Critical Processes in the Tropical Tropopause Layer Andrew Gettelman, NCAR + Q. Fu, P. Forster, W. J. Randel 11km, Tropical Atlantic (20N, 65W), August

TTL Importance TTL sets chemistry of lower stratosphere –Stratospheric H 2 O set in TTL –‘Short lived’ species set in TTL (Bromine) –Aerosols & precursors set in TTL (Sulfur) Radiation from TTL clouds affects climate Changes to TTL over time affect climate

Outline Definition of the TTL Key Processes Process Interactions & Variability Conclusions: how air and water vapor enter the stratosphere

A Transition Layer Above 12-14km -O 3 Increases -Lapse Rate Change Trop at 17km Folkins et al, 1999, Fig 1

TTL & Convective Outflow Lapse Rate (T)Ozone Folkins, JAS, 2001

Definition of the TTL Schematic Gettelman & Forster, JMSJ 2002

Key TTL ProcessesRadiation Large Scale Transport Tropical Waves Cloud Microphysics Convection OH Br SO 2 O3O3O3O3PANChemistry HNO 3

Convection Monsoon Convection, Ganges Valley, India

Convection (2) Amazon Basin, Brazil

Clouds above the Tropopause (also see Rossow talk) Gettelman, Sassi & Salby JGR 2002

Convective Mass Fluxes Küpper et al, 2004 CO O 3 Clouds Radiation Cloud Model ECMWF (BD) Jan Jul X * Model Upwelling

Impact of convection (also see Bretherton talk) A cloud resolving model indicates convection matters for temperature (due to long radiative timescales) Result depends on the circulation Kuang and Bretherton, 2004 Base Case SST+2 Background cooling

Non-local effect of Convection Non-UniformZonal Mean Equatorial HeatingT Response (K) Norton, JAS, 2005 Why: Tropical (Kelvin) wave response to latent heat (convection)

Radiation Balance of TTL Gettelman et al 2004, JGR LW SW Net Q clear =0 (LZH): 15km, 125hPa, 200ºK, 360K (  ) ±400m (1  ) Diff Radiation Models: ±300m, Diff Season/Location: ±500m Diurnal cycle: 1-2 km (lower for low SZA) Important for background atmos Also Fixed Anvil Temp hypothesis (see Hartmann poster)

Gas Contributions TTL Notes: CO 2 heating is actually critical for TTL! O 3 heating important from 17km up

Net Cloud Impact Tropical mean Heating Rates Corti et al 2005, GRL Full Sky all ISCCP Full Sky ISCCP mean Clear Sky Mean Balloon Clear Sky mean H2O Absorption in clouds dominates if no cloud below: causes heating Clouds Lower LZH

Convection T b < 200K Gettelman, Salby & Sassi, JGR 2002

HALOE H 2 O Convection Frequency(0.5, 1, 5, 10%) Tropopause ECMWF Temperatures (Shading) Large Scale TTL Transport Randel et al 2001, fig 6

TTL Trajectory Transport (also see Haynes talk) Analytical microphysical model on trajectories Reproduces seasonal, interannual UTH variations (Gettelman et al 2002; Dessler & Sherwood, 2000; Fueglistaler et al 2004) ObservationsModel

Microphysics in the TTL Cloud formation important: Clouds are important for Climate Chemical impact of clouds Clouds control condensation of H 2 O 1.Clouds do not form at RH=100% 2.Microphysics affect cloud formation

TTL Supersaturation PDF from Aircraft & Satellites: E. Pac, Jan 2004 Gettelman et al, J. Climate, in press, 2006

H 2 O Sensitivity to S ice S ice can change 100hPa H 2 O by 30% (Gettelman et al 2002, GRL) S ice Analytic Model: Change in 100hPa H 2 O

Waves Tropical waves affect T & H 2 O Waves affect minimum T (& H 2 O) Many scales of variability Examples: –Equatorial Kelvin waves –Gravity Waves from Convection

Tropical Waves, Clouds & T Boehm & Verlinde, 2000 GRL 2000, GRL Cloud Lidar Temp variations (- +)

Sensitivity of H 2 O to Waves Ratchet Effect: Increasing Temp Variance (  t ) Decreases H 2 O in TTL (Gettelman et al 2002, GRL) Microphysical model: waves change 100hPa H 2 O by 25%

Chemistry in the TTL (also see Lawrence Talk) Chemistry affects aerosols –Aerosols affect cloud microphysics and H 2 O vapor TTL clouds and H 2 O affect chemistry –UTLS H 2 O affects Ozone (through HO x ) TTL Ozone affected by short lived species –Bromine may affect Ozone in TTL –NO x & short lived compounds from surface affect O 3 Cirrus may contain Nitric Acid –Is this like polar ozone loss? Not really, but might affect cirrus cloud formation TTL Ozone is important for heating rates

TTL Summary (1) TTL transition between Strat-Trop –Many definitions, Thermodynamic one convenient –Trends in the TTL exist! Convection present up to cold point –Some into stratosphere, key is convection above Q clear =0 Radiative heating above Q clear =0 (15km) Transport after convective lofting, mixing 4-D circulation plays a big role –Monsoon circulations important (bypasses deep tropics)

TTL Summary (2) Microphysics can be important –Supersaturation strongly affects water vapor –Also impacts radiation, short lived species Tropical waves –Wave fluctuations dehydrate in ‘Ratchet effect’ (GW) –Coherent wave structures (Kelvin waves, MJO) Chemistry –May affect microphysics and H 2 O (HNO 3 ) –Short lived species processed in TTL affect L Strat O 3

Sorting out TTL Processes Use coupling between processes –Transport, Condensation/Microphysics Use natural modes of variability and observed changes to sort out processes Annual Cycle, [ENSO, QBO], interannual Do global models resolve the TTL?

HALOE H 2 O Convection Frequency(0.5, 1, 5, 10%) Tropopause ECMWF Temperatures (Shading) Interactions: TTL H 2 O & Clouds Randel et al 2001, fig 6

TTL Interannual Variations 82 hPa Water vapor anomalies Tropopause temperature anomalies (radiosondes and ERA40) Randel et al, 2004

Trajectory Models [H2O] e Correlated with T along trajectories

Models Can Simulate TTL WACCM3 coupled model 1km vertical resolution ~6 levels in TTL Gets basic relations right See poster for details! CP & LR Tropopause Q clear =0 Min O 3 Min  

Simulated Tape Recorder MOZART3 H 2 O (ppmv)UARS / HALOE Randel, et al., JGR, 106, 14313, 2001MATCH CCM3.6 column physics Park et al., 2003, JGR

How Does Air Enter Strat? Infrequent convection up to the cold point Radiative heating above Q clear =0 (15km) Large scale transport after convective lofting, mixing –Key is convection above Q clear =0 4-D circulation plays a big role –Monsoon circulations important –Some air may bypass tropical tropopause Tropical wave mixing/forcing (GW, Kelvin)

Schematic: Air Motion in TTL Schematic Gettelman & Forster, JMSJ 2002

How Does H 2 O Enter Strat? H 2 O tied to TTL & cold point temperatures Annual -> ENSO -> Interannual Changes in transport play a role Methane partial cause of long term trend Cloud microphysics/waves change H 2 O –Changes to IN (aerosol), nucleation, RH –Changes in chemistry –Changes to tropical wave spectra

What Controls TTL Temps? Convection –Direct input of low  e air Wave driven (Brewer-Dobson) circulation Radiative effects of convection, clouds –Long radiative damping time (low absorption) –Increases importance of forcing (bigger response) Dynamical responses to Waves & Clouds –Non-local equatorial wave response to convection –Gravity wave ratchet effect

The Last Word TTL definable region –Lapse rate minimum to cold point tropopause TTL exists due to balance of processes –Convection (lower bound) –Strat Circ, Waves (upper bound) –Radiation important in the region H 2 O in LS governed (0 order) by temp –Transport, Waves, microphysics important –Convection helps set temps (response to heating) Expect modest changes in TTL over time –Due to radiation changes. Convective changes uncertain Global models can simulate this region pretty well

Spectrally resolved LW cooling Brindley & Harries 1998 (SPARC 2000) H 2 O Continuum Pressure (hPa) CO2 15  m O3 9.6  m Wavenumber HeatingCooling H 2 O Rotation

Conceptual Picture (also see Sherwood talk) Convective Dehydration“Cold Trap” Dehydration Sherwood & Dessler, GRL, 2000; JAS, 2001 Holton & Gettelman, GRL, 2001; GRL, 2002 Cold Pool 18km, 420K 14km, 355K Tropopause Stratosphere Troposphere