139 research outputs found
HyBIS: Windows Guest Protection through Advanced Memory Introspection
Effectively protecting the Windows OS is a challenging task, since most
implementation details are not publicly known. Windows has always been the main
target of malwares that have exploited numerous bugs and vulnerabilities.
Recent trusted boot and additional integrity checks have rendered the Windows
OS less vulnerable to kernel-level rootkits. Nevertheless, guest Windows
Virtual Machines are becoming an increasingly interesting attack target. In
this work we introduce and analyze a novel Hypervisor-Based Introspection
System (HyBIS) we developed for protecting Windows OSes from malware and
rootkits. The HyBIS architecture is motivated and detailed, while targeted
experimental results show its effectiveness. Comparison with related work
highlights main HyBIS advantages such as: effective semantic introspection,
support for 64-bit architectures and for latest Windows (8.x and 10), advanced
malware disabling capabilities. We believe the research effort reported here
will pave the way to further advances in the security of Windows OSes
A Raman lidar at La Reunion (20.8° S, 55.5° E) for monitoring water vapour and cirrus distributions in the subtropical upper troposphere: preliminary analyses and description of a future system
A ground-based Rayleigh lidar has provided continuous observations of tropospheric water vapour profiles and cirrus cloud using a preliminary Raman channels setup on an existing Rayleigh lidar above La Reunion over the period 2002–2005. With this instrument, we performed a first measurement campaign of 350 independent water vapour profiles. A statistical study of the distribution of water vapour profiles is presented and some investigations concerning the calibration are discussed. Analysis regarding the cirrus clouds is presented and a classification has been performed showing 3 distinct classes. Based on these results, the characteristics and the design of a future lidar system, to be implemented at the new Reunion Island altitude observatory (2200 m) for long-term monitoring, is presented and numerical simulations of system performance have been realised to compare both instruments
Arctic stratospheric dehydration – Part 2: Microphysical modeling
Large areas of synoptic-scale ice PSCs (polar stratospheric clouds)
distinguished the Arctic winter 2009/2010 from other years and revealed
unprecedented evidence of water redistribution in the stratosphere. A unique
snapshot of water vapor repartitioning into ice particles was obtained under
extremely cold Arctic conditions with temperatures around 183 K.
Balloon-borne, aircraft and satellite-based measurements suggest that
synoptic-scale ice PSCs and concurrent reductions and enhancements in water
vapor are tightly linked with the observed de- and rehydration signatures,
respectively. In a companion paper (Part 1), water vapor and aerosol
backscatter measurements from the RECONCILE (Reconciliation of essential
process parameters for an enhanced predictability of Arctic stratospheric
ozone loss and its climate interactions) and LAPBIAT-II (Lapland
Atmosphere–Biosphere Facility) field campaigns have been analyzed in detail.
This paper uses a column version of the Zurich Optical and Microphysical box
Model (ZOMM) including newly developed NAT (nitric acid trihydrate) and ice
nucleation parameterizations. Particle sedimentation is calculated in order
to simulate the vertical redistribution of chemical species such as water and
nitric acid. Despite limitations given by wind shear and uncertainties in the
initial water vapor profile, the column modeling unequivocally shows that (1)
accounting for small-scale temperature fluctuations along the trajectories is
essential in order to reach agreement between simulated optical cloud properties and
observations, and (2) the use of recently developed heterogeneous ice
nucleation parameterizations allows the reproduction of the observed signatures of
de- and rehydration. Conversely, the vertical redistribution of
water measured cannot be explained in terms of homogeneous nucleation of ice clouds,
whose particle radii remain too small to cause significant dehydration
Tropopause and hygropause variability over the equatorial Indian Ocean during February and March 1999.
Measurements of temperature, water vapor, total water, ozone, and cloud properties were made above the western equatorial Indian Ocean in February and March 1999. The cold-point tropopause was at a mean pressure-altitude of 17 km, equivalent to a potential temperature of 380 K, and had a mean temperature of 190 K. Total water mixing ratios at the hygropause varied between 1.4 and 4.1 ppmv. The mean saturation water vapor mixing ratio at the cold point was 3.0 ppmv. This does not accurately represent the mean of the measured total water mixing ratios because the air was unsaturated at the cold point for about 40% of the measurements. As well as unsaturation at the cold point, saturation was observed above the cold point on almost 30% of the profiles. In such profiles the air was saturated with respect to water ice but was free of clouds (i.e., backscatter ratio <2) at potential temperatures more than 5 K above the tropopause and hygropause. Individual profiles show a great deal of variability in the potential temperatures of the cold point and hygropause. We attribute this to short timescale and space-scale perturbations superimposed on the seasonal cycle. There is neither a clear and consistent “setting” of the tropopause and hygropause to the same altitude by dehydration processes nor a clear and consistent separation of tropopause and hygropause by the Brewer-Dobson circulation. Similarly, neither the tropopause nor the hygropause provides a location where conditions consistently approach those implied by a simple “tropopause freeze drying” or “stratospheric fountain” hypothesis
Nitric acid trihydrate nucleation and denitrification in the Arctic stratosphere
Nitric acid trihydrate (NAT) particles in the polar stratosphere have been
shown to be responsible for vertical redistribution of reactive nitrogen
(NO<sub>y</sub>). Recent observations by Cloud–Aerosol Lidar with Orthogonal
Polarization (CALIOP) aboard the CALIPSO satellite have been explained in
terms of heterogeneous nucleation of NAT on foreign nuclei, revealing this to
be an important formation pathway for the NAT particles. In state of the art
global- or regional-scale models, heterogeneous NAT nucleation is currently
simulated in a very coarse manner using a constant, saturation-independent
nucleation rate. Here we present first simulations for the Arctic winter
2009/2010 applying a new saturation-dependent parametrisation of
heterogeneous NAT nucleation rates within the Chemical Lagrangian Model of
the Stratosphere (CLaMS). The simulation shows good agreement of chemical
trace species with in situ and remote sensing observations. The simulated polar stratospheric cloud (PSC)
optical properties agree much better with CALIOP observations than those
simulated with a constant nucleation rate model. A comparison of the
simulated particle size distributions with observations made using the
Forward Scattering Spectrometer Probe (FSSP) aboard the high altitude
research aircraft Geophysica, shows that the model reproduces the observed
size distribution, except for the very largest particles above 15 μm diameter. The vertical NO<sub>y</sub> redistribution caused by the
sedimentation of the NAT particles, in particular the denitrification and
nitrification signals observed by the ACE-FTS satellite instrument and the
in situ SIOUX instrument aboard the Geophysica, are reproduced by the
improved model, and a small improvement with respect to the constant
nucleation rate model is found
Validation of water vapour profiles from the Atmospheric Chemistry Experiment (ACE)
International audienceThe Atmospheric Chemistry Experiment (ACE) mission was launched in August 2003 to sound the atmosphere by solar occultation. Water vapour (H2O), one of the most important molecules for climate and atmospheric chemistry, is one of the key species provided by the two principal instruments, the infrared Fourier Transform Spectrometer (ACE-FTS) and the MAESTRO UV-Visible spectrometer (ACE-MAESTRO). The first instrument performs measurements on several lines in the 1362?2137 cm?1 range, from which vertically resolved H2O concentration profiles are retrieved, from 7 to 90 km altitude. ACE-MAESTRO measures profiles using the water absorption band in the near infrared part of the spectrum at 926.0?969.7 nm. This paper presents a comprehensive validation of the ACE-FTS profiles. We have compared the H2O volume mixing ratio profiles with space-borne (SAGE II, HALOE, POAM III, MIPAS, SMR) observations and measurements from balloon-borne frostpoint hygrometers and a ground based lidar. We show that the ACE-FTS measurements provide H2O profiles with small retrieval uncertainties in the stratosphere (better than 5% from 15 to 70 km, gradually increasing above). The situation is unclear in the upper troposphere, due mainly to the high variability of the water vapour volume mixing ratio in this region. A new water vapour data product from the ACE-MAESTRO (Measurement of Aerosol Extinction in the Stratosphere and Troposphere Retrieved by Occultation) is also presented and initial comparisons with ACE-FTS are discussed
The SPARC Water Vapor Assessment II: assessment of satellite measurements of upper tropospheric humidity
Nineteen limb-viewing data sets (occultation, passive thermal, and UV scattering) and two nadir upper tropospheric humidity (UTH) data sets are intercompared and also compared to frost-point hygrometer balloon sondes. The upper troposphere considered here covers the pressure range from 300–100 hPa. UTH is a challenging measurement, because concentrations vary between 2–1000 ppmv (parts per million by volume), with sharp changes in vertical gradients near the tropopause. Cloudiness in this region also makes the measurement challenging. The atmospheric temperature is also highly variable ranging from 180–250 K. The assessment of satellite-measured UTH is based on coincident comparisons with balloon frost-point hygrometer sondes, multi-month mapped comparisons, zonal mean time series comparisons, and coincident satellite-to-satellite comparisons. While the satellite fields show similar features in maps and time series, quantitatively they can differ by a factor of 2 in concentration, with strong dependencies on the amount of UTH. Additionally, time-lag response-corrected Vaisala RS92 radiosondes are compared to satellites and the frost-point hygrometer measurements. In summary, most satellite data sets reviewed here show on average ∼30 % agreement amongst themselves and frost-point data but with an additional ∼30 % variability about the mean bias. The Vaisala RS92 sonde, even with a time-lag correction, shows poor behavior for pressures less than 200 hPa
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