Cirrus climatology at mid-latitude observed with Lidar

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Cirrus climatology at mid-latitude observed
with Lidar
P. Keckhut, S. Bekki, A. Hauchecorne, F.
Borchi, A. Colette, C. David, and J.
Jumelet Climate, Ozone, and Sun Team Service
dAéronomie/IPSL, France Keckhut_at_aerov.jussieu.fr
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Outline

• Data description
• Climatology
• Clustering approach
• Stratospheric case
• Conclusions

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Lidar Observations

• were performed during nightime
• with a powerful system (350 mJ/pulse and
  telescope with f20 cm
• at 1 wavelength (532 nm)
• used a give lidar ratio of 18 sr-1
• Detection of optical thickness of 0.001

• Lidar observations are obtained
• at Observatory of Haute-Provence (44N, 6E),
  France
• since 1994
• continuously180 profiles/year

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Cirrus Climatology
Mid-latitude (44N) (from Goldfarb et al., GRL,
2001)
Southern tropic (21S) (from Cadet et al., GRL,
2002)
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Cirrus at OHP 1997-1999
T lt T A, B, C sub-visible cirrus t lt 0.03
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Cirrus type

• Derived geometric parameters
• Top height
• Bottom height
• Thickness
• .

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Cirrus altitude
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Dynamical tropopause estimates
Dynamical tropopause estimated from the Advection
Mimosa model

• PV advection on isentropic surface
• 6h ECWWF input T106
• Grid of 37x37 km
• Tropopause defined as 1.6-2 PV threshold (Blue)

Hauchecorne et al, JGR, 2002
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Distribution of the parameters
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Cirrus classes

• Multivariate analyses
• Princ. Comp. Analy.
• Cluster methods
• Lin. Discrim. Analys.

Class I II III
Occurrence () 36 27 35
Height (km) 8.6 0.9 9.8 0.7 11.5 0.9
Altitude relative to tropopause -78 -0.513 716
Thickness (km) 0.9 0.6 3.2 0.9 0.9 0.6
Temperature (C) -41 6 -50 6 -58 6
Keckhut et al., J. Appl. Meteo., 2005 (in press)
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Cirrus into the stratosphere
January 20th, 2000
threshold3xsnoise
thermal tropopause
Keckhut et al., Atmos. Chem. Phys., 5, 3407-3414,
2005
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Position relative to tropopause
Mimosa
OHP
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Air mass history

• Flexpart (Stohl, 1998)

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Conclusions

• Cirrus are observed for 50 .
• Optical depth of cirrus range from 1 to 0.001.
• The lowest range corresponds to the detection
  threshold.
• Geometric cirrus characteristics can be deduced
  with lidar, and allow clustering.
• 3 cirrus classes have been found.
• 1 case located in the stratosphere has been
  described that came isentropically from the
  subtropical troposphere.
• Will improve our clustering in adding new
  parameters temporal variability, lidar ratio,
  photometer-radiometer (XY0044-Thuillier et al.,
  XY0045-Cadet et al.)
• Investigate further the cirrus in the UTLS