CloudSat/Calipso data and plot calculation details

Jen Kay (jenkay at ucar dot edu), last updated 8-27-2008

 

CloudSat (a 94 GHz radar) and CALIOP (a 532/1064 nm depolarization lidar) provide a unique global view of cloud vertical structure.

I am working with the radar cloud mask and dBZ (2B-GEOPROF) and a co-located lidar cloud mask (2B-GEOPROF-LIDAR, termed RL). 

I use data from the R04 release, available June 2006-present.

 

More Information: CloudSat website, CloudSat data processing center, Calipso website

Example data:  radar, radar_lidar, dataqualityconcerns

 

Plots are available at the following websites:

Arctic R04 cloud fraction plots

Arctic R04 dBZ plots

Global R04 cloud fraction plots

Global R04 dBZ plots

 

Plot 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 thick and unique clouds in the column.

thick = Require 15 cloudy bins (cdz=3.6 km) or 30 cloudy bins (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 clutter.  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.  When I manually exclude bin1tobin3, these plots will have no attached to their name. 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.

 

4. Cloud top height and cloud thickness calculations (still experimentingÉ):

CldTopHt, CldDz, and CldTotDz calculations require that clouds have at least two bins (580 m thick) and that they are entirely contained within the specified height range.  For example, the all calculation includes clouds that are entirely contained from 0 to 20 km, whereas the low calculations include only clouds that are entirely contained from 0 to 2.88 km and the low+ calculations include only clouds that are entirely contained from 0 to 4.08 km. The individual cloud thickness calculation (CldDz) incorporates all individual contiguous clouds.  The total cloud thickness calculation (CldTotDz) is a sum of all individual clouds in a column.