Temperature climatology with Rayleigh lidar above Observatory of Haute-provence : dynamical feedback

International audienceRayleigh lidar in synergy with satellite observations (SSU and AMSU) allow insuring an efficient monitoring and showing that cooling has continued. New approach for trend detection has been developed allowing a better estimate of changes due to radiative forcing. Stratospheric Warmings and gravity waves contribute to insure a dynamical feedback of the long-term changes

Reconciliation of essential process parameters for an enhanced predictability of Arctic stratospheric ozone loss and its climate interactions

Significant reductions in stratospheric ozone occur inside the polar vortices each spring when chlorine radicals produced by heterogeneous reactions on cold particle surfaces in winter destroy ozone mainly in two catalytic cycles, the ClO dimer cycle and the ClO/BrO cycle. Chlorofluorocarbons (CFCs), which are responsible for most of the chlorine currently present in the stratosphere, have been banned by the Montreal Protocol and its amendments, and the ozone layer is predicted to recover to 1980 levels within the next few decades. During the same period, however, climate change is expected to alter the temperature, circulation patterns and chemical composition in the stratosphere, and possible geo-engineering ventures to mitigate climate change may lead to additional changes. To realistically predict the response of the ozone layer to such influences requires the correct representation of all relevant processes. The European project RECONCILE has comprehensively addressed remaining questions in the context of polar ozone depletion, with the objective to quantify the rates of some of the most relevant, yet still uncertain physical and chemical processes. To this end RECONCILE used a broad approach of laboratory experiments, two field missions in the Arctic winter 2009/10 employing the high altitude research aircraft M55-Geophysica and an extensive match ozone sonde campaign, as well as microphysical and chemical transport modelling and data assimilation. Some of the main outcomes of RECONCILE are as follows: (1) vortex meteorology: the 2009/10 Arctic winter was unusually cold at stratospheric levels during the six-week period from mid-December 2009 until the end of January 2010, with reduced transport and mixing across the polar vortex edge; polar vortex stability and how it is influenced by dynamic processes in the troposphere has led to unprecedented, synoptic-scale stratospheric regions with temperatures below the frost point; in these regions stratospheric ice clouds have been observed, extending over >106km2 during more than 3 weeks. (2) Particle microphysics: heterogeneous nucleation of nitric acid trihydrate (NAT) particles in the absence of ice has been unambiguously demonstrated; conversely, the synoptic scale ice clouds also appear to nucleate heterogeneously; a variety of possible heterogeneous nuclei has been characterised by chemical analysis of the non-volatile fraction of the background aerosol; substantial formation of solid particles and denitrification via their sedimentation has been observed and model parameterizations have been improved. (3) Chemistry: strong evidence has been found for significant chlorine activation not only on polar stratospheric clouds (PSCs) but also on cold binary aerosol; laboratory experiments and field data on the ClOOCl photolysis rate and other kinetic parameters have been shown to be consistent with an adequate degree of certainty; no evidence has been found that would support the existence of yet unknown chemical mechanisms making a significant contribution to polar ozone loss. (4) Global modelling: results from process studies have been implemented in a prognostic chemistry climate model (CCM); simulations with improved parameterisations of processes relevant for polar ozone depletion are evaluated against satellite data and other long term records using data assimilation and detrended fluctuation analysis. Finally, measurements and process studies within RECONCILE were also applied to the winter 2010/11, when special meteorological conditions led to the highest chemical ozone loss ever observed in the Arctic. In addition to quantifying the 2010/11 ozone loss and to understand its causes including possible connections to climate change, its impacts were addressed, such as changes in surface ultraviolet (UV) radiation in the densely populated northern mid-latitudes

Reconciliation of essential process parameters for an enhanced predictability of Arctic stratospheric ozone loss and its climate interactions : (RECONCILE) ; activities and results

The international research project RECONCILE has addressed central questions regarding polar ozone depletion, with the objective to quantify some of the most relevant yet still uncertain physical and chemical processes and thereby improve prognostic modelling capabilities to realistically predict the response of the ozone layer to climate change. This overview paper outlines the scope and the general approach of RECONCILE, and it provides a summary of observations and modelling in 2010 and 2011 that have generated an in many respects unprecedented dataset to study processes in the Arctic winter stratosphere. Principally, it summarises important outcomes of RECONCILE including (i) better constraints and enhanced consistency on the set of parameters governing catalytic ozone destruction cycles, (ii) a better understanding of the role of cold binary aerosols in heterogeneous chlorine activation, (iii) an improved scheme of polar stratospheric cloud (PSC) processes that includes heterogeneous nucleation of nitric acid trihydrate (NAT) and ice on non-volatile background aerosol leading to better model parameterisations with respect to denitrification, and (iv) long transient simulations with a chemistry-climate model (CCM) updated based on the results of RECONCILE that better reproduce past ozone trends in Antarctica and are deemed to produce more reliable predictions of future ozone trends. The process studies and the global simulations conducted in RECONCILE show that in the Arctic, ozone depletion uncertainties in the chemical and microphysical processes are now clearly smaller than the sensitivity to dynamic variability

Assessment of 16 years of satellite temperature profiles from SABER and MLS using lidar temperature profiles from OHP

International audienceWe have compared 2433 nights of Rayleigh lidar temperatures measured from January 2002 to March 2018 at L'Observatoire de Haute Provence (43.93 N, 5.71 E) with co-located temperature measurements from the Microwave Limb Sounder (MLS) and the Sounding of the Atmosphere by Broadband Emission Radiometry instrument (SABER). We have found systematic differences between the temperatures measured from the ground-based lidar and those measured from the space-borne satellites. In particular, a recurring winter stratopause relative cold bias in the satellite measurements with respect to the lidar (-6 K for SABER and -17 K for MLS), a summer mesospheric relative warm bias for SABER (6 K near 60 km), and a vertically structured bias for MLS (-4 to 4 K). By making use of the precise ranging information in the lidar data we have adjusted the stratopause geopotential altitude of the satellite measurements and have seen an improvement in the subsequent comparison. The winter relative cold bias between the lidar and SABER has been reduced to 1 K in both the stratosphere and mesosphere and the summer mesospheric warm bias is reduced to 2 K. Stratopause altitude corrections have reduced the relative cold bias between the lidar and MLS by 4 K in the early autumn and late spring but further work is required to address the apparent vertical oscillations in the MLS temperature profiles

Update of stratospheric temperature interannual variability and trends from space sounders and ground-based lidars observations

International audiencethe stratosphere is expected to cool, in conjunction with the global warming at the surface and in the troposphere, due to the increase of greenhouse gas concentration in the atmosphere, and also to stratospheric ozone loss. this is already observed but the rate of cooling is not constant and there is still a debate on its amplitude. several other factors may influence the evolution of the stratospheric temperature. external forcings, like the solar variability that modulate the UV solar flux and strong volcanic eruptions injecting aerosols in the stratosphere, participate to its decadal variability. the variability of the stratospheric dynamics is also adding some complexity to the system. For instance global climate models predicts an increase of the occurrence frequency of sudden stratospheric warming (SSW) events not yet confirmed by the observations. A monitoring of the stratospheric temperature evolution is crucially needed to better understand the complexity of the processes playing a role in the coupling between the stratosphere, the troposphere and the climate.the stratospheric temperature is measured at a global scale by satellite instruments; mainly microwave sounders aMsU (advanced Microwave sounding Unit) on board meteorological satellites. these sounders are very useful to provide the global overview but may suffer from biases and orbital drifts and have a poor vertical resolution in the upper stratosphere. since 2000 radio-occultation sensors, among them the Us-taiwan COsMiC constellation, provide well-resolved and accurate temperature profiles but limited to the upper troposphere-lower stratosphere. rayleigh lidars implemented within the nDaCC (network for the Detection of atmospheric Composition Change) international network measure accurately the temperature profile from the middle stratosphere to the upper mesosphere but in a very few locations. they are used climate change monitoring, dynamics studies and satellite validation.in this presentation we will present an update of the interannual variability and trends in the stratospheric temperature from aMsU, rayleigh lidar and radio- occultation measurements. similarities and differences in the temperature evolution captured by these various sensors will be evaluated. the contribution of anthropogenic and natural forcings to the observed changes will be discussed. a particular focus will be given to the role of SSW events to the stratospheric temperature evolution as a function of latitude and season

Self-confinement of wildfire smoke within long-lived vortices rising in the stratosphere

International audienceThe 2019-2020 Australian wildfires have produced a striking phenomenon in the stratosphere: an ascending disc of smoke contained within an anticyclonic vortex that persisted 3 months, travelled 66000 km and rose from 16 to 36 km. We analyse this exceptional structures and several of its companions with CALIOP data and the ERA5 reanalysis demonstrating its analogy with ellipsoidal free solutions of the quasi-geostrophic equation. A main difference is that here the vortex is maintained and rises due to the heating by the absorbing smoke. In the ERA5, where the wildfire smoke is missing, this forcing is exerted by the assimilation of spaceborne temperature profiles that produces an assimilation increment compensating the fast decay of the free solution. Based on these observations, we discuss the theoretical basis for the self-organisation and the stability of the smoke vortex. We show evidences that similar events, albeit of lesser magnitude, have already occurred, in particular during the Australian 2009 wildfire and the Canadian 2017 widlfire

A reel-down instrument system for profile measurements of water vapor, temperature, clouds, and aerosol beneathconstant-altitude scientific balloons

International audienceThe Tropical Tropopause Layer (14-18.5 km) is the gateway for most air entering the stratosphere, and therefore processes within this layer have an outsized influence in determining global stratospheric ozone and water vapor concentrations. Despite the importance of this layer there are few in situ measurements with the necessary detail to resolve the fine scale processes within this region. Here, we introduce a novel platform for high resolution in situ profiling that lowers and retracts a suspended instrument package beneath drifting long duration balloons in the tropics. During a 100-day 20 circumtropical flight, the instrument collected over 100 two-kilometer profiles of temperature, water vapor and aerosol at one-meter resolution, yielding unprecedented geographic sampling and vertical resolution. The instrument system integrates proven sensors for water vapor, temperature, pressure and cloud and aerosol particles with an innovative mechanical reeling and control system. A technical evaluation of the system performance demonstrated the feasibility of this new measurement platform for future missions with minor modifications. Six instruments planned for two upcoming field 25 campaigns are expected to provide over 4000 profiles through the TTL, quadrupling the number of high-resolution aircraft and balloon profiles collected to date. These and future measurements will provide the necessary resolution to diagnose the importance of competing mechanisms for the transport of water vapor across the TTL

First measurements of fine-vertical-scale wave impacts on the tropical lower stratosphere

International audienceAtmospheric waves in the tropical tropopause layer are recognized as a significant influence on processes that impact global climate. For example, waves drive the quasi-biennial oscillation (QBO) in equatorial stratospheric winds and modulate occurrences of cirrus clouds. However, the QBO in the lower stratosphere and thin cirrus have continued to elude accurate simulation in state-of-the-art climate models and seasonal forecast systems. We use first-of-their-kind profile measurements deployed beneath a long-duration balloon to provide new insights into impacts of fine-scale waves on equatorial cirrus clouds and the QBO just above the tropopause. Analysis of these balloon-borne measurements reveals previously uncharacterized fine-vertical-scale waves (1000km) and multiday periods. These waves affect cirrus clouds and QBO winds in ways that could explain current climate model shortcomings in representing these stratospheric influences on climate. Accurately simulating these fine-vertical-scale processes thus has the potential to improve sub-seasonal to near-term climate prediction

Long-Range Transport of Water Channelized through the Southern Subtropical Jet

In this study, an air mass (containing a cirrus cloud) was detected by light detection and ranging (lidar) above São Paulo (Brazil) in June 2007 and tracked around the globe, thanks to Lagrangian calculations as well as ground-based and satellite observations. Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) data were also used to provide locations of occurrence of cirrus around the globe and extract their respective macro physical parameters (altitude and temperature). An analysis of the air mass history based on Lagrangian trajectories reveals that water coming from the Equator is channelized through the southern subtropical jet for weeks. In this case, the back-trajectories showed that the cirrus cloud detected at São Paulo was a mixture of air masses from two different locations: (1) the active convective area located around the Equator, with transport into the upper troposphere that promotes cirrus cloud formation; and (2) the South Pacific Ocean, with transport that follows the subtropical jet stream (STJ). Air masses coming from equatorial convective regions are trapped by the jet, which contributes to maintaining the lifetime of the cirrus cloud for a few days. The cloud disappears near the African continent, due to a southern excursion and warmer temperatures, then reappears and is detected again by the lidar system in São Paulo after 12 days. The observed cloud is located at a similar altitude, revealing that sedimentation is small or compensated by radiative uplift

Lidar observations within the ARISE European network

International audienceA better understanding of climate change includes a better description of the variability at different altitudes, the vertical coupling between layers as well as the multi-scale interactions of the atmospheric processes. In response to these challenges numerical models including weather forecasts and operational analyses, are improved in both resolutions and vertical altitude range and new observations are expecting. Wind and temperature lidars provide useful information with an increased plus-value when they are combined with complementary information within a worldwide network. The proposed European infrastructure called the Atmospheric Dynamics Research Infrastructure in Europe (ARISE) start to deploy, in several stations (from polar to equatorial and tropical regions in the European longitude sector and adjacent regions), ground-based Lidar observations, microwave and OH radiometers and infrasound measurements in operation within the CTBT network (Comprehensive nuclear-Test-Ban Treaty). Such new data allow investigation on decadal trends, planetary waves, tides and gravity waves that can be used to validate or improve numerical models