• Mid-latitudes vs. Polar regions • Radars vs. Radiometerscloudsat.atmos.colostate.edu/snow/5slides-liu.pdfThe difference between mid-latitudes and polar regions - surface & airborne
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Snowfall Retrieval from Space
Guosheng Liu
Florida State University
• Mid-latitudes vs. Polar regions
• Radars vs. Radiometers
The difference between mid-latitudes and polar regions- surface & airborne radar obs
Barrow– Alaska (71°N) 2002 -2005 winters
MMCR
Wakasa Bay – Japan (~35°N) 2001&2003 January
APR-2 & Obama Doppler
Ze=56S1.2 (Matrosov 2006)
0 dBZ
20 dBZ
↓
Snowfall examples from CloudSat
snow rainsnow
02/08/2007
Ze-R relationships for Solid Precipitation
Precipitation (mm/h)
0.1 1
Ze (m
m6 m
-3)
10-1
100
101
102
103
104
Sector-13.4GHz (DDA)Sector-35.6GHz (DDA)Sector-94.0GHz (DDA)Dendrite-13.4GHz (DDA)Dendrite-35.6GHz (DDA)Dendrite-94.0GHz (DDA)Wakasa snow (Aonashi,2003)Snow_dry (Puhakka,1975)Snow (Sekhon & Srivastava,1970)Snow_dry (Imai,1960)Plate, column (Ohtake & Henmi,1970)Single crystals(Carlson&Marshall,1972)Snow_dry(Fujiyoshi et al.,1990)-9.4GHzGraupel_13.4GHz, den=0.25 (Mie)Graupel_35.6GHz, den=0.25 (Mie)Graupel_94.0GHz, den=0.25 (Mie)
5
13.4 GHz
35.6 GHz
94 GHz
Z-R relations for snowfallDepends on:
Size Distribution + particle shape
(Matrosov 2007)
High frequency measurement of snowfallδ T
B (K
)
-80-60-40-20
02040
89150220340
δ TB (K
)
-80
-60
-40
-20
0
20
183+-1183+-3183+-7
AMSUB (A1-B1)T B (K
)
200
210
220
T B (K
)210
220
230
Latitude
36.5 37.0 37.5 38.0 38.5
T B (K
)
230
240
250
183+-7
183+-3183+-1
150
89
Snowfall Retrieval From High –Frequency Microwave Satellite Observations
• Use surface and airborne radar snowfall observations as the basis to build the a-priori database
• Radiative transfer model utilizes nonspherical snowflakes scattering calculations
A Case Study (Jan 14 2001)
AMSU-B Retrieval
GMS IR Radar (AMeDAS)
3 Cases (1ox1o)
Retrieved Snowfall Rate (mm h-1)
0 1 2 3 4 5 6
AMeD
AS S
now
fall
Rat
e (m
m h
-1)
0
1
2
3
4
5
6
+ 0 hr+ 1 hr+ 2 hr+ 3 hr
Compare AMSU-B Retrieval with AMeDAS radar (3 cases, correlation coefficient: 0.79) Noh, Liu, et al. (2006)
Winter Snowfall Distribution
Winter Rainfall Distribution
SSM/T-2
snowfall
COADS snow
fraction
SSM/I
rainfall
COADS rain
fraction
Below 60Below 60°°NN
Liu & Curry (1996)
SSM/I 85GHz ΔTB 92/12/25-93/01/03, N. Pole – 70 N
-100
-50
0
50
100
-20
-10
0
10
20
0
2
4
6
8
10
0
100
200
300
0
2
4
6
8
-20 -10 0 10 20 30-110
-70
-30
10
50
-20 -10 0 10 20 30
85 GHz Brightness Temperature Anomaly (K)
(a) (b)
(c) (d)
(e) (f) CC: 0.32
CC: 0.71CC: 0.45
CC: 0.79CC: 0.76
CC: 0.59
LW DOWN SURF TEMP
CLOUD AMT
LWP
RADAR, 300m
DAILY SNOW
Liu & Curry (2003)
Detecting Snowfall From Space- what we knew and what we do not know
• From space radar (CloudSat, future new radars)– Pros: physically direct, only need Z to R conversion– Cons: CloudSat - spatial coverage, only a 1.4 km wide strip per orbit– Future radar ? (GPM radars can go up to ~67 degree latitudes), how about polar
regions ?– Need minimum detectable dBZ value -10 dBZ or smaller
• From High-Frequency Microwave Radiometers (AMSU-B, SSMIS, GMI)– Pros: More spatial and temporal coverage (4~6 satellites)– Cons: 1. weaker signature, 2. physically less direct, 3. surface contamination– Below ~60N degree, particularly over ocean, there have been attempts in retrieving
snow from HF-Microwave radiometer obs, – Above ~60 degree latitudes, ???
• Polar Regions:– Satellite radars see snow;– Radiometers? Need to explore
• Studies shows increase of TB associated with cloud/snow at 85, 37 GHz• How about even higher frequencies?
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