1. Modeling Tropical Tropopause Layer Processes Challenges: Spatial resolution, global domain, range of time scales Complex physical processes (e.g., cloud microphysics, convective transport, radiative transfer)

2. Hierarchy of modeling approaches Global, 3D Eulerian models (free-running GCMs or CTMs that assimilate data) TTL channel models with higher resolution Limited-domain cloud resolving models Trajectory models Semi-Lagrangian, 1D trajectory models

3. Three-dimensional, global Eulerian models E.g., GCMs, CCMs, forecast models Either free running (i.e., no forcing from atmospheric measurements) or assimilating winds, temperatures, etc. Advantages: Free-running models include full interaction between clouds, composition, thermal structure, radiation, and dynamics −e.g., can investigate impact of cloud heating on tropopause temperature and TTL transport Straightforward testing and improvement of parameterizations used in operational models Disadvantages: Poor horizontal and vertical resolution (typically 1 km in TTL) Questionable representation of cloud physics Questionable representation of heating rates (vertical transport)

4. Temperature variability near cold-point tropopause

5. 3-D Eulerian model representation of the TTL What the models do well: Large-scale TTL thermodynamic structure and circulation Brewer-Dobson circulation and annual cycle Large scale tropical-extratropical coupling What the models do poorly: Cold point temperature and variability Stratospheric water vapor Cloud fractions and microphysical properties Ozone distribution Extreme convection Small-scale gravity waves

6. Climate model representation of cold-point temperature (from CMIP5) GPS Considerable spread in model cold-point temperatures 191−195 K @100 hPa corresponds to H 2 O sat ≈ 3.5− 7 ppmv

7. CARMA Cirrus Microphysics C. Bardeen

8. Tropical Averages (20S-20N) C. Bardeen

9. TTL channel models (e.g., Evan et al., JGR, submitted, 2012) WRF simulations 42° S to 42°N and 180°W to 108°E; 36-km horizontal and 500 m vertical resolution Investigate processes controlling TTL temperature and water vapor 40% increase in TTL cloud ice increases cold-point temperature by 1.5 K WRF MERRA ERA-I

10. Using CTMs to model transport of short-lived substances into and through the TTL ( e.g., Aschmann et al., ACP, 2009)

11. Cloud-resolving model simulations of TTL cirrus (e.g., Dinh et al., JGR, 2010) 2D simulations of the interactions between clouds, radiation, and dynamics Radiatively driven convection can maintain the cloud Heating rates are small and the time scale for buildup of convection is on the order of a day

12. Cloud-resolving model simulations of TTL cirrus (e.g., Jensen et al., JGR, 2011) With lapse rate, shear, and ice crystal size based on observations, cloud does not persist long enough for small-scale convection to build up. Synoptic and mesoscale temperature variability may often limit cloud lifetime to < 12-24 hours. Need to examine lidar measurements of TTL cirrus structure

13. Lagrangian trajectory models Backward or forward trajectories (10-90 days) track paths of parcels on their journeys upward through the TTL – Slow vertical transport and rapid horizontal transport Used to calculate stratospheric entry humidity ([H 2 O] e ), source of air for TTL or stratosphere, transport pathways, TTL chemical composition, etc. Individual trajectory paths are uncertain, but statistical distribution is assumed to be robust Vertical winds: diabatic (using heating rates calculated from radiative transfer or kinematic (using horizontal winds and continuity equations) – Diabatic approach is less dispersive (Ploeger et al., 2010)

14. TTL Transport 30-day back trajectories from western Pacific

15. Fueglistaler et al.; Fueglistaler and Haynes (JGR, 2005) (Lagrangian cold-point) Lagrangian [H 2 O] e calculation gives good agreement with observations (H 2 O concentration, annual cycle, and interannual variability) Just using cold-point temperatures (ignoring horizontal transport) gives excessive water vapor

16. Bergman et al. (JGR, 2012) (Convective sources of stratospheric air) Convective influence determined from trajectory intersections with high convective clouds (using 3-hourly OLR) Transport to the stratosphere requires convection deep into the TTL as well as confinement to regions with upward motion

17. Bergman et al. (JGR, 2012) (Convective sources of stratospheric air) Convection that contributes to air entering the stratosphere is confined to localized regions.

18. Ashfold et al. (ACP, 2012) (Pathways from the boundary layer to the TTL) Western Pacific is an important source of air that enters the TTL

19. Konopka et al. (ACP, 2010) (Impact of in-mixing on TTL composition (CLAMS)) In-mixing associated with anticyclones is important for TTL O 3

20. Schoeberl et al. (ACP, 2012) (Comparison of stratospheric H 2 O using forward trajectories with different analyses) Using temperatures and winds from different analyses produces very different results

21. Liu et al. (JGR, 2010) (Quantitative assessment of advection-condensation calculations of stratospheric H 2 O) A-C calculations produce results that are too dry Need to include sub-grid scale temperature fluctuations Need to include persistent supersaturation within TTL cirrus Need to include incomplete removal of condensed water by sedimentation

22. Jensen and Pfister (JGR, 2004) (Temperature-curtain approach) Temperature profiles are extracted from analyses along trajectories Temperature and vertical wind curtains are used to drive 1-D cloud simulations with detailed microphysics Inclusion of microphysics increases the amount of water vapor that can pass through the cold trap

23. Trajectory approach uncertainties: TTL heating rates Large differences in TTL heating rates from analyses and radiative transfer calculations (  large differences in diagnosed vertical motions) J. Bergman

24. Trajectory approach uncertainties: convective cloud heights TRMM (precip radar) primarily detects continental convection Geostationary (IR) has variable cloud-top bias A-TRAIN (CALIPSO, CloudSat) miss late-afternoon/early-evening peak in continental convection Liu et al. (J. Clim., 2007)

25. How important is Asian monsoon anticyclone transport for Boreal summer stratospheric water vapor budget? Can convective hydration over the Tibetan Plateau short circuit the tropical cold-point tropopause? Fu et al. (PNAS, 2006) James et al. (GRL, 2008) Park et al. (JGR, 2009) Wright et al. (JGR, 2011) Chen et al. (ACP, 2012) Bergman et al. (JGR, 2012, submitted)

27. How important is TTL supersaturation? (ATTREX results) ATTREX measurements indicating RH ice pegged at 100% in clouds with numerous ice crystals provides assurance of H 2 O measurement accuracy

28. How important is TTL supersaturation? Large supersaturations within TTL cirrus are prevalent TTL cirrus ice concentrations are typically too low to efficiently remove vapor in excess of saturation

29. Accuracy of water vapor measurements MACPEX 23 April 2011 ~1.5 ppmv offset~0.7 ppmv offset DLH appears to agree with CIMS

30. TTL cirrus dehydration Two requirements for irreversible dehydration: 1.Sufficient ice concentration to deplete vapor within lifetime of clouds (or before ice crystals sediment out of the layer) 2.Sedimentation of ice crystals before cloud is destroyed by warming Low concentration cirrus do not effectively deplete vapor in excess of saturation – Time scale for supersaturation quenching is hours – Slow cooling can maintain supersautration High ice-concentration rapidly deplete vapor in excess of saturation, but… -2.5 ppmv condensed H 2 O at 100 hPa and N=1000 L -1  D≈8.5 μm  Fallspeed = 0.3 cm/s -approx 7 hour lifetime implies sedimentation of about 80 m. -only narrow dehydrated layers will be left behind

31. Future outlook Spatial resolution in global models is continually improving Global model improvements needed: – Focus on tropical tropopause temperature in model tuning – Evaluation and improvement of model TTL heating rates – Improvement of TTL cloud microphysics based on recent measurements – Improvement in convective parameterization cloud-top height distributions Outlook for future satellite measurements is woeful

32. Modeling science questions How important is Asian monsoon anticyclone transport for Boreal summer stratospheric water vapor budget? How important is extreme convection detrainment in the upper TTL? How can we use in situ and remote sensing data to improve representations of TTL processes in global models? How often do TTL cirrus effectively dehydrate air crossing the tropopause cold point? (how routinely does air pass through the cold point with large ice supersaturation?)

33. SEAC4RS (Aug-Sep, 2014?) ER-2 and DC-8 based at Singapore? ER-2 8 hour flight TTL profiling in Bay of Bengal, South China Sea, Gulf of Thailand, southern edge of anticyclone, etc.

34. ER-2 Payload + polarimeters

35. Using the ER-2 to profile through the TTL Dips from 65-70 Kft (≈20 km) to 45 Kft (≈13.5-14 km) 12 flights, climb-out + final descent + 2 dips  72 TTL profiles in the Asian monsoon region