Quantifying TOLNet ozone lidar accuracy during the 2014 DISCOVER-AQ and FRAPPE campaigns

The Tropospheric Ozone Lidar Network (TOLNet) is a unique network of lidar systems that measure high-resolution atmospheric profiles of ozone. The accurate characterization of these lidars is necessary to determine the uniformity of the network calibration. From July to August 2014, three lidars, the TROPospheric OZone (TROPOZ) lidar, the Tunable Optical Profiler for Aerosol and oZone (TOPAZ) lidar, and the Langley Mobile Ozone Lidar (LMOL), of TOLNet participated in the Deriving Information on Surface conditions from Column and Vertically Resolved Observations Relevant to Air Quality (DISCOVER-AQ) mission and the Front Range Air Pollution and Photochemistry Éxperiment (FRAPPÉ) to measure ozone variations from the boundary layer to the top of the troposphere. This study presents the analysis of the intercomparison between the TROPOZ, TOPAZ, and LMOL lidars, along with comparisons between the lidars and other in situ ozone instruments including ozonesondes and a P-3B airborne chemiluminescence sensor. The TOLNet lidars measured vertical ozone structures with an accuracy generally better than ±15 % within the troposphere. Larger differences occur at some individual altitudes in both the near-field and far-field range of the lidar systems, largely as expected. In terms of column average, the TOLNet lidars measured ozone with an accuracy better than ±5 % for both the intercomparison between the lidars and between the lidars and other instruments. These results indicate that these three TOLNet lidars are suitable for use in air quality, satellite validation, and ozone modeling efforts

The California baseline ozone transport study (CABOTS)

Ozone is one of the six criteria pollutants identified by the U.S. Clean Air Act Amendment of 1970 as particularly harmful to human health. Concentrations have decreased markedly across the United States over the past 50 years in response to regulatory efforts, but continuing research on its deleterious effects have spurred further reductions in the legal threshold. The South Coast and San Joaquin Valley Air Basins of California remain the only two extreme ozone nonattainment areas in the United States. Further reductions of ozone in the West are complicated by significant background concentrations whose relative importance increases as domestic anthropogenic contributions decline and the national standards continue to be lowered. These background concentrations derive largely from uncontrollable sources including stratospheric intrusions, wildfires, and intercontinental transport. Taken together the exogenous sources complicate regulatory strategies and necessitate a much more precise understanding of the timing and magnitude of their contributions to regional air pollution. The California Baseline Ozone Transport Study was a field campaign coordinated across Northern and Central California during spring and summer 2016 aimed at observing daily variations in the ozone columns crossing the North American coastline, as well as the modification of the ozone layering downwind across the mountainous topography of California to better understand the impacts of background ozone on surface air quality in complex terrain

Quantifying TOLNet Ozone Lidar Accuracy During the 2014 DISCOVER-AQ and FRAPP Campaigns

The Tropospheric Ozone Lidar Network (TOLNet) is a unique network of lidar systems that measure high-resolution atmospheric profiles of ozone. The accurate characterization of these lidars is necessary to determine the uniformity of the network calibration. From July to August 2014, three lidars, the TROPospheric OZone (TROPOZ) lidar, the Tunable Optical Profiler for Aerosol and oZone (TOPAZ) lidar, and the Langley Mobile Ozone Lidar (LMOL), of TOLNet participated in the Deriving Information on Surface conditions from Column and Vertically Resolved Observations Relevant to Air Quality (DISCOVER-AQ) mission and the Front Range Air Pollution and Photochemistry xperiment (FRAPP) to measure ozone variations from the boundary layer to the top of the troposphere. This study presents the analysis of the intercomparison between the TROPOZ, TOPAZ, and LMOL lidars, along with comparisons between the lidars and other in situ ozone instruments including ozonesondes and a P-3B airborne chemiluminescence sensor. The TOLNet lidars measured vertical ozone structures with an accuracy generally better than 15 % within the troposphere. Larger differences occur at some individual altitudes in both the near-field and far-field range of the lidar systems, largely as expected. In terms of column average, the TOLNet lidars measured ozone with an accuracy better than 5 % for both the intercomparison between the lidars and between the lidars and other instruments. These results indicate that these three TOLNet lidars are suitable for use in air quality, satellite validation, and ozone modeling efforts

Characterizing sources of high surface ozone events in the southwestern US with intensive field measurements and two global models

The detection and attribution of high background ozone (O3) events in the southwestern US is challenging but relevant to the effective implementation of the lowered National Ambient Air Quality Standard (NAAQS; 70&thinsp;ppbv). Here we leverage intensive field measurements from the Fires, Asian, and Stratospheric Transport&minus;Las Vegas Ozone Study (FAST-LVOS) in May&ndash;June&nbsp;2017, alongside high-resolution simulations with two global models (GFDL-AM4 and GEOS-Chem), to study the sources of O3 during high-O3 events. We show possible stratospheric influence on 4 out of the 10 events with daily maximum 8&thinsp;h average (MDA8) surface O3 above 65&thinsp;ppbv in the greater Las Vegas region. While O3 produced from regional anthropogenic emissions dominates pollution events in the Las Vegas Valley, stratospheric intrusions can mix with regional pollution to push surface O3 above 70&thinsp;ppbv. GFDL-AM4 captures the key characteristics of deep stratospheric intrusions consistent with ozonesondes, lidar profiles, and co-located measurements of O3, CO, and water vapor at Angel Peak, whereas GEOS-Chem has difficulty simulating the observed features and underestimates observed O3 by &sim;20&thinsp;ppbv at the surface. On days when observed MDA8 O3 exceeds 65&thinsp;ppbv and the AM4 stratospheric ozone tracer shows 20&ndash;40&thinsp;ppbv enhancements, GEOS-Chem simulates &sim;15&thinsp;ppbv lower US background O3 than GFDL-AM4. The two models also differ substantially during a wildfire event, with GEOS-Chem estimating &sim;15&thinsp;ppbv greater O3, in better agreement with lidar observations. At the surface, the two models bracket the observed MDA8 O3 values during the wildfire event. Both models capture the large-scale transport of Asian pollution, but neither resolves some fine-scale pollution plumes, as evidenced by aerosol backscatter, aircraft, and satellite measurements. US background O3 estimates from the two models differ by 5&thinsp;ppbv on average (greater in GFDL-AM4) and up to 15&thinsp;ppbv episodically. Uncertainties remain in the quantitative attribution of each event. Nevertheless, our multi-model approach tied closely to observational analysis yields some process insights, suggesting that elevated background O3 may pose challenges to achieving a potentially lower NAAQS level (e.g., 65&thinsp;ppbv) in the southwestern US. </div

Évaluation du transport isentropique à travers la barrière dynamique stratosphérique subtropicale de l'hémisphère sud

This thesis focuses on an evaluation of isentropic transport across the subtropical stratospheric dynamical barrier of the southern hemisphere. Our strategy consists in isentropic transport events reconstitution using MIMOSA high-resolution model to advect potential vorticity (PV) fields. This model was initialized by the European model ERA-40 winds and temperature fields computed over 26 years (1980-2005). DYBAL algorithm has calculated dynamical barrier and mixing intensity. Also the k-means algorithm was applied on PV field to reconstitute laminae which is the characteristic form of isentropic transport events. Finally, subtropical barrier permeability was evaluated by following exchanges across this barrier and the distribution of lateral routes determined. Impact of these events on ozone distribution was estimated as the influence of quasi-biennial oscillation and 11-years solar cycle. Results shows on isentrope 600 K an increase of the tropical reservoir and the mid-latitude size with the diminution of the polar vortex. The results indicate also the reduction of exchange intensity across subtropical barrier since the 1980's.Cette thèse est consacrée à l'évaluation des échanges entre le réservoir tropical et les moyennes latitudes au travers de la barrière dynamique stratosphérique subtropicale de l'hémisphère sud. La stratégie consiste à reconstituer le transport sur des surfaces isentropes avec le modèle d'advection de contours à haute résolution MIMOSA. Ce modèle a été alimenté par les champs de vorticité potentielle calculé sur 26 années consécutives (1980-2005) à partir des champs de vents et de température du modèle européen ERA-40. L'algorithme DYBAL a calculé l'intensité des barrières dynamiques (barrière subtropicale et vortex polaire) et du mélange. Couplé à l'algorithme des k-moyennes, il a permis la détection en coordonnées géographiques de la position des barrières et donc le calcul de l'extension méridienne des réservoirs stratosphériques. Cet algorithme a également été utilisé pour reconstituer les épisodes filamentaires caractéristiques du transport isentrope. Enfin, la perméabilité de la barrière subtropicale a été évaluée par le suivi des échanges et les routes privilégiées de ces échanges ont été mises en évidence. L'implication de ces événements sur le transport de l'ozone a été estimée ainsi que l'influence de l'oscillation quasi-biennale (QBO) et du cycle solaire de 11 ans. Les résultats présentent la variabilité dynamique de la stratosphère sur l'isentrope 600 K et montrent une augmentation de la taille du réservoir tropical et des moyennes latitudes en correspondance avec le rétrécissement du vortex polaire. Une diminution de l'intensité des échanges à travers la barrière dynamique subtropicale depuis les années 1980 est également mise en évidence

First Ozonesonde Measurements at Kerguelen Island (49.2°S 70.1°E) Radiosondages Ozone Complementaires aux Kerguelen ROCK campaign 2008-2009 (Polar International Year - IPEV)

International audienceCommunication about First Ozonesonde Measurements at Kerguelen Island (49.2°S 70.1°E) Radiosondages Ozone Complementaires aux Kerguelen ROCK campaign 2008-2009 (Polar International Year - IPEV

Evaluation du transport isentropique à travers la barrière dynamique stratosphérique subtropicale de l'hémisphère Sud

Cette thèse est consacrée à l'évaluation des échanges entre le réservoir tropical et les moyennes latitudes au travers de la barrière dynamique stratosphérique subtropicale de l'hémisphère sud. La stratégie consiste à reconstituer le transport sur des surfaces isentropes avec le modèle d'advection de contours à haute résolution MIMOSA. Ce modèle a été alimenté par les champs de vorticité potentielle calculée sur 26 années consécutives (1980-2005) à partir des champs de vents et de température du modèle européen ERA-40. L'algorithme DYBAL a calculé l'intensité des barrières dynamiques (barrière subtropicale et vortex polaire) et du mélange. Couplé à l'algorithme des k-moyennes, il a permis la détection en coordonnées géographiques de la position des barrières et donc le calcul de l'extension méridienne des réservoirs stratosphériques. Cet algorithme a également été utilisé pour reconstituer les épisodes filamentaires caractéristiques du transport isentrope. Enfin, la perméabilité de la barrière subtropicale a été évaluée par le suivi des échanges et les routes privilégiées de ces échanges ont été mise en évidence. L'implication de ces événements sur le transport de l'ozone a été estimée ainsi que l'influence de l'oscillation quasi-biennale (QBO) et du cycle solaire-de 11 ans. Les résultats présentent la variabilité dynamique de la stratosphère sur l'isentrope 600K et montrent une augmentation de la taille du réservoir tropical et des moyennes latitudes en correspondance avec le rétrécissement du vortex polaire. Ces résultats indiquent également la diminution de l'intensité des échanges au travers de la barrière dynamique subtropicale depuis les années 1980.This thesis focuses on an evaluation of isentropic transport across the subtropical stratospheric dynamical barrier of the southern hemisphere. Our strategy consists in isentropic transport events reconstitution using MIMOSA high-resolution model to advect potential vorticity (PV) fields. This mode was initialized by the european model ERA-40 winds and temperature fields computed over 26 years (1980-2005). DYBAL algorithm has calculated dynamical barrier and mixing intensity. Also the k-means algorithm was applied on PV field to reconstitute laminae which is the characteristic form of isentropic transport events. Finally, subtropical barrier permeability was evaluated by following exchanges across this barrier and the distribution of lateral routes determined. Impact of these events on ozone distribution was estimated as the influence of quasi-biennial oscillation and 11-years solar cycle. Results shows on isentrope 600K an increase of the tropical reservoir and the mid-latitude size with the diminution of the polar vortex. The results indicate also the reduction of exchange intensity across subtropical barrier since the 1980's.SAINT DENIS/REUNION-Droit Lettre (974112101) / SudocSudocFranceReunionFRR

Temperature variability and trends in the UT-LS over a subtropical site: Reunion (20.8° S, 55.5° E)

International audienceThis paper mainly focuses on the trends and variability of the UT-LS temperature using radiosonde observations carried out over 16 years (January 1993 to December 2008) from a southern subtropical site, Reunion (20.8° S, 55.5° E), using a linear-regression fitting model. Two kinds of tropopause definitions, namely, cold point tropopause (CPT) and lapse rate tropopause (LRT) are used. In order to characterize and quantify the relationship between regional oceanic forcing and temperature at UT-LS, we took into account the Indian Ocean Dipole (IOD) for the estimation of temperature trends. Results show that the main component is the Annual Cycle (AC), particularly at tropopause (CPT, LRT) and in the lower stratosphere (LS) where more than 26.0±2.4% of temperature variability can be explained by AC. The influence of IOD on the variability of the temperature is at highest ratio at CPT and LS, with respectively 12.3±7.3% and 13.1±5.9%. The correlations between IOD and temperature anomalies at UT-LS are barely significant, which are found to be in close agreement with the results obtained by Rosenlof et al. (2008) over the western tropical Pacific Ocean. The temperature trend in the LS reveals a cooling of about −0.90±0.40 K per decade. The cooling trend at LS is found to be in close agreement with the others studies. Trend estimates in the LS suggest that IOD forcing contributes to increasing cooling by about 0.16±0.05 K per decade. Past works have shown that the additional carbon dioxide increase has a minor effect in the LS, and suggested that other effects than ozone and carbon dioxide changes have to be considered, in order to explain the observed temperature changes in the LS. From this study, we can suggest that the SST changes can be considered also, in addition to effects due to ozone and carbon dioxide changes, in order to explain the observed temperature changes in the LS. As a consequence, our results support the assumption that the Indian Ocean may have a slight impact on temperature variability and on temperature change in the LS over Reunion

20-year LiDAR observations of stratospheric sudden warming over a mid-latitude site, Observatoire de Haute Provence (OHP; 44° N, 6° E): case study and statistical characteristics

International audienceThe present study delineates the characteristics of Stratospheric Sudden Warming (SSW) events observed over the Observatoire de Haute Provence (OHP: 44° N, 6° E). The study uses 20 years of Rayleigh LiDAR temperature measurements for the period, 1982–2001, which corresponds to 2629 daily temperature profiles. Characteristics of warming events, such as type of warming (major and minor), magnitude of warming, height of occurrence and day period of occurrence are presented with emphasis on wave propagation and isentropic transport conditions. The major and minor warming events are classified with respect to temperature increase and reversal in the zonal wind direction in the polar region using reanalysis data from the National Centre for Environmental Prediction (NCEP). SSWs occur with a mean frequency of 2.15 events per winter season. The percentage of occurrence of major and minor warming events are found to be ~23% and ~77%, respectively. The observed major and minor SSW is associated with a descent of the stratopause layer by -6 to 6 km range. The heights of occurrences of major SSWs are distributed between 38 km and 54 km with magnitudes in the 12.2–35.7 K temperature range, while minor SSW occurrences appear in the 42–54 km range, closer to the usual stratopause layer (~47 km) and with a slightly larger range of temperature magnitude (10.2–32.8 K). The observed major and minor events are examined in connection with Quasi-Biennial Oscillation (QBO) phases