Our Common Future Under Climate Change

International Scientific Conference 7-10 JULY 2015 Paris, France

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Tuesday 7 July - 17:00-18:30 UPMC Jussieu - Amphi Astier

1108 - Middle Atmosphere influence on Climate

Parallel Session

Lead Convener(s): S. Godin Beekmann (CNRS, Guyancourt, France)

Convener(s): E. Blanc (CEA, Arpajon, France), A. Charlton-Perez (University of Reading, Reading, United Kingdom), M. Dameris (DLR-Deutsches Zentrum fuer Luft- und Raumfahrt, Oberpfaffenhofen, Germany), C. Claud (CNRS, Palaiseau, France)

17:00

Future stratospheric ozone in a changing climate

U. Langematz (Freie Universität Berlin, Berlin, Germany)

Abstract details
Future stratospheric ozone in a changing climate

U. Langematz (1)
(1) Freie Universität Berlin, Institut für Meteorologie, Berlin, Germany

Abstract content

As a result of the Montreal Protocol on Substances that Deplete the Ozone Layer and its subsequent amendments and adjustments that constrained the production and consumption of halocarbons, the decline of stratospheric global ozone seems to have ceased. Model projections suggest a future recovery of the global mean ozone column to levels around the year 1980, when only low levels of ozone depleting substances (ODSs) existed in the stratosphere. However, the timing of the return of ozone to historical levels depends not only on the concentrations of ODSs but is also affected by thermal and dynamical changes associated with increasing greenhouse gas concentrations. For example, while the amounts of ODSs steadily decrease in the stratosphere, with appropriate meteorological conditions and given the long lifetimes of ODSs, individual years with strong ozone decrease still may occur in the near future.

Here, an overview of future projections of the ozone layer based on chemistry-climate model simulations will be presented. The impact of climate change on stratospheric ozone recovery will be discussed.

17:20

Stratosphere–Troposphere Coupling in a Changing Climate

M. Baldwin (University of Exeter, Exeter, United Kingdom)

Abstract details
Stratosphere–Troposphere Coupling in a Changing Climate

M. Baldwin (1)
(1) University of Exeter, Exeter, United Kingdom

Abstract content

Stratospheric variability and change has substantial effects on surface weather and climate, especially on the Annular Modes, with shifts in the jet streams, storm tracks, precipitation, and likelihood of blocking events. Despite unambiguous observations of this phenomenon, as well as numerical simulations, a clear physical explanation of this downward coupling has been elusive. In this talk I will discuss recent advances in our understanding—how pressure changes (movement of mass) in the stratosphere affects surface climate.  However, movement of mass in the stratosphere is not sufficient to fully explain the observed surface changes—surface effects are than would be expected theoretically, and are larger than at the tropopause. This “tropospheric amplification” is easily quantified, and suggests a role for eddy feedbacks in response to the movement of mass. I will discuss the future implications for surface climate, jets, storm tracks, etc.—assuming that we know how the stratosphere will change during the remainder of this century.

17:40

Sub-seasonal climate predictability associated with an anomalously strong stratospheric polar vortex

O. Tripathi, (University of Reading, Reading, Berkshire, United Kingdom), A. Charlton-Perez (University of Reading, Reading, Berkshire, United Kingdom), M. Sigmond, (Environment Canada, Victoria, Canada), F. Vitart, (ECMWF, Reading, Berkshire, United Kingdom)

Abstract details
Sub-seasonal climate predictability associated with an anomalously strong stratospheric polar vortex

O. Tripathi, (1) ; A. Charlton-Perez (1) ; M. Sigmond, (2) ; F. Vitart, (3)
(1) University of Reading, Meteorology, Reading, Berkshire, United Kingdom; (2) Environment Canada, Canadian centre for climate modelling and analysis, Victoria, Canada; (3) ECMWF, Reading, Berkshire, United Kingdom

Abstract content

There has been a great deal of recent interest in producing weather forecasts on the 2-6 week sub-seasonal timescale which bridges the gap between medium-range (0-10 day) and seasonal (3-6 month) forecasts. While much of this interest is focused on the potential applications of skilful forecasts on the sub-seasonal range, understanding the potential sources of sub-seasonal forecast skill is a challenging and interesting problem particularly because of the likely state-dependence of this skill (Hudson et al., 2011). One such potential source of state-dependent skill for the Northern Hemisphere in winter is the occurrence of stratospheric sudden warming (SSW) events (Sigmond et al., 2013). Here we show, by analysing a set of sub-seasonal hindcasts, that there is enhanced predictability of surface temperature and circulation not only when the stratospheric vortex is anomalously weak following SSWs but also when the vortex is extremely strong. During the third and fourth weeks following anomalously strong polar vortex conditions northern Europe and northern Russia are on average three degrees Celsius warmer than their climate norm, with similarly sized cold anomalies over northwestern North America. Sub-seasonal forecasts initialised during strong vortex events are able to successfully capture their associated surface temperature and circulation anomalies. This results, for some regions, in a significant enhancement of forecast skill compared to forecasts initialised during cases when the stratospheric state is close to climatology. We demonstrate that the enhancement of skill for forecasts initialised during periods of strong vortex conditions is comparable to that achieved for forecasts initialised during SSW events. this result indicates that additional confidence can be placed in sub-seasonal forecasts when the stratospheric polar vortex is significantly disturbed from its normal state. This presentation will discuss this result and its implications for understanding the impact of stratospheric climate change and its tropospheric impact.

17:50

Characteristics of stratospheric warming events during Northern Winter

P. Maury, (CNRS, Palaiseau, France), C. Claud (CNRS, Palaiseau, France), E. Manzini (Max Planck Institut, Hamburg, Germany), A. Hauchecorne (CNRS, Guyancourt, France), P. Keckhut (LATMOS-IPSL, Guyancourt, France), K. Kodera (Solar-Terrestrial Environment Laboratory, Nagoya, Japan)

Abstract details
Characteristics of stratospheric warming events during Northern Winter

P. Maury, (1) ; C. Claud (1) ; E. Manzini (2) ; A. Hauchecorne (3) ; P. Keckhut (4) ; K. Kodera (5)
(1) CNRS, Ipsl/lmd, Palaiseau, France; (2) Max Planck Institut, Hamburg, Germany; (3) CNRS, Latmos, Guyancourt, France; (4) LATMOS-IPSL, Guyancourt, France; (5) Solar-Terrestrial Environment Laboratory, Nagoya university, Nagoya, Japan

Abstract content

The polar mid-stratosphere is characterized by the setting up of westerly winds around the pole during the wintertime; the so-called polar vortex. The polar vortex is one of the most variable features of the zonal-mean circulation of the earth atmosphere, due to a highly non linear interaction between planetary-scale Rossby waves and the zonal flow. Indeed, the interaction between the upward tropospheric propagating waves and the polar vortex leads to a zonal flow weakening, implying a large day-to-day vortex variability. In the most dramatic cases, the polar vortex breaks down, the stratospheric polar flow can reverse its direction and the temperatures can rise locally by more than 50K in a span of a few days. Such phenomena are known as major Sudden Stratospheric Warmings (SSWs) and constitute, since their discovery in 1952 (Scherhag,1952) the most impressive dynamical events in the physical climate system. On the contrary, situations where the temperature increase is not associated to a polar vortex breakdown are known as minor SSWs.

 

There is actually a renewed interest about SSWs since Baldwin and Dunkerton (2001) have shown that the major SSWs can influence weather in the troposphere. This stratospheric-tropospheric linkage has been statistically highlighted but no physical explanation has been proposed. Also, other studies, that incorporate both major and minor SSWs, show that events in the stratospheric zonal flow associated with SSWs present downward-propagating anomalies that can reach the troposphere (Limpasuvan et al 2004), implying that minor SSWs have to be also considered in the study of the stratospheric-tropospheric dynamical coupling.

 

In this study, we propose a global characterization of stratospheric warmings situations based on a temperature threshold in the 50-10hPa layer between 70N-90N, in order to better assess the properties of daily stratospheric temperature variability during the northern winter. The originality of this approach consists in evaluating the wintertime positive temperature anomalies in terms of intensity and duration without distinction between minor and major SSWs. We will show that there is a wide spectrum of warming types, where major SSWs are the most extreme, but other events – the minor SSWs – share some common properties with them. They can even have a surface signature if one look the stratospheric wave reflection on the polar vortex.

18:00

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

A. Hauchecorne (LATMOS-IPSL, Guyancourt, France), P. Keckhut (LATMOS-IPSL, Guyancourt, France), C. Claud (CNRS, Palaiseau, France), B. Funatsu, (CNRS, Rennes, France), S. Khaykin, (LATMOS-IPSL, Guyancourt, France), G. Angot, (LATMOS-IPSL, Guyancourt, France), P. Maury, (CNRS, Palaiseau, France)

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

A. Hauchecorne (1) ; P. Keckhut (1) ; C. Claud (2) ; B. Funatsu, (3) ; S. Khaykin, (1) ; G. Angot, (1) ; P. Maury, (2)
(1) LATMOS-IPSL, Guyancourt, France; (2) CNRS, Ipsl/lmd, Palaiseau, France; (3) CNRS, Letg-rennes costel, université rennes2, Rennes, France

Abstract content

The 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.

18:10

Role of the middle atmosphere for low-frequency climate variability

T. Reichler (University of Utah, Salt Lake City, Utah, United States of America), Z. Bowen (University of Utah, Salt Lake City, Utah, United States of America)

Abstract details
Role of the middle atmosphere for low-frequency climate variability

T. Reichler (1) ; Z. Bowen (1)
(1) University of Utah, Atmospheric Sciences, Salt Lake City, Utah, United States of America

Abstract content

It is commonly believed that the ocean represents the dominant source for climate variability on longer, interdecadal time scales and that this drives the low-frequency variability of the atmosphere. Here, we provide evidence for the existence of opposite pathways. Investigating long control simulations with coupled and uncoupled climate models we find considerable multi-decadal variability in the atmosphere that is independent of the ocean and that influences climate. The middle atmosphere represents one source for such low-frequency variability. The variability is related to relatively long-lived fluctuations in the strength of the stratospheric polar vortex, which in turn project on the state of the North Atlantic Oscillation. This creates signals in ocean temperatures over the deep convective region to the south of Greenland, which, over the course of several years, propagate into the deep ocean. These events modulate and drive intrinsic low-frequency variability in the Atlantic Multidecadal Overturning Circulation (AMOC) and explain about 20% of the natural AMOC variability. Our findings support the view that trends and low-frequency variations in the middle atmosphere extend their influence beyond the troposphere into the ocean and that this constitutes an important source of climate variability. We discuss natural and anthropogenic sources for such low-frequency stratospheric variability.

18:20

The millennium water vapour drop in the stratosphere in chemistry-climate model simulations

S. Brinkop (DLR-Deutsches Zentrum fuer Luft- und Raumfahrt, Oberpfaffenhofen, Germany), M. Dameris (DLR-Deutsches Zentrum fuer Luft- und Raumfahrt, Oberpfaffenhofen, Germany), P. Joeckel, (DLR-Deutsches Zentrum fuer Luft- und Raumfahrt, Oberpfaffenhofen, Germany), H. Garny, (DLR-Deutsches Zentrum fuer Luft- und Raumfahrt, Oberpfaffenhofen, Germany), S. Lossow, (KIT - Karlsruher Institut für Technologie, Karlsruhe, Germany), G. Stiller (KIT - Karlsruher Institut für Technologie, Karlsruhe, Germany)

Abstract details
The millennium water vapour drop in the stratosphere in chemistry-climate model simulations

S. Brinkop (1) ; M. Dameris (1) ; P. Joeckel, (1) ; H. Garny, (1) ; S. Lossow, (2) ; G. Stiller (2)
(1) DLR-Deutsches Zentrum fuer Luft- und Raumfahrt, Institut fuer physik der atmosphäre, Oberpfaffenhofen, Germany; (2) KIT - Karlsruher Institut für Technologie, Imk-asf, Karlsruhe, Germany

Abstract content

This study investigates the millennium water vapour drop, the abrupt and severe water vapour decline in thestratosphere beginning in year 2000, by means of various simulations using the Chemistry-Climate Model (CCM)EMAC. Since the beginning 1980s, balloon borne stratospheric water vapour measurements and correspondingsatellite measurements starting in the early 1990s indicated a long-term steady increase of water vapour concentrations.However, the multi-year data sets also show significant fluctuations on different time scales. In theyear 2000, an extraordinary sudden drop of stratospheric water vapour concentration has been observed followedby persistent low values for several years. Solomon et al. (2010) showed that this drop slowed down the rate ofincrease in global surface temperature over the following decade by about 25%. So far, the stratospheric watervapour variations observed by satellite from 1992 to 2012 are not reproduced by CCM simulations forced byobserved changes in sea surface temperatures, greenhouse gases and ozone-depleting substances (Gettelman et al.,2010, Randel and Jensen, 2013).However, the CCM EMAC is able to reproduce the signature and pattern of the water vapour disturbances inagreement with those derived from observations. In this paper we present results of a hierarchy of simulationswith the CCM EMAC, demonstrating that it is possible to retrace the observed water vapour fluctuations in thestratosphere (incl. the millennium drop), if suitable inner and outer boundary conditions are applied.