ADS)

    Byrne, S.; Zuber, M. T.

    2006-10-01

    Given the present rate of erosion on the southern residual ice cap, it is unlikely that any part of the cap is older than a few centuries. Unless we're lucky, why is there a residual cap present today for us to observe? We propose a solution involving constant destruction and renewal of the cap.

  16. Transformation of Polar Ice Sublimate Residue into Martian Circumpolar Sand

    NASA Technical Reports Server (NTRS)

    Saunders, R. S.; Parker, T. J.; Stephens, J. B.; Laue, E. G.; Fanale, F. P.

    1985-01-01

    The experimental demonstration that a credible Martian sand may be formed from dust-bearing ice provides a new set of possible explanations for some of the observed Martian aeolian landforms. It is hypothesized that a light-weight fluffy rind is formed on the polar caps. This could provide material easily entrainable by Martian winds, which generally blow equatorward from the poles. These winds would peel the fluffy rind from the surface of the sublimating summer polar caps and from the equatorward slopes of the polar troughs. These pieces of material would then be rolled into lumps (of high sailarea/mass ratio) by the wind. They would become pigmented as they saltate across the surface, perhaps gathering carbonaceous meteoritic dust or other impurities on their surfaces, or through chemical reactions with the ice-free environment away from their point of origin. Once they became trapped in topographic wind shadows, they would form dune structures because they are hydraulically equivalent to sand particles.

  17. Evolution of lunar polar ice stability

    NASA Astrophysics Data System (ADS)

    Siegler, Matt; Paige, David; Williams, Jean-Pierre; Bills, Bruce

    2015-07-01

    The polar regions of the Moon and Mercury both have permanently shadowed environments, potentially capable of harboring ice (cold traps). While cold traps are likely to have been stable for nearly 4 Gyr on Mercury, this has not been the case for the Moon. Roughly 3 ± 1 Gya, when the Moon is believed to have resided at approximately half of its current semimajor axis, lunar obliquities have been calculated to have reached as high as 77°. At this time, lunar polar temperatures were much warmer and cold traps did not exist. Since that era, lunar obliquity has secularly decreased, creating environments over approximately the last 1-2 Gyr where ice could be stable (assuming near current recession rates). We argue that the paucity of ice in the present lunar cold traps is evidence that no cometary impact has occurred in the past billion years that is similar to the one(s) which are thought to have delivered volatiles to Mercury's poles. However, the present ice distribution may be compatible with a cometary impact if it occurred not in today's lunar thermal environment, but in a past one. If ice were delivered during a past epoch, the distribution of ground ice would be dictated not by present day temperatures, but rather by these ancient, warmer, temperatures. In this paper, we attempt to recreate the thermal environments for past lunar orbital configurations to characterize the history of lunar environments capable of harboring ice. We will develop models of ice stability and mobility to examine likely fossil remains of past ice delivery (e.g. a comet impact) that could be observed on the present Moon. We attempt to quantify when in the Moon's outward evolution areas first became stable for ice deposition and when ice mobility would have ceased.

  18. Self-sustaining Mars colonies utilizing the North Polar Cap and the Martian atmosphere.

    PubMed

    Powell, J; Maise, G; Paniagua, J

    2001-01-01

    A revolutionary new concept for the early establishment of robust, self-sustaining Martian colonies is described. The colonies would be located on the North Polar Cap of Mars and utilize readily available water ice and the CO2 Martian atmosphere as raw materials to produce all of the propellants, fuel, air, water, plastics, food, and other supplies needed by the colony. The colonists would live in thermally insulated large, comfortable habitats under the ice surface, fully shielded from cosmic rays. The habitats and supplies would be produced by a compact, lightweight (~4 metric tons) nuclear powered robotic unit termed ALPH (Atomic Liberation of Propellant and Habitat), which would land 2 years before the colonists arrived. Using a compact, lightweight 5 MW (th) nuclear reactor/steam turbine (1 MW(e)) power source and small process units (e.g., H2O electrolyzer, H2 and O2 liquefiers, methanator, plastic polymerizer, food producer, etc.) ALPH would stockpile many hundreds of tons of supplies in melt cavities under the ice, plus insulated habitats, to be in place and ready for use when the colonists landed. With the stockpiled supplies, the colonists would construct and operate rovers and flyers to explore the surface of Mars. ALPH greatly reduces the amount of Earth supplied material needed and enables large permanent colonies on Mars. It also greatly reduces human and mission risks and vastly increases the capability not only for exploration of the surrounding Martian surface, but also the ice cap itself. The North Polar Cap is at the center of the vast ancient ocean that covered much of the Martian Northern Hemisphere. Small, nuclear heated robotic probes would travel deep (1 km or more) inside the ice cap, collecting data on its internal structure, the composition and properties of the ancient Martian atmosphere, and possible evidence of ancient life forms (microfossils, traces of DNA, etc.) that were deposited either by wind or as remnants of the ancient ocean

  19. Microbial diversity on Icelandic glaciers and ice caps.

    PubMed

    Lutz, Stefanie; Anesio, Alexandre M; Edwards, Arwyn; Benning, Liane G

    2015-01-01

    Algae are important primary colonizers of snow and glacial ice, but hitherto little is known about their ecology on Iceland's glaciers and ice caps. Due do the close proximity of active volcanoes delivering large amounts of ash and dust, they are special ecosystems. This study provides the first investigation of the presence and diversity of microbial communities on all major Icelandic glaciers and ice caps over a 3 year period. Using high-throughput sequencing of the small subunit ribosomal RNA genes (16S and 18S), we assessed the snow community structure and complemented these analyses with a comprehensive suite of physical-, geo-, and biochemical characterizations of the aqueous and solid components contained in snow and ice samples. Our data reveal that a limited number of snow algal taxa (Chloromonas polyptera, Raphidonema sempervirens and two uncultured Chlamydomonadaceae) support a rich community comprising of other micro-eukaryotes, bacteria and archaea. Proteobacteria and Bacteroidetes were the dominant bacterial phyla. Archaea were also detected in sites where snow algae dominated and they mainly belong to the Nitrososphaerales, which are known as important ammonia oxidizers. Multivariate analyses indicated no relationships between nutrient data and microbial community structure. However, the aqueous geochemical simulations suggest that the microbial communities were not nutrient limited because of the equilibrium of snow with the nutrient-rich and fast dissolving volcanic ash. Increasing algal secondary carotenoid contents in the last stages of the melt seasons have previously been associated with a decrease in surface albedo, which in turn could potentially have an impact on the melt rates of Icelandic glaciers. PMID:25941518

  20. Microbial diversity on Icelandic glaciers and ice caps

    PubMed Central

    Lutz, Stefanie; Anesio, Alexandre M.; Edwards, Arwyn; Benning, Liane G.

    2015-01-01

    Algae are important primary colonizers of snow and glacial ice, but hitherto little is known about their ecology on Iceland's glaciers and ice caps. Due do the close proximity of active volcanoes delivering large amounts of ash and dust, they are special ecosystems. This study provides the first investigation of the presence and diversity of microbial communities on all major Icelandic glaciers and ice caps over a 3 year period. Using high-throughput sequencing of the small subunit ribosomal RNA genes (16S and 18S), we assessed the snow community structure and complemented these analyses with a comprehensive suite of physical-, geo-, and biochemical characterizations of the aqueous and solid components contained in snow and ice samples. Our data reveal that a limited number of snow algal taxa (Chloromonas polyptera, Raphidonema sempervirens and two uncultured Chlamydomonadaceae) support a rich community comprising of other micro-eukaryotes, bacteria and archaea. Proteobacteria and Bacteroidetes were the dominant bacterial phyla. Archaea were also detected in sites where snow algae dominated and they mainly belong to the Nitrososphaerales, which are known as important ammonia oxidizers. Multivariate analyses indicated no relationships between nutrient data and microbial community structure. However, the aqueous geochemical simulations suggest that the microbial communities were not nutrient limited because of the equilibrium of snow with the nutrient-rich and fast dissolving volcanic ash. Increasing algal secondary carotenoid contents in the last stages of the melt seasons have previously been associated with a decrease in surface albedo, which in turn could potentially have an impact on the melt rates of Icelandic glaciers. PMID:25941518

  1. Extending permanent volcano monitoring networks into Iceland's ice caps

    NASA Astrophysics Data System (ADS)

    Vogfjörd, Kristín S.; Bergsson, Bergur H.; Kjartansson, Vilhjálmur; Jónsson, Thorsteinn; Ófeigsson, Benedikt G.; Roberts, Matthew J.; Jóhannesson, Tómas; Pálsson, Finnur; Magnússon, Eyjólfur; Erlendsson, Pálmi; Ingvarsson, Thorgils; Pálssson, Sighvatur K.

    2015-04-01

    The goals of the FUTUREVOLC project are the establishment of a volcano Supersite in Iceland to enable access to volcanological data from the country's many volcanoes and the development of a multiparametric volcano monitoring and early warning system. However, the location of some of Iceland's most active volcanoes inside the country's largest ice cap, Vatnajökull, makes these goals difficult to achieve as it hinders access and proper monitoring of seismic and deformation signals from the volcanoes. To overcome these obstacles, one of the developments in the project involves experimenting with extending the permanent real-time networks into the ice cap, including installation of stations in the glacier ice. At the onset of the project, only one permanent seismic and GPS site existed within Vatnajökull, on the caldera rim of the Grímsvötn volcano. Two years into the project both seismic and GPS stations have been successfully installed and operated inside the glacier; on rock outcrops as well as on the glacier surface. The specific problems to overcome are (i) harsh weather conditions requiring sturdy and resilient equipment and site installations, (ii) darkness during winter months shutting down power generation for several weeks, (iii) high snow accumulation burying the instruments, solar panels and communication and GPS antennae, and in some locations (iv) extreme icing conditions blocking transmission signals and connection to GPS satellites, as well as excluding the possibility of power generation by wind generators. In 2013, two permanent seismic stations and one GPS station were installed on rock outcrops within the ice cap in locations with 3G connections and powered by solar panels and enough battery storage to sustain operation during the darkest winter months. These sites have successfully operated for over a year with mostly regular maintenance requirements, transmitting data in real-time to IMO for analysis. Preparations for two permanent seismic

  2. Holocene Fluctuations of North Ice Cap, a Proxy for Climate Conditions along the Northwestern Margin of the Greenland Ice Sheet

    NASA Astrophysics Data System (ADS)

    Kelly, M. A.; Osterberg, E. C.; Lasher, G. E.; Farnsworth, L. B.; Howley, J. A.; Axford, Y.; Zimmerman, S. R. H.

    2015-12-01

    North Ice Cap (~76.9°N, 68°W, summit elevation 1322 m asl), a small, independent ice cap in northwestern Greenland, is located within ~25 km of the Greenland Ice Sheet margin and Harald Molkte Bræ outlet glacier. We present geochronological, geomorphic and sedimentological data constraining the Holocene extents of North Ice Cap and suggest that its past fluctuations can be used as a proxy for climate conditions along the northwestern margin of the Greenland Ice Sheet. Prior work by Goldthwait (1960) used glacial geomorphology and radiocarbon ages of subfossil plants emerging along shear planes in the ice cap margin to suggest that that North Ice Cap was not present during the early Holocene and nucleated in the middle to late Holocene time, with the onset of colder conditions. Subfossil plants emerging at shear planes in the North Ice Cap margin yield radiocarbon ages of ~4.8-5.9 cal kyr BP (Goldthwait, 1960) and ~AD 1000-1350 (950-600 cal yr BP), indicating times when the ice cap was smaller than at present. In situ subfossil plants exposed by recent ice cap retreat date to ~AD 1500-1840 (450-110 cal yr BP) and indicate small fluctuations of the ice cap margin. 10Be ages of an unweathered, lichen-free drift <100 m from the present North Ice Cap margin range from ~500 to 8000 yrs ago. We suggest that the drift was deposited during the last ~500 yrs and that the older 10Be ages are influenced by 10Be inherited from a prior period of exposure. We also infer ice cap fluctuations using geochemical data from a Holocene-long sediment core from Deltasø, a downstream lake that currently receives meltwater from North Ice Cap. The recent recession of the North Ice Cap margin influenced a catastrophic drainage of a large proglacial lake, Søndre Snesø, that our field team documented in August 2012. To our knowledge, this is the first significant lowering of Søndre Snesø in historical time.

  3. Nature and History of Cenozoic Polar Ice Covers: The Case of the Greenland Ice Sheet

    NASA Astrophysics Data System (ADS)

    Spielhagen, R.; Thiede, J.

    2009-04-01

    The nature of the modern climate System is characterized by steep temperature gradients between the tropical and polar climatic zones and finds its most spectacular expression in the formation of ice caps in high Northern and Southern latitudes. While polar regions of Planet Earth have been glaciated repeatedly in the long course of their geological history, the Cenozoic transition from a „greenhouse" to an „icehouse" has in fact produced a unique climatic scenario with bipolar glacation, different from all previous glacial events. The Greenland ice sheet is a remainder of the Northern Hemisphere last glacial maximum ice sheets and represents hence a spectacular anomaly. Geological records from Tertiary and Quaternary terrestrial and oceanic sections have documented the presence of ice caps and sea ice covers both on the Southern as well on the Northern hemisphere since Eocene times, aqpprox. 45 Mio. years ago. While this was well known in the case of Antarctica already for some time, previous ideas about the origin of Northern hemisphere glaciation during Pliocene times (approx. 2-3 Mio. years ago) have been superceded by the dramatic findings of coarse, terrigenous ice rafted detritus in Eocene sediments from Lomonosov Ridge (close to the North Pole) apparently slightly older than the oldest Antarctic records of ice rafting.The histories of the onset of Cenozoic glaciation in high Northern and Southern latitudes remain enigmatic and are presently subjects of international geological drilling projects, with prospects to reveal some of their secrets over the coming decades. By virtue of the physical porperties of ice and the processes controlling the dynamics of the turn-over of the ice-sheets only young records of glacial ice caps on Antarctica and on Greemnland have been preserved, on Greenland with ice probably not older than a few hundred thousand years, on Antarctica potentially as old as 1.5-2 Mio. years. Deep-sea cores with their records od ice

  4. Numerical Modeling of the Last Glacial Maximum Yellowstone Ice Cap Captures Asymmetry in Moraine Ages

    NASA Astrophysics Data System (ADS)

    Anderson, L. S.; Wickert, A. D.; Colgan, W. T.; Anderson, R. S.

    2014-12-01

    The Last Glacial Maximum (LGM) Yellowstone Ice Cap was the largest continuous ice body in the US Rocky Mountains. Terminal moraine ages derived from cosmogenic radionuclide dating (e.g., Licciardi and Pierce, 2008) constrain the timing of maximum Ice Cap extent. Importantly, the moraine ages vary by several thousand years around the Ice Cap; ages on the eastern outlet glaciers are significantly younger than their western counterparts. In order to interpret these observations within the context of LGM climate in North America, we perform two numerical glacier modeling experiments: 1) We model the initiation and growth of the Ice Cap to steady state; and 2) We estimate the range of LGM climate states which led to the formation of the Ice Cap. We use an efficient semi-implicit 2-D glacier model coupled to a fully implicit solution for flexural isostasy, allowing for transient links between climatic forcing, ice thickness, and earth surface deflection. Independent of parameter selection, the Ice Cap initiates in the Absaroka and Beartooth mountains and then advances across the Yellowstone plateau to the west. The Ice Cap advances to its maximum extent first to the older eastern moraines and last to the younger western and northwestern moraines. This suggests that the moraine ages may reflect the timescale required for the Ice Cap to advance across the high elevation Yellowstone plateau rather than the timing of local LGM climate. With no change in annual precipitation from the present, a mean summer temperature drop of 8-9° C is required to form the Ice Cap. Further parameter searches provide the full range of LGM paleoclimate states that led to the Yellowstone Ice Cap. Using our preferred parameter set, we find that the timescale for the growth of the complete Ice Cap is roughly 10,000 years. Isostatic subsidence helps explain the long timescale of Ice Cap growth. The Yellowstone Ice Cap caused a maximum surface deflection of 300 m (using a constant effective elastic

  5. Subsurface radar sounding of the martian polar cap: radiative transfer approach

    NASA Astrophysics Data System (ADS)

    Ilyushin, Ya. A.; Seu, R.; Phillips, R. J.

    2005-12-01

    The problem of subsurface radar sounding of the martian polar caps [Ilyushin, 2004. Martian northern polar cap: layering and possible implications for radar sounding. Planet. Space Sci. 52, 1195-1207] is considered from the point of view of incoherent radiative transfer theory. Since it has been previously shown that the radar signal field within the polar cap has diffuse structure, there is a need for a statistical approach to the problem. Radiative transfer theory, which is now well developed, seems to be the most appropriate formalism for this approach. Several physical models of polar caps have been formulated. The asymptotic solutions for all proposed models are derived here. In the present paper only the case of orbital ground penetrating radar is considered, because it is of great interest in relationship to currently developed radar experiments. In principle, the approach is believed to be applicable to a wide class of short pulse and compressed chirp radar experiments, including both orbital and landed instruments and media more complicated than a simple plane parallel geometry. This work, however, is postponed to future papers. Techniques for retrieval of physical properties of polar caps from the radar measurements are proposed. From the observational data, the macroscopic parameters of the medium appearing in radiative transfer theory, i.e. the single scattering albedo and volume extinction coefficient can be estimated. These estimates put certain constraints on the physical parameters of the medium model introduced in the paper. With some additional information, known a priori or from other observations, these estimates can be used to retrieve physically meaningful information, for example, the average content of impurities in the ice.

  6. Rapidly Melting Ice Caps of Northern Baffin Island: Insights From Cosmogenic and Conventional Radiocarbon Dating

    NASA Astrophysics Data System (ADS)

    Anderson, R. K.; Miller, G. H.; Briner, J. P.; Lifton, N.; Devogel, S. B.

    2006-12-01

    The interior plateau of northern Baffin Island in the eastern Canadian Arctic is home to several small (< 50 km2) ice caps whose melt has been well recorded since 1949. Modern equilibrium line altitude (ELA) is well above all existing ice and a continuation of current climatic conditions will lead to the disappearance of all ice on the plateau in the future. Between 2000 and 2005, approximately 1 km2 of ice was lost per year, equivalent to ~1.3% of the total ice cover on the plateau. To put this current melt into a larger picture of ice-cap history on the plateau since deglaciation 6 ka, several techniques have been used in concert. The recent extent of the ice caps during the Little Ice Age can be estimated from the preservation of lichen trimlines across much of the plateau. These trimlines represent previous multi-year snow or ice cover and their aerial extent can be measured via satellite imagery. Based on these measurements, modern ice caps represent only ~3% of ice-cap extent during the Little Ice Age. Radiocarbon dating of moss, preserved beneath the ice caps due to their cold-based nature, suggests a sudden expansion of ice cover around 520 calendar years before present (cal BP), indicated by a mode of 7 dates of approximately this age. This coincides with a pulse of global volcanic activity; predicted cooling from increased aerosol loading may have triggered rapid ice-cap growth. However, dead moss emerging at three sites is more than 1000 years old, with a maximum age of 1326±15 cal BP, indicating that portions of the remaining ice caps have remained intact from more than 1000 years Further constraints on ice cap size are provided by 14C cosmogenic exposure dating. 14C concentrations in rocks at the modern ice margin are too low to be the result of continuous exposure since deglaciation followed by shielding for 500-1000 years by ice cover. Exposure history modeling indicates at least one additional prior period of ice cover of approximately 1000 years

  7. ICESat Estimates of Elevation and Volume Changes of Greenland Ice Caps

    NASA Astrophysics Data System (ADS)

    Robbins, J. W.; Zwally, J.; Yi, D.; Li, J.; Saba, J. L.

    2012-12-01

    ICESat Laser Altimetry acquired over the period 2003-2008 has been processed to provide estimates of changes in elevation for each aligned laser footprint. These are then interpolated, geographically, yielding estimates of volume change on nearly two dozen peripheral ice caps, mostly located in northern Greenland. Definition of ice cap edges are provided by the Greenland Mapping Project 90m, high-resolution, ice mask (GIMP). The results provide a geometric measure of sub-decadal ice cap gain or loss, with the outcome being that more ice caps are losing volume than gaining. Ice caps ranging in size from 200 to 7500 square km have been considered. Over the five-years, ice cap volume changes range from -1.586 cubic km for the Ikke Opmålt cap (2965.1 sq. km areal extent) to +0.582 cubic km on the Kronprins Christian Land cap (7414.6 sq. km). The corresponding averaged rates of elevation change range from -0.535 m/yr to +0.079 m/yr, respectively. Estimates of elevation changes from variations in the rate of firn compaction are also applied. Additionally, examination of time histories of ICESat elevation profiles crossing select ice caps reveal seasonal losses and gains.

  8. Effective area for northern Polar Cap index data

    NASA Astrophysics Data System (ADS)

    Stauning, Peter

    2016-07-01

    The northern (PCN) and southern (PCS) Polar Cap indices are used, among other, in applications to forecast geomagnetic storms and substorms. The index values are based on geomagnetic observations that for the forecast are transmitted in real-time from selected stations, PCN on data from Qaanaaq (Thule) in Greenland and PCS on geomagnetic data from Vostok in Antarctica. Observational conditions in the harsh polar environments are difficult and data transmission links are vulnerable. Hence, it could be advantageous to base real-time PC index values on data from multiple sites in order to safeguard the forecasts. The presentation shall compare PCN index values derived from a range of further observatories in Greenland and Canada in order to delimit an effective Polar Cap area for providing geomagnetic data for a useful index and to settle whether reliable (preliminary) index values could be derived from other than the standard observatories particularly during strongly disturbed conditions.

  9. The spatial coherence of Schumann activity in the polar cap

    NASA Astrophysics Data System (ADS)

    Holtham, P. M.; McAskill, B. J.

    1988-02-01

    The spatial coherence of the first two Schumann resonant modes has been studied at two locations in the polar cap separated by 1100 km. Measurements were made at Assistance Bay and Mould Bay, which have geomagnetic latitudes of 83 and 79 deg, respectively, and satellite time-keeping was employed to accurately synchronize the field stations. The coherence was found to be high, typically 95 percent for the first Schumann mode, and was unaffected by changes in Kp, a storm sudden commencement, or a solar flare event. Polarization rotations were observed between the two stations, which could most likely be attributed to the coastline effect. The results are consistent with a stable propagation of Schumann activity from midlatitudes to high latitudes that is relatively unaffected by changes in the polar cap ionosphere.

  10. Frost streaks in the south polar cap of Mars

    NASA Technical Reports Server (NTRS)

    Thomas, P.; Veverka, J.; Campos-Marquetti, R.

    1979-01-01

    Viking Orbiter images of the annual south polar cap on Mars exhibit elongated bright features that are associated with craters and resemble wind streaks observed elsewhere on Mars. The study focuses on the well-documented frost streaks. The discussion covers the morphology of frost streaks, occurrence, seasonal behavior, thickness of frost in streak deposits, wind patterns inferred from frost streaks and other eolian features in the south polar region, formation of frost streaks, and other locales of preferential frost accumulation. The form and seasonal behavior of the bright elongated albedo markings which extend from the rims of many craters in the south polar cap suggest that they are accumulations of CO2 frost in the lee of craters. The frost streaks appear in the fall, increasing in length but not changing in direction during fall and winter. The frost streaks indicate a prograde circulation pattern of near-surface winds around the pole. Other details are also presented.

  11. Direct observations of the evolution of polar cap ionization patches.

    PubMed

    Zhang, Qing-He; Zhang, Bei-Chen; Lockwood, Michael; Hu, Hong-Qiao; Moen, Jøran; Ruohoniemi, J Michael; Thomas, Evan G; Zhang, Shun-Rong; Yang, Hui-Gen; Liu, Rui-Yuan; McWilliams, Kathryn A; Baker, Joseph B H

    2013-03-29

    Patches of ionization are common in the polar ionosphere, where their motion and associated density gradients give variable disturbances to high-frequency (HF) radio communications, over-the-horizon radar location errors, and disruption and errors to satellite navigation and communication. Their formation and evolution are poorly understood, particularly under disturbed space weather conditions. We report direct observations of the full evolution of patches during a geomagnetic storm, including formation, polar cap entry, transpolar evolution, polar cap exit, and sunward return flow. Our observations show that modulation of nightside reconnection in the substorm cycle of the magnetosphere helps form the gaps between patches where steady convection would give a "tongue" of ionization (TOI). PMID:23539601

  12. Space weather challenges of the polar cap ionosphere

    NASA Astrophysics Data System (ADS)

    Moen, Jøran; Oksavik, Kjellmar; Alfonsi, Lucilla; Daabakk, Yvonne; Romano, Vineenzo; Spogli, Luca

    2013-01-01

    This paper presents research on polar cap ionosphere space weather phenomena conducted during the European Cooperation in Science and Technology (COST) action ES0803 from 2008 to 2012. The main part of the work has been directed toward the study of plasma instabilities and scintillations in association with cusp flow channels and polar cap electron density structures/patches, which is considered as critical knowledge in order to develop forecast models for scintillations in the polar cap. We have approached this problem by multi-instrument techniques that comprise the EISCAT Svalbard Radar, SuperDARN radars, in-situ rocket, and GPS scintillation measurements. The Discussion section aims to unify the bits and pieces of highly specialized information from several papers into a generalized picture. The cusp ionosphere appears as a hot region in GPS scintillation climatology maps. Our results are consistent with the existing view that scintillations in the cusp and the polar cap ionosphere are mainly due to multi-scale structures generated by instability processes associated with the cross-polar transport of polar cap patches. We have demonstrated that the SuperDARN convection model can be used to track these patches backward and forward in time. Hence, once a patch has been detected in the cusp inflow region, SuperDARN can be used to forecast its destination in the future. However, the high-density gradient of polar cap patches is not the only prerequisite for high-latitude scintillations. Unprecedented high-resolution rocket measurements reveal that the cusp ionosphere is associated with filamentary precipitation giving rise to kilometer scale gradients onto which the gradient drift instability can operate very efficiently. Cusp ionosphere scintillations also occur during IMF BZ north conditions, which further substantiates that particle precipitation can play a key role to initialize plasma structuring. Furthermore, the cusp is associated with flow channels and

  13. Variations in Surface Texture of the North Polar Residual Cap of Mars

    NASA Technical Reports Server (NTRS)

    Milkovich, S. M.; Byrne, S.; Russell, P. S.

    2011-01-01

    The northern polar residual cap (NPRC) of Mars is a water ice deposit with a rough surface made up of pits, knobs, and linear depressions on scales of tens of meters. This roughness manifests as a series of bright mounds and dark hollows in visible images; these bright and dark patches have a characteristic wavelength and orientation. Spectral data indicate that the surface of the NPRC is composed of large-grained (and therefore old) water ice. Due to the presence of this old ice, it is thought that the NPRC is in a current state of net loss of material a result potentially at odds with impact crater statistics, which suggest ongoing deposition over the past 10-20 Kyr.

  14. The Geomorphic Footprint of Ice Streaming in the Newfoundland Ice Cap Mapped from Remotely Sensed Data

    NASA Astrophysics Data System (ADS)

    Blundon, Phillip

    Although ice streams have long been proposed within the Newfoundland Ice Cap, this work confirms, for the first time, ice stream operation within terrestrial areas. Through the application of a multi-scale mapping approach several ice stream footprints were identified and characterized. These footprints are characterized by convergence of elongated flow-parallel landforms including drumlins, mega flutes, and crag-and-tail hills. Detailed investigation of the Exploits Ice Stream showed that variations in landform morphology mimic predicted velocity fields within ice steams. All flow sets are characterized by generally thin sediment cover and typically display some form of topographic control, suggesting that topography was more important in controlling ice stream location than the presence of a soft deformable bed. Investigation of landform mapping procedures using Shuttle Radar Topography Mission (SRTM) digital elevation models and aerial photographs, shows that while not as detailed, mapping from SRTM DEMs was able to produce landform maps showing trends similar to those identified on aerial photographs, highlighting their use in reconnaissance level landform mapping.

  15. When is O+ Observed in the High Altitude Polar Cap?

    NASA Technical Reports Server (NTRS)

    Elliott, H. A.; Comfort, R. H.; Craven, P. D.; Chandler, M. O.; Moore, T. E.

    2000-01-01

    Solar wind and IMF properties are correlated with the properties of O+ and H+ in the polar cap at altitudes greater than 5.5 Re geocentric using the Thermal Ion Dynamics Experiment (TIDE) on the Polar satellite. O+ is of primary interest in this study because the fraction of O+ present in the magnetosphere is commonly used as a measure of the ionospheric contribution to the magnetosphere. O+ is observed to be most abundant at lower latitudes when the solar wind speed is low and across most of the polar cap at high solar winds speeds and Kp. As the solar wind dynamic pressures increases more O+ is present in the polar cap. The O+ density is also shown to be more highly correlated with the solar wind dynamic pressure when IMF Bz is positive. H+ was not as well correlated with solar wind and IMF parameters although some correlation with IMF By is observed. H+ is more plentiful when IMF By is negative than when it is positive. In this data set H+ is very dominate so that if this plasma makes it to the plasma sheet its contribution to the plasma sheet would have a very low O+ to H+ ratio.

  16. Sedimentation Waves on the Martian North Polar Cap: Analogy with Megadunes in Antarctica

    NASA Astrophysics Data System (ADS)

    Herny, C.; Masse, M.; Bourgeois, O.; Carpy, S.; Le Mouelic, S.; Appéré, T.; Smith, I. B.; Spiga, A.; Perret, L.; Rodriguez, S.; Piquet, T.; Gaudin, D.; Le Menn, E.

    2014-12-01

    Complex feedbacks between katabatic winds and the cryosphere may lead to the development of sedimentation waves at the surface of ice sheets. These have been first described and named megadunes in Antarctica. Here we use topographic data, optical images, spectroscopic data and radar soundings, acquired by Mars orbiters, to show that the surface of the Martian North Polar Cap displays two superimposed sets of sedimentation waves with differing wavelengths. These sedimentation waves grow and migrate upwind in response to the development of periodic accumulation/ablation patterns controlled by katabatic winds. They have similarities with Antarctic megadunes regarding their surface morphology, texture, grain size, and internal stratigraphic architecture. Based on this analogy, we are currently developing a model of ice/wind interaction at the surface of ice sheets. In Antarctica the accumulation processes on megadunes fields is generally attributed to the wind-blown snow transport while on sedimentation waves of the North Polar Cap of Mars the accumulation seems to be dominated by sublimation/condensation processes at the surface. The model is designed to explore the implication of the water vapor mass transfer and heat transfer on the development of sedimentation waves both on Mars and Earth.

  17. Lineations on the ``White'' Accumulation Areas of the Residual Northern Ice Cap of Mars: Their Relation to the ``Accublation'' and Ice Flow Hypothesis

    NASA Astrophysics Data System (ADS)

    Fisher, David A.; Winebrenner, Dale P.; Stern, Harry

    2002-09-01

    Mars Orbiter Camera (MOC) images of the whiter areas of the residual North Polar Cap (P. C. Thomas et al. 2000, Nature404, 161-164) show a gentle hummocky pitted surface that has been popularly called "cottage cheese" terrain. The pits are 1 or 2 m deep and tens of meters across. They are typically joined in roughly linear strings or long depressions and these features are referred to here as "lineations." The lineations tend to have one or occasionally two preferred directions. We have examined the MOC imagery for the North Cap and using high-resolution images that have good wide-angle context images were able to determine the lineation angles for 31 sites scattered over most of the ice cap. We propose a process that will produce linear features in the white areas, then relate the orientation of the lineations over much of the North Cap to these processes and the inferred ice flow direction. There is first-order agreement between the measured sign of the lineation angles and those predicted assuming ice flow. Higher accumulations and velocities are predicted in the catchment for ice that flows into Chasma Boreale. This comes from the indications that katabatic winds are concentrated in this catchment.

  18. Palmer Quest: A Feasible Nuclear Fission "Vision Mission" to the Mars Polar Caps

    NASA Technical Reports Server (NTRS)

    Carsey, F. D.; Beegle, L. W.; Nakagawa, R.; Elliott, J. O.; Matthews, J. B.; Coleman, M. L.; Hecht, M. H.; Ivaniov, A. B.; Head, J. W.; Milkovich, S.

    2005-01-01

    We are engaged in a NASA Vision Mission study, called Palmer Quest after the American Antarctic explorer Nathaniel Palmer, to assess the presence of life and evaluate the habitability of the basal domain of the Mars polar caps. We address this goal through four objectives: 1. Determine the presence of amino acids, nutrients, and geochemical heterogeneity in the ice sheet. 2. Quantify and characterize the provenance of the amino acids in Mars ice. 3. Assess the stratification of outcropped units for indications of habitable zones. 4. Determine the accumulation of ice, mineralogic material, and amino acids in Mars ice caps over the present epoch. Because of the defined scientific goal for the vision mission, the Palmer Quest focus is astrobiological; however, the results of the study make us optimistic that aggressive multi-platform in-situ missions that address a wide range of objectives, such as climate change, can be supported by variations of the approach used on this mission. Mission Overview: The Palmer Quest baseline

  19. Review of methods to derive a Polar Cap (PC) index.

    NASA Astrophysics Data System (ADS)

    Stauning, Peter

    2016-07-01

    Since a Polar Cap (PC) index was introduced in 1985, several different methods have been used to derive index values. Basically, the northern (PCN) and southern (PCS) are based on geomagnetic recordings at Qaanaaq (Thule) and Vostok, respectively. However, different derivation methods can give index values differing by more than a factor 2. The PC indices are used, among other, in scientific analyses to link solar wind conditions to relevant geophysical effects and in forecast efforts to establish numerical criteria for imminent risk of geomagnetic storms and substorms. Thus, it is unfortunate that several different versions of the PC index have been in use, often without specifically mentioning the index version being used or without ensuring that proper documention and specification of the derivation method is available. The presentation shall briefly describe the basic calculation of a Polar Cap index and point specifically to the differences between the different derivation methods and to the consequences for the index values

  20. Condensation phase of the Martian south polar cap

    NASA Technical Reports Server (NTRS)

    Capuano, J.; Reed, M.; James, P. B.

    1992-01-01

    One type of database that can be useful in limiting models of the Mars surface-atmosphere system is the time dependent boundary of CO2 frost for the polar caps. Data acquired by the thermal infrared sensors on spacecraft are not limited by the lighting problems that hamper visual observations. The surface temperature of solid CO2 is limited by Clapeyron's equation as a function of the local partial pressure of CO2 gas. The growth was studied of the Martian south polar cap using the Viking IRTM dataset. These data are available in five bands, four of which should correspond to surface radiation in clear conditions; the 20 micron data was examined in the first phase.

  1. Polar cap F layer patches: structure and dynamics

    SciTech Connect

    Weber, E.J.; Klobuchar, J.A.; Buchau, J.; Carlson, H.C.; Livingston, R.C.

    1986-11-01

    Coordinated measurements of F-region plasma patches were conducted on February 3/4, 1984, from Thule and Sondrestrom, Greenland. Optical, ionsonde, amplitude scintillation, total electron content (TEC), and incoherent scatter radar measurements were combined to reveal several new aspects of the structure and transport of these localized regions of enhanced F region ionization. For the first time, these patches were directly tracked flowing in the antisunward direction over distances of 3000 km from the center of the polar cap to the poleward edge of the auroral oval. Quantative measurements of TEC show increases of 10-15 TEC units within the patches, above a background polar cap value of 5 TEC units. Amplitude scintillation measurements show the presence of ionospheric irregularities through the entire patch, with a weak indication of stronger scintillation on the trailing (or E x B unstable) edge.

  2. Polar cap F layer patches: structure and dynamics

    SciTech Connect

    Weber, E.J.; Klobuchar, J.A.; Buchau, J.; Carlson H.C. Jr.; Livingston, R.C.; De La Beaujardiere, O.; McCready, M.; Moore, J.G.; Bishop, G.J.

    1986-11-01

    Coordinated measurements of F region plasma patches were conducted on February 3/4, 1984, from Thule and Sondrestrom, Greenland. Optical, ionosonde, amplitude scintillation, total electron content (TEC), and incoherent scatter radar measurements were combined to reveal several new aspects of the structure and transport of these localized regions of enhanced F region ionization. For the first time these patches were directly tracked flowing in the antisunward direction over distances of 3000 km from the center of the polar cap to the poleward edge of the auroral oval. Quantitative measurements of TEC show increases of 10--15 TEC units within the patches, above a background polar cap value of 5 TEC units. Amplitude scintillation measurements show the presence of ionospheric irregularities through the entire patch, with a weak indication of stronger scintillation on the trailing (or E x B unstable) edge.

  3. On magnetic pair production above fast pulsar polar caps

    NASA Technical Reports Server (NTRS)

    An, S.

    1985-01-01

    Magnetic pair production is one of high-energy electromagnetic conversion processes important to the development of pair-photon cascades in pulsars. On the basis of current polar cap models, the properties of magnetic pair production in fast pulsars are discussed. Suppose there is a roughly dipole magnetic field at the stellar surface, the author estimate the effects on non-zero curvature of magnetic field lines upon curvature radiation from primary particles and pair production rate near the surface of pulsars.

  4. Pulsar Polar Cap and Slot Gap Models: Confronting Fermi Data

    NASA Technical Reports Server (NTRS)

    Harding, Alice K.

    2012-01-01

    Rotation-powered pulsars are excellent laboratories for studying particle acceleration as well as fundamental physics of strong gravity, strong magnetic fields and relativity. I will review acceleration and gamma-ray emission from the pulsar polar cap and slot gap. Predictions of these models can be tested with the data set on pulsars collected by the Large Area Telescope on the Fermi Gamma-Ray Telescope over the last four years, using both detailed light curve fitting and population synthesis.

  5. May the continuous trapping of atmospheric water on the permanent South polar cap affect the global atmospheric D/H ratio on Mars?

    NASA Astrophysics Data System (ADS)

    Chassefiere, E.; Montmessin, F.; Fouchet, T.; Forget, F.

    It is generally admitted that thermal escape is the only process responsible for hydrogen isotopic fractionation in Mars atmosphere (enrichment by a factor of 5.5 relative to SMOW value). The aim of the present paper is to show that thermodynamic processes (condensation/ sublimation) may potentially play a significant role in fractionating atmospheric H2O. The cycle of Martian H2O is complex. During northern summer, the North permanent water ice cap is assumed to release a few precipitable microns (pr. μ m), globally averaged, to the atmosphere. Part of this water vapor finally returns to North cap during northern winter, whereas a small fraction (<10%) is trapped in the South permanent carbonic ice cap, which acts as a permanent sink. Water vapor is probably cycled through regolith by adsorption/deposition and further sublimation/desorption. It is believed that the ultimate fate of water molecules released by the North water ice cap, and/or by the permafrost, is to stick to the South carbonic ice cap, with a time scale longer than one seasonal cycle. If so, a molecule released by the North cap must undergo a number of adsorption/desorption and deposition/sublimation cycles, through regolith and polar caps, before being trapped irreversibly in South cap carbonic ice. Recent IR observations of pure water ice on South polar cap by Mars-Express during southern spring show that water, migrating southward together with the edge of the retreating seasonal south CO2 cap, is finally deposited near cap edges in substantial amount. The fraction of this deposited water not released back to the atmosphere at later times (southern summer), therefore incorporated to carbonic ice, is not well known at present time. Because, during southern winter, water vapor above the South permanent cap is much depleted in deuterium, by at least a factor of 3 (Montmessin et al, AGU meeting, 2003), the polar cap tends to be depleted in deuterium (similarly to Earth's case), with a related

  6. Polar volatiles on Mars - Theory versus observation. [solid carbon dioxide in north residual cap

    NASA Technical Reports Server (NTRS)

    Murray, B. C.; Malin, M. C.

    1973-01-01

    Synthesis of the results of the Mariner 9 mission, as they pertain to polar volatiles, and comparison of them with a description of the solid-vapor equilibrium relations believed to be presently active on Mars. The discovery by Mariner 9 of extensive volcanic deposits on portions of the Martian surface suggests that the total amount of CO2 liberated to the surface probably exceeds that now present in the atmosphere. Thus excess CO2 in the solid form is to be expected in the polar areas. Although the simplified model of Leighton and Murray (1966), which predicts a permanent CO2 cap, has significant deficiencies both theoretically and observationally, the seasonal caps are composed of CO2, as predicted, excess CO2 is quite likely, and a permanent deposit of solid CO2 evidently is in equilibrium with atmospheric CO2. It is suggested that there must be a large reservoir of solid CO2 in gaseous equilibrium with the atmosphere, but buried immediately below the exposed residual water-ice cap. This reservoir is believed to be located near the north pole. The principal effect of such a reservoir is to average out annual and longer-term fluctuations in the polar heat balance.

  7. The Contribution of Water Ice Clouds to the Water Cycle in the North Polar Region of Mars: Preliminary Analysis

    NASA Technical Reports Server (NTRS)

    Bass, D. S.; Tamppari, L. K.

    2000-01-01

    While it has long been known that Mars' north residual polar cap and the Martian regolith are significant sources of atmospheric water vapor, the amount of water vapor observed in the northern spring season by the Viking Mars Atmospheric Water Detector instrument (MAWD) cannot be attributed to cap and regolith sources alone. Kahn suggested that ice hazes may be the mechanism by which additional water is supplied to the Martian atmosphere. Additionally, a significant decrease in atmospheric water vapor was observed in the late northern summer that could not be correlated with the return of the cold seasonal C02 ice. While the detection of water ice clouds on Mars indicate that water exists in Mars' atmosphere in several different phases, the extent to which water ice clouds play a role in moving water through the Martian atmosphere remains uncertain. Work by Bass et. al. suggested that the time dependence of water ice cap seasonal variability and the increase in atmospheric water vapor depended on the polar cap center reaching 200K, the night time saturation temperature. Additionally, they demonstrated that a decrease in atmospheric water vapor may be attributed to deposition of water ice onto the surface of the polar cap; temperatures were still too warm at this time in the summer for the deposition of carbon dioxide. However, whether water ice clouds contribute significantly to this variability is unknown. Additional information is contained in original extended abstract.

  8. Monthly average polar sea-ice concentration

    USGS Publications Warehouse

    Schweitzer, Peter N.

    1995-01-01

    The data contained in this CD-ROM depict monthly averages of sea-ice concentration in the modern polar oceans. These averages were derived from the Scanning Multichannel Microwave Radiometer (SMMR) and Special Sensor Microwave/Imager (SSM/I) instruments aboard satellites of the U.S. Air Force Defense Meteorological Satellite Program from 1978 through 1992. The data are provided as 8-bit images using the Hierarchical Data Format (HDF) developed by the National Center for Supercomputing Applications.

  9. Localized polar cap flow enhancement tracing using airglow patches: Statistical properties, IMF dependence, and contribution to polar cap convection

    NASA Astrophysics Data System (ADS)

    Zou, Ying; Nishimura, Yukitoshi; Lyons, Larry R.; Shiokawa, Kazuo; Donovan, Eric F.; Ruohoniemi, J. Michael; McWilliams, Kathryn A.; Nishitani, Nozomu

    2015-05-01

    Recent radar observations have suggested that polar cap flows are highly structured and that localized flow enhancements can lead to nightside auroral disturbances. However, knowledge of these flows is limited to available echo regions. Utilizing wide spatial coverage by an all-sky imager at Resolute Bay and simultaneous Super Dual Auroral Radar Network measurements, we statistically determined properties of such flows and their interplanetary magnetic field (IMF) dependence. We found that narrow flow enhancements are well collocated with airglow patches with substantially larger velocities (≥200 m/s) than the weak large-scale background flows. The flow azimuthal widths are similar to the patch widths. During the evolution across the polar cap, the flow directions and speeds are consistent with the patch propagation directions and speeds. These correspondences indicate that patches can optically trace localized flow enhancements reflecting the flow width, speed, and direction. Such associations were found common (~67%) in statistics, and the typical flow speed, propagation time, and width within our observation areas are 600 m/s, tens of minutes, and 200-300 km, respectively. By examining IMF dependence of the occurrence and properties of these flows, we found that they tend to be observed under By-dominated IMF. Flow speeds are large under oscillating IMF clock angles. Localized flow enhancements are usually observed as a channel elongated in the noon-midnight meridian and directed toward premidnight (postmidnight) for +By (-By). The potential drops across localized flow enhancements account for ~10-40% of the cross polar cap potential, indicating that they significantly contribute to polar cap plasma transport.

  10. Observations of the north polar water ice annulus on Mars using THEMIS and TES

    USGS Publications Warehouse

    Wagstaff, K.L.; Titus, T.N.; Ivanov, A.B.; Castano, R.; Bandfield, J.L.

    2008-01-01

    The Martian seasonal CO2 ice caps advance and retreat each year. In the spring, as the CO2 cap gradually retreats, it leaves behind an extensive defrosting zone from the solid CO2 cap to the location where all CO2 frost has sublimated. We have been studying this phenomenon in the north polar region using data from the THermal EMission Imaging System (THEMIS), a visible and infra-red (IR) camera on the Mars Odyssey spacecraft, and the Thermal Emission Spectrometer (TES) on Mars Global Surveyor. Recently, we discovered that some THEMIS images of the CO2 defrosting zone contain evidence for a distinct defrosting phenomenon: some areas just south of the CO2 cap edge are too bright in visible wavelengths to be defrosted terrain, but too warm in the IR to be CO2 ice. We hypothesize that we are seeing evidence for a seasonal annulus of water ice (frost) that recedes with the seasonal CO2 cap, as predicted by previous workers. In this paper, we describe our observations with THEMIS and compare them to simultaneous observations by TES and OMEGA. All three instruments find that this phenomenon is distinct from the CO2 cap and most likely composed of water ice. We also find strong evidence that the annulus widens as it recedes. Finally, we show that this annulus can be detected in the raw THEMIS data as it is collected, enabling future long-term onboard monitoring. ?? 2007.

  11. The Martian polar CAP - Radiative effects of ozone, clouds, and airborne dust

    NASA Astrophysics Data System (ADS)

    Lindner, B. L.

    1990-02-01

    The solar and thermal flux striking the polar cap of Mars is computed for various ozone, dust, and cloud abundances and for three solar zenith angles. Ozone does not significantly affect the total energy budget of the polar cap. Hence the observed hemispherical asymmetry in ozone abundance causes only an insignificant hemispherical asymmetry in the polar caps. Vertical optical depths of dust and cloud ranging from zero to 1 cause little change in the total flux absorbed by the polar cap near its edge but increase the absorbed flux significantly as one travels poleward. Hemispherical asymmetries in dust abundance, cloud cover, and surface pressure combine to cause a significant hemispherical asymmetry in the total flux absorbed by the residual polar caps, which helps to explain the dichotomy in the residual polar caps on Mars. Other processes which affect the energy budget of the polar cap are proposed and reviewed, particularly with respect to their interaction with the radiative effects of clouds and dust.

  12. Slab Ice and Snow Flurries in the Mars Northern Polar Night

    NASA Technical Reports Server (NTRS)

    1999-01-01

    In the 1970s, spacecraft observations of the polar regions of Mars revealed polar brightness temperatures that were significantly below the expected kinetic temperatures for CO_2 sublimation. For the past few decades, we have speculated as to the nature of these Martian polar cold spots. Are the cold spots surface or atmospheric effects? Do the cold spots behave as blackbodies, or do they have emissivities less than unity? Two developments have allowed us to answer these questions: (1) the measurement of the optical constants of CO_2 by Gary Hansen (1997) and (2) direct thermal spectroscopy of the north polar cap by MGS TES (Kieffer et al., 1998).

    With a few possible excepts, cold spots are surface effects. The CO_2 frost in cold regions of the polar cap show a strong absorption feature at 25 microns that is indicative of fine-grained CO_2, thus explaining the low brightness temperatures observed by the Viking IRTM. Brightness temperatures at 18 microns are usually consistent with expected kinetic surface temperatures. In many cases, the brightness temperatures at 15 microns reveals an atmosphere that is too warm for CO_2 condensation to occur.

    Cold spot formation is strongly dependent on topography, forming preferentially near craters and on slopes of the perennial cap. While cold spots are surface effects, the formation of the fine-grained CO_2 deposits is not entirely restricted to surface formation. TES data, combined with MOLA cloud data (Ivanov and Muhleman, 1999), suggest that at least a few of these cold spots were formed from atmospheric condensates.

    Another major component to the north polar cap composition is slab CO_2 ice. Slab ice has near unity spectral emissivity (Kieffer et al.,1999; Hansen, 1998) and appears to have a low albedo. Two explanations for the low albedo are that the slab ice is intrinsically dark or the slab ice is transparent and we are seeing through to the underlying substrate. Regions of the cap where T_18-T_25 <5

  13. Physical processes in polar stratospheric ice clouds

    NASA Technical Reports Server (NTRS)

    Toon, Owen B.; Turco, Richard; Jordan, Joseph

    1988-01-01

    A one dimensional model of cloud microphysics was used to simulate the formation and evolution of polar stratospheric ice clouds. Some of the processes which are included in the model are outlined. It is found that the clouds must undergo preferential nucleation upon the existing aerosols just as do tropospheric cirrus clouds. Therefore, there is an energy barrier between stratospheric nitric acid particles and ice particles implying that nitric acid does not form a continuous set of solutions between the trihydrate and ice. The Kelvin barrier is not significant in controlling the rate of formation of ice particles. It was found that the cloud properties are sensitive to the rate at which the air parcels cool. In wave clouds, with cooling rates of hundreds of degrees per day, most of the existing aerosols nucleate and become ice particles. Such clouds have particles with sizes on the order of a few microns, optical depths on order of unity and are probably not efficient at removing materials from the stratosphere. In clouds which form with cooling rates of a few degrees per day or less, only a small fraction of the aerosols become cloud particles. In such clouds the particle radius is larger than 10 microns, the optical depths are low and water vapor is efficiently removed. Seasonal simulations show that the lowest water vapor mixing ratio is determined by the lowest temperature reached, and that the time when clouds disappear is controlled by the time when temperatures begin to rise above the minimum values.

  14. Transient bright "halos" on the South Polar Residual Cap of Mars: Implications for mass-balance

    NASA Astrophysics Data System (ADS)

    Becerra, Patricio; Byrne, Shane; Brown, Adrian J.

    2015-05-01

    Spacecraft imaging of Mars' south polar region during mid-southern summer of Mars year 28 (2007) observed bright halo-like features surrounding many of the pits, scarps and slopes of the heavily eroded carbon dioxide ice of the South Polar Residual Cap (SPRC). These features had not been observed before, and have not been observed since. We report on the results of an observational study of these halos, and spectral modeling of the SPRC surface at the time of their appearance. Image analysis was performed using data from MRO's Context Camera (CTX), and High Resolution Imaging Science Experiment (HiRISE), as well as images from Mars Global Surveyor's (MGS) Mars Orbiter Camera (MOC). Data from MRO's Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) were used for the spectral analysis of the SPRC ice at the time of the halos. These data were compared with a Hapke reflectance model of the surface to constrain their formation mechanism. We find that the unique appearance of the halos is intimately linked to a near-perihelion global dust storm that occurred shortly before they were observed. The combination of vigorous summertime sublimation of carbon dioxide ice from sloped surfaces on the SPRC and simultaneous settling of dust from the global storm, resulted in a sublimation wind that deflected settling dust particles away from the edges of these slopes, keeping these areas relatively free of dust compared to the rest of the cap. The fact that the halos were not exhumed in subsequent years indicates a positive mass-balance for flat portions of the SPRC in those years. A net accumulation mass-balance on flat surfaces of the SPRC is required to preserve the cap, as it is constantly being eroded by the expansion of the pits and scarps that populate its surface.

  15. Fourier analysis of polar cap electric field and current distributions

    NASA Technical Reports Server (NTRS)

    Barbosa, D. D.

    1984-01-01

    A theoretical study of high-latitude electric fields and currents, using analytic Fourier analysis methods, is conducted. A two-dimensional planar model of the ionosphere with an enhanced conductivity auroral belt and field-aligned currents at the edges is employed. Two separate topics are treated. A field-aligned current element near the cusp region of the polar cap is included to investigate the modifications to the convection pattern by the east-west component of the interplanetary magnetic field. It is shown that a sizable one-cell structure is induced near the cusp which diverts equipotential contours to the dawnside or duskside, depending on the sign of the cusp current. This produces characteristic dawn-dusk asymmetries to the electric field that have been previously observed over the polar cap. The second topic is concerned with the electric field configuration obtained in the limit of perfect shielding, where the field is totally excluded equatorward of the auroral oval. When realistic field-aligned current distributions are used, the result is to produce severely distorted, crescent-shaped equipotential contours over the cap. Exact, analytic formulae applicable to this case are also provided.

  16. MARCI and MOC observations of the atmosphere and surface cap in the north polar region of Mars

    NASA Astrophysics Data System (ADS)

    Cantor, Bruce A.; James, Philip B.; Calvin, Wendy M.

    2010-07-01

    We used MGS-MOC and MRO-MARCI daily mapping images of the North Polar Region of Mars from 16 August 2005 ( Ls = 270°) to 21 May 2009 ( Ls = 270°), covering portions of three consecutive martian years (MY 27-MY 29), to observe the seasonal behavior of the polar ice cap and atmospheric phenomena. The rate of cap regression was similar in MY 28 and MY 29, but was advanced by 3.5° of Ls (˜7-8 sols) in MY 29. The spatial and temporal behaviors of dust and condensate clouds were similar in the two years and generally in accord with prior years. Dust storms (>100 km 2) were observed in all seasons, with peak activity occurring at Ls = 10-20° from 50°N to 70°N and at Ls = 135-140° from 70°N to 90°N. The most active quadrant was 0-90°W in MY 28, shifting to 180-270°W in MY 29. The majority of regional storms in both years developed in longitudes from 10°W to 60°W. During late summer the larger storms obscure the North Polar Region in a cloud of dust that transitions to north polar hood condensate clouds around autumnal equinox. Changes in the distribution of perennial ice deposits, especially in Olympia Planum, were observed between the 2 years, with the MY 29 ice distribution being the most extensive observed to date. Modeling suggests that the small, bright ice patches on the residual cap are not the result of slope or elevation effects. Rather we suggest that they are the result of local meteorological effects on ice deposition. The annual darkening and brightening of peripheral areas of the residual cap around summer solstice can be explained by the sublimation of a brighter frost layer revealing an underlying darker, ice rich layer that itself either sublimes to reveal brighter material below or acts as a cold trap, attracting condensation of water vapor that brightens the surface. An alternative explanation invokes transport and deposition of dust on the surface from the cap interior, and later removal of that dust. The decrease in cap albedo and

  17. Mercury radar imaging: evidence for polar ice.

    PubMed

    Slade, M A; Butler, B J; Muhleman, D O

    1992-10-23

    The first unambiguous full-disk radar mapping of Mercury at 3.5-centimeter wavelength, with the Goldstone 70-meter antenna transmitting and 26 antennas of the Very Large Array receiving, has provided evidence for the presence of polar ice. The radar experiments, conducted on 8 and 23 August 1991, were designed to image the half of Mercury not photographed by Mariner 10. The orbital geometry allowed viewing beyond the north pole of Mercury; a highly reflective region was clearly visible on the north pole during both experiments. This polar region has areas in which the circular polarization ratio (pt) was 1.0 to 1.4; values < approximately 0.1 are typical for terrestrial planets. Such high values of have hitherto been observed in radar observations only from icy regions of Mars and icy outer planet satellites. PMID:17748898

  18. A Sublimation Model for the Martian Polar Swiss-Cheese Features. Observational and Modeling Studies of the South Polar Residual Cap

    NASA Technical Reports Server (NTRS)

    Byrne, Shane; Ingersoll, Andrew P.

    2002-01-01

    In their pioneering work Leighton and Murray argued that the Mars atmosphere, which is 95 percent CO2 today, is controlled by vapor equilibrium with a much larger polar reservoir of solid CO2. Here we argue that the polar reservoir is small and cannot function as a long-term buffer to the more massive atmosphere. Our work is based on modeling the circular depressions (Swiss-cheese features) in the south polar cap. We argue that a solid CO2 layer approximately 8 meters thick is being etched away to reveal water ice underneath. Preliminary results from the THEMIS (Thermal Emission Imaging System) instrument seem to confirm our model.

  19. Earth's polar cap ionization patches lead to ion upflow

    NASA Astrophysics Data System (ADS)

    Zhang, Q. H.; Zong, Q.; Lockwood, M. M.; Liang, J.; Zhang, B.; Moen, J. I.; Zhang, S.; Zhang, Y.; Ruohoniemi, J. M.; Thomas, E. G.; Liu, R.; Dunlop, M. W.; Yang, H. G.; Hu, H.; Liu, Y.; Lester, M.

    2014-12-01

    The Earth constantly losses matter through ions escaping from the polar ionosphere. This makes the ionosphere as an important source of plasma for the magnetosphere and could modulate atmospheric isotope abundances on geological timescales, depending on what fraction of the upflowing ions subsequently return to the ionosphere and what fraction are ejected into interplanetary space. It has been proposed that the magnetosphere is dynamically modulated by the presence of the ionospheric ions, particularly heavy ions O+, during magnetic substorms and storms. The origin and formation mechanism of ionospheric ion upflow is, however, poorly understood, particularly under disturbed space weather conditions. We report simultaneous direct observations of ion upflow and a patch of ionization at the center of the polar cap region during a geomagnetic storm. Our observations indicate enhanced fluxes of upwelling O+ ions originate from the patch and were accelerated by the enhanced ambipolar electric field. This enhancement is caused by soft electron precipitations. Polar cap patches therefore provide an important source of upwelling ions for accelerations mechanisms at greater altitudes which can eject the ions. These observations give new insight into the processes of ionosphere-magnetosphere coupling and the potential loss of terrestrial water dissociation products into space which, although extremely slow in the case of Earth, may be significant for other planets and moons.

  20. Zonally averaged thermal balance and stability models for nitrogen polar caps on Triton

    NASA Technical Reports Server (NTRS)

    Stansberry, John A.; Lunine, J. I.; Porco, C. C.; Mcewen, A. S.

    1990-01-01

    Voyager four-color imaging data of Triton are analyzed to calculate the bolometric hemispheric albedo as a function of latitude and longitude. Zonal averages of these data have been incorporated into a thermal balance model involving insolation, reradiation, and latent heat of sublimation of N2 ice for the surface. The current average bolometric albedo of Triton's polar caps is 0.8, implying an effective temperature of 34.2 K and a surface pressure of N2 of 1.6 microbar for unit emissivity. This pressure is an order of magnitude lower than the surface pressure of 18 microbar inferred from Voyager data (Broadfoot et al., 1989; Conrath et al., 1989), a discrepancy that can be reconciled if the emissivity of the N2 on Triton's surface is 0.66. The model predicts that Triton's surface north of 15 deg N latitude is experiencing deposition of N2 frosts, as are the bright portions of the south polar cap near the equator. This result explains why the south cap covers nearly the entire southern hemisphere of Triton.

  1. 35 GHz Measurements of CO2 Crystals for Simulating Observations of the Martian Polar Caps

    NASA Technical Reports Server (NTRS)

    Foster, J. L.; Chang, A. T. C.; Hall, D. K.; Tait, A. B.; Barton, J. S.

    1998-01-01

    In order to learn more about the Martian polar caps, it is important to compare and contrast the behavior of both frozen H2O and CO2 in different parts of the electromagnetic spectrum. Relatively little attention has been given, thus far, to observing the thermal microwave part of the spectrum. In this experiment, passive microwave radiation emanating from within a 33 cm snowpack was measured with a 35 GHz hand-held radiometer, and in addition to the natural snow measurements, the radiometer was used to measure the microwave emission and scattering from layers of manufactured CO2 (dry ice). A 1 m x 2 m plate of aluminum sheet metal was positioned beneath the natural snow so that microwave emissions from the underlying soil layers would be minimized. Compared to the natural snow crystals, results for the dry ice layers exhibit lower' microwave brightness temperatures for similar thicknesses, regardless of the incidence angle of the radiometer. For example, at 50 degree H (horizontal polarization) and with a covering of 21 cm of snow and 18 cm of dry ice, the brightness temperatures were 150 K and 76 K, respectively. When the snow depth was 33 cm, the brightness temperature was 144 K, and when the total thickness of the dry ice was 27 cm, the brightness temperature was 86 K. The lower brightness temperatures are due to a combination of the lower physical temperature and the larger crystal sizes of the commercial CO2 Crystals compared to the snow crystals. As the crystal size approaches the size of the microwave wavelength, it scatters microwave radiation more effectively, thus lowering the brightness temperature. The dry ice crystals in this experiment were about an order of magnitude larger than the snow crystals and three orders of magnitude larger than the CO2 Crystals produced in the cold stage of a scanning electron microscope. Spreading soil, approximately 2 mm in thickness, on the dry ice appeared to have no effect on the brightness temperatures.

  2. Magnetohydrostatics in the polar caps of accreting magnetized white dwarfs

    NASA Astrophysics Data System (ADS)

    Hameury, J. M.; Lasota, J. P.

    1985-04-01

    The mechanism of quasi-periodic luminosity variations seen in cataclysmic variable stars is investigated theoretically. Numerical calculations are performed for the model proposed by Livio (1984), in which matter accreted onto the polar caps of a magnetized white dwarf causes repeated breaking of the magnetic-field lines; the method is based (by analogy) on the analysis of magnetic-field disruption in magnetized neutron stars of Hameury et al. (1983). It is found that any such magnetic-field breaking gives recurrence times orders of magnitude greater than those actually observed in magnetized cataclysmic variables suggesting that some other mechanism must be found for the quasi-periodic variations.

  3. Seasonal recession of Mars' south polar cap in 1986

    NASA Technical Reports Server (NTRS)

    James, Philip B.; Martin, Leonard J.; Henson, Jean R.; Birch, Peter V.

    1990-01-01

    Photographs of Mars obtained during the 1986 opposition of the planet have been used to derive the regression curve for the south polar cap between Ls = 190 deg and Ls = 255 deg. The 1986 regression appears to have been unexceptional until after Ls = 230 deg, when it becomes retarded relative to the normal established by the 1971 and 1977 regressions. A study of the data as a function of the filter used suggests that circumpolar clouds were present in early spring, unlike the case in the 1977 recession.

  4. Plasma density increase in the high altitude polar cap

    NASA Astrophysics Data System (ADS)

    Kitanoya, Yugo; Abe, Takumi; Mukai, Toshifumi

    In general situation, the electron density in the ionosphere decreases with altitude. As for the latitudinal variation, the electron density is generally smaller in the polar cap than in the midor low-latitude region. Few reliable measurements have been made to estimate thermal electron density and temperature with a simple instrument such as Langmuir probe in the highaltitude polar cap region. For example, only the limited amount of the electron temperature and density data are available for the high-altitude (> 3000 km) polar cap, where the density is generally less than 2.0*103 [/cm3 ]. Since the plasma density significantly correlates with the solar activity, thermal plasma density becomes smaller for the minimum solar activity period. Thermal Electron energy Distribution (TED) instrument onboard "AKEBONO" (EXOS-D) satellite has been operated in two modes; 1) DC mode to obtain the probe characteristic, 2) SH (second harmonic) mode to estimate the electron energy distribution function based on Druyvesteyn method, from which the electron temperature and density can be estimated even on the condition of low electron density. On the basis of statistical study of the Akebono observation for over 10 years, it is found that the electron number density occasionally increases up to 3.0-4.0*103 [/cm3 ] above altitude of 3000 km. While the electron temperature is believed to be about 8000 K at such a high altitude, the temperature inside the high density region is observed to be lower than that by several thousand degrees. It is noticeable that such a density enhancement occurs during the geomagnetically active period at solar maximum. The high density region is observed to exist not in whole but in part of the polar cap. In addition, it is obvious from the Suprathermal Mass Spectrometer (SMS) observations that the H+ velocity parallel to the upward field aligned direction is observed to be lower in the high density region than the surrounding region. Also, it is

  5. Ice in the lunar polar regions revisited

    NASA Astrophysics Data System (ADS)

    Hodges, R. Richard

    2002-02-01

    The common wisdom that water ice may exist in lunar polar cold traps has become a significant factor in the selection of space research objectives. The purpose of this paper is to address two topics that are missing from the discourse on lunar water: the effect that the pristine cleanliness of the regolith has on water transport on the moon, and the limits on water exposure implied by the extremely high adsorption potentials of the surfaces of soil grains. Water transport is characterized by chemisorption on soil grains and the mixing of ``wet'' grains into the regolith by meteoritic gardening. Ballistic lateral flow, which is generally thought to be an efficient conduit for moving water to the poles, is actually a secondary phenomenon that is facilitated by solar wind and micrometeor erosion but not by thermal desorption, as is the case for the dominant lunar exospheric gases, He and 40Ar. Simulation results show that even under the most optimistic conditions, less than 7% of the water accumulated in the regolith resides in the polar cold traps, where water concentrations cannot be greater than 350 ppm. More important, when realistic transport parameters are used in the simulator, the polar water concentration is reduced by almost 2 orders of magnitude. In a word, the concept of water ice at the lunar poles is insupportable.

  6. POLAR/TIDE Perigee Observations of Thermal O(+) Characteristics in the Polar Cap Region

    NASA Technical Reports Server (NTRS)

    Stevenson, B. A.; Horwitz, J. L.; Su, Y. J.; Elliott, Heather A.; Comfort, Richard H.; Craven, Paul D.; Chandler, Michael O.; Moore, Thomas E.; Giles, Barbara L.; Pollock, Craig J.

    1998-01-01

    We analyze in situ moment measurements of thermal O(+) from the Thermal Ion Dynamics Experiment (TIDE) on POLAR for April - May, 1996. These measurements were obtained near 5000 km altitude within the polar cap ionosphere - magnetosphere interface region. Su explored certain aspects of O(+) parameters in this region. In this report, we hope to expand our knowledge of the O(+) behavior by examining relationships of densities, parallel velocities, and temperatures to the convection velocities, IMF By and Bz components. Preliminary studies with the convection velocities currently require further analysis. In doing so, we are guided in part by the Cleft Ion Fountain paradigm and model developed by which involves downward O(+) flows in the polar magnetosphere. Initial results tend to indicate that in the extreme antisunward region of the polar cap, the density decreases with increasing convection velocity.

  7. Expanded Late Wisconsinan ice cap and ice sheet margins in the western Queen Elizabeth Islands, Arctic Canada

    NASA Astrophysics Data System (ADS)

    Nixon, F. Chantel; England, John H.

    2014-05-01

    Recent mapping of surficial geology and geomorphology in the western Canadian High Arctic (Melville and Eglinton islands), together with new radiocarbon dates acquired from ice-contact raised marine sediments, document expanded late Wisconsinan ice limits for the northwest Laurentide Ice Sheet and the western Innuitian Ice Sheet. An extension of the northwestern margin of the Laurentide Ice Sheet onto Eglinton Island is proposed based on evidence from till containing erratics derived from the Canadian Shield and a pattern of meltwater channels indicating ice retreat offshore into M'Clure Strait. Expansion of the western Melville Island Ice Cap (part of the western, lowland sector of the Innuitian Ice Sheet) to its offshore late Wisconsinan limit was facilitated by coalescence with the Laurentide Ice Sheet, whose buttressing allowed thickening to occur. Estimates of ice extent and thickness (>500 m) of the western Melville Island Ice Cap are in agreement with high marine limits (≤70 m asl). Lateral and proglacial meltwater channels, moraines and glaciomarine, glaciolacustrine and glaciofluvial deposits indicate radial retreat of the western Melville Island Ice Cap onto central highlands after ˜13.0 cal ka BP. Older marine limit shorelines on southern Eglinton Island (˜13.6 cal ka BP) are broadly synchronous with the early and rapid deglaciation of other areas formerly glaciated by the northwestern Laurentide Ice Sheet to the southeast and southwest (˜14.2-13.6 cal ka BP). The collapse of the northwest Laurentide Ice Sheet in M'Clure Strait beginning at ˜14.2 cal ka BP, in addition to prior inferred thinning, opens the possibility that it made a significant contribution to meltwater pulse 1A.

  8. Characteristics of GPS TEC variations in the polar cap ionosphere

    NASA Astrophysics Data System (ADS)

    Watson, Chris; Jayachandran, P. T.; MacDougall, John W.

    2016-05-01

    This paper presents statistical characteristics (occurrence rate, amplitude, and frequency) of low-frequency (<100 mHz) variations in total electron content (TEC) observed in the polar cap ionosphere. TEC variations were primarily associated with mesoscale (tens to hundreds of kilometers) ionization structures and were observed by five Global Positioning System (GPS) receivers over a 6 year period (2009-2014). The altitude of ionization structures was estimated by using colocated ionosonde radars. High data rate receivers combined with broad spatial coverage of multisatellite TEC measurements provided high-resolution magnetic local time/latitude maps of TEC variation characteristics, which were examined as a function of solar cycle and season. These high-resolution maps improve upon the current observational picture of mesoscale structuring in the polar cap and provide accurate links to particular magnetospheric source regions. Occurrence of TEC variations was consistently highest in dayside regions mapping to low latitude and plasma mantle boundary layers, while largest-amplitude TEC variations were observed in dayside regions close to the polar cusp, and lower latitudes around midnight. Occurrence and amplitude of TEC variations increased significantly during the ascending phase of the solar cycle, independent of solar wind conditions, while seasonal statistics showed highest dayside occurrence and amplitude in winter months, lowest in summer, and highest nightside occurrence and amplitude around equinox. A surprising result in the frequency distributions of TEC variations was discrete frequencies of about 2 and 4 mHz, which appeared to originate from regions corresponding to the plasma mantle, immediately poleward of the polar cusp.

  9. The Changing South Polar Cap of Mars: 1999-2005

    NASA Technical Reports Server (NTRS)

    2005-01-01

    13 July 2005 The south polar residual cap of Mars is composed of layered, frozen carbon dioxide. In 1999, the Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) showed that the carbon dioxide layers have been eroded to form a variety of circular pits, arcuate scarps, troughs, buttes, and mesas. In 2001, MOC images designed to provide repeated views of the areas imaged in 1999 -- with the hope of creating stereo (3-D) images, so that the height of scarps and depth of pits could be measured -- showed that the scarps had retreated, pits enlarged, and buttes and mesas shrank. Only carbon dioxide is volatile enough in the martian environment to have caused such dramatic changes -- the scarps were seen to retreat at an average rate of 3 meters (about 3 yards) per Mars year. Most of the scarp retreat occurs during the southern summer season; in some areas the scarps move as much as 8 meters, in others, only 1 meter per Mars year.

    Three Mars years have now elapsed since MOC first surveyed the south polar cap in 1999. Over the past several months, MGS MOC has been re-imaging areas that were seen in 1999, 2001, and 2003, to develop a detailed look at how the landscape has been changing. This animated GIF provides an example of the dramatic changes that have occurred during the past three martian years. The first image, a sub-frame of M09-05244, was acquired on 21 November 1999. The second image, a sub-frame of S06-00973, was obtained on 11 May 2005. The animation shows the changes that have occurred between 1999 and 2005. Each summer, the cap has lost more carbon dioxide. This may mean that the carbon dioxide content of the martian atmosphere has been increasing, bit by very tiny little bit, each of the years that MGS has been orbiting the red planet. These observations also imply that there was once a time, in the not-too-distant past (because there are no impact craters on the polar cap), when the atmosphere was somewhat thinner and colder, to permit the layers

  10. Composition of Auroral Polar Cap Boundary Ion Conics

    NASA Astrophysics Data System (ADS)

    Tung, Y.; Carlson, C. W.; McFadden, J. P.; Parks, G. K.; Lund, E. J.; Eriksson, S.; Ergun, R. E.

    2002-12-01

    Ion conics have frequently been observed by FAST on the auroral polar cap boundary, which we have defined as where the ion energy flux sharply drops off. These polar cap boundary (PCB) ion conics are particularly prevalent in the nightside sector near midnight. Of medium energies (100 eV to 1 keV), these ion conics are characterized by intense number fluxes and often constitute the majority of the outflow from the nightside auroral oval. An earlier study has reported that the PCB ion outflow consisted predominantly of H+ and He+, while a separate study presented data that showed PCB ion conics that consisted primarily of oxygen ions. Possible explanations for the composition change include solar cycle variation or seasonal variation. We will explore through a systematic consideration of FAST orbits from 1997 through 2000 the change in composition of PCB ion conics. Since neither the solar cycle nor the seasons alone seem to explain the variation in ion composition of the PCB ion conics, we will consider alternative possibilities such as convection, IMF dependence, or auroral activity level and history.

  11. Does a "substorm precursor" exist in the polar cap?

    NASA Astrophysics Data System (ADS)

    Nosikova, Nataliya; Lorentzen, Dag; Yagova, Nadezda; Baddeley, Lisa; Pilipenko, Vyacheslav; Kozyreva, Olga

    2015-04-01

    An isolated auroral substorm, which occurs without external triggering, can develop as a result of inner instabilities in the geomagnetic tail. The comparative analysis of presubstorm variations of the geomagnetic field and particle flux in the geomagnetic tail along with geomagnetic and auroral disturbances in the polar caps is of key importance for the discrimination between direct triggering and intra-magnetospheric processes in a substorm onset. In the present study we compare the auroral disturbances and geomagnetic pulsations in the frequency range 1-5 mHz (Pc5/Pi3) at nighttime high latitudes during both quiet geomagnetic intervals preceding isolated substorms and non-substorm intervals. Superposed epoch analysis is applied to reveal pre-substorm variations ("substorm precursors"). The data from IMAGE magnetometer network, the Meridian Scanning photometer (Svalbard), and particle flux measured by GEOTAIL, has been used. The effect of presubstorm activation (Yagova, 2000) is reproduced during the solar minimum conditions. References Yagova N., V. Pilipenko, A. Rodger, V. Papitashvili, J. Watermann, Long period ULF activity at the polar cap preceding substorm, in: Proc. 5th International Conference on Substorms, St. Peterburg, Russia (ESA SP-443), 603-606, 2000.

  12. Gravity Waves Near 300 km Over the Polar Caps

    NASA Technical Reports Server (NTRS)

    Johnson, F. S.; Hanson, W. B.; Hodges, R. R.; Coley, W. R.; Carignan, G. R.; Spencer, N. W.

    1995-01-01

    Distinctive wave forms in the distributions of vertical velocity and temperature of both neutral particles and ions are frequently observed from Dynamics Explorer 2 at altitudes above 250 km over the polar caps. These are interpreted as being due to internal gravity waves propagating in the neutral atmosphere. The disturbances characterized by vertical velocity perturbations of the order of 100 m/s and horizontal wave lengths along the satellite path of about 500 km. They often extend across the entire polar cap. The associated temperature perturbations indicate that the horizontal phase progression is from the nightside to the dayside. Vertical displacements are inferred to be of the order of 10 km and the periods to be of the order of 10(exp 3) s. The waves must propagate in the neutral atmosphere, but they usually are most clearly recognizable in the observations of ion vertical velocity and ion temperature. By combining the neutral pressure calculated from the observed neutral concentration and temperature with the vertical component of the neutral velocity, an upward energy flux of the order of 0.04 erg/sq cm-s at 250 km has been calculated, which is about equal to the maximum total solar ultraviolet heat input above that altitude. Upward energy fluxes calculated from observations on orbital passes at altitudes from 250 to 560 km indicate relatively little attenuation with altitude.

  13. Monitoring the perennial martian northern polar cap with MGS MOC

    NASA Astrophysics Data System (ADS)

    Hale, A. Snyder; Bass, D. S.; Tamppari, L. K.

    2005-04-01

    We have used the Mars Global Surveyor Mars Orbiter Camera Wide Angle (MGS MOC WA) dataset to study albedo trends on the martian northern residual cap. Six study regions were selected, the Chasma Boreale source region, three regions near the center of the cap ("fish hook" region, latitude = 87°; "bottle opener" region, latitude = 87°, "steep-shallow" region, latitude = 85°), and two lower latitude regions (crater, latitude = 77°, and polar outlier, latitude = 82°), and the albedos of these six regions were examined. These regions were chosen due to their good temporal coverage in the MOC dataset, as well as having been studied by other researchers (Bass et al., 2000, Icarus 144, 382-396; Calvin and Titus, 2004, Lunar Planet. Sci. XXXV, Abstract 1455). The picture which emerges is complex. Most areas experience a combination of darkening and brightening through the northern summer; only one area consistently brightens (the polar outlier region). A good deal of interannual repeatability in each region's albedo behavior is seen, however. Possible causes for the observed complex behaviors include dust deposition from late summer storms, sintering of frost grains over the course of the summer, and cold trapping of volatiles on bright, cold surfaces.

  14. Glacio-isostatic crustal movements caused by historical volume change of the Vatnajokull ice cap, Iceland

    NASA Technical Reports Server (NTRS)

    Sigmundsson, Freysteinn; Einarsson, Pall

    1992-01-01

    Measurements of the lake level of Lake Langisjor at the SW edge of the Vatnajokull ice cap indicate a tilt of 0.26 +/- 0.06 microrad/yr away from the ice cap in the years of 1959-1991. The tilt is too large to be explained as an elastic Earth response to ice retreat this century, or to be caused by change in the gravitational pull of the ice cap, but it can be explained by sub-lithospheric viscous adjustment. Regional subsidence in historical times in SE Iceland can similarly be attributed to viscous adjustment resulting from the increased load of Vatnajokull during the Little Ice Age. The inferred sublithospheric viscosity is 1 x 10 exp 18 - 5 x 10 exp 19 Pa s.

  15. The Drangajökull ice cap, northwest Iceland, persisted into the early-mid Holocene

    NASA Astrophysics Data System (ADS)

    Schomacker, Anders; Brynjólfsson, Skafti; Andreassen, Julie M.; Gudmundsdóttir, Esther Ruth; Olsen, Jesper; Odgaard, Bent V.; Håkansson, Lena; Ingólfsson, Ólafur; Larsen, Nicolaj K.

    2016-09-01

    Most glaciers and ice caps in Iceland experienced rapid deglaciation in the early Holocene, reaching a minimum extent during the Holocene Thermal Maximum. Here we present evidence of the Holocene glacial history from lake sediment cores retrieved from seven threshold lakes around the Drangajökull ice cap in the Vestfirðir peninsula, NW Iceland. The sediment cores show on/off signals of glacial meltwater activity, as minerogenic material deposited from glacial meltwater alternates with organic-rich material (gyttja) deposited without glacial meltwater. We base the chronology of the sediment cores on 14C ages and geochemical identification of key tephra layers with known ages. A 25-cm thick layer of the Saksunarvatn tephra in Lake Skorarvatn indicates that the northern part of the ice cap had reached a similar size as today or was smaller already by 10.2 cal kyr BP. However, 14C ages of lake sediment cores from the highlands southeast of Drangajökull suggest that this part of the ice cap was larger than today until 7.8-7.2 cal kyr BP. Even today, the Drangajökull ice cap has a different behavior than the main ice caps in Iceland, characterized by a very low glaciation limit. Because palaeoclimatic proxies show an early-mid Holocene temperature optimum in this part of Iceland, we suggest that the persistence of Drangajökull into the early Holocene and, possibly, also the entire Holocene was due to high winter precipitation.

  16. Swarm In Situ Observations of F-Region Polar Cap Patches Created by Cusp Ionization

    NASA Astrophysics Data System (ADS)

    Goodwin, L. V.; Iserhienrhien, B.; Miles, D. M.; Patra, S.; van der Meeren, C.; Buchert, S. C.; Burchill, J. K.; Clausen, L.; Knudsen, D. J.; McWilliams, K. A.; Moen, J.

    2014-12-01

    Multi-point in situ measurements from the Swarm spacecraft provide a novel tool to investigate the creation, transport, and evolution of polar cap patches. The string-of-pearls spacecraft configuration allow the motion and dynamics of electron density to be resolved on a one minute timescale. Swarm flew northward through the Scandinavian dayside cusp, passing through auroral features and high frequency radar backscatter. The observations reveal that plasma flow channels, the transport of photoionized plasma, and cusp particle precipitation are all important processes involved in creating the structures which become polar cap patches. Newly created electron density structures are transported across the polar cap via convection. The observed time-history of density structure indicates that particle impact ionization can add structure to both photoionized plasma and lower density polar cap plasma. Newly created and highly structured plasma evolves into lower density, less structured polar cap patches as they transit the polar cap.

  17. Modeling the Quiet Time Outflow Solution in the Polar Cap

    NASA Technical Reports Server (NTRS)

    Glocer, Alex

    2011-01-01

    We use the Polar Wind Outflow Model (PWOM) to study the geomagnetically quiet conditions in the polar cap during solar maximum, The PWOM solves the gyrotropic transport equations for O(+), H(+), and He(+) along several magnetic field lines in the polar region in order to reconstruct the full 3D solution. We directly compare our simulation results to the data based empirical model of Kitamura et al. [2011] of electron density, which is based on 63 months of Akebono satellite observations. The modeled ion and electron temperatures are also compared with a statistical compilation of quiet time data obtained by the EISCAT Svalbard Radar (ESR) and Intercosmos Satellites (Kitamura et al. [2011]). The data and model agree reasonably well. This study shows that photoelectrons play an important role in explaining the differences between sunlit and dark results, ion composition, as well as ion and electron temperatures of the quiet time polar wind solution. Moreover, these results provide validation of the PWOM's ability to model the quiet time ((background" solution.

  18. Integrated firn elevation change model for glaciers and ice caps

    NASA Astrophysics Data System (ADS)

    Saß, Björn; Sauter, Tobias; Braun, Matthias

    2016-04-01

    We present the development of a firn compaction model in order to improve the volume to mass conversion of geodetic glacier mass balance measurements. The model is applied on the Arctic ice cap Vestfonna. Vestfonna is located on the island Nordaustlandet in the north east of Svalbard. Vestfonna covers about 2400 km² and has a dome like shape with well-defined outlet glaciers. Elevation and volume changes measured by e.g. satellite techniques are becoming more and more popular. They are carried out over observation periods of variable length and often covering different meteorological and snow hydrological regimes. The elevation change measurements compose of various components including dynamic adjustments, firn compaction and mass loss by downwasting. Currently, geodetic glacier mass balances are frequently converted from elevation change measurements using a constant conversion factor of 850 kg m‑³ or the density of ice (917 kg m‑³) for entire glacier basins. However, the natural conditions are rarely that static. Other studies used constant densities for the ablation (900 kg m‑³) and accumulation (600 kg m‑³) areas, whereby density variations with varying meteorological and climate conditions are not considered. Hence, each approach bears additional uncertainties from the volume to mass conversion that are strongly affected by the type and timing of the repeat measurements. We link and adapt existing models of surface energy balance, accumulation and snow and firn processes in order to improve the volume to mass conversion by considering the firn compaction component. Energy exchange at the surface is computed by a surface energy balance approach and driven by meteorological variables like incoming short-wave radiation, air temperature, relative humidity, air pressure, wind speed, all-phase precipitation, and cloud cover fraction. Snow and firn processes are addressed by a coupled subsurface model, implemented with a non-equidistant layer

  19. Dust-Driven Halos on the Martian South Polar Residual CAP

    NASA Astrophysics Data System (ADS)

    Becerra, P.; Byrne, S.; Brown, A. J.

    2013-12-01

    The CO2 ice South Polar Residual Cap (SPRC) on Mars may be a sensitive indicator of inter-annual planetary climate variability. Imaging by HiRISE [1], and CTX [2] found that many scarps and pits in the 'Swiss cheese terrain' [3] of the SPRC exhibited a bright 'halo' around their edges. These halos appeared during Martian southern summer in Mars Year 28 (MY28, [4]), and have been observed in only one of eight mars years for which observations at high enough resolution exist. We hypothesize that the formation of these features is linked to the late-summer global dust storm of MY28 and report on observations and formation models. We surveyed HiRISE, CTX, and CRISM [5] data to constrain the optical properties and composition of the halos, as well as their time of appearance and location within the SPRC. The halos appeared throughout most of the surface area of the SPRC between Ls 280° and 330° in MY28. The widest portions of the halos occurred adjacent to north-facing walls, and the brightest parts adjacent to sun-facing walls, which points to a connection between insolation and halo appearance. CRISM spectral products rule out the presence of water ice as a factor in the halos' appearance. These data also imply larger CO2 ice grain sizes where the bright halos were seen, which are normally associated with lower, rather than higher, albedos [6]. Thus, we also ruled out CO2 ice grain size differences as the main cause for the halos. The remaining possibility is that the halos appeared due to differences in dust content between the terrain adjacent to the pit walls and the surrounding ice. To investigate this we made a Hapke [7] surface reflectance model in which the CO2 ice grain size, dust volumetric content and dust particle size were free parameters. We used the HiRISE and CRISM bandpass coefficients to simulate HiRISE I/F values and CRISM spectra, and attempted to match the HiRISE RED I/F, HiRISE BG/RED color ratio, and the CRISM 1.43 μm band depths. A self

  20. Heating of the Sunlit Polar Cap Ionosphere by Reflected Photoelectrons

    NASA Astrophysics Data System (ADS)

    Varney, R. H.; Solomon, S. C.; Nicolls, M. J.

    2014-12-01

    Photoelectrons escape from the ionosphere on sunlit polar cap field lines. In order for those field lines to carry zero current without significant heavy ion outflow or cold electron inflow, field-aligned potential drops must form to reflect a portion of the escaping photoelectron population back to the ionosphere. Using a 1-D ionosphere-polar wind model and measurements from the Resolute Bay Incoherent Scatter Radar (RISR-N), this paper shows that these reflected photoelectrons are a significant source of heat for the sunlit polar cap ionosphere. The model includes a kinetic suprathermal electron transport solver, and it allows energy input from the upper boundary in three different ways: thermal conduction, soft precipitation, and potentials that reflect photoelectrons. The simulations confirm that reflection potentials of several 10s of eV are required to prevent cold electron inflow and demonstrate that the flux tube integrated change in electron heating rate (FTICEHR) associated with reflected photoelectrons can reach 109 eV cm-2s-1. Soft precipitation can produce FTICEHR of comparable magnitudes, but this extra heating is divided among more electrons as a result of electron impact ionization. Simulations with no reflected photoelectrons and with downward field-aligned currents (FAC) primarily carried by the escaping photoelectrons have electron temperatures which are ~250-500 K lower than the RISR-N measurements in the 300-600 km region; however, simulations with reflected photoelectrons, zero FAC, and no other form of heat flux through the upper boundary can satisfactorily reproduce the RISR-N data.

  1. Heating of the sunlit polar cap ionosphere by reflected photoelectrons

    NASA Astrophysics Data System (ADS)

    Varney, R. H.; Solomon, S. C.; Nicolls, M. J.

    2014-10-01

    Photoelectrons escape from the ionosphere on sunlit polar cap field lines. In order for those field lines to carry zero current without significant heavy ion outflow or cold electron inflow, field-aligned potential drops must form to reflect a portion of the escaping photoelectron population back to the ionosphere. Using a 1-D ionosphere-polar wind model and measurements from the Resolute Bay Incoherent Scatter Radar (RISR-N), this paper shows that these reflected photoelectrons are a significant source of heat for the sunlit polar cap ionosphere. The model includes a kinetic suprathermal electron transport solver, and it allows energy input from the upper boundary in three different ways: thermal conduction, soft precipitation, and potentials that reflect photoelectrons. The simulations confirm that reflection potentials of several tens of eV are required to prevent cold electron inflow and demonstrate that the flux tube integrated change in electron heating rate (FTICEHR) associated with reflected photoelectrons can reach 109eV cm-2s-1. Soft precipitation can produce FTICEHR of comparable magnitudes, but this extra heating is divided among more electrons as a result of electron impact ionization. Simulations with no reflected photoelectrons and with downward field-aligned currents (FAC) primarily carried by the escaping photoelectrons have electron temperatures which are ˜250-500 K lower than the RISR-N measurements in the 300-600 km region; however, simulations with reflected photoelectrons, zero FAC, and no other form of heat flux through the upper boundary can satisfactorily reproduce the RISR-N data.

  2. Correlation of Martian South Polar CO2 Seasonal Cap Retreat With Low Altitude Clouds: A Control On Annual Accumulation

    NASA Astrophysics Data System (ADS)

    Smith, Isaac; Spiga, Aymeric

    2014-05-01

    Both the north and south polar layered deposits (NPLD and SPLD) comprise the majority of surface ice on Mars and offer a historical record for understanding recent climate. Of importance, the deposits undergo seasonal variability, between winter (when CO2 ice frost covers the polar regions) and summer (when the CO2 ice has sublimed). Recent evidence has shown that winds and atmospheric deposition played major roles for forming the spiral troughs that cover the NPLD. Observations of low altitude clouds (or visible expressions of katabatic jumps), radar stratigraphy, and surface morphology, in combination with high resolution mesoscale simulations from the Laboratoire de Météorologie Dynamique, demonstrate that ice is transported across the NPLD by wind to form and modify the troughs [Smith et al., 2013]. We employ the same techniques on the SPLD to find that the processes affecting southern spiral troughs are very similar, although there is an additional seasonal component not detected on the NPLD. Clouds, as mechanisms of deposition, retreat pole-ward during southern spring and summer. The retreat is matched spatially to modeled high speed winds near the CO2 seasonal ice cap boundary. Our mesoscale simulations reveal that topographic heights of the SPLD primarily drive slope-wind (katabatic) circulations. This existing circulation is reinforced by an additional thermally-direct circulation driven by the retreating CO2 ice in proximity to nearby exposed low albedo deposits, explaining why enhanced winds (and trough clouds) are mostly found in the vicinity of the CO2 seasonal ice boundary. In one simulation, at Ls 290°, the ice line is located so that the slope winds produced by the SPLD topography are optimally enhanced (up to 20 ms-1) by thermally directed circulations caused by a nearly 100 K thermal contrast. This work, in combination with detailed stratigraphic analysis from ground penetrating radar indicates that sites of deposition and retention of ice on

  3. A perchlorate brine lubricated deformable bed facilitating flow of the north polar cap of Mars: Possible mechanism for water table recharging

    NASA Astrophysics Data System (ADS)

    Fisher, David A.; Hecht, Michael H.; Kounaves, Samuel P.; Catling, David C.

    2010-02-01

    The Phoenix Wet Chemistry Lab (WCL) discovered substantial amounts of magnesium, calcium, and sodium perchlorate in the soil of polar Mars. Magnesium perchlorate is likely the dominant salt in the polar region's soils. But it could be that the cations are contributed by a mixture of Mg, Ca, and Na. Mg, Ca, and Na perchlorate brines can stay liquid as low as ˜-69, -74, -32°C, respectively. WCL reports 0.7 % (wt) of the soil is pure perchlorate, and if 5% of the northern permanent ice cap is soil, then the perchlorate could make about 1/2800 of the ice cap. This suggests there could be enough perchlorate in the ice cap to generate about 1-3 m of brine at the bed. Large areas under the north polar cap have basal temperatures above -69°C so the Mg and Ca perchlorate brines would be liquid. Because of its high density, the perchlorate brine would pool over impervious layers and make the bed into a perchlorate sludge, which could be mobilized and deformed by the weight of the overburden of ice and soil. The sludge would be deformed and moved outward and stop where the basal temperature dropped below -69°C. During the warmest climates, any frozen cold dam at the edge could be breached and the brine reintroduced to the polar surface. Some of the brine could have penetrated downward under the ice cap. This mobile sludge-bed ice cap has been modeled with a 2-D time-varying model. Results of such model runs have similarities to measured layers found by shallow subsurface radar.

  4. A Novel Approach to Exploring the Mars Polar Caps

    NASA Technical Reports Server (NTRS)

    Brophy, John R.; Carsey, Frank D.; Rodgers, David H.; Soderblom, L. A.; Wilcox, Brian H.

    2000-01-01

    The Martian polar caps contain some of the most important scientific sites on the planet. There is much interest in exploring them with a view to understanding their role in the Mars climate system. By gaining access to the stratigraphy of the polar terrain, it is probable that one can access the climate history of the planet. Additionally, investigations aimed at localizing subsurface water--liquid or solid--are not only of great scientific interest but are also germane to the long-term interests of the manned space flight program. A major difficulty with polar exploration is access. Current techniques using chemical propulsion, Holman transfers, and direct-entry landers with aeroshells have limited capability to access the polar terrain. For the near term the authors propose a new approach to solving this transportation issue by using Solar Electric Propulsion (SEP), recently flight demonstrated on NASA's DS1 Mission to an asteroid and a comet. For a longer-term approach there are additional ways in which access to Mars, as well as other planets, can be significantly improved. These include the use of Chaos orbit theory to enable transportation between LaGrange points in the solar system, gossamer structures enabling very low-mass mobility, and advanced ascent vehicles. In this paper the authors describe how a 1000-kG payload can be transported to the surface of Mars and a polar sample obtained and returned to Earth in less than five years using SEP. A vision of how this approach can be integrated into a long-term Mars exploration strategy building toward the future is also discussed.

  5. Estimates of total quantity of meteorites in the East Antarctic ice cap

    NASA Technical Reports Server (NTRS)

    Olsen, E. J.

    1981-01-01

    Based on a steady-state model of the East Antarctic ice cap, and current estimates of meteorite influx, a model is developed which predicts that the steady-state number of meteorites being carried in or on the ice is at least 760,000. This large meteorite population does not require unusual influx conditions, since the cold, dry climate preserves virtually all meteorites that fall with the exception of the fragile, porous carbonaceous chondrites. Application of the model to the Greenland ice cap yields a steady-state population of about 61,000 meteorites.

  6. Neoglacial ice expansion and late Holocene cold-based ice cap dynamics on Cumberland Peninsula, Baffin Island, Arctic Canada

    NASA Astrophysics Data System (ADS)

    Margreth, Annina; Dyke, Arthur S.; Gosse, John C.; Telka, Alice M.

    2014-05-01

    Radiocarbon dating of fossil flora and fauna collected along receding cold-based ice caps and cold-based sections of polythermal glaciers on Cumberland Peninsula reveal insights into Neoglacial ice expansion and late Holocene ice dynamics. The taphonomic advantages of subfossilized moss were exploited to precisely document regional expansions of ice caps through the late Holocene. When compared with climate proxies and records of volcanic eruptions, the moss radiocarbon age distributions indicate i) onset of Neoglaciation shortly after 5 ka, concomitant with increased sea ice cover, ii) intensification of ice expansion between 1.9 and 1.1 ka, followed by halt of ice growth, or ice recession during the Medieval Warm Period, and iii) renewed ice expansion after 0.8 ka, in response to cooling related to a combination of large volcanic eruptions and low solar activity. Overall, the observations support a model of near-instantaneous glacial response to regional climate controls and that these responses were synchronous throughout eastern Canadian Arctic and possibly eastern Greenland.

  7. Emergent Dead Vegetation and Paired Cosmogenic Isotope Constraints on Ice Cap Activity, Baffin Island, Arctic Canada

    NASA Astrophysics Data System (ADS)

    Pendleton, S.; Miller, G. H.

    2014-12-01

    Recent summer warming has now raised the equilibrium line above almost all ice caps on Baffin Island, resulting in surface lowering and marginal recession everywhere. As cold-based ice recedes it frequently exposes in situ tundra plants that were living at the time ice expanded across the site. Radiocarbon dates for each plant records when cold summers dropped regional snowline below the site, killing the plants, and snowline remained below the site until the collection date. The kill dates also represent the last time that the climate was warm enough to expose the sampling location. Seventy-six vegetation samples collected in 2013 from the Penny Ice Cap region have been dated, with significant age populations at ~0.5, 1.8, 2.3, and 3.6 ka. The absence of ages around ~1, 2, 3, 4.5, and 5.5 ka suggest periods of either no snowline depression or stability. Sixteen vegetation samples returned ages of >45 ka (2 revisited sites from 2010, 14 new). It is postulated that these radiocarbon dead samples were last exposed during the last interglaciation (~120 ka), the last time climate was as warm as present. In addition to plant collections, bedrock exposures at the ice margins were sampled for 26Al/10Be cosmogenic nuclide dating. Seven samples from and around the Penny Ice cap have returned maximum exposure ages from ~ 0.6-0.9 ma and total histories of ~0.6-1.5 ma. In general, samples from the larger Penny Ice Cap exhibited lower amounts of exposure (~20% of total history) than those samples from smaller, localized ice caps (~55%). Radiocarbon dead sites north of the Penny Ice cap experienced significantly more exposure over their lifetimes than their counterparts east of the Penny Ice cap, suggesting significant differences in local and regional land ice fluctuations over the last 2 million years. Utilizing both the method of in situ moss and 26Al/10Be dating provides new insight into both the recent activity and long-term evolution of ice on Baffin Island. In particular

  8. Polar cap plasma patch primary linear instability growth rates compared

    NASA Astrophysics Data System (ADS)

    Burston, Robert; Mitchell, Cathryn; Astin, Ivan

    2016-04-01

    Four primary plasma instability processes have been proposed in the literature to explain the generation of phase scintillation associated with polar cap plasma patches. These are the gradient drift, current convective, and Kelvin-Helmholtz instabilities and a small-scale "turbulence" process. In this paper the range of possible values of the linear growth rates for each of these processes is explored using Dynamics Explorer 2 satellite observations. It is found that the inertial turbulence instability is the dominant process, followed by inertial gradient drift, collisional turbulence, and collisional shortwave current convective instabilities. The other processes, such as Kelvin-Helmholtz, collisional gradient drift, and inertial shortwave current convective instabilities, very rarely (<1% of the time) give rise to a growth rate exceeding 1/60, that is deemed to be significant (in publications) to give rise to GPS scintillation.

  9. Topography of the South Polar Cap and Layered Deposits of Mars: Viking Stereo Grametry at Regional and Local Scales

    NASA Astrophysics Data System (ADS)

    Schenk, P.; Moore, J.; Stoker, C.

    1998-01-01

    Layered deposits and residual polar caps on Mars may record the deposition of ice and sediment modulated by periodic climate change. Topographic information relating to layer thicknesses, erosional processes, and formation of dark spirals within these deposits has been sparce or unreliable until the arrival of MOLA in orbit in September 1997. To assist in evaluating these terrains prior to launch and to assess formation and erosion processes in the polar deposits, we have assembled Viking stereo mosaics of the region and have produced the first reliable DEM models of the south polar deposits using automated stereogrammetry tools. Here we report our preliminary topographic results, pending final image pointing updates. The maximum total thickness of the layered deposits in the south polar region is 2.5 km. The thick layered deposits consist of a series of megaterraces. Each terrace is several tens of kilometers wide and is flat or slopes very gently toward the pole. These terraces step downward from a central plateau near the south pole. Terraces are bounded by relatively steep scarps 100-500 meters high that face toward the equator. These scarps correspond to the pattern of dark spirals observed within the residual cap in southern summer, and are interpreted as ice or frost-free surfaces warmed by solar insolation. Several tongue-shaped troughs, with rounded cirquelike heads, are observed near the margins of the deposit. These troughs are 300-600 meters in deep and may be similar to troughs observed in the northern polar deposit.

  10. Physical State of the ``Bright'' South Seasonal Polar Cap From OMEGA Observations

    NASA Astrophysics Data System (ADS)

    Doute, S.; Schmidt, F.; Schmitt, B.; Vincendon, M.; Langevin, Y.; Gondet, B.; Bibring, J.

    2009-12-01

    The composition, physical state and texture of the South Seasonal Polar Cap (SSPC) have important consequences on energy balance. The imaging spectrometer OMEGA on board Mars Express has acquired the most comprehensive set of observations to date in the near-infrared (0.93-5.1 microns) on the SSPC from mid-winter solstice (Ls=110° , December 2004) to the end of the recession at Ls=320° (November 2005) [1]. The time resolution is 3 days to one month and the spatial resolution ranges from 700m to 10 km/pixel. [1] showed that during southern spring and summer, there is a very complex evolution in terms of effective grain size of CO2 ice and contamination by dust or H2O ice. H2O ice does not play a significant role except close to the end of the recession. [2] systematically segmented the South Seasonal Polar Cap into different spectral units and tested diverse surface representations by the modeling of spectral end-members and average unit spectra. Here we focus on the “bright” part of the SSPC corresponding to spectral unit SSPC1 (I.b of [1]). Regions belonging to this unit have a very bright albedo (≈ 0.6-0.8) associated with strong CO2 ice absorption features. According to [1] such characteristics are compatible with granular CO2 deposits with grain size in the range of 5 cm implying an extremely low contamination by dust and water ice. Furthermore, from their study of a representative region at 34° E, 76° S, the albedo increases from Ls=223° up to a maximum at Ls=240° and then decreases until total disappearance of the ice. The albedo increase would require a decrease of grain size if the granular model is really relevant. However the mean free path within CO2 ice as well as its thermodynamic behavior would rather favor a porous CO2 slab model [3]. Then photometric effects could be expected that could explain the brightening. In this paper we propose to further study the physical state of the “bright” part of the SSPC and its evolution by

  11. Spatial and Depth Distribution of Sub-surface Ice in the Polar Regions of Mars.

    NASA Astrophysics Data System (ADS)

    Boynton, W.; Kim, K.; Janes, D.; Kerry, K.; Williams, R.; Reedy, R.; Drake, D.

    The Mars Odyssey spacecraft has been in its mapping orbit for slightly over one Mars year. The Gamma-Ray Spectrometer (GRS) has been collecting data with the boom extended since June 2002 and has not quite collected a full Mars year of data in this configuration. Nevertheless, the statistical precision in the polar regions is such that the spatial resolution of the GRS maps are only slightly degraded by having to average over a larger region to improve the signal-to-noise ratio. Especially in the northern region, clear spatially resolved regions of different apparent ice contents can be resolved. For example in the region near 315E E. longitude, near the mouth of Chasma Boreale, has distinctly less ice (or deeper ice) than do the regions of similar latitude but at other longitudes. Although less easily resolved, it appears that the region around the Olympia Planitia also has less ice than regions surrounding it. In the case of Olympia Planitia, the hydrogen gamma ray signal is lower even than regions more equatorward at the same longitude. We have completed a detailed examination of the ground-truth calibration of the GRS by comparing the signal to that expected from a pure water ice northern residual cap. Doing so allows us to set accurate limits on the distribution of ice (really ice equivalent hydrogen) abundance with depth. Over much of the north polar region we can set limits that the distribution of ice with depth. If we assume the ice is buried beneath a hydrogen-poor dust layer, we can also set a limit on how deep the ice can be buried by assuming the lower ice-rich layer is pure ice. In this case the ice cannot be buried by more than 10 to 20 g/cm2 of hydrogen-poor dust, otherwise the gamma-ray flux would be too weak to account for the observed signal. If, on the other hand, we make the assumption that there is no dust layer to attenuate the gamma-ray signal, the ice content must be between 35% and 50% ice by mass. Because it is likely that there is at

  12. Polar Cap Disturbances: Mesosphere and Thermosphere-Ionosphere Response to Solar-Terrestrial Interactions

    NASA Technical Reports Server (NTRS)

    Sivjee, G.; McEwen, D.; Walterscheid, R.

    2003-01-01

    The Polar Cap is the Upper-Atmosphere cum Mag-netosphere region which is enclosed by the poleward boundary of the Auroral Oval and is threaded by open geomagnetic tield lines. In this region, there is normally a steady precipition (Polar "drizzle") of low energy (w 300eV) electrons that excite optical emissions from the ionosphere. At times, enhanced ionization patches are formed near the Dayside Cusp regions that drift across the Polar Cap towards the Night Sector of the Auroral Oval. Discrete auroral arcs and auroras formed during Solar Magnetic Cloud (SMC)/Coronal Mass Ejection (CME) events are also observed in the Polar Cap. Spectrophotometric observations of all these Polar Cap phenomena provide a measure of the average energy as well a energy flux of the electrons precipitating in the Polar Cap region during these disturbances. Such measurements also point to modulations of the Polar Cap Mesosphere-Lower Thermosphere (MLT) air density and temperature by zonally symmetric tides whose Hough functions peak in the Polar region. MLT cooling during Stratospheric Warming events and their relation to Polar Vortex and associated Gravity wave activities are also observed at the Polar Cap sites.

  13. Sedimentation waves on the Martian North Polar Cap: Analogy with megadunes in Antarctica

    NASA Astrophysics Data System (ADS)

    Herny, C.; Massé, M.; Bourgeois, O.; Carpy, S.; Le Mouélic, S.; Appéré, T.; Smith, I. B.; Spiga, A.; Rodriguez, S.

    2014-10-01

    Complex interactions between katabatic winds and the cryosphere may lead to the formation of sedimentation waves at the surface of ice sheets. These have been first described and named snow megadunes in Antarctica. Here we use topographic data, optical images, subsurface radar soundings and spectroscopic data acquired by Mars orbiters, to show that the surface of the Martian North Polar Cap displays two superimposed sets of sedimentation waves with differing wavelengths. These sedimentation waves have similarities with Antarctic snow megadunes regarding their surface morphology, texture, grain size asymmetry, and internal stratigraphic architecture. Both sets of Martian sedimentation waves present young ice and occasional sastrugi fields, indicative of net accumulation, on their shallow-dipping upwind sides, their tops and the intervening troughs. Old layers of dusty ice, indicative of net ablation, are exhumed on the steep-dipping downwind sides of the larger waves. Smooth surfaces of coarse-grained ice, indicative of reduced accumulation associated with sublimation metamorphism, cover the steep-dipping downwind sides of the smaller waves. These surface characteristics and the internal stratigraphy revealed by radar soundings are consistent with the interpretation that both sets of Martian sedimentation waves grow and migrate upwind in response to the development of periodic accumulation/ablation patterns controlled by katabatic winds. The recognition of these sedimentation waves provides the basis for the development of a common model of ice/wind interaction at the surface of Martian and terrestrial glaciers. Martian smaller waves, characterized by reduced net accumulation on their downwind sides, are analogous to Antarctic snow megadunes that have been described so far. A terrestrial equivalent remains to be discovered for the larger Martian waves, characterized by net ablation on their downwind sides.

  14. 3-D Radar Imaging Reveals Deep Structures and Buried Craters Within the Martian Polar Caps

    NASA Astrophysics Data System (ADS)

    Putzig, N. E.; Foss, F. J., II; Campbell, B. A.; Phillips, R. J.; Smith, I. B.

    2015-12-01

    We use Shallow Radar (SHARAD) observations on thousands of orbital passes by the Mars Reconnaissance Orbiter to produce fully imaged 3-D data volumes encompassing both polar ice caps of Mars. Greatly clarifying the view of subsurface features, a completed volume for Planum Boreum provides new constraints on the nature and timing of emplacement of the northern polar deposits and their relationship to climate. The standard method of mapping subsurface features with single-pass 2-D radargrams has been very fruitful (see Brothers et al. 2015, JGR 120 in press, and references therein), but a full assessment of internal structures has been hindered by interfering off-nadir echoes from spiral troughs and other variable topography prevalent on both caps. By assembling the SHARAD radargrams into a volume and applying a 3-D imaging process (migration) borrowed from seismic processing techniques, we enhance the signal-to-noise ratio while repositioning the echoes to their proper locations, thereby unraveling the interference. As part of the process, we correct ionospheric distortions and delays of the radar echoes (Campbell et al. 2014, IEEE GRSL 11 #3). Interfaces painstakingly mapped in radargrams (e.g., the basal-unit surface, a buried chasma) are clearly visible in the 3-D volume, and new features are revealed. Structures may now be mapped through trough-rich regions, including a widespread sequence that provides corroborative evidence of recent ice ages (Smith et al. 2015, LPSC XLVI #2574). Distinctive radar signatures associated with known, partially buried craters also occur elsewhere in the volume but without surface expression. Presumably, these are fully buried craters that may provide a new means to estimate the age of the deposits. Preliminary work for Planum Australe demonstrates that the 3-D processing currently underway will illuminate deep structures that are broadly obfuscated in 2-D radargrams by a shallow scatterer (Campbell et al. 2015, LPSC XLVI #2366).

  15. Complex Burial and Exhumation of South Polar Cap Pitted Terrain

    NASA Technical Reports Server (NTRS)

    2000-01-01

    This image is illuminated by sunlight from the upper left. The two prominent bright stripes at the left/center of the image are covered with bright frost and thus create the illusion that they are sunlit from the lower left.

    The large pits, troughs, and 'swiss cheese' of the south polar residual cap appear to have been formed in the upper 4 or 5 layers of the polar material. Each layer is approximately 2 meters (6.6 feet) thick. Some Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) images of this terrain show examples in which older pitted and eroded layers have been previously buried and are now being exhumed. The example shown here includes two narrow, diagonal slopes that trend from upper left toward lower right at the left/center portion of the frame. Along the bottoms of these slopes are revealed a layer that underlies them in which there are many more pits and troughs than in the upper layer. It is likely in this case that the lower layer formed its pits and troughs before it was covered by the upper layer. This observation suggests that the troughs, pits, and 'swiss cheese' features of the south polar cap are very old and form over long time scales.

    The picture is located near 84.6oS, 45.1oW, and covers an area 3 km by 5 km (1.9 x 3.1 mi) at a resolution of about 3.8 meters (12 ft) per pixel. The image was taken during southern spring on August 29, 1999.

    Malin Space Science Systems and the California Institute of Technology built the MOC using spare hardware from the Mars Observer mission. MSSS operates the camera from its facilities in San Diego, CA. The Jet Propulsion Laboratory's Mars Surveyor Operations Project operates the Mars Global Surveyor spacecraft with its industrial partner, Lockheed Martin Astronautics, from facilities in Pasadena, CA and Denver, CO.

  16. Snow algae in an ice core drilled on Grigoriev Ice cap in the Kyrgyz Tien Shen Mountains

    NASA Astrophysics Data System (ADS)

    Honda, M.; Takeuchi, N.; Sera, S.; Fujita, K.; Okamoto, S.; Naoki, K.; Aizen, V. B.

    2012-12-01

    Snow algae are photosynthetic microorganisms and are living on the surfase of glaciers. They grow on melting surface from spring to summer and their biomass and community structure are changed with physical and chemical conditions on glaciers. Ice cores drilled from glaciers also contain snow algae that grew in the past. Studying biomass and community structure of snow algae in ice cores could reveal the temporal variation in snow algae in the past, and also environmental conditions relating propagation of snow algae. In this study, we anlalyzed snow algae preserved in an ice core of Grigoriev Ice cap located in eastern Kyrgyzstan of the central Asia, and to describe their temporal variations for the last 200 years. The ice core drilling was carried out on September in 2007 on the Grigoriev Ice cap in the Kyrgyz Tien Shen Mountains. A 87 m long ice core from the surface to the bedrock was recovered at the top of the ice cap. The core was horizontally cut every 5 cm (total 1212 samples). The samples were melted and preserved as a 3% formalin solution. After the sample water was filtered through a hydrophilized PTFE membrane filter, observed by microscope. Snow algae in the sample water were counting. The algal biomass was represented by the cell number per unit water volume. Here, we showed the results between the surface to the 64 m in depth. We also analyzed the snow algal communities on the surface of the ice cap collected from five different sites from the top down to the terminus. Microscopy revealed that the ice core contained three taxa of filamentous cyanobacteria, an unicellular cyanobacterium, and two green algae. They were also found on the ice or snow surface of the i Ice cap. The quantitative analyses of the algae in the part of upper 64 m deep of the ice core samples revealed that the algal biomass varied significantly and showed many peaks. Furthermore, the biomass profile differed among the taxa. The filamentous cyanobacterium varied from 0.0 to 4

  17. Radiative transfer in layered media: Application to the radar sounding of Martian polar ices. II

    NASA Astrophysics Data System (ADS)

    Ilyushin, Ya. A.

    2007-01-01

    The paper addresses the problem of the retrieval of the physical parameters of the Martian polar ices from the ground-penetrating radar (GPR) measurements. The results of the previous paper [Ilyushin, Y.A., Seu, R., Phillips, R.J., 2005. Subsurface radar sounding of the Martian polar cap: radiative transfer approach. Planet. Space Sci. 53(14-15), 1427-1436, doi: 10.1016/j.pss.2005.08.002] are further developed. Several electrical models of the Martian polar caps are considered, and several radiative transfer models, appropriate for layered media, are reviewed and compared to each other. Both 1D case, applicable to the orbital GPR instruments, and 2D and 3D geometry, applicable to the landed radars, are studied. A technique for retrieval of the average loss in the medium, which can be attributed to the impurities content in the ice, is proposed. The retrieval technique is numerically tested with the exact solutions of electromagnetic equations for the waves in the layered media. Numerical tests show that the loss in the medium can be determined from the observed radar signal in the whole range of values, expected to be the case in Martian polar caps.

  18. Application of Polar Cap (PC) indices in analyses and forecasts of geophysical conditions

    NASA Astrophysics Data System (ADS)

    Stauning, Peter

    2016-07-01

    The Polar Cap (PC) indices could be considered to represent the input of power from the solar wind to the Earth's magnetosphere. The indices have been used to analyse interplanetary electric fields, effects of solar wind pressure pulses, cross polar cap voltages and polar cap diameter, ionospheric Joule heating, and other issues of polar cap dynamics. The PC indices have also been used to predict auroral electrojet intensities and global auroral power as well as ring current intensities. For specific space weather purposes the PC indices could be used to forecast substorm development and predict associated power line disturbances in the subauroral regions. The presentation shall outline the general background for applying the PC indices in analyses or forecasts of solar wind-magnetosphere-ionosphere interactions and provide illustrative examples of the use of the Polar Cap indices in specific cases

  19. Field-Aligned Electric Potential in the Polar Cap

    NASA Astrophysics Data System (ADS)

    Wing, S.; Hildebrand, L.

    2014-12-01

    Reconnection with the interplanetary magnetic field (IMF) on the dayside magnetosphere opens the previously closed Earth's field line, allowing solar wind particles to enter the magnetosphere, some of which precipitate into the ionosphere. As the open-field line ExB convects to the nightside, fewer ions can enter the magnetosphere. As a result, field-aligned (parallel) electric potential increases with latitude to prevent more electrons from entering, in order to maintain charge quasi-neutrality. The APL open-field line model predicts that the parallel potential drop increases from cusp to mantle to polar rain. This trend has been confirmed in a study that compared phase space densities of ACE solar wind electrons to those of DMSP precipitating electrons. However, the same study also found that sometimes there is an anomaly: the parallel potential drop would have the opposite polarity such that solar wind electrons are accelerated downward in the afternoon polar cap. Using DMSP magnetometer and particle precipitation data, we show that this accelerating potential drop can be found often in the poleward upward field-aligned current region. The velocity shear at the magnetopause boundary leads to a voltage drop across the boundary, which drives the upward field-aligned currents. At higher latitude or further away from noon, the field line maps to the magnetopause location that is further down the magnetotail where the magnetosheath velocity shear is higher and density is lower. When the velocity shear and hence field-aligned current density (J//) is too high or density too low, parallel potential develops to accelerate more electron downward, in accordance with Knight relation.

  20. Growth and Decay of the South Polar Residual Cap of Mars

    NASA Astrophysics Data System (ADS)

    Byrne, S.; McEwen, A.; HiRISE Team

    2008-12-01

    The southern residual ice cap (SRC) is composed of high-albedo solid CO2, is a few meters thick and has areas at its margins and in its interior where the underlying water ice of the polar layered deposits shows through. Previous observations show that pits within the SRC expose sections of layering in the CO2 ice (up to 10m thick) and are expanding by meters/year (Thomas et al., Icarus, 2005). The expansion of these pits is a problem as their spatial density and expansion rates indicate that there should be nothing left of the SRC within a century or so. Our analysis of pit expansion rates indicates that they increase during periods of dust-storm activity. The sensitivity of SRC evolution to climate indicates that its stratigraphy is likely also a valuable source of information about recent climate variability. We are using HiRISE data to constrain landscape evolution models of CO2 ice landscapes to quantify the history of the SRC and the connection of its stratigraphy to martian climate. Here we report on two investigations utilizing different models. 1. We use a landscape evolution model to simulate growth of an accumulating CO2 deposit. This model shows pits naturally form in this landscape, without any associated change in climate, due to increases in surface roughness with time and the feedback between slope and ice ablation. Comparison of model results with the current SRC indicates the thickest sections of stratigraphy likely represent up to 100 martian years of accumulation. 2. HiRISE data shows that some pits expand by faster retreat of the lower ice layers, undercutting of the upper bright ice and subsequent mass-wasting. A separate model that can handle topographic overhangs has been developed and is being used to investigate this behavior. Using this model to reproduce the non- circular aspects of the pit-shapes and their expansion rates (which HiRISE can measure as a function of azimuth) constrains properties of the lower CO2 ice layers such as

  1. Mesoscale variability of water vapor, surface ice aging and precipitation in the Martian polar regions

    NASA Astrophysics Data System (ADS)

    Evdokimova, Nadezda; Rodin, Alexander V.; Kuzmin, Ruslan; Fedorova, Anna

    We present the results of analysis of the H2 O and CO2 ices and the atmospheric water vapor distribution in the polar regions of Mars, based on the OMEGA C channel data obtained during the period of MY 26-27. We employ observations of the North polar cap (NPC) obtain during the aphelion campaigns of 26-27 MY, and corresponding South polar cap (SPC) observations obtained during the perihelion season. In both cases ices were mapped using spectral indices corresponding to specific adsorption bands. At the NPC where H2 O ices is presented during the spring-summer season we used square-based index of the 1.5 µm for estimation of the net ice content and one of the 1.25 µm band for the analysis of ice microstructure. At the SPC square indices are unreliable because of contamination of narrow CO2 absorption bands, so the relative depth of 1.5 µm was used for mapping of H2 O ice. CO2 ice was mapped using 1.57 µm band. In both hemispheres, wave-2 and wave-3 structures were observed in the circumpolar regions during limited period of time. At the NPC wave-2 pattern was found in the 1.25 µm index distribution during early aphelion season that presumably reflects enhanced aging rates of the NPC frost caused by cyclonic wind system in the circumpolar vortex, resulting in enlargement of grains in the optically active skin layer. Later in the aphelion season, wave-2 pattern is followed by wave-3 which is a consequence of change of the leading wavenumber in the polar vortex. At the SPC, wave-3 pattern is observed during the shot period when seasonal CO2 ice cap retreats. We interpret this structure as the outcropping of H2 O ice deposits accumulated during south hemisphere for autumn-winter season. Water vapor distribution inferred from OMEGA data also demonstrates zonal variations correlating with such wave structures. GCM simulations with comprehensive treatment of the water cycle reproduce stationary cyclonic eddies during the string-summer, and transient wave-3 system

  2. Electron polar cap and the boundary of open geomagnetic field lines.

    NASA Technical Reports Server (NTRS)

    Evans, L. C.; Stone, E. C.

    1972-01-01

    A total of 333 observations of the boundary of the polar access region for electrons (energies greater than 530 keV) provides a comprehensive map of the electron polar cap. The boundary of the electron polar cap, which should occur at the latitude separating open and closed field lines, is consistent with previously reported closed field line limits determined from trapped-particle data. The boundary, which is sharply defined, seems to occur at one of three discrete latitudes. Although the electron flux is generally uniform across the polar cap, a limited region of reduced access is observed about 10% of the time.

  3. Buried CO2 Ice traces in South Polar Layered Deposits of Mars detected by radar sounder

    NASA Astrophysics Data System (ADS)

    Castaldo, L.; Mège, D.; Orosei, R.; Séjourné, A.

    2014-12-01

    SHARAD (SHAllow RADar) is the subsurface sounding radar provided by the Italian Space Agency (ASI) as a facility instrument to NASA's 2005 Mars Reconnaissance Orbiter (MRO). The Reduced Data Record of SHARAD data covering the area of the South Polar Layered Deposits (SPLD), has been used. The elaboration and interpretation of the data, aimed to estimate electromagnetic properties of surface layers, has been performed in terms of permittivity. The theory of electromagnetic scattering from fractal surfaces, and the estimation of geometric parameters from topographic data by Mars Orbiter Laser Altimeter (MOLA) which was one of five instruments on board the Mars Global Surveyor (MGS) spacecraft, has been used. A deep analysis of inversion has been made on all Mars and extended to the South Polar Caps in order to extract the area with a permittivity constant of CO2 ice. Several corrections have been applied to the data, moreover the calibration of the signal requires the determination of a constant that takes into account the power gain due to the radar system and the surface in order to compensate the power losses due to the orbitographic phenomena. The determination of regions with high probability of buried CO2 ice in the first layer of the Martian surface, is obtained extracting the real part of the permittivity constant of the CO2 ice (~2), estimated by other means. The permittivity of CO2ice is extracted from the Global Permittivity Map of Mars using the global standard deviation of itself as following: ɛCO2ice=ɛCO2ice+ Σ (1)where Σ=±std(ɛMapMars)/2Figure 1(a) shows the south polar areas where the values of the permittivity point to the possibility of a CO2 ice layer. Figure 1(b) is the corresponding geologic map. The comparison between the two maps indicates that the area with probable buried CO2 overlaps Hesperian and Amazonian polar units (Hp, Hesperian plains-forming deposits marked by narrow sinuous, anabranching ridges and irregular depressions, and

  4. Polar sea ice observations by means of microwave radiometry

    NASA Technical Reports Server (NTRS)

    Gloersen, P.; Chang, T. C.; Wilheit, T. T.; Campbell, W. J.

    1973-01-01

    Principles pertinent to the utilization of 1.55 cm wavelength radiation emanating from the surface of the earth for studying the changing characteristics of polar sea ice are briefly reviewed. Recent data obtained at that wavelength with an imaging radiometer on-board the Nimbus 5 satellite are used to illustrate how the seasonal changes in extent of sea ice in both polar regions may be monitored free of atmospheric interference. Within a season, changes in the compactness of the sea ice are also observed from the satellite. Some substantial areas of the Arctic sea ice canopy identified as first-year ice in the past winter were observed not to melt this summer, a graphic illustration of the eventual formation of multiyear ice in the Arctic. Finally, the microwave emissivity of some of the multiyear ice areas near the North Pole was found to increase significantly in the summer, probably due to liquid water content in the firm layer.

  5. Lunar polar ice deposits: scientific and utilization objectives of the Lunar Ice Discovery Mission proposal.

    PubMed

    Duke, Michael B

    2002-03-01

    The Clementine mission has revived interest in the possibility that ice exists in shadowed craters near the lunar poles. Theoretically, the problem is complex, with several possible sources of water (meteoroid, asteroid, comet impact), several possible loss mechanisms (impact vaporization, sputtering, photoionization), and burial by meteorite impact. Opinions of modelers have ranged from no ice to several times 10(16) g of ice in the cold traps. Clementine bistatic radar data have been interpreted in favor of the presence of ice, while Arecibo radar data do not confirm its presence. The Lunar Prospector mission, planned to be flown in the fall of 1997, could gather new evidence for the existence of ice. If ice is present, both scientific and utilitarian objectives would be addressed by a lunar polar rover, such as that proposed to the NASA Discovery program, but not selected. The lunar polar rover remains the best way to understand the distribution and characteristics of lunar polar ice. PMID:11902177

  6. Comparisons of the North Polar Cap of Mars and the Earth's Northern Hemisphere snow cover

    NASA Technical Reports Server (NTRS)

    Foster, J.; Owe, M.; Capen, C.

    1985-01-01

    The boundaries of the polar caps of Mars have been measured on more than 3000 photographs since 1905 from the plate collection at the Lowell Observatory. For the Earth the polar caps have been accurately mapped only since the mid 1960's when satellites were first available to synoptically view the polar regions. The polar caps of both planets wax and wane in response to changes in the seasons, and interannual differences in polar cap behavior on Mars as well as Earth are intimately linked to global energy balance. In this study data on the year to year variations in the extent of the polar caps of Mars and Earth were assembled and analyzed together with data on annual variations in solar activity to determine if associations exist between these data. It was found that virtually no correlation exists between measurements of Mars north polar cap and solar variability. An inverse relationship was found between variations in the size of the north polar caps of Mars and Earth, although only 6 years of concurrent data were available for comparison.

  7. POLAR/TIDE Survey of Thermal O+ Characteristics near 5000km Altitude over the Polar Cap

    NASA Technical Reports Server (NTRS)

    Stevenson, B. A.; Horwitz, J. L.; Su, Y. J.; Elliott, Heather A.; Comfort, Richard H.; Moore, Thomas E.; Giles, Barbara A.; Craven, Paul D.; Chandler, Michael O.; Pollock, Craig J.

    1998-01-01

    We analyze measurements of thermal 0+ parameters from the Thermal Ion Dynamics Experiment (TIDE) on POLAR for April - May, 1996 obtained near 5000 km altitude within the polar cap ionosphere - magnetosphere interface region. Certain aspects of O+ parameters in this region were explored by Su et. al. [1998]. In this report, we hope to extend our understanding of the O+ behavior by examining relationships of densities, parallel velocities, and temperatures to the convection velocities, IMF By and Bz components. Preliminary results with the convection velocities are currently being analyzed. In doing so, we are guided in part by the Cleft Ion Fountain paradigm and model developed by Horwitz and Lockwood [1985] which involves downward O+ flows in the polar magnetosphere.

  8. Landscape Evolution and the Reincarnation of the Residual CO2 Ice Cap of Mars

    NASA Astrophysics Data System (ADS)

    Byrne, S.; Zuber, M.

    2006-12-01

    Observations of the southern residual CO2 cap of Mars reveal a wide range of landforms including flat-floored quasi-circular pits with steep walls (dubbed Swiss-cheese features). Interannual comparisons show that these depressions are expanding laterally at rates of ~2m/yr to ~4m/yr, prompting suggestions of climate change. The residual CO2 ice cap is up to 10m thick and underlain by an involatile basement, it also contains layers roughly 2m thick representing different accumulation episodes in the recent past. Changes in the appearance of the residual ice between the Mariner 9 and Viking missions indicate that the top-most layer was deposited in that time-frame, soon after the global dust storm of 1971. The spatial density of the Swiss-cheese features, and the rate at which they expand, mean that it is unlikely that any part of the residual ice cap is older than a few centuries. Given this, we may ask: how can there be a residual cap present today for us to observe? To answer this and other questions we have developed a model to examine the evolution of a CO2 ice landscape. This model reproduces the morphologies and expansion rates seen in the actual residual CO2 ice cap. Our model results indicate that the fate of CO2 ice surfaces is controlled by their surface roughness. Surface roughness always increases with time, which results in an unstable situation. When the surface roughness exceeds a critical point small pits can begin to develop. The walls of these pits rapidly steepen and begin retreating which enlarges and deepens the pit. This situation always occurs even if the surface of the CO2 slab has a high enough albedo to have a net mass gain each year. Once these pits begin expanding they quickly erode the entire ice slab. When the underlying non-CO2 material is exposed, it will not frost over again if Mars were to repeat like clockwork every year. We conclude that interannual climatic variability is actually a requirement for the continued existence of a

  9. Ice Shelf Modeling: A Cross-Polar Bayesian Statistical Approach

    NASA Astrophysics Data System (ADS)

    Kirchner, N.; Furrer, R.; Jakobsson, M.; Zwally, H. J.

    2010-12-01

    Ice streams interlink glacial terrestrial and marine environments: embedded in a grounded inland ice such as the Antarctic Ice Sheet or the paleo ice sheets covering extensive parts of the Eurasian and Amerasian Arctic respectively, ice streams are major drainage agents facilitating the discharge of substantial portions of continental ice into the ocean. At their seaward side, ice streams can either extend onto the ocean as floating ice tongues (such as the Drygalsky Ice Tongue/East Antarctica), or feed large ice shelves (as is the case for e.g. the Siple Coast and the Ross Ice Shelf/West Antarctica). The flow behavior of ice streams has been recognized to be intimately linked with configurational changes in their attached ice shelves; in particular, ice shelf disintegration is associated with rapid ice stream retreat and increased mass discharge from the continental ice mass, contributing eventually to sea level rise. Investigations of ice stream retreat mechanism are however incomplete if based on terrestrial records only: rather, the dynamics of ice shelves (and, eventually, the impact of the ocean on the latter) must be accounted for. However, since floating ice shelves leave hardly any traces behind when melting, uncertainty regarding the spatio-temporal distribution and evolution of ice shelves in times prior to instrumented and recorded observation is high, calling thus for a statistical modeling approach. Complementing ongoing large-scale numerical modeling efforts (Pollard & DeConto, 2009), we model the configuration of ice shelves by using a Bayesian Hiearchial Modeling (BHM) approach. We adopt a cross-polar perspective accounting for the fact that currently, ice shelves exist mainly along the coastline of Antarctica (and are virtually non-existing in the Arctic), while Arctic Ocean ice shelves repeatedly impacted the Arctic ocean basin during former glacial periods. Modeled Arctic ocean ice shelf configurations are compared with geological spatial

  10. Changes of the Arctic Ice Caps from ICESat and GRACE - A study of mass balance.

    NASA Astrophysics Data System (ADS)

    Nilsson, Johan; Sandberg Sørensen, Louise; Barletta, Valentina Roberta; Forsberg, René

    2013-04-01

    Data from ICESat, compared with GRACE data, were used to estimate the mass balance of the smaller Arctic ice caps on Svalbard, Iceland and the Canadian Arctic from the years 2003-2009. In this study we used the repeat track method to estimate the surface elevation change of the Arctic ice caps from ICESat altimetry. The GRACE mass balance was obtained using a point mass modeling method, which allowed a better separation of the dominant signal from the Greenland Ice Sheet. In the ICESat part of the study we used several different methods for estimating the mass balance. The methods where based on both interpolation and extrapolation of the elevation change estimates over the ice caps, using both parametric and non-parametric approaches. We found that all Arctic ice caps show a consistent negative mass balance from the year 2003-2009. Ranging from -3 to -26 Gt/yr from the ICESat estimates for the different regions, which is in good agreement with the GRACE results. Also found is that the choice of method used for the ICESat analysis can have a significant impact on the mass balance.