Physics and Chemistry of the Mesopause Region

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1 2001 CEDAR-SCSTEP Lngmnt, Clrad June 17-22, 2001 Tutrial Lecture #6 by Anne Smith ACD/NCAR, USA Physics and Chemistry f the Mespause Regin

2 Physics and Chemistry f the Mespause Regin A. K. Smith NCAR Prcesses invlved in the cupling be tween cmpsitin, energy and dynamics Imprtance f external frcing

3 utline cmpsitin f the mespause regin: hw it differs frm ther regins impact f dynamics and energy n cm psitin impact f cmpsitin n energy and dy namics example: rle f C2 in mespause struc ture example: f gravity waves phtchemical destabilizatin

4 Definitins mespause: altitude f the temperature mini mum, which varies n seasnal and shrter time scales; the talk will cnsider the range km. cmpsitin: mstly cncerned with the variable part f the cmpsitin, making up <1% f the ttal mixing rati: density f species/ttal density energetics: the thermal budget & the prcesses fr cnverting between heat and ther frms f energy vertical scale: fr the mdels, lg(pressure) scaled t give apprximate altitude Nte: many f the illustratins are taken frm numer ical mdels

5 HRDI Mean Temperatures fr July MSIS Mean Temperatures fr July frm rtland et al., JGR, CD in =5 r CD " B I 90 CD P 2^ r ^q I...I...I...I!' inlunl'irlimilmiliiiiliiiiliiiil C _JLS^S'ji s LZ YS nrthern hemisphere 70 ]iiii i!iil\ii[ H winter CD 200 LZ* - - ' - * YS =3 4-» 180 CD ~ 160 Q. E CD 4-> I <3h 3-6h >6 h gegraph c YS *jr - *-- LZ r 100 r 90 i- 80 iiii iiii nn nn f summer i iiii nn mi 70 «C 6YS c latitude \ LZ* 11" " i' b- 200 I 180 \ 160 'r 140 frm vn Zahn et al., GRL,

6 Which atms <& mlecules are present? THERMSPHERE decrease in prprtin f dminant mlecules (2, N2) increase in several simple mlecules (N, C) increasing dminance f atms mre excited states reactins can be slw because f lw density ins and in reactins are imprtant STRATSPHERE & LWER MESSPHERE breakdwn f larger mlecules prduced in the trpsphere larger rle fr atms than in the trpsphere density is still high enugh fr 3-bdy reactins sharp daytime maximum f sme atms & cm punds (, CI, H, H, N, etc.) nly ne excited species (^D)) plays a signifi cant rle catalytic cycles f Nx, Clx and Hx destry zne

7 Which atms <& mlecules are present? UPPER MESSPHERE dminant mlecules (2, N2) still well mixed cncentratins f N, C can be large excited states participate in chemistry (N(2D)) r energetics (e.g., 02(15I)) a few trpspheric mlecules remain: H2f C2 increasing rle fr atms, particularly and H decreasing density affects 3-bdy reactins phtchemically driven diurnal variatins f mst minr species catalytic cycle f Hx dminates zne destruc tin ins (N+) begin t have an effect n neutrals

8 altitude (km) 05 CD CD 1 i i t i 1 i i i i I i i i y I i i i i i i i i i i i i i i i i i "- ~ 1 i i i i w \ - -* : \ : \ i H- 1 - t» 1 / \ K ^ s z ' ^"""^^ ^*^ 1» \ x ' ^ s^*"^ - z 01 X ^>v^ \ ' j^ \ 1 ~~ ~~ "* s // ~ S \ \ / i ' Z \ -v / \ \ / ^ z z s. ** ^ / \ \ / f^ z Z. N ^* / \ \ / **^^ i N "** «^ 03 V ** * "' \\ / ^-'S^**- N - \\/ -v*-**"^ x " \ - \ vit -^^^ ->*c w 1 ' ~ ^ y^>^\ *" z =- V C^" \ 1 \ ffi / / s \ X s ^ \ /> - ^. \ jr _ h-* N. \ J-^ z 1 S>v *- "*s^ ) VS. j. "" ^^"^ s*^^^^,» "* ^s?»* ^^^"^ 1 r X ^~*~~, l * "* ^^^^ -' "' z r X I 1 E = i i i i i i i i i i i i i i i i i i i 1 i i i i 1 i i i i 1 i i i i 1 i t i i = r 3 C a w P i ' 0 - ~ - \ ^^ ^ ~ - z

9 What are the imprtant species? 1) frm the pint f view f cntrlling the cmpsi tin: : prduced lcally frm 2 and 3, transprted dwnward frm thermsphere; increases strngly with altitude 3: prduced frm +2; rapidly destryed dur ing the day H, H, H2: prduced during the day frm H2, r transprted dwnward frm thermsphere (H) 2) frm the pint f view f measurements 3 C02 sdium and ther metals excited species that emit: 02(15I), H, etc.

10 Trace Gas Mixing Rati 100 TTl MMI TTTTTTIT] l\"titmi 1 I I illll 1 I I lllil l-ljrvmij TT r/lhij l"l ITIHI 1 I I lllll 1 I IIIIII \ CC 70 /» ' / / \ / I I I IMIll l/l I llllll 1 1 v I mmiii I 1 1mml 1 1 "I"'!» ' 1mill 1 1 mint I I I Mill n1 n xu1 n-10 1Q-y1 n-9 10-a1 n-8 1Q-71 n-7 1Q-b1 n-6 10-d 10-* 1Q-j 1Q. 10 \ / \ 1

11 Which reactins ccur? phtlysis, e.g: 3+/11/ -» +2 sun angle slar flux clumn f absrbing gases weakly n temperature 2-bdy reactins, e.g: density f reactants temperature 3-bdy reactins, e.g: ++M - 2+M density f reactants temperature density *M is any atm r mlecule

12 Day/Night Differences Daytime Sunlight splits mlecules: 2, 3, H2 Absrptin generates excited states f atms and mlecules that can react chemically r pass their energy alng t anther species Nighttime at lwer altitudes atms & radicals recmbine int mre stable mlecules (e.g., and H, H, H02 - H20 -* 2, 3 and H persist at the mespause & abve Transprt dynamics is similar except fr phase f the tides & prcesses affected by tides vertical transprt can be very different because f gradients

13 Glbal lg(mixing rati) f 0 at fur lcal times 0 LT 6 LT -ndel s;ep: 960 UT: 0.0 Dy: 196 ndel step: 960 UT: 0.0 Day LT 18 LT rr>: m: -M.0 mdel step: 960 UT: 0.0 Dy: 196»ai: mn: mdel step: 960 UT: 0.0 Dy: 196

14 Impact f anthrpgenic gases n cmpsi tin increased C2 >- cling increased hydrcarbns -> zne lss Impact f dynamics n cmpsitin winds advect species temperature affects reactin rates winds and temperature cntrl prpagatin and dissipatin f waves Impact f energetics n cmpsitin phtlysis affected by incident radiative flux atmic/mlecular energy levels changed by ab srptin f radiatin energetic particles can generate inized r excited states temperature affects reactin rates

15 temperature ABSLUTE DIFFERENCE (K) _ --10 E ~3 a, bfl C 10U _-10' 90S 60S 30S Eq 30N latitudes (angular degrees) 60N 90N

16 03 relative difference (%) E M a 60- bfl G 90S 60S 30S Eq 30N latitudes (angular degrees) 60N 90N

17 Diffusive transprt mlecular diffusin diffusive cmpnent reduces gradients "advective" cmpnent mves species differen tially effects n mespause H, H2, C2, temperature diffusin rate varies with temperature eddy diffusin caused by turbulence r by any unreslved dy namical scales imprtant in the vertical because f strng mixing rati gradients limited measurements mass mixing, i.e., all species (mixing rati) and ptential temperature have same diffusin cef ficient extremely variable due t intermittent dynamics

18 Fig. 5. Cmparisn f measured and calculated C mixing ratis E Q> s A--ISAMS EV18 SL3-Mean TIME-GCM -GS ' I I I I L L_j i i i Ul i i i u Vlume mixing rati (ppmv) UpeT- P*"-**-5 *"*Xt

19 Advective transprt r variability gravity waves hurs hurs-seasnal tides hurs days-seasnal planetary waves days weeks-seasnal mean circulatin seasnal annual General rules: time scale f variability increases with spa tial scale prpagatin f lw frequency waves (plan etary and gravity waves) strngly affected by znal wind

20 SUNRISE/SUNSET ANMALY 120p HALE N MARCH 199. t F i- 11Fr u I- / 1 ' / ~ 10 VLUME MIXING RATI 10 frm Marsh & Russell, GRL, 2000

% Difference frm Mean W 0600 HRS -40-20 0 20 LATITUDE (DEG) 40-40 20 0 20 LATITUDE

21 % Difference frm Mean W 0600 HRS LATITUDE (DEG) LATITUDE (DEG) % Difference frm Mean Ml Hlkli ijiliu'i W 1800 HRS X LJ x LATITUDE (DEG) 40

22 fx (m/s/day) ; January :-.i 90S 60S 30S Eq latitudes (angular degrees) 30N 60N 90N

23 (qui) amssaid Z Q z Z en U S,8 ^ c 3 Bd d C3 00 X I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I [ I! I c S (ui>i) Qptuppg d- 0

24 lg-p altitude (km) 3 C/3 B3 P H Pressure (mb)

25 lg-p altitude (km) m CD 3 CD 0\ >-. P 3 H! CD P U3 pa C D- Q W EL*0 p. 03 z CA z Pressure (mb)

26 Qualitative feature f the mean circulatin mmentum frm wave dissipatin drives summer t winter flw rising in summer, sinking in winter gives adiabatic frcing IR radiatin respnds t lcal tempera ture but... IR emissins are inefficient because f cld mespause temperatures strnger temperature respnse than wuld ccur fr cmparable mmentum frcing in a warmer regin

27 Impact f cmpsitin n energetics absrptin f slar radiatin depends n cmpsitin: 2: wavelengths nm (Lyman-a, Schumann- Runge cntinuum, Schumann-Runge bands) 3: wavelengths nm (Hartley band) absrbed energy ges int: breaking chemical bnds exciting vibratinal r rtatinal levels f riginal absrber r its prducts cnverted immediately t heat

28 200 S-R cntinuum S-R bands < T^^ r < i WAVELENGTH (nm) altitude at which flux is attenuated by 1/e frm Brasseur &i Slmn, Aernmy f the Middle Atmsphere

29 What happens t the energy f phtlysis? energy used t break bnds is "stred" in the prducts and can be cnverted t heat when they react heat-releasing reactins can ccur hurs r days after and far away frm riginal absrptin Reactin + 3 -> M-* 02 + M + H - H H02 -> H + 02 H M - H02 + M M-»03 + M H + 3 -> H + 02 * * * * * * reactin rate decreases with temperature

30 Chemical Heating Spring, Day Chemical Ptential Heating (K/day) Spring, Night Chemicql Ptential Heating (K/day) <D < X \_ Q. Q. < Latitude Latitude frm MIynczak and Slmn, JGR, 1993

31 What happens t the energy f excited states? cnverted t heat: s + hv - 02(}/\g) + ^D) 02(1A5) » heat transferred by cllisin: ^D) (15I9) radiated ut f regin 02(1A5) hv 2(151) -> 02 + hv reacts: N(2D) N +

32 Magnitude &l distributin f terms in the ther mal budget diffusin advectin by the mean circulatin direct slar 02 heating* direct slar 3 heating* chemical heating* infrared cling * minus fractin lst thrugh emissin (airglw)

33 lg-p altitude (km) (S) C g P r-1- H- ca c & j~. P v: cjq ffl EL*0. a a> aq d

34 lg-p altitude (km) p a- P a- p ' cr Q P r-t» Q cr - 5 P P C P

35 lg-p altitude (km) g G t sr p i K» CTQ G P- P P P era m. CD w G P 2 Pressure (mb)

36 lg-p altitude (km) G>-> cr P r-f- rjq p c p >-* - 5 P

37 Chemical Heating (K/day) January E M p n i B latitudes (angular degrees) 90N

38 Ig-p altitude (km) -J C G I I I I I I I I I I I I I I I I I I I I I i i I I I I I I I I I I I I I I I G p a- > p r-f- < CD G > era. p c 9- CD ' w / 5 / Q W. / C 43 P 8- - fl CD CD V) ". / sp p I G :, _ \ 2 \ SI Pressure (mb)

39 EXAMPLE F INTERACTIN plar mespause temperature determined by adiabatic prcesses f wave-driven circu latin heating & cling (C2 cling rate; chem ical heating) upward mtin (summer ple): adiabatic cling high C02 enhancement t IR cling

40 lg-p altitude (km) 3 C v G i i i i i i i i i I i i i i i i i i i I I I I I I I I I I I I I I I I I I I I I I I l I l l n C p p p Pressure (mb)

41 lg-p altitude (km) s G cd CD H P r-t n CD CD G CD HI CD CD G a- s= CD r-t- ^ C - & 3 5 i-t b a. P I - S _ I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I i i i i r b Pressure (mb)

42 IMPACT F GLBAL C02 STRUCTURE psitive feedback enhances the cld summer, warm winter temperature differences mdel results may underestimate magni tude because f neglect f mlecular dif fusin

43 Phtchemical Destabilizatin f gravity waves Air parcel trajectry in a prpagating gravity wave cld warm Cmpsitin and density high, ttal density lw lwer, higher ttal density

44 midnight density f and 3 gravity wave unstable grwth rate 100 Density (cm') Grwth Rate (10V) slid: Kzz high; w=0 dashed: Kzz lw; w=upward frm Xu et al. JASTP, in press

45 variatin in grwth rate with wavelength 50 1x103 2x10 3x10" 4x103 Hrizntal Wavelength (km ) cutff fr Kzz = 102m2/s Phtchemical destabilizatin mre likely fr: lw temperature lw diffusin sharp vertical gradients f lng vertical, shrt hrizntal wavelengths

46 Cmpsitin variability regular diurnal, seasnal and interannual time scales irregular variability due t frcing frm abve (energy) and belw (waves) feedback affects all scales f mtin frm mean circulatin t individual gravity waves cntrls the cnversin f energy t heat

Chapter 11: Atmosphere

Chapter 11: Atmosphere Chapter 11: Atmsphere Sectin 1: Atmspheric Basics Objectives 1. Describe the cmpsitin f the atmsphere. 2. Cmpare and cntrast the varius layers f the atmsphere. 3. Identify three methds f transferring energy