1 proposed new uses for the ceilometer network christine chiu ewan oconner, robin hogan, james...
TRANSCRIPT
![Page 1: 1 Proposed new uses for the Ceilometer Network Christine Chiu Ewan OConner, Robin Hogan, James Holmes University of Reading](https://reader031.vdocument.in/reader031/viewer/2022013100/5515f9c5550346a2308b48b4/html5/thumbnails/1.jpg)
1
Proposed new usesfor the Ceilometer Network
Christine Chiu Ewan O’Conner, Robin Hogan, James Holmes
University of Reading
![Page 2: 1 Proposed new uses for the Ceilometer Network Christine Chiu Ewan OConner, Robin Hogan, James Holmes University of Reading](https://reader031.vdocument.in/reader031/viewer/2022013100/5515f9c5550346a2308b48b4/html5/thumbnails/2.jpg)
Outline
2
How well the method performs and how we can work together
0
100
200
300
400
500
600
0 10 20 30 40 50 60 70 80 90 100
Cloud radar
Ceilometer
What we propose to observe and why this is new
How we retrieve cloud optical depth from ceilometer data
![Page 3: 1 Proposed new uses for the Ceilometer Network Christine Chiu Ewan OConner, Robin Hogan, James Holmes University of Reading](https://reader031.vdocument.in/reader031/viewer/2022013100/5515f9c5550346a2308b48b4/html5/thumbnails/3.jpg)
Ceilometers have been used to observe aerosols and clouds
• Cloud base height for all cloud cases
• Cloud optical depth for thin clouds
• How about thick clouds?
3
![Page 4: 1 Proposed new uses for the Ceilometer Network Christine Chiu Ewan OConner, Robin Hogan, James Holmes University of Reading](https://reader031.vdocument.in/reader031/viewer/2022013100/5515f9c5550346a2308b48b4/html5/thumbnails/4.jpg)
Cloud optical depth is the great unknown• Differences between climate models: factor 2-4
(Zhang et al., JGR, 2005)
• Differences between ground-based methods: factor 2-4 (Turner et al., BAMS, 2007)
4
![Page 5: 1 Proposed new uses for the Ceilometer Network Christine Chiu Ewan OConner, Robin Hogan, James Holmes University of Reading](https://reader031.vdocument.in/reader031/viewer/2022013100/5515f9c5550346a2308b48b4/html5/thumbnails/5.jpg)
5
Multi-filter rotating shadowband radiometer (MFRSR)
works only for overcast cases
![Page 6: 1 Proposed new uses for the Ceilometer Network Christine Chiu Ewan OConner, Robin Hogan, James Holmes University of Reading](https://reader031.vdocument.in/reader031/viewer/2022013100/5515f9c5550346a2308b48b4/html5/thumbnails/6.jpg)
6
AERONET cloud mode provides routine cloud optical depth measurements
Normal aerosol mode(sun-seeking)
Cloud mode(zenith-pointing)
Chiu et al. (JGR, 2010)
![Page 7: 1 Proposed new uses for the Ceilometer Network Christine Chiu Ewan OConner, Robin Hogan, James Holmes University of Reading](https://reader031.vdocument.in/reader031/viewer/2022013100/5515f9c5550346a2308b48b4/html5/thumbnails/7.jpg)
Fractional day
Zenith Radiance
(arbitrary unit)
cloudy
clear
“solar background light” (a lidar noise source)
Ceilometers measure zenith
radiance too!
lidar
lidarshoots
lidar
Sunshoots
Signal
no
![Page 8: 1 Proposed new uses for the Ceilometer Network Christine Chiu Ewan OConner, Robin Hogan, James Holmes University of Reading](https://reader031.vdocument.in/reader031/viewer/2022013100/5515f9c5550346a2308b48b4/html5/thumbnails/8.jpg)
8
1-channel zenith radiance measurements are ambiguous for cloud retrievals in a 1D radiative transfer world
Cloud optical depth
Zenith Radiance
plane-parallel
3D simulations
![Page 9: 1 Proposed new uses for the Ceilometer Network Christine Chiu Ewan OConner, Robin Hogan, James Holmes University of Reading](https://reader031.vdocument.in/reader031/viewer/2022013100/5515f9c5550346a2308b48b4/html5/thumbnails/9.jpg)
Thick clouds – ceilometer’s active beam is completely
attenuated
9
![Page 10: 1 Proposed new uses for the Ceilometer Network Christine Chiu Ewan OConner, Robin Hogan, James Holmes University of Reading](https://reader031.vdocument.in/reader031/viewer/2022013100/5515f9c5550346a2308b48b4/html5/thumbnails/10.jpg)
10
Use known overcast and clear-sky cases to develop our classification scheme
Overcast thick clouds
• Cloud optical depth > 10 continuously at least for 1 hour
Clear-sky
• Cloud optical depth < 3 continuously at least for 1hour
![Page 11: 1 Proposed new uses for the Ceilometer Network Christine Chiu Ewan OConner, Robin Hogan, James Holmes University of Reading](https://reader031.vdocument.in/reader031/viewer/2022013100/5515f9c5550346a2308b48b4/html5/thumbnails/11.jpg)
Determine if ceilometer’s active beam is completely attenuated
• Find the cloud top layer using cloud flags in Cloudnet products
11
Backscatter signal (sr-1 m-1)
Range (km)
cloud top
• Calculate the mean backscatter signal from the cloud top to 1 km above
![Page 12: 1 Proposed new uses for the Ceilometer Network Christine Chiu Ewan OConner, Robin Hogan, James Holmes University of Reading](https://reader031.vdocument.in/reader031/viewer/2022013100/5515f9c5550346a2308b48b4/html5/thumbnails/12.jpg)
12
Histogram of mean backscatter for clear-sky cases
•This threshold properly indentifies 97% of clear-sky cases
0 100counts
clear-sky cases
clear
mean backscatter (log scale) between cloud top and 1km above
Altitude (km)
cloudy
![Page 13: 1 Proposed new uses for the Ceilometer Network Christine Chiu Ewan OConner, Robin Hogan, James Holmes University of Reading](https://reader031.vdocument.in/reader031/viewer/2022013100/5515f9c5550346a2308b48b4/html5/thumbnails/13.jpg)
13
Histogram of mean backscatter for overcast clouds
•This threshold properly indentifies 86% of cloudy cases
mean backscatter (log scale) between cloud top and 1km above
0 100countsAltitude (km)
clearcloudy
![Page 14: 1 Proposed new uses for the Ceilometer Network Christine Chiu Ewan OConner, Robin Hogan, James Holmes University of Reading](https://reader031.vdocument.in/reader031/viewer/2022013100/5515f9c5550346a2308b48b4/html5/thumbnails/14.jpg)
14
Evaluate our classification scheme using cloud mode retrievals
Cloud optical depth from AERONET cloud mode
Cloud optical depth from ceilometer
• drizzling
• thin clouds
• time/spatial resolution
![Page 15: 1 Proposed new uses for the Ceilometer Network Christine Chiu Ewan OConner, Robin Hogan, James Holmes University of Reading](https://reader031.vdocument.in/reader031/viewer/2022013100/5515f9c5550346a2308b48b4/html5/thumbnails/15.jpg)
Intercomparison at Chilbolton and Oklahoma sites
15
![Page 16: 1 Proposed new uses for the Ceilometer Network Christine Chiu Ewan OConner, Robin Hogan, James Holmes University of Reading](https://reader031.vdocument.in/reader031/viewer/2022013100/5515f9c5550346a2308b48b4/html5/thumbnails/16.jpg)
16
Comparison to other instruments
• AERONET cloud mode observations
• Microwave radiometer
• Cloud radarτ =
3
2
LWP
reff
reff in μm,
Liquid Water Path in g/m2
![Page 17: 1 Proposed new uses for the Ceilometer Network Christine Chiu Ewan OConner, Robin Hogan, James Holmes University of Reading](https://reader031.vdocument.in/reader031/viewer/2022013100/5515f9c5550346a2308b48b4/html5/thumbnails/17.jpg)
17
Example from Chilbolton 2010/08/17
Attenuated backscatter coefficient
Reflectivity
![Page 18: 1 Proposed new uses for the Ceilometer Network Christine Chiu Ewan OConner, Robin Hogan, James Holmes University of Reading](https://reader031.vdocument.in/reader031/viewer/2022013100/5515f9c5550346a2308b48b4/html5/thumbnails/18.jpg)
0
20
40
60
80
100
8 9 10 11 12 13 14 15
ct75K
18
Retrievals from ceilometer, cloud mode and MWR agree well
ct75K
Aeronet
Time (UTC)
Cloud optical depthMWR
![Page 19: 1 Proposed new uses for the Ceilometer Network Christine Chiu Ewan OConner, Robin Hogan, James Holmes University of Reading](https://reader031.vdocument.in/reader031/viewer/2022013100/5515f9c5550346a2308b48b4/html5/thumbnails/19.jpg)
19
Example – cirrus cloud (Oklahoma)
Time (UTC)
Attenuated backscatter coefficient
Reflectivity
![Page 20: 1 Proposed new uses for the Ceilometer Network Christine Chiu Ewan OConner, Robin Hogan, James Holmes University of Reading](https://reader031.vdocument.in/reader031/viewer/2022013100/5515f9c5550346a2308b48b4/html5/thumbnails/20.jpg)
20
Retrievals difference could be up to 30% if using a wrong cloud phase
0
1
2
3
4
5
18 18.5 19 19.5 20 20.5 21
water phase
0
1
2
3
4
5
18 18.5 19 19.5 20 20.5 21
ice phase (D180)
0
1
2
3
4
5
18 18.5 19 19.5 20 20.5 21
ice phase (D60)
Time (UTC)
Cloud optical depth
![Page 21: 1 Proposed new uses for the Ceilometer Network Christine Chiu Ewan OConner, Robin Hogan, James Holmes University of Reading](https://reader031.vdocument.in/reader031/viewer/2022013100/5515f9c5550346a2308b48b4/html5/thumbnails/21.jpg)
21
Ice water paths derived from various empirical relationships
Time (UTC)
Ice water path (g/m2)
0
50
100
150
200
250
18 18.5 19 19.5 20 20.5 21
Wang and Sassen (2002)Ebert and Curry (1992)Heymsfield et al 2003 (midlatitude)Cloudnet: Z-T?
![Page 22: 1 Proposed new uses for the Ceilometer Network Christine Chiu Ewan OConner, Robin Hogan, James Holmes University of Reading](https://reader031.vdocument.in/reader031/viewer/2022013100/5515f9c5550346a2308b48b4/html5/thumbnails/22.jpg)
22
A more complex case – water cloud and thick ice cloud (Oklahoma)
Attenuated backscatter coefficient
Reflectivity
![Page 23: 1 Proposed new uses for the Ceilometer Network Christine Chiu Ewan OConner, Robin Hogan, James Holmes University of Reading](https://reader031.vdocument.in/reader031/viewer/2022013100/5515f9c5550346a2308b48b4/html5/thumbnails/23.jpg)
23
Agreement is shown again for water clouds
0
20
40
60
80
100
15 15.5 16 16.5 17
MWR0
20
40
60
80
100
ceilometer
Time (UTC)
Retrieved cloud optical depth
0
20
40
60
80
100
15 15.5 16 16.5 17
AERONET
![Page 24: 1 Proposed new uses for the Ceilometer Network Christine Chiu Ewan OConner, Robin Hogan, James Holmes University of Reading](https://reader031.vdocument.in/reader031/viewer/2022013100/5515f9c5550346a2308b48b4/html5/thumbnails/24.jpg)
0
5
10
15
20
25
30
35
21 21.5 22 22.5 23 23.5 24
MWRice phase with D60liquid phase
24
Cloud optical depth could differ 30 –40% due to cloud phase
Time (UTC)
Retrieved cloud optical depth
![Page 25: 1 Proposed new uses for the Ceilometer Network Christine Chiu Ewan OConner, Robin Hogan, James Holmes University of Reading](https://reader031.vdocument.in/reader031/viewer/2022013100/5515f9c5550346a2308b48b4/html5/thumbnails/25.jpg)
25
Water clouds at the Oklahoma site in 2007 May-November
0
100
200
300
400
500
600
0 10 20 30 40 50 60 70 80 90 100
Cloud radar
Ceilometer
cloud optical depth
Occurrence counts
![Page 26: 1 Proposed new uses for the Ceilometer Network Christine Chiu Ewan OConner, Robin Hogan, James Holmes University of Reading](https://reader031.vdocument.in/reader031/viewer/2022013100/5515f9c5550346a2308b48b4/html5/thumbnails/26.jpg)
26
Difference between ceilometer and lidar applications
Pros
• Seem easier to cross-calibrate ceilometer solar background light data
• Smaller impact from aerosol and Rayleigh scattering at ceilometer wavelengths
Cons
• Surface albedo could fluctuate quite significantly at 905 nm
• A few weak water vapor absorption lines around 905 nm
![Page 27: 1 Proposed new uses for the Ceilometer Network Christine Chiu Ewan OConner, Robin Hogan, James Holmes University of Reading](https://reader031.vdocument.in/reader031/viewer/2022013100/5515f9c5550346a2308b48b4/html5/thumbnails/27.jpg)
Summary
• The use of solar background light can greatly enhance current cloud products of ceilometer networks
• Confident about cloud optical depth retrievals for water clouds
• Continue testing our classification algorithm that distinguishes optically thin and thick clouds
• A lot of work needs to be done for retrieving ice- and mixed-phase clouds
27