Cirrus Clouds. MOD 10. Overview. Cirrus clouds – definition and historical notes Picture gallery Frequency of cirrus clouds Generation mechanisms Properties of cirrus clouds Climate issues related to cirrus clouds Recommended book: Cirrus (Lynch et al., Eds.), Oxford UP, 2002.
Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.
Cirrus clouds – definition and historical notes
Frequency of cirrus clouds
Properties of cirrus clouds
Climate issues related to cirrus clouds
Recommended book: Cirrus (Lynch et al., Eds.), Oxford UP, 2002
Ci spissatus means dense cirrus.
Fibratus means fibrous appearance of Ci.
Ice crystals are driven away from the
main cloud and evaporate.
Slow development of a cirrus cloud deck,
with some wave action making the
Cirrus clouds with a rounded “head”
A cirrus cloud with a mare’s tail is
called cirrus uncinus.
The mare’s tail is due to ice crystals falling in a sheared wind field.
While falling into subsaturated air below,the ice crystals evaporate, set free latent heat, which can induce instable stratification, local convection and new formation of ice crystals
above the shear layer.
A rather uniform cirrus cloud deck
A rather clumpy cirrus cloud deck
Contrails over central Europe on 4th May 1995 at 7:43 UTC based on NOAA12 AVHRR
after about 2 min contrails start to
break up into waves and rings,
then ice crystals start to evaporate
of adiabatic heating in the downward travelling vortices), however
a faint spoor of an ice curtain extending from the flight altitude down
to the location of the vortices (secondary wake) stays persistent.
survives, a strong contrail appears that can undergo
supersaturation is high enough. This can also be modelled,
Gerz et al. 1997)
Satellite data generally yield frequency of occurrence, i.e.
F = #(data with cirrus)/#(all data).
Result depends on sensor sensitivity.
GOES/VAS: 25-30% (over con. US)
HIRS: 43% (globally)
SAGE II: 50-70% (including sub-visual Ci)
Warren et al (ground based): 75% over indonesia.
Whereas the human eye can detect Ci clouds down to =0.03, some
satellite sensors view down to =10-4.
from Don Wylie’s
Wang et al, JGR, 1996
MLS data, Spichtinger et al., QJRMS, 2003
Sausen et al., TAC, 1998
The actual coverage
of persistent (line-shaped,
i.e. young) contrails
depends on the actual
The main aviation flight
paths show up here.
Sausen et al., TAC, 1998
All these mechanisms imply upward vertical motion.
(There may be some ice formation in downward motion, via contact nucleation and via efflorescence nucleation).
Eleftheratos and Zerefos, 2005
The basic generation mechanisms are reflected in the satellite climatologies:
Tropical convection most important source of water vapour in the UT; keeps Ci alive even far away from and long after the convective event.
Jet stream related Ci occurs in the NE flowing parts of the jet, SE of the jet core. Very little Ci NW of the jet core, no Ci in the trough.
Thermodynamic contrail formation criterion: Schmidt (1941), Appleman (1953), reviewed and extended by Schumann (1996).
In contrast to natural cirrus clouds, contrails can already form at lower ambient humidity, in principle already under totally dry conditions (RHi=0%).
Water saturation must be reached during the mixing process.
Only under ice-supersaturated conditions contrails can survive the initial jet- (20 s) and vortex-phases (ca. 2 min), to disperse then and spread by diffusion and wind shear into the atmosphere until it can only hardly be distinguished from natural cirrus clouds.
It is conceivable, but not yet proven, that also the aerosol emitted from jet engines can lead to cirrus formation later on, even when no contrail was formed initially.
Adapted from Lynch (2002), after Dowling and Radke (1990)
Nakaya created the first systematic classification scheme for snowflakes.
Classification of falling snow into 41 individual morphological types.
The most complex classification scheme is an extension of Nakaya's table, published by Magono and Lee in 1966. There are 80 separate morphological types in their classification scheme.
K. G. Libbrecht Caltech
Predominant crystal habit depends vortices
in a complex way on temperature and
supersaturation during the history of
crystal growth. Other factors may also
play a role.
Global radiative impact (W/m2) of various high cloud types on the energy budget at three altitudes
Adapted from Chen et al. (2000). Ranges are: Thin (0.02<<3.55), Moderate (3.55 <<22.63), Thick (>22.63).