Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | , and 1 Chemistry -line Edwards- and Physics Discussions , A. Rap Atmospheric ff 2 , J.-J. Morcrette 2 O scheme is suitable for any global ect of using the CoMeCAT scheme 2 ff /H 4 O variation in fair agreement with satellite 2 , A. Untch 480 479 1 scheme has also been used to derive a source 4 stratospheric distribution on these RF calculations 4 field and with observations from the Halogen Occul- O distributions in the ECMWF GCM present realistic 4 2 , i.e. the same order of magnitude, and opposite sign, as the 2 − , M. P. Chipperfield 1 climatology used by the ECMWF model, CoMeCAT produces up to 2 K 2 ect of the new CH 4 ff value, the CoMeCAT distributions produce an overall decrease in the annual 4 This discussion paper is/has beenand under Physics review (ACP). for Please the refer journal to Atmospheric the Chemistry corresponding final paper in ACP if available. Institute for Climate and Atmospheric Science, School of EarthEuropean and Centre Environment, for Medium-Range Weather Forecasts, Reading, UK is of up toinclusion of 30 mW aircraft m contrails formation in the radiative model. methane description has in thethe GCM default CH radiation scheme iscooling also in explored. the Compared tropical to for lower radiative forcing stratosphere. (RF) calculations The hasSlingo e been (E-S) investigated using radiative the transfer o 3-D model. CH Compared tomean the net RF, use with of theitudes. largest a decrease tropospheric The found e global over the Southern Hemisphere high lat- lower above 10 hPa). Theterm potential transport of within the the new ECMWFthe CoMeCAT model free scheme running is for GCM exploited evaluating to to long- ERA-40GCM assess and shows the ERA-Interim similar impacts reanalyses. transport of In patterns this nudging ysis case, to data, the the ERA-Interim nudged CTM producing forced better by results the than corresponding ERA-40. reanal- The impact that the new model and here isCTM shown and to in provide theGCM. realistic Simulation ECMWF results profiles (European from in Centrewith the the the for new full-chemistry 3-D Medium-Range stratospheric CTM TOMCAT/SLIMCAT Weathertation CH scheme Forecasts) Experiment are (HALOE). in The goodfor CH agreement stratospheric water.the CTM Stratospheric produce water vertical incrementsobservations. and latitudinal obtained Stratospheric H in H overall this features although way concentrations within are lower than in the CTM run (up to 0.5 ppmv A new linear parameterisation foroped stratospheric and methane tested. (CoMeCAT) has(CTM) been The and devel- tested scheme within is thegeneral same derived circulation chemistry from model model (GCM). a itself, The as 3-D new well CH full as in chemistry an independent transport model Abstract A. J. Simmons 1 University of Leeds, UK 2 Received: 10 October 2011 – Accepted:Correspondence 5 to: November 2011 B. – M. Published: Monge-Sanz 6 ([email protected]) JanuaryPublished 2012 by Copernicus Publications on behalf of the European Geosciences Union. On the uses of astratospheric new methane linear in scheme global for models: water source, transport tracer and radiative forcing B. M. Monge-Sanz Atmos. Chem. Phys. Discuss., 12,www.atmos-chem-phys-discuss.net/12/479/2012/ 479–523, 2012 doi:10.5194/acpd-12-479-2012 © Author(s) 2012. CC Attribution 3.0 License. 5 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | , , , 4 H (1) ), for Jones Austin Dethof ; ). 2006 , 1950 2004 , . Methane has , 4 McCormack et al. McCormack et al. ; O as the main source O( found in most general O. 2 2 2 4 McNally et al. 2007 ; O and CH , 2 precision, which is beyond Randel et al. 1 and H 1999 4 , Bates and Nicolet Austin et al. ; ) which, as discussed below in more detail, 2004 482 481 , Saunders et al. O. Therefore, a realistic representation of CH and chlorofluorocarbons (CFCs). However, the 2 2007 ( ). In a global model the total hydrogen amount 4 1988 , O, CH in the stratosphere, mesospheric photolysis, transport erent aspects of the DAS/NWP model to interact with a 2 2 4 ff H ,H + 3 Austin et al. O parameterisation simple enough for forecasting purposes, 2 CO 2 is also uniformly distributed in the stratosphere when the last two H O is the oxidation of methane (e.g. 2 + H . The current scheme also includes a sink term representing the pho- Le Texier et al. 4 4 MacKenzie and Harwood ; ; CH O in the mesosphere. At the basis of such scheme is the observational · ) confirmed that this is true within 0.05 ppmv 2 2 1984 + , 2003 , O 2007 2 ( ) but, as discussed in the rest), of and this the section, lack). there of are an Also, issues interactive most they link of still between the do CH models not used to obtain these parameterisations were two- H parts per million by volume 1 O vapour simulations within 3-D global models are problematic due to the variety = The current European Centre for Medium-Range Weather Forecasts (ECMWF) A few approaches exist for the parameterisation of water vapour in the stratosphere must be conserved under mixing and transport. More recent studies have shown Implementing an H Water vapour in the stratosphere is not only a radiatively active constituent but is also 2 Dethof tolysis of H 2008 dimensional therefore, missing the influencethe of scheme proposed longitudinal by features. Theovercomes these exception is problems but requiresusually tracers available in (e.g. NWP an and age-of-air DAS tracer) models. that are not model includes a simple parameterisationoxidation of of CH stratospheric water vapour based on the ( 2008 solve. Among2003 such issues are the lack of a realistic latitudinal variability ( that the quantity terms are neglected, i.e. theet last al. two terms arethe small precision (e.g. of available measurementsno of sources stratospheric in H theoxidation stratosphere, results apart in the from productionis the of crucial entry H to through correctly parameterise the a tropopause, source and of its stratospheric H of stratospheric H and Pyle H as a simply globally averaged value. This is of relevance for H circulation models (GCMs) which, in spite of being a major GHG, is often represented These processes also depend onon others, convection and e.g. tropospheric tropopause entry temperatures.the above rate In factors, depends e.g. addition, mainly radiation, feedbacksperatures. stratospheric exist circulation between and An all tropical accurate tropopauseplicated simulation tem- task of that stratospheric requiressimilar water di accuracy vapour so is that larger therefore biases a in com- one factor arewhile not considering detrimental all for the theOne relevant others. processes of in the an current accurate problems way is is the not poor straightforward. representation of CH H of processes involved. Thesult distribution of of a water combinationlayer vapour of (TTL), in factors: oxidation the of stratosphere Humidityand is entry CH mixing the within rate re- the through stratosphere the and tropical exchange tropopause processes through the tropopause. models for operational weathersimplified forecasting, and parameterisations these of modelsgases must the (GHGs) therefore species such include as mostdescription O relevant of to these gases them,purposes. is, i.e. in many greenhouse cases, still too simple forkey for current many physical stratospheric and chemical processes,mation, e.g. liquid polar aerosol stratospheric composition cloud and (PSC) production for- of the OH radical. Still, stratospheric Numerical weather prediction (NWP) models andtinely data assimilate assimilation satellite systems radiances (e.g. (DAS) rou- which a realistic descriptionchemistry of calculations stratospheric are radiatively prohibitively expensive active at gases the resolutions is used essential. by NWP/DAS Full 1 Introduction 5 5 20 25 15 10 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | (7) (8) (6) , by Kin- q ) : 2 are functions τ 2 1988 ( τ and chemistry, such as 1 τ 4 and 1 τ oxidation source (due for 4 for the pseudo-reaction that k Le Texier et al. in days. cient as a function of pressure are used 2 ffi τ 2 k ) ). and and 1 2004 τ 1 484 483 , 1999 k , , and ) used the Thin Air 2-D photochemical model ( 1 − O] increases at a rate 2 ). There is no latitudinal or seasonal dependency in- 2004 ( as Randel et al. ) to obtain the rate coe 6 1984 ( Simmons et al. 10 (kg/kg). In addition, above approximately 60 km a term for the oxidation process described by 1993 × 6 , 4 6 − . ] (10) 8 ppmv ( are given in s . 4 are defined using appropriate timescale factors ), 10 6 2 2 2 × k ∼ k can be determined from a model with detailed CH [CH ). q · 1 2 25 1 2 . O] (2) τ τ O]) (4) k · · O (9) k 2 4 O] 2 and and 2 was obtained as a function of latitude, altitude and season using the expres- 2 − = 1 1 [H 1 2003 ] (3) 1 [H )) (5) k dt k 4 , 2H [H k + Q q q − ] d k 4 − − 8 86400 86400 −→ . 2 1 [CH 4 Q Q = = O loss by photolysis has to be added, and so the complete ECMWF humidity pa- 1 ( ( (6 MacKenzie and Harwood Both The rate = 2 1 2 1 1 1 k Dethof k nersley and Harwood groups the whole CH CH the rate sion similate stratospheric humidity datafield operationally, directly but in uses theshapes the analysis. the background stratospheric humidity Therefore, humidity, ultimatelyand it temperature constrained is fields to the ( observations model by dynamics the and wind physics which of pressure so thatBrasseur the and photochemical Solomon lifetimecluded of in water the vapour ECMWF follows scheme,instance nor that to any increasing shown variation tropospheric in in concentrations the of CH this gas). ECMWF does not as- k k where by ECMWF, where analytical( forms for simply dividing by 1 where was done in thepersonal past communication, with the 2004). 2D-model of Nevertheless, the a University simpler of option Edinburgh (B. is Harwood, used at present k H rameterisation is k that the vmr of water vapour [H 2 with a value of 2[CH or by using Eq. ( k evidence that the following quantity is fairly uniformly distributed in the stratosphere where [ ] stands for volume mixing ratio (vmr). The ECMWF model assumes, therefore, which is expressed in ppmv and can also be written in terms of specific humidity, 5 5 15 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 4 4 in 4 and (11) in the tracer 7 oxida- 4 4 4 the water oxidation), e 4 | ) in the con- O . Then results 2 4 ), in which a 2-D 2008 ( cients is explained ffi 2004 ( O concentrations in a 2 O increments but also a MacKenzie and Harwood 2 . 8 ) with a 2-D photochemical 6 tracer and therefore focused on oxidised depends on the time air 4 4 McCormack et al. shows the results from the ECMWF in Eq. ( 6 2 k ) and the ECMWF GCM. 486 485 and 2006 MacKenzie and Harwood , 1 O entry. At present, the kind of parameterisation k ) described a parameterisation for water vapour 2 to be t ers from that in ) and ff 2008 ( , the methane oxidation term, can be expressed as cients B )] (12b) ffi 2008 ( ,t ) is its high altitude range, however their study was mainly ) could not be implemented by ECMWF due to the lack of O directly and, in a similar way to Chipperfield x 2 ( cients for Methane from a Chemistry And Transport model) and time 4 ffi -line radiative forcing calculations are discussed in Sect. x 2008 2007 ( ) studied the evolution of stratospheric H ( ff CH tracers in its Integrated Forecasting System (IFS). − 4 and, correspondingly, Sect. ) γ 2007 5 ( B ) (12a) − ) the mean age-of-air for that particular location, and H tracer for the global GCM. Therefore, the new method we propose has γ t + ( ,t in this paper presents the new linear approach used to parameterise CH McCormack et al. 4 − 0 A | x t 2 ( 4 ( = . The observations used for validation are introduced in Sect. McCormack et al. γ e ) , the entry term, and | Austin et al. 3 O, two major GHGs which have the potential to improve the assimilation of radi- O in the stratosphere, while the calculation of the linear coe A = ,t O [CH 2 2 ), they obtain the coe 2 · x γ 2 H O( O concentrations coming from the CCM photochemistry scheme (via CH McCormack et al. Section Unlike Recently Austin et al. = = 2 2 2004 Methane is produced at thetransported Earth’s into surface the through stratosphere human mainly and natural through activities, the and tropical tropopause. CH GCM simulations. O the summary and conclusions from the paper are in Sect. 2 Linear approach for methane in Sect. and H from the new scheme withinwater, the CTM in simulations are Sect. presented, for both methane and called CoMeCAT (Coe can be implemented CTMTOMCAT/SLIMCAT within ( any global model and has been here tested within the ceptual approach of thethe parameterisation, stratosphere as and ours then focuses usingthis on it way to parameterising our obtain CH new arealistic scheme source CH provides of not stratospheric water onlythe vapour. stratospheric advantage In H of providingand H a consistent stratosphericances in parameterisation a of data assimilation bothsuitable system for CH (DAS), internal as transport well as checks to in provide the a GCM. realistic CH The new scheme, which has been model was used, wewe use present a in 3-D chemistry-transport this paper model also (CTM). di The linear scheme in concerned with the mesosphericresults region for (10–0.001 our hPa) stratospheric and study. provides no comparative ( model as function of altitude, latitude and season. The main advantage of the scheme age-of-air and CH production and loss tosimilar be to used the in current avariation. ECMWF high They approach, altitude wanted with NWP/DAS to the avoid system.the improvement the parameterisation inclusion of Their of of including method H a latitudinal is CH vapour amount remaining from theused H in stratospheric location H where A chemistry climate model (CCM)H ensemble run fromand 1960–2005. concentrations obtained They from examined ation the parameterisation and involving also entry mean rates, age-of-air, CH masses as have the spent amount in of the CH stratosphere. They formulated the water concentration at a B with 5 5 25 15 20 10 15 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | ) 4 15 (18) (17) ): can be L ], 2007 4 , O tendencies 2 ). 1 ` . Since the three edre − L s 1 − ). ) and [CH 1 T − ) where the last two terms 1 molecule 3 can be written as 4 loss rate (s Cariolle and Teyss 4 ; ). 1986 ) (16) , 5.2 ´ T e 488 487 is the CH varies with temperature. − L T ´ L equ ( 2 c + are ]) i 1, 2, 3) are given in (cm 4 c = i ( [CH i [Cl] (15) destruction depend on temperature ( k 3 − O (14a) 4 ] k Cariolle and D relates to how cients 2 4 has been parameterised following the CoMeCAT approach and represents how the loss rate adjusts with changes in the CH + 2 H OHHCl (14b) (14c) ffi 4 ´ e ( 1 c + + + c ] D)] 3 3 3 ([CH 4 1 ] (13) 1 ´ equ 4 c scheme presented above can also be used to obtain H O observations (see Sect. CH CH CH ∂t in the stratosphere takes place mainly through the following reactions [O( 2 [CH + 4 2 0 4 0 ∂ [CH due to chemistry corresponds to k → → →

has no stratospheric source except entry through the tropopause, the c ] 2 L 4 + 4 Cl 4 − D) − = 0 OH 1 )

+ = = ∂L + 4 [CH ] ,T O( 0 [OH] 4 4 4 ∂T ∂ ∂L 1 O] is only destroyed, our new scheme parameterises the loss rate L + 2 CH k 4 4 is the loss rate for a given reference state (subscript 0 indicates values obtained at = = = ∂t ∂t CH We have implemented such scheme in TOMCAT/SLIMCAT 3-D runs, and ECMWF In this case the coe Full chemistry 3-D models such as SLIMCAT calculate the oxidation rate in Eq. ( Loss of CH Based on such reactions, the oxidation rate of CH = [H [CH 0 1 2 (CH 0 ∂ ∂ c c c compared to H GCM runs, where CH written as have been neglected, the time tendency for water vapour in the stratosphere can be L Since CH CoMeCAT CH in the stratosphere. Based on an approximation of Eq. ( L a reference state), concentration, while 2.1 Scheme for water vapour analytically from the involved reactions.a However, in simplified order to methane provide NWP scheme,CH models an with alternative approachreactions has involved in been CH exploredparameterised here. following a As scheme similarby to Cariolle the and one D proposed for the ozone tendency L CH spheric CH stratosphere is only destroyed by oxidation, therefore, the time tendency of strato- where [ ] indicates concentrations and where the rate constants 5 5 10 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | ] i ) ) 4 k ) for 1 ) has [CH 2011 2005 ( ). The c , , 60 km), 13 2 ∼ c ) run 323. shows the , 2008 1 cient ( 3 c Brasseur and and the other ffi , 2006 0 0 for January and , , which leads to increase implies c c x T 4 . Further details on ). The temperature shows how temper- Uppala et al. 2 horizontal resolution concentration causes c 4 for January, April, July cient ◦ 5 % with respect to the 4 ] and ffi 2 4 ± 2005 7.5 Monge-Sanz et al. 1 hPa and are almost 1 yr Monge-Sanz , ∼ × Chipperfield ◦ ] of [CH loss rate takes place. Above 4 4 ). The reference state values of Kouker 14 , so the scheme actually parame- 4 K to obtain i c ± and temperature. Figure 4 , is plotted in Fig. τ ect occurs in the LS region and above the ), is obtained from a control run in which the cients 0 ff 489 490 ffi , variations in [CH 1 cients can be found in c cient c ffi lifetime, are in overall agreement with those in cients for each latitude, level and month of the year. ), explained by the fact that a CH ffi 4 2 ffi 3 concentrations have on the loss rate (coe (coe 4 0 cients for a stratospheric ozone scheme. To calculate the (Fig. increase causes an increased loss rate. cients L . To obtain ffi 4 L in the full-chemistry SLIMCAT has been widely validated, and 2 ffi c 4 cients (loss tendency with respect to temperature) are negative every- coe loss. The opposite e ffi 2 and 4 4 c 1 cients have been calculated from full-chemistry runs of the global 3-D c ). . In the middle stratosphere, an increase in CH ffi L are directly provided by the zonal output of the SLIMCAT initial state on the loss decreases (lifetime increases) due to the decrease in the abundance − T 2005 4 ). The negative sign agrees with the fact that by increasing temperature, cients and climatologies are provided as 5 look-up tables ( = ( cients plots the zonal mean of the reference values for 0 4 ffi L ffi 1 ) for every month. cients, the TOMCAT box model was initialised with the zonally averaged output ] and T 4 ffi The CoMeCAT zonal mean CH The values of Methane time tendency is controlled mainly by the first coe The reference loss rate Figure July. Stratospheric CH compares very well withfield corresponds MIPAS to observations ECMWF (e.g. operational data for 2004 interpolated ontoand the CTM October. grid. The minimumover lifetime the values are summer reached pole, at 1 region hPa, where CH the maximumof CH OH. The lifetime values in Fig. calculation results in a set of coe The coe and 3.2 The new CH where except in theLS equatorial (Fig. LS (between 100–200 hPa) and in the Arctic summer reference state are introduced; andthe variations runs of used to calculate the coe ature changes feedback onbeen the included loss when rate. calculatingterises the Note coe thata the decrease minus in sign lossa in rate decrease Eq. of ( ClOa at decrease around in 40 km CH stratopause, and where a an CH overall decrease of HO 15th of each month.the Then, coe perturbed runs of the box model are carried out to obtain Solomon terms add corrections dueimpact to that changes changes in inthe CH CH months of January, April, July and October. Similarly, Fig. [CH zonal 3-D output is usedcalculated without from the alteration three to chemical initialise reactions the in box Eq. model. ( The loss rate is corresponds to January to Decemberbox 2004. model From were the carried initial state out;conditions. five one 2-day control In runs run these of and the adopted runs for four the the perturbation box chemistry model runs is from wasmatching 24 the latitudes, computed the and initial every 24 resolution levels 20 (from min. ofmodel the surface also the up The uses to full-chemistry the resolution same run chemistry used module as for the the full initialisation. SLIMCAT model. The box for the calculation ofcoe coe of a full-chemistry simulation ofRun the 323 SLIMCAT 3-D is modeland ( a 24 multiannual vertical SLIMCAT levels run (L24).from 1977–2001 that The and uses run by is aconfiguration ECMWF driven is operational 7.5 by identical winds ERA-40 to from winds thedoes 2002–2006. ( 3-D not The CTM consider box (chemical transport model descriptions, processes. resolution The etc.) period but chosen it to initialise the box model 3.1 Calculation methodology CoMeCAT coe CTM,TOMCAT/SLIMCAT similar to the method employed in 3 CoMeCAT coe 5 5 10 25 25 15 20 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | ]. O 4 2 CH S), and erences ◦ Bregman ff ) and H ; ect, coming ff N-80 erences over ◦ ff 1996 2002 , , cients, calculated ffi tracer in these 3-D O measurements at 4 erences between the 2 observations is better ff ). Two SLIMCAT-mode 4 correspond to year 2000; 5 Park et al. 2011 ( , 4 ]. concentrations from the param- 4 4 concentrations are slightly smaller Chipperfield et al. CH ). Both simulations, CoMeCAT and 3 ). 4 loss. The decrease in loss over the 2[ than observed over the tropical mid- ) and 10 % for H ) of CH 4 Dee et al. − 4 6 − 2007 1996 1993 , O 10 , , c) is explained by a secondary e 491 492 2 × 4 0 . erences with the full-chemistry run323 and with ff and H 4 Feng et al. Park et al. ; Russell et al. (run13) and one full-chemistry (run323). Also two TOMCAT- 2006 4 , erences concentrated around 10 hPa at high latitudes in both O tracer were 7 ff 2 ). The HALOE data used in our study correspond to the third ) and ERA-Interim winds ( fields (CoMeCAT and full-chemistry) are smaller than the di vertical levels) runs driven by ERA-40 winds, one implementing the 4 1996 ect in this region. 2005 θ , ff - , measurements above 100 hPa. Results in Fig. σ Eyring et al. erent from the year used to compute the CoMeCAT coe 4 ; ff ) increases, which means more CH shows the annual mean zonal average CH -p vertical coordinate) runs, both implementing the CoMeCAT scheme, one describes the 3-D CTM runs that have been performed using ERA-40 winds 15 σ 5 2006 1 , Uppala et al. Harries et al. driven by ERA-40 and the other by ERA-Interim winds. The CH (with hybrid CoMeCAT scheme for CH mode ( with HALOE is good; modelledup concentrations, to both 0.20 CoMeCAT ppmv andSH, full-chemistry, lower are with than maximum HALOE di hemispheres. in the CoMeCAT most simulatesstratosphere upper more and levels most CH upper (above levelstwo 20 at modelled hPa) CH high in NH the latitudes.between The the di modelled fields and HALOE observations. full-chemistry used the sametion ECMWF is ERA-40 able winds. tothe capture The tropics all CoMeCAT above general parameterisa- features 10(up hPa, and to where variability. 0.05 ppmv), CoMeCAT There0.10 CH as ppmv are well more di as than SLIMCAT in full-chemistry LS over high the latitudes, Arctic. where The CoMeCAT overall simulates agreement up to ( 5 CoMeCAT in the SLIMCAT CTM Table 5.1 CoMeCAT against full-chemistry 5.1.1 Methane cross-sections Figure eterisation in run13,HALOE as CH well aswhich di is di for the meteorological conditions of 2004 (Sect. CTM runs was initialised withThe the same concentrations from climatology the was referencetime used climatology step, [ to to prevent overwrite the surface the valuesinitial tracer from values value drifting for during the at the H the model surface simulations. at The every November 1991 – November 2005.than The 7 accuracy % for between these CH 1–100the hPa same ( altitude range. Suchused HALOE data for have several been widely modelet validated results and al. have validations been (e.g. ( HALOE data are zonally averaged49 and pressure are available levels for (from 41 100–0.01 latitudes hPa); (80 the monthly time series covers the period public release v19 (W. Randel and F. Wu, personal communication, 2007). These 4 HALOE observations of CH The results of the model simulationsHalogen have Occultation been Experiment validated (HALOE) against instrument, observations on fromResearch board the the Satellite Upper Atmosphere (UARS, Arctic summer (positive contours infrom Fig. decreased OH concentrationstemperature e at higher temperature, that outweighs the direct in Eq. ( 5 5 20 20 15 10 15 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | ) p − σ ) larger erence. ff θ erences of ff ). erent latitudes. . ff 1 − 2007 , erent CTM runs have K kg erences being the too ff 1 ff − s , for five di 2 6 m reference field as the CTM O. The runs were performed 6 2 4 − erences smaller than 0.1 ppmv), 10 , also within 0.1 ppmv di ff 6 = and H Monge-Sanz et al. 4 vertical distributions from the CoMeCAT and the potential temperature ( 4 2 O tendencies from CoMeCAT. We define erences occur above 1 hPa, where CoMe- 2 ) one (run13) and also one TOMCAT ( ff 494 493 θ − σ O is between 0.2–0.8 ppmv larger than observed by 2 0.6 ppmv in the range 100–50 hPa, then agreement in O in the ECMWF model. One additional ECMWF run ∼ distributions and its value is: 1PVU than the SLIMCAT run13. Above 1.0 hPa di 2 4 4 by up to 0.1 ppmv, and below 30 hPa, where the parameteri- and H 4 4 ) is used to obtain H 300 K. in the ECMWF GCM erently in the tropics and outside the tropical region. In the tropics 18 vertical coordinate. The overall agreement in the LS (up to 10 hPa) 4 ff θ > p shows annually averaged CH − 6 σ shows water vertical profiles for the 2000 annual average from CoMeCAT N) it is defined as the level at which the minimum temperature is reached, potential vorticity unit ◦ ). 7 erences occur above 10 hPa. At the highest levels the agreement with obser- ff describes the runs carried out with this model to examine the ability of CoMe- 6.2 2 S–15 PVU is ◦ 2 Figure larger di vations is good for fif4 and SLIMCAT run13 in Fig. The ECMWF runsruns. were Figure initialised withscheme in the the same CTMbeen CH and included, in the the default ECMWF SLIMCAT ( run GCM (run (run14) fif4). for a Twoalso di better uses comparison a againstis the good ECMWF between runs, all which, runs like and the observations GCM, (with di 6.1 ECMWF CoMeCAT CH CAT to reproduce CH was performed to evaluate the(Sect. impact of CoMeCAT on the ECMWF radiation scheme CAT scheme. 6 CoMeCAT CH A series of runs withinCAT the scheme ECMWF to GCM (IFS) parameterise havewith stratospheric been carried the CH out Cy36r1 using theTable model CoMe- version (operational in 2010) with a resolution of T159L60. the middle stratosphere (50–3 hPa)high is latitudes very where good CoMeCAT for H allHALOE. Above latitudes, 3 except hPa, over CoMeCAT again southern producesthan larger observed. concentrations (0.2–0.5 The ppmv) discrepancyHALOE over in southern the high LS is latitudes most between probably CoMeCAT due and to the lack of Antarctic dehydration in the CoMe- CoMeCAT shows a wet bias of along with HALOE observations.CAT The approach, overall the variability best is agreement well is found captured over by NH the high CoMe- and mid latitudes. In the LS the tropopause di (15 while outside the tropicspotential the vorticity stratospheric (PV) is waterthan larger scheme 380 K, than is or 2 used if PVU when the absolute 5.2 CoMeCAT water distributions within theTo CTM obtain CoMeCAT water distributions withthe the ECMWF SLIMCAT CTM, analysis the is humidity used fielddescribed from in in the troposphere, Eq. while ( in the stratosphere the relation CAT overestimates CH sation, especially at southernfull-chemistry midlatitudes, (up results to 0.05 in ppmv smallerin smaller). concentrations good CoMeCAT in than agreement the the TOMCAT with runsphere (run14) full-chemistry it is simulates in also more the CH up LS, to but 0.25 ppmv in widelyin the occur the middle and highest and run14 levels at results upperfast tropical in vertical strato- latitudes, up transport the to in reason the 0.40 for ppmv run TOMCAT-mode these more ( di than run323 Annual averaged (yearchemistry run 2000) 323 between 100–0.2 verticalThe hPa are CoMeCAT shown distributions vertical in Fig. distribution fromfull in chemistry CoMeCAT the run. SLIMCAT and The run most the (run13) significant agrees di full- well with the 5.1.2 Methane vertical profiles 5 5 25 20 15 10 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | ; ); field field, ) also 2007 4 4 2006 , ), while Ploeger , ; 2006 ( Curry et al. 2008 , 2010 , as dynamical winter Collins et al. 4 climatology (run fif4) in Curry et al. Liu et al. 4 Monge-Sanz et al. erences in temperature in ff Tegtmeier et al. . erent: the CTM obtains it from ; 6 ff oxidation. 4 ). 2008 value of 1.72 ppmv was used by the , ), such value is typical of tropospheric fields of both runs (fipj-fif4) are shown 4 erences in the mid-upper stratosphere distributions from the CoMeCAT tracer ff 4 2008 ) with a simplified treatment for the chem- 4 , ) to cause temperature biases in the upper 2009 concentrations (e.g. , 4 496 495 field had been reported to be too noisy in the 1992 2008 , w ( ¨ uger et al. Kr ; as a well-mixed gas, which is unrealistic above the 4 erences (up to 0.50 ppmv) over mid and high latitudes is considered both in the shortwave (SW) and the long- ff 2004 erences here. 4 erences in the CH , ff di Bechtold et al. S) between 10–100 hPa; temperature values in this region O resulting from the CH ff 2 ◦ 4 Hollingsworth et al. Monge-Sanz . The ECMWF McFarlane et al. , CFC-11 and CFC-12. They found a general cooling of the 4 w N–20 ◦ ). Nevertheless, definitive conclusions cannot be drawn on this issue O, CH 2 shows the June-July-August (JJA) averaged di distributions. Di 2011 ), in agreement with our comparison in Fig. Fueglistaler et al. , 4 8 . The largest CH 9 2011 ) showed the impact that relaxing the well-mixed approximation for some green- , In order to evaluate the impact that CoMeCAT has on the ECMWF temperature field, Figure In past versions of the IFS GCM a global CH 2006 in Fig. the ECMWF model using thethe default IFS operational ECMWF radiation CH scheme(run and fipj). using Absorption the bywave CH CH (LW) in thetropics two (between runs. 20 Withare CoMeCAT, temperature up decreases to appear 2.0 Kobserved over lower the over than the with winter thevariability IFS hemisphere between default the cannot climatology. two be compared Theferent related runs temperature CH can to changes be CH larger than changes induced by dif- of the run allows usin to the examine summer temperature hemisphere, di variability and can in be the too large tropical into UTLS winter determine region. high temperature latitudes, di However, as the well dynamical as in low tropospheric levels, compared to the newthe default ECMWF climatology, radiation CoMeCAT scheme, hasamined. and been For temperature this, made the changes IFS interactive run ininstead with fipj of the has the been GCM default carried GEMS have out, climatology, in beenGCM is which coupled run ex- the to CoMeCAT is CH the GCM a radiation 1-yr scheme. forecast This with an additional spin-up period of 2 months. The length reanalysis of the Globalsitu and data regional project Earth-system (GEMS, Monitoring using Satellite and in- stratosphere compared toradiation the scheme. use In of theincluded the IFS in CoMeCAT version the tracer used radiation in coupled scheme the to present is the study, a the ECMWF two-dimensional default CH climatology derived from the levels and was shown by ECMWF radiation scheme ( since the vertical motionthe used divergence in of the the model horizontalvertical runs winds, wind while is velocity the di ECMWFpast runs (e.g. use the instantaneous port achieved in theDee et recent al. ECMWF model versions (e.g. than the full-chemistry (byin up the to SH 0.2 the ppmv)the underestimation at tropics (up high the to and ECMWF 0.3stratosphere. ppmv) midlatitudes run takes in This, is place together the very between with NH; closethan 5–50 hPa. the TOMCAT while to forced fact the Over by that SLIMCAT ERA-40 in runs winds, the in shows upper the the levels LS improvement fif4 and in is the middle more vertical realistic trans- 6.2 Impact on the ECMWF stratosphericMethane temperature is a strongstratosphere, and greenhouse cools the gas mesosphere/upper thatuse stratosphere. Despite warms only this, the most a GCMs troposphere fixed and constant middle/lower value for CH found increases in temperature inpole. the upper winter stratosphere, of up to 8 K over the Between 1–10 hPa the ECMWF CoMeCAT run (fif4) simulates smaller concentrations i.e. these models considertropopause. CH Using a simpler( parameterisation approach thanhouse CoMeCAT, gases (GHGs) haderal in circulation the model stratosphere. ( Theyical used the loss Canadian of AGCM3stratosphere N gen- compared to the use ofcaused well-mixed by concentrations the for additional these H GHGs, mainly more recent studies point toet a al. significant noise reduction (e.g. 5 5 25 15 20 10 10 15 25 20 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | ; ). is O 2 4 ) run 2006 O ob- is the p 2007 ect the 2 , ( ff − M σ shows H ects on tem- ff a). These too erences (up to 11 ff erences and the 10 ff di Schmidt et al. 4 ; ). Compared to the free- distribution closer to that 1 Monge-Sanz et al. 1996 4 , -line CTM driven by the same ERA- ects. Here we have used this tracer ect that nudging the ECMWF GCM ff ff ff tracer. The experiments fh22 and fh23 Jeuken et al. 4 498 497 concentrations at almost all levels and latitudes. annually averaged cross-sections for the free- 4 4 is not straightforward. The largest e ). Such an approach consists of relaxing, or nudging, in the ECMWF runs have been compared against 8 4 O from CoMeCAT in the CTM. Figure 2 2009 , c), compared to the SLIMCAT run (Fig. 10 scheme has provided the GCM with a tracer that can be used the nudging parameter, the evolution of a certain model variable )) (19) 4 x G Douville ect observed when running CoMeCAT in the TOMCAT ( − ; ects and transport ff ff ect that nudging has on stratospheric transport of tracers compared to an erences in Fig. ff ff x ( shows CoMeCAT CH 2008 G , + values in the upper stratosphere are related to the excessive vertical trans- 10 x 4 ) have been produced with the same GCM version and the same CoMeCAT ( 2 M = Thus, in a nudged GCM, an upper limit to the quality of the dynamical fields is set The TOMCAT run forced by ERA-Interim brings the CH Figure Nudging will improve temperature and fast horizontal wind fields; however, the impact The CoMeCAT CH is given by x ∂t ∂ tained from theHALOE CoMeCAT observations CH and H by the meteorological datanudged used GCM for shows the the same nudging.40 problems fields, as When the while ERA-40 o the fieldsway distribution in are the of used, TOMCAT the ERA-Interim the run stratospheric and tracers in also the6.4 improves GCM nudged in to a ERA-Interim CoMeCAT similar water fields. in the GCM The ECMWF default (currently operational) stratospheric water scheme, and H from the SLIMCAT run.better agreement with the Similarly, free-running the GCMtoo than GCM fh22. fast This run stratospheric indicates transport that nudged theimproved in to e in ERA-40 ERA-Interim. ERA-Interim had (fh23) on stratospheric is tracers in is significantly At the upper most levelstween (above 0.2 1 ppmv hPa) (at the GCM highis run latitudes) similar nudged and to to 0.3 the ERA-40 ppmvforced produces e (at by be- the ERA-40 tropics) (Fig. high more CH than fi6n.port This exhibited by ERA-40 inTherefore, our TOMCAT simulations, results see suggest e.g. thatfeatures nudging in is bringing ERA-40, the with GCM the closer associated to known the problems. transport been done. running experiment fi6n,run13 the and the nudged run14 CoMeCAT-TOMCAT and runsrunning run15 fi6n, fh22 fh22 (Table results and in larger fh23, CH the CoMeCAT-SLIMCAT the free-running GCM, to our knowledge this is the first time this kind of evaluation has 6.3 Nudging e The use of nudgedthese GCMs models is closer increasing to over theTelford recent et real al. years atmosphere as ( a potential way to make 0.35 ppmv) appear above 10 hPa.temperature The di match betweenperature these may CH appear above theradiative tropical heating tropopause rate because is for this atmost region significant. a the relative overall minimum and also the vertical gradient in CH for the on-line evaluation ofto long-term assess transport the e e are found between 10–100 hPa, while over the tropics the largest di of nudging ona the suitable slow tracer. stratospherichas meridional Here for circulation we the needs have transport explored(Table to the of be e the tested CoMeCAT with CH instantaneously every 6 h. x parameterisation as the run fi6n,to however, in ERA-40 fh22 values the dynamical (year variables 2000) are relaxed and to ERA-Interim in fh23. The relaxation is done the GCM dynamicalmodel fields operator towards and meteorological (re)analyses, so that, if 5 5 25 15 20 10 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 4 ). O O 7 2 2 Up- ). The ]. 4 2006 , CH 2[ distribution, have − 6 4 O from the default − 2 O distributions show ). This scheme does 2 10 × 0 2003 . , O at some latitudes (Fig. 2 23 (longitude x latitude x alti- × O in the ECMWF run is 2.5 ppmv 2 O, i.e. 7 Dethof 2 72 Oikonomou and O’Neill × O, which indicates a characteristic of this 2 a). On the other hand, the problems shown O distributions in the CTM and the ECMWF O increase in the stratosphere due to CH 2 500 499 2 11 O field would be far too low in the stratosphere 2 ect (RE) of the CoMeCAT CH a) and 2.0 ppmv smaller than HALOE observa- b. Compared to the performance of the same ff ) with a 144 11 11 O from an ECMWF run (fif4) using this default strato- 2 a) the ECMWF run shows lower water values (up to 1996 , 11 -line version of the Edwards-Slingo (E-S) radiative transfer O scheme ff 2 O scheme in previous analysis versions, e.g. in ERA-40 ( 2 O scheme from CoMeCAT 2 d shows H 11 ), have been partially overcome due to a more realistic transport in the e). This bias is present in all three ECMWF simulations, independent of O scheme which also makes the concentration gradients realistic. Com- e). In the ECMWF model, CoMeCAT produces vertical distributions of H 2 2005 11 c). It can be seen that the H , 11 11 Edwards and Slingo erences between the CoMeCAT H ff (Fig. ff ature, ozone and wateralbedo vapour. (averaged Monthly over the mean period climatological 1983–2005) cloud are taken fields from and the surface International Satellite 7 Radiative forcing implications Further calculations of the radiativebeen e performed with the o model ( tude) resolution. Thisthe radiative shortwave model and a uses delta-Eddington 9 2E-S stream bands model scattering employs in solver a at monthly the all averaged wavelengths. longwave climatology The based and on 6 ERA-40 data bands for in temper- pala et al. more recent ECMWF model versions (like the one used for run fif4). by the ECMWF default H runs partly arise fromSLIMCAT run the is fact forced thatthe by fi6n 6-hourly concentrations comes ERA-40 entering from analyses. throughthat the the This is free-running tropopause, last adopted GCM it factor forbias while is is with the the conditioning the respect troposphere analysed to intoo HALOE humidity high the in field water the CTM values LS runs. thatmulated (100 enter hPa) throughout the ( the ERA-40 CoMeCAT entire scheme presents stratosphere fromhigher causing a the concentrations the tropopause than 10 CoMeCAT % are HALOE CTM (Fig. accu- run wet to present The distribution ofmodel water (run from fi6n) the is CoMeCAT shown scheme in implemented Fig. in the ECMWF 0.5 ppmv lower abovetion 10 (Fig. hPa). Thesimilar SLIMCAT to run those is fromwhere closer the CoMeCAT to can IFS the simulate defaultThe HALOE up di scheme, distribu- to except 0.4 ppmv at more high H levels (above 10 hPa), tions (Fig. the scheme used toversion obtain of stratospheric the H ECMWF GCM that will require further6.4.2 investigation. ECMWF new H scheme in SLIMCAT (Fig. in the absence of aECMWF source H parameterisation, up topared to 1.5 the ppmv CTM are run added anda to by negative HALOE the bias observations, default the in ECMWF thesmaller H tropical than LS around in 100 hPa; the H CTM run (Fig. concentrations are around 0.5 ppmv lowercarried than out HALOE. (run One fif5) control in run whicho has the also source been of water in the stratosphere has been switched spheric water scheme. At high latitudes in the upper levels (above 5 hPa) fif4 H 6.4.1 ECMWF default H The ECMWF stratospheric water currentlyfixed comes profile from of a water parameterisation vapournot based observed include on any lifetime a latitudinal (e.g. variation,culation relying to on the get accuracyoxidation. the of correct the Figure Brewer-Dobson amount cir- of H ECMWF model (run fi6n).ECMWF scheme Also (run shown fif4),source in and scheme the from is same an used ECMWF in figuresame the control are initial stratosphere. conditions run H as (fif5) The the ECMWF in CTM runs CoMeCAT which for are no H initialised water with the cross-sections averaged over 2000 obtained from CoMeCAT in the CTM and in the 5 5 20 25 15 10 25 20 15 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | . 4 2 − compared field in the 4 4 erences due ). Clouds are ff 11.0 mW m − ). The smallest 1999 , 2010 cients (conditions for in the ECMWF model , er ffi ff 4 ect to the one we have should be accompanied S), and the largest over ff ◦ 4 erences, at the tropopause ff N–20 Rap et al. ◦ distributions. When running CoMe- 4 (the same for every calendar month) 4 Rossow and Schi 502 501 cients). distribution from the CoMeCAT CH ffi 4 ), which means that E-S runs with a more realistic O, than that obtained with the present version of the 2 2005 , ect has been evaluated for each calendar month by taking . Nevertheless, the inclusion of realistic profiles for other ff O increments are missed in our comparison. On the other ects that realistic GHGs vertical distributions in the strato- 12 2 ff . 4 performs well in the TOMCAT/SLIMCAT CTM, showing very O (e.g. from ERA-Interim) would produce a larger warming ef- are found over the tropics (20 2 monthly means from run13 are provided to the radiation model). 4 4 12 value of 1.80 ppmv for CH Uppala et al. erent conditions has been proved by showing results for atmospheric 4 ff O and CFCs, is expected to have a similar e 2 ering from those used to calculate the scheme coe ff shows the annual mean values of the net RE di parameterisation scheme (CoMeCAT) has been developed for the strato- erences with observations are found at high latitudes, especially in the SH, 4 erences are of the same order of magnitude as those obtained when includ- ect due to larger water vapour concentrations would partly compensate the ff 12 ff ff erences are found in all regions, with a global average value of erence between two runs of the radiation code: One “control” run using a global ff ff erences shown in Fig. erences in Fig. ect of the associated H The CoMeCAT CH The inclusion of CoMeCAT in the ECMWF model allows the possibility of explor- The e Figure These results imply that RE calculations using a well-mixed approximation that over- The CoMeCAT radiative e ff ff ff ing long-term transport features in the GCM. In particular, we have used CoMeCAT good agreement with observations from HALOElargest and di with CTM full-chemistry runs.where The CoMeCAT (and full-chemistry) runsto with ERA-40 HALOE, underestimate by CH upwell in to the 0.3 ECMWF ppmv GCM,CAT at interactively producing with altitudes realistic the CH around GCMcools 10 radiation hPa. the scheme, tropical the LS CoMeCAT new region alsoclimatology. CH (up performs to 2 K) compared to the use of the default GEMS CH to parameterise stratospheric water vapourthe in scheme the to di two 3-Dconditions models. di The adaptability of year 2004 were used to obtain the coe shown here for methane.should be Although done beyond on thesphere the have scope for e radiative of forcing this calculations paper, and, therefore, future climate research studies. 8 Conclusions A new CH sphere, and tested within a 3-D CTM and a 3-D GCM. The scheme has also been used fect, coming from stratospheric H E-S model. This remains as a future line ofdi research. GHGs, like N field of stratospheric H Cloud Climatology Project (ISCCP) archive ( tive di These di ing aircraft contrails formationdi in the radiative model ( stratosphere (e.g. SLIMCAT run13 (CH The value of 1.80 ppmvthis is the way, value with used these byonly two the to runs CoMeCAT stratospheric runs of CH in the the troposphere. E-S In model, weafter can allowing evaluate for stratospheric RE adjustment, di betweendiation the runs. ’perturbed’ and Changing the ’control’the from ra- much the more constant realistic 1.80 distribution ppmv in value the used stratosphere in results in the global control cooling; run nega- to Antarctica. estimates stratospheric methaneglobally. concentrations However, will a overestimatenot cautionary take surface note into has warming accountby to that an be the increase in reduction made the in here: sourceact stratospheric of on stratospheric RE CH our calculations water RE vapour. in the Thatthe calculations opposite extra surface water sense, do levels. vapour i.e. Since will cooling our the twoe stratosphere runs and of warming the E-Shand, use the the same ERA-40 ERA-40 climatology climatology used the here for the E-S runs is known to be too dry in the added to three vertical levels, corresponding to low, middle andthe high di clouds. 3-D constant CH and one ’perturbed’ run taking the CH 5 5 25 15 20 10 15 10 25 20 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | , O 2 than pre- O distribu- 4 2 Bechtold et al. ; profile, with latitude concentrations to be 2008 4 , 4 0.6 ppmv. This is at least ∼ Monge-Sanz 485 , . This implies that a realistic representa- 2 over mid and high latitudes, with a global − 482 2 -line Edwards-Slingo (E-S) radiation model − 504 503 distributions to those obtained with TOMCAT ff 4 , 2007. ´ olm for valuable communications on the ECMWF H O distributions show a realistic spatial variability and ) highlighted the need for better representations of ¨ 2 omel, H.: Evolution of Water Vapor Concentrations and 11.0 mW m − 2010 O and CFCs would also improve the representation of the ( 2 in the stratosphere. Including a realistic CH We thank Elias H 4 O in climate models to better simulate and interpret decadal surface 2 erent sign, as the incorporation of aircraft contrail formation. The use doi:10.1175/JAS3866.1 ff time tendency obtained from CoMeCAT has been used in both models Solomon et al. 4 ect on the calculated radiative forcing values of the same order of magni- ff ect of using CoMeCAT in conjunction with similar schemes for other GHGs in ff ), and shown to reduce temperature biases in the stratosphere. As a next step, Stratospheric Age of Air64, in 905–921, Coupled Chemistry-Climate Model Simulations, J. Atmos. Sci., The CoMeCAT scheme also opens new possibilities for climate studies. In spite of The CoMeCAT scheme is a more realistic treatment for stratospheric CH The CH -p) run by ERA-40. Nudging the GCM to ERA-Interim brought about improvements, σ Acknowledgements. as a slow evolvingspheric boundary for processes the is troposphere,In key and to addition, a realistic increase description thestratospheric of H accuracy strato- of long-termwarming trends; climate the predictions. CoMeCAT scheme could also contribute in this respect. has an e tude, but of di of CoMeCAT instead ofradiative a forcing well-mixed values approximation by up inannually to averaged the decrease 30 mW stratosphere of m hastion reduced of vertical distribution ofradiative GHGs forcing in and the climate stratosphere is warmingstratosphere necessary projections. plays to In a better this constrain similar sense role it to can be that said played that by the the oceans: the stratosphere acts scheme and Piers Forster for helpfulradiation. discussions on This the interaction work ofand the has scheme the been with EU the partially GEOMON GCM funded project. by the NERC Research Award NE/F004575/1 References Austin, J., Wilson, J., Li, F., and V being the second mostfixed value important for greenhouse CH gas,dependence and most linked climate to other modelsduce model changes use variables (like to only temperature), radiative is a forcingCoMeCAT expected results methane to in pro- distribution climate models. in In the our o study, including the viously included in ECMWF. Improvingstratosphere the was initially representation tested of in the greenhouse2009 ECMWF gases IFS in ( the the e IFS should be investigated;diatively implementing active gases schemes like similar N tostratosphere in CoMeCAT for the other ECMWF GCM. ra- in In the addition, ECMWF including model thisused would type to also of constrain enable methane humidity the analyses scheme assimilation in of the CH stratosphere. wet bias at the tropopause.forms well. In ECMWF the CoMeCAT ECMWF H good model the agreement CoMeCAT with water HALOE approachstratosphere observations, per- (of except up for to a 2.0 ppmv). dry bias in the tropical lower the advantages and deficienciesof of the the ECMWF analyses IFS used,transport to and of ERA-40 stratospheric nudging is tracers. a not recommended, recent at version least for applications(CTM and involving GCM) to parameterisetions the obtained source from of stratospheric CoMeCATobservations, in water. except The the H for CTM a runspartly are wet due in to bias the good in use agreement the of with LS ERA-40 HALOE region humidity values of in the troposphere, which present a ERA-Interim and ERA-40 toERA-40 transport analyses produced the similar stratospheric( CH tracer. 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J., and Saunders, R., Matricardi, M., and Brunel, P.: An improved fast radiative transfer model for 5 30 25 20 15 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | none O scheme 2 CoMeCAT H ECMWF default ECMWF default ECMWF default d) JULY T(K) d) JULY scheme none b) JANUARY T(K) b) JANUARY 4 CoMeCAT CoMeCAT CoMeCAT CoMeCAT CH O schemes. 2 512 511 and H 4 ] (ppmv) (left panels), and temperature (K) (right panels) 4 GCM [CH Free GCM Free GCM Free GCM Nudged to ERA-40 every 6h Nudged to ERA-Interim every 6h c) JULY CH4 (ppmv) c) JULY a) JANUARY CH4 (ppmv) a) JANUARY ECMWF runs with CoMeCAT CH Zonal mean of CoMeCAT fh22 fif4 fi6n fif5 fh23 ECMWF run Fig. 1. reference terms for January (top row) and July (bottom row). Table 2. Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | ) in 1 c January, cient (a) ffi ] (coe 4 October. (d) b) APRIL b) d) OCTOBER July and lifetime values (in days) for (c) 4 April, 514 513 (b) January, (a) ) for 1 − October. c) JULY a) JANUARY (d) ppmv 1 − day July and 14 − (c) Altitude/latitude distribution of CoMeCAT CH Altitude/latitude distribution of the CoMeCAT loss tendency with [CH April, units of (10 Fig. 3. (b) Fig. 2. Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | (a) cient ffi erences (in ff erences between ff di (c) October. (d) b) APRIL b) d) OCTOBER July and (c) April, the colour scale indicates most positive di distribution (ppmv) from the CoMeCAT scheme in the CTM (b) goes from larger concentrations (darkest green) to smaller 4 (c) 516 515 (a) and (b) January, (a) ) ) ) c)c a)a b)b ) for zonally averaged CH erences (in darkest blue). 1 ff − (a) K c) JULY 1 − . Colour scale in panel a) JANUARY (c) day 16 and − (b) erences between CoMeCAT and full-chemistry run of SLIMCAT (run323) and ff di Annual mean for 2000 of Altitude/latitude distribution of the CoMeCAT loss tendency with temperature (coe (b) ) in units of (10 2 Fig. 5. run13, CoMeCAT and HALOE observations. Theand model 0.05 simulations ppmv use for ERA-40 winds. Contour values are 0.20 ppmv for concentrations (darkest blue); while for panels Fig. 4. c darkest green) and most negative di Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | S (as labelled). ◦ 4ºN S and 40 ◦ IFS fif4 IFS fi6n 4ºN N, 70 IFS fif4 SLIM run13 HALOE H2O HALOE ◦ SLIM run13 run14 TOM HALOE CH4 HALOE FULL-CHEM N, 4 ◦ 40ºN 40ºS N, 40 ◦ S (as labelled). 518 517 40ºN ◦ 40ºS S and 40 ◦ 70ºN 70ºS distributions (ppmv) for year 2000 from the CoMeCAT scheme in 4 O distributions (ppmv) for year 2000 from the CoMeCAT scheme 2 N, 70 ) for the latitudes 70 ◦ 70ºS 70ºN 2 N, 4 ◦ N, 40 ◦ Annually averaged H Annually averaged CH Fig. 7. in the SLIMCAT run13ECMWF (black line), run fi6n ECMWF (solid defaultthe green run latitudes line) fif4 70 and (dashed HALOE green observations line), (red CoMeCAT line). in Profiles correspond to Fig. 6. SLIMCAT run13 (solid black line), TOMCATblack run14 line) (blue line) run and fif4 in the (Table ECMWF GCM (dashed HALOE observations have also been includedrun323 (solid (dashed red red line), line). as well as the CTM full-chemistry Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | climatology 4 10 7 5 4 3 2 1.5 1 0.5 -0.5 -1 -2 -3 -4 -5 -7 -10 climatology 4 erences (dark red). ff S O erences (dark blue) to most S 80 O ff t (JJA) 2000 between the S 60 O ve differences (dark blue) to most S 40 O 20 O 38 520 519 fipj-fif4 N 0 O in the radiation scheme) and run fif4 (GEMS CH erences (dark blue) to most positive di N 20 4 in the radiation scheme) and run fif4 (GEMS CH O ff 4 concentrations between the CoMeCAT distribution and ECMWF CoMeCAT- clim IFS avg JJA 2000 clim IFS avg CoMeCAT- 4 N 40 O Average of temp 20000101 1200 step 4344 Expver fipj (180.0W-180.0E) 20000101 1200 step 4344 Expver Average of temp N 60 O 80 1 2 3 4 5 6 8 10 20 30 40 50 60 80 0.2 0.3 0.4 0.5 0.6 0.8 100 200 300 400 500 600 800 1000 Differences in temperature averaged over June-July-Augus erences (dark red). erences in temperature, averaged over June-July-August (JJA) 2000, between the erences in the CH ff ff ff Di Di in the radiation scheme). Colour scale goes from most negati positive differences (dark red). Fig. 8. ECMWF runs fipj (CoMeCAT CH Fig. 9. GEMS climatology in the radiationscale scheme, goes averaged from for June-July-August most (JJA) negative 2000. di Colour Fig. 8. ECMWF runs fipj (CoMeCAT CH positive di in the radiation scheme). Colour scale goes from most negative di Contour interval is 0.05 ppmv. Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | ECMWF (d) CoMeCAT in the the TOMCAT run14 the TOMCAT run15 (a) (c) (e) d) fif4 (default) avg 2000 d) fif4 (default) avg ECMWF control run fif5, b) CoMeCAT free IFS (fi6n) free b) CoMeCAT b) fi6n (comecat) avg 2000 avg b) fi6n (comecat) (c) d) CoMeCAT IFS nudged ERA-40 (fh22) IFS nudged ERA-40 d) CoMeCAT 522 521 the free-running GCM fi6n, distributions (ppmv) for year 2000 from the CoMeCAT (b) 4 HALOE instrument. Colour scale goes from larger concen- the GCM run fh23 nudged to ERA-Interim. Colour scale goes (e) the GCM run fh22 nudged to ERA-40, (f) (d) e) HALOE avg 2000 avg e) HALOE c) fif5 (ctrl.) avg 2000 c) fif5 (ctrl.) avg a) CTM CoMeCAT avg 2000 avg a) CTM CoMeCAT a) CoMeCAT SLIMCAT (run13) (run13) SLIMCAT a) CoMeCAT CoMeCAT in ECMWF run fi6n, c) CoMeCAT TOMCAT ERA-40 (run14) TOMCAT c) CoMeCAT ERA-Int (run15)TOMCAT e) CoMeCAT f)IFS nudged ERA-Int (fh23) CoMeCAT (b) the SLIMCAT CTM run13, O (ppmv) cross-sections averaged over 2000 obtained from 2 H Annually averaged zonal CH (a) Fig. 11. forced by ERA-40 fields, SLIMCAT run13, trations (orange) to smaller concentrations (dark blue). Contour interval is 0.5 ppmv. Fig. 10. forced by ERA-Interim and default scheme in run fif4 and tracer in from larger concentrations (dark green)is to 0.20 ppmv. smaller concentrations (dark blue). Contour interval Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | ect (cooling) and ) found over high 2 ff − scheme is, therefore, a 4 30 mW m − ) induced by using the CoMeCAT 2 − ect (up to ff ect of the new CH ff 523 ect (warming). The e ff for details). In the colour scale, blue is for negative radiative e 7 Annually averaged net radiative forcing (mW m instead of a default constant value of 1.80 ppmv in the Edwards-Slingo radiation model 4 red for positive radiative e general annual average cooling, withlatitudes. the strongest e Fig. 12. (see Sect. CH