Les effets directs et semi-directs des aérosols sur le climat régional du sud de l'Afrique pendant la saison d'hiver austral

Le modèle climatique régional RegCM3 est utilisépour examiner les effets direct et semi-direct des aérosols sur le climat du sud de l'Afrique pendant l'hiver austral (juin-septembre). La sensibilité des effets simulés aux différents inventaires d'émissions de combustion de biomasse et aux différentes conditions aux limites est evaluer, afin d'estimer l'incertitude associée à ces paramètres. La sensibilité aux conditions aux limites derivées de réanalyses est modeste, mais le forçage radiatif des aérosols varie linéairement en réponse au différents inventaires testées jusqu'à un facteur deux. Le forçage radiatif est toujours négatif, alors que le forçage radiatif au sommet de l'atmosphère est negatif sur la plupart du domaine sauf au-dessus les régions de savane ou le contenu atmosphérique d'aérosols est élevée. Même si la magnitude du forçage radiatif varie, les simulations pour la période présente montrent des impacts climatiques comparables. La température de surface diminue sur la plupart de la région, ce signale qui réduit le biais du modèle sur l'ouest du sous-continent. L'échauffement en altitude est lié à la charge d'aérosols absorbants et cela, en combinaison avec la réduction de température en surface, mène à la stabilisation de la basse atmosphère. Toutefois, dans la moyenne troposphère de la zone équatoriale (entre 8°N et 5°S) cet échauffement à pour résultat un effet de 'pompe à chaleur en altitude'. Cet effet augmente la convection, les précipitations et l'humidité du sol, en accélérant le cycle hydrologique dans cette région. Une étude de la variabilité interannuelle des effets climatiques des aérosols montre que les changements des précipitations en moyenne saisonnière sont plus variables d'un an à l'autre que les changements de température de surface. Par contre, malgré des différences significatives entre les conditions synoptiques, la variabilité synoptique des impacts climatiques des aérosols est faible.The regional climate model RegCM3 is used to investigate the direct and semi-direct aerosol effects on the southern African climate during the austral winter season (June-September). The sensitivity of simulated aerosol-climate effects to different biomass burning inventories, boundary conditions and sea surface temperature (SST) feedbacks is tested to assess the range of uncertainty associated with these parameters. Little sensitivity to boundary forcing is found, while the aerosol radiative forcing (RF) varies approximately linearly by up to a factor of two, in response to the factor of two difference between emissions inventories. In all cases the surface RF is negative, while the top-to-atmosphere RF is negative over most of the domain but positive over high-albedo savannah regions where aerosol loading is high. Sensitivity to SST feedbacks is negligible in RegCM3. Although the magnitude of simulated RF varies, all simulations show similar aerosol-climate impacts. Surface temperature decreases over most of the subcontinent, a signal which acts to reduce model bias over the western half of the region. The absorbing nature of the simulated aerosol burden results in heating at altitude, which, in combination with the surface cooling, serves to increase stability in the lower atmosphere over most of the subcontinent. In the middle troposphere, however, this warming induces an elevated heat-pump effect in the equatorial regions between approximately 8°N and 5°S. This enhances convection, precipitation as well as soil moisture, effectively spinning-up the hydrological cycle in the tropics. An investigation of the interannual variability of the simulated aerosol radiative impacts showed that seasonal average precipitation changes varied more from year to year than aerosol-induced surface temperature changes. In contrast, despite significant differences between synoptic conditions, there is little synoptic-scale variability of aerosol-climate impacts

Direct and semi-direct aerosol effects on the southern African regional climate during the austral winter season

Includes abstract.Includes bibliographical references (p. 195-219).The regional climate model RegCM3 is used to investigate the direct and semi-direct aerosol effects on the southern African climate during the austral winter season (June-September). The sensitivity of simulated aerosol-climate effects to different biomass burning inventories, boundary conditions and sea surface temperature (SST) feedbacks is tested to assess the range of uncertainty associated with these parameters

Trajectory matching of ozonesondes and MOZAIC measurements in the UTLS – Part 2: Application to the global ozonesonde network

Both balloon-borne electrochemical ozonesondes and MOZAIC (measurements of ozone, water vapour, carbon monoxide and nitrogen oxides by in-service Airbus aircraft) provide very valuable data sets for ozone studies in the upper troposphere/lower stratosphere (UTLS). Although MOZAIC's highly accurate UV-photometers are regularly inspected and recalibrated annually, recent analyses cast some doubt on the long-term stability of their ozone analysers. To investigate this further, we perform a 16 yr comparison (1994–2009) of UTLS ozone measurements from balloon-borne ozonesondes and MOZAIC. The analysis uses fully three-dimensional trajectories computed from ERA-Interim (European Centre for Medium-Range Weather Forecasts Re-analysis) wind fields to find matches between the two measurement platforms. Although different sensor types (Brewer-Mast and Electrochemical Concentration Cell ozonesondes) were used, most of the 28 launch sites considered show considerable differences of up to 25% compared to MOZAIC in the mid-1990s, followed by a systematic tendency to smaller differences of around 5–10% in subsequent years. The reason for the difference before 1998 remains unclear, but observations from both sondes and MOZAIC require further examination to be reliable enough for use in robust long-term trend analyses starting before 1998. According to our analysis, ozonesonde measurements at tropopause altitudes appear to be rather insensitive to changing the type of the Electrochemical Concentration Cell ozonesonde, provided the cathode sensing solution strength remains unchanged. Scoresbysund (Greenland) showed systematically 5% higher readings after changing from Science Pump Corporation sondes to ENSCI Corporation sondes, while a 1.0% KI cathode electrolyte was retained

Investigating Person Identification in Security Settings with Virtual Reality

Person identification at airports requires the comparison of a passport photograph with its bearer. In psychology, this process is typically studied with static pairs of face photographs that require identity match (same person shown) versus mismatch (two different people) decisions, but this approach provides a limited proxy for studying how environment and social interaction factors affect this task. This thesis explores the feasibility of virtual reality (VR) as a solution to this problem, by examining the identity matching of avatars in a VR airport. In Chapter 2, facial photographs of real people are successfully rendered into VR avatars in a manner that preserves image and identity information (Experiments 1 to 3). Furthermore, identity matching of avatar pairs reflects similar cognitive processes to the matching of face photographs (Experiments 4 and 5), a pattern which holds when assessed in a VR airport (Experiments 6 and 7). Chapter 3 then examines whether a simulation of a passport control task in VR can provide a useful tool for selecting personnel for real-world tasks (Experiment 8). The classification of identity mismatches, the detection of which is of paramount importance in security settings, correlated across conventional laboratory face matching tests and the VR passport control task. Social interaction factors, such as body language, may further influence face matching performance, which was explored in Chapter 4. Whilst performance was unaffected when observers were not instructed explicitly to utilise body language (Experiments 9 and 10), when instructed body language enhanced detection of identity mismatches yet also increased false classification of matches (Experiments 11 to 13). This effect was driven by increased activity levels rather than body language that simply differed from normal behaviour, and occurred independently of individuals' face-matching ability (Experiment 14). This thesis concludes with a summary of how VR can open up many avenues for face-matching research, by facilitating the study of new environment and social interaction factors that may be relevant in real-world operational settings

The Upper Stratospheric Solar Cycle Ozone Response

The solar cycle (SC) stratospheric ozone response is thought to influence surface weather and climate. To understand the chain of processes and ensure climate models adequately represent them, it is important to detect and quantify an accurate SC ozone response from observations. Chemistry climate models (CCMs) and observations display a range of upper stratosphere (1–10 hPa) zonally averaged spatial responses; this and the recommended data set for comparison remains disputed. Recent data‐merging advancements have led to more robust observational data. Using these data, we show that the observed SC signal exhibits an upper stratosphere U‐shaped spatial structure with lobes emanating from the tropics (5–10 hPa) to high altitudes at midlatitudes (1–3 hPa). We confirm this using two independent chemistry climate models in specified dynamics mode and an idealized timeslice experiment. We recommend the BASICv2 ozone composite to best represent historical upper stratospheric solar variability, and that those based on SBUV alone should not be used

Body Language Influences on Facial Identification at Passport Control: An Exploration in Virtual Reality

Person identification at airports requires the matching of a passport photograph to its bearer. One aim of this process is to find identity impostors, who use valid identity documents of similar-looking people to avoid detection. In psychology, this process has been studied extensively with static pairs of face photographs that require identity match (same person shown) versus mismatch (two different people) decisions. However, this approach provides a limited proxy for studying how other factors, such as nonverbal behaviour, affect this task. The current study investigated the influence of body language on facial identity matching within a virtual reality airport environment, by manipulating activity levels of person avatars queueing at passport control. In a series of six experiments, detection of identity mismatches was unaffected when observers were not instructed to utilise body language. By contrast, under explicit instruction to look out for unusual body language, these cues enhanced detection of mismatches but also increased false classification of matches. This effect was driven by increased activity levels rather than body language that simply differed from the behaviour of the majority of passengers. The implications and limitations of these findings are discussed

Real-time pollen monitoring using digital holography

We present the first validation of the SwisensPoleno, currently the only operational automatic pollen mon-itoring system based on digital holography. The device pro-vides in-flight images of all coarse aerosols, and here wedevelop a two-step classification algorithm that uses theseimages to identify a range of pollen taxa. Deterministiccriteria based on the shape of the particle are applied toinitially distinguish between intact pollen grains and othercoarse particulate matter. This first level of discriminationidentifies pollen with an accuracy of 96 %. Thereafter, in-dividual pollen taxa are recognized using supervised learn-ing techniques. The algorithm is trained using data obtainedby inserting known pollen types into the device, and out ofeight pollen taxa six can be identified with an accuracy ofabove 90 %. In addition to the ability to correctly identifyaerosols, an automatic pollen monitoring system needs to beable to correctly determine particle concentrations. To fur-ther verify the device, controlled chamber experiments us-ing polystyrene latex beads were performed. This providedreference aerosols with traceable particle size and numberconcentrations in order to ensure particle size and samplingvolume were correctly characterized