Lagrangian modeling of the mixing layer

Transcription

1 Lagrangian modeling of the mixing layer P. Konopka and L. L. Pan export/p.konopka. Research Center Juelich, ICG-I: Stratosphere, Germany

2 Objectives Common sense:...mixing is an important part of transport, in particular in vicinity of the tropopause where all relevant species have strong vertical and horizontal gradients... Mixing in experimental data: mainly manifests in tracer/tracer correlations, e.g. in CO/O 3 correlation as a deviation from an idealized L-shape (unmixed) correlation Mixing in the models (here in CLaMS) Transport = Advection (Trajectories) + Mixing (driven by deformation in the flow) (in most Eulerian models numerical diffusion outweighs physical mixing!) What do we learn from START-8 and CLaMS about transport (mixing)?

3 Objectives Common sense:...mixing is an important part of transport, in particular in vicinity of the tropopause where all relevant species have strong vertical and horizontal gradients... Mixing in experimental data: mainly manifests in tracer/tracer correlations, e.g. in CO/O 3 correlation as a deviation from an idealized L-shape (unmixed) correlation Mixing in the models (here in CLaMS) Transport = Advection (Trajectories) + Mixing (driven by deformation in the flow) (in most Eulerian models numerical diffusion outweighs physical mixing!) What do we learn from START-8 and CLaMS about transport (mixing)? Configuration of CLaMS: Multi-annual, global, run from 21 until for the whole troposphere and stratosphere (Konopka et al, ACP, 27) 1 km/ m hor/vert resolution near the tropopause CO/O3 with simplified chemistry lower boundary: O3=, CO from MOPITT observations below 5 hpa O3 above θ = 5 K - HALOE Climatology high resolution (5 km) nested runs start from the multi-annual runs about 2 weeks before the START-8 flights (Vogel et al.)

4 CO/O 3 correlations from CLaMS O 3 [ppbv] APR 8 31 K 32 K 34 K 37 K PDF (%) all CLaMS air parcels with: lat > 25 N, θ < 38 K.17 2 PV= CO [ppbv]

5 CO/O 3 correlations from CLaMS O 3 [ppbv] APR 8 31 K 32 K 34 K 37 K PDF (%) all CLaMS air parcels with: lat > 25 N, θ < 38 K.17 2 PV=2 mixing on the tropical side of the CO [ppbv] jet

6 O 3 [ppbv] CO/O 3 correlations from CLaMS 25_ Hybrid Pot. Temperature, ζ, [K] APR K 32 K 34 K 37 K _ PDF (%) all CLaMS air parcels with: lat > 25 N, θ < 38 K Equivalent Latitude, [deg N] CO_6_7_O3_8_ PDF (%) PV=2 mixing on the tropical side of the CO [ppbv] jet

7 CO/O 3 correlations from CLaMS O 3 [ppbv] APR 8 31 K 32 K 34 K 37 K mixing on the polar side of the jet PDF (%) all CLaMS air parcels with: lat > 25 N, θ < 38 K.17 2 PV=2 mixing on the tropical side of the CO [ppbv] jet

8 O 3 [ppbv] CO/O 3 correlations from CLaMS 25_ Hybrid Pot. Temperature, ζ, [K] APR K 32 K 34 K 37 K 25. mixing on the polar side of the jet 25_ PDF (%) all CLaMS air parcels with: lat > 25 N, θ < 38 K Equivalent Latitude, [deg N] CO_9_11_O3_19_ PDF (%) PV=2 mixing on the tropical side of the CO [ppbv] jet

9 O 3 [ppbv] CO/O 3 correlations from CLaMS APR 8 31 K 32 K 34 K 37 K mixing on the polar side of the jet PDF (%) comparison with START-8 all CLaMS air parcels thankswith: to Jasna lat > 25 N, θ < 38 Pittman K 2 PV=2 mixing on the tropical side of the CO [ppbv] jet Jet as a transport barrier in winter and spring e.g. Ray et al., JGR, 24

10 O 3 [ppbv] CO/O 3 correlations from CLaMS APR 8 31 K 32 K 34 K 37 K mixing on the polar side of the jet PDF (%) comparison with WACCAM all CLaMS air parcels thankswith: to Dalon lat > 25 N, θ < 38 Stone K 2 PV=2 mixing on the tropical side of the CO [ppbv] jet Jet as a transport barrier in winter and spring e.g. Ray et al., JGR, 24

11 Degree of mixing derived from CO/O 3 correlation Empirical mixing state: 1. CO< ppbv - pure stratosphere 2. O 3 <75 ppbv - pure troposphere 3. For other CO/O 3 values, we normalize CO and O 3, i.e.: x =CO/CO max and y =O 3 /O 3 max 4. Define (empirical mixing state): 8 < y/x f(x, y) = (x + y) : x/y x > y y > x from Kunz et al. JGR, 29 i.e. mixing is the highest along the diagonal and far away from the origin

12 Degree of mixing derived from CO/O 3 correlation from Kunz et al. JGR, 29

13 Mixing layer derived from CO/O 3 correlation Degree of mixing, f mix Log. Pressure Altitude [km] Therm. Trop PV = 2 Jet Longitude [deg] Degree of mixing from CLaMS CO/O 3 correlation stratospheric intrusion on 28.4 (see also Vogel et al.)

14 How good are our simulations? Degree of mixing, fmix Longitude [deg].5 fmix CLaMS fmix(exp)<.5 fmix(exp)> Log. Pressure Altitude [km] CLaMS versus observations stratospheric intrusion on 28.4 (see also Vogel et al.)

15 How good are our simulations? Degree of mixing, f mix Log. Pressure Altitude [km] Therm. Trop PV = 2 Jet freshly mixed Longitude [deg] History of mixing: yellow - mixing in CLaMS occured in last 72 hours

16 How good are our simulations? Degree of mixing, fmix Log. Pressure Altitude [km] fmix CLaMS fmix(exp)<.5 fmix(exp)> Longitude [deg] CLaMS versus observations tropospheric intrusion on 18.4 (see also Vogel et al.)

17 How good are our simulations? Degree of mixing, f mix Log. Pressure Altitude [km] Therm. Trop PV = 2 Jet freshly mixed Longitude [deg] History of mixing: yellow - mixing in CLaMS occured in last 72 hours

18 How sensitivity is the mixing layer in CLaMS? O 3 [ppbv] APR 8 31 K 32 K 34 K 37 K O 3 [ppbv] APR 8 PDF (%) PV= CO [ppbv] reference case CO [ppbv] PV=2 CLaMS with reduced intensity of mixing : not enough mixing in the troposphere Mixing driven by the Richardson number: Ri = u z g θ T z 2 + v z 2, Ri < Ri c

19 How sensitivity is the layer in CLaMS? Degree of mixing, f mix Log. Pressure Altitude [km] Therm. Trop PV = 2 Jet Longitude [deg] Degree of mixing, f mix Reference (top) versus too weak tropospheric mixing (right) Log. Pressure Altitude [km] Therm. Trop PV = 2 Jet Longitude [deg] 29.5.

20 How sensitivity is the mixing layer in CLaMS? O 3 [ppbv] APR 8 31 K 32 K 34 K 37 K O 3 [ppbv] APR 8 PDF (%) PV= CO [ppbv] 2 PV= CO [ppbv] reference case (with annually averaged mass conservation) CLaMS with a not balanced Brewer-Dobson circulation : not enough upwelling in the tropics : freedom in the diabatic vertical velocities

21 How sensitivity is the layer in CLaMS? Degree of mixing, f mix Log. Pressure Altitude [km] Therm. Trop PV = 2 Jet Longitude [deg] Degree of mixing, f mix Reference (top) versus not balanced Brewer Dobson circulation (right) Log. Pressure Altitude [km] Therm. Trop PV = 2 Jet Longitude [deg] 29.5.

22 Conclusions Degree of mixing can be diagnosed ( experimentally and from a model) by using tracer correlations (here PDFs of CO/O 3 ) and an empirical function quantifying the position of air parcel in the tracer space f mix. Position of the mixing layer (relative to the tropopause) strongly sensitive to the quality of the vertical velocities (Brewer-Dobson circulation) Generally: diabatic ( θ) approach better than kinematic (Ω), see Plöger et al, JGR, 29 Thickness of the mixing layer sensitive to the mixing intensity in the model (CLaMS - still not enough mixing in the troposphere) History of mixing deduced from CLaMS: - fresh mixing (less than 72 hours) in the stratospheric intrusion on aged mixing (more than 5 days) in the tropospheric intrusion on 18.4