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Observations of convective cooling in the tropical tropopause layer in AIRS data
Hyun Cheol Kim Andrew E. Dessler
May 3, 2005 Department of Meteorology, University of Maryland, College Park
Observations of convective cooling in the tropical tropopause layer - - PowerPoint PPT Presentation
Observations of convective cooling in the tropical tropopause layer - - PowerPoint PPT Presentation
Observations of convective cooling in the tropical tropopause layer in AIRS data Hyun Cheol Kim Andrew E. Dessler May 3, 2005 Department of Meteorology, University of Maryland, College Park Convective impact in the Tropical Tropopause Layer T
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Tropical tropopause layer
16 km 8 km Equator Pole Pole Tropopause
Dehydration Convection Radiative heating TTL
= Q &
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Data (1)
AIRS (Atmospheric Infrared Sounder)
- Level 2 temperature profile
- Horizontal resolution/coverage : 50 km/Global
- Vertical resolution : 28 levels (1100 - 0.1mb)
- Temporal resolution : 2/day
- Error : < 1 K
- Ocean only
- Feb. 2003 and Jul. 2003
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Data (2)
NCEP/AWS Infrared Global Geostationary Composite
- Global composite images from four weather satellites in
geosynchronous orbit (GMS, GOES-East, GOES-West, Meteosat)
- 11 micron Brightness Temperature
- Horizontal resolution/coverage : 14 km/Global
- Temporal resolution : 48/day
- Feb. 2003 and Jul. 2003
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Methodology
Local monthly mean temperature profiles for 1°x1 °
boxes (AIRS)
Individual temperature anomalies (AIRS) Assigning convective stage for each temperature
anomalies using NCEP/AWS IR image.
Averaging temperature anomalies according to their
convective stages
) , , , ( 1 ) (
, ,
z t lat lon T n z T
t lat lon i
- =
- For convective stages 0,1,…,5
) , , ( ) , , , ( ) , , , ( z lat lon T z t lat lon T z t lat lon T
mean i i
- =
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Convective stages
C208 :the fraction of pixels in a box with brightness
temperatures below 208K (NCEP/AWS IR image)
10 %
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Mean temperature anomaly profile
(Feb. 2003)
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Cooling rate
Cooling rate = -7 K/day
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Tropopause cooling
Adiabatic lifting
- Cold point analysis shows the tropopause moves downward
during active convection diabatic component
Cloud-top radiative cooling
- No diurnal cycle in cooling amount
( Net cloud cooling = in-cloud cooling + solar heating)
Turbulent mixing of overshooting air
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Radiative cooling? – diurnal separation
Net cloud-top cooling = in-cloud cooling + solar heating
100 hPa 1000 hPa
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Turbulent mixing of overshooting cloud
) (
- =
=
a m
dt df dt d Q
day K K day K Q dt df
a
/ 35 . 375 355 / 7 =
- =
- =
- +
- =
) 1 ( f f
a m
(for one convective event) In tropical average: 0.35/day * 3% = 1.05 %/day ~3 months turnover time
Overshooting air Environmental air Mixture θa, ma θ, m θm
m m m f
a a
+ =
where
Cooling rate :
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Conclusion
This study shows a clear signal of cooling near the
tropical tropopause during active convection.
Estimated cooling rate is –7 K/day. This tropopause cooling during active convection
cannot be explained by cloud-top radiative cooling. We suggest that mixing of overshooting air with its environment can possibly contribute to this cooling.
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Overshooting convective cloud
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The End
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Sensitivity test
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Adiabatic lifting?
T P θ+Δθ θ-Δθ θ Adiabatic
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Adiabatic lifting?
T P θ+Δθ θ-Δθ θ Diabatic
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Cloud-top radiative cooling?(Ackerman et al, 1988)
In-cloud heating Solar heating
Net cloud-top heating = in-cloud heating + solar heating
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Cooling at 100 hPa (Potential temperature anomaly)
K
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Cloud-top cooing? - Tb distribution
Cloud fraction to cause –7 k/day 70%