1. An Overview of the Tropical Tropopause Layer
Andrew Gettelman
National Center for Atmospheric Research (NCAR), Boulder, CO

2. Outline Road Map Motivation Definition of the TTL & Overview
Radiation Balance of the TTL
Key Questions

3. Our ‘Tour’ (2 days) Basics Clouds and Convection (Pfister)
Water Vapor (Randel)
TTL Transport & Waves (Fujiwara)
Trace Species & Chemistry (Thompson)
Stratospheric Dynamics (Alexander)
Techniques
Aircraft Observations (Rosenlof)
Ground Based Observations (Hasebe/Shibata)
Satellites (Shiotani)
Modeling (Jensen)
Data Assimilation (Miyazaki)

4. TTL Impacts stratospheric composition
See: Stratosphere: Alexander Talk
Brewer, 1949, QJRMS

5. TTL Transport: Water Vapor
Rosenlof, 2003
Randel Talk: Water Vapor; Shiotani: Satellites

6. Impact of stratospheric H2O
Randel H2O Talk; Gettelman: Radiation
Stratospheric H2O changes are an extra radiative forcing
Solomon et al 2010

7. TTL Transport: Short Lived Species
Observations show additional Bromine in the Lower Stratosphere
from Very Short Lived Species (VSLS): impacts ozone: Thompson Chem Talk
WMO2007, Chapter 2

8. Climate Trends are seen in TTL
Seidel et al 2008, Nat. Geosci.
TTL

9. Defining the TTL

10. Profiles: Extratropics
Boulder, 40N
Tropopause relative
Sharp jump in O3 starts right below tropopause
Ground Based Observations (Hasebe/Shibata)
Data: Vömel, Plot: Pan, in
Gettelman et al 2011., Rev Geopys

11. Tropical Profiles Sharp ‘Cold Point’ Ozone increases 3km below it
What is going on?
Longer transport times, changes in balance of processes
TTL
Soundings: Samoa, March 1996 Ground Based Observations (Hasebe/Shibata)
Folkins et al 1999

12. Idealized T Profiles e=const Dry Adiabat Rad Equil T=const
Gettelman & Forster 2002, JMSJ
e=const
Dry Adiabat
Rad Equil
T=const

13. W. Pacific T Soundings
Koror: 7N 135E
Gettelman & Forster 2002, JMSJ

14. TTL & Convective Outflow
Lapse Rate (T) Ozone
Folkins, JAS, 2002
Thompson: Trace Species and Chemistry

15. Simulating TTL structure
Solid: Sondes
Dotted: WACCM
Thin Dot: CAM
Dashed: CMAM
Gray: TTL Avg
stations
Lapse rate profiles from GCMs: Min O3 similar to Min LR (LRM)
Gettelman & Birner, 2007, JGR, Fig 3

16. Tropopause Horizontal Structure
NCEP Reanalysis Seasonal Mean Tropopause Temp
(Yes: the temperatures are biased +3K or so. Focus on the gradients)
Data Assimilation (Miyazaki)

17. Key TTL Processes Radiation OH Br SO2 O3 PAN Chemistry HNO3
Large Scale Transport
Convection
Cloud Microphysics
Tropical Waves

18. Instantaneous TTL picture is complicated
Satellites (Shiotani); Clouds (Pfister)
3 July :15 UT,
Through the Asian Monsoon
White: GFS 50km trop
Black: GEOS5 trop
Wind speed
Potential Temperature
Pan and Munchak, 2011, JGR, Fig 2

19. TTL ‘Characteristics’
Rev. Geo. 2009

20. Difficulties in Observing the TTL
“The TTL is high”: few available platforms can reach it from the ground
“The TTL is low”: tough to do radiative transfer remotely (especially from space)
Sharp gradients
Clouds and other ‘radiative obscurities’
Limits observations for analysis (assimilation)

21. Tropical Tropopause Layer
Radiation (Gettelman) ; Transport (Fujiwara)
Gettelman & Forster 2002

22. Convection
Clouds are Complicated! (Pfister)

23. Convection in the TTL (TRMM)
Clouds and Convection (Pfister)
Liu and Zipser, 2005, JGR, Fig 2

24. Clouds above the Tropopause: 1330LT
Pan & Munchak, 2011, Fig 7

25. Clouds at the tropopause
Clouds and Convection (Pfister)
Yang et al 2010, JGR, fig 3

26. Convective Turnover Time
CPT
Gz min
Qclear=0
TTL
tc~2yrs
tc~6-9mo
tc<1mo
Gettelman et al 2002, JGR, Fig 9

27. Simulating TTL Clouds (Global Models)
Models do ‘okay’ on gross measures of cloud occurrence.
Not for the right reasons…
Modeling: Jensen
Gettelman & Birner, 2007, JGR, Figure 10

28. TTL Ice Super-saturation
Ice clouds do not form at 100% RH. Need significant ice supersaturation.
High TTL supersaturations observed. Ice formation mechanisms uncertain.
Aircraft Observations (Rosenlof)
PDF from Aircraft & Satellites: E. Pac, Jan 2004

29. Large Scale TTL Transport
Water Vapor (Randel); TTL Transport & Waves (Fujiwara)
Randel et al 2001, fig 6
HALOE H2O
Convection Frequency (0.5, 1, 5, 10%)
Tropopause
ECMWF Temperatures (Shading)

30. Interannual Variations of Temp & H2O
Temperature and Water Vapor are Coupled
Fueglistaler & Haynes, 2005, JGR, fig2

31. Tropical Waves, Clouds & T
2000, GRL
Boehm & Verlinde, 2000 GRL
Temp variations (- +)
Cloud Lidar
Waves in the TTL alter temperatures, water vapor and clouds
TTL Transport & Waves (Fujiwara)

32. Chemistry in the TTL Chemistry affects aerosols
Aerosols affect cloud microphysics and H2O vapor
TTL clouds and H2O affect chemistry
UTLS H2O affects Ozone (through HOx)

33. “One Atmosphere – One Photochemistry”
Traditional View: [HO2] & [OH] produced by O1D+H2O and CH4 oxidation
Real world: UT [HO2] & [OH] also produced by photolysis of precursors (acetone and peroxides) lofted from the surface
NO is important for regulation of HOx (via [HO2]/[OH] ratio) and controls tropospheric ozone production efficiency
Bromine matters for ozone in LS: precursors may transit TTL
Ozone Loss by Process
47°N, March 1993
Standard view of ozone loss in UT/LS:
“HOx rules”
Bromine might be important in TTL!
Trace Species & Chemistry (Thompson)
From Salawich

34. Simulated TTL Structure
Modeling (Jensen)
Simulated TTL Structure
Gettelman & Birner, 2007, JGR, Fig 5
Contours: CMAM GCM, Squares: Sondes

35. Brief Summary…. TTL is a transition region
Important for Tropospheric Climate and Stratospheric Chemistry
Complex interplay of processes
Have some understanding of connections
Observations remain a challenge
Can represent the TTL (broadly) in global models
Now, on to the Radiative Balance….

36. Radiation Balance of the TTLLW SW
Net
Gettelman et al 2004, JGR
What drives zero heating level? (LZH or Qclr=0)

37. Gas Contributions
TTL
LZH occurs when (A) H2O tails off and (B) O3 increases. CO2 trop

38. Variations in Qclear=0
SZA: Avg
SZA Noon
± 1s
Qclear=0 location: 15km, 125hPa, 200ºK, 360K (q)
Profiles vary from average by ±400m (1s)
Different Models: ±300m, Season/Location: ±500m
Diurnal Variation: 1-2 km (lower for low SZA)
Clouds raise Qclear=0 by up to 1km (more LW cooling)

39. Tropical mean Heating Rates
Impact of Clouds
Tropical mean Heating Rates
All Sky ISCCP (mean)
All Sky ISCCP + LIDAR
Clear Sky Mean
Clear Sky T & O3
Corti et al 2005, GRL

40. TTL Profiles of Cloud HeatingSW LW
Net
Yang et al 2010, JGR, Fig 10

41. Simulated TTL Radative Balance
TTL Thermal Budget is a balance between latent heat (COND) and radiative cooling (Q-NET) below Qclr=0 and rad heating and dynamics above *
Gettelman & Birner, 2007, JGR, Fig 4

42. Radiation balance of the TTL
H2O dominates up to the TTL
CO2 important right at the tropopause (and above)
O3 above the tropopause
Heating drives transport in the TTL
Clouds affect these heating rates: clouds in the TTL heat, lowers Q=0 level.
Clouds below increase LW cooling above
Raises Q=0 level LW SW
Net
Note: TTL vertical motion and transport is not strictly radiative. Large scale dynamics matters. Upward vertical motion can exist below Q=0 level

43. Key Questions: Rad Balance
What is the role of clouds in the heat budget of the TTL? Especially: cirrus and thin cirrus
How does the radiative role of TTL clouds in change in space and with season?
How do small scale motions & waves interact with radiation?
How will TTL radiative properties change with anthropogenic forcing?

44. References (1)
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