An Overview of the Lower and Middle Atmosphere

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 --

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: 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

   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 120-210 nm) Charged particles comprise the ionosphere

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°

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°

Large Scale Circulations and the Tropopause Stratospheric Tropical Air 20km 400 K Tropical Tropopause Z: ~18 km T: -80°C θ: ~375-400 K P: 80-100 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: ~325-340 K P: 200 hPa JP Polar Tropopause Stratospheric Arctic Air JA Z: ~6-9 km T: -45°C θ: ~300-315 K P: 300-400 hPa 300 K 5km 90°N 60°N 30°N 0°

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

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

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

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

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

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

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) Departures from Climatology 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 Departures from Climatology 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