1. An Overview of the Lower and Middle Atmosphere

2. Thermal Structure of the Atmosphere
Troposphere:
Stratosphere:
From the tropopause to ~50km / 1 hPa
Temperature increases to ~273 K at the stratopause (marked by a reversal of the dT/dz trend)
Chemical composition similar to troposphere, except…
- Water vapor  Low concentration,
clouds rare but can happen
- Ozone  High concentration,
up to 4 x 10-4 % by volume
Ozone region
-- Ozone Max --

3. In the Stratosphere: Ozone production and destruction is exothermic.
O2 + O  O3 (production)
O3 + O  2O2 (destruction)
Produces heat ( λ < 310 nm )
The Chapman Cycle

4. In the Stratosphere: Polar Stratospheric Clouds:
Contain a combination of water, nitric acid and sulfuric acid
One of many things that can destroy ozone
Form below 195 K (~ km)

5. Thermal Structure of the Atmosphere
Troposphere: 
Stratosphere:
PMCs
Mesosphere:
Between 50 – 80 km
Temperature decreases with height, to 180 K at 80 km, can be as low as 140 K
Polar mesospheric clouds can form near the mesopause (coldest point in the atm), have climate implications
PSCs
-- Ozone Max --
Ozone region
Middle atmosphere:
Everything between the tropopause and the thermosphere, including the stratosphere and mesosphere

6.    Thermal Structure of the Atmosphere Troposphere: Stratosphere:
PMCs
Mesosphere:
Thermosphere:
Temperature increases with height, to 500/2,000 K at 250/500 km (quite/active sun)
PSCs
-- Ozone Max --
Ozone region
Increasing T associated with absorption of solar radiation by molecular oxygen
Photodissociation of O2
O2 + hν  O + O (ionization)
(λ nm)
Charged particles comprise the ionosphere

8. Large Scale Circulations and the Tropopause
20km
Tropopause
15km
Stratosphere
JST
10km JP
Troposphere
ST Front JA
Ferrel Cell
Hadley Cell
5km
Polar Cell
ITCZ
Polar Front
Polar Easterlies
Easterly Trades
90°N
60°N
30°N 0°

9. Large Scale Circulations and the Tropopause
Stratospheric Tropical Air
20km
????
Tropical
Tropopause
Stratospheric Midlatitude Air
15km
Secondary Tropical Tropopause
JST
Midlatitude Tropopause
Stratospheric Polar Air
10km JP
Polar
Tropopause
Troposphere
Stratospheric Arctic Air
ST Front JA
Ferrel Cell
Hadley Cell
5km
Polar Cell
ITCZ
Polar Front
Polar Easterlies
Easterly Trades
90°N
60°N
30°N 0°

10. Large Scale Circulations and the Tropopause
Stratospheric Tropical Air
20km
400 K
Tropical
Tropopause
Z: ~18 km T: -80°C
θ: ~ K
P: hPa
Stratospheric Midlatitude Air
15km
350 K
JST
Midlatitude Tropopause
Secondary Tropical Tropopause
Stratospheric Polar Air
330 K
Z: ~12 km
(convective top)
10km
Z: ~12 km
T: -60°C
θ: ~ K
P: 200 hPa JP
Polar
Tropopause
Stratospheric Arctic Air JA
Z: ~6-9 km
T: -45°C
θ: ~ K
P: hPa
300 K
5km
90°N
60°N
30°N 0°

11. Tropopause Definitions
Thermal Definitions of the Tropopause
Lapse Rate Tropopause (LRT): 2 km layer where dT/dt < 2 K km-1
Cold Point Tropopause (CPT): level of min. temperature (tropics)
Tropical Thermal Tropopause (TTT): Since LRT & CPT are 0.5 km apart (LRT being lower), TTT is combination of the two
Secondary Tropical Tropopause (STT): level of max convective outflow
Clear-Sky Radiative Tropopause: Clear-sky heating rate = 0; below descent, above ascent
Ozone Tropopause
Based on increasing ozone mixing ratio with height.
On synoptic timescales  material surface
Dynamic Tropopause
Defined by a potential vorticity (PV) surface (±2 or ±1.5 PVU)
For conservative flow  material surface
Useful in dynamics (weather!)
Tropical Tropopause Layer (TTL)
Region of the tropical atmosphere between the convective outflow and thermal tropopause (~12-17 km)
Coldest T over equatorial W. Pacific
Cold T  very low water vapor
Source region of stratospheric air
Source: SPARC

12. Climatology of the Lower & Middle Atm
DJF
Climatology of the Lower & Middle Atm
JJA
From the ECMWF/ERA-40 Atlas

13. Stratospheric Polar Vortex
In the Winter Hemisphere:
1. Long dark polar night +
2. O3 heating shuts down +
3. Radiative cooling over pole +
4. Sharp meridional T gradient +
Stratospheric westerlies
(via thermal wind relationship) =
Stratospheric Polar Vortex

14. Winter in the Stratosphere
Wind Speed
Winter in the Stratosphere
Air Temperature

15. Seasonal Climatology - Lower & Middle Atm
DJF
Seasonal Climatology - Lower & Middle Atm
JJA
From the ECMWF/ERA-40 Atlas

16. Seasonal Climatology - Lower & Middle Atm
DJF
Seasonal Climatology - Lower & Middle Atm
JJA
From the ECMWF/ERA-40 Atlas

17. The Basics: Stratospheric Circulation
Winter Hemisphere
Longwave cooling  Cold pole
Cold polar vortex W-ly stratospheric jet
W-ly from surface to stratopause  Vertically propagating Planetary waves
Summer Hemisphere
Ozone warming  Warm pole
Warm pole E-ly stratospheric jet
From W-ly to E-ly with height  No vertically propagating waves

18. Troposphere-Stratosphere Interaction
Source: Natl. Acad. Sci, U.S.A. via SPARC-WCRP 2

19. Departures from Climatology
The Quasi-Biennual Oscillation (QBO)
Time-height section of
monthly mean
zonal winds
at equatorial stations:
Canton Island, 3°S/172°W
(Jan Aug 1967)
Gan/Maledive Islands, 1°S/73°E
(Sep Dec 1975)
Singapore, 1°N/104°E
(since Jan 1976)
Isopleths are at 10 m/s intervals; westerlies are shaded
(updated from Naujokat, 1986)
Departures from Climatology

20. Departures from Climatology
Sudden Stratospheric Warming
(SSW)
Southern Hemisphere
September 2002
Departures from Climatology
Potential vorticity on the 850K isentropic surface (near 10 hPa)
Figure from SPARC

21. Sudden Stratospheric Warming of January 2009

22. The Basics: Troposphere-Stratosphere Interaction
Northern Annular Mode (NAM)
 A measure of the vertical structure of the AO
Source: NCDC/NOAA
Measure of the amplitude of the 1000 hPa flow
Baldwin and Dunkerton, 2001 3

23. Sudden Stratospheric Warming of January 2009
Late January SSW
 Impacts in the troposphere on the order of days
Downward Propagation
What are the dynamics associated with the progression
of the height anomalies from the stratosphere to the
troposphere???

24. Sudden Stratospheric Warming
Northern Hemisphere
January 2013
ATM 525 Case Study Project