Investigation of mountain permafrost in the Kozia Dolinka valley,Tatra Mountains,Poland

The Kozia Dolinka valley lies at an altitude above 1900 m a.s.l. on the northern slope of the main ridge of the High Tatra Mountains. Mountain permafrost occurrences were studied with the use of BTS, infrared imaging, water and ground temperature measurements and DC resistivity soundings. The data suggest the existence of isolated patches of permafrost. The lowest observed bottom temperature of winter snow values was in the order of-10C. DC soundings revealed the existence of a high resistivity layer of limited extent. Permafrost seasonal monitoring was conducted with resistivity soundings. Measurements were carried out in spring-autumn 1999, when a distinct change in permafrost thickness was observed.     

基于高光谱资料对FY-1C/1D气象卫星进行交叉定标

介绍了利用AQUA卫星高光谱AIRS资料对FY-1C、FY-1D气象卫星热红外通道进行交叉定标的方法及定标结果。首先利用卫星轨道预报软件预报出AQUA与FY-1C以及AQUA与FY-1D卫星交叉点,再对交叉区域卫星资料进行像元投影和像元匹配,像元匹配包括时间、观测角度、环境均匀性等检验。以AIRS探测结果作为辐射基准,利用其观测值和FY-1卫星热红外通道光谱响应函数进行光谱匹配,最终得到FY-1卫星热红外通道的准真值并与FY-1卫星的业务产品进行比较分析。对FY-1C、FY-1D两年多卫星资料进行多次交叉比对,结果表明FY-1C通道4比AIRS观测亮温低1.3K左右,通道5低3.6K左右;而FY-1D通道4比AIRS观测亮温低0.3K左右,通道5低3.6K左右。这个准真值与FY-1观测的计数值进行再定标得到新的定标系数。     

中国黑碳气溶胶分布特征与辐射强迫的模拟研究

利用区域气候模式RegCM3模拟2000年我国黑碳气溶胶的分布特征和辐射强迫。结果表明,黑碳气溶胶主要分布在我国黄河以南、青藏高原以东的广大区域,柱含量由南向北递减;柱含量最大值在0.6mg／m^2以上,出现在中南、四川盆地、湖南、贵州、广西、广东西部和云南南部等地区;青藏高原南侧黑碳气溶胶次高值区的存在,反映了气溶胶的跨国界输送并影响区域气候的特点。黑碳气溶胶的大气顶辐射强迫介于0.1—0.8w／m^2之间,地表辐射强迫介于-0.1— -2.0W／m^2之间,两者分布特征与柱含量分布特征基本一致。同柱含量相似,黑碳气溶胶大气顸辐射强迫和地表辐射强迫也有明显的季节性变化,春季最大,秋、冬季次之,夏季最小。     

Optical attenuation in fog at a wavelength of 1.55 micrometers

As part of a series of studies on laser propagation for terrestrial free space optical (FSO) telecommunications or laser telecommunications, an experiment was conducted to determine the relationship between visibility in fog and optical attenuation (dB/km) at a laser wavelength of 1.55 μm. In the telecommunications industry, a semi-empirical equation, called the Kruse formula [Kruse, P.W., McGlauchlin, L., McQuistan, R.B., 1962. Elements of infrared technology: generation, transmission, and detection. John Wiley and Sons, New York] is typically used to calculate expected attenuation for a given meteorological visibility. The Kruse formula, however, was developed to relate meteorological visibility to optical attenuation over wavelengths from the visible to the near infrared (IR), and for dust and small particle aerosols with dimensions much smaller than the wavelength. Typically, suspended small aerosols have diameters that average about 0.1 μm while fog droplets have diameters that range upward from 2.5 μm with mean diameters that exceed 10 μm in some fogs. Therefore, application of the Kruse formula to attenuation in fog is not appropriate since fogs consist mainly of particles much larger than the laser wavelength. As part of the experiment, a transmissometer with an 85-m baseline and a dynamic range of 60 dB operated for thirteen months in an area prone to radiation fog. A commercial visibility sensor, similar to those used at airports, was located near the middle of the optical path of the transmissometer and operated over the same period. The largest attenuation measured at this site was just over 300 dB/km, corresponding to a visibility of 32 m. The key finding of the study is that the generally accepted Kruse formula relating visibility and optical attenuation may be too pessimistic at low visibilities, and actual attenuation values for a given visibility may be more than 20% lower than previously thought. At visibilities exceeding about 650 m, the Kruse formula gives a good estimate of optical attenuation.     

An accretion-jet model for 3C 84: Interpreting the spectral energy distribution and Faraday rotation measure

3C 84 is a well-known supermassive black hole that can be used to explore jet and accretion physics. In this work, we model the multiwavelength spectral energy distribution (SED) of the 3C 84, and find that the SED is difficult to fit with pure advection dominated accretion flow (ADAF) or pure jet model. Using a coupled ADAF-jet model to fit the SED of 3C 84, it is found that the radio emission and the millimeter emission can be naturally reproduced by the synchrotron radiation of nonthermal electrons in the jet, and that the X-ray emission may predominantly come from inverse Compton radiation from electrons in ADAF. According to the Rotation Measure (RM) obtained by the polarization observation, we consider the possible location of the polarizing source and found that the calculated RM in the jet is roughly consistent with the observational constraints. These results will help us better understand jets produced by black holes.     

Atomic oxygen distribution in the Venus mesosphere from observations of O2 infrared airglow by VIRTIS-Venus Express

This VIRTIS instrument on board Venus Express has collected spectrally resolved images of the Venus nightside limb that show the presence of the (0,0) band of the infrared atmospheric system of O₂ at 1.27 μm. The emission is produced by three-body recombination of oxygen atoms created by photodissociation of CO₂ on the dayside. It is consistently bright so that emission limb profiles can be extracted from the images. The vertical distribution of O₂() may be derived following Abel inversion of the radiance limb profiles. Assuming photochemical equilibrium, it is combined with the CO₂ vertical distribution to determine the atomic oxygen density. The uncertainties on the O density caused by the Abel inversion reach a few percent at the peak, increasing to about 50% near 120 km. We first analyze a case when the CO₂ density was derived from a stellar occultation observed with the SPICAV spectrometer simultaneously with an image of the O₂ limb airglow. In other cases, an average CO₂ profile deduced from a series of ultraviolet stellar occultations is used to derive the O profile, leading to uncertainties on the O density less than 30%. It is found that the maximum O density is generally located between 94 and 115 km with a mean value of 104 km. It ranges from less than 1×¹⁰¹¹ to about 5×¹⁰¹¹ cm⁻³ with a global mean of 2.2×¹⁰¹¹ cm⁻³. These values are in reasonable agreement with the VIRA midnight oxygen profile. The vertical O distribution is generally in good agreement with the oxygen profile calculated with a one-dimensional chemical-diffusive model. No statistical latitudinal dependence of the altitude of the oxygen peak is observed, but the maximum O density tends to decrease with increasing northern latitudes. The latitudinal distribution at a given time exhibits large variations in the O density profile and its vertical structure. The vertical oxygen distribution frequently shows multiple peaks possibly caused by waves or variations in the structure of turbulent transport. It is concluded that the O₂ infrared night airglow is a powerful tool to map the distribution of atomic oxygen in the mesosphere between 90 and 115 km and improve future Venus reference atmosphere models.     

Titan at 3 microns: Newly identified spectral features and an improved analysis of haze opacity

We have reanalyzed the high-resolution spectrum of Titan between 2.87 and 3.12 μm observed with NIRSPEC/Keck II on 2001 Nov. 21 in southern summer, using updated CH₃D and C₂H₆ line-by-line models. From new synthetic spectra, we identify all but a few of the previously unidentified significant absorption spectral features in this wavelength range as due to these two species, both of which had been previously detected by Voyager and ground-based observations at other wavelengths. We also derive opacities and reflectivities of haze particles as functions of altitude for the 2.87-2.92 μm wavelength range, where Titan's atmosphere is partially transparent down to the surface. The extinction per unit altitude is observed to increase from 100 km (∼8 mbar) toward lower altitude. The derived total optical depth is approximately 1.1 for the 2.87-2.92 μm range. At wavelengths increasing beyond 2.92 μm the haze layers become much more optically thick, and the surface is rapidly hidden from view. These conclusions apply to equatorial and southern-temperate regions on Titan, excluding polar regions. We also find it unlikely that there is a large enhancement of the tropospheric CH₄ mole fraction over the value reported from analysis of the Huygens/GCMS observations.     

Jupiter's hydrocarbon polar brightening: Discovery of 3-micron line emission from south polar CH4, C2H2, and C2H6

Jupiter exhibits bright H⁺₃ auroral arcs at 3-4 microns that cool the hot (>1000 K) ionosphere above the ∼¹⁰−7 bar level through the infrared bands of this trace constituent. Below the ¹⁰−7 bar level significant cooling proceeds through infrared active bands of CH₄, C₂H₂, and C₂H₆. We report the discovery of 3-micron line emission from these hydrocarbon species in spectra of the jovian south polar region obtained on April 18 and 20, 2006 (UT) with CGS4 on the United Kingdom Infrared Telescope. Estimated cooling rates through these molecules are 7.5×¹⁰−3, 1.4×¹⁰−3, and , respectively, for a total nearly half that of H⁺₃. We derive a temperature of 450 ± 50 K in the ¹⁰−7-¹⁰−5 bar region from the C₂H₂ lines.     

A survey of Karin cluster asteroids with the Spitzer Space Telescope

The Karin cluster is one of the youngest known families of main-belt asteroids, dating back to a collisional event only 5.8±0.2 Myr ago. Using the Spitzer Space Telescope we have photometrically sampled the thermal continua (3.5-22 μm) of 17 Karin cluster asteroids of different sizes, down to the smallest members discovered so far, in order to make the first direct measurements of their sizes and albedos and study the physical properties of their surfaces. Our targets are also amongst the smallest main-belt asteroids observed to date in the mid-infrared. The derived diameters range from 17.3 km for 832 Karin to 1.5 km for 75176, with typical uncertainties of 10%. The mean albedo is pv=0.215±0.015, compared to 0.20±0.07 for 832 Karin itself (for H=11.2±0.3), consistent with the view that the Karin asteroids are closely related physically as well as dynamically. The albedo distribution (0.12?pv?0.32) is consistent with the range associated with S-type asteroids but the variation from one object to another appears to be significant. Contrary to the case for near-Earth asteroids, our data show no evidence of an albedo dependence on size. However, the mean albedo is lower than expected for young, fresh “S-type” surfaces, suggesting that space weathering can darken main-belt asteroid surfaces on very short timescales. Our data are also suggestive of a connection between surface roughness and albedo, which may reflect rejuvenation of weathered surfaces by impact gardening. While the available data allow only estimates of lower limits for thermal inertia, we find no evidence for the relatively high values of thermal inertia reported for some similarly sized near-Earth asteroids. Our results constitute the first observational confirmation of the legitimacy of assumptions made in recent modeling of the formation of the Karin cluster via a single catastrophic collision 5.8±0.2 Myr ago.     

Yearly and seasonal variations of low albedo surfaces on Mars in the OMEGA/MEx dataset: Constraints on aerosols properties and dust deposits

The time variations of spectral properties of dark martian surface features are investigated using the OMEGA near-IR dataset. The analyzed period covers two Mars years, spanning from early 2004 to early 2008 (includes the 2007 global dust event). Radiative transfer modeling indicates that the apparent albedo variations of low to mid-latitude dark regions are consistent with those produced by the varying optical depth of atmospheric dust as measured simultaneously from the ground by the Mars Exploration Rovers. We observe only a few significant albedo changes that can be attributed to surface phenomena. They are small-scaled and located at the boundaries between bright and dark regions. We then investigate the variations of the mean particle size of aerosols using the evolution of the observed dark region spectra between 1 and 2.5 μm. Overall, we find that the observed changes in the spectral slope are consistent with a mean particle size of aerosols varying with time between 1 and 2 μm. Observations with different solar zenith angles make it possible to characterize the aerosol layer at different altitudes, revealing a decrease of the particle size of aerosols as altitude increases.