P4.11
Using CloudSat Data to Validate Icing Products
Cory A. Wolff and Scott Landolt – NCAR/RAL
Thomas F. Lee and Cristian Mitrescu – NRL
Steven D. Miller - CIRA
CloudSat
Comparison to Aircraft-Measured CTZ
- Flight on 5 Nov 2006 along CloudSat track
- Two CTZ measurements from the aircraft
within 35 min of the CloudSat pass
Aircraft CTZ = 4596 m
Aircraft CTZ = 4560 m
CloudSat CTZ = 4580 m
CloudSat CTZ = 4250 m
Overall Comparisons
- January – March 2007
- On average, CIP CTZ was 327 m lower than
the CloudSat CTZ
- Varies with altitude of CloudSat CTZ
+ Positive difference means CIP CTZ
greater than CloudSat CTZ and vice versa
350
Cloud profiling radar (94 GHz)
Part of A-Train
240 m vertical resolution (surface to 30 km)
http://www.nrlmry.navy.mil/NEXSAT.html
Average Difference = 1405 m
CTZ < 3 km
300
Frequency
250
200
150
100
Current Icing Product (CIP)
50
4800
4320
3840
3360
2880
2400
1920
1440
0
960
480
-960
-480
-1440
-1920
-2400
-2880
-3360
-3840
-4320
-4800
0
CTZ Difference (m)
800
Average Difference = 529 m
CTZ 3-6 km
700
Comparison with CIP CTZ
- 20 Jan 2007 over western U.S. and Mexico
Frequency
600
500
400
300
200
100
4800
4320
3840
3360
2880
2400
1920
1440
960
480
0
-480
-960
-1440
-1920
-2400
-2880
-3360
-3840
-4800
CTZ Difference (m)
1200
Average Difference = -443 m
CTZ 6-9 km
Frequency
1000
Cloud Top (CTZ) Validation
- CIP CTZ: Matches GOES- measured cloud
top temperature to model sounding and puts
cloud top altitude at nearest model level
+ No prior validation done because of a lack
of good cloud top observations
800
600
400
200
1200
4800
4320
3840
3360
2880
2400
1920
1440
960
480
0
-480
-960
-1440
-1920
-2400
-2880
-3360
-3840
-4320
-4800
0
CTZ Difference (m)
Average Difference = -827 m
CTZ > 9 km
1000
- CloudSat CTZ: Cloud top altitude set to level
where first two valid, concurrent reflectivity
values are found when working down from top
Frequency
800
600
400
200
This research is in response to requirements and funding by the Federal Aviation Administration (FAA). The views
expressed here are those of the authors and do not necessarily represent the official policy or position of the FAA. The
NASA Applied Sciences Program and the NASA Aviation Safety and Security Program also support this project through the
NASA Advanced Satellite Aviation-weather Products (ASAP) project. The support of the research co-sponsor, the Office of
Naval Research under Program Element PE-0602435N, is gratefully acknowledged.
4800
4320
3840
3360
2880
2400
1920
1440
960
480
0
-480
-960
-1440
-1920
-2400
-2880
-3360
-3840
-4320
0
- CIP (black line) and CloudSat mostly agree
on the presence of clouds along the track
- Basic trends in CTZ are also followed well
- CIP overestimates tops of lower clouds from
22 – 24.5 °N, which is a well-known problem
- CIP also misses layered clouds at 35 °N
-4800
- Methodology: Find the difference between
the measured (CloudSat) and derived (CIP)
CTZ values
+ No comparisons within 1.5 km of the
surface due to clutter in CloudSat
+ Use observations within ± 30 min of CIP
valid time (top of hour)
+ Only match if 75% of CloudSat points
within a CIP grid point are cloudy
+ Median CloudSat CTZ compared to CIP
-4320
0
Hourly diagnosis of icing conditions
Icing probability, severity and SLD potential
Surface to 30,000 ft. (Cloud tops are higher)
http://www.rap.ucar.edu/icing/cip
CTZ Difference (m)
- Shifts from CIP being too high at lower
altitudes to being too low at higher altitudes
- At low levels temperature inversions are
known to cause high CTZ estimates
- At high levels the error could be from semitransparent cirrus causing warm readings
Background image from http://cloudsat.atmos.colostate.edu/cloud_art