1. Static Stability in the Global UTLS Observations of Long-term Mean Structure and Variability using GPS Radio Occultation Data
Kevin M. Grise
David W. J. Thompson
Thomas Birner
Department of Atmospheric Science
Colorado State University
Extratropical UTLS Workshop
Boulder, CO
October 19, 2009

2. Overview
Static stability is a fundamental quantity for atmospheric dynamics.
GPS radio occultation data provides the global coverage and high vertical resolution necessary to conduct a global survey of static stability in the upper troposphere and stratosphere.
Annual mean
Seasonal cycle
Longitudinal structure
Weekly and monthly variability

3. CHAMP GPS Radio Occultation Data
(Wickert et al. 2001)
Approximately 200 daily temperature profiles since May 2001
Global coverage
Independent of weather conditions
Interpolated to 100-m vertical resolution
Most accurate between 5 km and 30 km altitude

4. Static Stability Annual mean, Zonal mean Altitude-based Average
Tropopause-based Average
White lines highlight shading > 6.0 x 10-4 s-2

5. Static Stability: Extratropics
Annual mean, Zonal mean
Altitude-based Average
Tropopause Inversion Layer (TIL):
Sharp temperature inversion in narrow layer above extratropical tropopause
Zonal mean climatology is well established (e.g., Birner et al. 2002; Birner 2006; Randel et al. 2007).
Physical explanation for existence of TIL is still subject to some debate (e.g., Wirth 2003; Wirth and Szabo 2007; Randel et al. 2007).
Tropopause-based Average
White lines highlight shading > 6.0 x 10-4 s-2

6. Static Stability: Extratropics
Seasonal mean, Zonal mean
Summer polar TIL is stronger than winter polar TIL, particularly in SH.
SH stratospheric polar vortex has large N2 values.
White lines highlight shading > 6.0 x 10-4 s-2

7. Stratospheric Dynamic Variability
60°S - 90°S
2002:
Sudden stratospheric warming
2006:
Strong stratospheric polar vortex

8. Static Stability: Tropics
Annual mean, Zonal mean
Altitude-based Average
“Tropical TIL” :
Shallow N2 maximum centered at Equator (0-1 km above tropopause)
Broader N2 maxima centered between 10˚ and 20˚ latitude in each hemisphere (1-3 km above tropopause)
Tropopause-based Average
White lines highlight shading > 6.0 x 10-4 s-2

9. Longitudinal Structure: Tropics

10. Conclusions
Static stability in the extratropical UTLS is characterized by the tropopause inversion layer (TIL).
Large amplitude seasonal cycle in polar regions
Little coherent longitudinal structure
Wintertime strength in polar regions tied to stratospheric dynamic variability
Static stability in the tropical UTLS has a unique horizontally and vertically varying structure.
Equatorially centered maximum immediately above tropopause
Off-equatorial maxima 1-3 km above tropopause
Reminiscent of equatorial planetary wave response to tropical convection

12. Conventional Vertical Coordinates
Seasonal-mean, Zonal-mean
Summer polar TIL is stronger than winter polar TIL, particularly in SH.
SH stratospheric polar vortex has large N2 values.
N2 in tropics is strongest during boreal winter and has local maximum in winter hemisphere.

13. Static Stability: Tropics
Seasonal mean, Zonal mean
Tropical N2 structures are strongest during boreal winter.
Off-equatorial N2 maximum in winter hemisphere is slightly stronger than that in summer hemisphere.
White lines highlight shading > 6.0 x 10-4 s-2

14. Seasonal Cycle in Polar Regions

15. Seasonal Cycle in Tropics

16. Longitudinal Structure
1 km layer average of N2 above tropopause
Except for mid-latitude winter, the strength of the extratropical TIL exhibits little coherent longitudinal structure.

17. Intraseasonal Variability
Define a TIL index to represent the temporal evolution of near-tropopause static stability values.
1 km layer average of N2 anomalies above tropopause

18. Stratospheric Dynamic Variability
60°N-90°N, November-April
Units: 10-5 s-2
Positive (negative) N2 anomalies at leading edge of descending warm (cold) anomalies.
During winter, NH polar TIL strength appears to be strongly linked to stratospheric dynamic variability.

19. Stratosphere-Troposphere Coupling
Implications
Stratosphere-Troposphere Coupling
Static Stability
Zonal Wind
Thompson et al. (2006)
The maximum in static stability near the tropopause coincides with the period after lag 0 during which stratosphere-troposphere coupling is typically observed.

20. Quasi-Biennial Oscillation
20°N - 20°S
Descending positive N2 anomalies are associated with the easterly phase of the QBO.
The QBO appears to be the dominant driver of the strength of near-tropopause N2 values in the tropics.