Sudden Stratospheric Warming (SSW) and O3 T. Flury, K. Hocke, N. Kämpfer, A. Haefele Institute of Applied Physics, University of Bern ISSI workshop
Outline 1) GROMOS measures O3 depletion during SSW 2) Temperatures during the SSW 3) Wind shear 4) Trajectory analysis 5) Explanations
Facts about the SSW in Bern > Observations: Stratospheric warming above 35 km Stratospheric cooling between 15 30 km Ozone depletion between 20 50 km Strong wind shear at 35 km > Data sources: GROMOS ozone radiometer ECMWF temperatures and winds Payerne radiosonde temperatures MIAWARA and Aura/MLS water vapor
Overview of measurements in Bern
Ozone depletion 4.3 hpa 3.3 hpa 1.8 hpa > Depletion propagates downward > Lasts for more than 1 week. > Different signature in lower stratosphere 2.4 hpa
Northern Hemisphere Temperatures > Opposite temperature distribution at 20 km than at 40 km > Upper stratospheric warming, lower stratospheric cooling
Temperatures at Bern > Cooling in layer 20 30 km > Warming above 35 km > Since 1994 only 4 times T<190 K in the lower stratosphere measured at Payerne > T<190 K during SSW 1.Jan 04, 19. Jan 06 and 19 Feb 08
Payerne Radiosonde (46.8 N, 6.95 E) > T below PSC threshold > Strange behavior of ascent speed
Polar Stratospheric Clouds > Calipso satellite Lidar detects clouds > PSC can form for T<195 K in the lower stratosphere > Heterogeneous chemistry on PSC ice crystal surfaces reduces ozone > Air with reduced ozone values to find down stream of the PSC
Strong Wind Shear
TomTom: Tom's Trajectory Model Question: Where does the air come from? Method: Air parcel trajectories > No mesospheric trajectories available on Internet > Selfmade Simple Trajectory Model TomTom > Isentropic trajectories > Validation with Goddard Automailer and Hysplit for z<40 km Flow Chart of TomTom Model ECMWF wind data on 1.1 spaced grid and 60 height levels Trajectory Calculation + Visualisation MySQL database Matlab Output: Map + Trajectory Datafile
40 hour backward trajectories > Air from polar regions below 40 km > Air from tropical regions above 40 km > Cold air from polar vortex, further cooling through upward motion > Descent motion and adiabatic heating for the tropical air
Detailed Trajectories lower stratosphere
Detailed trajectories upper stratosphere
Water vapor enhancement Miawara and Aura/MLS H2O 30 8 hpa Aura/MLS 17 Feb 10 hpa (850 K,32 km) > Trajectories show that H2O rich air was brought to Switzerland from the polar vortex (yellow on MLS)
H2O as tracer 40 h backward trajectory. Start 19 Feb 08 18 Feb 08 17 Feb 08 19 Feb 08
Explanations for O3 depletion above 35 km Ralph Lehmann, AWI Potsdam, priv. comm. > Temperature dependent chemistry responsible > Box model shows decrease of the same amount due to warming at 1650 K (40 km)?
Explanations for O3 depletion around 20 km > In the lower stratosphere [O3] proportional to Temperature > Cold air from the pole transported to Switzerland
Summary > Sudden warming for z>35 km, cooling for z<35 km. > O3 depletion for z<35 km due to transport of polar air with low ozone values. Depletion in vortex due to PSC. > O3 depletion for z>35 km due to downward transport from tropical regions and enhanced chemical destruction due to temperature increase. > A SSW leads to O3 depletion at mid latitudes.