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1.
We used Mars Express HRSC and OMEGA data to investigate mesospheric cloud features observed in the equatorial belt of Mars from December 2007 until early March 2008. This period corresponds to early northern spring of Martian year 29. The reflection peak at 4.26 μm in OMEGA data identifies the clouds as CO2 ice clouds. HRSC observed the clouds together with OMEGA in five orbits. Cloud features are most prominent in the shortwave HRSC colour channels with wavelength centers at 440 and 530 nm, but rarely visible in all other channels. In the period of Ls 0-36°, OMEGA and HRSC together detected mesospheric CO2 ice clouds in 40 orbits. They occur in a latitude belt of ±20° around the equator and at longitudes between 240°E (Tharsis) in the West and 30°E (Sinus Meridiani) in the East. The clouds were observed between 3 and 5 p.m. local time with mainly ripple-like to filamentary cloud forms. The viewing angles of the HRSC blue and green colour channels differ by 6.6° and the resulting parallax can be used to directly measure cloud heights by means of ray intersection. 17 HRSC data takes were found to exhibit clouds with heights from 66 to 83 km with an accuracy of 1-2 km. The pushbroom imaging technique also yields a time delay for the two observations in the order of 5-15 s close to periapsis, and therefore time-related cloud movements can be detected. A method was developed to determine the across-track cloud displacements, which can directly be translated to wind velocities. Zonal cloud movements could be measured in 13 cases and were oriented from East to West. Related wind speeds range between 60 and 93 m/s with an accuracy of 10-13 m/s.  相似文献   

2.
We present measurements of the altitude and eastward velocity component of mesospheric clouds in 35 imaging sequences acquired by the Mars Odyssey (ODY) spacecraft’s Thermal Emission Imaging System visible imaging subsystem (THEMIS-VIS). We measure altitude by using the parallax drift of high-altitude features, and the velocity by exploiting the time delay in the THEMIS-VIS imaging sequence.We observe two distinct classes of mesospheric clouds: equatorial mesospheric clouds observed between 0° and 180° Ls; and northern mid-latitude clouds observed only in twilight in the 200–300° Ls period. The equatorial mesospheric clouds are quite rare in the THEMIS-VIS data set. We have detected them in only five imaging sequences, out of a total of 2048 multi-band equatorial imaging sequences. All five fall between 20° south and 0° latitude, and between 260° and 295° east longitude. The mid-latitude mesospheric clouds are apparently much more common; for these we find 30 examples out of 210 northern winter mid-latitude twilight imaging sequences. The observed mid-latitude clouds are found, with only one exception, in the Acidalia region, but this is quite likely an artifact of the pattern of THEMIS-VIS image targeting. Comparing our THEMIS-VIS images with daily global maps generated from Mars Orbiter Camera Wide Angle (MOC-WA) images, we find some evidence that some mid-latitude mesospheric cloud features correspond to cloud features commonly observed by MOC-WA. Comparing the velocity of our mesospheric clouds with a GCM, we find good agreement for the northern mid-latitude class, but also find that the GCM fails to match the strong easterly winds measured for the equatorial clouds.Applying a simple radiative transfer model to some of the equatorial mesospheric clouds, we find good model fits in two different imaging sequences. By using the observed radiance contrast between cloud and cloud-free regions at multiple visible-band wavelengths, these fits simultaneously constrain the optical depths and particles sizes of the clouds. The particle sizes are constrained primarily by the relative contrasts at the available wavelengths, and are found to be quite different in the two imaging sequences: reff = 0.1 μm and reff = 1.5 μm. The optical depths (constrained by the absolute contrasts) are substantial: 0.22 and 0.5, respectively. These optical depths imply a mass density that greatly exceeds the saturated mass density of water vapor at mesospheric temperatures, and so the aerosol particles are probably composed mainly of CO2 ice. Our simple radiative transfer model is not applicable to twilight, when the mid-latitude mesospheric clouds were observed, and so we leave the properties of these clouds as a question for further work.  相似文献   

3.
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 km2) 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 accompanying increase in near surface atmospheric stability may be related to the annual minimum of polar storm activity near northern summer solstice.  相似文献   

4.
The Mars Global Surveyor Mars Orbiter Camera was used to obtain global maps of the martian surface with equatorial resolution of 7.5 km/pixel in two wavelength ranges: blue (400-450 nm) and red (575-625 nm). The maps used were acquired between March 15, 1999 (Ls=110°) and July 31, 2001 (Ls=205°), corresponding to approximately one and a quarter martian years. Using the global maps, cloud area (in km2) has been measured daily for water ice clouds topographically corresponding to Olympus Mons, Ascraeus Mons, Pavonis Mons, Arsia Mons, Alba Patera, the western Valles Marineris canyon system, and for other small surface features in the region. Seasonal trends in cloud activity have been established for the three Tharsis volcanoes, Olympus Mons, and Alba Patera. Olympus, Ascraeus, and Pavonis Mons show cloud activity from about Ls=0°-220° with a peak in cloud area near Ls=100°. One of our most interesting observational results is that Alba Patera shows a double peaked feature in the cloud area with peaks at Ls=60° and 140° and a minimum near Ls=100°. Arsia Mons shows nearly continuous cloud activity. The altitudes of several of these clouds have been determined from the locations of the visual cloud tops, and optical depths were measured for a number of them using the DISORT code of Stamnes et al. (1988, Appl. Opt. 27, 2502-2509). Several aspects of the observations (e.g., cloud heights, effects of increased dust on cloud activity) are similar to simulations in Richardson et al. (2002, J. Geophys. Res. 107, 5064). A search for short period variations in the cloud areas revealed only indirect evidence for the diurnal cloud variability in the afternoon hours; unambiguous evidence for other periodicities was not found.  相似文献   

5.
The interval from Ls = 330° in Mars Year (MY) 26 until Ls = 84° in MY 27 has been used to compare and validate measurements from the Mars Global Surveyor Thermal Emission Spectrometer (TES) and the Mars Express Planetary Fourier Spectrometer (PFS). We studied differences between atmospheric temperatures observed by the two instruments. The best agreement between atmospheric temperatures was found at 50 Pa between 40°S and 40°N latitude, where differences were within ±5 K. For other atmospheric levels, differences as large as ∼25 K were observed between the two instruments at some locations. The largest temperature differences occurred mainly over the Hellas Planitia, Argyre Planitia, Tharsis and Valles Marineris regions.On this basis we report on the variability of the martian atmosphere during the 5.5 martian years of Mars climatology obtained by combining the two data sets from TES and PFS. Atmospheric temperatures at 50 Pa responded to the global-scale dust storms of MY 25 and in MY 28 raising temperatures from ∼220 K to ∼250 K during the daytime. An atmospheric temperature of ∼140 K at 50 Pa was observed poleward of 70°N during northern winter and poleward of 60°S during southern winter each year in both the PFS and TES results. Water vapor observed by the two spectrometers showed consistent seasonal and latitudinal variations.  相似文献   

6.
Michael D Smith 《Icarus》2004,167(1):148-165
We use infrared spectra returned by the Mars Global Surveyor Thermal Emission Spectrometer (TES) to retrieve atmospheric and surface temperature, dust and water ice aerosol optical depth, and water vapor column abundance. The data presented here span more than two martian years (Mars Year 24, Ls=104°, 1 March 1999 to Mars Year 26, Ls=180°, 4 May 2003). We present an overview of the seasonal (Ls), latitudinal, and longitudinal dependence of atmospheric quantities during this period, as well as an initial assessment of the interannual variability in the current martian climate. We find that the perihelion season (Ls=180°-360°) is relatively warm, dusty, free of water ice clouds, and shows a relatively high degree of interannual variability in dust optical depth and atmospheric temperature. On the other hand, the aphelion season (Ls=0°-180°) is relatively cool, cloudy, free of dust, and shows a low degree of interannual variability. Water vapor abundance shows a moderate amount of interannual variability at all seasons, but the most in the perihelion season. Much of the small amount of interannual variability that is observed in the aphelion season appears to be caused by perihelion-season planet-encircling dust storms. These dust storms increase albedo through deposition of bright dust on the surface causing cooler daytime surface and atmospheric temperatures well after dust optical depth returns to prestorm values.  相似文献   

7.
We have used the complete set of Mars Global Surveyor (MGS) Mars Daily Global Maps (MDGMs) to study martian weather in the southern hemisphere, focusing on curvilinear features, including frontal events and streaks. “Frontal events” refer to visible events that are morphologically analogous to terrestrial baroclinic storms. MDGMs show that visible frontal events were mainly concentrated in the 210-300°E (60-150°W) sector and the 0-60°E sector around the southern polar cap during Ls = 140-250° and Ls = 340-60°. The non-uniform spatial and temporal distributions of activity were also shown by MGS Thermal Emission Spectrometer transient temperature variations near the surface. “Streaks” refer to long curvilinear features in the polar hood or over the polar cap. They are an indicator of the shape of the polar vortex. Streaks in late winter usually show wavy segments between the 180° meridian and Argyre. Model results suggest that the zonal wave number m = 3 eastward traveling waves are important for their formation.  相似文献   

8.
Bruce A. Cantor 《Icarus》2007,186(1):60-96
From 15 September 1997 through 21 January 2006, only a single planet-encircling martian dust storm was observed by MGS-MOC. The onset of the storm occurred on 26 June 2001 (Ls=184.7°), earliest recorded to date. It was initiated in the southern mid-to-low latitudes by a series of local dust storm pulses that developed along the seasonal cap edge in Malea and in Hellas basin (Ls=176.2°-184.4°). The initial expansion of the storm, though asymmetric, was very rapid in all directions (3-32 m s−1). The main direction of propagation, however, was to the east, with the storm becoming planet encircling in the southern hemisphere on Ls=192.3°. Several distinct centers of active dust lifting were associated with the storm, with the longest persisting for 86 sols (Syria-Claritas). These regional storms helped generate and sustain a dust cloud (“haze”), which reached an altitude of about 60 km and a peak opacity of τdust∼5.0. By Ls=197.0°, the cloud had encircled the entire planet between 59.0° S and 60.0° N, obscuring all but the largest volcanoes. The decay phase began around Ls∼200.4° with atmospheric dust concentrations returning to nominal seasonal low-levels at Ls∼304.0°. Exponential decay time constants ranged from 30-117 sols. The storm caused substantial regional albedo changes (darkening and brightening) as a result of the redistribution (removal and deposition) of a thin veneer of surface dust at least 0.1-11.1 μm thick. It also caused changes in meteorological phenomena (i.e., dust storms, dust devils, clouds, recession of the polar caps, and possibly surface temperatures) that persisted for just a few weeks to more than a single Mars year. The redistribution of dust by large annual regional storms might help explain the long period (∼30 years) between the largest planet-encircling dust storms events.  相似文献   

9.
Variations of the upper cloud boundary and the CO, HF, and HCl mixing ratios were observed using the CSHELL spectrograph at NASA IRTF. The observations were made in three sessions (October 2007, January 2009, and June 2009) at early morning and late afternoon on Venus in the latitude range of ±60°. CO2 lines at 2.25 μm reveal variations of the cloud aerosol density (∼25%) and scale height near 65 km. The measured reflectivity of Venus at low latitudes is 0.7 at 2.25 μm and 0.028 at 3.66 μm, and the effective CO2 column density is smaller at 3.66 μm than those at 2.25 μm by a factor of 4. This agrees with the almost conservative multiple scattering at 2.25 μm and single scattering in the almost black aerosol at 3.66 μm. The expected difference is just a factor of (1 − g)−1 = 4, where g = 0.75 is the scattering asymmetry factor for Venus’ clouds. The observed CO mixing ratio is 52 ± 4 ppm near 08:00 and 40 ± 4 ppm near 16:30 at 68 km, and the higher ratio in the morning may be caused by extension of the CO morningside bulge to the cloud tops. The observed weak limb brightening in CO indicates an increase of the CO mixing ratio with altitude. HF is constant at 3.5 ± 0.2 ppb at 68 km in both morningside and afternoon observations and in the latitude range ±60°. Therefore the observations do not favor a bulge of HF, though HF is lighter than CO. Probably a source in the upper atmosphere facilitates the bulge formation. The recent measurements of HCl near 70 km are controversial (0.1 and 0.74 ppm) and require either a strong sink or a strong source of HCl in the clouds. The HCl lines of the (2-0) band are blended by the solar and telluric lines. Therefore we observed the P8 lines of the (1-0) band at 3.44 μm. These lines are spectrally clean and result in the HCl mixing ratio of 0.40 ± 0.03 ppm at 74 km. HCl does not vary with latitude within ±60°. Our observations support a uniformly mixed HCl throughout the Venus atmosphere.  相似文献   

10.
F. Altieri  L. Zasova  G. Bellucci  B. Gondet 《Icarus》2009,204(2):499-511
We present a method to derive the 2D maps of the O2 (a1Δg) airglow emission at 1.27 μm from the OMEGA/MEx nadir observations. The OMEGA imaging capabilities allow monitoring the 2D distribution, daily and seasonal variation of the O2 emission intensities with a detection limit of 4 MR. The highest values, of the order of ∼31 MR, are found on the south pole for 11 h < LT < 13 h, during the early spring (186° < Ls < 192°) of martian year (MY) 27, according to the Mars Year numbering scheme of Clancy et al. [Clancy, R.T., Wolff, M.J., Christensen, P.R., 2003. Mars aerosol studies with the MGS TES emission phase function observations: Optical depths, particle sizes, and ice cloud types versus latitude and solar longitude. J. Geophys. Res. 108. doi: 10.1029/2003JE002058]. In the polar regions the day-by-day variability, associated with polar vortex turbulences, is obtained of the order of 30-50% as predicted by the model [Lefévre, F., Lebonnois, S., Montmessin, F., Forget, F., 2004. Three-dimensional modeling of ozone on Mars. J. Geophys. Res. 109, E07004. doi: 10.1029/2004JE002268] and found by SPICAM [Perrier, S., Bertaux, J.-L., Lebonnois, S., Korablev, O., Fedorova, A., 2006. Global distribution of total ozone on Mars from SPICAM/MEX UV measurements. J. Geophys. Res. 111, E09S06. doi: 10.1029/2006JE002681]. In the considered set of data a maximum of the O2 emission is observed between 11 h and 15 h LT in the latitude range 70-85° during early spring on both hemispheres, while for the southern autumn-winter season a maximum is found between 50° and 60° in the southern hemisphere for MY28. Increase of intensity of the O2 emission observed from Ls 130° to 160° at southern high latitudes may be explained by increase of solar illumination conditions in the maps acquired during the considered period.Atmospheric waves crossing the terminator on the southern polar regions are observed for the first time during the MY28 early spring. The spatial scale of the waves ranges from 100 to 130 km, and the intensity fluctuations are of the order of 4MR.This study confirms the high potentiality of O2 (a1Δg) day glow as a passive tracer of the martian atmosphere dynamics at high latitudes.  相似文献   

11.
Michael D. Smith 《Icarus》2009,202(2):444-452
We use infrared images obtained by the Thermal Emission Imaging System (THEMIS) instrument on-board Mars Odyssey to retrieve the optical depth of dust and water ice aerosols over more than 3.5 martian years between February 2002 (MY 25, Ls=330°) and December 2008 (MY 29, Ls=183°). These data provide an important bridge between earlier TES observations and recent observations from Mars Express and Mars Reconnaissance Orbiter. An improvement to our earlier retrieval [Smith, M.D., Bandfield, J.L., Christensen, P.R., Richardson, M.I., 2003. J. Geophys. Res. 108, doi:10.1029/2003JE002114] to include atmospheric temperature information from THEMIS Band 10 observations leads to much improved retrievals during the largest dust storms. The new retrievals show moderate dust storm activity during Mars Years 26 and 27, although details of the strength and timing of dust storms is different from year to year. A planet-encircling dust storm event was observed during Mars Year 28 near Southern Hemisphere Summer solstice. A belt of low-latitude water ice clouds was observed during the aphelion season during each year, Mars Years 26 through 29. The optical depth of water ice clouds is somewhat higher in the THEMIS retrievals at ∼5:00 PM local time than in the TES retrievals at ∼2:00 PM, suggestive of possible local time variation of clouds.  相似文献   

12.
Atmospheric water vapor abundances in Mars’ north polar region (NPR, from 60° to 90°N) are mapped as function of latitude and longitude for spring and summer seasons, and their spatial, seasonal, and interannual variability is discussed. Water vapor data are from Mars Global Surveyor (MGS) Thermal Emission Spectrometer (TES) and the Viking Orbiter (VO) Mars Atmospheric Water Detector (MAWD). The data cover three complete northern spring-summer seasons in 1977-1978, 2000-2001 and 2002-2003, and shorter periods of spring-summer seasons during 1975, 1999 and 2004. Long term interannual variability in the averaged NPR abundances may exist, with Viking MAWD observations showing twice as much water vapor during summer as the MGS TES observations more than 10 martian years (MY) later. While the averaged abundances are very similar in TES observations for the same season in different years, the spatial distributions in the early summer season do vary significantly year over year. Spatial and temporal variabilities increase between Ls ∼ 80-140°, which may be related to vapor sublimation from the North Polar Residual Cap (NPRC), or to changes in circulation. Spatial variability is observed on scales of ∼100 km and temporal variability is observed on scales of <10 sols during summer. During late spring the TES water vapor spatial distribution is seen to correlate with the low topography/low albedo region of northern Acidalia Planitia (270-360°E), and with the dust spatial distribution across the NPR during late spring-early summer. Non-uniform vertical distribution of water vapor, a regolith source or atmospheric circulation ‘pooling’ of water vapor from the NPRC into the topographic depression may be behind the correlation with low topography/low albedo. Sublimation winds carrying water vapor off the NPRC and lifting surface dust in the areas surrounding the NPRC may explain the correlation between the water vapor and dust spatial distributions. Correlation between water vapor and dust in MAWD data are only observed over low topography/low albedo area. Maximum water vapor abundances are observed at Ls = 105-115° and outside of the NPRC at 75-80°N; the TES data, however, do not extend over the NPRC and thus, this conclusion may be biased. Some water vapor appears to be released in plumes or ‘outbursts’ in the MAWD and TES datasets during late spring and early summer. We propose that the sublimation rate of ice varies across the NPRC with varying surface winds, giving rise to the observed ‘outbursts’ at some seasons.  相似文献   

13.
Mesospheric clouds have been previously observed on Mars in a variety of datasets. However, because the clouds are optically thin and most missions have performed surface-focussed nadir sounding, geographic and seasonal coverage is sparse. We present new detections of mesospheric clouds using a limb spectra dataset with global coverage acquired by NASA’s Mars Climate Sounder (MCS) aboard Mars Reconnaissance Orbiter. Mesospheric aerosol layers, which can be CO2 ice, water ice or dust clouds, cause high radiances in limb spectra, either by thermal emission or scattering of sunlight. We employ an object recognition and classification algorithm to identify and map aerosol layers in limb spectra acquired between December 2006 and April 2011, covering more than two Mars years. We use data from MCS band A4, to show thermal signatures of day and nightside features, and A6, which is sensitive to short wave IR and visible daytime features only. This large dataset provides several thousand detections of mesospheric clouds, more than an order of magnitude more than in previous studies.Our results show that aerosol layers tend to occur in two distinct regimes. They form in equatorial regions (30°S–30°N) during the aphelion season/northern hemisphere summer (Ls < 150°), which is in agreement with previous published observations of mesospheric clouds. During perihelion/dust storm season (Ls > 150°) a greater number of features are observed and are distributed in two mid-latitude bands, with a southern hemisphere bias. We observe temporal and longitudinal clustering of cloud occurrence, which we suggest is consistent with a formation mechanism dictated by interaction of broad temperature regimes imposed by global circulation and the propagation to the mesosphere of small-scale dynamics such as gravity waves and thermal tides.Using calculated frost point temperatures and a parameterization based on synthetic spectra we find that aphelion clouds are present in generally cooler conditions and are spectrally more consistent with H2O or CO2 ice. A significant fraction has nearby temperature retrievals that are within a few degrees of the CO2 frost point, indicating a CO2 composition for those clouds. Perihelion season clouds are spectrally most similar to H2O ice and dust aerosols, consistent with temperature retrievals near to the clouds that are 30–80 K above the CO2 frost point.  相似文献   

14.
A distinctive terrain named cryptic region which is characterized by regions of low albedo and low temperature has been identified on the Martian south polar cap. In this zone, many fan- and spider-shaped features of km-scale appeared following the sublimation of the CO2 frost layer. These peculiar features were apparently caused by a wind-blown system of dust-laden jets. During the warming period starting at Ls∼180°, the seasonal ice cap regresses and fans and spiders appear in sequence. These surface features are repeatable events that tend to occupy the same areas from year to year. In this study, we use the Mars Orbiter camera (MOC) narrow-angle images to produce a statistical study of the time distributions of the fans and spiders as functions of Ls and as functions of the topography. The time variations and spatial distributions of these features are further correlated with the CO2 ice coverage measured by the Mars Orbiter laser altimeter (MOLA) instrument. We have documented that most of the fans are found in the early spring with Ls<230° and the fans and spiders coexist at Ls=250°±20°. It is also found that there is a strong dependence on latitude and altitude with fans and spiders most often observed at high latitude (>83°S) and high altitude (>2500 m). Our statistical result also indicates that the occurrence of fans is highly correlated with the thickness of the CO2 frost thus providing support for the venting model.  相似文献   

15.
Different missions have observed mesospheric clouds on Mars in the last years. The presence of these clouds implies, among other conditions, mesospheric temperatures below CO2 condensation temperature. We use a General Circulation Model to study the mesospheric temperatures and compare the observed distribution of the mesospheric clouds and the predicted climatology of mesospheric temperatures. Although the model does not usually predict temperatures below condensation for daytime conditions, in some regions the predicted temperatures are close enough to condensation that perturbations caused by small scale processes could produce local excursions below condensation. The location and time of the lowest temperatures predicted by the GCM correspond to a first order with the two observed populations of mesospheric clouds: equatorial clouds observed before and after the Northern summer solstice, and mid-latitude clouds observed around the Northern winter solstice. For the equatorial clouds season, the model predicts temperatures close to condensation at the longitude, latitude, altitude and local time where they have been observed. We find that the diurnal migrating thermal tide and non-migrating tides are at the root of the spatial confinement of the equatorial clouds. For the mid-latitude clouds season, the temperatures predicted by the model at the location of the observed clouds is too high. Stereo observations by two different instruments allow for the determination of the zonal speed of these clouds producing a rare dataset of mesospheric winds. We compare the mesospheric zonal winds predicted by the model with these observations, finding a good agreement, although in some cases the observed variability exceeds that predicted by the model.  相似文献   

16.
Mars Global Surveyor (MGS) visible (solarband bolometer) and thermal infrared (IR) spectral limb observations from the Thermal Emission Spectrometer (TES) support quantitative profile retrievals for dust opacity and particle sizes during the 2001 global dust event on Mars. The current analysis considers the behavior of dust lifted to altitudes above 30 km during the course of this storm; in terms of dust vertical mixing, particle sizes, and global distribution. TES global maps of visible (solarband) limb brightness at 60 km altitude indicate a global-scale, seasonally evolving (over 190-240° solar longitudes, LS) longitudinal corridor of vertically extended dust loading (which may be associated with a retrograde propagating, wavenumber 1 Rossby wave). Spherical radiative transfer analysis of selected limb profiles for TES visible and thermal IR radiances provide quantitative vertical profiles of dust opacity, indicating regional conditions of altitude-increasing dust mixing ratios. Observed infrared spectral dependences and visible-to-infrared opacity ratios of dust scattering over 30-60 km altitudes indicate particle sizes characteristic of lower altitudes (cross-section weighted effective radius, ), during conditions of significant dust transport to these altitudes. Conditions of reduced dust loading at 30-60 km altitudes present smaller dust particle sizes . These observations suggest rapid meridional transport at 30-80 km altitudes, with substantial longitudinal variation, of dust lifted to these altitudes over southern hemisphere atmospheric regions characterized by extraordinary (m/s) vertical advection velocities. By LS=230° dust loading above 50 km altitudes decreased markedly at southern latitudes, with a high altitude (60-80 km) haze of fine (likely) water ice particles appearing over 10°S-40°N latitudes.  相似文献   

17.
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18.
Venus was observed at 2.4 and 3.7 μm with a resolving power of 4×104 using the long-slit high-resolution spectrograph CSHELL at NASA IRTF. The observations were made along a chord that covered a latitude range of ± 60° at a local time near 8:00. The continuous reflectivity and limb brightening at 2.4 μm are fitted by the clouds with a single scattering albedo 1−a=0.01 and a pure absorbing layer with τ=0.09 above the clouds. The value of 1−a agrees with the refractive index of H2SO4 (85%) and the particle radius of 1 μm. The absorbing layer is similar to that observed by the UV spectrometer at the Pioneer Venus orbiter. However, its nature is puzzling. CO2 was measured using its R32 and R34 lines. The retrieved product of the CO2 abundance and airmass is constant at 1.9 km-atm along the instrument slit in the latitude range of ± 60°. The CO mixing ratio (measured using the P21 line) is rather constant at 70 ppm, and its variations of ∼10% may be caused by atmospheric dynamics. The observed value is higher than the 50 ppm retrieved previously from a spectrum of the full disk, possibly, because of some downward extension of the mesospheric morningside bulge of CO. The observations of the HF R3 line reveal a constant HF mixing ratio of 3.5±0.5 ppb within ± 60° of latitude, which is within the scatter in the previous measurements of HF. OCS has been detected for the first time at the cloud tops by summing 17 lines of the P-branch. The previous detections of OCS refer to the lower atmosphere at 30-35 km. The retrieved OCS mixing ratio varies with a scale height of 1 to 3 km. The mean OCS mixing ratio is ∼2 ppb at 70 km and ∼14 ppb at 64 km. Vertical motions in the atmosphere may change the OCS abundance. The detected OCS should significantly affect Venus' photochemistry. A sensitive search for H2S using its line at 2688.93 cm−1 results in a 3 sigma upper limit of 23 ppb, which is more restrictive than the previous limit of 100 ppb.  相似文献   

19.
We present lightcurve observations and multiband photometry for 107P/Wilson-Harrington using five small- and medium-sized telescopes. The lightcurve has shown a periodicity of 0.2979 day (7.15 h) and 0.0993 day (2.38 h), which has a commensurability of 3:1. The physical properties of the lightcurve indicate two models: (1) 107P/Wilson-Harrington is a tumbling object with a sidereal rotation period of 0.2979 day and a precession period of 0.0993 day. The shape has a long axis mode (LAM) of L1:L2:L3 = 1.0:1.0:1.6. The direction of the total rotational angular momentum is around λ = 310°, β = −10°, or λ = 132°, β = −17°. The nutation angle is approximately constant at 65°. (2) 107P/Wilson-Harrington is not a tumbler. The sidereal rotation period is 0.2979 day. The shape is nearly spherical but slightly hexagonal with a short axis mode (SAM) of L1:L2:L3 = 1.5:1.5:1.0. The pole orientation is around λ = 330°, β = −27°. In addition, the model includes the possibility of binary hosting. For both models, the sense of rotation is retrograde. Furthermore, multiband photometry indicates that the taxonomy class of 107P/Wilson-Harrington is C-type. No clear rotational color variations are confirmed on the surface.  相似文献   

20.
We report the observation of a cloud system on Titan that remained localized near 40°S latitude and 60°W longitude for at least 34 h. Ground-based observations obtained with the SINFONI imaging spectrograph at the Very Large Telescope over four consecutive nights recorded the lifetime and altitude of the unresolved cloud system. Concomitant measurements made by Cassini/VIMS over 3 h resolved changes in the altitude and opacity of individual regions within the system during this time. Clouds are measured from 13 to 37 km altitude with optical depths per pixel ranging from τ=0.13 to 7. Short timescale rise times are consistent with previous measurements of the evolution of mid-latitude clouds; however the long timescale localization of the cloud structure is unexplained. We speculate about the role of mesoscale circulation in relation to cloud formation.  相似文献   

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