Inter annual variability of dry air in tropical free troposphere

International audienceAs a dominant greenhouse gas, water vapor plays a key role in Earth's climate. Particularly in the low concentration regions, were sensitivity of outgoing long wave radiation is more important than in the moist regions like the in the mid troposphere. Thus, it is important to document and understand the water vapor spatiotemporal variability in the dry regions of the intertropical belt. In these regions the distribution of water vapor is controlled by large-scale dynamics that mixes air originating from the mid-latitude and from the Tropics. While the mechanism have been identified from theoretical studies, its role in explaining the variability at inter annual scale is still unclear. In the dry subtropical regions, the distribution of water vapor departs from Gaussian statistics. So, the arithmetical average is unsuitable to characterize the humidity field and its variability. In order to better apprehend this, the dry air occurrences is computed, using Relative Humidity at 500 hPa from NCEP reanalysis (RH500), to focus on the dry tail distribution of water vapor. We examined the inter annual variability of this dry air index during boreal summer (June-August) and winter (December-February) of the period 1978-2007. Then the study is focused on the subtropical dry air behaviour during the well know tropical inter annual mode of variability El Nino Southern Oscillation (ENSO). Indeed, the first mode of an Empirical Orthogonal Function on the dry occurrences of humidity in the tropical belt, which describes approximately 15 % of the inter annual variance, shows a strong ENSO pattern with important response in Pacific area. The relative role of temperature and moisture in shaping the variability and the changes in the dry occurrences of relative humidity is investigated. Relative Humidity is computed fixing interannual temperature constant and equal to the climatological mean (RH''500) and compared to the original distribution. The results show insignificant differences between the two variables, suggesting an important role of the water vapor content variability in explaining the variability of RH and a limited contribution of the temperature. This is further analyzed by using outputs from an advection-condensation model based on back trajectories computed from the NCEP wind field. The origin of dry air in regions of interest during ENSO events is then revealed. Some features of the last saturations regions are shown to be robust to the El Nino or La Nina phase. Beyond the Pacific Ocean region, signature of ENSO are weak and other atmospheric variability modes (e.g., NAO) are investigated to explain the inter annual variability there and will be presented at the conference

Inter annual variability of dry air in tropical free troposphere

International audienceAs a dominant greenhouse gas, water vapor plays a key role in Earth's climate. Particularly in the low concentration regions, were sensitivity of outgoing long wave radiation is more important than in the moist regions like the in the mid troposphere. Thus, it is important to document and understand the water vapor spatiotemporal variability in the dry regions of the intertropical belt. In these regions the distribution of water vapor is controlled by large-scale dynamics that mixes air originating from the mid-latitude and from the Tropics. While the mechanism have been identified from theoretical studies, its role in explaining the variability at inter annual scale is still unclear. In the dry subtropical regions, the distribution of water vapor departs from Gaussian statistics. So, the arithmetical average is unsuitable to characterize the humidity field and its variability. In order to better apprehend this, the dry air occurrences is computed, using Relative Humidity at 500 hPa from NCEP reanalysis (RH500), to focus on the dry tail distribution of water vapor. We examined the inter annual variability of this dry air index during boreal summer (June-August) and winter (December-February) of the period 1978-2007. Then the study is focused on the subtropical dry air behaviour during the well know tropical inter annual mode of variability El Nino Southern Oscillation (ENSO). Indeed, the first mode of an Empirical Orthogonal Function on the dry occurrences of humidity in the tropical belt, which describes approximately 15 % of the inter annual variance, shows a strong ENSO pattern with important response in Pacific area. The relative role of temperature and moisture in shaping the variability and the changes in the dry occurrences of relative humidity is investigated. Relative Humidity is computed fixing interannual temperature constant and equal to the climatological mean (RH''500) and compared to the original distribution. The results show insignificant differences between the two variables, suggesting an important role of the water vapor content variability in explaining the variability of RH and a limited contribution of the temperature. This is further analyzed by using outputs from an advection-condensation model based on back trajectories computed from the NCEP wind field. The origin of dry air in regions of interest during ENSO events is then revealed. Some features of the last saturations regions are shown to be robust to the El Nino or La Nina phase. Beyond the Pacific Ocean region, signature of ENSO are weak and other atmospheric variability modes (e.g., NAO) are investigated to explain the inter annual variability there and will be presented at the conference

Inter annual variability of dry air in tropical free troposphere

International audienceAs a dominant greenhouse gas, water vapor plays a key role in Earth's climate. Particularly in the low concentration regions, were sensitivity of outgoing long wave radiation is more important than in the moist regions like the in the mid troposphere. Thus, it is important to document and understand the water vapor spatiotemporal variability in the dry regions of the intertropical belt. In these regions the distribution of water vapor is controlled by large-scale dynamics that mixes air originating from the mid-latitude and from the Tropics. While the mechanism have been identified from theoretical studies, its role in explaining the variability at inter annual scale is still unclear. In the dry subtropical regions, the distribution of water vapor departs from Gaussian statistics. So, the arithmetical average is unsuitable to characterize the humidity field and its variability. In order to better apprehend this, the dry air occurrences is computed, using Relative Humidity at 500 hPa from NCEP reanalysis (RH500), to focus on the dry tail distribution of water vapor. We examined the inter annual variability of this dry air index during boreal summer (June-August) and winter (December-February) of the period 1978-2007. Then the study is focused on the subtropical dry air behaviour during the well know tropical inter annual mode of variability El Nino Southern Oscillation (ENSO). Indeed, the first mode of an Empirical Orthogonal Function on the dry occurrences of humidity in the tropical belt, which describes approximately 15 % of the inter annual variance, shows a strong ENSO pattern with important response in Pacific area. The relative role of temperature and moisture in shaping the variability and the changes in the dry occurrences of relative humidity is investigated. Relative Humidity is computed fixing interannual temperature constant and equal to the climatological mean (RH''500) and compared to the original distribution. The results show insignificant differences between the two variables, suggesting an important role of the water vapor content variability in explaining the variability of RH and a limited contribution of the temperature. This is further analyzed by using outputs from an advection-condensation model based on back trajectories computed from the NCEP wind field. The origin of dry air in regions of interest during ENSO events is then revealed. Some features of the last saturations regions are shown to be robust to the El Nino or La Nina phase. Beyond the Pacific Ocean region, signature of ENSO are weak and other atmospheric variability modes (e.g., NAO) are investigated to explain the inter annual variability there and will be presented at the conference

Studies of voluntary visual attention: Theory, methods, and psychometric issues

The paper discusses the study of voluntary visual attention (VVA), a relatively new area of active experimentation. VVA concerns "natural" viewing behavior or visual browsing when the subject is under no constraints regarding the distribution of attention. This is contrasted with traditional studies of directed visual attention, such as the typical study of visual judgment in tachistoscopic research. Discussed are (1) the logic of investigating VVA, (2) a comprehensive set of constructs that are thought to be of theoretical importance, (3) methods for calibrating these variables in terms of treatment parameters, (4) the logic of scaling both independent and dependent variables, (5) a summary of salient findings, (6) some recent findings not previously reported, and (7) an overview of the psychometric issues in the study of VVA

Factors Effecting the Fate and Transport of CL-20 in the Vadose Zone and Groundwater: Final Report 2002 - 2004 SERDP Project CP-1255

This SERDP-funded project was initiated to investigate the fate of CL-20 in the subsurface environment, with a focus on identification and quantification of geochemical and microbial reactions of CL-20. CL-20 can be released to the surface and subsurface terrestrial environment by: a) manufacturing processes, b) munition storage, and c) use with low order detonation or unexploded ordnance. The risk of far-field subsurface migration was assessed through labora-tory experiments with a variety of sediments and subsurface materials to quantify processes that control CL-20 sorption-limited migration and degradation. Results of this study show that CL-20 will exhibit differing behavior in the subsurface terrestrial environment: 1. CL-20 on the sediment surface will photodegrade and interact with plants/animals (described in other SERDP projects CU 1254, 1256). CL-20 will exhibit greater sorption in humid sediments to organic matter. Transport will be solubility limited (i.e., low CL-20 aqueous solubility). 2. CL-20 infiltration into soils (<2 m) from spills will be subject to sorption to soil organic matter (if present), and low to high biodegradation rates (weeks to years) depending on the microbial population (greater in humid environment). 3. CL-20 in the vadose zone (>2 m) will be, in most cases, subject to low sorption and low degradation rates, so would persist in the subsurface environment and be at risk for deep migration. Low water content in arid regions will result in a decrease in both sorption and the degradation rate. Measured degradation rates in unsaturated sediments of years would result in significant subsurface migration distances. 4. CL-20 in groundwater will be subject to some sorption but likely very slow degradation rates. CL-20 sorption will be greater than RDX. Most CL-20 degradation will be abiotic (ferrous iron and other transition metals), because most deep subsurface systems have extremely low natural microbial populations. Degradation rates will range from weeks (iron reducing systems) to years. Although CL-20 will move rapidly through most sediments in the terrestrial environment, subsurface remediation can be utilized for cleanup. Transformation of CL-20 to intermediates can be rapidly accomplished under: a) reducing conditions (CL-20 4.1 min. half-life, RDX 18 min. half-life), b) alkaline (pH >10) conditions, and c) bioremediation with added nutrients. CL-20 degradation to intermediates may be insufficient to mitigate environmental impact, as the toxicity of many of these compounds is unknown. Biostimulation in oxic to reducing systems by carbon and nutrient addition can mineralize CL-20, with the most rapid rates occurring under reducing conditions