The water vapour distribution in the Arctic lowermost stratosphere during the LAUTLOS campaign and related transport processes including stratosphere-troposphere exchange

International audienceBalloon-borne water vapour measurements during January and February 2004, which were obtained as part of the LAUTLOS campaign at Sodankylä, Finland, 67° N, were used to analyse the water vapour distribution in the wintertime Arctic lowermost stratosphere. A 2.5 km thick layer (or 30 K in the potential temperature scale) above the tropopause is characterized by a significant water vapour variability on a synoptic timescale with values between stratospheric and tropospheric, which is in good agreement with previously reported measurements. A cross-correlation analysis of ozone and water vapour confirms that this layer contains a mixture of stratospheric and tropospheric air masses. Some of the flights sampled laminae of enhanced water vapour above the tropopause. Meteorological analyses and backward trajectory calculations show that these features were related to filaments that had developed along the flanks of cut-off anticyclones, which had been active at this time over the Northern Atlantic. The role of the filaments was however not to transport water vapour from the troposphere to the stratosphere but rather to transport it within the stratosphere away from regions where intensive two-way stratosphere-troposphere exchange (STE) was identified. Intensive STE occurred around cut-off anticyclones in regions of strong winds, where calculations suggest the presence of clear-air turbulence (CAT). Evidences that CAT contributes to the troposphere-to-stratosphere transport (TST) are presented. However, statistically, relation between TST and CAT during the studied period is weak

The water vapour distribution in the Arctic lowermost stratosphere during LAUTLOS campaign and related transport processes including stratosphere-troposphere exchange

International audienceBalloon-borne water vapour measurements during January and February 2004, which were obtained as part of the LAUTLOS campaign at Sodankylä, Finland, 67° N, were used to analyse the water vapour distribution in the wintertime Arctic lowermost stratosphere. A 2.5 km thick layer (or 30 K in the potential temperature scale) above the local tropopause is characterized by a significant water vapour variability on a synoptic timescale with values between stratospheric and tropospheric, which is in good agreement with previously reported measurements. A cross-correlation analysis of ozone and water vapour confirms that this layer contains a mixture of stratospheric and tropospheric air masses. Some of the flights sampled laminae of enhanced water vapour above the tropopause. Meteorological analyses and backward trajectory calculations show that these features are related to filaments that had developed along the flanks of cut-off anticyclones, which had been active at this time over the Northern Atlantic. Cross-tropopause mass fluxes calculated following the Wei method are used to identify regions and processes that are important for stratosphere-troposphere exchange (STE) in high-latitudes. Intensive STE occurs around cut-off anticyclones in regions of strong winds, where calculations suggest the presence of developed clear-air turbulence. The decay of the filaments is also shown to be important for STE

How stratospheric are deep stratospheric intrusions? LUAMI 2008

A large-scale comparison of water-vapour vertical-sounding instruments took place over central Europe on 17 October 2008, during a rather homogeneous deep stratospheric intrusion event (LUAMI, Lindenberg Upper-Air Methods Intercomparison). The measurements were carried out at four observational sites: Payerne (Switzerland), Bilthoven (the Netherlands), Lindenberg (north-eastern Germany), and the Zugspitze mountain (Garmisch-Partenkichen, German Alps), and by an airborne water-vapour lidar system creating a transect of humidity profiles between all four stations. A high data quality was verified that strongly underlines the scientific findings. The intrusion layer was very dry with a minimum mixing ratios of 0 to 35 ppm on its lower west side, but did not drop below 120 ppm on the higher-lying east side (Lindenberg). The dryness hardens the findings of a preceding study (“Part 1”, Trickl et al., 2014) that, e.g., 73 % of deep intrusions reaching the German Alps and travelling 6 days or less exhibit minimum mixing ratios of 50 ppm and less. These low values reflect values found in the lowermost stratosphere and indicate very slow mixing with tropospheric air during the downward transport to the lower troposphere. The peak ozone values were around 70 ppb, confirming the idea that intrusion layers depart from the lowermost edge of the stratosphere. The data suggest an increase of ozone from the lower to the higher edge of the intrusion layer. This behaviour is also confirmed by stratospheric aerosol caught in the layer. Both observations are in agreement with the idea that sections of the vertical distributions of these constituents in the source region were transferred to central Europe without major change. LAGRANTO trajectory calculations demonstrated a rather shallow outflow from the stratosphere just above the dynamical tropopause, for the first time confirming the conclusions in “Part 1” from the Zugspitze CO observations. The trajectories qualitatively explain the temporal evolution of the intrusion layers above the four stations participating in the campaign

MemShield: GPU-assisted software memory encryption

Cryptographic algorithm implementations are vulnerable to Cold Boot attacks, which consist in exploiting the persistence of RAM cells across reboots or power down cycles to read the memory contents and recover precious sensitive data. The principal defensive weapon against Cold Boot attacks is memory encryption. In this work we propose MemShield, a memory encryption framework for user space applications that exploits a GPU to safely store the master key and perform the encryption/decryption operations. We developed a prototype that is completely transparent to existing applications and does not require changes to the OS kernel. We discuss the design, the related works, the implementation, the security analysis, and the performances of MemShield.Comment: 14 pages, 2 figures. In proceedings of the 18th International Conference on Applied Cryptography and Network Security, ACNS 2020, October 19-22 2020, Rome, Ital

Laboratory evaluation of the effect of nitric acid uptake on frost point hygrometer performance

Chilled mirror hygrometers (CMH) are widely used to measure water vapour in the troposphere and lower stratosphere from balloon-borne sondes. Systematic discrepancies among in situ water vapour instruments have been observed at low water vapour mixing ratios (<5 ppm) in the upper troposphere and lower stratosphere (UT/LS). Understanding the source of the measurement discrepancies is important for a more accurate and reliable determination of water vapour abundance in this region. We have conducted a laboratory study to investigate the potential interference of gas-phase nitric acid (HNO<sub>3</sub>) with the measurement of frost point temperature, and consequently the water vapour mixing ratio, determined by CMH under conditions representative of operation in the UT/LS. No detectable interference in the measured frost point temperature was found for HNO<sub>3</sub> mixing ratios of up to 4 ppb for exposure times up to 150 min. HNO<sub>3</sub> was observed to co-condense on the mirror frost, with the adsorbed mass increasing linearly with time at constant exposure levels. Over the duration of a typical balloon sonde ascent (90–120 min), the maximum accumulated HNO<sub>3</sub> amounts were comparable to monolayer coverage of the geometric mirror surface area, which corresponds to only a small fraction of the actual frost layer surface area. This small amount of co-condensed HNO<sub>3</sub> is consistent with the observed lack of HNO<sub>3</sub> interference in the frost point measurement because the CMH utilizes significant reductions (>10%) in surface reflectivity by the condensate to determine H<sub>2</sub>O

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