Journal of Geophysical Research: Atmospheres, 2016
Signatures of multiple stratospheric intrusions were observed on simultaneous and collocated ozon... more Signatures of multiple stratospheric intrusions were observed on simultaneous and collocated ozone and water vapor profiles retrieved by lidars and radiosondes at the Maïdo Observatory, Reunion Island (21°S, 55°E, 2160 m above sea level), during MAïdo LIdar Calibration CAmpaign in April 2013. A singular structure of the ozone vertical profile with three peaks (in excess of 90 ppbv, at~8,~10, and~13 km altitude) embedded in a thick dry layer of air suggested stratospheric intrusions with multiple origins. The hypothesis is corroborated by a synoptic analysis based on re-analyses. European Centre for Medium-Range Weather Forecasts ERA-Interim temporal series associated with 5 days Lagrangian back trajectories initialized on each ozone peak allows to capture their stratospheric origin. The ozone peak at the lowest altitude is associated with an irreversible tropopause folding process along the polar jet stream during an extratropical cutoff low formation. Simultaneous lidar water vapor profiles of this peak show that the anticorrelation with ozone has been removed, due to mixing processes. Back trajectories indicate that the two other ozone peaks observed at higher altitudes are associated with the dynamics of the subtropical jet stream and the lower stratosphere. The observations confirm the recent stratospheric origins. The highest ozone peak is explained by the horizontal distribution of the intrusion. Use of a Lagrangian Reverse Domain Filling model and of the Meso-NH Eulerian mesoscale model with a passive stratospheric tracer allow to further document the stratosphere-troposphere transport processes and to describe the detailed potential vorticity and ozone structures in which are embedded in the observed multiple stratospheric intrusions.
Stratospheric temperatures derived from five different lidars are compared. Although the lidars a... more Stratospheric temperatures derived from five different lidars are compared. Although the lidars are in five separate geographic locations, the evaluation is accomplished by comparing each of the sets of lidar data taken over the course of a year (1991-1992) with temperatures interpolated to each location from daily global temperature analyses from the National Meteorological Center (NMC). Average differences between the lidars and NMC temperatures vary for the different lidars by up to 6.7 K. Part of this large average temperature difference is shown to be due to the real temperature variation throughout the day, and the different times of observation of the NMC data and each of the lidar systems. Microwave limb sounder (MLS) data from the upper atmosphere research satellite are used to model the diurnal and semidiurnal variations in temperature for each lidar location, for each season. After adjusting for the temperature changes caused by variations in observation time, average temperature differences are reduced among four of the five lidars, compared with the NMC temperatures, but still vary by as much as 3.9 K at stratospheric altitudes between 30 and 45 km. Results of direct comparisons at two permanent lidar sites with a mobile lidar show that sometimes agreement within 1 to 2 K is achieved, but for other cases, larger average differences are seen. Since the precision of lidar temperatures has been estimated to be better than 1 K, further research is needed to reconcile this small expected error with the larger average differences deduced here using measurements made under operational conditions.
Seven year series of gravity wave (GW) potential energy at midlatitude stratosphere (10 to 50 km)... more Seven year series of gravity wave (GW) potential energy at midlatitude stratosphere (10 to 50 km) is constructed by combining temperature profiles provided by Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) GPS satellite constellation and Rayleigh lidar operating at Haute Provence observatory in Southern France. The combined series are used to evaluate the representation of GW in Modern Era Retrospective-Analysis for Research and Applications reanalysis. The seasonal and zonal variabilities of GW activity are diagnosed using zonal wind and wind divergence provided by ERA-Interim reanalysis. The spatiotemporal distribution of GW activity is found strongly dependent on the zonal wind variation, wind divergence, and topography. We show that anomalies in the wind divergence can serve as a proxy for locating synoptic-scale enhancements of GW. The analysis provides evidence for orographic GW excitation, and the results are compatible with geostrophic adjustment being an additional source of stratospheric GW. The seasonal GW variability can be largely explained by interaction with the mean flow and wave propagation.
Lidar system and radio-soundings were used to validate both air-density and low and high-resoluti... more Lidar system and radio-soundings were used to validate both air-density and low and high-resolution temperature profiles of the GOMOS instrument onboard ENVISAT-1 satellite. No bias greater than 7% was found for the air-density comparisons with lidar and there is a very strong global agreement. The conditions of the occultations have a large impact on the comparisons concerning the temperature profile. The "dark limb" measurement conditions show great agreement between 35 and 60 km with no bias greater than 5% whereas the "bright limb" measurement conditions show poor results. The High Resolution temperature shows a very interesting potential.
Context. Solar spectral irradiance (SSI) is the wavelength-dependent energy input to the top of t... more Context. Solar spectral irradiance (SSI) is the wavelength-dependent energy input to the top of the Earth’s atmosphere. Solar ultraviolet (UV) irradiance represents the primary forcing mechanism for the photochemistry, heating, and dynamics of the Earth’s atmosphere. Hence, both temporal and spectral variations in solar UV irradiance represent crucial inputs to the modeling and understanding of the behavior of the Earth’s atmosphere. Therefore, measuring the long-term solar UV irradiance variations over the 11-year solar activity cycle (and over longer timescales) is fundamental. Thus, each new solar spectral irradiance dataset based on long-term observations represents a major interest and can be used for further investigations of the long-term trend of solar activity and the construction of a homogeneous solar spectral irradiance record. Aims. The main objective of this article is to present a new solar spectral irradiance database (SOLAR-v) with the associated uncertainties. This...
In this paper we investigate daily variations in middle atmospheric water vapor and ozone based o... more In this paper we investigate daily variations in middle atmospheric water vapor and ozone based on data from two ground-based microwave radiometers located in the Alpine region of Europe. Temperature data are obtained from a lidar located near the two stations and from the SABER experiment on the TIMED satellite. This unique set of observations is complemented by three different three-dimensional (3-D) chemistry-climate models (Monitoring of Stratospheric Depletion of the Ozone Layer (MSDOL), Laboratoire de Météorologie Dynamique Reactive Processes Ruling the Ozone Budget in the Stratosphere (LMDz-REPROBUS), and Solar Climate Ozone Links (SOCOL)) and the 2-D atmospheric global-scale wave model (GSWM). The first part of the paper is focused on the first Climate and Weather of the Sun-Earth System (CAWSES) tidal campaign that consisted of a period of intensive measurements during September 2005. Variations in stratospheric water vapor are found to be in the order of 1% depending on altitude. Meridional advection of tidal nature is likely to be the dominant driving factor throughout the whole stratosphere, while vertical advection becomes more important in the mesosphere. Observed ozone variations in the upper stratosphere and lower mesosphere show amplitudes of several percent in accordance with photochemical models. Variations in lower stratospheric ozone are not solely governed by photochemistry but also by dynamics, with the temperature dependence of the photochemistry becoming more important. The second part presents an investigation of the seasonal dependence of daily variations. Models tend to underestimate the H 2 O diurnal amplitudes, especially during summer in the upper stratosphere. Good agreement between models and observations is found for ozone in the upper stratosphere, which reflects the fact that the O 3 daily variations are driven by the photochemistry that is well modeled.
A ground-based Rayleigh lidar has provided continuous observations of tropospheric water vapour p... more 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.
The international Network for the Detection of Atmospheric Composition Change (NDACC) is composed... more The international Network for the Detection of Atmospheric Composition Change (NDACC) is composed of more than 70 high-quality, remotesensing research stations for observing and understanding the physical and chemical state of the stratosphere and upper troposphere, and for assessing the impacts of stratosphere changes on the underlying troposphere and on global climate. While NDACC remains committed to monitoring changes in the stratosphere, with an emphasis on the long-term evolution of the ozone layer, its priorities have broadened considerably to encompass issues such as the detection of trends in overall atmospheric composition and understanding their impacts on the stratosphere and troposphere, and establishing links between climate change and atmospheric composition. Following five years of planning, instrument design, and implementation, NDACC began network operations in January 1991. Network details can be found at http://www.ndacc.org.
Atmospheric Chemistry and Physics Discussions, 2006
Using four years of Rayleigh lidar data collected from three different northern hemisphere statio... more Using four years of Rayleigh lidar data collected from three different northern hemisphere stations (Gadanki 13.5 • N, 79.2 • E ; Mt. Abu 24.5 • N, 72.7 • E and Observatoire de Haute Provence: OHP; 44 • N, 6 • E), the characteristics of double (separated) stratopause occurrence are presented here, for the first time. The characteristics are illustrated by a seasonal change during summer and winter and the variation in percentage of occurrence from place to place. It is found that the overall mean normal stratopause (NS) positioned at the middle level of double stratopause (upper and lower level) with its location nearer to the lower level of double stratopause (LDS) than to the upper level of double stratopause (UDS). The frequency distribution of NS, LDS and UDS demonstrated variability with location, indicating role of dynamical activity. By making use of a quasi-continuous 40 days of lidar observations over Gadanki and OHP, the responsibility of Gravity Wave (GW) and Planetary Wave (PW) activity for the LDS and UDS occurrence are examined and presented.
This publication provides a detailed study of one cirrus cloud observed by lidar at the Observato... more This publication provides a detailed study of one cirrus cloud observed by lidar at the Observatory of Haute-Provence ($44°N) in January 2006 in the vicinity of the tropopause (12-14 km/$136-190 hPa/328-355 K). The higher part of the air mass observed comes from the wet subtropics while the lower part comes from the midlatitudes. Both are advected by the Azores anticyclone, encounter cold temperatures ($205 K) above the North Atlantic Ocean, and flow eastward along the anticyclonic flank of the polar jet stream. A simulation of this cloud by an isentropic model is tested to see if synoptic-scale atmospheric structures could explain by itself the presence of such clouds. The developments made in the Modélisation Isentrope du transport Méso-échelle de l'Ozone Stratosphérique par Advection (MIMOSA) model to take into account the three phases of water and their interactions allow reproduction of the occurrence of the cirrus and its temporal evolution. MIMOSA-H 2 O reproduces the atmospheric water vapor structures observed with Atmospheric Infrared Sounder (AIRS) with, however, an apparent wet bias of around 50%. Reliable water vapor fields appear to be the main condition to correctly simulate such cirrus clouds. The model reproduces the cirrus cloud altitude for fall speeds around 1 cm/s and gives ice water content around 3-4 mg/m 3. Fall speed is also a critical parameter, and a better parameterization with altitude or other atmospheric conditions in the modeling of such cirrus clouds is required. This study also shows that supersaturation threshold impacts strongly the vertical and horizontal extension of the cirrus cloud but more slightly the ice water path.
Journal of Geophysical Research: Atmospheres, 1996
The NASA Goddard Space Flight Center (GSFC) mobile lidar system was deployed at the Observatoire ... more The NASA Goddard Space Flight Center (GSFC) mobile lidar system was deployed at the Observatoire de Haute Provence (OHP), during an Upper Atmosphere Research Satellite (UARS)/Network for Detection of Stratospheric Change (NDSC) correlative measurement campaign (July-August 1992). The objective of this campaign was twofold: to intercompare two independent lidars and to provide ground-based UARS correlative ozone and temperature validation measurements. This paper, for the first time, presents a coincident temperature intercomparison between two independently operating temperature lidar systems of similar capabilities. Systems and retrieval algorithms have been described and discussed in terms of error sources. The comparison of the two analysis have shown very similar results up to the upper mesosphere. The statistical mean differences of 0.5 K in the stratosphere and about 2 K in the mesosphere suggests insignificant bias throughout except below 35 km, where one of the data sets is contaminated by the volcanic aerosols from the eruption of Mount Pinatubo. Profiles of the rootmean-square (RMS) of the differences are in good agreement with random error estimates, except around 35-40 km where RMS is larger. These measurements can be used as the ground reference for UARS temperature validation. However, the spatial-temporal coincidence between satellite and lidar needs to be carefully considered for meaningful validation. 1. Introduction The idea for establishing a network of high-quality, remote sounding research stations for observing and understanding the anthropogenic changes in the stratosphere and any long-term impact on the Earth's atmosphere was first discussed at a workshop in 1986. In the following years, new instruments were developed and permanent sites were established. In January 1991 the international Network for Detection of Stratospheric Change (NDSC) [Kurylo and Soloman, 1990] became operational. To provide the best latitude coverage possible, it was proposed that the network would consist of at least seven stations: midlatitude, polar, and tropical, one in each hemisphere, and one near the equator. Each of the primary NDSC stations will be equ-1Hughes STX Corporation,
The Beaufort Sea high (BSH) plays an important role in forcing Arctic sea ice and the Beaufort Gy... more The Beaufort Sea high (BSH) plays an important role in forcing Arctic sea ice and the Beaufort Gyre. This study examines the variability and long-term trends of atmospheric circulation over the Chukchi and Beaufort Seas using the ECMWF Interim Re-Analysis (ERA-Interim) for the period 1979–2012. Because of the mobility of the BSH through the year, EOF analysis is applied to the sea level pressure (SLP) field in order to investigate the principal patterns of BSH variability. In each season, the three leading EOF modes explain nearly 90% of the total variance and reflect a strengthened or weakened BSH centered over the western Arctic Ocean (EOF1), a north–south dipole-like SLP anomaly (EOF2), and a west–east dipole-like SLP anomaly (EOF3), respectively. These three EOF modes offer distinct influences on local climate in each season and have different connections with the large-scale climate variability modes in winter. In particular, the second principal component (PC2) associated with...
An updated assessment of uncertainties in ''observed'' climatological winds and temperatures in t... more An updated assessment of uncertainties in ''observed'' climatological winds and temperatures in the middle atmosphere (over altitudes ϳ10-80 km) is provided by detailed intercomparisons of contemporary and historic datasets. These datasets include global meteorological analyses and assimilations, climatologies derived from research satellite measurements, historical reference atmosphere circulation statistics, rocketsonde wind and temperature data, and lidar temperature measurements. The comparisons focus on a few basic circulation statistics (temperatures and zonal winds), with special attention given to tropical variability. Notable differences are found between analyses for temperatures near the tropical tropopause and polar lower stratosphere, temperatures near the global stratopause, and zonal winds throughout the Tropics. Comparisons of historical reference atmosphere and rocketsonde temperatures with more recent global analyses show the influence of decadal-scale cooling of the stratosphere and mesosphere. Detailed comparisons of the tropical semiannual oscillation (SAO) and quasibiennial oscillation (QBO) show large differences in amplitude between analyses; recent data assimilation schemes show the best agreement with equatorial radiosonde, rocket, and satellite data.
Journal of Atmospheric and Solar-Terrestrial Physics, 2003
The study of the variability of stratospheric aerosols and the transfer between the di erent atmo... more The study of the variability of stratospheric aerosols and the transfer between the di erent atmospheric regions improves our understanding of dynamical processes involved in isentropic exchanges that take place episodically in the lower stratosphere through the subtropical barrier. One useful approach consists in combining in situ ground-based and global measurements with numerical analyses. The present paper reports on a case study of a horizontal transfer evidenced ÿrst by Rayleigh-Mie LIDAR observations over Durban (29:9 • S, 31:0 • E, South Africa). Additional data from MeteoSat and SAGE-2 experiments, and from ECMWF meteorological analysis have been used in this study. Contour advection maps of potential vorticity from the MIMOSA model derived from ECMWF ÿelds, were also used. By the end of April, 1999, LIDAR observations showed that aerosol extinction, in the lower stratosphere, has increased signiÿcantly and abnormally in comparison with other LIDAR and SAGE-2 observations recorded for the period from April 20 to June 14, 1999. The dynamical context of this case study seems to exclude the possibility of a local in uence of the subtropical jet stream or tropical convection, which could inject air masses enriched with tropospheric aerosols into the stratosphere. On the contrary, a high-resolution model based on PV advection calculations and ECMWF meteorological analyses shows that air masses are isentropically advected from the equatorial zone close to Brazil. They cross the southern barrier of the tropical reservoir due to laminae stretching and reach the southern subcontinent of Africa 5-6 days later.
This study provides an analysis of cirrus cloud properties at midlatitude in the southern part of... more This study provides an analysis of cirrus cloud properties at midlatitude in the southern part of France from ground-based and spaceborne lidars. A climatology of cirrus cloud properties and their evolution over more than 12 yr is presented and compared to other mid-latitude climatological studies. Cirrus clouds occur ∼ 37 % of the total observation time and remain quasi-constant across seasons with a variation within ∼ 5 % around the mean occurrence. Similar results are obtained from CALIOP and the ground-based lidar, with a mean difference in occurrence of ∼ 5 % between both instruments. From the ground-based lidar data, a slight decrease in occurrence of ∼ 3 % per decade is observed but found statistically insignificant. Based on a clustering analysis of cirrus cloud parameters, three distinct classes have been identified and investigations concerning their origin are discussed. Properties of these different classes are analysed, showing that thin cirrus in the upper troposphere represent ∼ 50 % of cloud cover detected in summer and fall, decreasing by 15-20 % for other seasons.
Journal of Geophysical Research: Atmospheres, 2016
Signatures of multiple stratospheric intrusions were observed on simultaneous and collocated ozon... more Signatures of multiple stratospheric intrusions were observed on simultaneous and collocated ozone and water vapor profiles retrieved by lidars and radiosondes at the Maïdo Observatory, Reunion Island (21°S, 55°E, 2160 m above sea level), during MAïdo LIdar Calibration CAmpaign in April 2013. A singular structure of the ozone vertical profile with three peaks (in excess of 90 ppbv, at~8,~10, and~13 km altitude) embedded in a thick dry layer of air suggested stratospheric intrusions with multiple origins. The hypothesis is corroborated by a synoptic analysis based on re-analyses. European Centre for Medium-Range Weather Forecasts ERA-Interim temporal series associated with 5 days Lagrangian back trajectories initialized on each ozone peak allows to capture their stratospheric origin. The ozone peak at the lowest altitude is associated with an irreversible tropopause folding process along the polar jet stream during an extratropical cutoff low formation. Simultaneous lidar water vapor profiles of this peak show that the anticorrelation with ozone has been removed, due to mixing processes. Back trajectories indicate that the two other ozone peaks observed at higher altitudes are associated with the dynamics of the subtropical jet stream and the lower stratosphere. The observations confirm the recent stratospheric origins. The highest ozone peak is explained by the horizontal distribution of the intrusion. Use of a Lagrangian Reverse Domain Filling model and of the Meso-NH Eulerian mesoscale model with a passive stratospheric tracer allow to further document the stratosphere-troposphere transport processes and to describe the detailed potential vorticity and ozone structures in which are embedded in the observed multiple stratospheric intrusions.
Stratospheric temperatures derived from five different lidars are compared. Although the lidars a... more Stratospheric temperatures derived from five different lidars are compared. Although the lidars are in five separate geographic locations, the evaluation is accomplished by comparing each of the sets of lidar data taken over the course of a year (1991-1992) with temperatures interpolated to each location from daily global temperature analyses from the National Meteorological Center (NMC). Average differences between the lidars and NMC temperatures vary for the different lidars by up to 6.7 K. Part of this large average temperature difference is shown to be due to the real temperature variation throughout the day, and the different times of observation of the NMC data and each of the lidar systems. Microwave limb sounder (MLS) data from the upper atmosphere research satellite are used to model the diurnal and semidiurnal variations in temperature for each lidar location, for each season. After adjusting for the temperature changes caused by variations in observation time, average temperature differences are reduced among four of the five lidars, compared with the NMC temperatures, but still vary by as much as 3.9 K at stratospheric altitudes between 30 and 45 km. Results of direct comparisons at two permanent lidar sites with a mobile lidar show that sometimes agreement within 1 to 2 K is achieved, but for other cases, larger average differences are seen. Since the precision of lidar temperatures has been estimated to be better than 1 K, further research is needed to reconcile this small expected error with the larger average differences deduced here using measurements made under operational conditions.
Seven year series of gravity wave (GW) potential energy at midlatitude stratosphere (10 to 50 km)... more Seven year series of gravity wave (GW) potential energy at midlatitude stratosphere (10 to 50 km) is constructed by combining temperature profiles provided by Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) GPS satellite constellation and Rayleigh lidar operating at Haute Provence observatory in Southern France. The combined series are used to evaluate the representation of GW in Modern Era Retrospective-Analysis for Research and Applications reanalysis. The seasonal and zonal variabilities of GW activity are diagnosed using zonal wind and wind divergence provided by ERA-Interim reanalysis. The spatiotemporal distribution of GW activity is found strongly dependent on the zonal wind variation, wind divergence, and topography. We show that anomalies in the wind divergence can serve as a proxy for locating synoptic-scale enhancements of GW. The analysis provides evidence for orographic GW excitation, and the results are compatible with geostrophic adjustment being an additional source of stratospheric GW. The seasonal GW variability can be largely explained by interaction with the mean flow and wave propagation.
Lidar system and radio-soundings were used to validate both air-density and low and high-resoluti... more Lidar system and radio-soundings were used to validate both air-density and low and high-resolution temperature profiles of the GOMOS instrument onboard ENVISAT-1 satellite. No bias greater than 7% was found for the air-density comparisons with lidar and there is a very strong global agreement. The conditions of the occultations have a large impact on the comparisons concerning the temperature profile. The "dark limb" measurement conditions show great agreement between 35 and 60 km with no bias greater than 5% whereas the "bright limb" measurement conditions show poor results. The High Resolution temperature shows a very interesting potential.
Context. Solar spectral irradiance (SSI) is the wavelength-dependent energy input to the top of t... more Context. Solar spectral irradiance (SSI) is the wavelength-dependent energy input to the top of the Earth’s atmosphere. Solar ultraviolet (UV) irradiance represents the primary forcing mechanism for the photochemistry, heating, and dynamics of the Earth’s atmosphere. Hence, both temporal and spectral variations in solar UV irradiance represent crucial inputs to the modeling and understanding of the behavior of the Earth’s atmosphere. Therefore, measuring the long-term solar UV irradiance variations over the 11-year solar activity cycle (and over longer timescales) is fundamental. Thus, each new solar spectral irradiance dataset based on long-term observations represents a major interest and can be used for further investigations of the long-term trend of solar activity and the construction of a homogeneous solar spectral irradiance record. Aims. The main objective of this article is to present a new solar spectral irradiance database (SOLAR-v) with the associated uncertainties. This...
In this paper we investigate daily variations in middle atmospheric water vapor and ozone based o... more In this paper we investigate daily variations in middle atmospheric water vapor and ozone based on data from two ground-based microwave radiometers located in the Alpine region of Europe. Temperature data are obtained from a lidar located near the two stations and from the SABER experiment on the TIMED satellite. This unique set of observations is complemented by three different three-dimensional (3-D) chemistry-climate models (Monitoring of Stratospheric Depletion of the Ozone Layer (MSDOL), Laboratoire de Météorologie Dynamique Reactive Processes Ruling the Ozone Budget in the Stratosphere (LMDz-REPROBUS), and Solar Climate Ozone Links (SOCOL)) and the 2-D atmospheric global-scale wave model (GSWM). The first part of the paper is focused on the first Climate and Weather of the Sun-Earth System (CAWSES) tidal campaign that consisted of a period of intensive measurements during September 2005. Variations in stratospheric water vapor are found to be in the order of 1% depending on altitude. Meridional advection of tidal nature is likely to be the dominant driving factor throughout the whole stratosphere, while vertical advection becomes more important in the mesosphere. Observed ozone variations in the upper stratosphere and lower mesosphere show amplitudes of several percent in accordance with photochemical models. Variations in lower stratospheric ozone are not solely governed by photochemistry but also by dynamics, with the temperature dependence of the photochemistry becoming more important. The second part presents an investigation of the seasonal dependence of daily variations. Models tend to underestimate the H 2 O diurnal amplitudes, especially during summer in the upper stratosphere. Good agreement between models and observations is found for ozone in the upper stratosphere, which reflects the fact that the O 3 daily variations are driven by the photochemistry that is well modeled.
A ground-based Rayleigh lidar has provided continuous observations of tropospheric water vapour p... more 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.
The international Network for the Detection of Atmospheric Composition Change (NDACC) is composed... more The international Network for the Detection of Atmospheric Composition Change (NDACC) is composed of more than 70 high-quality, remotesensing research stations for observing and understanding the physical and chemical state of the stratosphere and upper troposphere, and for assessing the impacts of stratosphere changes on the underlying troposphere and on global climate. While NDACC remains committed to monitoring changes in the stratosphere, with an emphasis on the long-term evolution of the ozone layer, its priorities have broadened considerably to encompass issues such as the detection of trends in overall atmospheric composition and understanding their impacts on the stratosphere and troposphere, and establishing links between climate change and atmospheric composition. Following five years of planning, instrument design, and implementation, NDACC began network operations in January 1991. Network details can be found at http://www.ndacc.org.
Atmospheric Chemistry and Physics Discussions, 2006
Using four years of Rayleigh lidar data collected from three different northern hemisphere statio... more Using four years of Rayleigh lidar data collected from three different northern hemisphere stations (Gadanki 13.5 • N, 79.2 • E ; Mt. Abu 24.5 • N, 72.7 • E and Observatoire de Haute Provence: OHP; 44 • N, 6 • E), the characteristics of double (separated) stratopause occurrence are presented here, for the first time. The characteristics are illustrated by a seasonal change during summer and winter and the variation in percentage of occurrence from place to place. It is found that the overall mean normal stratopause (NS) positioned at the middle level of double stratopause (upper and lower level) with its location nearer to the lower level of double stratopause (LDS) than to the upper level of double stratopause (UDS). The frequency distribution of NS, LDS and UDS demonstrated variability with location, indicating role of dynamical activity. By making use of a quasi-continuous 40 days of lidar observations over Gadanki and OHP, the responsibility of Gravity Wave (GW) and Planetary Wave (PW) activity for the LDS and UDS occurrence are examined and presented.
This publication provides a detailed study of one cirrus cloud observed by lidar at the Observato... more This publication provides a detailed study of one cirrus cloud observed by lidar at the Observatory of Haute-Provence ($44°N) in January 2006 in the vicinity of the tropopause (12-14 km/$136-190 hPa/328-355 K). The higher part of the air mass observed comes from the wet subtropics while the lower part comes from the midlatitudes. Both are advected by the Azores anticyclone, encounter cold temperatures ($205 K) above the North Atlantic Ocean, and flow eastward along the anticyclonic flank of the polar jet stream. A simulation of this cloud by an isentropic model is tested to see if synoptic-scale atmospheric structures could explain by itself the presence of such clouds. The developments made in the Modélisation Isentrope du transport Méso-échelle de l'Ozone Stratosphérique par Advection (MIMOSA) model to take into account the three phases of water and their interactions allow reproduction of the occurrence of the cirrus and its temporal evolution. MIMOSA-H 2 O reproduces the atmospheric water vapor structures observed with Atmospheric Infrared Sounder (AIRS) with, however, an apparent wet bias of around 50%. Reliable water vapor fields appear to be the main condition to correctly simulate such cirrus clouds. The model reproduces the cirrus cloud altitude for fall speeds around 1 cm/s and gives ice water content around 3-4 mg/m 3. Fall speed is also a critical parameter, and a better parameterization with altitude or other atmospheric conditions in the modeling of such cirrus clouds is required. This study also shows that supersaturation threshold impacts strongly the vertical and horizontal extension of the cirrus cloud but more slightly the ice water path.
Journal of Geophysical Research: Atmospheres, 1996
The NASA Goddard Space Flight Center (GSFC) mobile lidar system was deployed at the Observatoire ... more The NASA Goddard Space Flight Center (GSFC) mobile lidar system was deployed at the Observatoire de Haute Provence (OHP), during an Upper Atmosphere Research Satellite (UARS)/Network for Detection of Stratospheric Change (NDSC) correlative measurement campaign (July-August 1992). The objective of this campaign was twofold: to intercompare two independent lidars and to provide ground-based UARS correlative ozone and temperature validation measurements. This paper, for the first time, presents a coincident temperature intercomparison between two independently operating temperature lidar systems of similar capabilities. Systems and retrieval algorithms have been described and discussed in terms of error sources. The comparison of the two analysis have shown very similar results up to the upper mesosphere. The statistical mean differences of 0.5 K in the stratosphere and about 2 K in the mesosphere suggests insignificant bias throughout except below 35 km, where one of the data sets is contaminated by the volcanic aerosols from the eruption of Mount Pinatubo. Profiles of the rootmean-square (RMS) of the differences are in good agreement with random error estimates, except around 35-40 km where RMS is larger. These measurements can be used as the ground reference for UARS temperature validation. However, the spatial-temporal coincidence between satellite and lidar needs to be carefully considered for meaningful validation. 1. Introduction The idea for establishing a network of high-quality, remote sounding research stations for observing and understanding the anthropogenic changes in the stratosphere and any long-term impact on the Earth's atmosphere was first discussed at a workshop in 1986. In the following years, new instruments were developed and permanent sites were established. In January 1991 the international Network for Detection of Stratospheric Change (NDSC) [Kurylo and Soloman, 1990] became operational. To provide the best latitude coverage possible, it was proposed that the network would consist of at least seven stations: midlatitude, polar, and tropical, one in each hemisphere, and one near the equator. Each of the primary NDSC stations will be equ-1Hughes STX Corporation,
The Beaufort Sea high (BSH) plays an important role in forcing Arctic sea ice and the Beaufort Gy... more The Beaufort Sea high (BSH) plays an important role in forcing Arctic sea ice and the Beaufort Gyre. This study examines the variability and long-term trends of atmospheric circulation over the Chukchi and Beaufort Seas using the ECMWF Interim Re-Analysis (ERA-Interim) for the period 1979–2012. Because of the mobility of the BSH through the year, EOF analysis is applied to the sea level pressure (SLP) field in order to investigate the principal patterns of BSH variability. In each season, the three leading EOF modes explain nearly 90% of the total variance and reflect a strengthened or weakened BSH centered over the western Arctic Ocean (EOF1), a north–south dipole-like SLP anomaly (EOF2), and a west–east dipole-like SLP anomaly (EOF3), respectively. These three EOF modes offer distinct influences on local climate in each season and have different connections with the large-scale climate variability modes in winter. In particular, the second principal component (PC2) associated with...
An updated assessment of uncertainties in ''observed'' climatological winds and temperatures in t... more An updated assessment of uncertainties in ''observed'' climatological winds and temperatures in the middle atmosphere (over altitudes ϳ10-80 km) is provided by detailed intercomparisons of contemporary and historic datasets. These datasets include global meteorological analyses and assimilations, climatologies derived from research satellite measurements, historical reference atmosphere circulation statistics, rocketsonde wind and temperature data, and lidar temperature measurements. The comparisons focus on a few basic circulation statistics (temperatures and zonal winds), with special attention given to tropical variability. Notable differences are found between analyses for temperatures near the tropical tropopause and polar lower stratosphere, temperatures near the global stratopause, and zonal winds throughout the Tropics. Comparisons of historical reference atmosphere and rocketsonde temperatures with more recent global analyses show the influence of decadal-scale cooling of the stratosphere and mesosphere. Detailed comparisons of the tropical semiannual oscillation (SAO) and quasibiennial oscillation (QBO) show large differences in amplitude between analyses; recent data assimilation schemes show the best agreement with equatorial radiosonde, rocket, and satellite data.
Journal of Atmospheric and Solar-Terrestrial Physics, 2003
The study of the variability of stratospheric aerosols and the transfer between the di erent atmo... more The study of the variability of stratospheric aerosols and the transfer between the di erent atmospheric regions improves our understanding of dynamical processes involved in isentropic exchanges that take place episodically in the lower stratosphere through the subtropical barrier. One useful approach consists in combining in situ ground-based and global measurements with numerical analyses. The present paper reports on a case study of a horizontal transfer evidenced ÿrst by Rayleigh-Mie LIDAR observations over Durban (29:9 • S, 31:0 • E, South Africa). Additional data from MeteoSat and SAGE-2 experiments, and from ECMWF meteorological analysis have been used in this study. Contour advection maps of potential vorticity from the MIMOSA model derived from ECMWF ÿelds, were also used. By the end of April, 1999, LIDAR observations showed that aerosol extinction, in the lower stratosphere, has increased signiÿcantly and abnormally in comparison with other LIDAR and SAGE-2 observations recorded for the period from April 20 to June 14, 1999. The dynamical context of this case study seems to exclude the possibility of a local in uence of the subtropical jet stream or tropical convection, which could inject air masses enriched with tropospheric aerosols into the stratosphere. On the contrary, a high-resolution model based on PV advection calculations and ECMWF meteorological analyses shows that air masses are isentropically advected from the equatorial zone close to Brazil. They cross the southern barrier of the tropical reservoir due to laminae stretching and reach the southern subcontinent of Africa 5-6 days later.
This study provides an analysis of cirrus cloud properties at midlatitude in the southern part of... more This study provides an analysis of cirrus cloud properties at midlatitude in the southern part of France from ground-based and spaceborne lidars. A climatology of cirrus cloud properties and their evolution over more than 12 yr is presented and compared to other mid-latitude climatological studies. Cirrus clouds occur ∼ 37 % of the total observation time and remain quasi-constant across seasons with a variation within ∼ 5 % around the mean occurrence. Similar results are obtained from CALIOP and the ground-based lidar, with a mean difference in occurrence of ∼ 5 % between both instruments. From the ground-based lidar data, a slight decrease in occurrence of ∼ 3 % per decade is observed but found statistically insignificant. Based on a clustering analysis of cirrus cloud parameters, three distinct classes have been identified and investigations concerning their origin are discussed. Properties of these different classes are analysed, showing that thin cirrus in the upper troposphere represent ∼ 50 % of cloud cover detected in summer and fall, decreasing by 15-20 % for other seasons.
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Papers by P. Keckhut