Download Structure

An Overview
of the
Lower and
Middle
Atmosphere
Thermal Structure of the Atmosphere
Troposphere:

-- Ozone Max --
Ozone region
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
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
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 (~ 15-25 km)
Thermal Structure of the Atmosphere
Troposphere:
Stratosphere:
Mesosphere:
Ozone region
PMCs
PSCs -- Ozone Max --


•
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
Middle atmosphere:
Everything between the tropopause
and the thermosphere, including the
stratosphere and mesosphere
Thermal Structure of the Atmosphere
Troposphere:
Stratosphere:
Mesosphere:
PMCs



Thermosphere:
PSCs -- Ozone Max --
Ozone region
•
•
•
Temperature increases with height, to
500/2,000 K at 250/500 km
(quite/active sun)
Increasing T associated with
absorption of solar radiation by
molecular oxygen
Photodissociation of O2
O2 + hν  O + O (ionization)
(λ 120-210 nm)
Charged particles comprise the
ionosphere
Large Scale Circulations and the Tropopause
15km
Stratosphere
20km
Troposphere
10km
Hadley
Cell
Ferrel
Cell
5km
Polar
Cell
Polar Easterlies
90°N
Easterly Trades
60°N
30°N
0°
Large Scale Circulations and the Tropopause
Stratospheric Tropical Air
20km
Stratospheric
Midlatitude Air
15km
Secondary Tropical
Tropopause
10km
Stratospheric
Arctic Air
Hadley
Cell
Ferrel
Cell
5km
Troposphere
Stratospheric
Polar Air
Polar
Cell
Polar Easterlies
90°N
Easterly Trades
60°N
30°N
0°
Large Scale Circulations and the Tropopause
Stratospheric Tropical Air
20km
400 K
Stratospheric
Midlatitude Air
15km
350 K
330 K
10km
Stratospheric
Arctic Air
5km
300 K
90°N
Stratospheric
Polar Air
Z: ~12 km
T: -60°C
θ: ~325-340 K
P: 200 hPa
Z: ~18 km T: -80°C
θ: ~375-400 K
P: 80-100 hPa
Secondary Tropical
Tropopause
Z: ~12 km
(convective top)
Z: ~6-9 km
T: -45°C
θ: ~300-315 K
P: 300-400 hPa
60°N
30°N
0°
Tropopause Definitions
Thermal Definitions of the Tropopause
1. Lapse Rate Tropopause (LRT): 2 km layer where
dT/dt < 2 K km-1
2. Cold Point Tropopause (CPT): level of min.
temperature (tropics)
3. Tropical Thermal Tropopause (TTT): Since LRT &
CPT are 0.5 km apart (LRT being lower), TTT is
combination of the two
4. Secondary Tropical Tropopause (STT): level of
max convective outflow
5. 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
From the ECMWF/ERA-40 Atlas
JJA
DJF
Climatology of the Lower & Middle Atm
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
+
5. Stratospheric westerlies
(via thermal wind relationship)
=
Stratospheric Polar Vortex
Air Temperature
Wind Speed
Winter in the Stratosphere
From the ECMWF/ERA-40 Atlas
JJA
DJF
Seasonal Climatology - Lower & Middle Atm
From the ECMWF/ERA-40 Atlas
JJA
DJF
Seasonal Climatology - Lower & Middle Atm
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
Troposphere-Stratosphere Interaction
Source: Natl. Acad. Sci, U.S.A. via SPARC-WCRP
2
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 1953 - Aug 1967)
Gan/Maledive Islands, 1°S/73°E
(Sep 1967 - Dec 1975)
Singapore, 1°N/104°E
(since Jan 1976)
Isopleths are at 10 m/s intervals;
westerlies are shaded
(updated from Naujokat, 1986)
http://www.geo.fu-berlin.de/en/met/ag/strat/produkte/qbo/index.html
http://www.nwra.com/resumes/baldwin/
Departures from Climatology
Sudden
Stratospheric
Warming
(SSW)
Southern
Hemisphere
September 2002
Potential vorticity on
the 850K isentropic
surface (near 10 hPa)
Figure from SPARC
Sudden Stratospheric Warming of January 2009
http://curriculum.pmartineau.webfactional.com/wp-content/svw_gallery/test/gif/2009_01_28.gif
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
Sudden Stratospheric Warming of January 2009
Late January SSW  Impacts in the troposphere on the order of 45-90 days
Downward Propagation  What are the dynamics associated with the progression
of the height anomalies from the stratosphere to the
troposphere???
Sudden
Stratospheric
Warming
Northern
Hemisphere
January 2013
ATM 525 Case Study Project
http://www.atmos.albany.edu/facstaff/andrea/webmaps/2013ssw.html