Title: Long-Term Evolution of the Tropical Cold Point Tropopause Simulation Results and Attribution Analysis Thomas Reichler, U. of Utah, Salt Lake City, USA John Austin, UCAR-NOAA-GFDL, Princeton, USA
1Long-Term Evolution of the Tropical Cold Point
TropopauseSimulation Results and Attribution
AnalysisThomas Reichler, U. of Utah, Salt Lake
City, USAJohn Austin, UCAR-NOAA-GFDL, Princeton,
USA
2Motivation
- Tropical tropopause is closely related to climate
change - Examples
- Tropopause controls stratospheric water vapor
- Tropopause is controlled by tropical upwelling,
QBO, tropo-spheric and stratospheric temperature
changes -
- Exact cause-and-effect relationship between
climate change and tropopause change is unclear -
- Outline
- Simulations with coupled chemistry climate model
- Past and future evolution of tropical tropopause
- Identify factors for change
- regression analysis
- conceptual model
3Methodology
- GFDL-AMTRAC stratosphere resolving coupled
chemistry climate model (2.5x2.5, L48) - Simulation 1960-2100, 3 members
- PAST 1960-1990, historical forcings (SST, GHG,
ODS) - FUTURE 1990-2100, IPCC-A1B and WMO (2003)
forcings, SSTs from GFDL-CM2.1 - Cold point tropopause
- Interpolation after Reichler et al. (2003)
- Lapse rate definition 0 K/km
- Zonal averages (22S-22N) and annual means
4Tropical Tropopause Evolution
- Heights
- PAST Increase
- FUTURE Increase
- 1960-2100 ca. 1 km or ca. 10
-
- Temperatures
- Climatologically important transition
- PAST Cooling
- FUTURE warming
5Decadal Trends
Tropics PAST FUTURE Tropics PAST FUTURE Global 1980-2004 OBS Global 1980-2004 OBS
Height m/dec. 70 64 123 64
Temperature K/dec. -0.13 0.25 -0.27 -0.41
61. Linear Regression Model
- Fit tropical tropopause parameters (temperature,
pressure, height) to a linear regression model
using the following four factors - AER Aerosols (60 hPa at equator)
- SST Tropical SSTs (22S-22N)
- O3 Total ozone (globally averaged)
- UPW Tropical mass upwelling (77 hPa), BDC
- These factors represent major processes known to
influence the tropopause.
7Regression Parameters Evolution
8Regression Analysis Heights
- Contribution of each term to tropopause height
- UPW - most important
- SST - comes second
9Regression Analysis Temperatures
- O3 - dominates PAST
- SST - dominates FUTURE
- UPW - probably strongly related to SST
- AER - small impact
102. Conceptual Tropopause Model
- Shepherd (2002) Constant lapse rates above (?s)
and below (?t) tropopause - Explain tropopause change by temperature change
below (?Tt) and above (?Ts )
- ?Tt gt 0 height ? temperature ?
- ?Ts lt 0 height ? temperature ?
- Staten and Reichler (2008) show
and
11Testing the Simple Model
- Test impact of simulated temperature trends above
?Ts (0, LS) and below ?Tt (0, LT, UT) on
tropopause itself
- PAST LS (and UT)
- FUTURE (LS and) UT
?s -4 K/km, ?t 6 K/km
12Cause and Effect Analysis
Change per century ?Ztrop ?Ttrop ?TUT ?TLS O3 UPW GHG
PAST 700 -1.3 2.5 -5 ?? ?? ?
FUTURE 640 2.5 5 0 ? ? ??
13Conceptual vs. Regression Model
Conceptual Regression
PAST ?T? O3 UPW GHG O3
PAST ?Z? O3 UPW GHG UPW
FUTURE ?T? GHG (SSTs) SST O3
FUTURE ?Z? GHG (SSTs) UPW
- In the PAST, ozone depletion was most important
for cooling and lifting the tropopause - In the FUTURE, greenhouse gas increase will be
most responsible for warming and lifting the
tropopause
14Thank You
More info Austin and Reichler (2008, JGR)
15Trend Analysis