2006-present Global Cloud
Fractions from CloudSat (R04)
Analysis by Jen Kay (jenkay at ucar dot edu), last
updated 8-11-2008
Other CloudSat/CALIOP
plots: Arctic,
Global
R04 dBZ plots, Old
(not updated) R03 plots
Background:
CloudSat (a 94 GHz radar) and CALIOP (a 532/1064
nm depolarization lidar) provide a unique global view of cloud vertical
structure. Calculation details are at the bottom of this page. These results are from a radar-only
cloud mask (2B-GEOPROF version R04) and a combined radar-lidar cloud mask
(2B-GEOPROF version R04 and 2B-GEOPROF-LIDAR version R04, termed RL).
2x2 Degree
Monthly Zonal Mean Movies:
LatHt_2deg_asl_nobin1tobin3
(individual
files)
LatHt_2deg_asl_nobin1tobin3_RL
2x2 Degree
Seasonal Cloud Fraction Maps (radar only):
JJA_06: nolow,
nouniqlow,
mid,
high,
uniqhigh,
thick30,
total
SON_06: nolow,
nouniqlow,
mid,
high,
uniqhigh,
thick30,
total
DJF_06: nolow,
nouniqlow,
mid,
high,
uniqhigh,
thick30,
total
MAM_07: nolow,
nouniqlow,
mid,
high,
uniqhigh,
thick30,
total
JJA_07: nolow,
nouniqlow,
mid,
high,
uniqhigh,
thick30,
total
SON_07: nolow,
nouniqlow,
mid,
high,
uniqhigh,
thick30,
total
DJF_07: nolow,
nouniqlow,
mid,
high,
uniqhigh,
thick30,
total
MAM_08: nolow,
nouniqlow,
mid,
high,
uniqhigh,
thick30,
total
2x2 Degree
Seasonal Cloud Fraction Maps (radar+lidar):
JA_06_RL*: nolow,
nouniqlow,
mid,
high,
uniqhigh,
thick30,
total
SON_06_RL: nolow,
nouniqlow,
mid,
high,
uniqhigh,
thick30,
total
DJF_06_RL: nolow,
nouniqlow,
mid,
high,
uniqhigh,
thick30,
total
MAM_07_RL: nolow,
nouniqlow,
mid,
high,
uniqhigh,
thick30,
total
JJA_07_RL*: nolow,
nouniqlow,
mid,
high,
uniqhigh,
thick30,
total
*NOTE: During these
periods, the 2B-GEOPROF-LIDAR files have periods with no Arctic data. I have manually
removed these *bad* data granules from the analysis. As a result, the RL maps have different temporal sampling
than the radar-only maps. I have
not done a thorough investigation of this issue outside of the Arctic, so use
these maps with some caution.
Time Series
(need2do):
Global (82 S-82 N), radar
only: total, low, uniqlow
Global (82 S-82 N),
radar+lidar: total, low, uniqlow
###
Calculation Details ###
1. Cloud ID:
For the CloudSat only
analysis, a positive cloud ID results if the 2B-GEOPROF cloud mask equals 20,
30, 40. For more information on
2B-GEOPROF cloud mask, see the quality
statement. For identification
of specific cloud types (binning by profile) or for calculation of cloud
thickness or cloud top height, I require 2 cloudy bins (cloud thickness (dz) ge
580 m). The 2B-GEOPROF-LIDAR
product provides the fraction of the radar volume that is identified as cloud
by the lidar. If any lidar
cloud is present in the radar volume (i.e., fraction > 1%), I count this as
a positive cloud ID.
2. Cloud type definitions follow CAM pressure-based
cloud type definitions:
low = 1200-700 hPa (0-2.75 km asl)
mid = 700-400 hPa
(2.75-7 km asl)
high = 400-50 hPa (7 - 22.5 km asl)
I converted the
pressure-based definition to a height-asl definition (using log(P) altitude,
H=7.5 km).
For fun - I also identify
total, thick, and unique clouds in the column.
total = Require 4 cloudy bins (i.e., total cdz = 0.96) at
any height.
thick = Require 30 cloudy bins (i.e., total cdz = 7.2 km) at
any height in the column.
uniq = Require less than 2 bins outside of the specified
height range have a positive cloud ID.
3. CloudSat Surface Clutter:
Because CloudSat receives a
large amount of backscatter from the surface, the range bins close the ground
surface are contaminated by surface scatter. For R03 - the net result is that CloudSat has trouble identifying
clouds in the bottom km of the profile (i.e., 0-0.96 km agl). For R04 – CloudSat has trouble
identifying clouds in the bottom 720 m of the profile. If LatHt_asl_nobin1tobin3 zonal mean
plots were the same as LatHt_asl zonal mean plots, I would not have worried about
the distinction of whether I have manually excluded bin1tobin3. However, the LatHt_asl_nobin1tobin3
version has higher low cloud fraction than the LatHt_asl version. Thus, in general, I will manually
exclude bin1tobin3 and these plots will have no attached to their name. In summary, trust the plots with no bin1 to bin3 –
they represent the best CloudSat view of cloudiness in the atmosphere and are
valid only above 720 m agl.)
More Information:
CloudSat website, CloudSat data processing center,
Calipso website
